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v2.4.1.9

Allowance for Loan and Lease Losses (Summary of Activity In Allowance for Loan and Lease Losses) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | $ 233,394us-gaap_FinancingReceivableAllowanceForCreditLosses | $ 319,018us-gaap_FinancingReceivableAllowanceForCreditLosses |  | $ 270,144us-gaap_FinancingReceivableAllowanceForCreditLosses
Reclassification | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification | 7,368fcnca_FinancingReceivableAllowanceofCreditLossesReclassification | [1] | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification
Provisions | 640us-gaap_ProvisionForLoanLeaseAndOtherLosses | (32,255)us-gaap_ProvisionForLoanLeaseAndOtherLosses |  | 142,885us-gaap_ProvisionForLoanLeaseAndOtherLosses
Charge-offs | (37,770)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs | (68,026)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs |  | (100,478)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Recoveries | 8,202us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery | 7,289us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery |  | 6,467us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Net charge-offs | (29,568)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet | (60,737)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet |  | (94,011)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
Ending balance | 204,466us-gaap_FinancingReceivableAllowanceForCreditLosses | 233,394us-gaap_FinancingReceivableAllowanceForCreditLosses |  | 319,018us-gaap_FinancingReceivableAllowanceForCreditLosses
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 204,466us-gaap_FinancingReceivableAllowanceForCreditLosses | 233,394us-gaap_FinancingReceivableAllowanceForCreditLosses |  | 319,018us-gaap_FinancingReceivableAllowanceForCreditLosses
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 119,593us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 132,146us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment |  |
Loans and leases collectively evaluated for impairment | 17,463,374us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | 11,972,152us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 17,582,967fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities | 12,104,298fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 1,186,498us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet | 1,029,426us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet |  | 1,809,235us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet
Commercial |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 11,263,074fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 8,499,348fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 726,123us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 781,307us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Construction and land development |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 550,568fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 319,847fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 78,079us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 78,915us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Mortgage |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 7,552,948fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 6,362,490fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 577,518us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 642,891us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Other commercial real estate |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 244,875fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 178,754fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 40,193us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 41,381us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Commercial and industrial |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,988,934fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 1,081,158fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 27,254us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 17,254us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Lease financing |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 571,916fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 381,763fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Other |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 353,833fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 175,336fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 3,079us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 866us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Consumer and Other |  |  |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 3,079us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 866us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Noncommercial |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Reclassification | 7,368fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 6,319,893fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 3,604,950fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 460,375us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 248,119us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommercial | Mortgage |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,520,542fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 982,421fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 382,340us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 213,851us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommercial | Construction and land development |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 120,097fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 122,792fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 912us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 2,583us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommercial | Revolving mortgage |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,561,800fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 2,113,285fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 74,109us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 30,834us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommercial | Consumer |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,117,454fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 386,452fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net | 3,014us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 851us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommercial | Non-specific |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Reclassification | (15,772)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |  |
Non-PCI Loans |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 179,874us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 179,046us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 180,883us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | 7,368fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 15,260us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 19,289us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 42,046us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (20,499)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (33,118)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (50,208)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 8,202us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 7,289us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 6,325us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Net charge-offs | (12,297)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (25,829)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (43,883)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 182,837us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 179,874us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 179,046us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 15,717us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,161us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 167,120us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 169,713us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 182,837us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 179,874us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 179,046us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 119,593us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 132,146us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 17,582,967fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 12,104,298fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Construction and land development |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 10,335us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,031us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 5,467us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | 5,141fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 1,735us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,809us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 9,665us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (316)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (4,685)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (9,546)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 207us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,039us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 445us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 11,961us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,335us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 6,031us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 92us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 103us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 11,869us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,232us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 11,961us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,335us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 6,031us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 1,620us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,272us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 548,948us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 317,575us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 550,568fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 319,847fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 100,257us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 80,229us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 67,486us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | 27,421fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | (16,746)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (4,485)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 18,198us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (1,147)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (3,904)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (7,081)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 2,825us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 996us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,626us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 85,189us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 100,257us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 80,229us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 8,610us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,873us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 76,579us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 93,384us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 85,189us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 100,257us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 80,229us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 82,803us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 97,111us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 7,470,145us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,265,379us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 7,552,948fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,362,490fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Other commercial real estate |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 1,009us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,059us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,169us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (815)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | (401)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (32)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 130us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (312)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (254)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 124us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 109us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 14us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 732us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,009us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,059us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 112us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 209us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 620us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 800us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 732us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,009us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,059us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 584us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,878us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 244,291us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 176,876us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 244,875fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 178,754fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Commercial and industrial |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 22,362us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 14,050us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 23,723us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | 7,551fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 10,441us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,333us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (4,982)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (3,014)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (4,785)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (5,472)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 938us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,213us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 781us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 30,727us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 22,362us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 14,050us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 1,743us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 771us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 28,984us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 21,591us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 30,727us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 22,362us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 14,050us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 11,040us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 9,300us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 1,977,894us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,071,858us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,988,934fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,081,158fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Lease financing |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 4,749us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,521us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 3,288us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (253)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | (473)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,646us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 498us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (100)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (272)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (361)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 110us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 107us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 96us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 4,286us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,749us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 3,521us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 150us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 54us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 4,136us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,695us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 4,286us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,749us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 3,521us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 623us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 188us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 571,293us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 381,575us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 571,916fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 381,763fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Other |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 190us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,175us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,315us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (1,288)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 3,007us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 308us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (116)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (13)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (6)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (28)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 4us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 3,184us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 190us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,175us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 1,972us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 1,212us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 190us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 3,184us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 190us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,175us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 2,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 351,833us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 175,336us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 353,833fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 175,336fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial |  |  |  |
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 6,319,893fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,604,950fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial | Mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 10,511us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,836us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 8,879us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | 5,717fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 1,219us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,786us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (782)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (1,260)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (2,387)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (4,790)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 191us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 559us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 529us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 10,661us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,511us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 3,836us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 1,360us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,586us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 9,301us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 8,925us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 10,661us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,511us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 3,836us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 14,913us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,539us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 2,505,629us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 966,882us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,520,542fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 982,421fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial | Construction and land development |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 681us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,721us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,427us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (478)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 245us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (379)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,161us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (118)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (392)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (1,047)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 84us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 209us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 180us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 892us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 681us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,721us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 71us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 72us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 821us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 609us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 892us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 681us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,721us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 1,340us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,108us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 118,757us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 121,684us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 120,097fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 122,792fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial | Revolving mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 16,239us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 25,185us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 27,045us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (9,838)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 6,301us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,296us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 8,783us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (4,744)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (6,064)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (11,341)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 854us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 660us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 698us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 18,650us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 16,239us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 25,185us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 1,052us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 372us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 17,598us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,867us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 18,650us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 16,239us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 25,185us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 3,675us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,596us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 2,558,125us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,109,689us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,561,800fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,113,285fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial | Consumer |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 13,541us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 25,389us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 25,962us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (10,018)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 9,932us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,085us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 7,763us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | (9,787)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (10,311)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | (10,288)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 2,869us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,396us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,952us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 16,555us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 13,541us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 25,389us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
ALLL for loans and leases individually evaluated for impairment | 555us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 121us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases collectively evaluated for impairment | 16,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 13,420us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Total allowance for loan and lease losses | 16,555us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 13,541us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 25,389us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Loans and leases individually evaluated for impairment | 995us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,154us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases collectively evaluated for impairment | 1,116,459us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 385,298us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,117,454fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 386,452fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommercial | Non-specific |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,850us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 14,122us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Reclassification |  | (15,772)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Provisions | 0us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | (78)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,728us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Charge-offs | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Ending balance | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 15,850us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 15,850us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Loans Acquired With Deteriorated Credit Quality [Member] |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 53,520us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 139,972us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 89,261us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Reclassification |  | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | [1] |
Provisions | (14,620)us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (51,544)us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 100,839us-gaap_ProvisionForLoanLeaseAndOtherLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (17,271)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (34,908)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (50,270)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 142us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Net charge-offs | (17,271)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (34,908)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (50,128)us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 21,629us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 53,520us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 139,972us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 21,629us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 53,520us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 139,972us-gaap_FinancingReceivableAllowanceForCreditLosses / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 21,629us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 53,520us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality |  | 1,029,426us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Commercial | Construction and land development |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 1,320us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 31,186us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 16,693us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | 1,284us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (22,942)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 23,160us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (2,454)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (6,924)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (8,667)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 150us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,320us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 31,186us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 150us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,320us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 31,186us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 150us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,320us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 78,079us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 78,915us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Commercial | Mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 29,906us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 50,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 39,557us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | (7,903)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (3,872)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 34,227us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (11,868)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (16,497)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (23,509)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 10,135us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 29,906us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 50,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 10,135us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 29,906us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 50,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 10,135us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 29,906us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 577,518us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 642,891us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Commercial | Other commercial real estate |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 1,354us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 11,234us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 16,862us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | (1,385)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (8,949)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (4,372)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | 106us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (931)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (1,256)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Ending balance | 75us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,354us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 11,234us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 75us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,354us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 11,234us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 75us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 1,354us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 40,193us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 41,381us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Commercial | Commercial and industrial |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 5,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 8,897us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 5,500us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | (2,023)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 470us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 11,839us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (2,012)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (4,092)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (8,442)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 1,240us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 5,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 8,897us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 1,240us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 5,275us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 8,897us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 1,240us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 5,275us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 27,254us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 17,254us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Commercial | Lease financing |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 13us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | 0us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (13)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 0us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 0us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Noncommercial | Mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 11,802us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 19,837us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 5,433us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | (5,576)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (5,487)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 18,401us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (406)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (2,548)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (4,139)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 142us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 5,820us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 11,802us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 19,837us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 5,820us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 11,802us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 19,837us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 5,820us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 11,802us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 382,339us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 213,851us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Noncommercial | Construction and land development |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 682us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 8,287us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 4,652us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | (395)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (4,170)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 6,520us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (104)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (3,435)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (2,885)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 183us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 682us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 8,287us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 183us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 682us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 8,287us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 183us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 682us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 912us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 2,583us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Noncommercial | Revolving mortgage |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
Beginning balance | 2,959us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 9,754us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 77us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Provisions | 1,523us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (6,399)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 10,796us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (483)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (396)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (1,119)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Ending balance | 3,999us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 2,959us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 9,754us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 3,999us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 2,959us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 9,754us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 3,999us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 2,959us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | 74,109us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 30,834us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] | Noncommercial | Consumer and Other |  |  |  |
Allowance for Loan and Lease Losses [Roll Forward] |  |  |  |
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Provisions | (145)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (195)us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 281us-gaap_ProvisionForLoanLeaseAndOtherLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Charge-offs | (50)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | (85)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | (253)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Recoveries | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
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Allowance for Loans and Leases Evaluated for Impairment [Abstract] |  |  |  |
Total allowance for loan and lease losses | 27us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 222us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  | 502us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember
Loan and Lease Acquired with Deteriorated Credit Quality [Abstract] |  |  |  |
ALLL for loans and leases acquired with deteriorated credit quality | 27us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | 222us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
Loans and leases acquired with deteriorated credit quality | $ 6,094us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | $ 1,717us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConsumerAndOtherMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
[1] | Reclassification results from enhancements to the ALLL calculation during the second quarter of 2013 that resulted in the allocation of $15.8 million previously designated as 'nonspecific' to other loan classes and the absorption of $7.4 million of the reserve for unfunded commitments related to unfunded, revocable loan commitments into the ALLL. Further discussion is contained in Note A.

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