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v2.4.1.9

Loans and Leases (Composition of the Loans and Leases Outstanding By Credit Quality Indicator) (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2013
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | $ 1,247,343 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet | $ 1,186,498 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet | $ 1,270,818 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet | $ 1,029,426 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet
Commercial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 11,493,458 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 11,263,074 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 791,756 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 726,123 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 608,556 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 550,568 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 70,049 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 78,079 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 7,591,745 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 7,552,948 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 653,846 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 577,518 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 262,293 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 244,875 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 40,841 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 40,193 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,072,414 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 1,988,934 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 24,134 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 27,254 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 603,737 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 571,916 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 354,713 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 353,833 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
PCI loans | 2,886 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 3,079 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial | Pass |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 11,070,735 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 10,825,323 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 371,135 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 342,172 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 590,298 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 525,711 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 13,832 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 13,514 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 7,341,243 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 7,284,714 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 333,368 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 300,187 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 260,592 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 242,053 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 9,727 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 11,033 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,931,078 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 1,859,415 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 13,525 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 16,637 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 597,464 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 564,319 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Pass | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 350,060 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 349,111 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
PCI loans | 683 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember | 801 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember |  |
Commercial | Special Mention |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 157,884 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 182,453 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 141,884 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 125,195 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 15,679 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 20,025 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 4,287 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 6,063 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 115,411 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 129,247 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 118,209 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 98,724 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 501 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 909 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 16,425 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 16,271 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 21,771 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 27,683 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 2,963 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 4,137 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,609 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 3,205 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Special Mention | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,913 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 1,384 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
PCI loans | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember |  |
Commercial | Substandard |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 149,792 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 157,333 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 259,917 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 247,138 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,291 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 4,720 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 44,663 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 53,739 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 131,672 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 134,677 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 193,435 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 171,920 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,049 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 1,765 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 12,948 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 12,889 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 8,806 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 8,878 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 6,739 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 6,312 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 3,284 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 3,955 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Substandard | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,690 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 3,338 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
PCI loans | 2,132 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember | 2,278 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember |  |
Commercial | Doubtful |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 6,770 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 2,895 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 15,437 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 9,241 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 4,656 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 2,809 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,039 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 2,366 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 8,456 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 6,302 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 1,741 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 4,402 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 164 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 513 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 130 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 329 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 365 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Doubtful | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
PCI loans | 71 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_DoubtfulMember |  |
Commercial | Ungraded |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 108,277 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 95,070 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 3,383 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 2,377 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 288 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 112 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 2,611 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 1,954 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,380 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 1,944 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 378 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 385 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 151 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 148 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 106,357 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 92,794 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 394 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 38 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 51 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 72 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Commercial | Ungraded | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 50 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 0 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
PCI loans | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember | 0 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = fcnca_UngradedMember |  |
Noncommerical |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | 455,587 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 460,375 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommerical | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | 380,490 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 382,340 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommerical | Revolving mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | 70,363 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 74,109 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommerical | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | 874 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 912 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Noncommerical | Consumer |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
PCI loans | 3,860 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember | 3,014 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |
Purchased credit-impaired | Noncommerical |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Current | 388,349 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 398,225 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
PCI loans | 455,587 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 460,375 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
30-59 Days Past Due | 21,672 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 12,984 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
60-89 Days Past Due | 7,836 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 10,443 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
90 Days or Greater | 37,730 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 38,723 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
Purchased credit-impaired | Noncommerical | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Current | 320,607 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 326,589 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
PCI loans | 380,490 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 382,340 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
30-59 Days Past Due | 18,742 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 11,432 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
60-89 Days Past Due | 6,804 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 10,073 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
90 Days or Greater | 34,337 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 34,246 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
Purchased credit-impaired | Noncommerical | Revolving mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Current | 63,579 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 68,548 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
PCI loans | 70,363 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 74,109 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
30-59 Days Past Due | 2,800 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 1,405 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
60-89 Days Past Due | 1,019 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 345 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
90 Days or Greater | 2,965 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 3,811 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
Purchased credit-impaired | Noncommerical | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Current | 592 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 506 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
PCI loans | 874 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 912 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
30-59 Days Past Due | 0 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 0 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
60-89 Days Past Due | 0 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 0 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
90 Days or Greater | 282 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 406 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
Purchased credit-impaired | Noncommerical | Consumer |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Current | 3,571 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 2,582 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
PCI loans | 3,860 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 3,014 us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
30-59 Days Past Due | 130 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 147 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
60-89 Days Past Due | 13 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 25 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
90 Days or Greater | 146 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember | 260 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_PurchasedcreditimpairedMember |  |
Non-PCI Loans |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 17,844,414 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 17,582,967 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 17,732,161 us-gaap_FinancingReceivableRecordedInvestmentCurrent / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 17,481,500 us-gaap_FinancingReceivableRecordedInvestmentCurrent / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 71,450 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 57,321 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 15,735 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 19,548 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 25,068 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 24,598 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 608,556 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 550,568 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 604,091 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 547,766 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 2,709 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,796 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 712 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 621 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 1,044 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 385 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 7,591,745 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 7,552,948 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 7,554,745 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 7,528,738 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 22,635 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 11,367 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 5,920 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,782 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 8,445 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 8,061 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Other commercial real estate |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 262,293 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 244,875 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 261,456 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 244,497 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 583 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 206 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 58 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 70 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 196 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 102 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,072,414 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,988,934 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 2,063,830 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,984,168 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 6,290 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,843 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 1,724 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,545 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 570 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 378 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Lease financing |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 603,737 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 571,916 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 603,250 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 570,275 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 476 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,631 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 11 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 8 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 0 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Commercial | Other |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 354,713 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 353,833 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 354,135 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 351,721 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 380 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 146 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 65 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,966 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 133 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommerical |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 6,350,956 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,319,893 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 6,290,654 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,254,335 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 38,377 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 39,332 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 7,245 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,556 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 14,680 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,670 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommerical | Mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,524,549 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,520,542 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 2,490,453 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,482,281 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 21,844 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 23,288 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 2,896 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,018 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 9,356 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 8,955 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommerical | Revolving mortgage |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 2,528,257 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,561,800 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 2,510,879 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,542,807 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 10,288 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 11,097 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 2,794 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,433 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 4,296 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 5,463 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommerical | Construction and land development |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 170,208 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 120,097 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 168,199 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 119,094 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 2,009 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 370 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 0 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 486 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | 0 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 147 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Non-PCI Loans | Noncommerical | Consumer |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans and leases, not acquired in a transfer accounted for as debt securities | 1,127,942 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,117,454 fcnca_Loansandleasesnotacquiredinatransferaccountedforasdebtsecurities / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Current | 1,121,123 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,110,153 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
30-59 Days Past Due | 4,236 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 4,577 us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
60-89 Days Past Due | 1,555 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,619 us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
90 Days or Greater | $ 1,028 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | $ 1,105 us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |

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- Definition The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and other-than-temporary impairments), for loans accounted for as debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544 + Details
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- Definition Financing receivables that are less than 60 days past due but more than 29 days past due. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524 + Details
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- Definition Financing receivables that are less than 90 days past due but more than 59 days past due. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524 + Details
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