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v2.4.1.9

Allowance for Loan and Lease Losses (Allocation of Allowance for Loan and Lease Losses) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Loans And Leases, Growth | $ 907,800,000fcnca_LoansAndLeasesGrowth |  |  |
Reclassification | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification | 7,368,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification | [1] | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification
Unpaid principal balance | 2,057,691,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance | 1,833,955,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance |  |
Financing Receivable, Individually Evaluated for Impairment | 119,593,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 132,146,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment |  |
Noncommercial |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification | 7,368,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |  |
Noncommercial | Non-specific |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification | (15,772,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember |  |  |
Commercial Mortgage [Member] |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Allowance for Credit Losses, Change During Period | 1,700,000fcnca_AllowanceforCreditLossesChangeDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_CommercialMortgageMember |  |  |
Non-PCI Loans |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 7,368,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 133,466,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 145,485,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 15,717,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,161,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 119,593,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 132,146,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment, Change During Period | (12,600,000)fcnca_FinancingReceivableIndividuallyEvaluatedforImpairmentChangeDuringPeriod / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |  |
Average balance | 127,421,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 151,330,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 158,426,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 5,427,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 7,817,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 6,735,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Financing Receivable, Collectively Evaluated for Impairment, Change During Period | 5,490,000,000fcnca_FinancingReceivableCollectivelyEvaluatedforImpairmentChangeDuringPeriod / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |  |
Non-PCI Loans | Commercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 5,141,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 6,945,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 7,306,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 92,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 103,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 1,620,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,272,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 1,689,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,414,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 22,493,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 83,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 270,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 399,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Commercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 27,421,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 87,702,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 103,522,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 8,610,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 6,873,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 82,803,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 97,111,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 86,250,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 105,628,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 96,082,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 3,698,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 5,702,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 4,630,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Commercial | Other commercial real estate |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (815,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 913,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,279,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 112,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 209,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 584,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,878,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 2,125,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 2,658,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,690,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 80,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 144,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 142,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Commercial | Commercial and industrial |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 7,551,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 12,197,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 10,393,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 1,743,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 771,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 11,040,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 9,300,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 13,433,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 12,772,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 13,658,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 580,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 642,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 788,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Commercial | Lease financing |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (253,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 623,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 188,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 150,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 54,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 623,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 188,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 774,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 350,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 497,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 44,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 22,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 37,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Commercial | Other |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (1,288,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 2,000,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |  |
ALLL for loans and leases individually evaluated for impairment | 1,972,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 2,000,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 528,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 424,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 29,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 0us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 23,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Noncommercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 5,717,000fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 15,746,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,939,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 1,360,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,586,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 14,913,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,539,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 15,487,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 15,470,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 14,951,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 593,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 444,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 586,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Noncommercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (478,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 1,340,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,108,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 71,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 72,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 1,340,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,108,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 1,678,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 958,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,850,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 98,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 55,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 41,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Noncommercial | Revolving mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (9,838,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 4,933,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,596,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 1,052,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 372,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 3,675,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 3,596,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 3,922,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 5,653,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 2,931,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 134,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 485,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 68,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Noncommercial | Consumer |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (10,018,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Unpaid principal balance | 1,067,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,154,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
ALLL for loans and leases individually evaluated for impairment | 555,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 121,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Financing Receivable, Individually Evaluated for Impairment | 995,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,154,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |
Average balance | 1,535,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 1,427,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 1,850,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Interest income recognized | 88,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | 53,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  | 21,000us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember
Non-PCI Loans | Noncommercial | Non-specific |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | (15,772,000)fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_NonSpecificMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember | [1] |
Non-PCI Loans | Other |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment, Change During Period | 2,000,000fcnca_FinancingReceivableIndividuallyEvaluatedforImpairmentChangeDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_OtherLoansMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember |  |  |
Non-PCI Loans | With A Recorded Allowance |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 87,007,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 83,678,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 996,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 1,025,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 57,324,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 57,819,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Other commercial real estate |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 112,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 783,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Commercial and industrial |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 10,319,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 7,197,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Lease financing |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 319,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 133,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Commercial | Other |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 2,000,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |  |
Non-PCI Loans | With A Recorded Allowance | Noncommercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 10,198,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 11,534,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Noncommercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 1,077,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 651,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Noncommercial | Revolving mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 3,675,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 3,382,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With A Recorded Allowance | Noncommercial | Consumer |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 987,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember | 1,154,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 32,586,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 48,468,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 624,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 1,247,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 25,479,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 39,292,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Other commercial real estate |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 472,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 1,095,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_CommercialRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Commercial and industrial |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 721,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 2,103,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_CommercialAndIndustrialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Lease financing |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 304,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 55,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_FinanceLeasesFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Commercial | Other |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_OtherLoansMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |  |
Non-PCI Loans | With No Recorded Allowance | Noncommercial | Mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 4,715,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 4,005,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_MortgageReceivablesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Noncommercial | Construction and land development |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 263,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 457,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = fcnca_ConstructionAndLandDevelopmentNoncommercialMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Noncommercial | Revolving mortgage |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 214,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Non-PCI Loans | With No Recorded Allowance | Noncommercial | Consumer |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 8,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = us-gaap_ConsumerLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fcnca_NoncommercialSegmentMember / fcnca_LoanDesignationAxis = fcnca_NonPCILoansMember / us-gaap_ValuationAllowancesAndReservesTypeAxis = fcnca_WithNoRecordedAllowanceMember |  |
Loans Acquired With Deteriorated Credit Quality [Member] |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Reclassification |  | 0fcnca_FinancingReceivableAllowanceofCreditLossesReclassification / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | [1] |
Acquired loans which have adverse change in expected cash flows | $ 285,636,000fcnca_AcquiredLoansWhichHaveAdverseChangeInExpectedCashFlows / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember | $ 459,947,000fcnca_AcquiredLoansWhichHaveAdverseChangeInExpectedCashFlows / fcnca_LoanDesignationAxis = fcnca_LoansAcquiredWithDeterioratedCreditQualityMember |  |
[1] | Reclassification results from enhancements to the ALLL calculation during the second quarter of 2013 that resulted in the allocation of $15.8 million previously designated as 'nonspecific' to other loan classes and the absorption of $7.4 million of the reserve for unfunded commitments related to unfunded, revocable loan commitments into the ALLL. Further discussion is contained in Note A.

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