This category includes all loans, excluding purchased credit-impaired loans that are accounted for in accordance with ASC 310-30. These loans are accounted for in accordance with ASC 310-20.

No definition available.

+ Details

Name:	fcnca_LoansandLeasesnotacquiredintransferaccountedforasdebtsecurities
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_MortgageReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=fcnca_OtherRealEstateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=fcnca_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=fcnca_OtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fcnca_NoncommercialSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Leases (Loans and Leases Outstanding) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Non-PCI loans	$ 24,248,329	$ 22,833,827
PCI loans	638,018	762,998	$ 834,167	$ 809,169
Total loans and leases	24,886,347	23,596,825
Commercial
Non-PCI loans	15,740,383	14,799,054
PCI loans	317,014	393,419
Commercial \| Construction and land development
Non-PCI loans	679,203	669,215
Commercial \| Mortgage
Non-PCI loans	10,486,372	9,729,022
Commercial \| Other commercial real estate
Non-PCI loans	471,532	473,433
Commercial \| Commercial and industrial
Non-PCI loans	3,189,337	2,730,407
Commercial \| Lease financing
Non-PCI loans	616,951	894,801
Commercial \| Other
Non-PCI loans	296,988	302,176
Noncommercial
Non-PCI loans	8,507,946	8,034,773
PCI loans	321,004
Noncommercial \| Construction and land development
Non-PCI loans	241,436	248,289
Noncommercial \| Mortgage
Non-PCI loans	4,073,235	3,523,786
PCI loans		369,579
Noncommercial \| Revolving mortgage
Non-PCI loans	2,570,096	2,701,525
Noncommercial \| Consumer
Non-PCI loans	$ 1,623,179	$ 1,561,173