XML 100 R81.htm IDEA: XBRL DOCUMENT v3.25.4

ALLOWANCE FOR LOAN AND LEASE LOSSES - Schedule of Components of Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Receivables [Abstract]
Day 2 Provision for Loan and Lease Losses	$ 0	$ 0	$ 462
Provision for loan and lease losses	530	469	703
Provision for credit losses	530	469	1,165
Day 2 Provision for Off-Balance Sheet Credit Exposure	0	0	254
Benefit for off-balance sheet credit exposure	(18)	(38)	(44)
Total (benefit) provision for off-balance sheet credit exposure	(18)	(38)	210
Provision for other receivables	2	0	0
Provision for credit losses	$ 514	$ 431	$ 1,375

X

- Definition

Credit Loss Expense (Reversal)

+ References

No definition available.

+ Details

Name:	fcnca_CreditLossExpenseReversal
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Financing Receivable, Credit Loss, Expense

+ References

No definition available.

+ Details

Name:	fcnca_FinancingReceivableCreditLossExpense
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Financing Receivable, Excluding Accrued Interest, Purchased without Credit Deterioration, Allowance for Credit Loss at Acquisition Date

+ References

No definition available.

+ Details

Name:	fcnca_FinancingReceivableExcludingAccruedInterestPurchasedWithoutCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Off-Balance-Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal), Acquired In Acquisition

+ References

No definition available.

+ Details

Name:	fcnca_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversalAcquiredInAcquisition
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Off-Balance-Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal), Excluding Amount Acquired In Acquisition

+ References

No definition available.

+ Details

Name:	fcnca_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversalExcludingAmountAcquiredInAcquisition
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) with previously recorded allowance and not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-9

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

Name:	us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_ReceivablesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration