XML 149 R130.htm IDEA: XBRL DOCUMENT v3.25.4

REGULATORY CAPITAL - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($)	Dec. 31, 2024
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	0.0571	0.0704
Basel III conservation buffers, total risk-based capital	0.0250
FCB
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	0.0562	0.0666
Dividend restrictions, additional maximum amount of distribution	$ 6,570
Payments of dividends	$ 1,680

X

- Definition

Banking Regulation, Dividend Restrictions, Maximum Additional Amount Of Distribution

+ References

No definition available.

+ Details

Name:	fcnca_BankingRegulationDividendRestrictionsMaximumAdditionalAmountOfDistribution
Namespace Prefix:	fcnca_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Banking Regulation, Total Risk-Based Capital Ratio, Capital Conservation Buffer

+ References

No definition available.

+ Details

Name:	fcnca_BankingRegulationTotalRiskBasedCapitalRatioCapitalConservationBuffer
Namespace Prefix:	fcnca_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Banking Regulation, Total Risk-Based Capital Ratio, Conservation Buffer, Minimum

+ References

No definition available.

+ Details

Name:	fcnca_BankingRegulationTotalRiskBasedCapitalRatioConservationBufferMinimum
Namespace Prefix:	fcnca_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

+ Details

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

X

- Definition

Cash outflow in the form of ordinary dividends to common shareholders, preferred shareholders and noncontrolling interests, generally out of earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ Details

Name:	us-gaap_PaymentsOfOrdinaryDividends
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	dei_LegalEntityAxis=fcnca_FCBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: