XML 165 R146.htm IDEA: XBRL DOCUMENT v3.25.4

EMPLOYEE BENEFIT PLANS - Schedule of Accrued Liabilities (Details) - Additional Benefits for Executives, Directors, and Officers - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Deferred Compensation Liability, Current and Noncurrent [Roll Forward]
Accrued liability as of January 1	$ 33	$ 34
Benefit expense and interest cost	2	3
Benefits paid	(3)	(4)
Accrued liability as of December 31	$ 32	$ 33
Discount rate at December 31	4.68%	4.86%

X

- Definition

Deferred Compensation Arrangement with Individual, Discount Rate

+ References

No definition available.

+ Details

Name:	fcnca_DeferredCompensationArrangementWithIndividualDiscountRate
Namespace Prefix:	fcnca_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Deferred Compensation Liability, Current and Noncurrent

+ References

No definition available.

+ Details

Name:	fcnca_DeferredCompensationLiabilityCurrentAndNoncurrentRollForward
Namespace Prefix:	fcnca_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 710
-SubTopic 10
-Name Accounting Standards Codification
-Section 30
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483043/710-10-30-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-1

+ Details

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

X

- Definition

Amount of distribution made to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

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

X

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_RetirementPlanNameAxis=fcnca_AdditionalBenefitsForExecutivesDirectorsAndOfficersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: