XML 95 R74.htm IDEA: XBRL DOCUMENT
v3.25.0.1

INVESTMENT SECURITIES - Schedule of Interest and Dividends on Investment Securities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Investments [Abstract] |  |  |
Interest income - taxable investment securities | $ 1,344 | $ 642 | $ 352
Interest income - nontaxable investment securities | 1 | 4 | 0
Dividend income - marketable equity securities | 2 | 2 | 2
Interest on investment securities | $ 1,347 | $ 648 | $ 354

X
- Definition Interest Income, Investment Securities, Operating, Tax Exempt + References No definition available. + Details
Name: | fcnca_InterestIncomeInvestmentSecuritiesOperatingTaxExempt
Namespace Prefix: | fcnca_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Interest Income, Investment Securities, Operating, Taxable + References No definition available. + Details
Name: | fcnca_InterestIncomeInvestmentSecuritiesOperatingTaxable
Namespace Prefix: | fcnca_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of dividend income on investment in equity security, classified as operating. + References No definition available. + Details
Name: | us-gaap_DividendIncomeEquitySecuritiesOperating
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph a -Publisher SEC Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph b -Subparagraph (1)(Instruction 4) -Publisher SEC + Details
Name: | us-gaap_InterestIncomeSecuritiesTaxable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration