LOANS - Interest Income Recognized for Non-Accrual Consumer Loans (Details) - Consumer loans - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Nonaccrual [Line Items]
Interest income	$ 6	$ 6
Loans sold and/or reclassified to held-for-sale	59	1,828
In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	4	5
In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	2	1
Residential mortgages \| In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	3	3
Residential mortgages \| In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	2	1
Home equity loans \| In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	1	2
Credit cards \| In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Credit cards \| In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Personal, small business and other \| In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Personal, small business and other \| In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	$ 0	$ 0

Total amount of portfolio loans sold and or reclassified to loans held-for-sale during the period.

No definition available.

Name:	c_SalesOrReclassificationOfPortfolioLoansToHeldForSale
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income on financing receivable on nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

+ Details

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

- 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/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=srt_NorthAmericaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=us-gaap_NonUsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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