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

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

No definition available.

+ Details

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

- Definition

Amount of fee received for commitment to originate or purchase financing receivable where likelihood of commitment being exercised is remote. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10095-111533

+ Details

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

+ Details

Name:	us-gaap_NotesReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

LOANS - Corporate Loans (Details) - USD ($) $ in Millions	3 Months Ended
LOANS - Corporate Loans (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Loans
Loans, net of unearned income	$ 665,988		$ 675,883
Lease financing
Loans
Loans, net of unearned income	600		700
Corporate
Loans
Loans, net of unearned income	391,954		387,044
Unearned income	(844)		(844)
Loans sold and/or reclassified to held-for-sale	500	$ 200
Corporate \| Commercial and industrial
Loans
Loans, net of unearned income	151,800		156,340
Corporate \| Financial institutions
Loans
Loans, net of unearned income	91,518		87,689
Corporate \| Mortgage and real estate
Loans
Loans, net of unearned income	72,142		72,038
Corporate \| Lease financing
Loans
Loans, net of unearned income	595		738
Corporate \| In North America offices
Loans
Loans, net of unearned income	203,207		201,632
Corporate \| In North America offices \| Commercial and industrial
Loans
Loans, net of unearned income	55,497		57,731
Corporate \| In North America offices \| Financial institutions
Loans
Loans, net of unearned income	57,009		55,809
Corporate \| In North America offices \| Mortgage and real estate
Loans
Loans, net of unearned income	60,976		60,675
Corporate \| In North America offices \| Installment and other
Loans
Loans, net of unearned income	29,186		26,744
Corporate \| In North America offices \| Lease financing
Loans
Loans, net of unearned income	539		673
Corporate \| In offices outside North America
Loans
Loans, net of unearned income	188,747		185,412
Corporate \| In offices outside North America \| Commercial and industrial
Loans
Loans, net of unearned income	102,666		104,072
Corporate \| In offices outside North America \| Financial institutions
Loans
Loans, net of unearned income	34,729		32,334
Corporate \| In offices outside North America \| Mortgage and real estate
Loans
Loans, net of unearned income	11,166		11,371
Corporate \| In offices outside North America \| Installment and other
Loans
Loans, net of unearned income	35,347		33,759
Corporate \| In offices outside North America \| Lease financing
Loans
Loans, net of unearned income	56		65
Corporate \| In offices outside North America \| Government and official institutions
Loans
Loans, net of unearned income	$ 4,783		$ 3,811