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 deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=84165051&loc=d3e45377-112738

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5074-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159169&loc=d3e10152-111534

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5074-111524

+ Details

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

- 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:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=c_LeaseFinancingMember
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		6 Months Ended
LOANS - Corporate Loans (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Loans
Loans, net of unearned income	$ 688,670		$ 688,670		$ 684,196
Corporate
Loans
Loans, net of unearned income	362,675		362,675		353,709
Net unearned income	(815)		(815)		(822)
Loans sold and/or reclassified to held-for-sale	800	$ 400	1,300	$ 500
Corporate \| Commercial and industrial
Loans
Loans, net of unearned income	150,987		150,987		145,286
Corporate \| Financial institutions
Loans
Loans, net of unearned income	83,279		83,279		83,868
Corporate \| Mortgage and real estate
Loans
Loans, net of unearned income	58,880		58,880		57,464
Corporate \| Lease financing
Loans
Loans, net of unearned income	1,477		1,477		1,531
Corporate \| In North America offices(1)
Loans
Total loans	188,390		188,390		184,488
Corporate \| In North America offices(1) \| Commercial and industrial
Loans
Total loans	54,519		54,519		52,063
Corporate \| In North America offices(1) \| Financial institutions
Loans
Total loans	47,610		47,610		48,447
Corporate \| In North America offices(1) \| Mortgage and real estate
Loans
Total loans	51,321		51,321		50,124
Corporate \| In North America offices(1) \| Installment, revolving credit and other
Loans
Total loans	33,555		33,555		32,425
Corporate \| In North America offices(1) \| Lease financing
Loans
Total loans	1,385		1,385		1,429
Corporate \| In offices outside North America(1)
Loans
Total loans	174,285		174,285		169,221
Corporate \| In offices outside North America(1) \| Commercial and industrial
Loans
Total loans	98,351		98,351		94,701
Corporate \| In offices outside North America(1) \| Financial institutions
Loans
Total loans	37,523		37,523		36,837
Corporate \| In offices outside North America(1) \| Mortgage and real estate
Loans
Total loans	7,577		7,577		7,376
Corporate \| In offices outside North America(1) \| Installment, revolving credit and other
Loans
Total loans	27,333		27,333		25,684
Corporate \| In offices outside North America(1) \| Lease financing
Loans
Total loans	92		92		103
Corporate \| In offices outside North America(1) \| Government and official institutions
Loans
Total loans	$ 3,409		$ 3,409		$ 4,520