GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill by Segment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Goodwill
Balance of goodwill at beginning of period	$ 25,009us-gaap_Goodwill	$ 25,673us-gaap_Goodwill
Disposals	(203)	(82)
Other	(1,214)us-gaap_GoodwillOtherChanges	(582)us-gaap_GoodwillOtherChanges
Intersegment transfers in/(out)	0us-gaap_GoodwillTransfers
Balance of goodwill at end of period	23,592us-gaap_Goodwill	25,009us-gaap_Goodwill
Global Consumer Banking
Goodwill
Balance of goodwill at beginning of period	13,985	14,539
Disposals	(86)	(82)
Other	(505)	(472)
Intersegment transfers in/(out)	(177)
Balance of goodwill at end of period	13,217	13,985
Institutional Clients Group
Goodwill
Balance of goodwill at beginning of period	10,868	10,981
Disposals	(1)	0
Other	(711)	(113)
Intersegment transfers in/(out)	0
Balance of goodwill at end of period	10,156	10,868
Citi Holdings
Goodwill
Balance of goodwill at beginning of period	156	153
Disposals	(116)	0
Other	2	3
Intersegment transfers in/(out)	177
Balance of goodwill at end of period	$ 219	$ 156

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

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

- Definition

Amount of other (increase) decrease of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

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- Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of transfers of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized among segments.

+ References

No definition available.

+ Details

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

- Definition

Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

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Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=c_GlobalConsumerBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=c_InstitutionalClientsGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: