INVESTMENTS (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Investments summary
Securities available-for-sale, at fair value	$ 278,297	$ 274,572
Debt securities held-to-maturity	14,910	29,107
Non-marketable equity securities carried at fair value	8,345	6,602
Non-marketable equity securities carried at cost	8,022	7,883
Total investments	309,574	318,164
Securities available-for-sale
Securities available-for-sale, at fair value	278,297	274,572
Mortgage-backed securities
Investments summary
Securities available-for-sale, at fair value	38,566	26,506
Securities available-for-sale
Amortized cost	38,064	26,490
Gross unrealized gains	649	468
Gross unrealized losses	147	452
Securities available-for-sale, at fair value	38,566	26,506
U.S. government-sponsored agency guaranteed
Investments summary
Securities available-for-sale, at fair value	36,206	23,623
Securities available-for-sale
Amortized cost	35,708	23,433
Gross unrealized gains	621	425
Gross unrealized losses	123	235
Securities available-for-sale, at fair value	36,206	23,623
Prime
Investments summary
Securities available-for-sale, at fair value	184	1,826
Securities available-for-sale
Amortized cost	186	1,985
Gross unrealized gains	2	18
Gross unrealized losses	4	177
Securities available-for-sale, at fair value	184	1,826
Alt-A
Investments summary
Securities available-for-sale, at fair value	11	48
Securities available-for-sale
Amortized cost	23	46
Gross unrealized gains	1	2
Gross unrealized losses	13
Securities available-for-sale, at fair value	11	48
Subprime
Investments summary
Securities available-for-sale, at fair value		119
Securities available-for-sale
Amortized cost		119
Gross unrealized gains		1
Gross unrealized losses		1
Securities available-for-sale, at fair value		119
Non-U.S. residential
Investments summary
Securities available-for-sale, at fair value	1,643	316
Securities available-for-sale
Amortized cost	1,637	315
Gross unrealized gains	6	1
Securities available-for-sale, at fair value	1,643	316
Commercial.
Investments summary
Securities available-for-sale, at fair value	522	574
Securities available-for-sale
Amortized cost	510	592
Gross unrealized gains	19	21
Gross unrealized losses	7	39
Securities available-for-sale, at fair value	522	574
U.S. Treasury and federal agency securities
Investments summary
Securities available-for-sale, at fair value	90,350	102,062
Securities available-for-sale
Amortized cost	89,133	101,363
Gross unrealized gains	1,252	810
Gross unrealized losses	35	111
Securities available-for-sale, at fair value	90,350	102,062
U.S. Treasury
Investments summary
Securities available-for-sale, at fair value	43,380	58,448
Securities available-for-sale
Amortized cost	42,668	58,069
Gross unrealized gains	743	435
Gross unrealized losses	31	56
Securities available-for-sale, at fair value	43,380	58,448
Agency obligations
Investments summary
Securities available-for-sale, at fair value	46,970	43,614
Securities available-for-sale
Amortized cost	46,465	43,294
Gross unrealized gains	509	375
Gross unrealized losses	4	55
Securities available-for-sale, at fair value	46,970	43,614
State and municipal securities
Investments summary
Securities available-for-sale, at fair value	13,331	13,235
Securities available-for-sale
Amortized cost	15,527	15,660
Gross unrealized gains	69	75
Gross unrealized losses	2,265	2,500
Securities available-for-sale, at fair value	13,331	13,235
Foreign government
Investments summary
Securities available-for-sale, at fair value	102,083	99,679
Securities available-for-sale
Amortized cost	101,723	99,110
Gross unrealized gains	784	984
Gross unrealized losses	424	415
Securities available-for-sale, at fair value	102,083	99,679
Corporate
Investments summary
Securities available-for-sale, at fair value	16,667	16,170
Securities available-for-sale
Amortized cost	16,350	15,910
Gross unrealized gains	355	319
Gross unrealized losses	38	59
Securities available-for-sale, at fair value	16,667	16,170
Asset-based financing
Investments summary
Securities available-for-sale, at fair value	9,654	9,048
Securities available-for-sale
Amortized cost	9,646	9,085
Gross unrealized gains	47	31
Gross unrealized losses	39	68
Securities available-for-sale, at fair value	9,654	9,048
Other debt securities
Investments summary
Securities available-for-sale, at fair value	2,185	1,912
Securities available-for-sale
Amortized cost	2,218	1,948
Gross unrealized gains	22	24
Gross unrealized losses	55	60
Securities available-for-sale, at fair value	2,185	1,912
Total debt securities AFS
Investments summary
Securities available-for-sale, at fair value	272,836	268,612
Securities available-for-sale
Amortized cost	272,661	269,566
Gross unrealized gains	3,178	2,711
Gross unrealized losses	3,003	3,665
Securities available-for-sale, at fair value	272,836	268,612
Marketable equity securities AFS
Investments summary
Securities available-for-sale, at fair value	5,461	5,960
Securities available-for-sale
Amortized cost	3,570	3,791
Gross unrealized gains	2,099	2,380
Gross unrealized losses	208	211
Securities available-for-sale, at fair value	5,461	5,960
Total securities AFS
Investments summary
Securities available-for-sale, at fair value	278,297	274,572
Securities available-for-sale
Amortized cost	276,231	273,357
Gross unrealized gains	5,277	5,091
Gross unrealized losses	3,211	3,876
Securities available-for-sale, at fair value	$ 278,297	$ 274,572

This item represents the gross unrealized gains for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized gains are the excess of the fair value of the Available-for-sale Securities over their carrying value as of the reporting date.

Name:	c_AvailableForSaleSecuritiesUnrealizedGainsGross
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date.

+ Details

Name:	c_AvailableForSaleSecuritiesUnrealizedLossesGross
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	c_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix:	c
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the fair value of non-marketable equity securities.

+ Details

Name:	c_NonMarketableEquitySecuritiesFairValue
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	c_ScheduleOfAvailableForSaleSecuritiesAbstract
Namespace Prefix:	c
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 16

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 22

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 12
-Subparagraph b

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 14

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 7
-Footnote 2

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 19

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the aggregate carrying amount of all cost-method investments held by the Company. Generally, such investments do not have readily determinable fair values and are not required to be accounted for by the equity method. The carrying amount of such securities equates to cost, adjusted for other-than-temporary impairment. The cost method and lower-of-cost or market, an adaptation of the cost method, is generally followed for most investments in noncontrolled corporations, in some corporate joint ventures, and to a lesser extent in unconsolidated subsidiaries, particularly foreign.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 03-1
-Paragraph 22
-Subparagraph a

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 18
-Subparagraph a

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 18
-Paragraph 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 4

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 4
-Subparagraph c

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 18
-Paragraph 6
-Subparagraph a

+ Details

Name:	us-gaap_CostMethodInvestmentsAggregateCarryingAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity; such investments are measured at amortized cost (carrying value). The held-to-maturity category is for those securities that the Entity has the positive intent and ability to hold until maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Chapter 3
-Section A
-Paragraph 4, 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 17

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 7, 8, 9, 10, 11

+ Details

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Sum of the carrying amounts as of the balance sheet date of current and noncurrent investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Subparagraph h
-Article 7

+ Details

Name:	us-gaap_Investments
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant