LOANS - Consumer Loan Delinquency (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Loans receivable
Loans, net of unearned income	$ 621,054	$ 644,635
Loans at fair value	6,575	5,901
Residential first mortgages | Less than or equal to 80% | Loan to Values (LTVs)
Loans receivable
Loans	47,303	48,163
Residential first mortgages | 80% but less than or equal to 100% | Loan to Values (LTVs)
Loans receivable
Loans	8,619	9,480
Residential first mortgages | Greater than 100% | Loan to Values (LTVs)
Loans receivable
Loans	2,464	2,670
Residential first mortgages | Less than 620 | Consumer
Loans receivable
Loans	8,071	8,911
Residential first mortgages | ≥ 620 but less than 660 | Consumer
Loans receivable
Loans	4,981	5,463
Residential first mortgages | Equal to or greater than 660 | Consumer
Loans receivable
Loans	45,207	45,783
Home equity loans | Less than or equal to 80% | Loan to Values (LTVs)
Loans receivable
Loans	14,330	14,638
Home equity loans | 80% but less than or equal to 100% | Loan to Values (LTVs)
Loans receivable
Loans	6,729	7,267
Home equity loans | Greater than 100% | Loan to Values (LTVs)
Loans receivable
Loans	4,588	4,641
Home equity loans | Less than 620 | Consumer
Loans receivable
Loans	3,124	3,257
Home equity loans | ≥ 620 but less than 660 | Consumer
Loans receivable
Loans	2,367	2,456
Home equity loans | Equal to or greater than 660 | Consumer
Loans receivable
Loans	20,271	20,957
Credit cards | Less than 620 | Consumer
Loans receivable
Loans	7,558	7,647
Credit cards | ≥ 620 but less than 660 | Consumer
Loans receivable
Loans	9,935	10,296
Credit cards | Equal to or greater than 660 | Consumer
Loans receivable
Loans	85,779	92,877
Installment and other | Less than 620 | Consumer
Loans receivable
Loans	324	4,015
Installment and other | ≥ 620 but less than 660 | Consumer
Loans receivable
Loans	248	2,520
Installment and other | Equal to or greater than 660 | Consumer
Loans receivable
Loans	2,576	5,150
Open-ended consumer loans
Loans receivable
Minimum number of payments made consecutively for the loans to be re-aged	3
Consumer
Loans receivable
Period within which default occurred post-modification	1 year
Number of days past due, non-accrual status	60 days
Loans, current	331,243	357,348
Loans, net of unearned income	341,706	369,970
Loans, total non-accrual	5,593	5,924
Loans, 90 days past due and accruing	3,804	4,372
Loans less than this number of days past due are considered current	30 days	30 days
Consumer | Minimum
Loans receivable
Minimum number of payments made consecutively for the loans to be re-aged	1
Consumer | Maximum
Loans receivable
Minimum number of payments made consecutively for the loans to be re-aged	3
Consumer | Less than or equal to 80% | Loan to Values (LTVs)
Loans receivable
Loans	61,633	62,801
Consumer | 80% but less than or equal to 100% | Loan to Values (LTVs)
Loans receivable
Loans	15,348	16,747
Consumer | Greater than 100% | Loan to Values (LTVs)
Loans receivable
Loans	7,052	7,311
Consumer | Less than 620 | Consumer
Loans receivable
Loans	19,077	23,830
Consumer | ≥ 620 but less than 660 | Consumer
Loans receivable
Loans	17,531	20,735
Consumer | Equal to or greater than 660 | Consumer
Loans receivable
Loans	153,833	164,767
Consumer | Government-guaranteed
Loans receivable
Loans, past due	2,652	3,443
Consumer | 30 to 89 Days Past Due
Loans receivable
Loans, past due	3,859	4,529
Consumer | Equal to greater than 90 days past due
Loans receivable
Loans, past due	3,952	4,650
Consumer | Residential first mortgages
Loans receivable
Number of days past due, non-accrual status	90 days	90 days
Loans at fair value	38	43
Consumer | Home equity loans
Loans receivable
Number of days past due, non-accrual status	90 days
Consumer | Credit cards
Loans receivable
Number of days past due, non-accrual status	180 days
Consumer | Installment and other
Loans receivable
Number of days past due, non-accrual status	90 days
Consumer | Commercial market loans
Loans receivable
Number of days past due, non-accrual status	90 days
Consumer | Total GCB and Citi Holdings Consumer
Loans receivable
Loans, current	331,016	357,110
Loans, net of unearned income	341,461	369,711
Loans, total non-accrual	5,564	5,894
Loans, 90 days past due and accruing	3,804	4,372
Consumer | Total GCB and Citi Holdings Consumer | Government-guaranteed
Loans receivable
Loans, past due	2,652	3,443
Consumer | Total GCB and Citi Holdings Consumer | 30 to 89 Days Past Due
Loans receivable
Loans, past due	3,850	4,519
Consumer | Total GCB and Citi Holdings Consumer | Equal to greater than 90 days past due
Loans receivable
Loans, past due	3,943	4,639
Consumer | Other
Loans receivable
Loans, current	227	238
Loans, net of unearned income	245	259
Loans, total non-accrual	29	30
Loans, 90 days past due and accruing	0	0
Consumer | Other | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | Other | 30 to 89 Days Past Due
Loans receivable
Loans, past due	9	10
Consumer | Other | Equal to greater than 90 days past due
Loans receivable
Loans, past due	9	11
Consumer | Open-ended consumer loans
Loans receivable
Number of re-age modification limitations in twelve months	1
Number of re-age modification limitations in five years	2
Consumer | Unsecured Revolving Loans
Loans receivable
Number of days past due, non-accrual status	180 days
Consumer | In North America Offices
Loans receivable
Loans, current	202,066	221,424
Loans, net of unearned income	210,216	231,517
Loans, total non-accrual	4,187	4,406
Loans, 90 days past due and accruing	3,497	4,050
Consumer | In North America Offices | Government-guaranteed
Loans receivable
Loans, past due	2,652	3,443
Consumer | In North America Offices | 30 to 89 Days Past Due
Loans receivable
Loans, past due	2,570	3,191
Consumer | In North America Offices | Equal to greater than 90 days past due
Loans receivable
Loans, past due	2,928	3,459
Consumer | In North America Offices | Residential first mortgages
Loans receivable
Loans, current	59,466	61,730
Loans, net of unearned income	64,295	67,824
Loans, total non-accrual	2,768	2,746
Loans, 90 days past due and accruing	2,285	2,759
Consumer | In North America Offices | Residential first mortgages | Government-guaranteed
Loans receivable
Loans, past due	2,652	3,443
Consumer | In North America Offices | Residential first mortgages | 30 to 89 Days Past Due
Loans receivable
Loans, past due	1,005	1,280
Consumer | In North America Offices | Residential first mortgages | 30 to 89 Days Past Due | Government-guaranteed
Loans receivable
Loans, past due	400	600
Consumer | In North America Offices | Residential first mortgages | Equal to greater than 90 days past due
Loans receivable
Loans, past due	1,172	1,371
Consumer | In North America Offices | Residential first mortgages | Equal to greater than 90 days past due | Government-guaranteed
Loans receivable
Loans, past due	2,300	2,800
Consumer | In North America Offices | Home equity loans
Loans receivable
Loans, current	26,339	27,262
Loans, net of unearned income	27,125	28,117
Loans, total non-accrual	1,273	1,271
Loans, 90 days past due and accruing	0	0
Consumer | In North America Offices | Home equity loans | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In North America Offices | Home equity loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	281	335
Consumer | In North America Offices | Home equity loans | Equal to greater than 90 days past due
Loans receivable
Loans, past due	505	520
Consumer | In North America Offices | Credit cards
Loans receivable
Loans, current	103,587	111,441
Loans, net of unearned income	105,955	114,028
Loans, total non-accrual	0	0
Loans, 90 days past due and accruing	1,198	1,273
Consumer | In North America Offices | Credit cards | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In North America Offices | Credit cards | 30 to 89 Days Past Due
Loans receivable
Loans, past due	1,170	1,316
Consumer | In North America Offices | Credit cards | Equal to greater than 90 days past due
Loans receivable
Loans, past due	1,198	1,271
Consumer | In North America Offices | Installment and other
Loans receivable
Loans, current	4,158	12,361
Loans, net of unearned income	4,257	12,874
Loans, total non-accrual	30	254
Loans, 90 days past due and accruing	3	3
Consumer | In North America Offices | Installment and other | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In North America Offices | Installment and other | 30 to 89 Days Past Due
Loans receivable
Loans, past due	60	229
Consumer | In North America Offices | Installment and other | Equal to greater than 90 days past due
Loans receivable
Loans, past due	39	284
Consumer | In North America Offices | Commercial market loans
Loans receivable
Loans, current	8,516	8,630
Loans, net of unearned income	8,584	8,674
Loans, total non-accrual	116	135
Loans, 90 days past due and accruing	11	15
Consumer | In North America Offices | Commercial market loans | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In North America Offices | Commercial market loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	54	31
Consumer | In North America Offices | Commercial market loans | Equal to greater than 90 days past due
Loans receivable
Loans, past due	14	13
Consumer | In offices outside North America
Loans receivable
Loans, current	128,950	135,686
Loans, net of unearned income	131,245	138,194
Loans, total non-accrual	1,377	1,488
Loans, 90 days past due and accruing	307	322
Consumer | In offices outside North America | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | 30 to 89 Days Past Due
Loans receivable
Loans, past due	1,280	1,328
Consumer | In offices outside North America | Equal to greater than 90 days past due
Loans receivable
Loans, past due	1,015	1,180
Consumer | In offices outside North America | Residential first mortgages
Loans receivable
Loans, current	41,663	44,782
Loans, net of unearned income	42,164	45,317
Loans, total non-accrual	434	454
Loans, 90 days past due and accruing	0	0
Consumer | In offices outside North America | Residential first mortgages | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Residential first mortgages | 30 to 89 Days Past Due
Loans receivable
Loans, past due	304	312
Consumer | In offices outside North America | Residential first mortgages | Equal to greater than 90 days past due
Loans receivable
Loans, past due	197	223
Consumer | In offices outside North America | Home equity loans
Loans receivable
Loans, current	0	0
Loans, net of unearned income	0	0
Loans, total non-accrual	0	0
Loans, 90 days past due and accruing	0	0
Consumer | In offices outside North America | Home equity loans | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Home equity loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Home equity loans | Equal to greater than 90 days past due
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Credit cards
Loans receivable
Loans, current	27,457	30,327
Loans, net of unearned income	28,512	31,482
Loans, total non-accrual	347	413
Loans, 90 days past due and accruing	307	322
Consumer | In offices outside North America | Credit cards | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Credit cards | 30 to 89 Days Past Due
Loans receivable
Loans, past due	567	602
Consumer | In offices outside North America | Credit cards | Equal to greater than 90 days past due
Loans receivable
Loans, past due	488	553
Consumer | In offices outside North America | Installment and other
Loans receivable
Loans, current	30,575	29,297
Loans, net of unearned income	31,053	29,774
Loans, total non-accrual	200	216
Loans, 90 days past due and accruing	0	0
Consumer | In offices outside North America | Installment and other | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Installment and other | 30 to 89 Days Past Due
Loans receivable
Loans, past due	334	328
Consumer | In offices outside North America | Installment and other | Equal to greater than 90 days past due
Loans receivable
Loans, past due	144	149
Consumer | In offices outside North America | Commercial market loans
Loans receivable
Loans, current	29,255	31,280
Loans, net of unearned income	29,516	31,621
Loans, total non-accrual	396	405
Loans, 90 days past due and accruing	0	0
Consumer | In offices outside North America | Commercial market loans | Government-guaranteed
Loans receivable
Loans, past due	0	0
Consumer | In offices outside North America | Commercial market loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	75	86
Consumer | In offices outside North America | Commercial market loans | Equal to greater than 90 days past due
Loans receivable
Loans, past due	$ 186	$ 255