LOANS (Details 2) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Loans receivable
Loans, net of unearned income	$ 657,551,000,000	$ 655,464,000,000
Loans at fair value	5,198,000,000	5,287,000,000
Residential First Mortgage Loans | Loan to Values (LTVs)
Residential Mortgage Loan to Values
Loan, credit indicator ratio less than or equal to 80%	46,072,000,000	41,555,000,000
Loan, credit indicator ratio greater than 80% but less than or equal to 100%	13,840,000,000	19,070,000,000
Loan, credit indicator ratio greater than 100%	5,660,000,000	14,995,000,000
Residential First Mortgage Loans | Consumer Credit Scores (FICOs)
Consumer Loans Credit Quality Indicators, FICO score
Loan, credit score less than 620	12,591,000,000	16,754,000,000
Loan, credit score equal to or greater than 620 but less than 660	6,779,000,000	8,013,000,000
Loan, credit score equal to or greater than 660	46,164,000,000	50,833,000,000
Home equity loans | Loan to Values (LTVs)
Residential Mortgage Loan to Values
Loan, credit indicator ratio less than or equal to 80%	14,534,000,000	12,611,000,000
Loan, credit indicator ratio greater than 80% but less than or equal to 100%	9,212,000,000	9,529,000,000
Loan, credit indicator ratio greater than 100%	7,221,000,000	13,153,000,000
Home equity loans | Consumer Credit Scores (FICOs)
Consumer Loans Credit Quality Indicators, FICO score
Loan, credit score less than 620	4,348,000,000	5,439,000,000
Loan, credit score equal to or greater than 620 but less than 660	2,903,000,000	3,208,000,000
Loan, credit score equal to or greater than 660	23,937,000,000	26,820,000,000
Credit cards | Consumer Credit Scores (FICOs)
Consumer Loans Credit Quality Indicators, FICO score
Loan, credit score less than 620	7,505,000,000	7,833,000,000
Loan, credit score equal to or greater than 620 but less than 660	10,156,000,000	10,304,000,000
Loan, credit score equal to or greater than 660	90,378,000,000	90,248,000,000
Installment and other | Consumer Credit Scores (FICOs)
Consumer Loans Credit Quality Indicators, FICO score
Loan, credit score less than 620	3,823,000,000	4,414,000,000
Loan, credit score equal to or greater than 620 but less than 660	2,381,000,000	2,417,000,000
Loan, credit score equal to or greater than 660	5,142,000,000	5,365,000,000
Consumer
Loans receivable
Loans, current	370,672,000,000	387,194,000,000
Loans, 30-89 days past due	6,074,000,000	7,755,000,000
Loans, greater than or equal to 90 days past due	5,649,000,000	7,722,000,000
Loans, Past due government guaranteed	5,427,000,000	6,000,000,000
Loans, net of unearned income	387,822,000,000	408,671,000,000
Loans, total non-accrual	7,203,000,000	9,196,000,000
Loans, 90 days past due and accruing	5,877,000,000	6,749,000,000
Loans less than this number of days past due are considered current	30 days	30 days
Loans at fair value	996,000,000	1,231,000,000
Consumer | Minimum
Residential Mortgage Loan to Values
Minimum number of payments made consecutively for the loans to be re-aged	1	1
Consumer | Maximum
Residential Mortgage Loan to Values
Minimum number of payments made consecutively for the loans to be re-aged	3	3
Consumer | Loan to Values (LTVs)
Residential Mortgage Loan to Values
Loan, credit indicator ratio less than or equal to 80%	60,606,000,000	54,166,000,000
Loan, credit indicator ratio greater than 80% but less than or equal to 100%	23,052,000,000	28,599,000,000
Loan, credit indicator ratio greater than 100%	12,881,000,000	28,148,000,000
Consumer | Consumer Credit Scores (FICOs)
Consumer Loans Credit Quality Indicators, FICO score
Loan, credit score less than 620	28,267,000,000	34,440,000,000
Loan, credit score equal to or greater than 620 but less than 660	22,219,000,000	23,942,000,000
Loan, credit score equal to or greater than 660	165,621,000,000	173,266,000,000
Consumer | Residential First Mortgage Loans
Loans receivable
Loans at fair value	1,000,000,000	1,200,000,000
Delinquency status
Number of days past due, non-accrual status	90 days	90 days
Consumer | Home equity loans
Delinquency status
Number of days past due, non-accrual status	90 days	90 days
Consumer | Credit cards
Delinquency status
Number of days past due, non-accrual status	180 days	180 days
Consumer | Installment and other
Delinquency status
Number of days past due, non-accrual status	90 days	90 days
Consumer | Commercial market loans
Delinquency status
Number of days past due, non-accrual status	90 days	90 days
Consumer | Other
Loans receivable
Loans, current	369,000,000	545,000,000
Loans, 30-89 days past due	14,000,000	18,000,000
Loans, greater than or equal to 90 days past due	18,000,000	29,000,000
Loans, net of unearned income	401,000,000	592,000,000
Loans, total non-accrual	48,000,000	81,000,000
Consumer | Total GCB and Citi Holdings Consumer
Loans receivable
Loans, current	370,303,000,000	386,649,000,000
Loans, 30-89 days past due	6,060,000,000	7,737,000,000
Loans, greater than or equal to 90 days past due	5,631,000,000	7,693,000,000
Loans, Past due government guaranteed	5,427,000,000	6,000,000,000
Loans, net of unearned income	387,421,000,000	408,079,000,000
Loans, total non-accrual	7,155,000,000	9,115,000,000
Loans, 90 days past due and accruing	5,877,000,000	6,749,000,000
Consumer | Unsecured Revolving Loans
Delinquency status
Number of days past due, non-accrual status	180 days	180 days
Consumer | In North America Offices
Loans receivable
Loans, current	229,313,000,000	241,616,000,000
Loans, 30-89 days past due	4,319,000,000	5,618,000,000
Loans, greater than or equal to 90 days past due	4,310,000,000	6,053,000,000
Loans, Past due government guaranteed	5,427,000,000	6,000,000,000
Loans, net of unearned income	243,369,000,000	259,287,000,000
Loans, total non-accrual	5,292,000,000	7,108,000,000
Loans, 90 days past due and accruing	5,453,000,000	6,241,000,000
Consumer | In North America Offices | Residential First Mortgage Loans
Loans receivable
Loans, current	67,381,000,000	75,791,000,000
Loans, 30-89 days past due	2,163,000,000	3,074,000,000
Loans, greater than or equal to 90 days past due	2,110,000,000	3,339,000,000
Loans, Past due government guaranteed	5,427,000,000	6,000,000,000
Loans, net of unearned income	77,081,000,000	88,204,000,000
Loans, total non-accrual	3,540,000,000	4,922,000,000
Loans, 90 days past due and accruing	4,159,000,000	4,695,000,000
Loans, 30-89 days past due, guaranteed by U.S. government-sponsored agencies	1,300,000,000	1,300,000,000
Loans, greater than or equal to 90 days past due, guaranteed by U.S. government-sponsored agencies	4,100,000,000	4,700,000,000
Consumer | In North America Offices | Home equity loans
Loans receivable
Loans, current	31,720,000,000	35,740,000,000
Loans, 30-89 days past due	438,000,000	642,000,000
Loans, greater than or equal to 90 days past due	663,000,000	843,000,000
Loans, net of unearned income	32,821,000,000	37,225,000,000
Loans, total non-accrual	1,398,000,000	1,797,000,000
Consumer | In North America Offices | Credit cards
Loans receivable
Loans, current	109,260,000,000	108,892,000,000
Loans, 30-89 days past due	1,455,000,000	1,582,000,000
Loans, greater than or equal to 90 days past due	1,283,000,000	1,527,000,000
Loans, net of unearned income	111,998,000,000	112,001,000,000
Loans, 90 days past due and accruing	1,283,000,000	1,527,000,000
Consumer | In North America Offices | Installment and other
Loans receivable
Loans, current	12,562,000,000	13,319,000,000
Loans, 30-89 days past due	224,000,000	288,000,000
Loans, greater than or equal to 90 days past due	224,000,000	325,000,000
Loans, net of unearned income	13,010,000,000	13,932,000,000
Loans, total non-accrual	229,000,000	179,000,000
Loans, 90 days past due and accruing	4,000,000	8,000,000
Consumer | In North America Offices | Commercial market loans
Loans receivable
Loans, current	8,390,000,000	7,874,000,000
Loans, 30-89 days past due	39,000,000	32,000,000
Loans, greater than or equal to 90 days past due	30,000,000	19,000,000
Loans, net of unearned income	8,459,000,000	7,925,000,000
Loans, total non-accrual	125,000,000	210,000,000
Loans, 90 days past due and accruing	7,000,000	11,000,000
Consumer | In offices outside North America
Loans receivable
Loans, current	140,990,000,000	145,033,000,000
Loans, 30-89 days past due	1,741,000,000	2,119,000,000
Loans, greater than or equal to 90 days past due	1,321,000,000	1,640,000,000
Loans, net of unearned income	144,052,000,000	148,792,000,000
Loans, total non-accrual	1,863,000,000	2,007,000,000
Loans, 90 days past due and accruing	424,000,000	508,000,000
Consumer | In offices outside North America | Residential First Mortgage Loans
Loans receivable
Loans, current	45,223,000,000	45,496,000,000
Loans, 30-89 days past due	458,000,000	547,000,000
Loans, greater than or equal to 90 days past due	326,000,000	485,000,000
Loans, net of unearned income	46,007,000,000	46,528,000,000
Loans, total non-accrual	567,000,000	807,000,000
Consumer | In offices outside North America | Home equity loans
Loans receivable
Loans, current		4,000,000
Loans, greater than or equal to 90 days past due		2,000,000
Loans, net of unearned income		6,000,000
Loans, total non-accrual		2,000,000
Consumer | In offices outside North America | Credit cards
Loans receivable
Loans, current	33,955,000,000	38,920,000,000
Loans, 30-89 days past due	754,000,000	970,000,000
Loans, greater than or equal to 90 days past due	621,000,000	805,000,000
Loans, net of unearned income	35,330,000,000	40,695,000,000
Loans, total non-accrual	375,000,000	516,000,000
Loans, 90 days past due and accruing	424,000,000	508,000,000
Consumer | In offices outside North America | Installment and other
Loans receivable
Loans, current	29,135,000,000	29,350,000,000
Loans, 30-89 days past due	423,000,000	496,000,000
Loans, greater than or equal to 90 days past due	172,000,000	167,000,000
Loans, net of unearned income	29,730,000,000	30,013,000,000
Loans, total non-accrual	243,000,000	254,000,000
Consumer | In offices outside North America | Commercial market loans
Loans receivable
Loans, current	32,677,000,000	31,263,000,000
Loans, 30-89 days past due	106,000,000	106,000,000
Loans, greater than or equal to 90 days past due	202,000,000	181,000,000
Loans, net of unearned income	32,985,000,000	31,550,000,000
Loans, total non-accrual	$ 678,000,000	$ 428,000,000
Open-ended consumer loans
Residential Mortgage Loan to Values
Minimum number of payments made consecutively for the loans to be re-aged	3	3
Number of re-age modification limitations in twelve months	1	1
Number of re-age modification limitations in five years	2	2