LOANS (Details 3) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
LOANS
Maximum period of loan modification under Citi's short-term modification programs			12 months
Number of quarters used to calculate the average recorded investment balance	4		4		4
Consumer
Financing receivable impaired
Recorded investment	$ 24,227,000,000		$ 24,227,000,000		$ 29,640,000,000
Unpaid principal balance	26,113,000,000		26,113,000,000		31,783,000,000
Related specific allowance	5,251,000,000		5,251,000,000		6,941,000,000
Average carrying value			26,412,000,000		29,592,000,000
Interest income recognized	298,000,000	450,000,000	982,000,000	1,214,000,000
Smaller-balance impaired consumer loans modified since January 1, 2008, dollar amount	23,900,000,000		23,900,000,000		29,200,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008	24,500,000,000		24,500,000,000		30,100,000,000
Consumer | New OCC guidance
Financing receivable impaired
Recorded investment in receivables reclassified to TDR as a result of new guidance issued by OCC		1,714,000,000		1,714,000,000
Consumer | Residential First Mortgage Loans
Financing receivable impaired
Recorded investment	17,071,000,000		17,071,000,000		20,870,000,000
Unpaid principal balance	18,051,000,000		18,051,000,000		22,062,000,000
Related specific allowance	2,615,000,000		2,615,000,000		3,585,000,000
Average carrying value			18,633,000,000		19,956,000,000
Interest income recognized	179,000,000	251,000,000	604,000,000	674,000,000
Impaired financing receivable without specific allowance	2,201,000,000		2,201,000,000		2,344,000,000
Consumer | Residential First Mortgage Loans | New OCC guidance
Financing receivable impaired
Recorded investment in receivables reclassified to TDR as a result of new guidance issued by OCC		1,327,000,000		1,327,000,000
Consumer | Home equity loans
Financing receivable impaired
Recorded investment	2,234,000,000		2,234,000,000		2,135,000,000
Unpaid principal balance	2,832,000,000		2,832,000,000		2,727,000,000
Related specific allowance	595,000,000		595,000,000		636,000,000
Average carrying value			2,115,000,000		1,911,000,000
Interest income recognized	23,000,000	31,000,000	61,000,000	64,000,000
Impaired financing receivable without specific allowance	421,000,000		421,000,000		378,000,000
Consumer | Home equity loans | New OCC guidance
Financing receivable impaired
Recorded investment in receivables reclassified to TDR as a result of new guidance issued by OCC		387,000,000		387,000,000
Consumer | Credit cards
Financing receivable impaired
Recorded investment	3,490,000,000		3,490,000,000		4,584,000,000
Unpaid principal balance	3,535,000,000		3,535,000,000		4,639,000,000
Related specific allowance	1,274,000,000		1,274,000,000		1,800,000,000
Average carrying value			4,032,000,000		5,272,000,000
Interest income recognized	56,000,000	75,000,000	182,000,000	240,000,000
Consumer | Individual installment and other
Financing receivable impaired
Recorded investment	1,075,000,000		1,075,000,000		1,612,000,000
Unpaid principal balance	1,099,000,000		1,099,000,000		1,618,000,000
Related specific allowance	588,000,000		588,000,000		860,000,000
Average carrying value			1,218,000,000		1,958,000,000
Interest income recognized	35,000,000	88,000,000	118,000,000	218,000,000
Consumer | Commercial market loans
Financing receivable impaired
Recorded investment	357,000,000		357,000,000		439,000,000
Unpaid principal balance	596,000,000		596,000,000		737,000,000
Related specific allowance	179,000,000		179,000,000		60,000,000
Average carrying value			414,000,000		495,000,000
Interest income recognized	5,000,000	5,000,000	17,000,000	18,000,000
Impaired financing receivable without specific allowance	$ 133,000,000		$ 133,000,000		$ 183,000,000