LOANS (Details 3) (USD $)	3 Months Ended			12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Consumer	Mar. 31, 2012 Consumer	Dec. 31, 2012 Consumer	Sep. 30, 2012 Consumer New OCC guidance	Mar. 31, 2013 Consumer Residential First Mortgage Loans	Mar. 31, 2012 Consumer Residential First Mortgage Loans	Dec. 31, 2012 Consumer Residential First Mortgage Loans	Sep. 30, 2012 Consumer Residential First Mortgage Loans New OCC guidance	Mar. 31, 2013 Consumer Home equity loans	Mar. 31, 2012 Consumer Home equity loans	Dec. 31, 2012 Consumer Home equity loans	Sep. 30, 2012 Consumer Home equity loans New OCC guidance	Mar. 31, 2013 Consumer Credit cards	Mar. 31, 2012 Consumer Credit cards	Dec. 31, 2012 Consumer Credit cards	Mar. 31, 2013 Consumer Individual installment and other	Mar. 31, 2012 Consumer Individual installment and other	Dec. 31, 2012 Consumer Individual installment and other	Mar. 31, 2013 Consumer Commercial market loans	Mar. 31, 2012 Consumer Commercial market loans	Dec. 31, 2012 Consumer Commercial market loans
LOANS
Maximum period of loan modification under Citi's short-term modification programs	12 months
Financing receivable impaired
Recorded investment in receivables reclassified to TDR as a result of new guidance issued by OCC					$ 1,714,000,000				$ 1,327,000,000				$ 387,000,000
Recorded investment		27,139,000,000		29,640,000,000		19,268,000,000		20,870,000,000		2,057,000,000		2,135,000,000		4,279,000,000		4,584,000,000	1,093,000,000		1,612,000,000	442,000,000		439,000,000
Unpaid principal balance		29,064,000,000		31,783,000,000		20,220,000,000		22,062,000,000		2,653,000,000		2,727,000,000		4,341,000,000		4,639,000,000	1,130,000,000		1,618,000,000	720,000,000		737,000,000
Related specific allowance		6,042,000,000		6,941,000,000		3,199,000,000		3,585,000,000		529,000,000		636,000,000		1,596,000,000		1,800,000,000	657,000,000		860,000,000	61,000,000		60,000,000
Average carrying value		29,004,000,000		29,592,000,000		20,004,000,000		19,956,000,000		1,999,000,000		1,911,000,000		4,849,000,000		5,272,000,000	1,679,000,000		1,958,000,000	473,000,000		495,000,000
Interest income recognized		356,000,000	390,000,000			217,000,000	215,000,000			21,000,000	15,000,000			65,000,000	87,000,000		49,000,000	69,000,000		4,000,000	4,000,000
Impaired financing receivable without specific allowance						2,240,000,000		2,344,000,000		423,000,000		378,000,000								184,000,000		183,000,000
Smaller-balance impaired consumer loans modified since January 1, 2008, dollar amount		26,700,000,000		29,200,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008		$ 27,600,000,000		$ 30,100,000,000