LOANS (Details 3) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012 month	Jun. 30, 2012 month	Dec. 31, 2011 month	Sep. 30, 2011	Jun. 30, 2012 Consumer	Jun. 30, 2011 Consumer	Jun. 30, 2012 Consumer	Jun. 30, 2011 Consumer	Dec. 31, 2011 Consumer	Sep. 30, 2011 Consumer Impairment of loan	Jun. 30, 2012 Consumer Residential First Mortgage Loans	Jun. 30, 2011 Consumer Residential First Mortgage Loans	Jun. 30, 2012 Consumer Residential First Mortgage Loans	Jun. 30, 2011 Consumer Residential First Mortgage Loans	Dec. 31, 2011 Consumer Residential First Mortgage Loans	Jun. 30, 2012 Consumer Home equity loans	Jun. 30, 2011 Consumer Home equity loans	Jun. 30, 2012 Consumer Home equity loans	Jun. 30, 2011 Consumer Home equity loans	Dec. 31, 2011 Consumer Home equity loans	Jun. 30, 2012 Consumer Credit cards	Jun. 30, 2011 Consumer Credit cards	Jun. 30, 2012 Consumer Credit cards	Jun. 30, 2011 Consumer Credit cards	Dec. 31, 2011 Consumer Credit cards	Jun. 30, 2012 Consumer Individual installment and other	Jun. 30, 2011 Consumer Individual installment and other	Jun. 30, 2012 Consumer Individual installment and other	Jun. 30, 2011 Consumer Individual installment and other	Dec. 31, 2011 Consumer Individual installment and other	Jun. 30, 2012 Consumer Commercial market loans	Jun. 30, 2011 Consumer Commercial market loans	Jun. 30, 2012 Consumer Commercial market loans	Jun. 30, 2011 Consumer Commercial market loans	Dec. 31, 2011 Consumer Commercial market loans
LOANS
Maximum period of loan modification under Citi's short-term modification programs (in months)	12	12	12
Financing receivable impaired
Recorded investment				$ 1,170,000,000	$ 28,387,000,000		$ 28,387,000,000		$ 30,863,000,000	$ 1,170,000,000	$ 18,710,000,000		$ 18,710,000,000		$ 19,616,000,000	$ 1,668,000,000		$ 1,668,000,000		$ 1,771,000,000	$ 5,520,000,000		$ 5,520,000,000		$ 6,695,000,000	$ 1,999,000,000		$ 1,999,000,000		$ 2,264,000,000	$ 490,000,000		$ 490,000,000		$ 517,000,000
Unpaid principal balance					30,512,000,000		30,512,000,000		32,418,000,000		20,122,000,000		20,122,000,000		20,803,000,000	1,787,000,000		1,787,000,000		1,823,000,000	5,575,000,000		5,575,000,000		6,743,000,000	2,272,000,000		2,272,000,000		2,267,000,000	756,000,000		756,000,000		782,000,000
Related specific allowance				467,000,000	7,507,000,000		7,507,000,000		8,885,000,000	467,000,000	3,042,000,000		3,042,000,000		3,404,000,000	1,098,000,000		1,098,000,000		1,252,000,000	2,505,000,000		2,505,000,000		3,122,000,000	788,000,000		788,000,000		1,032,000,000	74,000,000		74,000,000		75,000,000
Average carrying value							29,970,000,000		30,080,000,000				19,175,000,000		18,642,000,000			1,751,000,000		1,680,000,000			6,264,000,000		6,542,000,000			2,287,000,000		2,644,000,000			493,000,000		572,000,000
Interest income recognized					373,000,000	461,000,000	764,000,000	851,000,000			209,000,000	253,000,000	423,000,000	454,000,000		17,000,000	18,000,000	32,000,000	30,000,000		78,000,000	101,000,000	166,000,000	198,000,000		60,000,000	82,000,000	130,000,000	152,000,000		9,000,000	7,000,000	13,000,000	17,000,000
Impaired financing receivable without specific allowance											884,000,000		884,000,000		858,000,000	40,000,000		40,000,000		16,000,000											165,000,000		165,000,000		182,000,000
Smaller-balance impaired consumer loans modified since January 1, 2008, dollar amount					27,900,000,000		27,900,000,000		30,300,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008					$ 28,900,000,000		$ 28,900,000,000		$ 31,500,000,000