LOANS (Details 3) (USD $)	3 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	3 Months Ended		12 Months Ended
	Mar. 31, 2012 M	Mar. 31, 2011	Sep. 30, 2011	Mar. 31, 2012 Consumer	Mar. 31, 2011 Consumer	Dec. 31, 2011 Consumer	Sep. 30, 2011 Consumer Impairment of loan	Mar. 31, 2012 Consumer Residential First Mortgage Loans	Mar. 31, 2011 Consumer Residential First Mortgage Loans	Dec. 31, 2011 Consumer Residential First Mortgage Loans	Mar. 31, 2012 Consumer Home equity loans	Mar. 31, 2011 Consumer Home equity loans	Dec. 31, 2011 Consumer Home equity loans	Mar. 31, 2012 Consumer Credit cards	Mar. 31, 2011 Consumer Credit cards	Dec. 31, 2011 Consumer Credit cards	Mar. 31, 2012 Consumer Individual installment and other	Mar. 31, 2011 Consumer Individual installment and other	Dec. 31, 2011 Consumer Individual installment and other	Mar. 31, 2012 Consumer Commercial market loans	Mar. 31, 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
Financing receivable impaired
Recorded investment			$ 1,170,000,000	$ 29,492,000,000		$ 30,863,000,000	$ 1,170,000,000	$ 19,076,000,000		$ 19,616,000,000	$ 1,706,000,000		$ 1,771,000,000	$ 5,971,000,000		$ 6,695,000,000	$ 2,208,000,000		$ 2,264,000,000	$ 531,000,000		$ 517,000,000
Principal balance				31,391,000,000		32,418,000,000		20,561,000,000		20,803,000,000	1,821,000,000		1,823,000,000	6,031,000,000		6,743,000,000	2,209,000,000		2,267,000,000	769,000,000		782,000,000
Related specific allowance			467,000,000	7,940,000,000		8,885,000,000	467,000,000	2,995,000,000		3,404,000,000	1,149,000,000		1,252,000,000	2,788,000,000		3,122,000,000	937,000,000		1,032,000,000	71,000,000		75,000,000
Average carrying value				30,310,000,000		30,080,000,000		19,087,000,000		18,642,000,000	1,763,000,000		1,680,000,000	6,465,000,000		6,542,000,000	2,472,000,000		2,644,000,000	523,000,000		572,000,000
Interest income recognized		13,000,000		390,000,000	390,000,000			215,000,000	201,000,000		15,000,000	12,000,000		87,000,000	97,000,000		69,000,000	71,000,000		4,000,000	9,000,000
Impaired financing receivable without specific allowance								929,000,000		858,000,000	61,000,000		16,000,000							203,000,000		182,000,000
Smaller-balance impaired consumer loans modified since January 1, 2008, dollar amount				29,000,000,000		30,300,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008				$ 30,000,000,000		$ 31,500,000,000