LOANS (Details 3) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
LOANS
Maximum period of loan modification under Citi's short-term modification programs (in months)	12		12
Dollar amount of loans included under Citi's short-term modification programs	$ 4,000,000,000		$ 4,000,000,000
Financing receivable impaired
Related specific allowance	467,000,000		467,000,000
Average carrying value	1,170,000,000		1,170,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008	1,170,000,000		1,170,000,000
Consumer
Financing receivable impaired
Recorded investment	31,136,000,000		31,136,000,000		27,318,000,000
Unpaid principal balance	32,563,000,000		32,563,000,000		28,731,000,000
Related specific allowance	9,005,000,000		9,005,000,000		7,735,000,000
Average carrying value	29,196,000,000		29,196,000,000		24,466,000,000
Interest income recognized	417,000,000	425,000,000	1,268,000,000	1,306,000,000
Smaller-balance impaired consumer loans modified since January 1, 2008, dollar amount	30,700,000,000		30,700,000,000		26,600,000,000
Amounts of such outstanding modified consumer loans, including those modified prior to 2008	31,900,000,000		31,900,000,000		28,200,000,000
Consumer | Credit cards
Financing receivable impaired
Recorded investment	6,869,000,000		6,869,000,000		5,906,000,000
Unpaid principal balance	6,913,000,000		6,913,000,000		5,906,000,000
Related specific allowance	3,201,000,000		3,201,000,000		3,237,000,000
Average carrying value	6,345,000,000		6,345,000,000		5,314,000,000
Interest income recognized	98,000,000		296,000,000
Consumer | Residential First Mortgage Loans
Financing receivable impaired
Recorded investment	19,296,000,000		19,296,000,000		16,225,000,000
Unpaid principal balance	20,429,000,000		20,429,000,000		17,287,000,000
Related specific allowance	3,380,000,000		3,380,000,000		2,783,000,000
Average carrying value	17,794,000,000		17,794,000,000		13,606,000,000
Interest income recognized	220,000,000		674,000,000
Impaired financing receivable without specific allowance	1,002,000,000		1,002,000,000		1,050,000,000
Consumer | Home equity loans
Financing receivable impaired
Recorded investment	1,859,000,000		1,859,000,000		1,205,000,000
Unpaid principal balance	1,909,000,000		1,909,000,000		1,256,000,000
Related specific allowance	1,065,000,000		1,065,000,000		393,000,000
Average carrying value	1,539,000,000		1,539,000,000		1,010,000,000
Interest income recognized	21,000,000		51,000,000
Impaired financing receivable without specific allowance	18,000,000		18,000,000		6,000,000
Consumer | Individual installment and other
Financing receivable impaired
Recorded investment	2,678,000,000		2,678,000,000		3,286,000,000
Unpaid principal balance	2,679,000,000		2,679,000,000		3,348,000,000
Related specific allowance	1,296,000,000		1,296,000,000		1,177,000,000
Average carrying value	2,899,000,000		2,899,000,000		3,627,000,000
Interest income recognized	75,000,000		228,000,000
Consumer | Commercial market loans
Financing receivable impaired
Recorded investment	434,000,000		434,000,000		696,000,000
Unpaid principal balance	633,000,000		633,000,000		934,000,000
Related specific allowance	63,000,000		63,000,000		145,000,000
Average carrying value	619,000,000		619,000,000		909,000,000
Interest income recognized	3,000,000		19,000,000
Impaired financing receivable without specific allowance	$ 194,000,000		$ 194,000,000		$ 323,000,000