SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Credit Card Securitizations (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Ownership interests in principal amount of trust credit card receivables
Sold to investors via trust-issued securities	$ 30,700,000,000		$ 30,700,000,000		$ 37,000,000,000
Retained by Citigroup as trust-issued securities	8,600,000,000		8,600,000,000		10,100,000,000
Retained by Citigroup via non-certificated interests	15,500,000,000		15,500,000,000		14,200,000,000
Total ownership interests in principal amount of trust credit card receivables	54,800,000,000		54,800,000,000		$ 61,300,000,000
Credit card securitizations
Securitized credit card receivables
Gains (losses) recognized on the securitization			0
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	0	$ 3,100,000,000	0	$ 9,900,000,000
Pay down of maturing notes	$ (700,000,000)	$ (2,800,000,000)	$ (6,500,000,000)	$ (4,100,000,000)