SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Credit Card Securitizations (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Securitized credit card receivables
Gains (losses) recognized on the securitization			$ 0
Ownership interests in principal amount of trust credit card receivables
Sold to investors via trust-issued securities	$ 31,300,000,000		31,300,000,000		$ 37,000,000,000
Retained by Citigroup as trust-issued securities	9,000,000,000		9,000,000,000		10,100,000,000
Retained by Citigroup via non-certificated interests	15,900,000,000		15,900,000,000		14,200,000,000
Total ownership interests in principal amount of trust credit card receivables	56,200,000,000		56,200,000,000		$ 61,300,000,000
Credit card securitizations
Cash Flows Between Transferor and Transferee
Proceeds from new securitizations	0	$ 2,400,000,000	0	$ 6,800,000,000
Pay down of maturing notes	$ (3,100,000,000)	$ (1,300,000,000)	$ (5,800,000,000)	$ (1,300,000,000)