SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Credit Card Securitizations (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) trust	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Securitized credit card receivables
Number of trusts to hold securitized credit card receivables | trust	2
Ownership interests in principal amount of trust credit card receivables
Sold to investors via trust-issued securities	$ 27,500,000,000		$ 29,700,000,000
Retained by Citigroup as trust-issued securities	8,100,000,000		9,400,000,000
Retained by Citigroup via non-certificated interests	16,100,000,000		16,500,000,000
Total ownership interests in principal amount of trust credit card receivables	51,700,000,000		$ 55,600,000,000
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	$ 0
Pay down of maturing notes	$ (2,200,000,000)	$ (2,700,000,000)