DISCONTINUED OPERATIONS AND SIGNIFICANT DISPOSALS - Discontinued Operations (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2013 transaction
Results of Discontinued Operations
Total revenues, net of interest expense	$ 0	$ 0
Loss from discontinued operations	(3)	(8)
Gain on sale	0	0
Benefit for income taxes	(1)	(3)
Loss from discontinued operations, net of taxes	(2)	(5)
Brazil Creditcard
Results of Discontinued Operations
Loss from discontinued operations, net of taxes	0	(2)
Citi Capital Advisors Business
Discontinued operations
Number of transactions | transaction			2
Results of Discontinued Operations
Loss from discontinued operations, net of taxes	0	1
Egg Banking PLC
Results of Discontinued Operations
Loss from discontinued operations, net of taxes	$ (2)	$ (4)