DISCONTINUED OPERATIONS AND SIGNIFICANT DISPOSALS - Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013 transaction	Dec. 31, 2014
Results of Discontinued Operations
Total revenues, net of interest expense	$ 0	$ 69
Income (loss) from discontinued operations	(8)	40
Provision (benefit) for income taxes	(3)	3
Income (loss) from discontinued operations, net of taxes	(5)	37
Brazil Creditcard
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	(2)	53
Citi Capital Advisors Business
Discontinued operations
Number of transactions			2
Ownership interest (as a percent)	24.90%
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	1	(2)
Egg Banking PLC
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	(4)	(14)
German retail banking operations
Discontinued operations
Residual costs associated with banking operations tax effect				$ 20