DISCONTINUED OPERATIONS AND SIGNIFICANT DISPOSALS - Discontinued Operations (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 transaction
Results of Discontinued Operations
Total revenues, net of interest expense	$ 0	$ 4,000,000	$ 0	$ 73,000,000
Income (loss) from discontinued operations	9,000,000	(3,000,000)	1,000,000	37,000,000
Provision for income taxes	3,000,000	19,000,000	0	22,000,000
Income (loss) from discontinued operations, net of taxes	6,000,000	(22,000,000)	1,000,000	15,000,000
Brazil Creditcard
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	8,000,000	3,000,000	$ 6,000,000	56,000,000
Citi Capital Advisors Business
Discontinued operations
Number of transactions | transaction						2
Ownership interest (as a percent)			24.90%
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	0	0	$ 1,000,000	(2,000,000)
Egg Banking PLC
Results of Discontinued Operations
Income (loss) from discontinued operations, net of taxes	$ (2,000,000)	$ (5,000,000)	$ (6,000,000)	$ (19,000,000)
German retail banking operations
Discontinued operations
Residual costs associated with banking operations tax effect					$ 20,000,000