SUBSEQUENT EVENTS - Narrative (Details) - USD ($)						12 Months Ended
	Feb. 25, 2016	Jan. 22, 2016	Jan. 08, 2016	Jan. 07, 2016	Apr. 06, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Subsequent Event [Line Items]
Dividends declared and paid (in dollars per Share)						$ 0.4	$ 1.43	$ 2.12
Dividends paid to common stockholders						$ 143,000,000	$ 16,000,000
Dividends						214,000,000
Subsequent Event
Subsequent Event [Line Items]
Dividends declared and paid (in dollars per Share)		$ 0.10
Dividends paid to common stockholders		$ 53,000,000
Student | Subsequent Event
Subsequent Event [Line Items]
Termination fee				$ 1,000,000
Minimum | Student | Subsequent Event
Subsequent Event [Line Items]
Minimum quarterly purchase commitment				125,000,000
Aggregate purchase principal balance				500,000,000
Maximum | Student | Subsequent Event
Subsequent Event [Line Items]
Aggregate purchase principal balance				$ 1,000,000,000
Student loan
Subsequent Event [Line Items]
Loans purchased during period						$ 957,000,000	$ 59,000,000
Student loan | Subsequent Event
Subsequent Event [Line Items]
Loans purchased during period			$ 369,000,000
Series A Preferred Stock
Subsequent Event [Line Items]
Preferred stock, dividend rate					5.50%
Series A Preferred Stock | Subsequent Event
Subsequent Event [Line Items]
Preferred stock, dividend rate	5.50%
Preferred stock dividend declared (in dollars per share)	$ 27.50
Dividends	$ 7,000,000