Goodwill and Other Intangible Assets - Key Economic Assumptions (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Weighted-average prepayment speed assumption (“CPR”)	12.07%	9.81%
Impact on fair value of 10% adverse change	$ (275)	$ (275)
Impact on fair value of 20% adverse change	$ (534)	$ (529)
Weighted-average option adjusted spread	9.85%	9.54%
Impact on fair value of 100 basis points adverse change	$ (213)	$ (258)
Impact on fair value of 200 basis points adverse change	$ (410)	$ (498)