Servicing Activities - Loan Servicing Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Transfers and Servicing [Abstract]
Servicing fees from capitalized portfolio	$ 22	$ 67	$ 125	$ 204
Subservicing fees	17	17	38	53
Late fees and other ancillary revenue	6	9	21	27
Loss on sale of MSRs	(3)	0	(16)	(2)
Curtailment interest paid to investors	0	(4)	(6)	(11)
Loan servicing income	42	89	162	271
Change in fair value of mortgage servicing rights and related derivatives	(35)	(50)	(93)	(133)
Change in fair value of MSRs secured liability	28	0	27	0
Net loan servicing income	35	39	96	138
MSR yield on secured asset	$ 14		$ 15
Net derivative gains (losses) related to mortgage servicing rights		$ (4)		$ 139