Servicing Activities - Loan Servicing Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Transfers and Servicing [Abstract]
Servicing fees from capitalized portfolio	$ 6	$ 48	$ 12	$ 102
Subservicing fees	16	10	33	21
MSR yield on secured asset	13	1	27	1
Late fees and other ancillary revenue	10	6	18	15
Loss on sale of MSRs and related costs	(1)	(4)	(1)	(13)
Curtailment interest paid to investors	0	(3)	(1)	(6)
Loan servicing income	44	58	88	120
Change in fair value of mortgage servicing rights and related derivatives	(10)	(29)	13	(58)
Change in fair value of MSRs secured liability	6	(1)	(18)	(1)
Net loan servicing income	$ 40	$ 28	$ 83	$ 61