Mortgage Servicing Rights ("MSRs") and Related Liabilities - Servicing Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Transfers and Servicing [Abstract]
Contractually specified servicing fees	$ 297	$ 281
Other service-related income	49	50
Incentive and modification income	10	7
Late fees	27	25
Reverse servicing fees	6	9
Mark-to-market adjustments	(383)	(293)
Counterparty revenue share	(76)	(48)
Amortization, net of accretion	(76)	(23)
Total servicing revenue	(146)	8
Cumulative incurred losses related to advances and other receivables associated with inactive and liquidated loans	10	11
Servicing fee income accretion expense	68	36
Accretion of MSL	$ 8	$ 18