Mortgage Servicing Rights and Related Liabilities - Servicing Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Transfers and Servicing [Abstract]
Contractually specified servicing fees	$ 276	$ 297
Other service-related income	145	49
Incentive and modification income	14	10
Late fees	18	27
Reverse servicing fees	5	6
Mark-to-market adjustments	354	(383)
Counterparty revenue share	(83)	(76)
Amortization, net of accretion	(153)	(76)
Total revenues - Servicing	576	(146)
Cumulative incurred losses related to advances and other receivables associated with inactive and liquidated loans	12	10
Servicing fee income accretion expense	76	68
Accretion of MSL	$ 3	$ 8