Mortgage Servicing Rights and Related Liabilities - UPB related to owned MSRs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Owned Service Loans [Line Items]
Fair Value	$ 2,663	$ 3,496
Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	266,667	296,782
Fair Value	2,663	3,496
Credit sensitive | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	122,422	147,895
Fair Value	1,206	1,613
Interest sensitive | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	144,245	148,887
Fair Value	1,457	1,883
Agency | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	220,139	240,688
Fair Value	2,234	2,944
Non-agency | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	46,528	56,094
Fair Value	$ 429	$ 552