Mortgage Servicing Rights and Related Liabilities - UPB related to owned MSRs (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Owned Service Loans [Line Items]
UPB	$ 277,975	$ 296,782
Fair Value	2,757	3,496	$ 3,505
Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	277,975	296,782
Fair Value	2,757	3,496
Credit sensitive | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	131,105	147,895
Fair Value	1,307	1,613
Interest sensitive | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	146,870	148,887
Fair Value	1,450	1,883
Agency | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	228,680	240,688
Fair Value	2,308	2,944
Non-agency | Mortgage servicing rights
Owned Service Loans [Line Items]
UPB	49,295	56,094
Fair Value	$ 449	$ 552