Mortgage Servicing Rights ("MSRs") and Related Liabilities - Fair Value Sensitivity Analysis (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Mortgage servicing rights
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Total Prepayment Speeds, 10% Adverse Change	$ (158)	$ (165)
Total Prepayment Speeds, 20% Adverse Change	(305)	(317)
Excess spread financing
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Total Prepayment Speeds, 10% Adverse Change	48	46
Total Prepayment Speeds, 20% Adverse Change	98	96
100 Basis Points | Mortgage servicing rights
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Discount Rate, Adverse Change	(111)	(127)
100 Basis Points | Excess spread financing
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Discount Rate, Adverse Change	43	46
200 Basis Points | Mortgage servicing rights
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Discount Rate, Adverse Change	(214)	(245)
200 Basis Points | Excess spread financing
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Discount Rate, Adverse Change	$ 89	$ 95