Mortgage Servicing Rights and Related Liabilities - Fair Value Sensitivity Analysis (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
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	$ 28	$ 41
Total prepayment speeds, 20% adverse change	58	84
Excess Spread Financing | 100 bps Adverse Change
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	26	30
Excess Spread Financing | 200 bps Adverse Change
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	54	62
Forward 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	(148)	(181)
Total prepayment speeds, 20% adverse change	(286)	(347)
Cost to service loan, 10% adverse change	(46)	(45)
Cost to service loan, 20% adverse change	(93)	(89)
Forward mortgage servicing rights | 100 bps Adverse Change
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	(141)	(100)
Forward mortgage servicing rights | 200 bps Adverse Change
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	$ (272)	$ (192)