Mortgage Servicing Rights and Related Liabilities - Fair Value Sensitivity Analysis (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
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	$ 10	$ 11
Total prepayment speeds, 20% adverse change	20	22
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	16
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	32
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		19
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		40
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	(219)	(136)
Total prepayment speeds, 20% adverse change	(425)	(264)
Cost to service loan, 10% adverse change	(89)	(61)
Cost to service loan, 20% adverse change	(178)	(122)
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	(368)
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	$ (706)
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		(266)
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		$ (511)