Mortgage Servicing Rights and Related Liabilities - Fair Value Sensitivity Analysis (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Mortgage Servicing Right [Member]
Excess Spread Financing - Hypothetical Sensitivities
Total prepayment speeds, 10% Adverse Change	$ (145)	$ (181)
Total prepayment speeds, 20% Adverse Change	(279)	(347)
Cost to Service per Loan, 10% Adverse Change	(45)	(45)
Cost to Service per Loan, 20% Adverse Change	(89)	(89)
Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
Total prepayment speeds, 10% Adverse Change	30	41
Total prepayment speeds, 20% Adverse Change	63	84
100 bps Adverse Change \| Mortgage Servicing Right [Member]
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	(133)	(100)
100 bps Adverse Change \| Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	28	30
200 bps Adverse Change \| Mortgage Servicing Right [Member]
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	(257)	(192)
200 bps Adverse Change \| Excess spread financing
Excess Spread Financing - Hypothetical Sensitivities
Discount Rate	$ 58	$ 62

The hypothetical financial impact of a 10 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

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The hypothetical financial impact of a 10 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse change of the specified assumption on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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The hypothetical financial impact of a 20 percent adverse change of prepayment speed on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The hypothetical financial impact of a specified adverse percentage change in discount rate on the fair value of transferor's interests in transferred financial assets (including any servicing assets or servicing liabilities) as of the balance sheet date.

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