Fair Value of Financial Instruments - Additional Information (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Residential loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 2,670,000,000	$ 5,200,000,000
Business purpose residential loans, at fair value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	124,000,000	301,000,000
Multifamily loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 0	$ 1,430,000,000
Real estate securities \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Dealer marks of securities (as a percent)	83.00%	83.00%
Carrying value for which dealer quotes have been received (as a percent)	95.00%	95.00%
Difference of internal valuation than dealer marks (as a percent)	1.00%	1.00%
Home appreciation options
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 11,000,000
Excess MSR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	1,000,000	$ 8,000,000
Servicer advance investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	1,000,000	70,000,000
Residential Subordinate Securities \| Subordinate Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	40,000,000	247,000,000
Residential Senior Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 16,000,000	$ 50,000,000
Mortgage servicing rights \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Difference of internal valuation than dealer marks (as a percent)	5.00%	5.00%

Fair Value, Option, Assets, Aggregate Carrying Amount During Period

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Percentage Difference Of Internal Valuation Than Dealer Marks

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- Definition

Percentage of Carrying Value for Which Dealer Quotes Were Received on Securities

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Percentage of Third-party Dealer Quotes Received on Securities.

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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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