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Fair Value of Financial Instruments - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 333 | $ 654
Residential loans |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 6,990 | 8,380
Business purpose residential loans, held-for-sale, at fair value |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 4,020 | 168
Multifamily loans |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 1,430 | 2,130
Real estate securities | Maximum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Dealer marks of securities | 83.00% |
Percentage of carrying value for which dealer quotes were received on securities | 94.00% |
Percentage difference of internal valuation than dealer marks | 1.00% |
Servicer advance investments |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 70 | 396
Excess MSRs |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 8 | $ 25
Shared Home Appreciation Options |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 43 |
MSRs | Maximum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Percentage difference of internal valuation than dealer marks | 2.00% |

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