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Fair Value of Financial Instruments - Additional Information (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Residential loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 1,530,000,000	$ 2,530,000,000
Business purpose residential loans, at fair value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 112,000,000	$ 177,000,000
Real estate securities | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Dealer marks of securities (as a percent)	88.00%	88.00%
Carrying value for which dealer quotes have been received (as a percent)	96.00%	96.00%
Difference of internal valuation than dealer marks (as a percent)	1.00%	1.00%
Residential Senior Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 2,000,000	$ 34,000,000
Residential Subordinate Securities | Subordinate Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	86,000,000	206,000,000
Servicer advance investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	0	69,000,000
Excess MSR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 5,000,000	$ 7,000,000
Mortgage servicing rights | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Difference of internal valuation than dealer marks (as a percent)	2.00%	2.00%

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