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Fair Value of Financial Instruments - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Real estate securities | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Dealer marks of securities	85.00%
Percentage of carrying value for which dealer quotes were received on securities	93.00%
Percentage difference of internal valuation than dealer marks	1.00%
Residential Senior Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 109	$ 47
Residential Subordinate Securities | Subordinate Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	545	594
Residential loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	8,380	$ 5,640
Business purpose residential loans | Subordinate Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	168
Multifamily loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	2,130
Servicer advance investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	396
Excess MSRs
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 25
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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