Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 18,000,000	$ 96,000,000
Residential loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	172,000,000	2,860,000,000
Business purpose residential loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	260,000,000	956,000,000
Servicer advance investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	0	179,000,000
Excess MSR
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	0	11,000,000
Shared home appreciation options
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 0	$ 4,000,000