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Short-Term Debt - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Nov. 15, 2018	Nov. 30, 2014
Short-term Debt [Line Items]
Trading securities pledged as collateral	$ 881,000,000
Average balance of short-term debt	1,610,000,000	$ 1,370,000,000
Accrued interest payable on short-term debt	4,000,000		$ 4,000,000
Convertible notes				$ 201,000,000
Committed line of credit	10,000,000
Fair value of mortgage backed securities securing loan (in excess)	4,000,000
Committed line of credit with financial institutions, outstanding	0		$ 0
Convertible Debt \| Exchangeable Senior Notes Due 2019
Short-term Debt [Line Items]
Accrued interest payable on short-term debt	4,000,000
Debt Instrument interest rate			5.625%		5.625%
Unamortized deferred issuance costs			$ 1,000,000
Sequoia securities \| Sequoia Choice
Short-term Debt [Line Items]
Trading securities pledged as collateral	146,000,000		130,000,000
Sequoia securities \| Freddie Mac SLST
Short-term Debt [Line Items]
Trading securities pledged as collateral	196,000,000		229,000,000
Sequoia securities \| Freddie Mac K-Series
Short-term Debt [Line Items]
Trading securities pledged as collateral	18,000,000		18,000,000
Residential
Short-term Debt [Line Items]
Securities pledged as collateral	966,000,000		844,000,000
Single-family rental loans, held-for-sale at fair value
Short-term Debt [Line Items]
Collateral amounts	49,000,000		28,000,000
Residential bridge loans, held-for-investment at fair value
Short-term Debt [Line Items]
Collateral amounts	93,000,000		98,000,000
Residential Loans
Short-term Debt [Line Items]
Loan pledged as collateral	579,000,000		$ 935,000,000
Single-family rental loans held-for-sale, at fair value \| Business purpose loan working capital
Short-term Debt [Line Items]
Loan pledged as collateral	5,000,000
Other Assets \| Business purpose loan working capital
Short-term Debt [Line Items]
Loan pledged as collateral	7,000,000
Servicer advance financing
Short-term Debt [Line Items]
Collateral amounts	282,000,000
Accrued interest payable on short-term debt	400,000
Unamortized capitalized commitment costs	2,000,000
5 Arches, LLC \| Single-family rental loans, held-for-sale at fair value
Short-term Debt [Line Items]
Collateral amounts	$ 5,000,000