Short-Term Debt - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Average balance of short-term debt	$ 1,300,000,000	$ 1,970,000,000
Accrued interest payable on short-term debt	3,000,000	3,000,000	$ 6,000,000
Committed line of credit	10,000,000	10,000,000
Fair value of mortgage backed securities securing loan (in excess)	3,000,000	3,000,000
Amount outstanding under credit facilities	0	0	0
Sequoia securities \| Sequoia Choice \| Short Term Borrowing Agreement
Short-term Debt [Line Items]
Trading securities pledged as collateral	59,543,000	59,543,000	111,341,000
Sequoia securities \| Freddie Mac SLST \| Short Term Borrowing Agreement
Short-term Debt [Line Items]
Trading securities pledged as collateral	334,043,000	334,043,000	381,640,000
Sequoia securities \| Freddie Mac K-Series \| Short Term Borrowing Agreement
Short-term Debt [Line Items]
Trading securities pledged as collateral	24,384,000	24,384,000	$ 252,284,000
Residential Loans
Short-term Debt [Line Items]
Fair value of servicer advances, cash and restricted cash	283,000,000	283,000,000
Residential Loans
Short-term Debt [Line Items]
Loan pledged as collateral	15,000,000	15,000,000
Servicer advance financing
Short-term Debt [Line Items]
Collateral amounts	250,000,000	250,000,000
Accrued interest payable on short-term debt	100,000	100,000
Unamortized capitalized commitment costs	$ 1,000,000	$ 1,000,000

Servicing Asset, Cash And Restricted Cash at Fair Value, Amount

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Amount of assets pledged to secure a debt instrument.

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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The fair value as of the balance sheet date of financial instruments and other positions owned by the entity and pledged to counterparties as collateral, including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities.

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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