Loans Subject to Repurchase from Ginnie Mae (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans subject to repurchase	$ 5,395	$ 560
Financial Asset, Equal to or Greater than 90 Days Past Due \| Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans subject to repurchase	$ 5,095

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