Mortgage Loans Held for Sale and Investment - Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans held for sale – UPB	$ 3,735	$ 3,949
Mark-to-market adjustment	187	128
Total mortgage loans held for sale	3,922	4,077
UPB	33	29
Ginnie Mae Repurchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB	$ 28	$ 25