Mortgage Loans Held for Sale and Investment - Held For Sale (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans held for sale - UPB	$ 3,949	$ 1,568
Mark-to-market adjustment	128	63
Total mortgage loans held for sale	4,077	1,631	$ 1,514	$ 1,891
UPB	29	45
Fair Value	22	42
Ginnie Mae Repurchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB	$ 25	$ 40