Mortgage Loans Held for Sale and Investment - Mortgage Loans Held for Sale (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB	$ 31	$ 45
Fair Value	26	42
Ginnie Mae Repurchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB	26	40
Mortgages loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans held for sale – UPB	4,110	1,568
Mark-to-market adjustment	157	63
Total mortgage loans held for sale	$ 4,267	$ 1,631