Guarantees Repurchased Mortgage Loan (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Repurchased mortgage loans, carrying value	$ 242	$ 272
Performing Financial Instruments [Member] | Loans Held For Investment [Member]
Repurchased mortgage loans, carrying value	230	255
Nonperforming Financing Receivable [Member] | Loans Held For Investment [Member]
Repurchased mortgage loans, carrying value	$ 12	$ 17