Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 36	$ 40	$ 36	$ 40	$ 39	$ 39	$ 40	$ 40
Mortgage Repurchase Reserve, Provision for Mortgage Loan Repurchase Losses	$ (3)	$ 0	$ (3)	$ 0