Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 39	$ 48	$ 39	$ 48	$ 40	$ 40	$ 51	$ 57
Mortgage Repurchase Reserve, Provision for Mortgage Loan Repurchase Losses	0	(3)	0	(9)
Charge Offs For Mortgage Loan Repurchase Losses	$ (1)	$ 0	$ (1)	$ 0