Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 39	$ 40	$ 57	$ 85
Mortgage Repurchase Reserve, Provision for Mortgage Loan Repurchase Losses	0	(17)	(12)
Charge Offs For Mortgage Loan Repurchase Losses	$ (1)	$ 0	$ (16)