Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 36	$ 39	$ 36	$ 39	$ 36	$ 39	$ 40	$ 40
Mortgage Repurchase Reserve, Provision for Mortgage Loan Repurchase Losses	1	0	(2)	0
Charge Offs For Mortgage Loan Repurchase Losses	$ 1	$ 1	$ 1	$ 1