Guarantees Mortgage Loans Repurchase Reserve Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Reserve For Mortgage Loan Repurchase Losses	$ 23	$ 36	$ 23	$ 36	$ 24	$ 26	$ 39	$ 39
Mortgage Repurchase Reserve, Provision for Mortgage Loan Repurchase Losses	$ (1)	$ (3)	$ (3)	$ (3)