Loans And Allowance For Credit Losses (Summary Of Net Financial Impact On Interest Income Due To Interest Rate Modifications Below Market For Accruing TDR Loans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Net financial impact on interest income	$ 1	$ 1
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Net financial impact on interest income	1	1
1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Net financial impact on interest income	$ 1	$ 1