Loans And Allowance For Credit Losses (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) mo Billing_Cycles d Payments	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Subsequent Event [Line Items]
Loans and Leases Receivable, Deferred Income	$ 65,000,000	$ 77,000,000
Current Fiscal Year End Date	--12-31
Financing Receivable, Minimum Number Of Days Past Due for Nonaccrual Status | d	90
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 1,000,000
Financing Receivable, Nonaccrual, Threshold for Evaluation of Impairment	$ 1,000,000
Financing Receivable, Troubled Debt Restructurting, Minimum Number Of Months For Borrower To Meet Terms For TDR Status | mo	6
Total reversal amount to allowance for loan and lease losses due to an increased cash flows from acquired loans	$ 1,000,000
Unfunded Lending Commitments on Troubled Debt Restructuring	22,000,000	14,000,000
Recorded investment in loans modified with favorable interest rates	$ 120,000,000	128,000,000
Financing Receivable, Closed-end Loans, Minimum Number Of Monthly Payments in Arrears When Reported as Past Due | Payments	2
Financing Recevable, Open-end Credit, Number of Billing Cycles in Arrears When Reported as Past Due | Billing_Cycles	2
Financing Receivable, Other, Minimum Number of Days Unpaid When Reported as Past Due | d	30
Owner Occupied And Commercial Real Estate Loans Unamortized Premiums	$ 16,000,000	20,000,000
Land Development Loans	220,000,000	290,000,000
Loans and Leases Receivable, Collateral for Secured Borrowings	25,600,000,000	24,000,000,000
Principle amount of loans held for sale sold	900,000,000	1,400,000,000	$ 1,400,000,000
Payments for Origination and Purchases of Loans Held-for-sale	800,000,000
Additions to Loans Held For Sale		1,400,000,000	1,400,000,000
Principal Balance of Loans Sold, Serviced Loans	2,200,000,000	2,000,000,000
Income From Loans Sold Excluding Servicing			2,000,000,000
Loans and Leases Receivable, Gain (Loss) on Sales, Net	$ 13,000,000
Loans Sold and Serviced		18,000,000	18,000,000
Number Of Days For Consumer Loans To Be Charged Off | d	180
Loans Modified As Troubled Debt Restructurings Loans	$ 94,000,000	73,000,000
Total reversal amount to allowance for loan and lease losses due to increased cash flows from acquired loans		2,000,000	4,000,000
Additional interest income due to increased cash flows from acquired loans	18,000,000	19,000,000	$ 32,000,000
Other Real Estate, Foreclosed Assets, Residential Real Estate	1,000,000	2,000,000
Other Real Estate, In Process of Forecloseing Assets	$ 10,000,000	$ 10,000,000
Commercial Portfolio Segment [Member]
Subsequent Event [Line Items]
Financing Receivable, Subsequent Payment Default Period, Number Of Days | d	90
Consumer Portfolio Segment [Member]
Subsequent Event [Line Items]
Financing Receivable, Subsequent Payment Default Period, Number Of Days | d	60