Loans And Allowance For Credit Losses (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans pledged at the Federal Home Loan Bank as collateral for borrowings and letters of credit obtained to secure public deposits	$ 4,100,000,000
Loans Pledged to the Federal Reserve Bank as collateral for discount window borrowings	$ 1,600,000,000
Period after which loans are deemed in default (in days)	90 days
Effect on Interest Income Resulting From Modification to Credit Card Loans	$ (1,100,000)
Commitments to lend additional funds to customers with restructured loans	5,400,000
Mortgages Held-for-sale, Fair Value Disclosure	108,000	$ 9,181,000
Unpaid Principal Balance on Personal Real Estate Loans Held for Sale	108,000
Student Loans Held for Sale, Lower of Cost or Fair Value	6,100,000
HFS Loans on non accrual status	0
HFS loans past due and still accruing	0
Foreclosed real estate	422,000	365,000
Personal property acquired in repossession	2,300,000	$ 5,500,000
Business [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Nonaccrual, No Allowance	7,000,000.0
Real Estate - Business [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Nonaccrual, No Allowance	$ 540,000