Credit Quality And Allowance For Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Retail loans secured by residential real estate in process of foreclosure	$ 0.0		$ 0.0		$ 0.0
Commitments to lend additional funds to TDR borrowers	24.0		$ 24.0		$ 31.0
Principal Deferrals
Days past due defined as subsequent default			90 days	90 days
Balance	64.0	$ 174.0	$ 64.0	$ 174.0
Subsequent default during period	0.0	0.0	$ 0.0	$ 0.0
Interest Rate Reductions
Days past due defined as subsequent default			90 days	90 days
Balance	3.0	2.0	$ 3.0	$ 2.0
Subsequent default during period	0.0	0.0	$ 0.0	$ 0.0
AB Note Restructures
Days past due defined as subsequent default			90 days	90 days
Balance	0.0	31.0	$ 0.0	$ 31.0
Subsequent default during period	$ 0.0	$ 0.0	$ 0.0	$ 0.0