Goodwill And Intangible Assets (Summary of Intangible Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 284.9	$ 182.3
Accumulated Amortization	(124.8)	(116.3)
Net Carrying Amount	160.1	66.0
Core deposit intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	222.4	126.3
Accumulated Amortization	(86.6)	(79.7)
Net Carrying Amount	135.8	46.6
Trade names
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	27.7	24.7
Accumulated Amortization	(13.6)	(12.7)
Net Carrying Amount	14.1	12.0
Customer relationships
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	27.4	23.9
Accumulated Amortization	(17.2)	(16.2)
Net Carrying Amount	10.2	7.7
Other
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	7.4	7.4
Accumulated Amortization	$ (7.4)	(7.7)
Intangible Assets, Rentals Below Current Market Rates		$ (0.3)