Goodwill And Intangible Assets (Summary of Intangible Assets Rollforward) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning Balance	$ 66.0
Intangible assets acquired	102.6
Amortization	(8.5)
Intangible Assets, Ending Balance	160.1
Core deposit intangibles
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning Balance	46.6
Intangible assets acquired	96.1
Amortization	(6.9)
Intangible Assets, Ending Balance	135.8
Trade names
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning Balance	12.0
Intangible assets acquired	3.0
Amortization	(0.9)
Intangible Assets, Ending Balance	14.1
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Beginning Balance	7.7
Intangible assets acquired	3.5
Amortization	(1.0)
Intangible Assets, Ending Balance	10.2
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Rentals Below Current Market Rates	(0.3)
Intangible Assets Amortization, Rentals Below Current Market Rates	$ (0.3)