Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019
Entity Information [Line Items]
Off-Balance Sheet, Credit Loss, Liability	$ (2.1)	$ (0.2)	$ 0.0	$ 0.0
Credit Extension Commitments	2,122.4		2,067.0
Unused Credit Card Lines
Entity Information [Line Items]
Credit Extension Commitments	1,480.5		1,450.5
Standby Letter of Credit
Entity Information [Line Items]
Credit Extension Commitments	$ 56.2		$ 42.7
Cumulative Effect, Period of Adoption, Adjustment
Entity Information [Line Items]
Off-Balance Sheet, Credit Loss, Liability		$ (2.3)		$ 0.0