Other Real Estate Owned (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Repossessed Assets [Abstract]
Real Estate Acquired Through Foreclosure, Acquired Through Acquisition	$ 0.0	$ 2.4	$ 0.0	$ 2.4
Real Estate Acquired Through Foreclosure [Roll Forward]
Beginning balance	8.2	21.1	8.5	14.4
Additions	0.3	4.9	1.2	13.3
Valuation adjustments	0.0	(0.1)	0.0	(0.4)
Dispositions	(2.0)	(0.7)	(3.2)	(2.1)
Ending balance	6.5	$ 27.6	6.5	$ 27.6
Carrying values of foreclosed residential real estate properties	2.2		2.2		$ 2.3
Consumer mortgage loans collateralized by residential real estate property in the process of foreclosure	$ 0.2		$ 0.2		$ 1.4