Other Real Estate Owned (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Real Estate Acquired Through Foreclosure [Roll Forward]
Beginning balance	$ 27.5	$ 14.9	$ 14.4	$ 10.1
OREO acquired through acquisition	0.0	0.6	2.4	0.6
Additions	0.7	3.2	14.0	10.6
Valuation adjustments	(0.2)	(0.1)	(0.7)	(0.1)
Dispositions	(10.2)	(1.3)	(12.3)	(3.9)
Ending balance	17.8	$ 17.3	17.8	$ 17.3
Carrying values of foreclosed residential real estate properties	2.7		2.7		$ 2.0
Consumer mortgage loans collateralized by residential real estate property in the process of foreclosure	$ 0.6		$ 0.6		$ 0.4