Investments in Qualified Affordable Housing Projects and Federal Historic Projects - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Remaining unfunded equity contributions	$ 134.2		$ 134.2		$ 131.3
Qualified Affordable Housing Projects
Schedule of Equity Method Investments [Line Items]
Amortization expense	5.2	$ 3.6	15.6	$ 8.5
Tax credits and other benefits	6.5	$ 4.5	19.4	$ 10.5
Remaining investment amount	219.9		219.9		195.8
Federal Historical Projects and Ohio Historical Preservation Projects
Schedule of Equity Method Investments [Line Items]
Remaining investment amount	52.4		52.4		$ 43.6
Federal Historical Projects
Schedule of Equity Method Investments [Line Items]
Amortization expense	0.4		0.8
Tax credits and other benefits	0.5		1.1
Ohio Historical Preservation Projects
Schedule of Equity Method Investments [Line Items]
Tax credits and other benefits	$ 0.4		$ 0.9