Investments in Qualified Affordable Housing Projects, Federal Historical Projects and New Market Tax Credits - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Remaining unfunded equity contributions	$ 131.3	$ 56.2
Qualified Affordable Housing Projects
Schedule of Equity Method Investments [Line Items]
Amortization expense	13.3	9.9	$ 9.6
Tax credits and other benefits	16.6	11.6	$ 12.5
Remaining investment amount	195.8	$ 90.9
Federal Historical Projects
Schedule of Equity Method Investments [Line Items]
Amortization expense	4.0
Tax credits and other benefits	4.6
Remaining investment amount	$ 43.6