Stock-Based Incentive Plans Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 12.6	$ 10.9	$ 10.6
Liability classified awards expense	1.0	3.2	3.1
Total pretax stock-based compensation expense	13.6	14.1	13.7
Book income tax benefit	(3.4)	(3.5)	(3.5)
Total stock-based compensation expense, net of tax	$ 10.2	$ 10.6	$ 10.2