Stock-Based Incentive Plans Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 10.9	$ 10.6	$ 10.9
Liability classified awards (credit)	3.2	3.1	(1.0)
Total pretax stock-based compensation expense	14.1	13.7	9.9
Book income tax benefit	(3.5)	(3.5)	(3.8)
Total stock-based compensation expense, net of tax	$ 10.6	$ 10.2	$ 6.1