Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost:
Amortization of finance lease assets	$ 1.5	$ 1.5
Interest on lease liabilities	1.1	1.2
Total finance lease cost	2.6	2.7
Operating lease cost	74.4	70.2
Short-term lease cost	18.0	19.2
Variable lease cost	12.9	13.7
Total lease cost	$ 107.9	$ 105.8