Leases - Components of Total Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance lease expense:
Amortization of right-of-use asset	$ 0.0	$ 5.2
Interest on lease liability	0.0	0.1
Operating lease expense:
Long-term operating lease expense	23.1	28.7
Short-term lease expense	22.1	32.0
Variable lease expense	11.8	7.7
Impairments	6.8	0.0
Total lease expense	$ 63.8	$ 68.4