Leases - Lease Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Finance leases - ROU assets	$ 58.0	$ 58.2
Finance leases - Accumulated depreciation	(25.7)	(22.6)
Operating leases - ROU assets	132.9	127.4
Operating leases - Accumulated depreciation	(64.5)	(51.3)
Total lease assets	100.7	111.7
Finance leases	(10.9)	(10.5)
Operating leases	(23.0)	(24.3)
Finance leases	(20.2)	(23.9)
Operating leases	(47.7)	(53.2)
Total lease liabilities	$ (101.8)	$ (111.9)
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other non-current assets	Other non-current assets
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term debt, less current portion	Long-term debt, less current portion
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current portion of long-term debt	Current portion of long-term debt