Commitments and Contingencies - Accruals and Estimated Future Payments of Environmental Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Undiscounted environmental liabilities	$ 84.6	$ 42.4
Total accrued environmental liabilities	143.3	76.1
2019	2.9
2020	3.1
2021	3.2
2022	3.7
2023	2.8
Thereafter	61.7
Discounted environmental liabilities, gross	77.4
Less: Discount applied	18.7
Discounted environmental liabilities	$ 58.7	$ 33.7