Disclosure Periods Prior to Adoption of ASU 2016-02 (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 01, 2017	Dec. 31, 2017	Dec. 31, 2018
Future minimum lease and royalty payments [Line Items]
Operating Leases, Rent Expense	$ 57.0	$ 144.2	$ 158.0
Capital Leases
2019			28.2
2020			8.0
2021			0.4
2022			0.4
2023			0.5
2024 and thereafter			8.8
Total minimum lease payments			46.3
Less interest			6.3
Present value of minimum capital lease payments			40.0
Operating Leases
2019			47.6
2020			27.6
2021			15.9
2022			11.8
2023			12.1
2024 and thereafter			12.1
Total minimum lease payment			127.1
Coal Lease and Royalty Obligations
2019			5.4
2020			5.5
2021			5.6
2022			5.4
2023			5.5
2024 and thereafter			36.2
Total minimum lease payments			$ 63.6