Commitments and Contingencies (Details) $ in Millions				1 Months Ended			3 Months Ended		9 Months Ended
	Jun. 30, 2018 mi	Mar. 31, 2016 company	Mar. 13, 2013 company mi	Sep. 30, 2017 company mi	Sep. 30, 2016 mi	Mar. 31, 2016 mi	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($) entity	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($) entity	Dec. 31, 2018 USD ($)	Mar. 04, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Accrued probable future environmental expenditures							$ 113.6		$ 113.6		$ 111.9
Expense related to environmental activities								$ 3.6		$ 15.4
Proceeds from insurance recoveries							4.0	$ 1.5		$ 3.8
Cost of Sales
Schedule of Equity Method Investments [Line Items]
Expense related to environmental activities							2.4		6.4
Proceeds from insurance recoveries									4.0
Calvert City
Schedule of Equity Method Investments [Line Items]
Accrued probable future environmental expenditures							$ 101.8		$ 101.8
Contamination of Passaic River Study Area
Schedule of Equity Method Investments [Line Items]
Approximate number of other companies assuming responsibility | company			70
Contamination of Passaic River Study Area | Lower Passaic River
Schedule of Equity Method Investments [Line Items]
Length of portion of river | mi	8		17	8	8	8
Total estimated cost of remedy												$ 1,400.0
Number of companies receiving notice of potential liability | company		100
Number of companies receiving notice of process to allocate remedial costs | company				80
Number of entities named in suit | entity								100		100