Commitments and Contingencies (Environmental) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Environmental Remediation Expense	$ 2.4	$ 2.8
Fair Value, Measurements, Recurring
Loss Contingencies [Line Items]
Obligations, Fair Value Disclosure	13.0	$ 15.8
Montana
Loss Contingencies [Line Items]
Environmental Remediation Expense	$ 0.0
Shreveport
Loss Contingencies [Line Items]
Environmental penalty	0.1
Capital Expenditure | Montana
Loss Contingencies [Line Items]
Environmental Remediation Expense	$ 0.0