Accumulated Other Comprehensive Income - Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation Adjustment	$ 0.1	$ (0.8)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax, beginning of period	(4.5)
Translation Adjustment Functional to Reporting Currency, Gain (Loss), Reclassified to Earnings, Net of Tax	0.0
Foreign Currency Translation Adjustment	0.1
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax, end of period	(4.4)
Prior Service Credit (Cost) Associated with Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income loss prior service cost credit arising during period net of tax, beginning of period	44.6
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax	(2.2)
Prior service cost for the period	0.0
Accumulated other comprehensive income loss prior service cost credit arising during period net of tax, end of period	42.4
Total Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation Adjustment	0.1	$ (0.8)
Accumulated other comprehensive income, beginning of period	40.1
Other Comprehensive Income Reclassification Adjustment Net Of Tax	(2.2)
Accumulated other comprehensive income (loss), current period change, net of tax	0.1
Accumulated other comprehensive income, end of period	$ 38.0