Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (240.3)	$ (250.1)
Other comprehensive income (loss) before reclassifications	2.0	(2.5)
Amounts reclassified from accumulated other comprehensive income (net of tax)	3.7	4.8
Net current-period other comprehensive income (loss)	5.7	2.3
Ending balance	(234.6)	(247.8)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(1.3)	(1.7)
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(12.4)	(4.6)
Other comprehensive income (loss) before reclassifications	2.0	(2.5)
Amounts reclassified from accumulated other comprehensive income (net of tax)	0.0	0.0
Net current-period other comprehensive income (loss)	2.0	(2.5)
Ending balance	(10.4)	(7.1)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(227.9)	(245.5)
Other comprehensive income (loss) before reclassifications	0.0	0.0
Amounts reclassified from accumulated other comprehensive income (net of tax)	3.7	4.8
Net current-period other comprehensive income (loss)	3.7	4.8
Ending balance	$ (224.2)	$ (240.7)