Accumulated Other Comprehensive Income (Loss) - Change in AOCI Balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 441.9
Other comprehensive income before reclassification	$ (19.8)	$ 8.4	(16.2)	$ 12.9
Amounts reclassified from accumulated other comprehensive income	1.3	1.0	2.7	2.0
Ending balance	410.6		410.6
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(135.3)	(151.5)	(140.3)	(157.0)
Ending balance	(153.8)	(142.1)	(153.8)	(142.1)
Pension and Other Postretirement Benefits (1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(112.5)	(107.8)	(113.9)	(108.6)
Other comprehensive income before reclassification	0.0	0.0	0.0	0.0
Amounts reclassified from accumulated other comprehensive income	1.4	0.8	2.8	1.6
Ending balance	(111.1)	(107.0)	(111.1)	(107.0)
Derivatives Designated as Hedges (1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2.5	0.3	1.4	(0.1)
Other comprehensive income before reclassification	0.5	(0.3)	1.6	(0.1)
Amounts reclassified from accumulated other comprehensive income	(0.1)	0.2	(0.1)	0.4
Ending balance	2.9	0.2	2.9	0.2
Foreign Currency Translation (1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(25.3)	(44.0)	(27.8)	(48.3)
Other comprehensive income before reclassification	(20.3)	8.7	(17.8)	13.0
Amounts reclassified from accumulated other comprehensive income	0.0	0.0	0.0	0.0
Ending balance	$ (45.6)	$ (35.3)	$ (45.6)	$ (35.3)