Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at Beginning of Period	$ (773.6)	$ (488.1)
Other comprehensive loss before reclassifications	(22.8)	(8.9)
Amounts reclassified from accumulated other comprehensive loss	2.2	0.9
Net change in accumulated other comprehensive loss	(20.6)	(8.0)
Balance at End of Period	(794.2)	(496.1)
Changes in the Fair Value of Derivatives
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at Beginning of Period			(0.1)	(0.2)
Balance at End of Period	(0.1)	(0.2)	(0.1)	(0.2)
Pension and Other Postretirement Benefits Plan Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at Beginning of Period	(762.3)	(521.4)
Amounts reclassified from accumulated other comprehensive loss, Pension and Other Postretirement Benefits Plan cost	2.2	0.9
Net change in accumulated other comprehensive loss	2.2	0.9
Balance at End of Period	(760.1)	(520.5)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at Beginning of Period	(11.2)	33.5
Other comprehensive loss before reclassifications, Translation Adjustments	(22.8)	(8.9)
Net change in accumulated other comprehensive loss	(22.8)	(8.9)
Balance at End of Period	$ (34.0)	$ 24.6