Comprehensive Income - Schedule of Reclassification From Accumulated Other Comprehensive Loss (Detail) (Pension and Other Postretirement Benefits Plan Cost, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Pension and Other Postretirement Benefits Plan Cost
Amortization of pension and other postretirement benefits plan cost:
Net actuarial loss	$ 10.2	[1]	$ 7.8	[1]
Net prior service credit	(6.7)	[1]	(6.4)	[1]
Reclassifications before tax	3.5		1.4
Income tax expense	1.3		0.5
Reclassifications, net of tax	$ 2.2		$ 0.9

[1] These accumulated other comprehensive income (loss) components are included in the calculation of net periodic pension and other postretirement benefits plan income recognized in cost of sales and selling, general and administrative expenses in the Condensed Consolidated Statements of Operations (see Note 7, Employee Benefits).