Employee Postretirement Benefits - Schedule of Postretirement Benefit Amounts Recognized in Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 32.7	$ 52.7
Prior service cost (credit)	0.4	0.4
Amount recognized	33.1	53.1
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(23.8)	(17.2)
Prior service cost (credit)	(0.4)	(0.7)
Amount recognized	$ (24.2)	$ (17.9)