Amounts in Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain	$ (1,284.8)	$ (957.5)
Net transition obligation	(0.1)	(0.2)
Net prior service credit
Total	(1,284.9)	(957.7)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain	(8.0)	35.6
Net transition obligation
Net prior service credit	58.3	78.4
Total	$ 50.3	$ 114.0