Retirement Plans - Amounts in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain	$ (1,229.9)	$ (1,284.8)
Net transition obligation	(0.1)	(0.1)
Net prior service credit	0.0	0.0
Total	(1,230.0)	(1,284.9)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain	24.1	(8.0)
Net transition obligation	0.0	0.0
Net prior service credit	31.5	58.3
Total	$ 55.6	$ 50.3