Postretirement Benefit Plans - Net Loss and Prior Service Cost that will be Amortized from Accumulated Other Comprehensive Income Loss (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 12.3
Prior service cost (credit)	(5.6)
Total	6.7
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	7.4
Prior service cost (credit)	0.9
Total	8.3
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	4.9
Prior service cost (credit)	(6.5)
Total	$ (1.6)