Postretirement Health Care Plan Change in Accumulated in Postretirement Benefit Obligation (Detail) - Other Postretirement Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning Balance	$ 33.4	$ 31.2
Service Cost	0.1	0.1	$ 0.1
Interest Cost	1.4	1.5	1.2
Actuarial Loss	(0.2)	3.0
Net Claims Paid	(2.5)	(3.1)
Medicare Subsidy	0.0	0.7
Ending Balance	$ 32.2	$ 33.4	$ 31.2