Amounts Related to Postretirement Plans Not Reclassified in Entirely out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of prior service cost	[1]	$ (1.4)	$ (0.8)
Amortization of actuarial losses	[1]	38.6	48.3
Total before tax		37.2	47.5
Income tax benefit		(1.4)	(2.3)
Net of tax		$ 35.8	$ 45.2

[1] These items are included in net periodic postretirement cost (see note (c)).