Amounts Related to Postretirement Plans Not Reclassified in Entirely out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of prior service cost	[1]	$ (0.8)	$ (0.5)	$ (2.3)	$ (0.4)
Amortization of actuarial losses	[1]	47.8	37.6	143.1	112.9
Amortization of Curtailment gain	[1]				(0.6)
Total before tax		47.0	37.1	140.8	111.9
Income tax benefit		(3.9)	(1.5)	(6.9)	(4.4)
Net of tax		$ 43.1	$ 35.6	$ 133.9	$ 107.5

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