Amounts Related to Postretirement Plans Not Reclassified in Entirely out of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of prior service cost	$ (0.5)	[1]	$ (0.2)	[1]	$ (0.4)	[1]	$ 0.3	[1]
Amortization of actuarial losses	37.6	[1]	48.3	[1]	112.9	[1]	143.6	[1]
Amortization of Curtailment gain					(0.6)	[1]
Total before tax	37.1		48.1		111.9		143.9
Income tax benefit	(1.5)		(1.0)		(4.4)		(4.7)
Net of tax	$ 35.6		$ 47.1		$ 107.5		$ 139.2

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