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, 2013		Sep. 30, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of prior service cost	$ (0.2)	[1]	$ 0.3	[1]
Amortization of actuarial losses	48.3	[1]	143.6	[1]
Total before tax	48.1		143.9
Income tax benefit	(1.0)		(4.7)
Net of tax	$ 47.1		$ 139.2

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