Amounts Related to Postretirement Plans Not Reclassified in Entirely out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of prior service cost	[1]	$ (0.7)	$ 0.1	$ (1.5)	$ 0.1
Amortization of actuarial losses	[1]	47.0	37.3	95.3	75.3
Amortization of Curtailment gain	[1]		(0.6)		(0.6)
Total before tax		46.3	36.8	93.8	74.8
Income tax benefit		(0.7)	(1.5)	(3.0)	(2.9)
Net of tax		$ 45.6	$ 35.3	$ 90.8	$ 71.9

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