Components of the Estimated Net Pension and Other Postretirement Benefit Plan (Income) Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.8	$ 1.9
Interest cost	44.6	47.4
Expected return on plan assets	(60.6)	(65.8)
Amortization, net	12.6	7.1
Net pension income	(2.6)	(9.4)
Other Postretirement Plan Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.8	1.7
Interest cost	4.1	4.6
Expected return on plan assets	(3.0)	(3.5)
Amortization, net	(4.9)	(5.0)
Net pension income	$ (2.0)	$ (2.2)