Components of the Estimated Net Pension and Other Postretirement Benefit Plan (Income) Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.8	$ 1.6	$ 1.6	$ 3.5
Interest cost	44.5	47.4	89.1	94.8
Expected return on plan assets	(60.6)	(65.8)	(121.2)	(131.6)
Amortization, net	12.6	6.8	25.2	13.9
Net benefits plan income	(2.7)	(10.0)	(5.3)	(19.4)
Other Postretirement Plan Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.9	1.6	3.7	3.3
Interest cost	4.0	4.6	8.1	9.2
Expected return on plan assets	(2.9)	(3.4)	(5.9)	(6.9)
Amortization, net	(5.0)	(4.9)	(9.9)	(9.9)
Net benefits plan income	$ (2.0)	$ (2.1)	$ (4.0)	$ (4.3)