Components of Net Pension Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Service cost	$ 6.2	$ 7.4	$ 19.1	$ 21.5
Interest cost	4.6	5.2	14.2	15.4
Expected return on plan assets	(8.2)	(8.1)	(24.7)	(23.9)
Settlement			0.7
Amortization of prior service cost	(1.3)	(0.3)	(2.7)	(0.7)
Amortization of unrecognized actuarial loss	3.2	1.9	9.9	5.6
Net periodic benefit cost	$ 4.5	$ 6.1	$ 16.5	$ 17.9