Components of 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
Schedule of Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Line Items]
Service cost	$ 16.0	$ 11.9	$ 48.0	$ 34.6
Interest on projected benefit obligation	20.3	21.0	61.0	61.8
Expected return on assets	(27.6)	(26.5)	(82.8)	(79.1)
Amortization of prior service costs	0.3	0.3	1.1	1.0
Recognized actuarial loss	10.8	4.5	32.4	17.7
Net pension expense	$ 19.8	$ 11.2	$ 59.7	$ 36.0