Components of Pension Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule of Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Line Items]
Service cost	$ 18.9	$ 17.1
Interest on projected benefit obligation	20.3	20.0
Expected return on assets	(29.9)	(27.4)
Amortization of prior service costs	0.3	0.4
Recognized actuarial loss	10.9	10.6
Net pension expense	$ 20.5	$ 20.7