Components of Total Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5.7	$ 4.9
Interest cost	5.0	4.7
Expected return on plan assets	(3.9)	(3.5)
Amortization prior service credit	(0.2)	(0.2)
Amortization of actuarial loss	3.0	2.2
Net Periodic Benefit Cost	$ 9.6	$ 8.1