Net Periodic Benefit Expenses Recognized for Post-Retirement Plans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18.9	$ 15.1	$ 13.5
Interest cost	13.1	13.1	12.0
Expected return on plan assets	(12.5)	(11.9)	(10.5)
Amortization of net actuarial loss from earlier periods	9.1	5.0	2.8
Amortization of net prior service costs from earlier periods	0.7	0.6	0.7
Settlement charges		1.6	1.3
Net periodic expense	29.3	23.5	19.8
Other Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.5	1.1	0.9
Interest cost	0.7	0.8	0.8
Amortization of net actuarial loss from earlier periods	0.3	0.3	0.1
Net periodic expense	$ 2.5	$ 2.2	$ 1.8