Components of Net Periodic Benefit Expense Related to Post-Retirement Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.2	$ 5.8
Interest cost	4.6	4.3
Expected return on plan assets	(4.3)	(3.6)
Amortization of net actuarial loss from earlier periods	2.6	3.4
Amortization of net prior service costs from earlier periods		0.2
Net periodic expense	8.1	10.1
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.5
Interest cost	0.3	0.2
Amortization of net actuarial loss from earlier periods		0.1
Net periodic expense	$ 0.8	$ 0.8