Components of Net Periodic Benefit Expense Related to Post-Retirement Plans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.5	$ 4.6	$ 16.3	$ 13.8
Interest cost	4.2	4.2	12.7	12.4
Expected return on plan assets	(3.6)	(3.7)	(10.8)	(10.7)
Amortization of net actuarial loss from earlier periods	3.1	1.7	9.3	5.0
Amortization of net prior service costs from earlier periods	0.1	0.2	0.5	0.5
Net periodic expense	9.3	7.0	28.0	21.0
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.5	1.6	1.3
Interest cost	$ 0.2	$ 0.2	$ 0.7	$ 0.7
Expected return on plan assets
Amortization of net actuarial loss from earlier periods	$ 0.1		$ 0.3
Amortization of net prior service costs from earlier periods
Net periodic expense	$ 0.8	$ 0.7	$ 2.6	$ 2.0