Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 24.2	$ 17.0	$ 45.8	$ 34.0
Interest on projected benefit obligation	23.3	23.1	46.2	46.1
Expected return on assets	(35.7)	(32.2)	(70.5)	(64.2)
Amortization of prior service costs	0.3	0.3	0.6	0.6
Recognized actuarial loss	10.5	5.2	20.6	10.4
Net pension expense	$ 22.6	$ 13.4	$ 42.7	$ 26.9