Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Curtailment	$ (5.3)
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost, net of employee contributions		$ 28.8	$ 29.6	$ 26.9
Interest cost		19.0	20.2	21.2
Expected return on plan assets		(32.1)	(31.3)	(27.9)
Amortization of net loss		10.8	12.4	10.4
Amortization of prior service cost		(0.4)	(0.4)	(0.4)
Curtailment		(5.3)	0.0	0.0
Net periodic pension cost		$ 20.8	$ 30.5	$ 30.2