Retirement Benefit Plans - Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 7.6	$ 7.6	$ 22.8	$ 22.8
Interest cost	4.7	7.2	19.3	18.3
Expected return on plan assets	(10.2)	(12.3)	(35.6)	(34.1)
Curtailment gain	(0.4)		(1.0)
Amortization of prior service cost	(1.9)	(1.1)	(5.8)	(3.4)
Amortization of unrecognized actuarial loss	5.1	5.0	15.1	13.5
Net periodic pension expense	$ 4.9	$ 6.4	$ 14.8	$ 17.1