Employee Benefit Plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.7	$ 2.5	$ 9.9
Interest cost	3.8	4.4
Expected return on plan assets	(3.2)	(4.5)
Amortization of unrecognized prior service cost	0.1	0.2
Recognized actuarial losses	3.6	3.2
Total	7.0	5.8	$ 22.9
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.1	0.2
Amortization of unrecognized prior service cost	(0.2)	(0.5)
Recognized actuarial losses	(0.1)	(0.1)
Total	$ (0.2)	$ (0.4)