Employee Benefit Plans - Schedule of Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Net actuarial gain (loss)	$ (38.0)	$ 0.3	$ (113.0)
Plan settlement			(0.2)
Amortization of unrecognized prior service cost (credit)	0.3	0.4	0.5
Amortization of unrecognized net actuarial loss	13.3	15.4	11.3
Total	(24.4)	16.1	(101.4)
OPEB
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Net actuarial gain (loss)	0.5	0.8	(1.4)
Plan amendments/curtailment	(0.1)		(0.2)
Amortization of unrecognized prior service cost (credit)	(1.8)	(1.9)	(2.0)
Total	$ (1.4)	$ (1.1)	$ (3.6)