Goodwill and Other Intangible Assets - Components of Other Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 142.4	$ 143.5
Accumulated Amortization	(113.1)	(103.6)
Net Book Value	29.3	39.9
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	139.5	140.6
Accumulated Amortization	(110.2)	(100.7)
Net Book Value	29.3	39.9
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	2.9	2.9
Accumulated Amortization	(2.9)	(2.9)
Net Book Value	$ 0.0	$ 0.0