Goodwill and Other Intangible Assets - Components of Other Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	$ 599.1	$ 582.9
Accumulated Amortization, total other intangible assets	(455.8)	(411.0)
Net Book Value, total other intangible assets	143.3	171.9
Client Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	534.1	517.9
Accumulated Amortization, total other intangible assets	(412.4)	(370.7)
Net Book Value, total other intangible assets	121.7	147.2
Patents
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	2.0	2.0
Accumulated Amortization, total other intangible assets	(2.0)	(2.0)
Trademarks, Licenses and Agreements
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	26.2	26.2
Accumulated Amortization, total other intangible assets	(25.2)	(24.4)
Net Book Value, total other intangible assets	1.0	1.8
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	36.8	36.8
Accumulated Amortization, total other intangible assets	(16.2)	(13.9)
Net Book Value, total other intangible assets	$ 20.6	$ 22.9