Goodwill and Other Intangible Assets - Components of Other Intangible Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	$ 588.2	$ 599.1
Accumulated Amortization, total other intangible assets	(461.0)	(455.8)
Net Book Value, total other intangible assets	127.2	143.3
Client Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	523.8	534.1
Accumulated Amortization, total other intangible assets	(416.7)	(412.4)
Net Book Value, total other intangible assets	107.1	121.7
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	25.8	26.2
Accumulated Amortization, total other intangible assets	(25.0)	(25.2)
Net Book Value, total other intangible assets	0.8	1.0
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	36.6	36.8
Accumulated Amortization, total other intangible assets	(17.3)	(16.2)
Net Book Value, total other intangible assets	$ 19.3	$ 20.6