Goodwill and Other Intangible Assets - Components of Other Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	$ 604.6	$ 599.1
Accumulated Amortization, total other intangible assets	(468.3)	(455.8)
Net Book Value, total other intangible assets	136.3	143.3
Client Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	539.5	534.1
Accumulated Amortization, total other intangible assets	(424.1)	(412.4)
Net Book Value, total other intangible assets	115.4	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	26.2	26.2
Accumulated Amortization, total other intangible assets	(25.3)	(25.2)
Net Book Value, total other intangible assets	0.9	1.0
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	36.9	36.8
Accumulated Amortization, total other intangible assets	(16.9)	(16.2)
Net Book Value, total other intangible assets	$ 20.0	$ 20.6