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, total other intangible assets	$ 586.6	$ 599.1
Accumulated Amortization, total other intangible assets	(466.4)	(455.8)
Net Book Value, total other intangible assets	120.2	143.3
Client Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	524.2	534.1
Accumulated Amortization, total other intangible assets	(423.2)	(412.4)
Net Book Value, total other intangible assets	101.0	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	25.7	26.2
Accumulated Amortization, total other intangible assets	(25.1)	(25.2)
Net Book Value, total other intangible assets	0.6	1.0
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	34.7	36.8
Accumulated Amortization, total other intangible assets	(16.1)	(16.2)
Net Book Value, total other intangible assets	$ 18.6	$ 20.6