Goodwill and Other Intangible Assets - Components of Other Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	$ 467.5	$ 471.3
Accumulated Amortization, total other intangible assets	(403.5)	(402.5)
Net Book Value, total other intangible assets	64.0	68.8
Client Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	413.5	417.0
Accumulated Amortization, total other intangible assets	(361.8)	(361.1)
Net Book Value, total other intangible assets	51.7	55.9
Trade Names
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	28.8	29.1
Accumulated Amortization, total other intangible assets	(16.5)	(16.2)
Net Book Value, total other intangible assets	12.3	12.9
Trademarks, Licenses and Agreements
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount, total other intangible assets	23.2	23.2
Accumulated Amortization, total other intangible assets	(23.2)	(23.2)
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)