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Intangible Assets - Major Classes of Amortizable Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net	$ 1,772.1	$ 1,644.6	[1]
Expiration Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	3,342.1	3,055.9
Accumulated amortization	(1,614.8)	(1,422.1)
Amortizable intangible assets, net	1,727.3	1,633.8
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	55.9	53.5
Accumulated amortization	(48.0)	(46.1)
Amortizable intangible assets, net	7.9	7.4
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	60.7	25.9
Accumulated amortization	(23.8)	(22.5)
Amortizable intangible assets, net	$ 36.9	$ 3.4
[1] See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to Topic 606.

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