Goodwill and Intangible Assets - Goodwill (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning balance, Goodwill Gross Carrying Amount	$ 1,211.8	$ 1,202.8
Acquired goodwill, Gross Carrying Amount	168.2
Foreign currency translation, Gross Carrying Amount	(8.4)	9.0
Ending balance, Goodwill Gross Carrying Amount	1,371.6	1,211.8
Beginning balance, Accumulated Impairment Loss	(145.4)	(144.3)
Impairment of goodwill, Accumulated Impairment Loss		(1.1)
Ending balance, Accumulated Impairment Loss	(145.4)	(145.4)
Beginning balance, Goodwill Net	1,066.4	1,058.5
Acquired goodwill, Net	168.2
Foreign currency translation, Net	(8.4)	9.0
Ending balance, Goodwill Net	$ 1,226.2	$ 1,066.4

Goodwill acquired during period gross.

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- Definition

Goodwill translation adjustments gross.

+ References

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Publisher FASB
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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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