Goodwill and Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets		$ 1,093.5	$ 1,076.4	$ 1,089.8
Accumulated amortization		(682.3)	(671.4)	(607.0)
Total amortizable intangible assets, net		411.2	405.0	482.8
Indefinite-lived trademarks		9.8	9.8	9.8
Total intangibles, net		$ 421.0	414.8	492.6
Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	[1]	15 years 9 months 18 days
Noncompete Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets		$ 0.2	0.2	0.2
Noncompete Agreements [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	[1]	4 months 24 days
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets		$ 1,092.3	$ 1,076.2	1,085.9
Customer Relationships [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	[1]	15 years 9 months 18 days
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Amortizable intangible assets		$ 1.0		$ 3.7
Trademarks [Member] | Weighted Average [Member]
Finite Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	[1]	1 year 9 months 18 days

[1] As of December 31, 2021.