Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		$ 11.1	$ 8.3	$ 10.1
Amounts Recorded in Earnings		26.0	6.8	7.0
Adjustments	[1]	(14.1)	(4.0)	(8.8)
Balance at End of Year		23.0	11.1	8.3
Allowance for Estimated Policy Cancellations [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		9.3	10.0	9.9
Amounts Recorded in Earnings		(0.5)	2.4	(1.3)
Adjustments	[2]	1.1	(3.1)	1.4
Balance at End of Year		9.9	9.3	10.0
Valuation Allowance for Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		135.2	154.9	94.9
Amounts Recorded in Earnings		60.6	(19.7)	60.0
Balance at End of Year		195.8	135.2	154.9
Accumulated Amortization of Expiration Lists, Non-compete Agreements and Trade Names [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		3,300.0	2,924.0	2,537.0
Amounts Recorded in Earnings		531.3	454.9	415.1
Adjustments	[3]	42.2	(78.9)	(28.1)
Balance at End of Year		$ 3,873.5	$ 3,300.0	$ 2,924.0

[1] Net activity of bad debt write offs and recoveries and acquired businesses.

[2] Additions to allowance related to acquired businesses.

[3] Elimination of fully amortized expiration lists, non-compete agreements and trade names, intangible asset/amortization reclassifications and disposal of acquired businesses.