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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions | 12 Months Ended
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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.

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