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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
SEC Schedule, 12-09, Allowance, Credit Loss [Member] |  |  |
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |
Balance at Beginning of Year | $ 8.7 | $ 10.0 | $ 13.5
Amounts Recorded in Earnings | 6.6 | 4.2 | 5.8
Adjustments | (5.2) | (5.5) | (9.3)
Balance at End of Year | 10.1 | 8.7 | 10.0
Allowance for Estimated Policy Cancellations [Member] |  |  |
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |
Balance at Beginning of Year | 8.3 | 7.8 | 7.4
Amounts Recorded in Earnings | 4.1 | 0.5 | (1.2)
Adjustments | (2.5) |  | 1.6
Balance at End of Year | 9.9 | 8.3 | 7.8
Valuation Allowance for Deferred Tax Assets [Member] |  |  |
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |
Balance at Beginning of Year | 80.5 | 67.4 | 79.1
Amounts Recorded in Earnings | 14.4 | 13.1 | (11.7)
Balance at End of Year | 94.9 | 80.5 | 67.4
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 | 2,087.5 | 1,750.4 | 1,490.7
Amounts Recorded in Earnings | 417.3 | 334.0 | 291.2
Adjustments | 32.2 | 3.1 | (31.5)
Balance at End of Year | $ 2,537.0 | $ 2,087.5 | $ 1,750.4

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