Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 10.0	$ 13.5	$ 12.8
Amounts Recorded in Earnings	4.2	5.8	5.4
Adjustments	(5.5)	(9.3)	(4.7)
Balance at End of Year	8.7	10.0	13.5
Allowance for Estimated Policy Cancellations [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	7.8	7.4	7.1
Amounts Recorded in Earnings	0.5	(1.2)	2.1
Adjustments		1.6	(1.8)
Balance at End of Year	8.3	7.8	7.4
Valuation Allowance for Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	67.4	79.1	66.8
Amounts Recorded in Earnings	13.1	(11.7)	12.3
Balance at End of Year	80.5	67.4	79.1
Accumulated Amortization of Expiration Lists, Noncompete Agreements and Trade Names [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	1,750.4	1,490.7	1,203.6
Amounts Recorded in Earnings	334.0	291.3	264.7
Adjustments	3.1	(31.6)	22.4
Balance at End of Year	$ 2,087.5	$ 1,750.4	$ 1,490.7