SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 14.1	$ 15.2	$ 15.9
Additions (Charged to costs and expenses)	13.1	10.9	12.4
Deductions	(15.2)	(12.0)	(13.1)
Balance at end of period	12.0	14.1	15.2
Allowance for doubtful accounts [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	6.2	6.3	9.3
Additions (Charged to costs and expenses)	13.1	10.9	10.1
Deductions	(14.2)	(11.0)	(13.1)
Balance at end of period	5.1	6.2	6.3
Allowance for uncollectible reinsurance recoverables [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	7.9	8.9	6.6
Additions (Charged to costs and expenses)			2.3
Deductions	(1.0)	(1.0)
Balance at end of period	$ 6.9	$ 7.9	$ 8.9