Receivables from Policyholders - Allowance for Expected Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	$ 2.9	$ 13.9
Provision for Expected Credit Losses	13.7	6.5
Write-offs of Uncollectible Receivables from Policyholders	(14.2)	(14.0)
Balance, End of Period	2.4	6.4
Premiums Receivable, Net	1,064.6	955.8
Variable Interest Entity, Primary Beneficiary
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.0
Balance, End of Period	0.0
Premiums Receivable, Net	11.9	2.7	$ 8.2
Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	2.6	12.9
Provision for Expected Credit Losses	13.5	6.3
Write-offs of Uncollectible Receivables from Policyholders	(13.9)	(13.8)
Balance, End of Period	2.2	5.4
Premiums Receivable, Net	1,056.4	906.0
Non-Core Operations
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.3	1.0
Provision for Expected Credit Losses	0.2	0.2
Write-offs of Uncollectible Receivables from Policyholders	(0.3)	(0.2)
Balance, End of Period	0.2	1.0
Premiums Receivable, Net	8.2	49.8
Specialty Property & Casualty Insurance | Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	2.6	12.9
Provision for Expected Credit Losses	13.4	6.2
Write-offs of Uncollectible Receivables from Policyholders	(13.8)	(13.7)
Balance, End of Period	2.2	5.4
Premiums Receivable, Net	1,046.1	895.5
Life Insurance | Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.0	0.0
Provision for Expected Credit Losses	0.1	0.1
Write-offs of Uncollectible Receivables from Policyholders	(0.1)	(0.1)
Balance, End of Period	0.0	0.0
Premiums Receivable, Net	$ 10.3	$ 10.5