Receivables from Policyholders - Allowance for Expected Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	$ 2.4	$ 6.4	$ 2.9	$ 13.9
Provision for Expected Credit Losses	13.2	7.8	26.9	14.3
Write-offs of Uncollectible Receivables from Policyholders	(13.6)	(9.4)	(27.8)	(23.4)
Balance, End of Period	2.0	4.8	2.0	4.8
Premiums Receivable, Net	1,050.3	993.2	1,050.3	993.2
Variable Interest Entity, Primary Beneficiary
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premiums Receivable, Net	11.6	5.2	11.6	5.2	$ 8.2
Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	2.2	5.4	2.6	12.9
Provision for Expected Credit Losses	13.2	7.5	26.7	13.8
Write-offs of Uncollectible Receivables from Policyholders	(13.6)	(8.6)	(27.5)	(22.4)
Balance, End of Period	1.8	4.3	1.8	4.3
Premiums Receivable, Net	1,042.9	963.7	1,042.9	963.7
Non-Core Operations
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.2	1.0	0.3	1.0
Provision for Expected Credit Losses	0.0	0.3	0.2	0.5
Write-offs of Uncollectible Receivables from Policyholders	0.0	(0.8)	(0.3)	(1.0)
Balance, End of Period	0.2	0.5	0.2	0.5
Premiums Receivable, Net	7.4	29.5	7.4	29.5
Specialty Property & Casualty Insurance | Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	2.2	5.4	2.6	12.9
Provision for Expected Credit Losses	13.2	7.5	26.6	13.7
Write-offs of Uncollectible Receivables from Policyholders	(13.6)	(8.6)	(27.4)	(22.3)
Balance, End of Period	1.8	4.3	1.8	4.3
Premiums Receivable, Net	1,031.8	952.5	1,031.8	952.5
Life Insurance | Operating Segments
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, Beginning of Year	0.0	0.0	0.0	0.0
Provision for Expected Credit Losses	0.0	0.0	0.1	0.1
Write-offs of Uncollectible Receivables from Policyholders	0.0	0.0	(0.1)	(0.1)
Balance, End of Period	0.0	0.0	0.0	0.0
Premiums Receivable, Net	$ 11.1	$ 11.2	$ 11.1	$ 11.2