Schedule V - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Valuation allowance for deferred tax assets
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 364.0	$ 322.4
Additions
Charged to costs and expenses	31.8	41.6
Charge to other accounts	0.0	0.0
(Deductions)	0.0	0.0
Balance at end of period	395.8	364.0
Allowance for premium receivables
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	2.8	2.5
Additions
Charged to costs and expenses	1.3	0.3
Charge to other accounts	0.0	0.0
(Deductions)	0.0	0.0
Balance at end of period	$ 4.1	$ 2.8