Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, Beginning of Year	$ 591.6	$ 635.6
Capitalizations	428.1	449.3
Amortization Expense	(393.2)	(453.8)
Experience Adjustment	(5.2)	(8.9)
Balance, End of Period	621.3	622.2
Property and Casualty Insurance Reserves
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, Beginning of Year	164.9	231.1
Capitalizations	378.4	407.1
Amortization Expense	(377.3)	(439.1)
Experience Adjustment	0.0	0.0
Balance, End of Period	166.0	199.1
Life and Health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, Beginning of Year	426.7	404.5
Capitalizations	49.7	42.2
Amortization Expense	(15.9)	(14.7)
Experience Adjustment	(5.2)	(8.9)
Balance, End of Period	$ 455.3	$ 423.1