Property and Casualty Insurance Reserves - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	$ 106.7	$ 36.4	$ (71.1)
Reinsurance recoverables	41.9	50.1
Premium Receivable, Credit Loss Expense (Reversal)	50.5	45.5
Premium Receivable, Allowance for Credit Loss, Writeoff	(57.8)	(46.9)
Specialty Automobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	85.3	28.2	(23.8)
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	12.4	(12.9)	(12.9)
Preferred Automobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	12.1	26.7	(8.2)
Homeowners
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	(6.5)	(2.1)	(19.7)
Other Personal Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	3.4	(3.5)	(6.5)
Property and Liability Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	106.7	36.4	(71.1)
Reinsurance recoverables	41.9	50.1	65.6	$ 101.9
Catastrophe
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred losses and LAE related to prior year (favorable) adverse development	$ (5.4)	$ 0.2	$ (17.1)