Property and Casualty Insurance Reserves - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	$ (28.3)	$ 55.8
Specialty Automobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	(31.3)	19.6
Personal Automobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	(17.2)	5.6
Homeowners
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	3.0	13.6
Other Personal Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	2.8	5.0
Commercial Automobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred Losses and LAE Related to Prior Years	$ 14.4	$ 11.1