Reserves - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
Reserves - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	$ (32.5)	$ 30.6
Sharing Economy and Small Commercial Businesses
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(57.1)	(11.0)
Sharing Economy
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(45.2)
Small Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(11.9)
Global Lifestyle
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	42.3	34.1
Global Housing
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(22.8)	0.6
Global Housing \| Prior Catastrophe Event
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(11.7)
Global Housing \| Non-catastrophe Losses
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	(11.1)
Other Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable (unfavorable) prior year development	$ 5.1	$ 6.9