Reserves - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	$ (65.0)	$ (15.0)
Sharing Economy and Small Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	6.9	30.0
Sharing Economy
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	8.4
Small Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(1.5)
Global Lifestyle
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(17.0)	(21.5)
Global Lifestyle | Net Favorable Development
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(20.9)
Global Lifestyle | Extended Service Contracts and Mobile
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(11.7)
Global Lifestyle | Credit and Other Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(9.2)
Global Automotive
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	3.9
Global Housing
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(48.4)	(22.3)
Global Housing | Prior Catastrophe Event
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(1.8)
Global Housing | Non-catastrophe Losses
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(46.6)
Global Housing | Non-catastrophe Losses | Homeowners
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	(35.1)
Other Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Unfavorable (favorable) prior year development	$ (6.5)	$ (1.2)