Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 9,050
Prior accident years	(100)	$ (59)
Gross loss and loss expense reserves, end of period	9,246
Property and Casualty Insurance
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	8,975	8,336
Less reinsurance recoverable	362	405
Net loss and loss expense reserves, beginning of period	8,613	7,931
Current accident year	1,370	1,376
Prior accident years	(100)	(59)
Total incurred	1,270	1,317
Current accident year	205	187
Prior accident years	832	859
Total paid	1,037	1,046
Net loss and loss expense reserves, end of period	8,846	8,202
Plus reinsurance recoverable	332	424
Gross loss and loss expense reserves, end of period	$ 9,178	$ 8,626