Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 8,626	$ 7,287	$ 8,336	$ 7,229
Less reinsurance recoverable	424	319	405	327
Net loss and loss expense reserves, beginning of period	8,202	6,968	7,931	6,902
Current accident year	1,363	1,299	2,739	2,296
Prior accident years	(101)	(59)	(160)	(100)
Total incurred	1,262	1,240	2,579	2,196
Current accident year	502	368	689	537
Prior accident years	579	524	1,438	1,245
Total paid	1,081	892	2,127	1,782
Net loss and loss expense reserves, end of period	8,383	7,316	8,383	7,316
Plus reinsurance recoverable	424	287	424	287
Gross loss and loss expense reserves, end of period	$ 8,807	$ 7,603	$ 8,807	$ 7,603