Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 7,603	$ 6,955	$ 7,229	$ 6,677
Less reinsurance recoverable	287	274	327	277
Net loss and loss expense reserves, beginning of period	7,316	6,681	6,902	6,400
Current accident year	1,391	1,090	3,687	3,072
Prior accident years	(43)	(102)	(143)	(331)
Total incurred	1,348	988	3,544	2,741
Current accident year	484	416	1,021	893
Prior accident years	464	349	1,709	1,344
Total paid	948	765	2,730	2,237
Net loss and loss expense reserves, end of period	7,716	6,904	7,716	6,904
Plus reinsurance recoverable	329	322	329	322
Gross loss and loss expense reserves, end of period	$ 8,045	$ 7,226	$ 8,045	$ 7,226