Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 7,287	$ 6,880	$ 7,229	$ 6,677
Less reinsurance recoverable	319	262	327	277
Net loss and loss expense reserves, beginning of period	6,968	6,618	6,902	6,400
Current accident year	1,299	949	2,296	1,982
Prior accident years	(59)	(119)	(100)	(229)
Total incurred	1,240	830	2,196	1,753
Current accident year	368	334	537	477
Prior accident years	524	433	1,245	995
Total paid	892	767	1,782	1,472
Net loss and loss expense reserves, end of period	7,316	6,681	7,316	6,681
Plus reinsurance recoverable	287	274	287	274
Gross loss and loss expense reserves, end of period	$ 7,603	$ 6,955	$ 7,603	$ 6,955