Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 7,229	$ 6,677
Less reinsurance recoverable	327	277
Net loss and loss expense reserves, beginning of period	6,902	6,400
Current accident year	997	1,033
Prior accident years	(41)	(110)
Total incurred	956	923
Current accident year	169	143
Prior accident years	721	562
Total paid	890	705
Net loss and loss expense reserves, end of period	6,968	6,618
Plus reinsurance recoverable	319	262
Gross loss and loss expense reserves, end of period	$ 7,287	$ 6,880