Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 8,336	$ 7,229
Less reinsurance recoverable	405	327
Net loss and loss expense reserves, beginning of period	7,931	6,902
Current accident year	1,376	997
Prior accident years	(59)	(41)
Total incurred	1,317	956
Current accident year	187	169
Prior accident years	859	721
Total paid	1,046	890
Net loss and loss expense reserves, end of period	8,202	6,968
Plus reinsurance recoverable	424	319
Gross loss and loss expense reserves, end of period	$ 8,626	$ 7,287