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, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period			$ 9,050
Prior accident years	$ (40)	$ (101)	(140)	$ (160)
Gross loss and loss expense reserves, end of period	9,555		9,555
Property and Casualty Insurance
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	9,178	8,626	8,975	8,336
Less reinsurance recoverable	332	424	362	405
Net loss and loss expense reserves, beginning of period	8,846	8,202	8,613	7,931
Current accident year	1,452	1,363	2,822	2,739
Prior accident years	(40)	(101)	(140)	(160)
Total incurred	1,412	1,262	2,682	2,579
Current accident year	483	502	688	689
Prior accident years	584	579	1,416	1,438
Total paid	1,067	1,081	2,104	2,127
Net loss and loss expense reserves, end of period	9,191	8,383	9,191	8,383
Plus reinsurance recoverable	303	424	303	424
Gross loss and loss expense reserves, end of period	$ 9,494	$ 8,807	$ 9,494	$ 8,807