Reinsurance - Consolidated Property Casualty Insurance Assumed and Ceded Business (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Property Casualty Insurance Assumed And Ceded Business
Earned premiums	$ 2,297	$ 2,033	$ 6,524	$ 5,894
Incurred loss and loss expenses	1,578	1,332	4,407	4,070
Consolidated Property And Casualty Insurance
Property Casualty Insurance Assumed And Ceded Business
Direct written premiums	2,285	1,939	6,772	5,869
Assumed written premiums	102	89	577	527
Ceded written premiums	(94)	(71)	(349)	(270)
Net written premiums	2,293	1,957	7,000	6,126
Direct earned premiums	2,179	1,912	6,128	5,478
Assumed earned premiums	159	142	466	435
Ceded earned premiums	(121)	(97)	(310)	(252)
Earned premiums	2,217	1,957	6,284	5,661
Direct incurred loss and loss expenses	1,415	1,220	3,960	3,784
Assumed incurred loss and loss expenses	103	82	242	216
Ceded incurred loss and loss expenses	(19)	(41)	(21)	(160)
Incurred loss and loss expenses	$ 1,499	$ 1,261	$ 4,181	$ 3,840

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