10-K Reinsurance (Summary Of Net Premiums Earned By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Premiums Earned By Segment [Line Items]
Premiums	$ 35,259	$ 33,722	$ 107,716	$ 99,583	$ 133,229	$ 117,373	$ 104,109
Commercial and Specialty Business Segment [Member]
Net Premiums Earned By Segment [Line Items]
Premiums					131,964	115,725	102,643
Other [Member]
Net Premiums Earned By Segment [Line Items]
Premiums					$ 1,265	$ 1,648	$ 1,466