Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 16,608	$ 17,086	$ 16,504	$ 16,132
Reinsurance recoverable on paid losses and loss expenses	[1]	1,790	1,773
Reinsurance recoverable on losses and loss expenses	[1]	18,398	18,859
Reinsurance recoverable on policy benefits	[1]	315	302
Reinsurance Recoverables on Unpaid Losses, Allowance		306	289
Reinsurance Recoverables on Paid Losses, Allowance		55	62
Reinsurance Recoverable, Allowance for Credit Loss, Total		361	351	$ 341	$ 329
Reinsurance Recoverables on Future Policy Benefits, Allowance		$ 1	$ 4

[1] Net of valuation allowance for uncollectible reinsurance.