Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 17,884	$ 17,086	$ 16,132	$ 14,576
Reinsurance recoverable on unpaid losses and loss expenses, allowance		285	289
Reinsurance recoverable on paid losses and loss expenses	[2]	2,068	1,773
Reinsurance recoverable on paid losses and loss expenses, allowance		82	62
Reinsurance recoverable on losses and loss expenses	[2]	19,952	18,859
Reinsurance recoverable on losses and loss expenses, allowance		367	351	$ 329
Reinsurance recoverable on policy benefits	[2]	280	302
Reinsurance recoverable on policy benefits, allowance		$ 0	$ 4

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net of valuation allowance for uncollectible reinsurance.