Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 17,128	$ 16,184	$ 14,647	$ 14,181
Reinsurance recoverable on unpaid losses and loss expenses, allowance		289	271
Reinsurance recoverable on paid losses and loss expenses	[2]	1,773	1,182
Reinsurance recoverable on paid losses and loss expenses, allowance		62	58
Reinsurance recoverable on losses and loss expenses	[2]	18,901	17,366
Reinsurance recoverable on losses and loss expenses, allowance		351	329	$ 314
Reinsurance recoverable on policy benefits	[2]	303	213
Reinsurance recoverable on policy benefits, allowance		$ 4	$ 4

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net of valuation allowance for uncollectible reinsurance.