Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 16,646	$ 16,184	$ 14,860	$ 14,647
Reinsurance Recoverables on Unpaid Losses, Allowance		276	271
Reinsurance recoverable on paid losses and loss expenses	[1]	1,115	1,182
Reinsurance Recoverables on Paid Losses, Allowance		53	58
Reinsurance recoverable on losses and loss expenses, net of valuation allowance - $329 and $329	[1]	17,761	17,366
Reinsurance Recoverable, Allowance for Credit Loss, Total		329	329	$ 317	$ 314
Reinsurance recoverable on policy benefits	[1]	208	213
Reinsurance Recoverables on Future Policy Benefits, Allowance		$ 4	$ 4

[1] Net of valuation allowance for uncollectible reinsurance.