Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Sep. 30, 2023		Dec. 31, 2022		Sep. 30, 2022	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 17,808		$ 17,086		$ 17,313	$ 16,132
Reinsurance recoverable on paid losses and loss expenses	[1],[2]	1,942		1,773
Reinsurance recoverable on losses and loss expenses		19,750	[1]	18,859	[2]
Reinsurance recoverable on policy benefits	[1],[2]	315		302
Reinsurance Recoverables on Unpaid Losses, Allowance		318		289
Reinsurance Recoverables on Paid Losses, Allowance		52		62
Reinsurance Recoverable, Allowance for Credit Loss, Total		370		351		$ 352	$ 329
Reinsurance Recoverables on Future Policy Benefits, Allowance		$ 1		$ 4

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net of valuation allowance for uncollectible reinsurance.