Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021	[2]
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses		$ 17,734	[1]	$ 17,884	[1]	$ 17,086	[2]	$ 16,132
Reinsurance recoverable on unpaid losses and loss expenses, allowance		242		285
Reinsurance recoverable on paid losses and loss expenses	[1]	2,043		2,068
Reinsurance recoverable on paid losses and loss expenses, allowance		68		82
Reinsurance recoverable on losses and loss expenses	[1]	19,777		19,952
Reinsurance recoverable on losses and loss expenses, allowance		310		367		$ 351
Reinsurance recoverable on policy benefits	[1]	289		280
Reinsurance recoverable on policy benefits, allowance		$ 0		$ 0

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net of valuation allowance for uncollectible reinsurance.