Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 18,081	$ 17,734	$ 17,163	$ 17,884
Reinsurance recoverable on paid losses and loss expenses	[1]	1,934	2,043
Reinsurance recoverable on losses and loss expenses	[1]	20,015	19,777
Reinsurance Recoverables on Unpaid Losses, Allowance		254	242
Reinsurance Recoverables on Paid Losses, Allowance		66	68
Reinsurance Recoverable, Allowance for Credit Loss, Total		320	310	$ 375	$ 367
Reinsurance recoverable on policy benefits	[1]	267	289
Reinsurance Recoverables on Future Policy Benefits, Allowance		$ 0	$ 0

[1] Net of valuation allowance for uncollectible reinsurance.