Reinsurance (Reinsurance Recoverable on Ceded Reinsurance) (Details) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Reinsurance recoverable on unpaid losses and loss expenses	[1]	$ 16,184	$ 14,647	$ 14,181	$ 14,689
Reinsurance recoverable on unpaid losses and loss expenses, allowance		271	257
Reinsurance recoverable on paid losses and loss expenses		1,182	945
Reinsurance recoverable on paid losses and loss expenses, allowance		58	57
Reinsurance recoverable on losses and loss expenses	[2]	17,366	15,592
Reinsurance recoverable on losses and loss expenses, allowance		329	314	$ 316
Reinsurance recoverable on policy benefits		213	206
Reinsurance recoverable on policy benefits, allowance		$ 4	$ 5

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net of valuation allowance for uncollectible reinsurance.