Reinsurance - Insurance Revenue (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Premiums Earned
Direct	$ 21,959	$ 20,316	$ 18,867
Assumed	1,000	829	696
Ceded	(1,716)	(1,568)	(1,381)
Premiums Earned, Net	21,026	19,390	17,999
Property and Casualty Insurance Products
Premiums Written
Direct	16,144	14,891	13,696
Assumed	975	718	631
Ceded	(1,642)	(1,490)	(1,378)
Net	15,477	14,119	12,949
Premiums Earned
Direct	15,514	14,328	13,204
Assumed	826	654	568
Ceded	(1,612)	(1,462)	(1,277)
Premiums Earned, Net	14,728	13,520	12,495
Group Insurance Policy [Member]
Premiums Earned
Direct	6,445	5,988	5,663
Assumed	174	175	128
Ceded	(104)	(106)	(104)
Premiums Earned, Net	$ 6,515	$ 6,057	$ 5,687

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