Reinsurance - Schedule of premiums written, earned and policy fees (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Premiums earned:
Premiums	$ 33,254	$ 31,856	$ 31,285
Policy Fees:
Net	2,797	2,913	3,005
Short-Duration Insurance
Premiums written:
Direct	31,445	32,025	30,910
Assumed	7,951	7,385	7,209
Ceded	(12,190)	(12,650)	(11,702)
Net	27,206	26,760	26,417
Premiums earned:
Direct	30,781	32,053	30,279
Assumed	7,050	7,137	6,640
Ceded	(12,268)	(12,425)	(11,301)
Premiums	25,563	26,765	25,618
Long-Duration Insurance
Premiums written:
Direct	4,706	4,739	4,604
Assumed	4,111	1,318	2,265
Ceded	(1,126)	(966)	(1,202)
Net	7,691	5,091	5,667
Policy Fees:
Direct	2,873	2,991	3,090
Assumed	0	0	0
Ceded	(76)	(78)	(85)
Net	$ 2,797	$ 2,913	$ 3,005

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