Schedule IV (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct	$ 31,208	$ 30,781	$ 32,053
Ceded Premiums Earned	11,618	12,267	12,425
Assumed	3,947	7,050	7,137
Premiums	$ 23,537	$ 25,564	$ 26,765
Percent of Amount Assumed to Net	16.80%	27.60%	26.70%
Accident and health
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct	$ 2,507	$ 2,612	$ 2,687
Ceded Premiums Earned	104	107	111
Assumed	30	35	75
Premiums	$ 2,433	$ 2,540	$ 2,651
Percent of Amount Assumed to Net	1.20%	1.40%	2.80%
Property and liability
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct	$ 28,701	$ 28,169	$ 29,366
Ceded Premiums Earned	11,514	12,160	12,314
Assumed	3,917	7,015	7,062
Premiums	$ 21,104	$ 23,024	$ 24,114
Percent of Amount Assumed to Net	18.60%	30.50%	29.30%