Investments - Components of net investment income (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Net Investment Income [Line Items]
Total investment income	$ 3,409	$ 3,522	$ 6,817	$ 6,896
Investment expenses	219	184	430	369
Net investment income	3,190	3,338	6,387	6,527
Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	3,169	3,173	6,312	6,207
Investment expenses	212	178	418	354
Net investment income	2,957	2,995	5,894	5,853
Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	240	349	505	689
Investment expenses	7	6	12	15
Net investment income	233	343	493	674
Available-for-sale fixed maturity securities, including short-term investments
Net Investment Income [Line Items]
Total investment income	2,599	2,414	5,176	4,858
Available-for-sale fixed maturity securities, including short-term investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	2,438	2,245	4,838	4,514
Available-for-sale fixed maturity securities, including short-term investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	161	169	338	344
Other fixed maturity securities
Net Investment Income [Line Items]
Total investment income	77	101	88	240
Other fixed maturity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	11	21	2	40
Other fixed maturity securities \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	66	80	86	200
Equity securities
Net Investment Income [Line Items]
Total investment income	14	30	3	28
Equity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	14	30	3	28
Equity securities \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	0	0	0	0
Interest on mortgage and other loans
Net Investment Income [Line Items]
Total investment income	699	737	1,410	1,445
Interest on mortgage and other loans \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	664	694	1,339	1,359
Interest on mortgage and other loans \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	35	43	71	86
Alternative investments
Net Investment Income [Line Items]
Total investment income	(21)	224	71	308
Alternative investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	0	169	59	249
Alternative investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(21)	55	12	59
Real estate
Net Investment Income [Line Items]
Total investment income	6	9	14	12
Real estate \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	7	7	16	12
Real estate \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(1)	2	(2)	0
Other investments
Net Investment Income [Line Items]
Total investment income	35	7	55	5
Other investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	35	7	55	5
Other investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	$ 0	$ 0	$ 0	$ 0