Investments - Components of net investment income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Net Investment Income [Line Items]
Total investment income	$ 3,479	$ 3,506	$ 10,296	$ 10,402
Investment expenses	209	186	639	555
Net investment income	3,270	3,320	9,657	9,847
Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	3,354	3,132	9,666	9,339
Investment expenses	204	180	622	534
Net investment income	3,150	2,952	9,044	8,805
Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	125	374	630	1,063
Investment expenses	5	6	17	21
Net investment income	120	368	613	1,042
Available-for-sale fixed maturity securities, including short-term investments
Net Investment Income [Line Items]
Total investment income	2,628	2,481	7,804	7,339
Available-for-sale fixed maturity securities, including short-term investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	2,467	2,316	7,305	6,830
Available-for-sale fixed maturity securities, including short-term investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	161	165	499	509
Other fixed maturity securities
Net Investment Income [Line Items]
Total investment income	(122)	157	(34)	397
Other fixed maturity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(1)	15	1	55
Other fixed maturity securities \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(121)	142	(35)	342
Equity securities
Net Investment Income [Line Items]
Total investment income	1	38	4	66
Equity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	1	38	4	66
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	703	724	2,113	2,169
Interest on mortgage and other loans \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	670	682	2,009	2,041
Interest on mortgage and other loans \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	33	42	104	128
Alternative investments
Net Investment Income [Line Items]
Total investment income	211	72	282	380
Alternative investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	159	47	218	296
Alternative investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	52	25	64	84
Real estate
Net Investment Income [Line Items]
Total investment income	9	12	23	24
Real estate \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	9	12	25	24
Real estate \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	0	0	(2)	0
Other investments
Net Investment Income [Line Items]
Total investment income	49	22	104	27
Other investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	49	22	104	27
Other investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	$ 0	$ 0	$ 0	$ 0