Investments - Components of net investment income (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Net Investment Income [Line Items]
Total investment income	$ 3,408	$ 3,374
Investment expenses	211	185
Net investment income	3,197	3,189
Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	3,143	3,034
Investment expenses	206	176
Net investment income	2,937	2,858
Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	265	340
Investment expenses	5	9
Net investment income	260	331
Available-for-sale fixed maturity securities, including short-term investments
Net Investment Income [Line Items]
Total investment income	2,577	2,444
Available-for-sale fixed maturity securities, including short-term investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	2,400	2,269
Available-for-sale fixed maturity securities, including short-term investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	177	175
Other fixed maturity securities
Net Investment Income [Line Items]
Total investment income	11	139
Other fixed maturity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(9)	19
Other fixed maturity securities \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	20	120
Equity securities
Net Investment Income [Line Items]
Total investment income	(11)	(2)
Equity securities \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(11)	(2)
Equity securities \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	0	0
Interest on mortgage and other loans
Net Investment Income [Line Items]
Total investment income	711	708
Interest on mortgage and other loans \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	675	665
Interest on mortgage and other loans \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	36	43
Alternative investments
Net Investment Income [Line Items]
Total investment income	92	84
Alternative investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	59	80
Alternative investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	33	4
Real estate
Net Investment Income [Line Items]
Total investment income	8	3
Real estate \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	9	5
Real estate \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	(1)	(2)
Other investments
Net Investment Income [Line Items]
Total investment income	20	(2)
Other investments \| Excluding Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	20	(2)
Other investments \| Fortitude Re Funds Withheld Assets
Net Investment Income [Line Items]
Total investment income	$ 0	$ 0