Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Investment Income:
Investment income, before expense	$ 801	$ 494	$ 2,561	$ 1,027
Investment expense	(37)	(30)	(115)	(97)
Net investment income	764	464	2,446	930
Fixed income securities
Net Investment Income:
Investment income, before expense	279	314	870	918
Equity securities
Net Investment Income:
Investment income, before expense	24	18	51	49
Mortgage loans
Net Investment Income:
Investment income, before expense	9	8	31	25
Limited partnership interests
Net Investment Income:
Investment income, before expense	438	123	1,467	(71)
Short-term investments
Net Investment Income:
Investment income, before expense	1	2	3	15
Other
Net Investment Income:
Investment income, before expense	$ 50	$ 29	$ 139	$ 91