Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income:
Investment income, before expense	$ 880	$ 948	$ 1,816	$ 2,679
Investment expense	(48)	(68)	(154)	(209)
Net investment income	832	880	1,662	2,470
Fixed income securities
Net Investment Income:
Investment income, before expense	541	546	1,597	1,627
Equity securities
Net Investment Income:
Investment income, before expense	24	57	61	155
Mortgage loans
Net Investment Income:
Investment income, before expense	54	54	165	161
Limited partnership interests
Net Investment Income:
Limited partnership interests	200	197	(212)	460
Short-term investments
Net Investment Income:
Investment income, before expense	2	28	21	80
Other
Net Investment Income:
Investment income, before expense	$ 59	$ 66	$ 184	$ 196