Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income:
Investment income, before expense	$ 948	$ 914	$ 2,679	$ 2,655
Investment expense	(68)	(70)	(209)	(201)
Net investment income	880	844	2,470	2,454
Fixed income securities
Net Investment Income:
Investment income, before expense	546	527	1,627	1,544
Equity securities
Net Investment Income:
Investment income, before expense	57	35	155	130
Mortgage loans
Net Investment Income:
Investment income, before expense	54	52	161	163
Limited partnership interests
Net Investment Income:
Investment income, before expense	197	210	460	563
Short-term investments
Net Investment Income:
Investment income, before expense	28	19	80	50
Other
Net Investment Income:
Investment income, before expense	$ 66	$ 71	$ 196	$ 205