Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Investment Income:
Investment income, before expense	$ 1,012	$ 890	$ 1,731	$ 1,741
Investment expense	(70)	(66)	(141)	(131)
Net investment income	942	824	1,590	1,610
Fixed income securities
Net Investment Income:
Investment income, before expense	543	509	1,081	1,017
Equity securities
Net Investment Income:
Investment income, before expense	68	61	98	95
Mortgage loans
Net Investment Income:
Investment income, before expense	54	60	107	111
Limited partnership interests
Net Investment Income:
Investment income, before expense	254	173	263	353
Short-term investments
Net Investment Income:
Investment income, before expense	26	19	52	31
Other
Net Investment Income:
Investment income, before expense	$ 67	$ 68	$ 130	$ 134