Investments (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Investment Income:
Investment income, before expense	$ 945	$ 803	$ 1,744	$ 1,578
Investment expense	(48)	(41)	(99)	(85)
Net investment income	897	762	1,645	1,493
Fixed income securities
Net Investment Income:
Investment income, before expense	527	520	1,045	1,038
Equity securities
Net Investment Income:
Investment income, before expense	49	44	93	72
Mortgage loans
Net Investment Income:
Investment income, before expense	50	53	105	106
Limited partnership interests
Net Investment Income:
Investment income, before expense	253	126	373	247
Short-term investments
Net Investment Income:
Investment income, before expense	6	3	12	7
Other
Net Investment Income:
Investment income, before expense	$ 60	$ 57	$ 116	$ 108