Investments (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income:
Investment income, before expense	$ 3,213	$ 3,306	$ 3,620
Investment expense	(171)	(150)	(161)
Net investment income	3,042	3,156	3,459
Fixed income securities
Net Investment Income:
Investment income, before expense	2,060	2,218	2,447
Equity securities
Net Investment Income:
Investment income, before expense	137	110	117
Mortgage loans
Net Investment Income:
Investment income, before expense	217	228	265
Limited partnership interests
Net Investment Income:
Investment income, before expense	561	549	614
Short-term investments
Net Investment Income:
Investment income, before expense	16	9	7
Other
Net Investment Income:
Investment income, before expense	$ 222	$ 192	$ 170