Investments - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net investment income
Investment income, before expense	$ 410	$ 461	$ 1,285	$ 1,379
Investment expense	(25)	(22)	(74)	(63)
Net investment income	385	439	1,211	1,316
Fixed income securities
Net investment income
Investment income, before expense	247	263	745	800
Mortgage loans
Net investment income
Investment income, before expense	44	46	141	140
Equity securities
Net investment income
Investment income, before expense	7	9	30	38
Limited partnership interests
Net investment income
Investment income, before expense	74	115	262	315
Net investment income	35		83
Short-term investments
Net investment income
Investment income, before expense	7	3	16	6
Policy loans
Net investment income
Investment income, before expense	8	8	23	23
Other
Net investment income
Investment income, before expense	23	$ 17	68	$ 57
Equity method limited partnerships \| Limited partnership interests
Net investment income
Net investment income	$ 39		$ 179

Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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