Investments - Net investment income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net investment income
Investment income, before expense	$ 1,515	$ 1,688	$ 1,864
Investment expense	(104)	(103)	(87)
Net investment income	1,411	1,585	1,777
Fixed income securities
Net investment income
Investment income, before expense	963	991	1,058
Mortgage loans
Net investment income
Investment income, before expense	190	188	182
Equity securities
Net investment income
Investment income, before expense	29	39	48
Limited partnership interests
Net investment income
Investment income, before expense	175	327	457
Short-term investments
Net investment income
Investment income, before expense	31	21	9
Policy loans
Net investment income
Investment income, before expense	34	31	31
Other
Net investment income
Investment income, before expense	$ 93	$ 91	$ 79

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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