Investments - Net investment income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net investment income
Short-term investments	$ 4,256	$ 3,027
Investment income, before expense	3,436	3,514	$ 3,613
Investment expense	(277)	(274)	(212)
Net investment income	3,159	3,240	3,401
Fixed income securities
Net investment income
Investment income, before expense	2,175	2,077	2,078
Equity securities
Net investment income
Investment income, before expense	206	170	174
Mortgage loans
Net investment income
Investment income, before expense	220	217	206
Limited partnership interests
Net investment income
Investment income, before expense	471	705	889
Short-term investments
Net investment income
Investment income, before expense	102	73	30
Other
Net investment income
Investment income, before expense	$ 262	$ 272	$ 236

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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