Investments - Net investment income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net investment income
Investment income, before expense	$ 3,514	$ 3,613	$ 3,213
Investment expense	(274)	(212)	(171)
Net investment income	3,240	3,401	3,042
Net investment income	(691)	0	0
Fixed income securities
Net investment income
Investment income, before expense	2,077	2,078	2,060
Equity securities
Net investment income
Investment income, before expense	170	174	137
Mortgage loans
Net investment income
Investment income, before expense	217	206	217
Limited partnership interests
Net investment income
Investment income, before expense	705	889	561
Net investment income	254
Short-term investments
Net investment income
Investment income, before expense	73	30	16
Other
Net investment income
Investment income, before expense	272	$ 236	$ 222
EMA limited partnerships \| Limited partnership interests
Net investment income
Investment income, before expense	$ 451

Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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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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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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