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Investments - Holding gains (losses) on equity securities still held (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Realized gains (losses) on securities |  | $ (266) | $ 5 | $ 19
Gross investment income |  | 2,116 | 1,852 | 1,716
Equity securities |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Realized gains (losses) on securities |  | (265) | $ 6 | $ 13
Accounting Standards Update 2016-01 | Equity securities still owned | Equity securities |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Net holding gains (losses) on equity securities |  | (257) |  |
Accounting Standards Update 2016-01 | Realized gains (losses) on securities | Equity securities still owned | Equity securities |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Realized gains (losses) on securities |  | (279) |  |
Net holding gains (losses) on equity securities | $ (228) | (279) |  |
Accounting Standards Update 2016-01 | Investment income | Equity securities still owned | Equity securities |  |  |  |
Holding Gains (Losses) on Equity Securities Still Held [Line Items] |  |  |  |
Gross investment income |  | $ 22 |  |

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- Definition Net holding gains (losses) on equity securities in net earnings on securities that were still owned. All equity securities other than those accounted for under the equity method are carried at fair value through net earnings. + References No definition available. + Details
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- Definition Amount, before 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
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- Definition Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI). + References No definition available. + Details
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