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Quarterly Operating Results (Unaudited) - Net investment income (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income |  |  |  |  |  |  |  |  | $ 2,132 | $ 2,303 | $ 2,094
Excluding Alternative Investments |  |  |  |  |  |  |  |  |  |  |
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income | $ 465 | $ 511 | $ 520 | $ 511 | $ 545 | $ 531 | $ 531 | $ 516 | 2,007 | 2,123 |
Alternative Investments |  |  |  |  |  |  |  |  |  |  |
Quarterly Operating Results (Unaudited) [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income | $ 83 | $ 61 | $ (52) | $ 33 | $ 48 | $ 57 | $ 49 | $ 26 | $ 125 | $ 180 |

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- Definition Quarterly operating results unaudited. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -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=120400993&loc=SL114874131-224263 + Details
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