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Investments and Related Matters Other Segments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Investments [Line Items] |  |  |
Investments | $ 8,337 | $ 10,015 |
Other Segments and Holding Company |  |  |
Schedule of Investments [Line Items] |  |  |
Investments | 1,470 | 483 |
Portion of unrealized (losses) gains that relates to equity securities still held | (339) | 67 | $ 0
Equity method investments | Other Segments and Holding Company |  |  |
Schedule of Investments [Line Items] |  |  |
Investments | 143 | 83 |
Other investments | Other Segments and Holding Company |  |  |
Schedule of Investments [Line Items] |  |  |
Investments | $ 1,327 | $ 400 |

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