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Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Fair Value Disclosures [Abstract] |  |  |  |
Gain on sale of marketable securities | $ 34 | $ 27 | $ 73 | $ 50

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- Definition Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI). + References No definition available. + Details
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