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Marketable and Other Securities Narrative (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018
Marketable Securities [Line Items] |  |  |
Sale proceeds from investments classified as available-for-sale and sold prior to maturity | $ 611 | $ 920 |
Lyft, Inc. [Member] | Level 3 [Member] | Other assets [Member] |  |  |
Marketable Securities [Line Items] |  |  |
Fair value of equity securities | 1,200 |  | $ 884
Lyft, Inc. [Member] | Level 3 [Member] | Interest Income and Other Non-Operating Income [Member] |  |  |
Marketable Securities [Line Items] |  |  |
Unrealized gain on securities | $ 285 |  |

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