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Financial Instruments - Effect of Net Investment Hedges (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Foreign exchange contracts |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) | $ (10) | $ 0 | $ (24) | $ 0
Foreign exchange contracts | Other (income) expense, net |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing | (4) | 0 | (7) | 0
Euro-denominated notes |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Amount of Pretax (Gain) Loss Recognized in Other Comprehensive Income (1) | 38 | 128 | (54) | 467
Euro-denominated notes | Other (income) expense, net |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Amount of Pretax (Gain) Loss Recognized in Other (income) expense, net for Amounts Excluded from Effectiveness Testing | $ 0 | $ 0 | $ 0 | $ 0

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