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Debt - Schedule of Commercial Paper (Details) - Commercial paper - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Debt Instrument [Line Items] |  |  |  |  |
Commercial paper outstanding | $ 843 |  | $ 843 |  | $ 250
Weighted average commercial paper outstanding | $ 639 | $ 744 | $ 482 | $ 437 |
Weighted average interest rate of commercial paper outstanding | 0.70% | 0.92% | 0.63% | 0.85% |

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