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Debt - Schedule of Commercial Paper (Details) - Commercial paper - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Debt Instrument [Line Items] |  |  |  |  |
Commercial paper outstanding | $ 546 |  | $ 546 |  | $ 250
Weighted average commercial paper outstanding | $ 656 | $ 820 | $ 541 | $ 566 |
Weighted average interest rate of commercial paper outstanding | 0.15% | 0.79% | 0.43% | 0.83% |

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