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Financial Instruments - Summary of Interest Rate Swaps Held (Details) | Sep. 30, 2018 USD ($) interest_rate_swap | Dec. 31, 2017 USD ($)
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Derivative [Line Items] |  |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 22 |
Total Swap Notional Amount | $ 26,549,000,000 | $ 25,595,000,000
5.00% notes due 2019 | Interest rate swap contracts |  |
Derivative [Line Items] |  |
Stated interest rate (as percent) | 5.00% |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 3 |
Total Swap Notional Amount | $ 550,000,000 |
1.85% notes due 2020 | Interest rate swap contracts |  |
Derivative [Line Items] |  |
Stated interest rate (as percent) | 1.85% |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 5 |
Total Swap Notional Amount | $ 1,250,000,000 |
3.875% notes due 2021 | Interest rate swap contracts |  |
Derivative [Line Items] |  |
Stated interest rate (as percent) | 3.875% |
Par Value of Debt | $ 1,150,000,000 |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 5 |
Total Swap Notional Amount | $ 1,150,000,000 |
2.40% notes due 2022 | Interest rate swap contracts |  |
Derivative [Line Items] |  |
Stated interest rate (as percent) | 2.40% |
Par Value of Debt | $ 1,000,000,000 |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 4 |
Total Swap Notional Amount | $ 1,000,000,000 |
2.35% notes due 2022 | Interest rate swap contracts |  |
Derivative [Line Items] |  |
Stated interest rate (as percent) | 2.35% |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held (in interest rate swaps) | interest_rate_swap | 5 |
Total Swap Notional Amount | $ 1,250,000,000 |

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