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Financial Instruments - Information About Interest Rate Swaps (Details) | Dec. 31, 2017 USD ($) interest_rate_swap | Dec. 31, 2016 USD ($)
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Derivative [Line Items] |  |
Number of Interest Rate Swaps Held | interest_rate_swap | 26 |
U.S. Dollar Notional | $ 25,595,000,000 | $ 25,539,000,000
1.30% notes due 2018 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,000,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 4 |
U.S. Dollar Notional | $ 1,000,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 1.30% |
5.00% notes due 2019 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 3 |
U.S. Dollar Notional | $ 550,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 5.00% |
1.85% notes due 2020 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 5 |
U.S. Dollar Notional | $ 1,250,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 1.85% |
3.875% notes due 2021 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,150,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 5 |
U.S. Dollar Notional | $ 1,150,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 3.875% |
2.40% notes due 2022 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,000,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 4 |
U.S. Dollar Notional | $ 1,000,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 2.40% |
2.35% notes due 2022 | Interest Rate Swap |  |
Derivative [Line Items] |  |
Par Value of Debt | $ 1,250,000,000 |
Number of Interest Rate Swaps Held | interest_rate_swap | 5 |
U.S. Dollar Notional | $ 1,250,000,000 |
Fixed-rate notes, stated interest rate (as percent) | 2.35% |

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