Fair Value of Financial Instruments - Estimated Carrying Amounts and Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions |
Jun. 30, 2018 |
Jun. 19, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions | |||
| Long-term debt, including current portion | $ 16,092 | $ 120 | $ 16,633 |
| Carrying Amount | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions | |||
| Notes receivable | 21 | 16 | |
| Long-term debt, including current portion | 15,969 | 16,603 | |
| Fair Value | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions | |||
| Notes receivable | 18 | 15 | |
| Long-term debt, including current portion | 16,163 | 16,894 | |
| Fair Value | Level 2 | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions | |||
| Long-term debt, including current portion | 9,586 | 8,934 | |
| Fair Value | Level 3 | |||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions | |||
| Long-term debt, including current portion | $ 6,577 | $ 7,960 |