Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Millions |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Carrying Value | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt, excluding current portion | $ 10,678 | $ 8,753 |
| Fair Value | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt, excluding current portion | $ 11,168 | $ 9,101 |