Financial Instruments (Details) - USD ($) |
Sep. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Short-Term Investments [Abstract] | ||
| Short-term investments | $ 330,000,000 | |
| Transfers out of level 2 | 0 | |
| Fair Value of Debt Instruments [Abstract] | ||
| Fair value of total debt | 17,900,000,000 | 15,200,000,000 |
| Fair value of total debt in excess of carrying value | 2,300,000,000 | 1,000,000,000 |
| Fixed rate debt securities containing call provisions | 155,000,000 | $ 155,000,000 |
| Significant Other Observable Inputs (Level 2) [Member] | Time Deposits [Member] | ||
| Short-Term Investments [Abstract] | ||
| Short-term investments | 310,000,000 | |
| Significant Other Observable Inputs (Level 2) [Member] | Government Agency Securities [Member] | ||
| Short-Term Investments [Abstract] | ||
| Short-term investments | $ 20,000,000 |