Assets And Liabilities Measured At Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Cash equivalents | $ 655 | $ 625 |
| Available-for-sale securities | 2,275 | 1,846 |
| Investments in and Advances to Affiliates, at Fair Value | 3,635 | 3,161 |
| Debt | 1,846 | 1,667 |
| Level 1 | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Cash equivalents | 655 | 625 |
| Available-for-sale securities | 2,275 | 1,846 |
| Investments in and Advances to Affiliates, at Fair Value | 3,635 | 3,161 |
| Significant Other Observable Inputs (Level 2) | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Debt | $ 1,846 | $ 1,667 |