Fair Value of Financial Instruments (Details) (USD $) | Sep. 30, 2011 | Dec. 31, 2010 |
|---|---|---|
Carrying Value [Member] | ||
| Assets [Abstract] | ||
| Marketable securities | $ 400,000,000 | |
| Liabilities [Abstract] | ||
| Long-term debt | 3,800,000,000 | 3,800,000,000 |
| Fixed rate debt, after interest rate swaps | 2,800,000,000 | |
| Variable rate debt, after interest rate swaps | 1,000,000,000 | |
Fair Value [Member] | ||
| Liabilities [Abstract] | ||
| Long-term debt | $ 5,000,000,000 | $ 4,600,000,000 |