Debt (Details) (USD $) | 9 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2011 | Dec. 31, 2010 | Sep. 30, 2010 | Sep. 30, 2011
5.375% Senior Notes, due 2012 [Member] | Dec. 31, 2010
5.375% Senior Notes, due 2012 [Member] | Sep. 30, 2010
5.375% Senior Notes, due 2012 [Member] | Sep. 30, 2011
5.9% Senior Notes, due 2017 [Member] | Dec. 31, 2010
5.9% Senior Notes, due 2017 [Member] | Sep. 30, 2010
5.9% Senior Notes, due 2017 [Member] | Sep. 30, 2011
6.55% Senior Notes, due 2037 [Member] | Dec. 31, 2010
6.55% Senior Notes, due 2037 [Member] | Sep. 30, 2010
6.55% Senior Notes, due 2037 [Member] | Jul. 30, 2013
3 Year Facility [Member] | |
| Short-term and long-term debt outstanding | |||||||||||||
| Note payable | $ 100,000 | $ 500,000 | $ 100,000 | ||||||||||
| Total debt | 1,198,000,000 | 1,198,300,000 | 1,197,900,000 | 399,900,000 | 399,900,000 | 399,900,000 | 399,400,000 | 399,300,000 | 399,300,000 | 398,600,000 | 398,600,000 | 398,600,000 | |
| Less: short-term debt including current maturities | 0 | 300,000 | 0 | ||||||||||
| Long-term debt | 1,198,000,000 | 1,198,000,000 | 1,197,900,000 | ||||||||||
| Debt (Textuals) [Abstract] | |||||||||||||
| Unamortized debt discount on senior notes | 100,000 | 600,000 | 1,400,000 | ||||||||||
| Line of Credit Facility [Line Items] | |||||||||||||
| Size of total commercial paper program | $ 1,200,000,000 | $ 1,200,000,000 | |||||||||||
| Commitment fee | 15.0 to 35.0 basis points, depending on credit rating and currently pay a commitment fee of 20.0 basis points | ||||||||||||
| Commitment fee, minimum percentage to pay depending on credit rating | 0.15% | ||||||||||||
| Commitment fee, maximum percentage to pay depending on credit rating | 0.35% | ||||||||||||
| Commitment fee, current percentage | 0.20% | ||||||||||||
| Indebtedness to cash flow ratio | not greater than 4 to 1 |