Credit Facilities, Short-term Borrowings and Long-term Debt (Details Textual 2) (USD $)	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Credit Facilities, Short-term Borrowings and Long-term Debt (Textuals)
Total bank loans	$ 100,000,000	$ 285,500,000	$ 0
Credit Facilities, Short-term Borrowings and Long-term Debt (Textuals)
Total unsecured bank lines of credit	1,500,000,000
Secured long-term debt, including current maturities	40,000
Bank Loan Borrowed For 15 Days [Member]
Credit Facilities, Short-term Borrowings and Long-term Debt (Textuals)
Total bank loans	100,000,000
Interest rate of bank loan	0.53%
Line Of Credit Expiring November 16 2012 [Member]
Credit Facilities, Short-term Borrowings and Long-term Debt (Textuals)
Total unsecured bank lines of credit	$ 1,500,000,000