Long- Term Debt (Details Textuals) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Long Term Debt (Textual) [Abstract]
Extinguishment of debt	$ 626
Senior Notes [Member]
Long Term Debt (Textual) [Abstract]
Extinguishment of debt	600
Interest rate on debt portion expected to be repaid	7.05%
Mortgage Bonds [Member]
Long Term Debt (Textual) [Abstract]
Mortgage bonds issued and sell	$ 225
Interest rate on debt portion expected to be repaid	4.60%
Maturity period of mortgage bonds	17 years