Financing (Details) (USD $)	3 Months Ended								1 Months Ended	6 Months Ended
	Mar. 31, 2012 First mortgage bonds EDE	Mar. 31, 2012 7.0% Series due 2024	Mar. 01, 2012 7.0% Series due 2024	Mar. 31, 2012 5.3% Pollution Control Series due 2013	Mar. 01, 2012 5.3% Pollution Control Series due 2013	Mar. 31, 2012 5.2% Pollution Control Series due 2013	Mar. 01, 2012 5.2% Pollution Control Series due 2013	Jun. 30, 2012 3.58% Series Due 2027	Apr. 30, 2012 3.58% Series Due 2027 Issuance of Debt [Member]	Jun. 30, 2012 3.58% Series Due 2027 Issuance of Debt [Member]
Financing
Interest rate, stated percentage		7.00%		5.30%		5.20%		3.58%
Amount called for redemption			$ 74,800,000		$ 8,000,000		$ 5,200,000
Aggregate principal amount of debt entered into in private placement									88,000,000
First settlement of bond issuance under private placement									38,000,000
Represents the amount of the June expected settlement in private placement offering										50,000,000
Maximum principal amount outstanding at any one time	$ 1,000,000,000