Financing (Details) (USD $)	6 Months Ended	1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended
	Jun. 30, 2012 First mortgage bonds EDE	Apr. 30, 2012 7.0% Series due 2024	Jun. 30, 2012 7.0% Series due 2024	Apr. 30, 2012 5.3% Pollution Control Series due 2013	Jun. 30, 2012 5.3% Pollution Control Series due 2013	Apr. 30, 2012 5.2% Pollution Control Series due 2013	Jun. 30, 2012 5.2% Pollution Control Series due 2013	Jun. 30, 2012 3.58% Series Due 2027	Jun. 30, 2012 3.58% Series Due 2027 Issuance of debt	Apr. 30, 2012 3.58% Series Due 2027 Issuance of debt
Financing
Interest rate, stated percentage			7.00%		5.30%		5.20%	3.58%
Debt redeemed		$ 74,800,000		$ 8,000,000		$ 5,200,000
Aggregate principal amount of debt entered into in private placement										88,000,000
Settlement of bond issuance under private placement									50,000,000	38,000,000
Maximum principal amount outstanding at any one time	$ 1,000,000,000