Description Of Business (Details)	3 Months Ended
	Mar. 31, 2013 item mi customer
Electrification area	400
Number of wholesale customers	3
Number of collective bargaining agreements with IBEW	3
Percentage of employees belonging to unions	70.00%
Expiration date of collective bargaining agreements	Jun. 30, 2017
Accepted By Board Of Directors On March 27, 2013 [Member]
Number of collective bargaining agreements ratified and accepted	2
Date of collective bargaining agreement acceptance	Mar. 27, 2013
Accepted By Board Of Directors On April 24, 2013 [Member]
Number of collective bargaining agreements ratified and accepted	1
Date of collective bargaining agreement acceptance	Apr. 24, 2013