LONG-TERM DEBT (Details) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended					12 Months Ended												1 Months Ended			1 Months Ended								1 Months Ended										1 Months Ended
	Dec. 31, 2011 state	Jan. 28, 2011	Dec. 31, 2010	Dec. 31, 2011 First mortgage bonds	Dec. 31, 2010 First mortgage bonds	Dec. 31, 2011 First mortgage bonds EDE Y M count	Dec. 31, 2011 First mortgage bonds EDG quarter numerator denominator	Dec. 31, 2011 7.20% Series due 2016 EDE	Dec. 31, 2010 7.20% Series due 2016 EDE	Dec. 31, 2011 5.3% Pollution Control Series due 2013 EDE	Dec. 31, 2010 5.3% Pollution Control Series due 2013 EDE	Dec. 31, 2011 5.2% Pollution Control Series due 2013 EDE	Dec. 31, 2010 5.2% Pollution Control Series due 2013 EDE	Dec. 31, 2011 5.875% Series due 2037 EDE	Dec. 31, 2010 5.875% Series due 2037 EDE	Dec. 31, 2011 6.375% Series due 2018 EDE	Dec. 31, 2010 6.375% Series due 2018 EDE	May 31, 2010 4.65% Series due 2020 EDE	Dec. 31, 2011 4.65% Series due 2020 EDE	Dec. 31, 2010 4.65% Series due 2020 EDE	Aug. 31, 2010 5.20% Series due 2040 EDE	Dec. 31, 2011 5.20% Series due 2040 EDE	Dec. 31, 2010 5.20% Series due 2040 EDE	Dec. 31, 2011 7.0% Series due 2024 EDE	Dec. 31, 2010 7.0% Series due 2024 EDE	Dec. 31, 2011 7.0% Series due 2024 EDE On or after April 1, 2012	Dec. 31, 2011 6.82% Series due 2036 EDG	Dec. 31, 2010 6.82% Series due 2036 EDG	Aug. 31, 2010 Senior Notes, 7.05% Series due 2022	Dec. 31, 2011 Senior Notes, 7.05% Series due 2022	Dec. 31, 2011 Senior Notes, 4.50% Series due 2013	Dec. 31, 2010 Senior Notes, 4.50% Series due 2013	Dec. 31, 2011 Senior Notes, 6.70% Series due 2033	Dec. 31, 2010 Senior Notes, 6.70% Series due 2033	Dec. 31, 2011 Senior Notes, 5.80% Series due 2035	Dec. 31, 2010 Senior Notes, 5.80% Series due 2035	Dec. 31, 2011 Other..	Dec. 31, 2010 Other..	Jun. 30, 2010 8.5% trust preferred securities
LONG-TERM DEBT
Less unamortized net discount	$ (924,000)		$ (1,033,000)
Total long-term debt, current and non current	693,192,000		693,953,000
Total long-term debt, current and non current	694,116,000			488,029,000	488,054,000			25,000,000	25,000,000	8,000,000	8,000,000	5,200,000	5,200,000	80,000,000	80,000,000	90,000,000	90,000,000		100,000,000	100,000,000		50,000,000	50,000,000	74,829,000	74,854,000		55,000,000	55,000,000			98,000,000	98,000,000	62,000,000	62,000,000	40,000,000	40,000,000	6,087,000	6,932,000
Current obligations of long term debt	(641,000)		(614,000)
Current obligations under capital lease	(292,000)		(267,000)
Total long-term debt	692,259,000		693,072,000
Percentage of principal amount at which the entity may redeem all the notes										100.00%		100.00%		100.00%		100.00%			100.00%			100.00%				100.00%	100.00%			100.00%	100.00%		100.00%		100.00%
Principal amount of first mortgage bonds issued																		100,000,000			50,000,000
Net proceeds (after payment of expenses)																		98,800,000			49,100,000
Aggregate principal amount redeemed																													48,300,000										50,000,000
Number of trust preferred securities redeemed (in shares)																																							2
Shelf registration statement, amount		400,000,000
Maximum principal amount outstanding at any one time						1,000,000,000	300,000,000
Number of states in the entity's electric service territory	4
Maximum amount of securities to be issued in the form of first mortgage bonds						250,000,000
Effective period to use proceeds under shelf to fund capital expenditures, refinancings of existing debt or general corporate needs (in years)						3
Number of consecutive months within the fifteen months preceding issuance to determine net earnings to annual interest requirement ratio						12
Number of months preceding issuance to determine net earnings to annual interest requirement ratio						15
Net earnings to annual interest requirement ratio (in counts)						2
Debt permitted to be issued on compliance of interest coverage ratio covenant						511,000,000	697,600,000
Interest rate assumed on debt permitted to be issued on compliance of interest coverage ratio covenant (as a percent)						6.00%
New bonds to be issued as a percentage of net property additions						60.00%	75.00%
Debt permitted to be issued on compliance of amount of retired bonds and percentage of net property additions covenant						$ 10,700,000
Number of most recent fiscal quarters used in calculating the interest coverage ratio as per the terms of debt instrument covenants							4
Numerator for ratio of EBITDA to interest charges, minimum							2.0
Denominator for ratio of EBITDA to interest charges, minimum							1