Long-Term Debt and Financing Obligations (Details) (USD $)										12 Months Ended			1 Months Ended												12 Months Ended											12 Months Ended																			12 Months Ended					0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Nuclear Fuel Financing	Dec. 31, 2011 Nuclear Fuel Financing	Dec. 31, 2012 Working Capital and General Purpose	Dec. 31, 2011 Working Capital and General Purpose	Dec. 31, 2012 Revolving Credit Facility	Dec. 31, 2012 Revolving Credit Facility Nuclear Fuel Financing	Dec. 31, 2012 Revolving Credit Facility Working Capital and General Purpose	Dec. 31, 2012 Revolving Credit Facility Expiring September 2016	Mar. 29, 2012 Revolving Credit Facility Expiring September 2016	Mar. 28, 2012 Revolving Credit Facility Expiring September 2016	Jun. 29, 2008 Short Term Borrowing	Dec. 31, 2012 Bonds and Notes	Dec. 31, 2011 Bonds and Notes	Dec. 31, 2012 Pollution Control Bonds		Dec. 31, 2011 Pollution Control Bonds		Aug. 27, 2012 Pollution Control Bonds 4.80% 2005 Series A Refunding Bonds, due 2040 [Member]	Dec. 31, 2012 Pollution Control Bonds 7.25% 2009 Series A Refunding Bonds, due 2040		Dec. 31, 2011 Pollution Control Bonds 7.25% 2009 Series A Refunding Bonds, due 2040		Dec. 31, 2012 Pollution Control Bonds 4.50% 2012 Series A Refunding Bonds, due 2042 [Member]		Aug. 28, 2012 Pollution Control Bonds 4.50% 2012 Series A Refunding Bonds, due 2042 [Member]	Dec. 31, 2011 Pollution Control Bonds 4.50% 2012 Series A Refunding Bonds, due 2042 [Member]		Aug. 01, 2012 Pollution Control Bonds 4.00% 2002 Series A Refunding Bonds, due 2032 [Member]	Jul. 31, 2012 Pollution Control Bonds 4.00% 2002 Series A Refunding Bonds, due 2032 [Member]	Dec. 31, 2012 Pollution Control Bonds 7.25% 2009 Series B Refunding Bonds, due 2040		Dec. 31, 2011 Pollution Control Bonds 7.25% 2009 Series B Refunding Bonds, due 2040		Dec. 31, 2012 Pollution Control Bonds 1.875% 2012 Series A Refunding Bonds, due 2032 [Member]		Aug. 28, 2012 Pollution Control Bonds 1.875% 2012 Series A Refunding Bonds, due 2032 [Member]	Dec. 31, 2011 Pollution Control Bonds 1.875% 2012 Series A Refunding Bonds, due 2032 [Member]		Dec. 31, 2012 Senior Notes		Dec. 31, 2011 Senior Notes		Dec. 31, 2012 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035		Dec. 31, 2011 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035		May 01, 2005 Senior Notes 6.00% Senior Notes, Net of Discount, due 2035	Dec. 31, 2012 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038		Dec. 31, 2011 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038		Jun. 01, 2008 Senior Notes 7.50% Senior Notes, Net of Discount, due 2038	Dec. 31, 2012 Senior Notes 3.30% Senior Notes, Net of Discount, due 2022 [Member]		Dec. 06, 2012 Senior Notes 3.30% Senior Notes, Net of Discount, due 2022 [Member]	Dec. 31, 2011 Senior Notes 3.30% Senior Notes, Net of Discount, due 2022 [Member]		Aug. 31, 2010 RGRT Senior Notes	Dec. 31, 2012 RGRT Senior Notes		Dec. 31, 2011 RGRT Senior Notes		Aug. 18, 2010 RGRT Senior Notes	Dec. 31, 2012 RGRT Senior Notes 3.67% Senior Notes, Series A, due 2015		Dec. 31, 2011 RGRT Senior Notes 3.67% Senior Notes, Series A, due 2015		Dec. 31, 2012 RGRT Senior Notes 4.47% Senior Notes, Series B, due 2017		Dec. 31, 2011 RGRT Senior Notes 4.47% Senior Notes, Series B, due 2017		Dec. 31, 2012 RGRT Senior Notes 5.04% Senior Notes, Series C, due 2020		Dec. 31, 2011 RGRT Senior Notes 5.04% Senior Notes, Series C, due 2020		Dec. 31, 2012 Financing Obligations Revolving Credit Facility		Dec. 31, 2011 Financing Obligations Revolving Credit Facility
Debt Instrument [Line Items]
Long-term Debt	$ 1,021,690,000	$ 883,176,000												$ 999,535,000	$ 849,797,000	$ 193,135,000	[1]	$ 193,135,000	[1]		$ 63,500,000	[1]	$ 63,500,000	[1]	$ 59,235,000	[1]		$ 59,235,000	[1]			$ 37,100,000	[1]	$ 37,100,000	[1]	$ 33,300,000	[1]		$ 33,300,000	[1]	$ 696,400,000	[2]	$ 546,662,000	[2]	$ 397,934,000	[2]	$ 397,894,000	[2]		$ 148,783,000	[2]	$ 148,768,000	[2]		$ 149,683,000	[2]		$ 0	[2]		$ 110,000,000	[3]	$ 110,000,000	[3]		$ 15,000,000	[3]	$ 15,000,000	[3]	$ 50,000,000	[3]	$ 50,000,000	[3]	$ 45,000,000	[3]	$ 45,000,000	[3]
Long-term Line of Credit							22,155,000																																																																							22,155,000	[4]	33,379,000	[4]
Long-term Debt, Current Maturities	0	(33,300,000)
Line of Credit, Current	(22,155,000)	(33,379,000)
Long-term debt	999,535,000	816,497,000
Number of tax exempt bond series																4
Debt Instrument, Interest Rate, Effective Percentage																					7.46%		7.46%		4.63%			4.63%				7.49%		7.49%		2.34%			2.34%						7.12%		7.12%			7.67%		7.67%			3.43%											3.87%		3.87%		4.62%		4.62%		5.16%		5.16%
Debt Instrument, Interest Rate, Stated Percentage																				4.80%	7.25%		7.25%		4.50%		4.50%	4.50%		4.00%		7.25%		7.25%		1.875%		1.875%	1.875%						6.00%		6.00%		6.00%	7.50%		7.50%		7.50%	3.30%		3.30%	3.30%								3.67%		3.67%		4.47%		4.47%		5.04%		5.04%
Debt Instrument Remarketed Date, Year																																				Sep. 01, 2017
Debt Instrument, Maturity Date										Sep. 23, 2016															Aug. 01, 2042											Jun. 01, 2032																			Dec. 15, 2022
Debt Instrument, Face Amount																				59,200,000											33,300,000																		400,000,000					150,000,000			150,000,000								110,000,000
Debt Instrument, Unamortized Discount																																																	2,300,000					1,300,000			300,000
Repayments of Short-term Debt													44,000,000
Redemption Price of Notes Equal to Principal Amount, Percentage																																																																	100.00%
Proceeds from Issuance of Long-term Debt																																																												109,400,000
Line of Credit Facility, Maximum Borrowing Capacity											300,000,000	200,000,000
Line of Credit Facility, Amount Outstanding			$ 22,200,000	$ 13,400,000	$ 0	$ 20,000,000		$ 22,200,000	$ 0
Line of Credit Weighted Average Interest Rate							1.50%

[1] Pollution Control Bonds (“PCBs”)The Company has four series of tax exempt unsecured PCBs in aggregate principal amount of $193.1 million. In August 2012, the 4.80% 2005 Series A (El Paso Electric Company Palo Verde Project) Pollution Control Refunding Revenue Bonds with an aggregate principal amount of $59.2 million was refunded at a fixed rate of 4.50% and will mature on August 1, 2042. The 4.00% 2002 Series A (El Paso Electric Company Four Corners Project) Pollution Control Refunding Revenue Bonds with an aggregate principal amount of $33.3 million was remarketed in August 2012 at a fixed rate of 1.875%, until September 1, 2017 when the bonds are subject to mandatory tender for purchase. These bonds will mature on June 1, 2032

[2] Senior NotesThe Senior Notes are unsecured obligations of the Company. They were issued pursuant to bond covenants that provide limitations on the Company’s ability to enter into certain transactions. The 6.00% senior notes have an aggregate principal amount of $400.0 million and were issued in May 2005. The proceeds, net of a $2.3 million discount, were used to fund the retirement of the Company's first mortgage bonds. The Company amortizes the loss associated with a cash flow hedge recorded in accumulated other comprehensive income to earnings as interest expense over the life of the 6.00% senior notes. See Note O, "Financial Instruments and Investments - Treasury Rate Locks". This amortization is included in the effective interest rate of the 6.00% senior notes. The 7.50% senior notes have an aggregate principal amount of $150.0 million and were issued in June 2008. The proceeds, net of a $1.3 million discount, were used to repay short-term borrowings of $44.0 million, fund capital expenditures and for other general corporate purposes.The 3.30% senior notes have an aggregate principal amount of $150.0 million, were issued in December 2012 and will mature on December 15, 2022. The gross proceeds, net of a $0.3 million discount, will be used to fund construction expenditures and for working capital and general corporate purposes.

[3] RGRT Senior NotesOn August 17, 2010, the Company and RGRT, a Texas grantor trust through which the Company finances its portion of fuel for Palo Verde, entered into a Note Purchase Agreement (the “Agreement”) with various institutional purchasers. Under the terms of the Agreement, RGRT sold to the purchasers $110 million aggregate principal amount of senior notes (the "Notes"). The Company guarantees the payment of principal and interest on the Notes. In the Company’s financial statements, the assets and liabilities of the RGRT are reported as assets and liabilities of the Company.RGRT will pay interest on the Notes on February 15 and August 15 of each year until maturity. RGRT may redeem the Notes, in whole or in part, at any time at a redemption price equal to 100% of the principal amount to be redeemed together with the interest on such principal amount accrued to the date of redemption, plus a make-whole amount based on the prevailing market interest rates. The Agreement requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2012.The sale of the Notes was made by RGRT in reliance on a private placement exemption from registration under the Securities Act of 1933, as amended.The proceeds of $109.4 million, net of issuance costs, from the sale of the Notes was used by RGRT to repay amounts borrowed under the revolving credit facility and will enable future nuclear fuel financing requirements of RGRT to be met with a combination of the Notes and amounts borrowed from the revolving credit facility.

[4] Revolving Credit FacilityOn March 29, 2012, the Company and RGRT entered into the Incremental Facility Assumption Agreement ("the Assumption Agreement") related to the revolving credit agreement (the “RCF”) with JP Morgan Chase Bank, N.A., as administrative agent and issuing bank, and Union Bank, N.A., as syndication agent, and various lending banks party thereto. The Assumption Agreement provides for the Company's exercise in full of the accordian feature provided for under the RCF, increasing the aggregate unsecured borrowing available from $200 million to $300 million. The RCF has a term ending September 2016. No other material modifications were made to the terms and conditions of the RCF.The RCF provides that amounts borrowed by the Company may be used for, among other things, working capital and general corporate purposes. Any amounts borrowed by RGRT may be used, among other things, to finance the acquisition and processing of nuclear fuel. Amounts borrowed by RGRT are guaranteed by the Company and the balance borrowed under the RCF is recorded as short-term borrowings on the consolidated balance sheet. The RCF is unsecured. The RCF requires compliance with certain covenants, including a total debt to capitalization ratio. The Company was in compliance with these requirements throughout 2012. As of December 31, 2012, the total amount borrowed by RGRT was $22.2 million for nuclear fuel under the RCF. No borrowings were outstanding under this facility for working capital and general corporate purposes. The weighted average interest rate on the RCF was 1.5% as of December 31, 2012.