Summary of Business and Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member]	Dec. 31, 2011 Texas-New Mexico Power Company [Member]	Dec. 31, 2010 Texas-New Mexico Power Company [Member]	Dec. 31, 2009 Texas-New Mexico Power Company [Member]	Sep. 23, 2011 Optim Energy [Member]	Sep. 22, 2011 Optim Energy [Member]	Dec. 31, 2010 Optim Energy [Member]	Jan. 04, 2012 Sale of Ownership Interst [Member] Optim Energy [Member]	Dec. 31, 2011 Coal [Member]	Dec. 31, 2010 Coal [Member]	Dec. 31, 2011 Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member] Operating_Leases	Dec. 31, 1986 Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member] Operating_Leases	Dec. 31, 1985 Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member] Operating_Leases	Dec. 31, 2004 EIP Transmission Line [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2003 EIP Transmission Line [Member] Public Service Company of New Mexico [Member]	Dec. 31, 1985 EIP Transmission Line [Member] Public Service Company of New Mexico [Member] Operating_Leases	Dec. 31, 2011 10.3% Lessor Notes [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 10.15% Lessor Notes [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 10.25% EIP Lessor Note Maturing in 2012 [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2010 10.25% EIP Lessor Note Maturing in 2012 [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 10.25% EIP Lessor Note Maturing in 2012 [Member] EIP Transmission Line [Member] Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]
Equity method investment,ownership percentage (as a percent)												50.00%
Cash and Cash Equivalents Maturity Term				3 months
Allowance for funds used during construction, capitalized interest					$ 1,500,000	$ 4,600,000	$ 8,000,000	$ 1,200,000	$ 200,000	$ 1,100,000
Debt, weighted average interest rate (as a percent)	6.60%	6.70%	6.90%
Interest costs incurred, capitalized	500,000	800,000	700,000		200,000	400,000	200,000	0	0	0
Prepaid coal, current															14,600,000	30,900,000
Number of operating leases (in ones)																	8	11	11			2
Notes receivable, stated percentage rate (as a percent)																							10.30%	10.15%			10.25%
Ownership percentage acquired (as a percent)																				40.00%	60.00%
Other investments	12,207,000	18,791,000			2,900,000	5,068,000		271,000	282,000																2,200,000	4,600,000
Impairment losses on securities held in the NDT					12,500,000	5,000,000	8,100,000
Ownership percentage, sold (as a percent)														1.00%
Equity Method Investments													$ 0
Cost method investment, ownership percentage (as a percent)											1.00%