Pension and Other Postretirement Benefit Plans (Details) (USD $)	3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013 Public Service Company of New Mexico [Member] Pension Plan [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] Pension Plan [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] Pension Plan [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] Pension Plan [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] Pension Plan [Member] Minimum [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] Pension Plan [Member] Maximum [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] OPEB [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] OPEB [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] OPEB [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] OPEB [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] Executive Retirement Program [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] Executive Retirement Program [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member] Executive Retirement Program [Member]	Jun. 30, 2012 Public Service Company of New Mexico [Member] Executive Retirement Program [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Mar. 31, 2013 Texas-New Mexico Power Company [Member] Pension Plan [Member] Minimum [Member]	Mar. 31, 2013 Texas-New Mexico Power Company [Member] Pension Plan [Member] Maximum [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] OPEB [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] OPEB [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] OPEB [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] OPEB [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member] Maximum [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member] Maximum [Member]	Jun. 30, 2013 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member] Maximum [Member]	Jun. 30, 2012 Texas-New Mexico Power Company [Member] Executive Retirement Program [Member] Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0	$ 0	$ 0			$ 65,000	$ 54,000	$ 130,000	$ 108,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0			$ 75,000	$ 61,000	$ 150,000	$ 122,000	$ 0	$ 0	$ 0	$ 0
Interest cost	7,035,000	8,058,000	14,071,000	16,116,000			1,029,000	1,324,000	2,057,000	2,648,000	180,000	219,000	360,000	438,000	772,000	909,000	1,544,000	1,818,000			141,000	156,000	283,000	312,000	9,000	11,000	18,000	22,000
Long-term return on plan assets	(10,482,000)	(10,325,000)	(20,965,000)	(20,650,000)			(1,261,000)	(1,225,000)	(2,522,000)	(2,450,000)	0	0	0	0	(1,212,000)	(1,331,000)	(2,425,000)	(2,662,000)			(126,000)	(129,000)	(252,000)	(258,000)	0	0	0	0
Amortization of net loss	3,710,000	2,629,000	7,420,000	5,258,000			1,061,000	972,000	2,121,000	1,944,000	58,000	21,000	116,000	42,000	262,000	115,000	524,000	230,000			0	(52,000)	0	(104,000)	0	0	0	0
Amortization of prior service cost	19,000	79,000	38,000	158,000			(336,000)	(336,000)	(672,000)	(672,000)	0	0	0	0	0	0	0	0			14,000	14,000	28,000	28,000	0	0	0	0
Net periodic benefit cost	282,000	441,000	564,000	882,000			558,000	789,000	1,114,000	1,578,000	238,000	240,000	476,000	480,000	(178,000)	(307,000)	(357,000)	(614,000)			104,000	50,000	209,000	100,000	9,000	11,000	18,000	22,000
Defined Benefit Plan, Contributions by Employer	0	0	60,000,000	77,700,000			1,100,000	800,000	1,600,000	1,600,000	400,000	300,000	800,000	700,000			1,000,000	5,300,000			300,000	0	300,000	300,000					100,000	100,000	100,000	100,000
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	49,100,000		49,100,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)					4.80%	5.20%													4.80%	5.20%
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year							$ 3,300,000		$ 3,300,000		$ 1,500,000		$ 1,500,000												$ 100,000		$ 100,000