Pension and Other Postretirement Benefit Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	8,058,000	8,202,000	24,174,000	24,606,000
Long-term return on plan assets	(10,325,000)	(9,269,000)	(30,975,000)	(27,807,000)
Amortization of net loss	2,629,000	2,302,000	7,887,000	6,906,000
Amortization of prior service cost	79,000	79,000	237,000	237,000
Net periodic benefit cost	441,000	1,314,000	1,323,000	3,942,000
Defined Benefit Plan, Contributions by Employer	0	20,500,000	77,700,000	34,000,000
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	74,400,000		74,400,000
Public Service Company of New Mexico [Member] | Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	5.30%
Public Service Company of New Mexico [Member] | Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	6.10%
Public Service Company of New Mexico [Member] | OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	54,000	65,000	162,000	195,000
Interest cost	1,324,000	1,345,000	3,972,000	4,035,000
Long-term return on plan assets	(1,225,000)	(1,347,000)	(3,675,000)	(4,041,000)
Amortization of net loss	972,000	801,000	2,916,000	2,403,000
Amortization of prior service cost	(336,000)	(662,000)	(1,008,000)	(1,986,000)
Net periodic benefit cost	789,000	202,000	2,367,000	606,000
Defined Benefit Plan, Contributions by Employer	800,000	700,000	2,400,000	1,900,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	3,200,000		3,200,000
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0	0
Interest cost	219,000	233,000	657,000	699,000
Long-term return on plan assets	0	0	0	0
Amortization of net loss	21,000	23,000	63,000	69,000
Amortization of prior service cost	0	0	0	0
Net periodic benefit cost	240,000	256,000	720,000	768,000
Defined Benefit Plan, Contributions by Employer	400,000	400,000	1,100,000	1,200,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	1,500,000		1,500,000
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0	0
Interest cost	909,000	951,000	2,727,000	2,853,000
Long-term return on plan assets	(1,331,000)	(1,368,000)	(3,993,000)	(4,104,000)
Amortization of net loss	115,000	86,000	345,000	258,000
Amortization of prior service cost	0	0	0	0
Net periodic benefit cost	(307,000)	(331,000)	(921,000)	(993,000)
Defined Benefit Plan, Contributions by Employer	0	800,000	5,300,000	1,000,000
Texas-New Mexico Power Company [Member] | Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	5.30%
Texas-New Mexico Power Company [Member] | Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate (as a percent)	6.10%
Texas-New Mexico Power Company [Member] | OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	61,000	77,000	183,000	231,000
Interest cost	156,000	163,000	468,000	489,000
Long-term return on plan assets	(129,000)	(133,000)	(387,000)	(399,000)
Amortization of net loss	(52,000)	(48,000)	(156,000)	(144,000)
Amortization of prior service cost	14,000	15,000	42,000	45,000
Net periodic benefit cost	50,000	74,000	150,000	222,000
Defined Benefit Plan, Contributions by Employer	0	0	300,000	400,000
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0	0
Interest cost	11,000	12,000	33,000	36,000
Long-term return on plan assets	0	0	0	0
Amortization of net loss	0	0	0	0
Amortization of prior service cost	0	0	0	0
Net periodic benefit cost	11,000	12,000	33,000	36,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	100,000		100,000
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member] | Maximum [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Contributions by Employer	$ 100,000	$ 100,000	$ 100,000	$ 100,000