Pension and Other Postretirement Benefit Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0
Interest cost	7,035,000	8,058,000
Long-term return on plan assets	(10,482,000)	(10,325,000)
Amortization of net loss	3,710,000	2,629,000
Amortization of prior service cost	19,000	79,000
Net periodic benefit cost	282,000	441,000
Defined Benefit Plan, Contributions by Employer	60,000,000	77,700,000
Defined Benefit Plan, Estimated Future Employer Contributions After Current Fiscal Year	49,100,000
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)	4.80%
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)	5.20%
Public Service Company of New Mexico [Member] | OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	65,000	54,000
Interest cost	1,028,000	1,324,000
Long-term return on plan assets	(1,261,000)	(1,225,000)
Amortization of net loss	1,061,000	972,000
Amortization of prior service cost	(336,000)	(336,000)
Net periodic benefit cost	557,000	789,000
Defined Benefit Plan, Contributions by Employer	500,000	800,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	3,300,000
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	180,000	219,000
Long-term return on plan assets	0	0
Amortization of net loss	58,000	21,000
Amortization of prior service cost	0	0
Net periodic benefit cost	238,000	240,000
Defined Benefit Plan, Contributions by Employer	400,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	1,500,000
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	772,000	909,000
Long-term return on plan assets	(1,212,000)	(1,331,000)
Amortization of net loss	262,000	115,000
Amortization of prior service cost	0	0
Net periodic benefit cost	(178,000)	(307,000)
Defined Benefit Plan, Contributions by Employer	1,000,000	5,300,000
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)	4.80%
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)	5.20%
Texas-New Mexico Power Company [Member] | OPEB [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	75,000	61,000
Interest cost	141,000	156,000
Long-term return on plan assets	(126,000)	(129,000)
Amortization of net loss	0	(52,000)
Amortization of prior service cost	14,000	14,000
Net periodic benefit cost	104,000	50,000
Defined Benefit Plan, Contributions by Employer	0	300,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	300,000
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0
Interest cost	9,000	11,000
Long-term return on plan assets	0	0
Amortization of net loss	0	0
Amortization of prior service cost	0	0
Net periodic benefit cost	9,000	11,000
Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year	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