Pension and Other Postretirement Benefit Plans Components of Net Periodic Benefit Cost (Income) Recognized (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost	32,804	34,073	34,439
Long-term return on plan assets	(37,075)	(37,354)	(38,763)
Amortization of net (gain) loss	9,209	6,450	3,818
Amortization of prior service cost (credit)	317	317	317
Net periodic benefit cost	5,255	3,486	(189)
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	59
Interest cost	930	1,053	1,135
Amortization of net (gain) loss	93	71	27
Amortization of prior service cost (credit)	0	0	10
Net periodic benefit cost	1,023	1,124	1,231
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	259	419	417
Interest cost	5,378	7,650	7,388
Long-term return on plan assets	(5,388)	(5,572)	(5,832)
Amortization of net (gain) loss	3,205	5,489	3,290
Amortization of prior service cost (credit)	(2,648)	(4,143)	(4,262)
Net periodic benefit cost	806	3,843	1,001
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	3,800	4,126	4,396
Long-term return on plan assets	(5,470)	(5,794)	(6,093)
Amortization of net (gain) loss	346	0	0
Amortization of prior service cost (credit)	0	0	0
Net periodic benefit cost	(1,324)	(1,668)	(1,697)
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	46	52	76
Amortization of net (gain) loss	0	(4)	0
Amortization of prior service cost (credit)	0	0	0
Net periodic benefit cost	46	48	76
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	306	289	260
Interest cost	654	711	733
Long-term return on plan assets	(533)	(514)	(495)
Amortization of net (gain) loss	(193)	(195)	(265)
Amortization of prior service cost (credit)	60	60	60
Net periodic benefit cost	$ 294	$ 351	$ 293