Income Taxes Summary of Income Tax Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning	$ 36,105,000	$ 22,591,000	$ 16,388,000
Additions based on tax positions	(790,000)	13,514,000	6,633,000
Reductions for tax positions of prior years	(15,735,000)	0	(430,000)
Settlements	0	0	0
Unrecognized Tax Benefits - End	19,580,000	36,105,000	22,591,000
PNMR [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits that would impact effective tax rate	3,800,000
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	17,000,000
Public Service Company of New Mexico [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning	11,918,000	(218,000)	69,000
Additions based on tax positions	(717,000)	12,136,000	(287,000)
Reductions for tax positions of prior years	(449,000)	0	0
Settlements	0	0	0
Unrecognized Tax Benefits - End	10,752,000	11,918,000	(218,000)
Unrecognized tax benefits that would impact effective tax rate	500,000
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	9,000,000
Texas-New Mexico Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning	7,788,000	6,796,000	541,000
Additions based on tax positions	(74,000)	992,000	6,255,000
Reductions for tax positions of prior years	(13,000)	0	0
Settlements	0	0	0
Unrecognized Tax Benefits - End	7,701,000	7,788,000	6,796,000
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 7,500,000