Pension and Other Postretirement Benefit Plans Narrative (Details) (USD $)	12 Months Ended		12 Months Ended							0 Months Ended	12 Months Ended
	Dec. 31, 2011	Jan. 30, 2009	Dec. 31, 2011 Pension Plan [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member]	Dec. 31, 2009 PNM Gas [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Pension Plan [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member] Pension Plan [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Other Postretirement Benefits [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member] Other Postretirement Benefits [Member]	Jan. 30, 2009 Public Service Company of New Mexico [Member] PNM Gas [Member] Other Postretirement Benefits [Member]	Dec. 31, 2011 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Dec. 31, 2010 Texas-New Mexico Power Company [Member] Pension Plan [Member]	Dec. 31, 2011 Texas-New Mexico Power Company [Member] Other Postretirement Benefits [Member]	Dec. 31, 2010 Texas-New Mexico Power Company [Member] Other Postretirement Benefits [Member]	Dec. 31, 2011 Equity Securities [Member] Pension Plan [Member]	Dec. 31, 2011 Equity Securities [Member] Other Postretirement Benefits [Member]	Dec. 31, 2011 Debt Securities [Member] Pension Plan [Member]	Dec. 31, 2011 Debt Securities [Member] Other Postretirement Benefits [Member]	Dec. 31, 2011 Alternative Investments [Member] Pension Plan [Member]	Dec. 31, 2011 Developed Countries Outside of United States [Member] Equity Securities [Member] Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Election of relieving losses in asset market value (in years)	2
Defined Benefit Plans, Gains and losses that lie outside the corridor, amortized (in years)	5 years
Benefit obligation, period increase (decrease)						$ (2,800,000)	$ (41,500,000)	$ (7,400,000)	$ 20,100,000		$ 1,200,000	$ (5,100,000)
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease) Due to Change in Demographics							9,000,000
Actuarial net (gains) losses					9,600,000	(1,197,000)	(51,379,000)	(712,000)	17,952,000		2,793,000	(5,113,000)	862,000	116,000
Actual plan asset allocations (as a percent)						8.00%		3.80%			7.70%		3.20%
Expected long-term return resulting from effect of one-percentage point decrease (as a percent)			1.00%	1.00%
Expected Long-term return on assets decrease resulting in increase net periodic costs In next fiscal year						5,000,000		600,000			600,000		100,000
Expected long-term return resulting from effect of one-percentage point increase (as a percent)			1.00%
Target plan asset allocations (as a percent)															42.00%	70.00%	41.00%	30.00%	17.00%	10.00%
Estimated future employer contributions in next fiscal year						77,700,000		2,500,000			5,300,000		200,000
Estimated future employer contributions from 2012-2016						85,300,000					1,800,000
Weighted average discount rate related to anticipated contributions (as a percent)			5.30%
Liability transfer resulting from sale		15,700,000
Net unamortized (gain) loss arising during period, net of tax										$ 2,900,000