Income Taxes Summary of Income Tax Contingencies (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning	$ 19,889,000us-gaap_UnrecognizedTaxBenefits	$ 19,198,000us-gaap_UnrecognizedTaxBenefits	$ 19,580,000us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions	623,000	(54,000)	2,046,000
Additions (reductions) for tax positions of prior years	(5,481,000)		(2,428,000)
Additions for tax positions of prior years		745,000
Settlement payments	0	0	0
Unrecognized Tax Benefits - End	15,031,000us-gaap_UnrecognizedTaxBenefits	19,889,000us-gaap_UnrecognizedTaxBenefits	19,198,000us-gaap_UnrecognizedTaxBenefits
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	11,073,000	10,382,000	10,752,000
Additions based on tax positions	623,000	(54,000)	1,152,000
Additions (reductions) for tax positions of prior years			(1,522,000)
Additions for tax positions of prior years	532,000	745,000
Settlement payments	0	0	0
Unrecognized Tax Benefits - End	12,228,000	11,073,000	10,382,000
Unrecognized tax benefits that would impact effective tax rate	1,900,000
Texas-New Mexico Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits - Beginning	6,796,000	6,796,000	7,701,000
Additions based on tax positions	0	0	0
Additions (reductions) for tax positions of prior years	(6,796,000)		(905,000)
Additions for tax positions of prior years		0
Settlement payments	0	0	0
Unrecognized Tax Benefits - End	0	6,796,000	6,796,000
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	$ 4,700,000

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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