Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - Public Service Company of New Mexico [Member] - Palo Verde Nuclear Generating Station [Member] - USD ($)		3 Months Ended
	May 16, 2014	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Department of energy, spent nuclear fuel removal January 2007 - June 2011 [Member]
Loss Contingencies [Line Items]
PNM's share of third party settlement claim						$ 5,900,000
Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member]
Loss Contingencies [Line Items]
PNM's share of third party settlement claim			$ 4,300,000
Litigation settlement, portion credited to customers			$ 3,100,000
Department of energy, spent nuclear fuel removal July 2014 - June 2015 [Member]
Loss Contingencies [Line Items]
PNM's share of third party settlement claim		$ 1,300,000
Litigation settlement, portion credited to customers		$ 500,000
Nuclear spent fuel and waste disposal [Member]
Loss Contingencies [Line Items]
Estimate of possible loss				$ 57,700,000
DOE adjusted one-mill fee	$ 0
Nuclear spent fuel and waste disposal [Member] | Other Deferred Credits [Member]
Loss Contingencies [Line Items]
Liability for interim storage costs				$ 12,100,000	$ 12,200,000