Commitments and Contingencies - WEG v. OSM NEPA Lawsuit (Details) - Public Service Company of New Mexico [Member] - WEG v OSM Lawsuit [Member]	Feb. 28, 2013 state mine lawsuit
Loss Contingencies [Line Items]
Number of mines affected | mine	7
Number of states | state	4
Number of claims filed for relief (in lawsuits)	15
San Juan Generating Station [Member]
Loss Contingencies [Line Items]
Number of claims filed for relief (in lawsuits)	2