Commitments and Contingencies - National Ambient Air Quality Standards (Details) - Public Service Company of New Mexico [Member]	Feb. 25, 2016	Mar. 02, 2015 lb / MMBTU T	Oct. 01, 2015 parts_per_billion	Sep. 30, 2015 parts_per_billion	May 14, 2015 lb / MMBTU	Jan. 31, 2010 parts_per_billion
Minimum [Member] \| San Juan Generating Station And Four Corners [Member]
Public Utilities, General Disclosures [Line Items]
Proposed government standard emission limit (in parts per billion)						60
Maximum [Member] \| San Juan Generating Station And Four Corners [Member]
Public Utilities, General Disclosures [Line Items]
Proposed government standard emission limit (in parts per billion)						70
Government standard emissions limit (in parts per billion)			70	75
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member]
Public Utilities, General Disclosures [Line Items]
Period of time to act on settlement		16 months
Emissions tons of SO2 per year \| T		16,000
National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] \| Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Emissions tons of SO2 per year \| T		2,600
SO2 emissions rate (in pounds per MMBTU) \| lb / MMBTU		0.45
National Ambient Air Quality Standards [Member] \| San Juan Generating Station [Member]
Public Utilities, General Disclosures [Line Items]
Revised SO2 emissions agreed upon (in pounds per MMBTU) \| lb / MMBTU					0.10
National Ambient Air Quality Standards, Proposed 2016 SO2 Rule [Member]
Public Utilities, General Disclosures [Line Items]
Period of time from state designation to provide implementation plans	36 months