Commitments and Contingencies - Liability and Insurance Matters (Details) - Public Service Company of New Mexico [Member] - Palo Verde Nuclear Generating Station [Member]	12 Months Ended
	Dec. 31, 2016 USD ($) generating_unit
Public Utilities, General Disclosures [Line Items]
Number of units (in generating units) | generating_unit	3
Nuclear Plant [Member]
Public Utilities, General Disclosures [Line Items]
Ownership percentage in nuclear reactor	10.20%
Number of units (in generating units) | generating_unit	3
Maximum potential assessment per incident	$ 38,900,000
Annual payment limitation related to incident	5,800,000
Aggregate amount of all risk insurance	2,750,000,000.00
Sublimit amount for non-nuclear property damage losses	2,250,000,000.00
Retrospective premium assessment	5,400,000
Nuclear Plant [Member] | Commercial Providers [Member]
Public Utilities, General Disclosures [Line Items]
Liability insurance coverage	450,000,000
Nuclear Plant [Member] | Industry Wide Retrospective Assessment Program [Member]
Public Utilities, General Disclosures [Line Items]
Liability insurance coverage	13,000,000,000.0
Nuclear Plant [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Liability insurance coverage	$ 13,400,000,000