Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - Public Service Company of New Mexico - Nuclear spent fuel and waste disposal - Palo Verde Nuclear Generating Station - USD ($)	May 16, 2014	Mar. 31, 2017	Dec. 31, 2016
Public Utilities, Commitments And Contingencies [Line Items]
Estimate of possible loss		$ 57,700,000
Revised annual fee, nuclear waste disposal	$ 0
Other deferred credits
Public Utilities, Commitments And Contingencies [Line Items]
Loss contingency accrual		$ 12,000,000	$ 12,100,000