Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - Public Service Company of New Mexico - Palo Verde Nuclear Generating Station - Nuclear spent fuel and waste disposal - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Estimate of possible loss	$ 57.7
Other deferred credits
Loss Contingencies [Line Items]
Liability for interim storage costs	$ 12.7	$ 12.4