Commitments, Contingencies and Uncertainties (Narrative) (Details) $ in Millions	Dec. 31, 2019 USD ($)	Nov. 18, 2019 MW
Loss Contingencies [Line Items]
Number of criteria emissions established under the Clear Air Act	6
Accrual for Environmental Loss Contingencies | $	$ 0.2
NMPRC
Long-term Purchase Commitment [Line Items]
Long-term Contracts for Purchase of Electric Power, number		3
Maximum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit	75
Minimum
Loss Contingencies [Line Items]
Public Utilities, Government Standard Emission Limit	70
Solar Plant at Santa Teresa, NM | NMPRC
Long-term Purchase Commitment [Line Items]
Electric capacity, requested		100
Solar Plant at Otero County, NM | NMPRC
Long-term Purchase Commitment [Line Items]
Electric capacity, requested		100
Battery Storage at Otero County, NM | NMPRC
Long-term Purchase Commitment [Line Items]
Electric capacity, requested		50
Battery Storage at Canutillo, NM | NMPRC
Long-term Purchase Commitment [Line Items]
Electric capacity, requested		50