Regulatory and Rate Matters - SJGS Abandonment Application (Details) - San Juan Generating Station - Public Service Company of New Mexico $ in Millions		12 Months Ended
	Jul. 01, 2019 USD ($) scenario MW	Dec. 31, 2019 USD ($)	Feb. 21, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Number of megawatts in natural gas-fired peaking plant (in megawatts) | MW	280
Number of megawatts in battery storage facilities (in megawatts) | MW	70
Solar distributed generation (in mw) | MW	350
Number of megawatts in battery storage facilities, replacement resource scenario (in megawatts) | MW	60
Number of replacement resource scenarios | scenario	3
Request issuance of energy transition bonds	$ 361.0	$ 361.0
Forecasted undepreciated investment	283.0
Plant decommissioning and coal mine reclamation costs	28.6
Upfront financing costs	9.6
Severance costs	20.0
Proceeds from securitization bonds	$ 19.8
Subsequent Event | Forecast
Public Utilities, General Disclosures [Line Items]
Forecasted undepreciated investment			$ 361.0