Commitments and Contingencies - National Ambient Air Quality Standards (Details) - parts_per_billion	Feb. 25, 2019	Oct. 01, 2015	Sep. 30, 2015
Public Service Company of New Mexico \| Maximum \| San Juan Generating Station And Four Corners
Public Utilities, General Disclosures [Line Items]
Government standard emissions limit (in parts per billion)	75	70	75

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