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Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Commitments and Contingencies - National Ambient Air Quality Standards (Details) - Public Service Company of New Mexico	Feb. 25, 2019 parts_per_billion	Oct. 01, 2015 parts_per_billion	Sep. 30, 2015 parts_per_billion	May 14, 2015 lb / MMBTU
Maximum \| San Juan Generating Station And Four Corners
Public Utilities, General Disclosures [Line Items]
Government standard emissions limit (in parts per billion) \| parts_per_billion	75	70	75
National Ambient Air Quality Standards \| San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Revised SO2 emissions agreed upon (in pounds per MMBTU) \| lb / MMBTU				0.10