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Regulatory and Rate Matters - TNMP Schedules (Details) - Texas-New Mexico Power Company - USD ($) $ in Millions						12 Months Ended
	Oct. 07, 2020	Mar. 27, 2020	Sep. 19, 2019	Mar. 21, 2019	Mar. 27, 2018	Feb. 28, 2021	Feb. 28, 2020	Feb. 28, 2019
Energy efficiency costs
Public Utilities, General Disclosures [Line Items]
Aggregate Collection Amount							$ 5.6	$ 6.0
Performance Bonus							$ 0.8	$ 1.1
Transmission Cost of Service Rates
Public Utilities, General Disclosures [Line Items]
Approved Increase in Rate Base	$ 10.8	$ 59.2	$ 21.9	$ 111.8	$ 32.0
Annual Increase in Revenue	$ 2.0	$ 7.8	$ 3.3	$ 14.3	$ 0.6
Subsequent Event | Energy efficiency costs
Public Utilities, General Disclosures [Line Items]
Aggregate Collection Amount						$ 5.9
Performance Bonus						$ 0.8

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Public Utilities, Increase Annual Transmission Service Revenue

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