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Regulatory and Rate Matters - Schedule of Transmission Cost of Service Rates (Details) - TNMP - USD ($) $ in Millions											12 Months Ended
	Sep. 22, 2023	Sep. 01, 2023	May 26, 2023	Mar. 25, 2023	Sep. 22, 2022	Sep. 01, 2022	Mar. 25, 2022	Sep. 20, 2021	Sep. 01, 2021	Mar. 12, 2021	Feb. 28, 2023	Feb. 28, 2022	Feb. 28, 2021
Energy efficiency costs
Public Utilities, General Disclosures [Line Items]
Aggregate Collection Amount			$ 6.6								$ 7.3	$ 7.2	$ 5.9
Performance Bonus			$ 1.2								$ 1.9	$ 2.3	$ 1.0
Transmission Cost of Service Rates
Public Utilities, General Disclosures [Line Items]
Approved Increase in Rate Base	$ 21.4			$ 150.5	$ 36.0		$ 95.6	$ 41.2		$ 112.6
Annual Increase in Revenue	$ 4.2			$ 19.4	$ 5.3		$ 14.2	$ 6.3		$ 14.1
Periodic Distribution Rate
Public Utilities, General Disclosures [Line Items]
Approved Increase in Rate Base		$ 157.0				$ 95.7			$ 104.5
Annual Increase in Revenue		$ 14.5				$ 6.8			$ 13.5

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