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Regulatory and Rate Matters - Transmission Cost of Service Rates (Details) - PUCT - TNMP - USD ($) $ in Millions	Mar. 12, 2021	Oct. 07, 2020	Mar. 27, 2020
Public Utilities, General Disclosures [Line Items]
Approved Increase in Rate Base	$ 112.6	$ 10.8	$ 59.2
Annual Increase in Revenue	$ 14.1	$ 2.0	$ 7.8

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Public Utilities, Increase Annual Transmission Service Revenue

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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