Commitments and Contingencies SPP Filing to Assign GridLiance Facilities to SPS Rate Zone (Details) $ in Millions	1 Months Ended
Aug. 31, 2018 USD ($)
Southwest Power Pool (SPP) [Member] \| SPP Open Access Transmission Tariff Upgrade Costs [Member] \| SPS [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Annual Transmission Revenue Requirement Increase (SPS)	$ 6

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