Commitments and Contingencies - SPP Filing to Assign GridLiance Facilities to SPS Rate Zone (Details) - Southwest Power Pool (SPP) - SPP Open Access Transmission Tariff Upgrade Costs - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
Aug. 31, 2018	Mar. 16, 2020	Sep. 30, 2021
Public Utilities, General Disclosures [Line Items]
Annual Transmission Revenue Requirement Increase	$ 10,000,000	$ 14,000,000
Annual Transmission Revenue Requirement Increase (SPS)	6,000,000	$ 9,000,000	$ 20,000,000
Annual Transmission Revenue Requirement (Other Utilities)	$ 4,000,000

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