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Gas Cost Adjustment NOPR (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Sep. 30, 2021
Public Utilities, General Disclosures [Line Items]
recoverability of costs in excess of forecasted amount - low end		9000.00%
recoverability of costs in excess of forecasted amount - high end		9500.00%
SPS | Southwest Power Pool (SPP) | SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Public Utilities, Billed Charges For Transmission Service Upgrades	$ 13

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