Gas Cost Adjustment NOPR (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jun. 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