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Gas Cost Adjustment NOPR (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
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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Public Utilities, Billed Charges For Transmission Service Upgrades

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