FERC NOPR on ROE Incentive Adders (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)
Southwest Power Pool (SPP) \| SPS \| SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Charges For Transmission Service Upgrades	$ 13

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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