Commitments and Contingencies SPS Filing to Modify Wholesale Transmission Rates (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Public Utilities, General Disclosure [Abstract]
Amount proposed changes would increase wholesale transmission revenues	$ 9.4
Amount of proposed changes would be recoverable	$ 4.4

Public Utilities, Amount proposed changes would increase wholesale transmission revenues

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration