Commitments and Contingencies Environmental Requirements - Air (Details) - SPS $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)
Implementation of the National Ambient Air Quality Standard for sulfur dioxide [Member] \| Harrington Units 1 and 2 [Member]
Loss Contingencies [Line Items]
Number of years unclassifiable areas will be monitored	3 years
Capital Addition Purchase Commitments [Member] \| Regional Haze Rules [Member] \| Tolk Units 1 and 2 [Member]
Loss Contingencies [Line Items]
Liability for estimated cost to comply with regulation	$ 600

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