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Revenues
 3 Months Ended
Mar. 31, 2025
Revenue from Contract with Customer [Abstract]  
Revenue
Revenue is classified by the type of goods/services rendered and market/customer type. SPS’ operating revenues consisted of the following:
Three Months Ended March 31
(Millions of Dollars)20252024
Major revenue types
Revenue from contracts with customers:
Residential$114 $86 
Commercial and Industrial288 217 
Other11 9 
Total retail413 312 
Wholesale25 36 
Transmission76 71 
Other1 — 
Total revenue from contracts with customers515 419 
Alternative revenue and other6 9 
Total revenues$521 $428