v3.26.3
Fair Value of Financial Assets and Liabilities - Recurring Fair Value Measurements (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Derivatives, Fair Value          
Return Cash Collateral $ 0   $ 0   $ 0
Changes in Level 3 Commodity Derivatives          
Derivative instruments designated as fair value hedges 0 $ 0 0 $ 0  
Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 64   64   79
Asset, netting [1] 0   0   0
Derivative Asset, Current 64   64   79
Commodity Contract [Member]          
Changes in Level 3 Commodity Derivatives          
Balance at beginning of period 87 184 79 67  
Purchases [2]     151 199  
Settlements [2] (9) (39) (69) (161)  
Net gains recognized as regulatory assets and liabilities [2] (14) (5) (97) 35  
Balance at end of period 64 $ 140 64 $ 140  
Level 1 | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 0   0   0
Level 2 | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 0   0   0
Level 3 | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 64   64   79
Other Derivative Instruments | Electric Commodity | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 64   64   79
Asset, netting [1] 0   0   0
Derivative Asset, Current 64   64   79
Other Derivative Instruments | Level 1 | Electric Commodity | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 0   0   0
Other Derivative Instruments | Level 2 | Electric Commodity | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross 0   0   0
Other Derivative Instruments | Level 3 | Electric Commodity | Fair Value, Recurring [Member]          
Derivatives, Fair Value          
Derivative asset, gross $ 64   $ 64   $ 79
[1] SPS nets derivative instruments and related collateral on its balance sheet when supported by a legally enforceable master netting agreement. At Sept. 30, 2026 and Dec. 31, 2025, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. Counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
[2] Relates primarily to FTR instruments administered by SPP.