Borrowings and Other Financing Instruments - Long-Term Borrowings (Details) $ in Millions	Sep. 30, 2026 USD ($)
SPS
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount	$ 158
Debt Instrument, Repurchase Amount	112
Series due August 15, 2036 \| Bonds \| SPS
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 650
Debt Instrument, Interest Rate, Stated Percentage	5.30%
Series due August 15, 2056 \| Bonds \| SPS
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550
Debt Instrument, Interest Rate, Stated Percentage	5.875%

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.

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