Borrowings and Other Financing Instruments Debt Repurchase (Details) - NSP-Minnesota $ in Millions	9 Months Ended
Sep. 30, 2025 USD ($)
Debt Disclosure [Abstract]
Debt Instrument, Repurchased Face Amount	$ 190.0
Debt Instrument, Repurchase Amount	122.0
Gain (Loss) on Repurchase of Debt Instrument	63.0
Debt Repurchase [Line Items]
Debt Instrument, Repurchased Face Amount	190.0
Debt Instrument, Repurchase Amount	122.0
Gain (Loss) on Repurchase of Debt Instrument	63.0
Interest Expense, Debt	$ 1.4
Series due March 1, 2050 \| Bonds [Member]
Debt Disclosure [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	2.90%
Debt Repurchase [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.90%
Series Due June 1, 2051 [Domain] \| Bonds [Member]
Debt Disclosure [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	2.60%
Debt Repurchase [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.60%
Series due April 1, 2052 \| Bonds [Member]
Debt Disclosure [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	3.20%
Debt Repurchase [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.20%

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Contractual interest rate for funds borrowed, under the debt agreement.

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Fair value amount of debt instrument that was repurchased.

+ References

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Face (par) amount of the original debt instrument that was repurchased.

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No definition available.

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Amount of gain (loss) from the difference between the repurchase price of a debt instrument initially issued by the entity and the net carrying amount of the debt at the time of its repurchase.

+ References

No definition available.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Debt Repurchase [Line Items]

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