Borrowings and Other Financing Instruments Bilateral Credit Agreement (Details) - USD ($) $ in Millions |
9 Months Ended | |
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Sep. 30, 2026 |
Dec. 31, 2025 |
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| Short-term Debt [Line Items] | ||
| Amount outstanding at period end | $ 3,060 | $ 1,550 |
| Letter of Credit | ||
| Short-term Debt [Line Items] | ||
| Amount outstanding at period end | $ 92 | 92 |
| Bilateral Credit Agreement [Member] | NSP-Minnesota | Letter of Credit | ||
| Short-term Debt [Line Items] | ||
| Debt Instrument, Term | 1 year | |
| Amount outstanding at period end | $ 59 | 59 |
| Credit Facility | $ 75 | $ 75 |
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- Definition Period between issuance and maturity of debt instrument, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. No definition available.
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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