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ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables) | 6 Months Ended
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Jun. 30, 2026
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] | The following table sets forth the effect of reclassifications from accumulated other comprehensive income (loss) in our consolidated statements of income for the periods indicated:
| Three Months Ended |  | Six Months Ended | Affected Line Item in the Consolidated Statements of Income
Details About Accumulated Other | June 30, |  | June 30,
Comprehensive Income (Loss) Components | 2026 | 2025 |  | 2026 | 2025 |
| (Thousands of dollars) |
Pension and other postemployment benefit plan obligations (a) |  |  |  |  |  |  |
Amortization of net gain (loss) | $ | (4,212) |  | $ | (1,834) |  |  | $ | (8,424) |  | $ | (3,668) |  |  |
Amortization of unrecognized prior service credit (cost) | (93) |  | (93) |  |  | (186) |  | (186) |  |  |
| (4,305) |  | (1,927) |  |  | (8,610) |  | (3,854) |  |  |
Regulatory adjustments (b) | 4,306 |  | 1,928 |  |  | 8,611 |  | 3,855 |  |  |
Amounts reclassified from accumulated other comprehensive income (loss) | 1 |  | 1 |  |  | 1 |  | 1 |  |  | Other income (expense), net
Available-for-sale securities |  |  |  |  |  |  |
Amounts reclassified from accumulated other comprehensive income (loss) | 3 |  | 4 |  |  | 35 |  | 7 |  |  | Other income (expense), net
Total reclassifications before tax | 4 |  | 5 |  |  | 36 |  | 8 |  |  | Income before income taxes
Tax effect of reclassifications | (1) |  | (1) |  |  | (8) |  | (2) |  |  | Income tax expense
Net reclassifications for the period | $ | 3 |  | $ | 4 |  |  | $ | 28 |  | $ | 6 |  |  | Net income
(a) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost (credit). See Note 9 for additional detail on our net periodic benefit cost (credit). (b) Regulatory adjustments represent pension and other postemployment benefit credits or costs expected to be recovered through rates and are deferred as part of our regulatory assets. See Note 3 for additional disclosures of regulatory assets and liabilities.

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- Definition Tabular disclosure of information about items reclassified out of accumulated other comprehensive income (loss). + References No definition available. + Details
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