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EMPLOYEE BENEFIT PLANS (Tables)
 9 Months Ended
Sep. 30, 2025
Employee Benefit Plans [Line Items]  
Schedule of Net Benefit Costs [Table Text Block]
The following tables set forth the components of net periodic benefit cost (credit) for our pension, inclusive of our defined benefit pension plan and supplemental executive retirement plan, and other postemployment benefit plans for the periods indicated:

Pension Benefits
Three Months EndedNine Months Ended
September 30,September 30,
2025202420252024
(Thousands of dollars)
Components of net periodic benefit cost (credit)
 
Service cost$1,337 $1,551 $4,011 $4,653 
Interest cost (a)
10,042 10,281 30,126 30,843 
Expected return on assets (a)
(11,910)(14,757)(35,730)(44,271)
Amortization of unrecognized prior service cost (credit) (a)
93 93 279 279 
Amortization of net loss (gain) (a)
1,865 1,446 5,595 4,338 
Net periodic benefit cost (credit)
$1,427 $(1,386)$4,281 $(4,158)
(a) These amounts, net of any amounts capitalized as a regulatory asset, have been recognized as other (income) expense, net in the consolidated statement of income. See Note 11 for additional detail.

Other Postemployment Benefits
Three Months EndedNine Months Ended
September 30,September 30,
2025202420252024
(Thousands of dollars)
Components of net periodic benefit cost (credit)
 
Service cost$123 $152 $369 $456 
Interest cost (a)
2,069 2,045 6,207 6,135 
Expected return on assets (a)
(2,212)(2,284)(6,636)(6,852)
Amortization of unrecognized prior service cost (credit) (a)
— — — — 
Amortization of net loss (gain) (a)
(31)(4)(93)(12)
Net periodic benefit cost (credit)
$(51)$(91)$(153)$(273)
(a) These amounts, net of any amounts capitalized as a regulatory asset, have been recognized as other (income) expense, net in the consolidated statement of income. See Note 11 for additional detail.