EMPLOYEE BENEFIT PLANS (Notes)

12 Months Ended

Dec. 31, 2025

Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]

Employee Benefit Plans (Notes)

EMPLOYEE BENEFIT PLANS

Defined Benefit Pension and Other Postemployment Benefit Plans

Defined Benefit Pension Plans - We have a defined benefit pension plan and a supplemental executive retirement plan for certain eligible employees, both of which are closed to new participants. Certain employees of the Texas Gas Service division are entitled to benefits under a frozen cash-balance pension plan. We fund our defined benefit pension costs at a level needed to maintain or exceed the minimum funding levels required by the Employee Retirement Income Security Act of 1974, as amended, and the Pension Protection Act of 2006.

Other Postemployment Benefit Plans - We sponsor health and welfare plans that provide postemployment medical and life insurance benefits to certain eligible employees who retire with at least five years of service. The postemployment medical plan is contributory based on hire date, age, and years of service, with retiree contributions adjusted periodically, and contains other cost-sharing features such as deductibles and coinsurance.

Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postemployment benefits for the periods indicated:

	December 31,
	2025	2024
Discount rate - pension plans	5.65%	5.70%
Discount rate - other postemployment plans	5.55%	5.75%
Compensation increase rate - pension plans	3.50% - 4.30%	3.50% - 4.30%

The following table sets forth the weighted-average assumptions used by us to determine the periodic benefit costs for pension and postemployment benefits for the periods indicated:

	Year Ended December 31,
	2025	2024	2023
Discount rate - pension plans	5.70%	5.30%	5.60%
Discount rate - other postemployment plans	5.75%	5.40%	5.70%
Expected long-term return on plan assets - pension plans	5.85%	6.70%	6.75%
Expected long-term return on plan assets - other postemployment plans	5.10%	5.20%	5.55%
Compensation increase rate - pension plans	3.50% - 4.30%	3.50% - 4.30%	3.60% - 5.00%

We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our defined benefit pension and other postemployment obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers, and other filtering criteria to remove unsuitable bonds.

We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We update our assumed mortality rates to incorporate new tables issued by the Society of Actuaries as needed.

Regulatory Treatment - The OCC, KCC, and regulatory authorities in Texas have approved the recovery of pension and other postemployment benefits costs through rates for Oklahoma Natural Gas, Kansas Gas Service, and Texas Gas Service, respectively. The costs recovered through rates are based on current funding requirements and the net periodic benefit cost for defined benefit pension and other postemployment costs. Differences, if any, between the net periodic benefit cost (credit), net of deferrals, and the amount recovered through rates are reflected in earnings.

We historically have recovered defined benefit pension and other postemployment benefit costs (credit) through rates. We believe it is probable that regulators will continue to include the net periodic pension and other postemployment benefit costs (credit) in our cost of service.

We capitalize all eligible service cost and non-service credit components pursuant to the accounting requirements of ASC Topic 980 (Regulated Operations) for rate-regulated entities, as these components are authorized by our regulators to be included in capitalized costs. Noncurrent regulatory liabilities in our consolidated balance sheets reflect the capitalized non-service credit components of $6.8 million and $6.7 million as of December 31, 2025 and 2024, respectively. See Note 3 for additional information.

Obligations and Funded Status - The following table sets forth our defined benefit pension and other postemployment benefit plans, benefit obligations, and fair value of plan assets for the periods indicated:

	Pension Benefits				Other Postemployment Benefits
	December 31,				December 31,
	2025		2024		2025		2024
Changes in Benefit Obligation	(Thousands of dollars)
Benefit obligation, beginning of period	$	731,117	$	803,605	$	150,984	$	158,535
Service cost	5,350		6,204		493		610
Interest cost	40,168		41,123		8,275		8,179
Plan participants’ contributions	—		—		2,428		2,631
Actuarial loss (gain)	14,685		(27,026)		6,701		(3,267)
Benefits paid	(50,705)		(54,099)		(16,124)		(15,704)
Settlements	(41,091)		(38,690)		—		—
Benefit obligation, end of period	$	699,524	$	731,117	$	152,757	$	150,984
Change in Plan Assets
Fair value of plan assets, beginning of period	$	725,401	$	795,381	$	179,489	$	181,608
Actual return on plan assets	60,118		22,322		10,844		8,404
Employer contributions	6,355		1,559		—		—
Plan participants’ contributions	—		—		2,428		2,631
Benefits paid	(50,705)		(54,099)		(13,550)		(13,154)
Settlements	(41,111)		(39,762)		—		—
Fair value of assets, end of period	700,058		725,401		179,211		179,489
Benefit asset (obligation), net	$	534	$	(5,716)	$	26,454	$	28,505
Noncurrent assets	$	20,558	$	14,377	$	26,454	$	28,505
Current liabilities	(1,409)		(1,409)		—		—
Noncurrent liabilities	(18,615)		(18,684)		—		—
Benefit asset (obligation), net	$	534	$	(5,716)	$	26,454	$	28,505

The accumulated benefit obligation for our defined benefit pension plans was $670.7 million and $703.4 million at December 31, 2025 and 2024, respectively.

For the years ended December 31, 2025 and 2024, the pension benefit obligations experienced actuarial losses and (gains) of $14.7 million and $(27.0) million, respectively, primarily due to the impact of changes in the discount rates used to calculate the benefit obligations.

In 2026, our contributions are expected to be $12.7 million to our defined benefit pension plans, and no contributions are expected to be made to our other postemployment benefit plans. In August 2025 and October 2024, we purchased group annuity contracts and transferred approximately $41.6 million and $39.0 million, respectively, of the assets and liabilities related to certain participants in our defined benefit pension plan to a third-party insurance company. Also in August 2025, a $5 million contribution was made to the defined benefit pension plan for the 2024 plan year.

The following tables set forth the components of net periodic benefit cost (credit) for our pension, inclusive of our defined benefit pension plan, supplemental executive retirement plan, and other postemployment benefit plans for the periods indicated:

		Pension Benefits
		Year Ended December 31,
		2025		2024		2023
	(Thousands of dollars)
Components of net periodic benefit cost (credit)
Service cost		$	5,350	$	6,204	$	7,242
Interest cost (a)		40,168		41,123		42,428
Expected return on assets (a)		(47,641)		(59,027)		(59,518)
Amortization of unrecognized prior service cost (credit) (a)		372		372		372
Amortization of net loss (gain) (a)		7,459		5,786		2,008
Net periodic benefit cost (credit)		$	5,708	$	(5,542)	$	(7,468)
(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 13 for additional detail.

	Other Postemployment Benefits
	Year Ended December 31,
	2025		2024		2023
	(Thousands of dollars)
Components of net periodic benefit cost (credit)
Service cost	$	493	$	610	$	730
Interest cost (a)	8,275		8,179		9,154
Expected return on assets (a)	(8,849)		(9,134)		(9,728)
Amortization of unrecognized prior service cost (credit) (a)	—		—		153
Amortization of net loss (gain) (a)	(124)		(16)		(48)
Net periodic benefit cost (credit)	$	(205)	$	(361)	$	261
(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 13 for additional detail.

We use a December 31 measurement date for our plans.

Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss), net of regulatory deferrals, related to our defined benefit pension benefits for the period indicated:

	Pension Benefits
	Year Ended December 31,
	2025		2024		2023
	(Thousands of dollars)
Net gain (loss) arising during the period	$	(118)	$	1,242	$	(619)
Amortization of net loss (gain)	(1)		(1)		1
Deferred income taxes	27		(281)		140
Total recognized in other comprehensive income (loss)	$	(92)	$	960	$	(478)

Due to our regulatory deferrals, there were no amounts recognized in other comprehensive income (loss) related to our other postemployment benefits for the periods presented.

The tables below set forth the amounts in accumulated other comprehensive income (loss) that had not yet been recognized as components of net periodic benefit credit for the periods indicated:

	Pension Benefits
	December 31,
	2025		2024
	(Thousands of dollars)
Prior service credit (cost)	$	(1,348)	$	(1,720)
Accumulated gain (loss)	(246,720)		(251,952)
Accumulated other comprehensive income (loss) before regulatory asset	(248,068)		(253,672)
Regulatory asset for regulated entities	247,795		253,517
Accumulated other comprehensive income (loss) after regulatory asset	(273)		(155)
Deferred income taxes	(40)		(67)
Accumulated other comprehensive income (loss), net of tax	$	(313)	$	(222)

	Other Postemployment Benefits
	December 31,
	2025		2024
	(Thousands of dollars)
Prior service credit (cost)	$	—	$	—
Accumulated gain (loss)	(3,764)		1,065
Accumulated other comprehensive income (loss) before regulatory asset	(3,764)		1,065
Regulatory asset for regulated entities	3,764		(1,065)
Accumulated other comprehensive income (loss) after regulatory asset	$	—	$	—

Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated:

	2025	2024
Health care cost-trend rate assumed for next year	7.50%	7.00%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)	5.00%	4.50%
Year that the rate reaches the ultimate trend rate	2036	2035

Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. To achieve this strategy, we have established a liability-driven investment strategy to change the allocations as the funded status of the defined benefit pension plan increases. The plan’s investments include a diverse blend of various domestic and international equities, investment-grade debt securities which mirror the cash flows of our liability, insurance contracts, and alternative investments. The current target allocation for the assets of our defined benefit pension plan is as follows:

Investment-grade bonds	70.0	%
U.S. large-cap equities	13.0	%
Alternative investments	7.0	%
Developed foreign equities	5.0	%
Mid-cap equities	3.0	%
Emerging markets equities	1.0	%
Small-cap equities	1.0	%
Total	100.0	%

As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock.

The current target allocation for the assets of our other postemployment benefits plan is 90 percent fixed income securities and 10 percent equity securities.

The following tables set forth our pension and other postemployment benefits plan assets by fair value category as of the measurement date:

	Pension Benefits
	December 31, 2025
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	82,902	$	—	$	—	$	82,902
Government obligations	175,874		17,814		—		193,688
Corporate obligations (b)	12,641		324,875		—		337,516
Cash and money market funds (c)	18,037		374		—		18,411
Insurance contracts and group annuity contracts	—		—		10,184		10,184
Total investments in fair value hierarchy	289,454		343,063		10,184		642,701
Accrued interest							5,261
Other investments (d)					52,096		52,096
Total investments	$	289,454	$	343,063	$	62,280	$	700,058

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(c) - This category primarily represents money market funds.

(d) - This category represents alternative investments such as hedge funds and other financial instruments which are valued at net asset value.

	Pension Benefits
	December 31, 2024
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	81,459	$	—	$	—	$	81,459
Government obligations	—		213,572		—		213,572
Corporate obligations (b)	—		328,915		—		328,915
Cash and money market funds (c)	624		24,737		—		25,361
Insurance contracts and group annuity contracts	—		—		11,177		11,177
Total investments in fair value hierarchy	82,083		567,224		11,177		660,484
Accrued interest							5,247
Other investments (d)					59,670		59,670
Total investments	$	82,083	$	567,224	$	70,847	$	725,401

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(c) - This category primarily represents money market funds.

(d) - This category represents alternative investments such as hedge funds and other financial instruments which are valued at net asset value.

	Other Postemployment Benefits
	December 31, 2025
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	7,510	$	—	$	—	$	7,510
Government obligations	44,212		—		—		44,212
Corporate obligations (b)	3,944		32,793		—		36,737
Cash and money market funds (c)	10,683		—		—		10,683
Insurance contracts (d)	—		79,218		—		79,218
Total investments in fair value hierarchy	66,349		112,011		—		178,360
Accrued interest							851
Total investments	$	66,349	$	112,011	$	—	$	179,211

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(c) - This category primarily represents money market funds.

(d) - This category includes equity securities and bonds held in a captive insurance product.

	Other Postemployment Benefits
	December 31, 2024
Asset Category	Level 1		Level 2		Level 3		Total
	(Thousands of dollars)
Investments:
Equity securities (a)	$	7,226	$	—	$	—	$	7,226
Government obligations	—		41,982		—		41,982
Corporate obligations (b)	—		36,411		—		36,411
Cash and money market funds (c)	—		12,167		—		12,167
Insurance contracts (d)	—		80,897		—		80,897
Total investments in fair value hierarchy	7,226		171,457		—		178,683
Accrued interest							806
Total investments	$	7,226	$	171,457	$	—	$	179,489

(a) - This category represents securities of the various market sectors from diverse industries.

(b) - This category represents bonds from diverse industries.

(c) - This category primarily represents money market funds.

(d) - This category includes equity securities and bonds held in a captive insurance product.

Insurance contracts and group annuity contracts include investments in the Immediate Participation Guarantee Fund (“IPG Fund”) with John Hancock are valued at fair value. John Hancock invests the IPG Fund in its general fund portfolio. The contract value of the IPG Fund at the end of the year, which approximates fair value, is estimated. The unobservable input used in the fair value measurement of the Plan’s IPG Fund investment contract is the interest rate of the investment contract. Generally, an increase or decrease in the difference between the contractual interest rate and the market interest rate is accompanied by a directionally opposed change in the fair value. The difference between this estimated balance and the actual balance, as subsequently determined by John Hancock, is charged or credited to the net assets of the plans.

Certain investments that are categorized as other investments in Level 3 represent alternative investments such as hedge funds and other financial instruments measured using the net asset value per share (or its equivalent) practical expedient.

The following tables set forth additional information regarding commitments and redemption limitations of these other investments at the periods indicated:

	December 31, 2025
	Fair Value		Unfunded Commitments		Redemption Frequency	Redemption Notice Period
	(Thousands of dollars)					(Days)
Grosvenor Registered Multi Limited Partnership	$	51,791	$	—	quarterly	65
K2 Institutional Investors II Limited Partnership	305		—		quarterly	91
Total other investments	$	52,096	$	—

	December 31, 2024
	Fair Value		Unfunded Commitments		Redemption Frequency	Redemption Notice Period
	(Thousands of dollars)					(Days)
Grosvenor Registered Multi Limited Partnership	$	29,642	$	—	quarterly	65
K2 Institutional Investors II Limited Partnership	30,028		—		quarterly	91
Total other investments	$	59,670	$	—

The following table sets forth the reconciliation of Level 3 fair value measurements of our pension plans for the periods indicated:

	Pension Benefits
	Insurance Contracts		Other Investments		Total
	(Thousands of dollars)
January 1, 2024	$	12,350	$	89,126	$	101,476
Unrealized gains	445		—		445
Unrealized losses	—		(2,984)		(2,984)
Expense	(167)		—		(167)
Purchases	—		1,408		1,408
Sales	—		(27,880)		(27,880)
Benefits paid	(1,451)		—		(1,451)
December 31, 2024	$	11,177	$	59,670	$	70,847
Unrealized gains	391		—		391
Unrealized losses	—		(12,024)		(12,024)
Expense	(33)		—		(33)
Purchases	—		23,345		23,345
Sales	—		(18,895)		(18,895)
Benefits paid	(1,351)		—		(1,351)
December 31, 2025	$	10,184	$	52,096	$	62,280

Pension and Other Postemployment Benefit Payments - Benefit payments for our defined benefit pension and other postemployment benefit plans for the year ended December 31, 2025 were $50.7 million and $16.1 million, respectively. The following table sets forth the pension benefits and other postemployment benefits payments expected to be paid in 2026 - 2035:

	Pension Benefits		Other Postemployment Benefits
Benefits to be paid in:	(Thousands of dollars)
2026	$	50,375	$	14,287
2027	50,552		13,936
2028	51,321		13,544
2029	51,320		13,268
2030	51,658		12,974
2031 through 2035	258,678		60,107

The expected benefits to be paid are based on the same assumptions used to measure our benefit obligations at December 31, 2025, and include estimated future employee service.

Other Employee Benefit Plans

401(k) Plan - We have a 401(k) plan which covers all eligible employees. Employee contributions are discretionary and we match 100 percent of each participant’s eligible contribution up to 6 percent of eligible compensation, subject to certain limits. Our contributions to the plan were $18.8 million, $17.7 million, and $16.7 million in 2025, 2024, and 2023, respectively.

We plan to make a discretionary profit-sharing contribution to the 401(k) Plan each quarter equal to 1 percent of each eligible participant’s eligible compensation during the quarter. Additional discretionary profit-sharing contributions may be made after the end of each year. Our profit-sharing contributions made to the plan were $12.0 million, $10.9 million, and $12.6 million in 2025, 2024, and 2023, respectively.

Nonqualified Deferred Compensation Plan - We have a nonqualified deferred compensation plan with obligations of $21.9 million and $18.9 million at December 31, 2025 and 2024, respectively, which are reported within other deferred credits in our consolidated balance sheets. These obligations represent the amount owed to plan participants and are treated as if invested in specified deemed investment options. A significant portion of the obligation is indirectly funded with key-person corporate-owned life insurance policies to offset costs associated with our nonqualified deferred compensation plan and the supplemental executive retirement plan. These corporate-owned life insurance policies are measured at cash surrender value of $46.2 million and $41.5 million at December 31, 2025 and 2024, respectively, and are reported within other assets in our consolidated balance sheets.

Gains (losses) on the corporate-owned life insurance policies are recognized in other income (expense), net within our consolidated statements of income; see Note 13 for additional detail of our other income (expense), net. Deferred compensation expense (income) associated with the nonqualified deferred compensation plan is recognized in operations and maintenance expense within our consolidated statements of income and was $2.5 million, $2.4 million, and $2.3 million for the years ended December 31, 2025, 2024, and 2023, respectively.