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BENEFIT PLANS: Defined Benefit Plan, Assumptions Used in Calculations, Benefit Obligations (Details) | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Pension Plan |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  | 7.40% | 7.40% | 7.40%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 5.10% | 5.45% |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | [1] | 4.43% | 4.49% |
Defined Benefit Plan, Plan Assets, Accounting Policy Election, Measurement Date |  | Dec. 31, 2023 | Dec. 31, 2022 |
Senior Management Security Plan |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  | 0.00% | 0.00% | 0.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 5.20% | 5.50% |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | [1] | 4.75% | 4.75% |
Defined Benefit Plan, Plan Assets, Accounting Policy Election, Measurement Date |  | Dec. 31, 2023 | Dec. 31, 2022 |
Postretirement Benefits |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  | 6.00% | 6.00% | 6.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 5.15% | 5.45% |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | [1] | 0.00% | 0.00% |
Postretirement Benefit, Medical Trend Rate |  | 6.70% | 5.80% | 6.30%
Health Care Cost Trend Rate Assumed for Next Fiscal Year |  | 3.50% | 3.50% |
Defined Benefit Plan, Plan Assets, Accounting Policy Election, Measurement Date |  | Dec. 31, 2023 | Dec. 31, 2022 |
Inflation rate | Pension Plan |  |  |  |
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  | 2.40% |  |
Composite merit increase | Pension Plan |  |  |  |
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  | 2.03% |  |
Merit salary increase first year of service | Pension Plan |  |  |  |
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  | 10.60% |  |
Merit salary increase fortieth year of service and beyond | Pension Plan |  |  |  |
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] |  |  |  |
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  | 3.40% |  |
[1] | The 2023 rate of compensation increase assumption for the pension plan includes an inflation component of 2.40% plus a 2.03% composite merit increase component that is based on employees' years of service. Merit salary increases are assumed to be 10.6% for employees in their first year of service and scale down to 3.4% for employees in their fortieth year of service and beyond.

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- Definition Postretirement Benefit, Medical Trend Rate + References No definition available. + Details
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- Definition Month-end measurement date applicable when an accounting policy election is made to measure plan assets and benefit obligations as of the month-end that is closest to the fiscal year-end, in YYYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (u) -SubTopic 20 -Topic 715 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(2) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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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. + References No definition available. + Details
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- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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