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Employee Benefit Plans: Assumptions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Trend Year | 2034 | 2031 |
Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Trend Year | 2034 | 2031 |
Black Hills Corporation | Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Post-65 for next year - All Plans | 6.69% | 7.00% |
Post-65 Ultimate trend rate - Black Hills Corp | 4.50% | 4.50% |
Black Hills Corporation | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Post-65 for next year - All Plans | 5.81% | 6.00% |
Post-65 Ultimate trend rate - Black Hills Corp | 4.50% | 4.50% |
Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 4.99% | 5.17% | 2.88%
Rate of increase in compensation levels | 3.04% | 3.06% | 3.08%
Expected long-term rate of return on assets | 6.00% | 4.25% | 4.50%
Rate of increase in compensation levels | 3.06% | 3.08% | 3.34%
Defined Benefit Plan Assumptions Used In Calculating Net Periodic Benefit Cost Expected Rate of Return On Assets For Next Fiscal Year | 6.00% |  |
2024 | $ 24.5 |  |
2025 | 25.4 |  |
2026 | 26.0 |  |
2027 | 25.9 |  |
2028 | 26.2 |  |
2029-2033 | $ 129.7 |  |
Pension Plan | Black Hills Corporation |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount Rate | 5.17% | 2.88% | 2.56%
Pension Plan | Black Hills Corporation Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Post-65 for next year - All Plans | 5.00% |  |
Supplemental Employee Retirement Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 4.93% | 5.13% | 2.77%
Rate of increase in compensation levels | 0.00% | 0.00% | 5.00%
Rate of increase in compensation levels | 0.00% | 0.00% | 5.00%
2024 | $ 2.4 |  |
2025 | 2.8 |  |
2026 | 2.8 |  |
2027 | 2.7 |  |
2028 | 2.6 |  |
2029-2033 | $ 11.7 |  |
Supplemental Employee Retirement Plan | Black Hills Corporation |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount Rate | 5.13% | 2.77% | 2.41%
Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 4.97% | 5.14% | 2.79%
Expected long-term rate of return on assets | 3.10% | 1.70% | 1.80%
2024 | $ 5.2 |  |
2025 | 5.0 |  |
2026 | 4.9 |  |
2027 | 4.8 |  |
2028 | 4.6 |  |
2029-2033 | $ 21.4 |  |
Other Postretirement Benefits Plan | Black Hills Corporation |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount Rate | 5.14% | 2.79% | 2.41%

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- Definition An assumption for the next fiscal year as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation + References No definition available. + 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 for present value of future retirement benefits cash flows, 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 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 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 Weighted average rate of compensation increase used to determine net periodic benefit cost 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 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 Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + 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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