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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%