v3.25.4
Employee Benefit Plans: Assumptions (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Trend Year 2035 2035  
Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Trend Year 2035 2033  
Black Hills Corporation | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 for next year - All Plans 7.00% 7.50%  
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 6.00% 6.50%  
Post-65 Ultimate trend rate - Black Hills Corp 4.50% 4.50%  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Interest cost effective discount rate 5.38% 5.63% 4.99%
Rate of increase in compensation levels 3.01% 3.04% 3.04%
Interest cost effective discount rate 5.63% 4.99% 5.17%
Expected long-term rate of return on assets 6.50% 6.00% 6.00%
Rate of increase in compensation levels 3.04% 3.04% 3.06%
Defined Benefit Plan Assumptions Used In Calculating Net Periodic Benefit Cost Expected Rate of Return On Assets For Next Fiscal Year 6.50%    
2026 $ 24.9    
2027 25.3    
2028 25.3    
2029 25.8    
2030 25.3    
2031- 2035 $ 123.6    
Pension Plan | Black Hills Corporation Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Post-65 for next year - All Plans 5.38%    
Supplemental Plans      
Defined Benefit Plan Disclosure [Line Items]      
Interest cost effective discount rate 5.22% 5.56% 4.93%
Rate of increase in compensation levels 0.00% 0.00% 0.00%
Interest cost effective discount rate 5.56% 4.93% 5.13%
Rate of increase in compensation levels 0.00% 0.00% 0.00%
2026 $ 2.8    
2027 2.8    
2028 2.7    
2029 2.5    
2030 2.4    
2031- 2035 $ 10.9    
Healthcare Plan      
Defined Benefit Plan Disclosure [Line Items]      
Interest cost effective discount rate 5.32% 5.60% 4.97%
Interest cost effective discount rate 5.60% 4.97% 5.14%
Expected long-term rate of return on assets 4.10% 3.50% 3.10%
2026 $ 5.2    
2027 5.1    
2028 4.9    
2029 4.7    
2030 4.6    
2031- 2035 $ 20.9