v3.25.2
Business Segment Information: Information Relating to Segments Statement of Income (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2024
Mar. 31, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information            
Revenue $ 439.0   $ 402.6   $ 1,244.2 $ 1,129.0
Fuel, purchased power and cost of natural gas sold 124.0   107.1   483.8 423.7
Operations and maintenance - Direct 73.3   69.9   150.0 132.9
Operations and maintenance - Allocated 74.3   71.8   151.3 142.3
Depreciation and amortization 69.8   66.6   139.0 132.5
Taxes other than income taxes 15.1   16.6   32.7 33.6
Operating income (loss) 82.5   70.6   287.4 264.0
Interest expense, net (48.9)   (42.6)   (100.3) (86.7)
Other income (expense), net (0.4)   0.4   0.6 (0.5)
Income tax (expense) (4.4)   (3.7)   (22.5) (20.6)
Net income 28.8 $ 136.4 24.7 $ 131.6 165.2 156.2
Net income attributable to non-controlling interest (1.3)   (1.9)   (3.5) (5.6)
Net income available for common stock 27.5   22.8   161.7 150.6
Corporate, Non-Segment            
Segment Reporting Information            
Revenue (3.9)   (4.5)   (7.8) (8.9)
Fuel, purchased power and cost of natural gas sold (0.2)   (0.1)   (0.1) (0.3)
Operations and maintenance - Direct (1.7)   (5.7)   (4.8) (8.2)
Depreciation and amortization           0.2
Operating income (loss) (2.0)   1.3   (2.9) (0.6)
Operating Segments | Electric Utilities            
Segment Reporting Information            
Revenue 219.9   205.1   456.6 427.3
Fuel, purchased power and cost of natural gas sold 55.3   45.9   122.5 100.8
Operations and maintenance - Direct 36.1   37.4   71.8 64.8
Operations and maintenance - Allocated 33.1   30.7   66.2 60.7
Depreciation and amortization 37.5   35.5   74.6 70.8
Taxes other than income taxes 8.9   9.3   18.2 19.3
Operating income (loss) 49.0   46.3   103.3 110.9
Operating Segments | Gas Utilities            
Segment Reporting Information            
Revenue 223.0   202.0   795.4 710.6
Fuel, purchased power and cost of natural gas sold 68.9   61.3   361.4 323.2
Operations and maintenance - Direct 38.9   38.2   83.0 76.3
Operations and maintenance - Allocated 41.2   41.1   85.1 81.6
Depreciation and amortization 32.3   31.1   64.4 61.5
Taxes other than income taxes 6.2   7.3   14.5 14.3
Operating income (loss) 35.5   23.0   187.0 153.7
External Customers            
Segment Reporting Information            
Revenue 439.0   402.6   1,244.2 1,129.0
External Customers | Operating Segments | Electric Utilities            
Segment Reporting Information            
Revenue 217.5   202.1   451.8 421.4
External Customers | Operating Segments | Gas Utilities            
Segment Reporting Information            
Revenue 221.5   200.5   792.4 707.6
Inter-segment | Corporate, Non-Segment            
Segment Reporting Information            
Revenue (3.9)   (4.5)   (7.8) (8.9)
Inter-segment | Operating Segments | Electric Utilities            
Segment Reporting Information            
Revenue 2.4   3.0   4.8 5.9
Inter-segment | Operating Segments | Gas Utilities            
Segment Reporting Information            
Revenue $ 1.5   $ 1.5   $ 3.0 $ 3.0