v3.25.2
COMPREHENSIVE 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
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Beginning balance $ 27,364.0 $ 26,986.1 $ 25,843.7 $ 25,285.9 $ 26,986.1 $ 25,285.9
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) (32.9) 23.4 22.3 (6.8) (9.5) 15.5
Ending balance 30,968.4 27,364.0 26,175.7 25,843.7 30,968.4 26,175.7
Total            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Beginning balance 20.3 (3.1) (62.3) (55.5) (3.1) (55.5)
Change in Fair Value Recognized in AOCI, Net of Tax (36.0)   13.9   1.2 31.8
Amount of (Gain) Loss Reclassified from AOCI 3.9   10.6   (13.6) (20.7)
Income Tax (Expense) Benefit 0.8   2.2   (2.9) (4.4)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit 3.1   8.4   (10.7) (16.3)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) (32.9) 23.4 22.3 (6.8) (9.5) 15.5
Ending balance (12.6) 20.3 (40.0) (62.3) (12.6) (40.0)
Pension and OPEB            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Beginning balance (104.6) (104.9) (152.9) (152.3) (104.9) (152.3)
Change in Fair Value Recognized in AOCI, Net of Tax 0.0   0.0   0.0 0.0
Amount of (Gain) Loss Reclassified from AOCI 0.3   (0.1)   0.7 (0.9)
Income Tax (Expense) Benefit 0.0   0.0   0.1 (0.2)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit 0.3   (0.1)   0.6 (0.7)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) 0.3   (0.1)   0.6 (0.7)
Ending balance (104.3) (104.6) (153.0) (152.9) (104.3) (153.0)
Amortization of Prior Service Cost (Credit)            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Amount of (Gain) Loss Reclassified from AOCI (0.3)   (1.3)   (0.4) (2.6)
Amortization of Actuarial (Gains) Losses            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Amount of (Gain) Loss Reclassified from AOCI 0.6   1.2   1.1 1.7
Commodity | Cash Flow Hedges            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Beginning balance 123.7 98.5 87.2 104.9 98.5 104.9
Change in Fair Value Recognized in AOCI, Net of Tax (36.0)   7.0   2.2 12.5
Amount of (Gain) Loss Reclassified from AOCI 4.8   11.8   (11.7) (17.5)
Income Tax (Expense) Benefit 1.0   2.3   (2.5) (3.8)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit 3.8   9.5   (9.2) (13.7)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) (32.2)   16.5   (7.0) (1.2)
Ending balance 91.5 123.7 103.7 87.2 91.5 103.7
Commodity | Cash Flow Hedges | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Amount of (Gain) Loss Reclassified from AOCI 4.8   11.8   (11.7) (17.5)
Interest Rate | Cash Flow Hedges            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Beginning balance 1.2 3.3 3.4 (8.1) 3.3 (8.1)
Change in Fair Value Recognized in AOCI, Net of Tax 0.0   6.9   (1.0) 19.3
Amount of (Gain) Loss Reclassified from AOCI (1.2)   (1.1)   (2.6) (2.3)
Income Tax (Expense) Benefit (0.2)   (0.1)   (0.5) (0.4)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit (1.0)   (1.0)   (2.1) (1.9)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS) (1.0)   5.9   (3.1) 17.4
Ending balance 0.2 $ 1.2 9.3 $ 3.4 0.2 9.3
Interest Rate | Cash Flow Hedges | Interest Expense            
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]            
Amount of (Gain) Loss Reclassified from AOCI $ (1.2)   $ (1.1)   $ (2.6) $ (2.3)