v3.26.1
Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning balance $ 11,927.5 $ 10,946.0 $ 11,659.9 $ 10,668.3
Other Comprehensive Income (Loss) before reclassifications (0.5) 0.9 (3.5) 2.0
Amounts reclassified from accumulated other comprehensive income (loss) 0.2 0.1 0.2 0.2
Net current-period other comprehensive income (loss) (0.3) 1.0 (3.3) 2.2
Ending balance 11,894.4 10,996.9 11,894.4 10,996.9
Interest Rate Risk        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Net current-period other comprehensive income (loss)     (0.2)  
Accumulated Other Comprehensive Income (Loss)        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning balance (9.2) (29.2) (6.2) (30.4)
Net current-period other comprehensive income (loss) (0.3)   (3.3)  
Ending balance (9.5) (28.2) (9.5) (28.2)
Gains and Losses on Securities        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning balance (1.1) (3.2) 0.1 (4.0)
Other Comprehensive Income (Loss) before reclassifications 0.6 1.0 (0.6) 1.8
Amounts reclassified from accumulated other comprehensive income (loss) 0.1 0.0 0.1 0.0
Net current-period other comprehensive income (loss) 0.7 1.0 (0.5) 1.8
Ending balance (0.4) (2.2) (0.4) (2.2)
Gains and Losses on Cash Flow Hedges        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning balance (13.7) (13.3) (13.6) (13.2)
Other Comprehensive Income (Loss) before reclassifications 0.0 0.0 0.0 0.0
Amounts reclassified from accumulated other comprehensive income (loss) (0.1) (0.1) (0.2) (0.2)
Net current-period other comprehensive income (loss) (0.1) (0.1)   (0.2)
Ending balance (13.8) (13.4) (13.8) (13.4)
Pension and OPEB Items        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning balance 5.6 (12.7) 7.3 (13.2)
Other Comprehensive Income (Loss) before reclassifications (1.1) (0.1) (2.9) 0.2
Amounts reclassified from accumulated other comprehensive income (loss) 0.2 0.2 0.3 0.4
Net current-period other comprehensive income (loss) (0.9) 0.1 (2.6) 0.6
Ending balance $ 4.7 $ (12.6) $ 4.7 $ (12.6)