v3.25.4
Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax $ 24.5 $ 0.3 $ 1.2  
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (0.3) 2.9 2.3  
Net current-period other comprehensive income (loss) 24.2 3.2 3.5  
Accumulated other comprehensive loss (6.2) (30.4)    
Partners' Capital, Including Portion Attributable to Noncontrolling Interest [Abstract] 11,659.9 10,668.3 10,136.3 $ 7,901.8
Gains and Losses on Securities        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax 5.0 1.5 3.1  
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (0.9) 1.8 0.8  
Net current-period other comprehensive income (loss) 4.1 3.3 3.9  
Partners' Capital, Including Portion Attributable to Noncontrolling Interest [Abstract] 0.1 (4.0) (7.3) (11.2)
Pension and OPEB Items        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax 19.5 (1.2) (1.4)  
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax 1.0 1.5 1.2  
Net current-period other comprehensive income (loss) 20.5 0.3 (0.2)  
Partners' Capital, Including Portion Attributable to Noncontrolling Interest [Abstract] 7.3 (13.2) (13.5) (13.3)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax 0.0 0.0 (0.5)  
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (0.4) (0.4) 0.3  
Net current-period other comprehensive income (loss) (0.4) (0.4) (0.2)  
Partners' Capital, Including Portion Attributable to Noncontrolling Interest [Abstract] (13.6) (13.2) (12.8) (12.6)
Accumulated Other Comprehensive Loss        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Net current-period other comprehensive income (loss) 24.2 3.2 3.5  
Partners' Capital, Including Portion Attributable to Noncontrolling Interest [Abstract] $ (6.2) $ (30.4) $ (33.6) $ (37.1)