v3.26.3
INVESTMENT IN TRANSMISSION AFFILIATES - CHANGES TO INVESTMENTS (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Changes to investments in transmission affiliates        
Equity in earnings of transmission affiliates $ 65.8 $ 54.8 $ 187.9 $ 160.3
Add: Capital contributions     173.0 142.4
Investment in transmission affiliates, balance at end of period 2,573.6 2,341.4 2,573.6 2,341.4
Transmission Affiliates        
Changes to investments in transmission affiliates        
Investment in transmission affiliates, balance at beginning of period 2,420.7 2,200.1 2,280.4 2,108.9
Equity in earnings of transmission affiliates 65.8 54.8 187.9 160.3
Add: Capital contributions 60.6 54.6 173.0 142.4
Less: Distributions 50.0 40.7 144.3 142.8
Less: Other 0.1      
Investment in transmission affiliates, balance at end of period $ 2,497.0 2,268.8 $ 2,497.0 2,268.8
ATC        
Investment in transmission affiliates        
Equity method investment, ownership interest (as a percent) 60.00%   60.00%  
Changes to investments in transmission affiliates        
Investment in transmission affiliates, balance at beginning of period $ 2,398.1 2,177.5 $ 2,256.9 2,085.1
Equity in earnings of transmission affiliates 65.5 54.2 186.9 154.5
Add: Capital contributions 60.6 54.6 173.0 142.4
Less: Distributions 50.0 40.7 142.7 136.4
Less: Other 0.1      
Investment in transmission affiliates, balance at end of period $ 2,474.1 2,245.6 $ 2,474.1 2,245.6
ATC Holdco        
Investment in transmission affiliates        
Equity method investment, ownership interest (as a percent) 75.00%   75.00%  
Changes to investments in transmission affiliates        
Investment in transmission affiliates, balance at beginning of period $ 22.6 22.6 $ 23.5 23.8
Equity in earnings of transmission affiliates 0.3 0.6 1.0 5.8
Add: Capital contributions 0.0 0.0 0.0 0.0
Less: Distributions 0.0 0.0 1.6 6.4
Less: Other 0.0      
Investment in transmission affiliates, balance at end of period $ 22.9 $ 23.2 $ 22.9 $ 23.2