v3.26.3
INVESTMENT IN TRANSMISSION AFFILIATES - SUMMARIZED FINANCIAL DATA (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Summarized financial data          
Operating revenues $ 2,290.6 $ 2,104.0 $ 7,786.9 $ 7,263.0  
Operating expenses 1,726.9 1,654.4 5,810.4 5,471.0  
Other expense, net 126.4 145.0 352.0 438.7  
Current assets 2,751.1   2,751.1   $ 3,284.7
Noncurrent assets 51,146.4   51,146.4   48,233.6
Total assets 53,897.5 49,808.9 53,897.5 49,808.9 51,518.3
Current liabilities 5,189.5   5,189.5   5,593.4
Long-term debt 19,717.2   19,717.2   18,498.1
Other noncurrent liabilities 960.3   960.3   963.4
Total liabilities and members' equity 53,897.5   53,897.5   51,518.3
ATC          
Summarized financial data          
Operating revenues 280.8 245.1 820.1 721.2  
Operating expenses 129.4 116.9 386.4 351.2  
Other expense, net 47.3 41.4 135.8 123.2  
Net income 104.1 $ 86.8 297.9 $ 246.8  
Current assets 165.8   165.8   137.5
Noncurrent assets 8,470.0   8,470.0   7,590.8
Total assets 8,635.8   8,635.8   7,728.3
Current liabilities 619.4   619.4   839.8
Long-term debt 3,798.5   3,798.5   3,156.3
Other noncurrent liabilities 768.5   768.5   638.9
Members' equity 3,449.4   3,449.4   3,093.3
Total liabilities and members' equity $ 8,635.8   $ 8,635.8   $ 7,728.3