v3.26.1
DEBT Schedule of Revolving Credit Agreements (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Line of Credit Facility [Line Items]    
Total available capacity $ 1,000  
Outstanding Balance 120 $ 589
Unused Capacity 880  
Line of Credit Facility, Maximum Borrowing Capacity 1,000  
ITC Holdings Corp.    
Line of Credit Facility [Line Items]    
Total available capacity 400  
Outstanding Balance 0  
Unused Capacity $ 400  
Debt, Weighted Average Interest Rate 0.00%  
Commitment Fee Rate 0.175%  
ITCTransmission    
Line of Credit Facility [Line Items]    
Total available capacity $ 200  
Outstanding Balance 35  
Unused Capacity $ 165  
Debt, Weighted Average Interest Rate 4.71%  
Commitment Fee Rate 0.10%  
METC LLC    
Line of Credit Facility [Line Items]    
Total available capacity $ 125  
Outstanding Balance 27  
Unused Capacity $ 98  
Debt, Weighted Average Interest Rate 4.71%  
Commitment Fee Rate 0.10%  
ITC Midwest LLC    
Line of Credit Facility [Line Items]    
Total available capacity $ 200  
Outstanding Balance 45  
Unused Capacity $ 155  
Debt, Weighted Average Interest Rate 4.71%  
Commitment Fee Rate 0.10%  
ITC Great Plains LLC    
Line of Credit Facility [Line Items]    
Total available capacity $ 75  
Outstanding Balance 13  
Unused Capacity $ 62  
Debt, Weighted Average Interest Rate 4.71%  
Commitment Fee Rate 0.10%