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VARIABLE INTEREST ENTITIES - TRANSMISSION AFFILIATES (Details) - USD ($)
$ in Millions
Jun. 30, 2022
Dec. 31, 2021
ATC    
Variable interest entities    
Ownership interest (as a percent) 60.00%  
Equity investment $ 1,813.6 $ 1,766.9
ATC Holdco    
Variable interest entities    
Ownership interest (as a percent) 75.00%  
Equity investment $ 23.6 $ 22.5