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AFFILIATED TRANSACTIONS (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Related Party Transaction [Line Items]          
Advances to Affiliate $ 71.0   $ 71.0    
Canadys Refined Coal [Member]          
Related Party Transaction [Line Items]          
Related Party Transaction, Due from (to) Related Party $ 17.3   $ 17.3   $ 4.9
Equity Method Investment, Ownership Percentage 40.00%   40.00%    
Related Party Transaction, Purchases from Related Party $ 44.8 $ 52.8 $ 77.3 $ 97.4  
Sales to Affiliates 44.6 52.5 76.9 96.8  
Due to Related Parties 17.4   17.4   4.9
Energy Marketing [Member]          
Related Party Transaction [Line Items]          
Due to Affiliate, Current 10.6   10.6   10.0
Cost of Natural Gas Purchases 0.0 34.3 60.0 58.2  
SCANA Services [Member]          
Related Party Transaction [Line Items]          
Related Party Transaction, Expenses from Transactions with Related Party 76.0 $ 82.9 135.4 $ 155.4  
Accounts Payable, Related Parties, Current 43.2   43.2   42.0
SCEG          
Related Party Transaction [Line Items]          
Due to Affiliate, Current 260.0   260.0   102.0
Due from Affiliate, Current $ 161.0   $ 161.0   $ 32.0