AFFILIATED TRANSACTIONS - SCEG (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Affiliated Transaction [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions	$ 3.7	$ 4.0	$ 7.8
Equity Method Investments	5.5	4.1	5.7
Related Party Transaction, Expenses from Transactions with Related Party	337.7	300.0	292.2
Canadys Refined Coal LLC [Member]
Affiliated Transaction [Line Items]
Related Party Transaction Purchases from Related Party	161.8	233.2	260.3
Sales to Affiliate	$ 160.8	232.0	259.0
Equity Method Investment, Ownership Percentage	40.00%
Related Party Tax Expense, Due from Affiliates, Current	$ 16.0	12.8
Related Party Tax Expense, Due to Affiliates, Current	16.1	12.9
SCE&G
Affiliated Transaction [Line Items]
Due to Affiliate, Current	122.0	113.0
Due from Affiliate, Current	16.0	22.0
Related Party Transaction, Due from (to) Related Party, Current		9.0
Accounts Payable, Related Parties, Current	63.5	57.0
CGT [Member]
Affiliated Transaction [Line Items]
Related Party Transaction Purchases from Related Party		3.4	30.0
Retail Gas and Energy Marketing Segment [Member]
Affiliated Transaction [Line Items]
Due to Affiliate, Current	8.8	7.5
Cost of Natural Gas Purchases	$ 111.5	$ 128.5	$ 195.7

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