SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) MW	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Reclassification Operations and Maintenance Expense	$ (2.0)		$ (8.0)
Reclassification Total Operating Expense	(2.0)		(8.0)
Reclassification Operating Income	2.0		8.0
Reclassification Other Income(Expense)	(2.0)		(8.0)
Property, Plant and Equipment, Net		$ 269.0		$ 270.0
SCEG
Reclassification Operations and Maintenance Expense	(1.0)		(6.0)
Reclassification Total Operating Expense	(1.0)		(6.0)
Reclassification Operating Income	1.0		6.0
Reclassification Other Income(Expense)	$ (1.0)		$ (6.0)
Property, Plant and Equipment, Net		73.0		$ 71.0
Genco
Property, Plant and Equipment, Net		$ 495.0
Power Generation Capacity Megawatts | MW		605
PSNC Energy [Member]
Percentage of natural gas inventory held by counterparties under asset management and supply service agreements (as a percent)		45.00%		39.00%
Natural gas inventory, carrying amount		$ 14.3		$ 11.5
PercentOfStorageFeesCreditedToRatePayers		75.00%