LONG-TERM AND SHORT-TERM DEBT (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
First Mortgage Bonds	$ 1,200.0
Gain (Loss) on Repurchase of Debt Instrument	$ 187.0
Line of Credit Facility, Priority	6
Related Party Transaction, Due from (to) Related Party, Current	$ 555.0	$ 282.0
Line of Credit Facility, Increase (Decrease), Net	1,000.0	1,200.0
Commercial Paper		73.2
Letters of Credit Outstanding, Amount	0.3	$ 0.3
Debt, Weighted Average Interest Rate		3.82%
Sub limit for line of credit borrowings	500.0
SCEG
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 67.8	$ 67.8