EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension and Other Postretirement Benefit Plans
Pension Contributions	No
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	$ 5.0	$ 5.3
Interest cost	8.5	9.4
Expected return on assets	(14.3)	(13.8)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	0.1	0.4
Defined Benefit Plan, Actuarial Net (Gains) Losses	3.0	3.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	2.3	5.2
Other Postretirement Benefits
Components of Net Periodic Benefit Cost
Service cost	1.2	1.2
Interest cost	2.7	2.9
Expected return on assets	0.0	0.0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	0.0	0.0
Defined Benefit Plan, Actuarial Net (Gains) Losses	0.5	0.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 4.4	4.5
SCEG
Pension and Other Postretirement Benefit Plans
Pension Contributions	No
SCEG | Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	$ 4.1	4.4
Interest cost	7.2	8.1
Expected return on assets	(12.1)	(11.8)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	0.1	0.3
Defined Benefit Plan, Actuarial Net (Gains) Losses	2.5	3.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	1.8	4.4
SCEG | Other Postretirement Benefits
Components of Net Periodic Benefit Cost
Service cost	1.0	1.0
Interest cost	2.1	2.4
Expected return on assets	0.0	0.0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	0.0	0.0
Defined Benefit Plan, Actuarial Net (Gains) Losses	0.4	0.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 3.5	$ 3.7