COMMITMENTS AND CONTINGENCIES (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments and contingencies
Utilities Operating Loss, Impairment, Net of Taxes	$ 2,700,000	$ 690,000,000
Costs Not to Be Recovered Under Merger Agreement	1,700,000,000
Utilities Operating Expense, Impairments	3,600,000	1,118,000,000
Remaining Impairment Loss	1,700,000,000
Write off unrecovered nuclear cost	3,966,000,000
Customer Refundable Fees, Refund Payments	$ 1,300,000,000
SCPSC Order Percentage Reduction Of Total Fuel Cost Component Of Retail Electric Rates To Reflect Lower Projected Fuel Costs And Eliminate Over-Collection Balances	5.00%
Operating Leases, Future Minimum Payments Due	$ 33,000,000
Environmental
Goal For Reduced Carbon Dioxide Emissions From 2005 Levels By 2030 Under Clean Air Act	32.00%
Nuclear Generation
Estimate of aggregate amount of subcontractor and vendor liens filed	$ 290,000,000
Loss Contingency, Damages Sought, Value	270,000,000
Asset Impairment Charges	4,000,000
Guaranty Fee Income	2,200,000,000
Long-term Line of Credit	1,800,000,000
Regulatory Request to Lower Revenues	445,000,000
SCPSC Order for Increase of Total Fuel Cost Component of Retail Electric Rates to produce a projected under recovery	0.035
Impairment Cost, Additional Liabilities, Post Merger	1,875,000,000
Monetization of guaranty settlement	1,094,000,000
Long-term Debt, Current Maturities	727,000,000	727,000,000
Short-term borrowings	248,000,000	350,000,000
Summer Station Unit 2 and Unit 3 [Domain]
Commitments and contingencies
Remaining Impairment Loss	1,300,000,000
Nuclear Generation
Short-term borrowings	248,000,000
Debt Instrument, Periodic Payment, Interest	301,000,000
SCEG
Commitments and contingencies
Utilities Operating Loss, Impairment, Net of Taxes	3,700,000,000
Utilities Operating Expense, Impairments	4,000,000
Operating Leases, Future Minimum Payments Due	26,000,000
Nuclear Insurance
Maximum liability assessment per reactor for each nuclear incident	127,300,000
Maximum Insurance Coverage For Each Nuclear Plant by ANI	450,000,000
Federal Limit on Public Liability Claims from Nuclear Incident Approximate	13,400,000,000
Maximum Federal Limit on Public Liability Claims Per Reactor for Each Year	18,900,000
Maximum Federal Limit on Public Liability Claims per Reactor for each Nuclear Incident at 2/3	84,800,000
Maximum Federal Limit on Public Liability Claims Per Incident for Each Year	$ 12,600,000
Inflation adjustment period for nuclear insurance	5
NEIL Maximum Insurance Coverage To Nuclear Facility For Property Damage And Outage Costs From Non-Nuclear Event	$ 2,330,000,000
NEIL Maximum Insurance Coverage of Accidental Property Damage	2,750,000,000
EMANI Maximum Retrospective Premium Assessment	2,000,000
EMANI Maximum Insurance Coverage for Summer Station Unit 1 For Property Damage And Outage Costs From Non-Nuclear Event	415,000,000
NEIL Maximum Prosepective Insurance Premium Per Nuclear Incident	22,300,000
NEIL Maximum Insurance Coverage to Nuclear Facility for Property Damage and Outage Costs	2,750,000,000
Environmental
Environmental Remediation Costs Recognized in Regulatory Assets	$ 24,300,000
Number of MGP decommissioned sites that contain residues of byproduct chemicals	4
Number Of States Required To Reduce Emissions Under CSAPR	28
Site Contingency MGP Estimated Environmental Remediation Costs	$ 9,900,000
Nuclear Generation
Estimate of aggregate amount of subcontractor and vendor liens filed	33,000,000
Asset Impairment Charges	4,000,000
Guarantee Settlement Receipts	1,200,000,000
Long-term Line of Credit	1,200,000,000
SCPSC Order for Increase of Total Fuel Cost Component of Retail Electric Rates to produce a projected under recovery	1,300,000
Long-term Debt, Current Maturities	723,000,000	723,000,000
Short-term borrowings	146,000,000	$ 252,000,000
SCEG
Commitments and contingencies
Utilities Operating Expense, Impairments	4,900,000,000
SCEG | SCEG
Nuclear Generation
Short-term borrowings	146,000,000
Debt Instrument, Periodic Payment, Interest	256,000,000
Summer Station Unit 2 and Unit 3 [Domain]
Commitments and contingencies
Write off unrecovered nuclear cost	$ 846,000,000
Nuclear Generation
Jointly Owned Utility Plant, Proportionate Ownership Share	55.00%
Estimate of aggregate amount of subcontractor and vendor liens filed	$ 60,000,000