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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
MW
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Significant Accounting Policies      
Long-term Debt, Current Maturities $ 727.0 $ 17.0  
Short-term borrowings 350.0 941.0  
Regulated Operating Revenue, Gas 874.0 788.0 $ 811.0
Pre-tax gain on sale of CGT and SCI     $ 342.0
Unbilled Receivables, Current 220.9 178.9  
Goodwill $ 210.0 $ 210.0  
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service 2.63% 2.61% 2.61%
Public Utilities, Allowance for Funds Used During Construction, Additions 5.60% 5.30% 6.10%
Property, Plant and Equipment, Net $ 270.0 $ 276.0  
Asset Management and Supply Service Agreements      
Future Operating Impairment Loss $ 4,800.0    
Earnings Per Share      
Weighted Average Shares Outstanding - Basic | shares 143 143 143
SCEG and GENCO [Member]      
Significant Accounting Policies      
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service 2.55% 2.56% 2.56%
SCE&G      
Significant Accounting Policies      
Long-term Debt, Current Maturities $ 723.0 $ 12.0  
Short-term borrowings 252.0 804.0  
Maintenance Costs 18.4    
Utilities Operating Expense, Maintenance 26.1 23.8  
Environmental Remediation Costs Recognized in Regulatory Assets 24.6    
Unbilled Receivables, Current $ 140.3 $ 117.6  
Accrual period of nuclear refueling charges (in months) 18    
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service 2.55% 2.56% 2.55%
Public Utilities, Allowance for Funds Used During Construction, Additions 3.90% 4.70% 5.60%
Property, Plant and Equipment, Net $ 71.0 $ 69.0  
Genco      
Significant Accounting Policies      
Power Generation Capacity Megawatts | MW 605    
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service 2.66% 2.66% 2.66%
Property, Plant and Equipment, Net $ 503.0    
PSNC Energy      
Significant Accounting Policies      
Goodwill 210.0    
Accumulated Amortization and Write-down, Goodwill $ 230.0    
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service 3.03% 2.90% 2.94%
Asset Management and Supply Service Agreements      
Natural gas inventory, carrying amount $ 11.5 $ 9.8  
Percentage of natural gas inventory held by counterparties under asset management and supply service agreements (as a percent) 39.00% 40.00%  
PercentOfStorageFeesCreditedToRatePayers 75.00%    
Summer Station Unit 1 [Domain]      
Significant Accounting Policies      
Jointly Owned Utility Plant, Proportionate Ownership Share 66.70% 66.70%  
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 1,500.0 $ 1,300.0  
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 637.6 634.4  
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress 110.1 167.7  
Summer Station Unit 1 [Domain] | SCE&G      
Significant Accounting Policies      
Accounts Receivable, Net $ 53.8 $ 76.2  
Summer Station New Units [Domain]      
Significant Accounting Policies      
Jointly Owned Utility Plant, Proportionate Ownership Share 55.00% 55.00%  
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress   $ 4,200.0  
SCE&G      
Significant Accounting Policies      
Decommissioning Liability, Noncurrent $ 786.4    
Decommissioning safe storage 60    
Payments to Acquire Investments to be Held in Decommissioning Trust Fund $ 3.2    
Amount accrued annually for nuclear fuel outages 17.2    
Nuclear refueling outage cost $ 23.2 $ 1.8