RATE AND OTHER REGULATORY MATTERS (Details 2) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2013	Dec. 31, 2016
Regulatory Assets
Asset Impairment Charges	$ 210.0
Regulatory Liability, Noncurrent	2,015.0		$ 930.0
Regulatory Assets, Noncurrent	6,690.0		2,130.0
SCEG
Regulatory Assets
Asset Impairment Charges	210.0
Regulatory Liability, Noncurrent	1,779.0		695.0
Regulatory Assets, Noncurrent	6,582.0		2,030.0
PSNC Energy [Member]
Regulatory Assets
Pipeline integrity management costs, amount deferred pending future approval of rate recovery	21.6
Pipeline integrity management costs, amount recovering beginning November 2016	20.3
Settlement Proceeds [Member] | Summer Station New Units [Domain]
Regulatory Assets
Regulatory Liability, Noncurrent	1,095.0		0.0
Settlement Proceeds [Member] | SCEG
Regulatory Assets
Regulatory Liability, Noncurrent	1,095.0		0.0
Asset Retirement Obligation Costs [Member]
Regulatory Assets
Regulatory Liability, Noncurrent	764.0		755.0
Asset Retirement Obligation Costs [Member] | SCEG
Regulatory Assets
Regulatory Liability, Noncurrent	535.0		529.0
Deferred gains on interest rate derivatives [Member]
Regulatory Assets
Regulatory Liability, Noncurrent	135.0		151.0
Deferred gains on interest rate derivatives [Member] | SCEG
Regulatory Assets
Regulatory Liability, Noncurrent	135.0		151.0
Other Regulatory Liability [Member]
Regulatory Assets
Regulatory Liability, Noncurrent	21.0		24.0
Other Regulatory Liability [Member] | SCEG
Regulatory Assets
Regulatory Liability, Noncurrent	14.0		15.0
Unrecovered nuclear project costs post impairment [Member]
Regulatory Assets
Regulatory Assets, Noncurrent			0.0
Unrecovered nuclear project costs post impairment [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	$ 4,520.0
Deferred Income Tax Charges [Member]
Regulatory Assets
Regulatory Asset, Amortization Period	85 years
Regulatory Assets, Noncurrent	$ 315.0		316.0
Deferred Income Tax Charges [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	$ 307.0		307.0
Asset Retirement Obligation Costs [Member]
Regulatory Assets
Regulatory Asset, Amortization Period	110 years
Regulatory Assets, Noncurrent	$ 424.0		425.0
Asset Retirement Obligation Costs [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	401.0		403.0
Pension Costs [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	$ 321.0		342.0
Pension Costs [Member] | SCEG
Regulatory Assets
Regulatory Asset, Amortization Period	11 years
Regulatory Assets, Noncurrent	$ 290.0		309.0
Pension costs, electric [Member] | SCEG
Regulatory Assets
Regulatory Asset, Amortization Period		30 years
Deferred Losses On Interest Rate Derivatives [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	632.0		620.0
Deferred Losses On Interest Rate Derivatives [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	632.0		620.0
unrecovered plant [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	108.0		117.0
unrecovered plant [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	108.0		117.0
Demand Side Management programs [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	$ 58.0		59.0
Demand Side Management programs [Member] | SCEG
Regulatory Assets
Regulatory Asset, Amortization Period	5 years
Regulatory Assets, Noncurrent	$ 58.0		59.0
carrying cost on nuclear [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	$ 46.0		32.0
carrying cost on nuclear [Member] | SCEG
Regulatory Assets
Regulatory Asset, Amortization Period	10 years
Regulatory Assets, Noncurrent	$ 46.0		32.0
Pipeline integrity management costs [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	47.0		33.0
Pipeline integrity management costs [Member] | SCEG
Regulatory Assets
Pipeline integrity management costs, annual amortization amount	1.9
Regulatory Assets, Noncurrent	$ 7.0		6.0
Pipeline integrity management costs [Member] | PSNC Energy [Member]
Regulatory Assets
Regulatory Asset, Amortization Period	5 years
Environmental Restoration Costs [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	$ 30.0		32.0
Environmental Restoration Costs [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	25.0		26.0
Storm Costs [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	22.0		20.0
Storm Costs [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	22.0		20.0
Deferred costs uncertain tax position [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	28.0		15.0
Deferred costs uncertain tax position [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	28.0		15.0
Other Regulatory Assets [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	139.0		119.0
Other Regulatory Assets [Member] | SCEG
Regulatory Assets
Regulatory Assets, Noncurrent	$ 138.0		$ 116.0