EMPLOYEE BENEFIT PLANS (Details) - USD ($) | 12 Months Ended | |
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year, Description | | no | | | |
Defined Benefit Plan, Accumulated Benefit Obligation | | $ 874,300,000 | $ 829,300,000 | | |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate | | 5.00% | | | |
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation | | $ 800,000 | 800,000 | | |
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation | | $ 700,000 | $ 700,000 | | |
Defined Benefit Plan Health Care Cost Trend Rate, Assumed | | 6.60% | | | |
Defined Benefit Plan, Target Allocation, Equity Securities | | 57.00% | 57.00% | | |
Defined Benefit Plan, Target Plan Asset Allocations | | 32.00% | 32.00% | | |
Defined Benefit Plan, Target Plan Asset Allocation, Hedge Funds | | 11.00% | 11.00% | | |
Other Postretirement Benefits | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Adoption of modified mortality tables in 2015, gain | | | $ 2,400,000 | | |
Defined Benefit Plan, Benefit Obligation | | $ 274,700,000 | 253,600,000 | $ 268,200,000 | |
Defined Benefit Plan, Service Cost | | 4,400,000 | 5,300,000 | 4,600,000 | |
Defined Benefit Plan, Interest Cost | | 12,100,000 | 11,400,000 | $ 12,000,000 | |
Defined Benefit Plan, Contributions by Plan Participants | | 1,700,000 | 2,400,000 | | |
Defined Benefit Plan, Actuarial Net (Gains) Losses | | (14,000,000) | 21,200,000 | | |
Defined Benefit Plan, Benefits Paid | | $ (11,100,000) | $ (12,500,000) | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | | 4.30% | 4.78% | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | | 3.00% | 3.00% | | |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate | | 5.00% | 5.00% | 5.00% | |
Defined Benefit Plan, Fair Value of Plan Assets | | $ 0 | $ 0 | | |
Defined Benefit Plan, Funded Status of Plan | | (274,700,000) | (253,600,000) | | |
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities | | (12,600,000) | (11,900,000) | | |
Other Postretirement Defined Benefit Plan, Liabilities, Noncurrent | | (262,100,000) | (241,700,000) | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax | | 2,500,000 | 1,700,000 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | | 0 | 0 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax | | 2,500,000 | 1,700,000 | | |
pension and other postretirement benefit plans, regulated assets, net gains, before tax | | 34,700,000 | 24,000,000 | | |
Pension and other postretirement benefit plans, regulatory assets, net prior service costs (credit), before tax | | 0 | 300,000 | | |
Pension and other postretirement benefit plans, regulatory assets, before tax | | 34,700,000 | 24,300,000 | | |
Defined Benefit Plan, Shared Costs Deferred | | 15.8 | 13.8 | | |
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax | | 11,100,000 | (18,000,000) | $ 19,400,000 | |
Regulatory assets, amortization of actuarial losses, pension and other postretirement benefit plans, net of tax | | (400,000) | (1,800,000) | 0 | |
Regulatory assets, amortization of prior service cost, pension and other postretirement benefit plans, net of tax | | (300,000) | (300,000) | (300,000) | |
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax | | $ 10,400,000 | $ 20,100,000 | $ 19,100,000 | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate | | 4.78% | 4.30% | 5.19% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase | | 3.00% | 3.00% | 3.75% | |
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year | | 7.00% | 7.00% | 7.40% | |
Pension Plan, Defined Benefit | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Adoption of modified mortality tables in 2015, gain | | | $ 21,500,000 | | |
Defined Benefit Plan, Benefit Obligation | | $ 904,300,000 | 855,400,000 | $ 919,500,000 | |
Defined Benefit Plan, Service Cost | | 20,700,000 | 24,100,000 | 20,000,000 | |
Defined Benefit Plan, Interest Cost | | 39,400,000 | 38,200,000 | 40,400,000 | |
Defined Benefit Plan, Contributions by Plan Participants | | 0 | 0 | | |
Defined Benefit Plan, Actuarial Net (Gains) Losses | | (45,000,000) | 62,400,000 | | |
Defined Benefit Plan, Benefits Paid | | $ (56,200,000) | $ (64,000,000) | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | | 4.22% | 4.68% | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | | 3.00% | 3.00% | | |
Defined Benefit Plan, Fair Value of Plan Assets | | $ 793,600,000 | $ 781,700,000 | 861,800,000 | |
Defined Benefit Plan, Actual Return on Plan Assets | | 68,100,000 | (16,100,000) | | |
Defined Benefit Plan, Funded Status of Plan | | (110,700,000) | (73,700,000) | | |
Defined Benefit Pension Plan, Liabilities, Noncurrent | | (110,700,000) | (73,700,000) | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax | | 10,400,000 | 10,400,000 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | | 100,000 | 200,000 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax | | 10,500,000 | 10,600,000 | | |
pension and other postretirement benefit plans, regulated assets, net gains, before tax | | 236,100,000 | 219,400,000 | | |
Pension and other postretirement benefit plans, regulatory assets, net prior service costs (credit), before tax | | 2,500,000 | 5,900,000 | | |
Pension and other postretirement benefit plans, regulatory assets, before tax | | 238,600,000 | 225,300,000 | | |
Defined Benefit Plan, Shared Costs Deferred | | 23.4 | 20.3 | | |
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax | | 29,400,000 | 9,200,000 | 101,300,000 | |
Regulatory assets, amortization of actuarial losses, pension and other postretirement benefit plans, net of tax | | (12,700,000) | (11,900,000) | (4,000,000) | |
Regulatory assets, amortization of prior service cost, pension and other postretirement benefit plans, net of tax | | (3,400,000) | (3,700,000) | (3,200,000) | |
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax | | $ 13,300,000 | $ 6,400,000 | $ 94,100,000 | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets | | 7.50% | 7.50% | 8.00% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate | | 4.68% | 4.20% | 5.03% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase | | 3.00% | 3.00% | 3.00% | |
SCE&G | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year, Description | | no | | | |
Defined Benefit Plan, Period for which Annual Base Earnings are Considered Under Average Pay Formula | | 3 | | | |
Defined Benefit Plan, Accumulated Benefit Obligation | | $ 742,900,000 | $ 702,000,000 | | |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate | | 5.00% | | | |
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation | | $ 600,000 | 600,000 | | |
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation | | $ 600,000 | $ 600,000 | | |
Defined Benefit Plan Health Care Cost Trend Rate, Assumed | | 6.60% | | | |
Defined Benefit Plan, Target Allocation, Equity Securities | | 57.00% | 57.00% | | |
Defined Benefit Plan, Target Plan Asset Allocations | | 32.00% | 32.00% | | |
Defined Benefit Plan, Target Plan Asset Allocation, Hedge Funds | | 11.00% | 11.00% | | |
SCE&G | Other Postretirement Benefits | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Adoption of modified mortality tables in 2015, gain | | | $ 2,000,000 | | |
Defined Benefit Plan, Benefit Obligation | | $ 207,200,000 | 191,700,000 | $ 204,100,000 | |
Defined Benefit Plan, Service Cost | | 3,600,000 | 4,400,000 | 3,600,000 | |
Defined Benefit Plan, Interest Cost | | 9,900,000 | 9,400,000 | $ 9,400,000 | |
Defined Benefit Plan, Contributions by Plan Participants | | 1,300,000 | 1,900,000 | | |
Defined Benefit Plan, Actuarial Net (Gains) Losses | | (11,500,000) | 15,700,000 | | |
Defined Benefit Plan, Benefits Paid | | (9,100,000) | (10,300,000) | | |
Defined Benefit Plan, Amounts Funded to Parent | | $ (1,700,000) | $ (2,100,000) | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | | 4.30% | 4.78% | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | | 3.00% | 3.00% | | |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate | | 5.00% | 5.00% | 5.00% | |
Defined Benefit Plan, Fair Value of Plan Assets | | $ 0 | $ 0 | | |
Defined Benefit Plan, Funded Status of Plan | | (207,200,000) | (191,700,000) | | |
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities | | (10,400,000) | (9,800,000) | | |
Other Postretirement Defined Benefit Plan, Liabilities, Noncurrent | | (196,800,000) | (181,900,000) | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax | | 1,000,000 | 700,000 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | | 0 | 0 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax | | 1,000,000 | 700,000 | | |
pension and other postretirement benefit plans, regulated assets, net gains, before tax | | 29,300,000 | 20,400,000 | | |
Pension and other postretirement benefit plans, regulatory assets, net prior service costs (credit), before tax | | 0 | 200,000 | | |
Pension and other postretirement benefit plans, regulatory assets, before tax | | 29,300,000 | 20,600,000 | | |
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax | | 9,200,000 | (14,000,000) | $ 15,800,000 | |
Regulatory assets, amortization of actuarial losses, pension and other postretirement benefit plans, net of tax | | (300,000) | (1,500,000) | 0 | |
Regulatory assets, amortization of prior service cost, pension and other postretirement benefit plans, net of tax | | (200,000) | (300,000) | (200,000) | |
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax | | $ 8,700,000 | $ 15,800,000 | $ 15,600,000 | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate | | 4.78% | 4.30% | 5.19% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase | | 3.00% | 3.00% | 3.75% | |
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year | | 7.00% | 7.00% | 7.40% | |
SCE&G | Pension Plan, Defined Benefit | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Adoption of modified mortality tables in 2015, gain | | | $ 18,200,000 | | |
Defined Benefit Plan, Benefit Obligation | | $ 768,400,000 | 724,000,000 | $ 773,700,000 | |
Defined Benefit Plan, Service Cost | | 16,900,000 | 19,300,000 | 16,000,000 | |
Defined Benefit Plan, Interest Cost | | 33,400,000 | 32,200,000 | 34,100,000 | |
Defined Benefit Plan, Contributions by Plan Participants | | 0 | 0 | | |
Defined Benefit Plan, Actuarial Net (Gains) Losses | | (41,800,000) | 47,000,000 | | |
Defined Benefit Plan, Benefits Paid | | (47,700,000) | (54,200,000) | | |
Defined Benefit Plan, Amounts Funded to Parent | | $ 0 | $ 0 | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | | 4.22% | 4.68% | | |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | | 3.00% | 3.00% | | |
Defined Benefit Plan, Fair Value of Plan Assets | | $ 732,900,000 | $ 720,100,000 | 783,600,000 | |
Defined Benefit Plan, Actual Return on Plan Assets | | 60,500,000 | (9,300,000) | | |
Defined Benefit Plan, Funded Status of Plan | | (35,500,000) | (3,900,000) | | |
Defined Benefit Pension Plan, Liabilities, Noncurrent | | (35,500,000) | (3,900,000) | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax | | 1,900,000 | 2,000,000 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | | 0 | 0 | | |
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax | | 1,900,000 | 2,000,000 | | |
pension and other postretirement benefit plans, regulated assets, net gains, before tax | | 208,800,000 | 193,700,000 | | |
Pension and other postretirement benefit plans, regulatory assets, net prior service costs (credit), before tax | | 2,200,000 | 5,200,000 | | |
Pension and other postretirement benefit plans, regulatory assets, before tax | | 211,000,000 | 198,900,000 | | |
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax | | 26,300,000 | 12,200,000 | 87,700,000 | |
Regulatory assets, amortization of actuarial losses, pension and other postretirement benefit plans, net of tax | | (11,200,000) | (10,400,000) | (3,500,000) | |
Regulatory assets, amortization of prior service cost, pension and other postretirement benefit plans, net of tax | | (3,000,000) | (3,100,000) | (2,800,000) | |
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax | | $ 12,100,000 | $ 1,300,000 | $ 81,400,000 | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets | | 7.50% | 7.50% | 8.00% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate | | 4.68% | 4.20% | 5.03% | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase | | 3.00% | 3.00% | 3.00% | |
Pension Costs [Member] | SCE&G | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Defined Benefit Plan, Deferred Debit Attributable to Share of Regulatory Authority | | $ 14,000,000 | | | $ 63,000,000 |
Regulatory assets, expected recovery period (in years) | | 11 years | | | |
Scenario, Forecast [Member] | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets | 7.25% | | | | |
Defined Benefit Plan, Target Allocation, Equity Securities | 58.00% | | | | |
Defined Benefit Plan, Target Plan Asset Allocations | 33.00% | | | | |
Defined Benefit Plan, Target Plan Asset Allocation, Hedge Funds | 9.00% | | | | |
Scenario, Forecast [Member] | SCE&G | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets | 7.25% | | | | |
Defined Benefit Plan, Target Allocation, Equity Securities | 58.00% | | | | |
Defined Benefit Plan, Target Plan Asset Allocations | 33.00% | | | | |
Defined Benefit Plan, Target Plan Asset Allocation, Hedge Funds | 9.00% | | | | |