REGULATORY MATTERS - MPC Regulatory Matters (Details)								1 Months Ended			12 Months Ended
	Jan. 01, 2020 USD ($)	Nov. 26, 2019 USD ($)	Jan. 01, 2019 USD ($)	May 08, 2018 USD ($)	Feb. 14, 2018 USD ($)	Feb. 07, 2018 USD ($)	Feb. 06, 2018 USD ($)	Feb. 29, 2020 USD ($)	Feb. 28, 2019 USD ($)	Feb. 28, 2018 USD ($)	Dec. 31, 2019 USD ($) filing	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 24, 2019 USD ($)	Aug. 07, 2018 USD ($)	Jul. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 3,838,000,000	$ 720,000,000
Major storms
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves											170,000,000	74,000,000	$ 41,000,000
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 1,275,000,000	211,000,000
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period											18 years
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 5,800,000
Base rate case filing, rate decrease percentage		0.60%
Base rate case filing, measurement input, average equity ratio		53.00%
Base rate case filing, measurement input, return on investment		7.728%
Performance evaluation plan, number of filings per calendar year | filing											2
Annual PEP filing rate increase amount						$ 26,000,000
Public utilities, approved return on equity						9.33%
Regulatory equity ratio						55.00%
Increase in annual base rate revenues															$ 21,600,000
Amount approved for recovery															$ 2,000,000
Net regulatory assets											$ 64,000,000	(35,000,000)
Retail rate of return on common equity															9.31%
Allowed equity ratio											50.00%				50.00%
Actual average equity ratio variance (more than)											1.00%
Percent ownership														50.00%
Public utilities, requested cost to complete environmental compliance projects														$ 66,000,000
Regulatory amortization period											5 years
PSC retail increase (decrease)											$ 2,000,000	7,000,000	(8,000,000)
Threshold above which actual damages are charged to the reserve											50,000
Wholesale accrual per annual SSR rate											$ 300,000
SRR rate											0.00%
Psc approved annual property damage reserve accrual											$ 1,000,000	2,000,000	4,000,000
Mississippi Power | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Proposed property damage reserve											54,000,000
Mississippi Power | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Proposed property damage reserve											1,000,000
Mississippi Power | Major storms
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves											$ 1,000,000	1,000,000	$ 3,000,000
Mississippi Power | Mississippi Public Service Commission
Schedule of Regulatory Assets and Liabilities [Line Items]
Period to agree on system restoration rider											3 years
Mississippi Power | MRA Revenue
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount			$ (16,000,000)
Over recovered fuel cost											$ 6,000,000	6,000,000
Mississippi Power | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 3,000,000					$ (35,000,000)	$ 39,000,000
Over recovered fuel cost											$ 23,000,000	8,000,000
Mississippi Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, requested rate increase (decrease), amount					$ 17,000,000
Allowed equity ratio															51.00%
Public utilities approved rate increase (decrease)					2.00%
Mississippi Power | Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved return on equity							8.60%
Public utilities, approved rate increase (decrease), amount							$ 99,300,000
Mississippi Power | Plant Greene County Units 1 And 2
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset																$ 17,000,000
Mississippi Power | Plant Watson
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset																	$ 41,000,000
Mississippi Power | Plant Daniel Units 1 & 2 (coal)
Schedule of Regulatory Assets and Liabilities [Line Items]
Percent ownership											50.00%
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 30,000,000	41,000,000
Mississippi Power | Remaining net book value of retired assets | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 14,000,000
Regulatory amortization period											12 years
Mississippi Power | Remaining net book value of retired assets | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 16,000,000
Regulatory amortization period											5 years
Mississippi Power | Contested Compensation Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ 4,000,000
Mississippi Power | Subsequent Event | MRA Revenue
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount	$ 1,000,000
Mississippi Power | Deferred credits related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets											$ (358,000,000)	$ (377,000,000)
Regulatory amortization period											8 years
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets											$ 106,000,000
Mississippi Power | Deferred credits related to income taxes | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period											3 years
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets											$ 18,000,000
Mississippi Power | Deferred credits related to income taxes | Kemper IGCC | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period											8 years
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets											$ 28,000,000
Mississippi Power | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities											44,000,000
Mississippi Power | Performance Settlement Agreement, Average Equity Ratio Differential
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities											4,000,000
Mississippi Power | ECO Settlement Agreement, Average Equity Ratio Differential
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities											$ 2,000,000
Mississippi Power And Gulf Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, requested cost to complete environmental compliance projects														125,000,000
Ash Pond Closure | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, requested cost to complete environmental compliance projects														$ 17,000,000
Scenario, Forecast | Mississippi Power | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount								$ (24,000,000)