REGULATORY MATTERS - Schedule of MPC Regulatory Assets and Labilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 3,838	$ 720
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,084)	(2,297)
Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(204)	(76)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(86)	(132)
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	4,381	2,933
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	1,275	211
Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	803	799
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	492	581
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	4,423	3,658
Regulatory asset	23
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 186	182
Regulatory amortization period	1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 323	346
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 64	(35)
Regulatory amortization period	5 years
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Mississippi Power | Deferred credits related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (358)	(377)
Regulatory amortization period	8 years
Tax Cuts and Jobs Act of 2017, deferred tax assets	$ 358
Tax Cuts and Jobs Act of 2017, protected deferred tax assets	252
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	106
System Restoration Rider, deferred tax assets	$ 8
Mississippi Power | Deferred credits related to income taxes | Retail electric revenues | Kemper County energy facility
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
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
Mississippi Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(189)	(185)
Mississippi Power | Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(55)	(56)
Mississippi Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (10)	(9)
Regulatory amortization period	1 year
Mississippi Power | Retiree benefit plans – regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 213	171
Mississippi Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 210	143
Regulatory amortization period	48 years
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 61	69
Regulatory amortization period	8 years
Regulatory asset	$ 78
Regulatory liabilities	18
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	30	41
Mississippi Power | Remaining net book value of retired assets | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 16
Regulatory amortization period	5 years
Mississippi Power | Remaining net book value of retired assets | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 14
Regulatory amortization period	12 years
Mississippi Power | Property tax
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 47	44
Regulatory amortization period	12 months
Mississippi Power | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 33	34
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	34	36
Mississippi Power | ECO carryforward
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	0	26
Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 48	$ 28
Regulatory amortization period	3 years
Mississippi Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	14 years
Mississippi Power | Kemper Retail
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	6 years
Mississippi Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 9
Mississippi Power | Other Miscellaneous Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 5
Regulatory amortization period	1 year
Mississippi Power | Fuel-hedging Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 27
Mississippi Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 6
Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	18 years
Maximum | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	80 years
Maximum | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Maximum | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Maximum | Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	22 years