Regulatory Matters - Schedule of MPC Regulatory Assets and Labilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 720	$ (1,894)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,297)	(2,684)
Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(76)	(135)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(132)	(104)
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	2,933	1,133
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	211	306
Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	799	814
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	581	625
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	3,658	3,931
Regulatory asset	28
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 182	183
Regulatory amortization period	1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 346	223
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (35)	(42)
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	$ (377)	(377)
Regulatory amortization period	8 years
Tax Cuts and Jobs Act of 2017, deferred tax assets	$ 377
Tax Cuts and Jobs Act of 2017, protected deferred tax assets	266
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	111
System Restoration Rider, deferred tax assets	9
Mississippi Power | Deferred credits related to income taxes | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	$ 46
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	$ 33
Mississippi Power | Deferred credits related to income taxes | Wholesale | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	15
Mississippi Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(185)	(178)
Mississippi Power | Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(56)	(57)
Mississippi Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (9)	0
Regulatory amortization period	1 year
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	6 years
Regulatory liabilities	$ 22
Mississippi Power | Retiree benefit plans – regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	171	174
Mississippi Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 143	95
Regulatory amortization period	48 years
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 69	88
Regulatory asset	91
Regulatory assets, noncurrent	22
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	41	44
Mississippi Power | Remaining net book value of retired assets | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	26
Mississippi Power | Remaining net book value of retired assets | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	15
Mississippi Power | Property tax
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 44	43
Regulatory amortization period	12 months
Mississippi Power | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 34	36
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	36	36
Mississippi Power | ECO carryforward
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	26	26
Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 28	$ 28
Regulatory amortization period	3 years
Mississippi Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Mississippi Power | Kemper Retail
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Regulatory asset	$ 75
Mississippi Power | Kemper Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 16
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	5 years
Mississippi Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 9
Mississippi Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 8
Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 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	50 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	50 years