Summary of Significant Accounting Policies - Reserves and Leveraged Leases (Details)			12 Months Ended
	Apr. 04, 2017 USD ($)	Apr. 01, 2017	Dec. 31, 2017 USD ($) kWh	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Feb. 03, 2017 USD ($)	Aug. 29, 2016 USD ($)	Feb. 29, 2016 USD ($)	Dec. 31, 2014 USD ($)
Net Investments from Leveraged Lease
Investment in leveraged leases			$ 86,000,000
Components of Income from Leveraged Lease
Other regulatory assets, current			604,000,000	$ 581,000,000
Other regulatory assets, deferred			6,943,000,000	6,851,000,000
Domestic And International Leveraged Lease
Net Investments from Leveraged Lease
Net rentals receivable			1,498,000,000	1,481,000,000
Unearned income			(723,000,000)	(707,000,000)
Investment in leveraged leases			775,000,000	774,000,000
Deferred taxes from leveraged leases			(252,000,000)	(309,000,000)
Net investment in leveraged leases			523,000,000	465,000,000
Components of Income from Leveraged Lease
Pretax leveraged lease income (loss)			25,000,000	25,000,000	$ 20,000,000
Net impact of Tax Reform Legislation			48,000,000	0	0
Income tax expense			(9,000,000)	(9,000,000)	(7,000,000)
Net leveraged lease income (loss)			$ 64,000,000	16,000,000	13,000,000
Maximum
Leveraged Lease [Line Items]
Leveraged lease agreement term			45 years
GEORGIA POWER CO
Leveraged Lease [Line Items]
Accrual under alternate rate plan			$ 30,000,000
Property Damage Reserve, Percentage of Balance		0.75
Components of Income from Leveraged Lease
Other regulatory assets, current			205,000,000	193,000,000
Other regulatory assets, deferred			2,932,000,000	2,774,000,000
GULF POWER CO
Leveraged Lease [Line Items]
Psc approved annual property damage reserve accrual			3,500,000
Threshold above which additional property damage reserves are authorized by PSC			3,500,000
Reserve Value to Resume Property Damage Reserve Accruals			0
Increase (decrease) in recoverable property damage costs	$ 31,000,000		$ 3,500,000	3,500,000	3,500,000
Recovery period for natural disaster reserve costs			60 days
Cumulative costs limit under PSC order			$ 100,000,000
Accrued Asset Recovery Damaged Property Costs, Storm Reserve			40,000,000
PSC approved annual uninsured injuries and damages accrual			1,600,000
Threshold above with additional uninsured injuries and damages accruals are authorized by PSC			1,600,000
Liability for claims and claims adjustment expense			2,100,000	1,400,000.0
Estimated liabilities for outstanding claims			0	0
Accrued reserves			40,000,000	40,000,000
Components of Income from Leveraged Lease
Regulatory asset							$ 63,000,000
Other regulatory assets, current			56,000,000	44,000,000
Other regulatory assets, deferred			502,000,000	512,000,000
GULF POWER CO | Maximum
Leveraged Lease [Line Items]
PSC approved target level for property damage reserve			55,000,000
Customer surcharge storm recovery costs			$ 4
Customer surcharge storm recovery capacity | kWh			1,000
PSC approved annual uninsured injuries and damages accrual			$ 2,000,000.0
GULF POWER CO | Minimum
Leveraged Lease [Line Items]
PSC approved target level for property damage reserve			48,000,000
MISSISSIPPI POWER CO
Leveraged Lease [Line Items]
Threshold above which actual damages are charged to the reserve			50,000
Psc approved annual property damage reserve accrual						$ 1,000,000		$ 3,000,000
Components of Income from Leveraged Lease
Retail accrual per annual SRR rate			3,000,000	4,000,000	3,000,000				$ 3,000,000
Wholesale accrual per annual SRR rate			300,000	300,000					$ 300,000
Other regulatory assets, current			125,000,000	115,000,000
Other regulatory assets, deferred			437,000,000	518,000,000
Traditional Operating Companies
Leveraged Lease [Line Items]
Accrued reserves			$ 41,000,000	40,000,000	$ 40,000,000
Mississippi Public Service Commission | MISSISSIPPI POWER CO
Components of Income from Leveraged Lease
Period to agree on system restoration rider			3 years
Retail
Components of Income from Leveraged Lease
Proposed property damage reserve			$ 56,000,000
Wholesale
Components of Income from Leveraged Lease
Proposed property damage reserve			1,000,000
Property damage reserves-liability | GEORGIA POWER CO
Components of Income from Leveraged Lease
Regulatory asset			333,000,000	206,000,000
Other regulatory assets, current			30,000,000	30,000,000
Other regulatory assets, deferred			303,000,000	176,000,000
Other current liabilities | GULF POWER CO
Leveraged Lease [Line Items]
Liability for claims and claims adjustment expense			1,600,000	$ 1,400,000
Other deferred credits and liabilities | GULF POWER CO
Leveraged Lease [Line Items]
Liability for claims and claims adjustment expense			$ 500,000