Summary of Significant Accounting Policies - Reserves and Leveraged Leases (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) kWh	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Aug. 29, 2016 USD ($)	Oct. 31, 2015 USD ($)
Components of Income from Leveraged Lease
Other Regulatory Assets Current	$ 581,000,000	$ 580,000,000
Other Regulatory Assets Deferred	6,851,000,000	4,989,000,000
Domestic And International Leveraged Lease
Net Investments from Leveraged Lease
Net rentals receivable	1,481,000,000	1,487,000,000
Unearned income	(707,000,000)	(732,000,000)
Investment in leveraged leases	774,000,000	755,000,000
Deferred taxes from leveraged leases	(309,000,000)	(303,000,000)
Net investment in leveraged leases	465,000,000	452,000,000
Components of Income from Leveraged Lease
Pretax leveraged lease income (loss)	25,000,000	20,000,000	$ 24,000,000
Income tax expense	(9,000,000)	(7,000,000)	(9,000,000)
Net leveraged lease income (loss)	$ 16,000,000	13,000,000	15,000,000
Maximum [Member]
Leveraged Lease [Line Items]
Leveraged lease agreement term	45 years
Georgia Power [Member]
Leveraged Lease [Line Items]
Accrual Under Alternate Rate Plan	$ 30,000,000
Components of Income from Leveraged Lease
Other Regulatory Assets Current	193,000,000	213,000,000
Other Regulatory Assets Deferred	2,774,000,000	2,152,000,000
Mississippi Power [Member]
Leveraged Lease [Line Items]
Threshold above which actual damages are charged to the reserve	50,000
Psc approved annual property damage reserve accrual					$ 3,000,000
Components of Income from Leveraged Lease
Retail Accrual Per Annual SRR Rate	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	115,000,000	95,000,000
Other Regulatory Assets Deferred	518,000,000	525,000,000
Gulf Power [Member]
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
Increase (decrease) in recoverable property damage costs	$ 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
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	1,400,000	0
Estimated liabilities for outstanding claims	0	1,700,000
Accrued reserves	40,000,000	38,000,000
Components of Income from Leveraged Lease
Regulatory asset				$ 63,000,000
Other Regulatory Assets Current	44,000,000	90,000,000
Other Regulatory Assets Deferred	512,000,000	427,000,000
Gulf Power [Member] | Maximum [Member]
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 [Member] | Minimum [Member]
Leveraged Lease [Line Items]
PSC approved target level for property damage reserve	48,000,000
Traditional Operating Companies
Leveraged Lease [Line Items]
Accrued reserves	$ 40,000,000	40,000,000	$ 40,000,000
Current Liabilities [Member] | Gulf Power [Member]
Leveraged Lease [Line Items]
Liability for claims and claims adjustment expense		1,600,000
Deferred Credits and Other Liabilities [Member] | Gulf Power [Member]
Leveraged Lease [Line Items]
Liability for claims and claims adjustment expense		100,000
Mississippi Public Service Commission [Member] | Mississippi Power [Member]
Components of Income from Leveraged Lease
Period To Agree On System Restoration Rider	3 years
Retail [Member]
Components of Income from Leveraged Lease
Proposed Property Damage Reserve	$ 66,000,000
Wholesale [Member]
Components of Income from Leveraged Lease
Proposed Property Damage Reserve	1,000,000
Property Damage Reserves Liability [Member] | Georgia Power [Member]
Components of Income from Leveraged Lease
Regulatory asset	206,000,000	92,000,000
Other Regulatory Assets Current	30,000,000	30,000,000
Other Regulatory Assets Deferred	$ 176,000,000	$ 62,000,000