Summary of Significant Accounting Policies - Property, Plant, and Equipment (Details) $ in Millions	1 Months Ended	6 Months Ended		12 Months Ended
	Jul. 31, 2016	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Property	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation		$ 48,836		$ 48,836	$ 41,648
Transmission		11,156		11,156	10,544
Distribution		18,418		18,418	17,670
General		4,629		4,629	4,377
Plant acquisition adjustment		126		126	123
Electric Utility Plant in Service		83,165		83,165	74,362
Transportation and distribution		11,996		11,996	0
Utility plant in service		95,161		95,161	74,362
Information technology equipment and software		544		544	222
Communications equipment		424		424	418
Storage facilities		1,463		1,463	0
Other		824		824	116
Other plant in service		3,255		3,255	756
Total plant in service		98,416		98,416	75,118
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Less: Accumulated amortization		(69)		(69)	(59)
Balance, net of amortization		144		144	152
Accrued property additions at year-end				1,500	844	$ 528
Capital Lease Obligations
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Non-cash property additions recognized				18	13	25
Office building
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Capital leased assets, gross		61		61	61
Nitrogen plant
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Capital leased assets, gross		83		83	83
Computer-related equipment
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Capital leased assets, gross		63		63	61
Gas pipeline
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Capital leased assets, gross		6		6	6
Southern Power [Member]
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end				$ 251	257	1
Alabama Power and Georgia Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Refueling cycles for minimum period				18 months
Refueling cycles maximum period				24 months
Southern Company Gas [Member] | Successor [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Utility plant in service		11,996		$ 11,996
Information technology equipment and software		324		324
Storage facilities		1,463		1,463
Other		725		725
Other plant in service		2,512		2,512
Total plant in service		14,508		$ 14,508
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end		63
Southern Company Gas [Member] | Predecessor [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Utility plant in service					9,912
Information technology equipment and software					415
Storage facilities					1,255
Other					570
Other plant in service					2,240
Total plant in service					12,152
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end			$ 41		48	31
Alabama Power [Member]
Property, Plant and Equipment [Line Items]
Number of units for which outage operations and maintenance expenses accrued | Property				2
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation		13,551		$ 13,551	12,820
Transmission		3,921		3,921	3,773
Distribution		6,707		6,707	6,432
General		1,840		1,840	1,713
Plant acquisition adjustment		12		12	12
Total plant in service		26,031		26,031	24,750
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end				$ 84	121	8
Period over which deferred costs are being amortized to nuclear operations and maintenance expenses				18 months
Georgia Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation		16,668		$ 16,668	15,386
Transmission		5,779		5,779	5,355
Distribution		9,553		9,553	9,151
General		1,813		1,813	1,921
Plant acquisition adjustment		28		28	28
Total plant in service		33,841		$ 33,841	31,841
Refueling cycles for minimum period				18 months
Refueling cycles maximum period				24 months
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end				$ 336	387	154
Gulf Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation		3,001		3,001	2,974
Transmission		706		706	691
Distribution		1,241		1,241	1,196
General		191		191	182
Plant acquisition adjustment		1		1	2
Total plant in service		5,140		5,140	5,045
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end				33	20	42
Mississippi Power [Member]
Property, Plant and Equipment [Line Items]
Regulatory amortization period	5 years
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation		2,632		2,632	2,723
Transmission		712		712	688
Distribution		916		916	891
General		520		520	503
Plant acquisition adjustment		85		85	81
Total plant in service		$ 4,865		4,865	4,886
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accrued property additions at year-end				$ 78	$ 105	$ 114
Kemper IGCC [Member] | Mississippi Power [Member]
Property, Plant and Equipment [Line Items]
Regulatory amortization period					10 years
Maximum [Member] | Southern Power [Member] | Natural Gas Generating Facility [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life				45 years
Maximum [Member] | Southern Power [Member] | Biomass Generating Facility [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life				40 years
Maximum [Member] | Southern Power [Member] | Solar Generating Facility [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life				35 years
Maximum [Member] | Southern Power [Member] | Wind Generating Facility [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life				30 years