Retirement Benefits - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	$ 6,851		$ 6,851	$ 4,989
Other deferred charges and assets	1,395		1,395	737
Other current liabilities	(683)		(683)	(484)
Employee benefit obligations	(2,299)		(2,299)	(2,582)
Other regulatory liabilities, deferred	(258)		(258)	(254)
Accumulated OCI	(180)		(180)	(130)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	5,866		5,866	5,564
Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	3,207		3,207	2,998
Other current liabilities	(53)		(53)	(46)
Employee benefit obligations	(749)		(749)	(1,262)
Other regulatory liabilities, deferred	(87)		(87)	0
Accumulated OCI	100		100	125
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	55		55	30
Net (Gain) Loss	3,165		3,165	3,093
Prior Service Cost, Estimated			12
Net (Gain) Loss, Estimated	162		162
Pension plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	4		4	3
Net (Gain) Loss	96		96	122
Prior Service Cost, Estimated			1
Net (Gain) Loss, Estimated	7		7
Pension plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	51		51	27
Net (Gain) Loss	3,069		3,069	2,971
Prior Service Cost, Estimated			11
Net (Gain) Loss, Estimated	155		155
Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	419		419	433
Other current liabilities	(4)		(4)	(4)
Employee benefit obligations	(1,349)		(1,349)	(1,152)
Other regulatory liabilities, deferred	(41)		(41)	(22)
Accumulated OCI	7		7	8
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	25		25	32
Net (Gain) Loss	360		360	387
Other postretirement benefit plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	0		0	0
Net (Gain) Loss	7		7	8
Other postretirement benefit plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	25		25	32
Net (Gain) Loss	353		353	379
Prior Service Cost, Estimated			6
Net (Gain) Loss, Estimated	13		13
Alabama Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	1,157		1,157	1,114
Other deferred charges and assets	163		163	103
Other current liabilities	(76)		(76)	(93)
Employee benefit obligations	(300)		(300)	(388)
Other regulatory liabilities, deferred	(100)		(100)	(136)
Accumulated OCI	(30)		(30)	(32)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	1,047		1,047	791
Alabama Power [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	870		870	822
Other current liabilities	(12)		(12)	(11)
Employee benefit obligations	(134)		(134)	(216)
Alabama Power [Member] | Pension plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	10		10	6
Net (Gain) Loss	860		860	816
Prior Service Cost, Estimated			3
Net (Gain) Loss, Estimated	42		42
Alabama Power [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	86		86	95
Employee benefit obligations	(134)		(134)	(142)
Other regulatory liabilities, deferred	(10)		(10)	(13)
Alabama Power [Member] | Other postretirement benefit plans | Regulatory Assets
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	76		76	82
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	15		15	19
Net (Gain) Loss	61		61	63
Prior Service Cost, Estimated			4
Net (Gain) Loss, Estimated	1		1
Georgia Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	2,774		2,774	2,152
Other deferred charges and assets	417		417	173
Other current liabilities	(182)		(182)	(154)
Employee benefit obligations	(703)		(703)	(949)
Accumulated OCI	(13)		(13)	(15)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	3,506		3,506	2,933
Georgia Power [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	1,129		1,129	1,076
Other current liabilities	(14)		(14)	(13)
Employee benefit obligations	(165)		(165)	(406)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	17		17	8
Net (Gain) Loss	1,112		1,112	1,068
Prior Service Cost, Estimated			3
Net (Gain) Loss, Estimated	57		57
Georgia Power [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	213		213	223
Employee benefit obligations	(493)		(493)	(496)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	6		6	8
Net (Gain) Loss	207		207	215
Prior Service Cost, Estimated			1
Net (Gain) Loss, Estimated	8		8
Gulf Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	512		512	427
Other deferred charges and assets	21		21	37
Other current liabilities	(31)		(31)	(29)
Employee benefit obligations	(96)		(96)	(129)
Other regulatory liabilities, deferred	(47)		(47)	(47)
Accumulated OCI	1		1	0
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	320		320	296
Gulf Power [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	153		153	142
Other current liabilities	(1)		(1)	(1)
Employee benefit obligations	(25)		(25)	(59)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	3		3	2
Net (Gain) Loss	150		150	140
Prior Service Cost, Estimated			1
Net (Gain) Loss, Estimated	7		7
Gulf Power [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	11		11	10
Other current liabilities	(1)		(1)	(1)
Employee benefit obligations	(64)		(64)	(63)
Other regulatory liabilities, deferred	(4)		(4)	(5)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net (Gain) Loss	(7)		(7)	(5)
Mississippi Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	518		518	525
Other deferred charges and assets	56		56	61
Other current liabilities	(19)		(19)	(41)
Employee benefit obligations	(115)		(115)	(153)
Other regulatory liabilities, deferred	(84)		(84)	(79)
Accumulated OCI	(4)		(4)	(6)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	737		737	667
Mississippi Power [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	154		154	144
Other current liabilities	(3)		(3)	(3)
Employee benefit obligations	(32)		(32)	(67)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	3		3	2
Net (Gain) Loss	151		151	142
Prior Service Cost, Estimated			1
Net (Gain) Loss, Estimated	7		7
Mississippi Power [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	21		21	21
Employee benefit obligations	(74)		(74)	(74)
Other regulatory liabilities, deferred	(2)		(2)	(3)
Predecessor [Member] | Southern Company Gas [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred				670
Other deferred charges and assets				153
Other current liabilities				(162)
Employee benefit obligations				(515)
Other regulatory liabilities, deferred				(53)
Accumulated OCI				(186)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets				(987)
Predecessor [Member] | Southern Company Gas [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred				88
Other deferred charges and assets				78
Other current liabilities				(4)
Employee benefit obligations				(294)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				(4)
Net (Gain) Loss				374
Prior Service Cost, Estimated		$ (1)		(2)	$ (2)
Predecessor [Member] | Southern Company Gas [Member] | Pension plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				(4)
Net (Gain) Loss				286
Predecessor [Member] | Southern Company Gas [Member] | Pension plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				0
Net (Gain) Loss				88
Predecessor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred				30
Employee benefit obligations				(219)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				(15)
Net (Gain) Loss				81
Prior Service Cost, Estimated		$ 1		3	$ 3
Predecessor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				0
Net (Gain) Loss				36
Predecessor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost				(15)
Net (Gain) Loss				$ 45
Successor [Member] | Southern Company Gas [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	973		973
Other deferred charges and assets	170		170
Other current liabilities	(108)		(108)
Employee benefit obligations	(441)		(441)
Other regulatory liabilities, deferred	(51)		(51)
Accumulated OCI	26		26
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	(715)		(715)
Successor [Member] | Southern Company Gas [Member] | Pension plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	267		267
Other deferred charges and assets	58		58
Other current liabilities	(2)		(2)
Employee benefit obligations	(206)		(206)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(2)		(2)
Net (Gain) Loss	226		226
Prior Service Cost, Estimated	0
Successor [Member] | Southern Company Gas [Member] | Pension plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	0		0
Net (Gain) Loss	(43)		(43)
Successor [Member] | Southern Company Gas [Member] | Pension plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(2)		(2)
Net (Gain) Loss	269		269
Prior Service Cost, Estimated			1
Net (Gain) Loss, Estimated	(21)		(21)
Successor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	52		52
Employee benefit obligations	(203)		(203)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(12)		(12)
Net (Gain) Loss	61		61
Prior Service Cost, Estimated	0
Successor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	0		0
Net (Gain) Loss	(3)		(3)
Successor [Member] | Southern Company Gas [Member] | Other postretirement benefit plans | Regulatory Assets
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(12)		(12)
Net (Gain) Loss	$ 64		$ 64