Income Taxes - Current and Deferred Income Tax Provisions (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
Federal -
Current			$ 1,184	$ (177)	$ 175
Deferred			(342)	1,266	695
Total federal taxes			842	1,089	870
State -
Current			(108)	(33)	93
Deferred			217	138	14
Total state taxes			109	105	107
Income taxes			951	1,194	977
Deferred income tax assets	$ 9,495		9,495	6,683
Alabama Power [Member]
Federal -
Current			103	110	198
Deferred			339	320	225
Total federal taxes			442	430	423
State -
Current			20	8	44
Deferred			69	68	45
Total state taxes			89	76	89
Income taxes			531	506	512
Deferred income tax assets	1,544		1,544	1,511
Georgia Power [Member]
Federal -
Current			391	515	295
Deferred			319	176	366
Total federal taxes			710	691	661
State -
Current			6	81	82
Deferred			64	(3)	(14)
Total state taxes			70	78	68
Income taxes			780	769	729
Deferred income tax assets	2,382		2,382	2,077
Gulf Power [Member]
Federal -
Current			34	(3)	23
Deferred			45	80	52
Total federal taxes			79	77	75
State -
Current			0	5	0
Deferred			12	10	13
Total state taxes			12	15	13
Income taxes			91	92	88
Deferred income tax assets	244		244	216
Mississippi Power [Member]
Federal -
Current			(31)	(768)	(431)
Deferred			(60)	704	183
Total federal taxes			(91)	(64)	(248)
State -
Current			(6)	(81)	1
Deferred			(7)	73	(38)
Total state taxes			(13)	(8)	(37)
Income taxes			(104)	(72)	(285)
Deferred income tax assets	1,024		1,024	1,400
Southern Power [Member]
Federal -
Current			928	12	179
Deferred			(1,098)	10	(166)
Total federal taxes			(170)	22	13
State -
Current			(60)	(32)	(14)
Deferred			35	31	(2)
Total state taxes			(25)	(1)	(16)
Income taxes			(195)	21	(3)
Deferred income tax assets	2,937		2,937	794
Southern Power [Member] | Unrealized Tax Credits [Member]
State -
Deferred income tax assets	1,685		1,685	551
Southern Power [Member] | Deferred Charges Related To Income Taxes, Current [Member] | Other Noncurrent Assets [Member] | Unrealized Tax Credits [Member]
State -
Deferred income tax assets	1,130		1,130	246	305
Successor [Member] | Southern Company Gas [Member]
Federal -
Current	0
Deferred	65
Total federal taxes	65
State -
Current	(16)
Deferred	27
Total state taxes	11
Income taxes	76
Deferred income tax assets	$ 598		$ 598
Predecessor [Member] | Southern Company Gas [Member]
Federal -
Current		$ 67		(13)	111
Deferred		8		198	184
Total federal taxes		75		185	295
State -
Current		12		10	38
Deferred		0		18	17
Total state taxes		12		28	55
Income taxes		$ 87		213	$ 350
Deferred income tax assets				$ 438