Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Activities:
Consolidated Net Income	$ 665	$ 501
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	823	639
Deferred income taxes	161	(4)
Allowance for equity funds used during construction	(57)	(53)
Stock based compensation expense	61	58
Estimated loss on Kemper IGCC	108	53
Mark-to-market adjustments	(81)	(2)
Other, net	(11)	(6)
Changes in certain current assets and liabilities —
-Receivables	312	235
-Prepayments	(111)	(65)
-Natural gas for sale, net of temporary LIFO liquidation	411	0
-Other current assets	(31)	(7)
-Accounts payable	(533)	(72)
-Accrued taxes	(212)	(57)
-Accrued compensation	(438)	(332)
-Retail fuel cost over recovery	(122)	25
-Other current liabilities	(48)	(35)
Net cash provided from operating activities	897	878
Investing Activities:
Business acquisitions, net of cash acquired	(1,020)	(114)
Property additions	(1,488)	(1,872)
Investment in restricted cash	(13)	(289)
Distribution of restricted cash	26	292
Nuclear decommissioning trust fund purchases	(224)	(316)
Nuclear decommissioning trust fund sales	218	311
Cost of removal, net of salvage	(61)	(52)
Change in construction payables, net	(170)	(94)
Investment in unconsolidated subsidiaries	(81)	0
Payments pursuant to LTSAs	(55)	(49)
Other investing activities	65	(14)
Net cash used for investing activities	(2,803)	(2,197)
Financing Activities:
Decrease in notes payable, net	573	294
Proceeds —
Long-term debt	1,409	1,997
Common stock	186	270
Short-term borrowings	4	0
Redemptions and repurchases —
Long-term debt	(608)	(888)
Short-term borrowings	0	(475)
Distributions to noncontrolling interests	(18)	(4)
Capital contributions from noncontrolling interests	71	131
Purchase of membership interests from noncontrolling interests	0	(129)
Payment of common stock dividends	(556)	(497)
Other financing activities	(36)	(30)
Net cash provided from financing activities	1,025	669
Net Change in Cash and Cash Equivalents	(881)	(650)
Cash and Cash Equivalents at Beginning of Period	1,975	1,404
Cash and Cash Equivalents at End of Period	1,094	754
Cash paid (received) during the period for —
Interest	461	224
Income taxes, net	(6)	(141)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	578	731
Alabama Power [Member]
Operating Activities:
Consolidated Net Income	178	160
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	219	211
Deferred income taxes	59	68
Allowance for equity funds used during construction	(8)	(10)
Other, net	(3)	(14)
Changes in certain current assets and liabilities —
-Receivables	30	191
-Fossil fuel stock	10	(27)
-Other current assets	(87)	(87)
-Accounts payable	(214)	(143)
-Accrued taxes	77	66
-Accrued compensation	(96)	(75)
-Retail fuel cost over recovery	(36)	(1)
-Other current liabilities	(9)	(8)
Net cash provided from operating activities	128	341
Investing Activities:
Property additions	(306)	(313)
Nuclear decommissioning trust fund purchases	(63)	(105)
Nuclear decommissioning trust fund sales	63	105
Cost of removal, net of salvage	(26)	(31)
Change in construction payables, net	5	(15)
Other investing activities	(2)	(9)
Net cash used for investing activities	(329)	(368)
Proceeds —
Senior notes	550	400
Capital contributions from parent company	314	236
Other long-term debt	0	45
Redemptions and repurchases —
Redemptions and repurchases — Senior notes	(200)	(200)
Payment of common stock dividends	(179)	(191)
Other financing activities	(8)	(13)
Net cash provided from financing activities	477	277
Net Change in Cash and Cash Equivalents	276	250
Cash and Cash Equivalents at Beginning of Period	420	194
Cash and Cash Equivalents at End of Period	696	444
Cash paid (received) during the period for —
Interest	84	76
Income taxes, net	0	(162)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	90	106
Georgia Power [Member]
Operating Activities:
Consolidated Net Income	264	273
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	271	261
Deferred income taxes	71	55
Allowance for equity funds used during construction	(13)	(14)
Deferred expenses	38	38
Pension, postretirement, and other employee benefits	(21)	(10)
Settlement of asset retirement obligations	(22)	(24)
Other, net	(29)	27
Changes in certain current assets and liabilities —
-Receivables	142	155
-Fossil fuel stock	(38)	36
-Prepaid income taxes	5	38
-Other current assets	(16)	12
-Accounts payable	(155)	4
-Accrued taxes	(235)	(235)
-Accrued compensation	(87)	(66)
-Retail fuel cost over recovery	(66)	14
-Other current liabilities	2	2
Net cash provided from operating activities	111	566
Investing Activities:
Property additions	(556)	(553)
Nuclear decommissioning trust fund purchases	(161)	(211)
Nuclear decommissioning trust fund sales	155	206
Cost of removal, net of salvage	(17)	(15)
Change in construction payables, net of joint owner portion	(36)	(101)
Payments pursuant to LTSAs	(22)	(11)
Sale of property	63	0
Other investing activities	8	(4)
Net cash used for investing activities	(566)	(689)
Financing Activities:
Decrease in notes payable, net	(391)	(158)
Proceeds —
Senior notes	850	650
Capital contributions from parent company	345	218
Redemptions and repurchases —
Pollution control revenue bonds	0	(4)
Redemptions and repurchases — Senior notes	0	(250)
Payment of common stock dividends	(320)	(326)
Other financing activities	(11)	(14)
Net cash provided from financing activities	473	116
Net Change in Cash and Cash Equivalents	18	(7)
Cash and Cash Equivalents at Beginning of Period	3	67
Cash and Cash Equivalents at End of Period	21	60
Cash paid (received) during the period for —
Interest	88	86
Income taxes, net	(5)	(88)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	320	290
Gulf Power [Member]
Operating Activities:
Consolidated Net Income	20	31
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	20	40
Deferred income taxes	5	9
Loss on Plant Scherer Unit 3	33	0
Other, net	(2)	(1)
Changes in certain current assets and liabilities —
-Receivables	(1)	35
-Fossil fuel stock	12	15
-Other current assets	6	2
-Accrued taxes	(4)	13
-Accrued compensation	(23)	(18)
-Over recovered regulatory clause revenues	(18)	1
-Other current liabilities	2	5
Net cash provided from operating activities	50	132
Investing Activities:
Property additions	(46)	(32)
Cost of removal, net of salvage	(2)	(2)
Change in construction payables, net	(7)	(6)
Other investing activities	(2)	(2)
Net cash used for investing activities	(57)	(42)
Financing Activities:
Decrease in notes payable, net	(168)	(85)
Proceeds —
Capital contributions from parent company	4	1
Common stock	175	0
Redemptions and repurchases —
Payment of common stock dividends	(31)	(30)
Other financing activities	3	(2)
Net cash provided from financing activities	(17)	(116)
Net Change in Cash and Cash Equivalents	(24)	(26)
Cash and Cash Equivalents at Beginning of Period	56	74
Cash and Cash Equivalents at End of Period	32	48
Cash paid (received) during the period for —
Interest	2	3
Income taxes, net	0	(25)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	26	15
Mississippi Power [Member]
Operating Activities:
Consolidated Net Income	(20)	11
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	49	39
Deferred income taxes	(47)	(4)
Allowance for equity funds used during construction	(35)	(29)
Estimated loss on Kemper IGCC	108	53
Other, net	(3)	(4)
Changes in certain current assets and liabilities —
-Other current assets	18	43
-Accounts payable	(35)	(22)
-Accrued taxes	(46)	(60)
-Accrued compensation	(22)	(16)
-Over recovered regulatory clause revenues	(12)	9
-Customer liability associated with Kemper refunds	0	(51)
-Other current liabilities	5	8
Net cash provided from operating activities	(40)	(23)
Investing Activities:
Property additions	(186)	(197)
Change in construction payables, net	0	(7)
Payments pursuant to LTSAs	1	(5)
Other investing activities	(5)	(5)
Net cash used for investing activities	(190)	(214)
Financing Activities:
Decrease in notes payable, net	9	0
Proceeds —
Short-term borrowings	4	0
Long-term debt to parent company	0	200
Other long-term debt	0	900
Redemptions and repurchases —
Short-term borrowings	0	(475)
Other long-term debt	0	(425)
Other financing activities	(1)	(2)
Net cash provided from financing activities	12	198
Net Change in Cash and Cash Equivalents	(218)	(39)
Cash and Cash Equivalents at Beginning of Period	224	98
Cash and Cash Equivalents at End of Period	6	59
Cash paid (received) during the period for —
Interest	13	12
Income taxes, net	0	(24)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	78	97
Southern Power [Member]
Operating Activities:
Consolidated Net Income	66	51
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	127	75
Deferred income taxes	36	(132)
Amortization of investment tax credits	(14)	(7)
Deferred revenues	(27)	(26)
Other, net	5	9
Changes in certain current assets and liabilities —
-Receivables	(7)	(3)
-Prepaid income taxes	(21)	(31)
-Other current assets	(6)	1
-Accounts payable	(38)	(12)
-Accrued taxes	(40)	(37)
-Other current liabilities	15	2
Net cash provided from operating activities	96	(110)
Investing Activities:
Business acquisitions, net of cash acquired	(1,020)	(114)
Property additions	(69)	(767)
Investment in restricted cash	(13)	(289)
Distribution of restricted cash	26	292
Change in construction payables, net	(125)	31
Payments pursuant to LTSAs	(31)	(25)
Other investing activities	(3)	(1)
Net cash used for investing activities	(1,235)	(873)
Financing Activities:
Decrease in notes payable, net	171	276
Redemptions and repurchases —
Distributions to noncontrolling interests	(18)	(4)
Capital contributions from noncontrolling interests	71	131
Purchase of membership interests from noncontrolling interests	0	(129)
Payment of common stock dividends	(79)	(68)
Other financing activities	(12)	0
Net cash provided from financing activities	133	206
Net Change in Cash and Cash Equivalents	(1,006)	(777)
Cash and Cash Equivalents at Beginning of Period	1,099	830
Cash and Cash Equivalents at End of Period	93	53
Cash paid (received) during the period for —
Interest	28	15
Income taxes, net	(1)	188
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	53	262
Southern Company Gas [Member]
Operating Activities:
Consolidated Net Income	239
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	120
Deferred income taxes	46
Pension, postretirement, and other employee benefits	(6)
Stock based compensation expense	11
Mark-to-market adjustments	(82)
Other, net	21
Changes in certain current assets and liabilities —
-Receivables	117
-Natural gas for sale, net of temporary LIFO liquidation	411
-Prepaid income taxes	24
-Other current assets	19
-Accounts payable	(216)
-Accrued taxes	19
-Accrued compensation	(14)
-Other current liabilities	49
Net cash provided from operating activities	758
Investing Activities:
Property additions	(301)
Cost of removal, net of salvage	(11)
Change in construction payables, net	(12)
Investment in unconsolidated subsidiaries	(81)
Other investing activities	0
Net cash used for investing activities	(405)
Financing Activities:
Decrease in notes payable, net	(234)
Redemptions and repurchases — First mortgage bonds	0
Redemptions and repurchases —
Distributions to noncontrolling interests	0
Payment of common stock dividends	(111)
Other financing activities	1
Net cash provided from financing activities	(344)
Net Change in Cash and Cash Equivalents	9
Cash and Cash Equivalents at Beginning of Period	19
Cash and Cash Equivalents at End of Period	28
Cash paid (received) during the period for —
Interest	41
Income taxes, net	0
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	$ 53
Predecessor [Member] | Southern Company Gas [Member]
Operating Activities:
Consolidated Net Income		193
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total		102
Deferred income taxes		14
Pension, postretirement, and other employee benefits		1
Stock based compensation expense		5
Mark-to-market adjustments		5
Other, net		(11)
Changes in certain current assets and liabilities —
-Receivables		34
-Natural gas for sale, net of temporary LIFO liquidation		363
-Prepaid income taxes		151
-Other current assets		27
-Accounts payable		(64)
-Accrued taxes		84
-Accrued compensation		(46)
-Other current liabilities		(17)
Net cash provided from operating activities		841
Investing Activities:
Property additions		(222)
Cost of removal, net of salvage		(15)
Change in construction payables, net		2
Investment in unconsolidated subsidiaries		(5)
Other investing activities		2
Net cash used for investing activities		(238)
Financing Activities:
Decrease in notes payable, net		(453)
Redemptions and repurchases — First mortgage bonds		(75)
Redemptions and repurchases —
Distributions to noncontrolling interests		(19)
Payment of common stock dividends		(64)
Other financing activities		9
Net cash provided from financing activities		(602)
Net Change in Cash and Cash Equivalents		1
Cash and Cash Equivalents at Beginning of Period		19
Cash and Cash Equivalents at End of Period		20
Cash paid (received) during the period for —
Interest		53
Income taxes, net		(132)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period		$ 51