SOUTHERN Co GAS (GAS) 10-Q 3 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2017shares
Document Information [Line Items]
Entity Registrant Name	SOUTHERN CO
Entity Central Index Key	92,122
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	994,598,783
Alabama Power [Member]
Document Information [Line Items]
Entity Registrant Name	ALABAMA POWER CO
Entity Central Index Key	3,153
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	30,537,500
Georgia Power [Member]
Document Information [Line Items]
Entity Registrant Name	GEORGIA POWER CO
Entity Central Index Key	41,091
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	9,261,500
Gulf Power [Member]
Document Information [Line Items]
Entity Registrant Name	GULF POWER CO
Entity Central Index Key	44,545
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	7,392,717
Mississippi Power [Member]
Document Information [Line Items]
Entity Registrant Name	MISSISSIPPI POWER CO
Entity Central Index Key	66,904
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	1,121,000
Southern Power [Member]
Document Information [Line Items]
Entity Registrant Name	SOUTHERN POWER CO
Entity Central Index Key	1,160,661
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	1,000
Southern Company Gas [Member]
Document Information [Line Items]
Entity Registrant Name	SOUTHERN Co GAS
Entity Central Index Key	1,004,155
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	100

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Revenues:
Retail electric revenues	$ 3,394	$ 3,377
Wholesale electric revenues	531	396
Other electric revenues	175	181
Natural gas revenues	1,530	0
Other revenues	141	38
Total operating revenues	5,771	3,992
Operating Expenses:
Fuel	996	911
Purchased power	179	165
Cost of natural gas	719	0
Cost of other sales	88	19
Other operations and maintenance	1,329	1,107
Depreciation and amortization	716	541
Taxes other than income taxes	330	256
Estimated loss on Kemper IGCC	108	53
Total operating expenses	4,465	3,052
Operating Income	1,306	940
Other Income and (Expense):
Allowance for equity funds used during construction	57	53
Earnings from equity method investments	39	0
Interest expense, net of amounts capitalized	(416)	(246)
Other income (expense), net	(6)	(29)
Total other income and (expense)	(326)	(222)
Earnings Before Income Taxes	980	718
Income taxes	315	217
Consolidated Net Income	665	501
Dividends on preferred and preference stock of subsidiaries	11	11
Net income (loss) attributable to noncontrolling interests	(4)	1
Consolidated Net Income Attributable to Southern Company	$ 658	$ 489
Earnings per share (EPS) —
Basic EPS (in dollars per share)	$ 0.66	$ 0.53
Diluted EPS (in dollars per share)	$ 0.66	$ 0.53
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	993	916
Diluted (in shares)	1,000	922
Cash dividends paid per share of common stock (in dollars per share)	$ 0.5600	$ 0.5425
Alabama Power [Member]
Operating Revenues:
Retail electric revenues	$ 1,227	$ 1,193
Wholesale revenues, non-affiliates	66	63
Wholesale revenues, affiliates	33	22
Other revenues	56	53
Total operating revenues	1,382	1,331
Operating Expenses:
Fuel	298	268
Purchased power, non-affiliates	34	36
Purchased power, affiliates	28	33
Other operations and maintenance	369	392
Depreciation and amortization	181	172
Taxes other than income taxes	96	97
Total operating expenses	1,006	998
Operating Income	376	333
Other Income and (Expense):
Allowance for equity funds used during construction	8	10
Interest expense, net of amounts capitalized	(75)	(73)
Other income (expense), net	(5)	(8)
Total other income and (expense)	(72)	(71)
Earnings Before Income Taxes	304	262
Income taxes	126	102
Consolidated Net Income	178	160
Dividends on preferred and preference stock of subsidiaries	4	4
Consolidated Net Income Attributable to Southern Company	174	156
Georgia Power [Member]
Operating Revenues:
Retail electric revenues	1,689	1,717
Wholesale revenues, non-affiliates	39	41
Wholesale revenues, affiliates	8	5
Other revenues	96	109
Total operating revenues	1,832	1,872
Operating Expenses:
Fuel	371	376
Purchased power, non-affiliates	88	83
Purchased power, affiliates	172	139
Other operations and maintenance	381	457
Depreciation and amortization	221	211
Taxes other than income taxes	98	97
Total operating expenses	1,331	1,363
Operating Income	501	509
Other Income and (Expense):
Allowance for equity funds used during construction	13	14
Interest expense, net of amounts capitalized	(101)	(94)
Other income (expense), net	20	17
Total other income and (expense)	(81)	(77)
Earnings Before Income Taxes	420	432
Income taxes	156	159
Consolidated Net Income	264	273
Dividends on preferred and preference stock of subsidiaries	4	4
Consolidated Net Income Attributable to Southern Company	260	269
Gulf Power [Member]
Operating Revenues:
Retail electric revenues	279	283
Wholesale revenues, non-affiliates	17	16
Wholesale revenues, affiliates	37	21
Other revenues	17	15
Total operating revenues	350	335
Operating Expenses:
Fuel	108	94
Purchased power, non-affiliates	32	30
Purchased power, affiliates	2	2
Other operations and maintenance	84	77
Depreciation and amortization	18	38
Taxes other than income taxes	27	29
Loss on Plant Scherer Unit 3	33	0
Total operating expenses	304	270
Operating Income	46	65
Other Income and (Expense):
Interest expense, net of amounts capitalized	(12)	(13)
Other income (expense), net	0	(1)
Total other income and (expense)	(12)	(14)
Earnings Before Income Taxes	34	51
Income taxes	14	20
Consolidated Net Income	20	31
Dividends on preferred and preference stock of subsidiaries	2	2
Consolidated Net Income Attributable to Southern Company	18	29
Mississippi Power [Member]
Operating Revenues:
Retail electric revenues	200	183
Wholesale revenues, non-affiliates	62	60
Wholesale revenues, affiliates	5	9
Other revenues	5	5
Total operating revenues	272	257
Operating Expenses:
Fuel	78	76
Purchased power, non-affiliates	1	0
Purchased power, affiliates	7	5
Other operations and maintenance	74	69
Depreciation and amortization	40	38
Taxes other than income taxes	26	26
Estimated loss on Kemper IGCC	108	53
Total operating expenses	334	267
Operating Income	(62)	(10)
Other Income and (Expense):
Allowance for equity funds used during construction	35	29
Interest expense, net of amounts capitalized	(19)	(16)
Other income (expense), net	(1)	(2)
Total other income and (expense)	15	11
Earnings Before Income Taxes	(47)	1
Income taxes	(27)	(10)
Consolidated Net Income	(20)	11
Dividends on preferred and preference stock of subsidiaries	0	0
Consolidated Net Income Attributable to Southern Company	(20)	11
Southern Power [Member]
Operating Revenues:
Wholesale revenues, non-affiliates	347	215
Wholesale revenues, affiliates	100	97
Other revenues	3	3
Total operating revenues	450	315
Operating Expenses:
Fuel	132	91
Purchased power, non-affiliates	25	13
Purchased power, affiliates	5	6
Other operations and maintenance	92	79
Depreciation and amortization	119	73
Taxes other than income taxes	12	6
Total operating expenses	385	268
Operating Income	65	47
Other Income and (Expense):
Interest expense, net of amounts capitalized	(50)	(21)
Other income (expense), net	(1)	2
Total other income and (expense)	(51)	(19)
Earnings Before Income Taxes	14	28
Income taxes	(52)	(23)
Consolidated Net Income	66	51
Net income (loss) attributable to noncontrolling interests	(4)	1
Consolidated Net Income Attributable to Southern Company	70	50
Southern Company Gas [Member]
Operating Revenues:
Natural gas revenues	1,530
Other revenues	30
Total operating revenues	1,560
Operating Expenses:
Cost of natural gas	719
Cost of other sales	7
Other operations and maintenance	253
Depreciation and amortization	120
Merger-related expenses	0
Taxes other than income taxes	70
Total operating expenses	1,169
Operating Income	391
Other Income and (Expense):
Earnings from equity method investments	39
Interest expense, net of amounts capitalized	(46)
Other income (expense), net	5
Total other income and (expense)	(2)
Earnings Before Income Taxes	389
Income taxes	150
Consolidated Net Income	239
Net income (loss) attributable to noncontrolling interests	0
Consolidated Net Income Attributable to Southern Company	$ 239
Predecessor [Member] | Southern Company Gas [Member]
Operating Revenues:
Natural gas revenues		1,302
Other revenues		32
Total operating revenues		1,334
Operating Expenses:
Cost of natural gas		571
Cost of other sales		7
Other operations and maintenance		241
Depreciation and amortization		102
Merger-related expenses		3
Taxes other than income taxes		62
Total operating expenses		986
Operating Income		348
Other Income and (Expense):
Earnings from equity method investments		1
Interest expense, net of amounts capitalized		(48)
Other income (expense), net		3
Total other income and (expense)		(44)
Earnings Before Income Taxes		304
Income taxes		111
Consolidated Net Income		193
Net income (loss) attributable to noncontrolling interests		11
Consolidated Net Income Attributable to Southern Company		$ 182

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Income (Unaudited) - Parenthetical - Southern Company Gas [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Excise taxes collected	$ 48
Predecessor [Member]
Excise taxes collected		$ 40

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Consolidated Net Income	$ 665	$ 501
Qualifying hedges:
Changes in fair value, net of tax	(9)	(117)
Reclassification adjustment for amounts included in net income, net of tax	(1)	2
Pension and other post retirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	1	1
Total other comprehensive income (loss)	(9)	(114)
Dividends on preferred and preference stock of subsidiaries	11	11
Comprehensive income (loss) attributable to noncontrolling interests	(4)	1
Consolidated Comprehensive Income Attributable to Southern Company	649	375
Alabama Power [Member]
Consolidated Net Income	178	160
Qualifying hedges:
Changes in fair value, net of tax	0	(2)
Reclassification adjustment for amounts included in net income, net of tax	1	1
Pension and other post retirement benefit plans:
Total other comprehensive income (loss)	1	(1)
Dividends on preferred and preference stock of subsidiaries	4	4
Consolidated Comprehensive Income Attributable to Southern Company	179	159
Georgia Power [Member]
Consolidated Net Income	264	273
Qualifying hedges:
Changes in fair value, net of tax	0	0
Reclassification adjustment for amounts included in net income, net of tax	1	1
Pension and other post retirement benefit plans:
Total other comprehensive income (loss)	1	1
Dividends on preferred and preference stock of subsidiaries	4	4
Consolidated Comprehensive Income Attributable to Southern Company	265	274
Gulf Power [Member]
Consolidated Net Income	20	31
Qualifying hedges:
Changes in fair value, net of tax	(1)	(3)
Pension and other post retirement benefit plans:
Total other comprehensive income (loss)	(1)	(3)
Dividends on preferred and preference stock of subsidiaries	2	2
Consolidated Comprehensive Income Attributable to Southern Company	19	28
Mississippi Power [Member]
Consolidated Net Income	(20)	11
Qualifying hedges:
Changes in fair value, net of tax	1	0
Pension and other post retirement benefit plans:
Total other comprehensive income (loss)	1	0
Dividends on preferred and preference stock of subsidiaries	0	0
Consolidated Comprehensive Income Attributable to Southern Company	(19)	11
Southern Power [Member]
Consolidated Net Income	66	51
Qualifying hedges:
Changes in fair value, net of tax	(8)	0
Reclassification adjustment for amounts included in net income, net of tax	(4)	1
Pension and other post retirement benefit plans:
Total other comprehensive income (loss)	(12)	1
Comprehensive income (loss) attributable to noncontrolling interests	(4)	1
Consolidated Comprehensive Income Attributable to Southern Company	58	51
Southern Company Gas [Member]
Consolidated Net Income	239
Qualifying hedges:
Changes in fair value, net of tax	(1)
Reclassification adjustment for amounts included in net income, net of tax	0
Pension and other post retirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	(1)
Total other comprehensive income (loss)	(2)
Comprehensive income (loss) attributable to noncontrolling interests	0
Consolidated Comprehensive Income Attributable to Southern Company	$ 237
Predecessor [Member] | Southern Company Gas [Member]
Consolidated Net Income		193
Qualifying hedges:
Changes in fair value, net of tax		(29)
Reclassification adjustment for amounts included in net income, net of tax		(1)
Pension and other post retirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax		3
Total other comprehensive income (loss)		(27)
Comprehensive income (loss) attributable to noncontrolling interests		11
Consolidated Comprehensive Income Attributable to Southern Company		$ 155

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in fair value, tax	$ (5,000,000)	$ (72,000,000)
Reclassification adjustment for qualified hedges, tax	(1,000,000)	1,000,000
Reclassification adjustment for pension and other post retirement benefit plans, tax	0	1,000,000
Alabama Power [Member]
Changes in fair value, tax	0	(1,000,000)
Reclassification adjustment for qualified hedges, tax	1,000,000	1,000,000
Georgia Power [Member]
Changes in fair value, tax	0	0
Reclassification adjustment for qualified hedges, tax	0	0
Gulf Power [Member]
Changes in fair value, tax	0	(2,000,000)
Mississippi Power [Member]
Changes in fair value, tax	0	0
Southern Power [Member]
Changes in fair value, tax	(4,000,000)	0
Reclassification adjustment for qualified hedges, tax	(3,000,000)	0
Southern Company Gas [Member]
Changes in fair value, tax	(1,000,000)
Reclassification adjustment for qualified hedges, tax	0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ (1,000,000)
Predecessor [Member] | Southern Company Gas [Member]
Changes in fair value, tax		(16,000,000)
Reclassification adjustment for qualified hedges, tax		0
Reclassification adjustment for pension and other post retirement benefit plans, tax		$ 2,000,000

Condensed Consolidated Stateme6

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

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net cash paid for capitalized interest	$ 25	$ 30
Alabama Power [Member]
Net cash paid for capitalized interest	3	4
Georgia Power [Member]
Net cash paid for capitalized interest	5	5
Gulf Power [Member]
Net cash paid for capitalized interest	0	0
Mississippi Power [Member]
Interest paid	25	22
Net cash paid for capitalized interest	12	10
Southern Power [Member]
Net cash paid for capitalized interest	2	10
Southern Company Gas [Member]
Net cash paid for capitalized interest	$ 3
Predecessor [Member] | Southern Company Gas [Member]
Net cash paid for capitalized interest		$ 1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 1,094	$ 1,975
Receivables —
Customer accounts receivable	1,560	1,565
Energy marketing receivable	493	623
Unbilled revenues	589	706
Under recovered regulatory clause revenues	47	18
Income taxes receivable, current	544	544
Other accounts and notes receivable	433	377
Accumulated provision for uncollectible accounts	(53)	(43)
Fossil fuel for generation	687	689
Materials and supplies	1,477	1,462
Natural gas for sale	346	631
Prepaid expenses	401	364
Other regulatory assets, current	560	581
Other current assets	249	230
Total current assets	8,427	9,722
Property, Plant, and Equipment:
In service	99,774	98,416
Less: Accumulated depreciation	30,330	29,852
Plant in service, net of depreciation	69,444	68,564
Nuclear fuel, at amortized cost	902	905
Construction work in progress	9,465	8,977
Total property, plant, and equipment	79,811	78,446
Other Property and Investments:
Goodwill	6,251	6,251
Equity investments in unconsolidated subsidiaries	1,615	1,549
Other intangible assets, net of amortization	935	970
Nuclear decommissioning trusts, at fair value	1,678	1,606
Leveraged leases	780	774
Miscellaneous property and investments	293	270
Total other property and investments	11,552	11,420
Deferred Charges and Other Assets:
Deferred charges related to income taxes	1,647	1,629
Unamortized loss on reacquired debt	218	223
Other regulatory assets, deferred	6,748	6,851
Other deferred charges and assets	1,357	1,406
Total deferred charges and other assets	9,970	10,109
Total Assets	109,760	109,697
Current Liabilities:
Securities due within one year	3,269	2,587
Notes payable	2,818	2,241
Energy marketing trade payables	471	597
Accounts payable —
Accounts payable	1,750	2,228
Customer deposits	541	558
Accrued taxes —
Accrued income taxes	258	193
Other accrued taxes	326	667
Unrecognized tax benefits	400	385
Accrued interest	453	518
Accrued compensation	461	915
Asset retirement obligations, current	386	378
Liabilities from risk management activities, net of collateral	63	107
Acquisitions payable	0	489
Other regulatory liabilities, current	221	236
Other current liabilities	867	818
Total current liabilities	12,284	12,917
Long-term Debt:
Long-term Debt	42,786	42,629
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	14,307	14,092
Deferred credits related to income taxes	215	219
Accumulated deferred investment tax credits	2,264	2,228
Employee benefit obligations	2,234	2,299
Asset retirement obligations, deferred	4,170	4,136
Accrued environmental remediation	388	397
Other cost of removal obligations	2,724	2,748
Other regulatory liabilities, deferred	237	258
Other deferred credits and liabilities	873	880
Total deferred credits and other liabilities	27,412	27,257
Total Liabilities	82,482	82,803
Redeemable Preferred Stock of Subsidiaries	118	118
Redeemable Noncontrolling Interests	164	164
Common Stockholders' Equity:
Par value	4,973	4,952
Paid-in capital	9,884	9,661
Treasury, at cost	(33)	(31)
Retained earnings (accumulated deficit)	10,459	10,356
Accumulated other comprehensive loss	(189)	(180)
Total Common Stockholders' Equity	25,094	24,758
Preferred and Preference Stock of Subsidiaries	609	609
Noncontrolling Interests	1,293	1,245
Total Stockholders' Equity	26,996	26,612
Total Liabilities and Stockholders' Equity	109,760	109,697
Alabama Power [Member]
Current Assets:
Cash and cash equivalents	696	420
Receivables —
Customer accounts receivable	326	348
Unbilled revenues	127	146
Other accounts and notes receivable	31	27
Affiliated	35	40
Accumulated provision for uncollectible accounts	(10)	(10)
Fossil fuel for generation	195	205
Materials and supplies	444	435
Prepaid expenses	106	34
Other regulatory assets, current	141	149
Other current assets	8	11
Total current assets	2,099	1,805
Property, Plant, and Equipment:
In service	26,134	26,031
Less: Accumulated depreciation	9,241	9,112
Plant in service, net of depreciation	16,893	16,919
Nuclear fuel, at amortized cost	332	336
Construction work in progress	642	491
Total property, plant, and equipment	17,867	17,746
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	65	66
Nuclear decommissioning trusts, at fair value	825	792
Miscellaneous property and investments	113	112
Total other property and investments	1,003	970
Deferred Charges and Other Assets:
Deferred charges related to income taxes	526	525
Deferred under recovered regulatory clause revenues	0	150
Other regulatory assets, deferred	1,218	1,157
Other deferred charges and assets	156	163
Total deferred charges and other assets	1,900	1,995
Total Assets	22,869	22,516
Current Liabilities:
Securities due within one year	361	561
Accounts payable —
Affiliated	224	297
Other	232	433
Customer deposits	90	88
Accrued taxes —
Accrued income taxes	95	45
Other accrued taxes	65	42
Accrued interest	65	78
Accrued compensation	95	193
Other regulatory liabilities, current	45	85
Other current liabilities	71	76
Total current liabilities	1,343	1,898
Long-term Debt:
Long-term Debt	7,081	6,535
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	4,714	4,654
Deferred credits related to income taxes	65	65
Accumulated deferred investment tax credits	108	110
Employee benefit obligations	288	300
Asset retirement obligations, deferred	1,523	1,503
Other cost of removal obligations	667	684
Other regulatory liabilities, deferred	88	100
Other deferred credits and liabilities	70	63
Total deferred credits and other liabilities	7,523	7,479
Total Liabilities	15,947	15,912
Redeemable Preferred Stock	85	85
Preference Stock	196	196
Common Stockholders' Equity:
Par value	1,222	1,222
Paid-in capital	2,936	2,613
Retained earnings (accumulated deficit)	2,513	2,518
Accumulated other comprehensive loss	(30)	(30)
Total Common Stockholders' Equity	6,641	6,323
Total Liabilities and Stockholders' Equity	22,869	22,516
Georgia Power [Member]
Current Assets:
Cash and cash equivalents	21	3
Receivables —
Customer accounts receivable	470	523
Unbilled revenues	200	224
Joint owner accounts receivable	146	57
Other accounts and notes receivable	57	81
Affiliated	12	18
Accumulated provision for uncollectible accounts	(3)	(3)
Fossil fuel for generation	336	298
Materials and supplies	474	479
Prepaid expenses	35	105
Other regulatory assets, current	195	193
Other current assets	38	38
Total current assets	1,981	2,016
Property, Plant, and Equipment:
In service	34,059	33,841
Less: Accumulated depreciation	11,443	11,317
Plant in service, net of depreciation	22,616	22,524
Nuclear fuel, at amortized cost	570	569
Construction work in progress	5,183	4,939
Total property, plant, and equipment	28,369	28,032
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	58	60
Nuclear decommissioning trusts, at fair value	853	814
Miscellaneous property and investments	46	46
Total other property and investments	957	920
Deferred Charges and Other Assets:
Deferred charges related to income taxes	676	676
Other regulatory assets, deferred	2,792	2,774
Other deferred charges and assets	473	417
Total deferred charges and other assets	3,941	3,867
Total Assets	35,248	34,835
Current Liabilities:
Securities due within one year	488	460
Notes payable	0	391
Accounts payable —
Affiliated	347	438
Other	657	589
Customer deposits	268	265
Accrued taxes —
Accrued income taxes	56	17
Other accrued taxes	115	390
Accrued interest	115	106
Accrued compensation	110	224
Asset retirement obligations, current	305	299
Other current liabilities	241	297
Total current liabilities	2,702	3,476
Long-term Debt:
Long-term Debt	11,042	10,225
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	6,073	6,000
Deferred credits related to income taxes	119	121
Accumulated deferred investment tax credits	253	256
Employee benefit obligations	673	703
Asset retirement obligations, deferred	2,256	2,233
Other deferred credits and liabilities	214	199
Total deferred credits and other liabilities	9,588	9,512
Total Liabilities	23,332	23,213
Redeemable Preferred Stock	45	45
Preference Stock	221	221
Common Stockholders' Equity:
Par value	398	398
Paid-in capital	7,238	6,885
Retained earnings (accumulated deficit)	4,026	4,086
Accumulated other comprehensive loss	(12)	(13)
Total Common Stockholders' Equity	11,650	11,356
Total Liabilities and Stockholders' Equity	35,248	34,835
Gulf Power [Member]
Current Assets:
Cash and cash equivalents	32	56
Receivables —
Customer accounts receivable	58	72
Unbilled revenues	52	55
Under recovered regulatory clause revenues	47	17
Other accounts and notes receivable	9	6
Affiliated	28	17
Accumulated provision for uncollectible accounts	(1)	(1)
Fossil fuel for generation	59	71
Materials and supplies	56	55
Other regulatory assets, current	50	44
Other current assets	22	30
Total current assets	412	422
Property, Plant, and Equipment:
In service	5,110	5,140
Less: Accumulated depreciation	1,401	1,382
Plant in service, net of depreciation	3,709	3,758
Construction work in progress	67	51
Total property, plant, and equipment	3,776	3,809
Deferred Charges and Other Assets:
Deferred charges related to income taxes	57	58
Other regulatory assets, deferred	501	512
Other deferred charges and assets	21	21
Total deferred charges and other assets	579	591
Total Assets	4,767	4,822
Current Liabilities:
Securities due within one year	92	87
Notes payable	100	268
Accounts payable —
Affiliated	47	59
Other	47	54
Customer deposits	35	35
Accrued taxes —
Other accrued taxes	16	20
Accrued interest	18	8
Accrued compensation	17	40
Deferred capacity expense, current	22	22
Asset retirement obligations, current	32	16
Other regulatory liabilities, current	5	16
Other current liabilities	30	24
Total current liabilities	461	649
Long-term Debt:
Long-term Debt	987	987
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	952	948
Employee benefit obligations	94	96
Deferred capacity expense	114	119
Asset retirement obligations, deferred	106	120
Other cost of removal obligations	226	249
Other regulatory liabilities, deferred	48	47
Other deferred credits and liabilities	78	71
Total deferred credits and other liabilities	1,618	1,650
Total Liabilities	3,066	3,286
Preference Stock	147	147
Common Stockholders' Equity:
Par value	678	503
Paid-in capital	594	589
Retained earnings (accumulated deficit)	282	296
Accumulated other comprehensive loss	0	1
Total Common Stockholders' Equity	1,554	1,389
Total Liabilities and Stockholders' Equity	4,767	4,822
Mississippi Power [Member]
Current Assets:
Cash and cash equivalents	6	224
Receivables —
Customer accounts receivable	26	29
Unbilled revenues	38	42
Income taxes receivable, current	544	544
Other accounts and notes receivable	17	14
Affiliated	14	15
Fossil fuel for generation	83	100
Materials and supplies	78	76
Other regulatory assets, current	113	115
Other current assets	3	8
Total current assets	922	1,167
Property, Plant, and Equipment:
In service	4,963	4,865
Less: Accumulated depreciation	1,303	1,289
Plant in service, net of depreciation	3,660	3,576
Construction work in progress	2,570	2,545
Total property, plant, and equipment	6,230	6,121
Other Property and Investments:
Total other property and investments	12	12
Deferred Charges and Other Assets:
Deferred charges related to income taxes	382	361
Other regulatory assets, deferred	520	518
Other deferred charges and assets	22	56
Total deferred charges and other assets	924	935
Total Assets	8,088	8,235
Current Liabilities:
Securities due within one year - parent	0	551
Securities due within one year	1,328	78
Notes payable	36	23
Accounts payable —
Affiliated	44	62
Other	112	135
Customer deposits	16	16
Accrued taxes —
Other accrued taxes	51	99
Unrecognized tax benefits	385	383
Accrued interest	50	46
Accrued compensation	20	42
Asset retirement obligations, current	27	32
Over recovered regulatory clause liabilities	39	51
Other current liabilities	22	20
Total current liabilities	2,130	1,538
Long-term Debt:
Long-term debt to parent	551	0
Long-term debt, non-affiliated	1,172	2,424
Long-term Debt	1,723	2,424
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	729	756
Employee benefit obligations	113	115
Asset retirement obligations, deferred	148	146
Other cost of removal obligations	172	170
Other regulatory liabilities, deferred	78	84
Other deferred credits and liabilities	36	26
Total deferred credits and other liabilities	1,276	1,297
Total Liabilities	5,129	5,259
Redeemable Preferred Stock	33	33
Common Stockholders' Equity:
Par value	38	38
Paid-in capital	3,526	3,525
Retained earnings (accumulated deficit)	(635)	(616)
Accumulated other comprehensive loss	(3)	(4)
Total Common Stockholders' Equity	2,926	2,943
Total Liabilities and Stockholders' Equity	8,088	8,235
Southern Power [Member]
Current Assets:
Cash and cash equivalents	93	1,099
Receivables —
Customer accounts receivable	111	102
Other accounts and notes receivable	32	34
Affiliated	62	57
Fossil fuel for generation	14	15
Materials and supplies	343	337
Prepaid income taxes	95	74
Other current assets	31	39
Total current assets	781	1,757
Property, Plant, and Equipment:
In service	13,493	12,728
Less: Accumulated depreciation	1,598	1,484
Plant in service, net of depreciation	11,895	11,244
Construction work in progress	328	398
Total property, plant, and equipment	12,223	11,642
Other Property and Investments:
Goodwill	2	2
Intangible assets, net (including goodwill)	430	436
Total other property and investments	430	436
Deferred Charges and Other Assets:
Prepaid LTSAs	120	101
Accumulated deferred income taxes	570	594
Other deferred charges and assets — affiliated	26	13
Other deferred charges and assets	531	626
Total deferred charges and other assets	1,247	1,334
Total Assets	14,681	15,169
Current Liabilities:
Securities due within one year	560	560
Notes payable	380	209
Accounts payable —
Affiliated	76	88
Other	129	278
Accrued taxes —
Accrued income taxes	48	148
Other accrued taxes	13	7
Accrued interest	47	36
Acquisitions payable	0	461
Contingent consideration	14	46
Other current liabilities	69	70
Total current liabilities	1,336	1,903
Long-term Debt:
Long-term Debt	5,088	5,068
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	157	152
Accumulated deferred investment tax credits	1,879	1,839
Asset retirement obligations, deferred	67	64
Other deferred credits and liabilities	288	304
Total deferred credits and other liabilities	2,391	2,359
Total Liabilities	8,815	9,330
Redeemable Noncontrolling Interests	164	164
Common Stockholders' Equity:
Par value	0	0
Paid-in capital	3,671	3,671
Retained earnings (accumulated deficit)	714	724
Accumulated other comprehensive loss	24	35
Total Common Stockholders' Equity	4,409	4,430
Noncontrolling interests	1,293	1,245
Total Stockholders' Equity	5,702	5,675
Total Liabilities and Stockholders' Equity	14,681	15,169
Southern Company Gas [Member]
Current Assets:
Cash and cash equivalents	28	19
Receivables —
Customer accounts receivable	453	364
Energy marketing receivable	493	623
Unbilled revenues	173	239
Other accounts and notes receivable	69	76
Accumulated provision for uncollectible accounts	(37)	(27)
Materials and supplies	25	26
Natural gas for sale	346	631
Prepaid expenses	54	55
Assets from risk management activities, net of collateral	138	128
Prepaid income taxes	0	24
Other regulatory assets, current	60	81
Other current assets	16	11
Total current assets	1,818	2,250
Property, Plant, and Equipment:
In service	14,660	14,508
Less: Accumulated depreciation	4,498	4,439
Plant in service, net of depreciation	10,162	10,069
Construction work in progress	625	496
Total property, plant, and equipment	10,787	10,565
Other Property and Investments:
Goodwill	5,967	5,967
Equity investments in unconsolidated subsidiaries	1,604	1,541
Other intangible assets, net of amortization	340	366
Miscellaneous property and investments	21	21
Total other property and investments	7,932	7,895
Deferred Charges and Other Assets:
Other regulatory assets, deferred	958	973
Other deferred charges and assets	188	170
Total deferred charges and other assets	1,146	1,143
Total Assets	21,683	21,853
Current Liabilities:
Securities due within one year	22	22
Notes payable	1,023	1,257
Energy marketing trade payables	471	597
Accounts payable —
Accounts payable	241	348
Customer deposits	131	153
Accrued taxes —
Accrued income taxes	50	26
Other accrued taxes	63	68
Accrued interest	59	48
Accrued compensation	43	58
Liabilities from risk management activities, net of collateral	18	62
Other regulatory liabilities, current	148	102
Accrued environmental remediation, current	66	69
Temporary LIFO liquidation	126	0
Other current liabilities	124	108
Total current liabilities	2,585	2,918
Long-term Debt:
Long-term Debt	5,246	5,259
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,059	1,975
Employee benefit obligations	434	441
Accrued environmental remediation	343	357
Other cost of removal obligations	1,630	1,616
Other regulatory liabilities, deferred	54	51
Other deferred credits and liabilities	88	127
Total deferred credits and other liabilities	4,608	4,567
Total Liabilities	12,439	12,744
Common Stockholders' Equity:
Par value	0	0
Paid-in capital	9,104	9,095
Retained earnings (accumulated deficit)	116	(12)
Accumulated other comprehensive loss	24	26
Total Stockholders' Equity	9,244	9,109
Total Liabilities and Stockholders' Equity	$ 21,683	$ 21,853

Condensed Consolidated Balance9

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Other intangible assets, accumulated amortization	$ 97,000,000	$ 62,000,000
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, shares issued (in shares)	995,000,000	991,000,000
Treasury shares at cost (in shares)	900,000	800,000
Alabama Power [Member]
Common stock, par value (in dollars per share)	$ 40	$ 40
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares outstanding (in shares)	30,537,500	30,537,500
Georgia Power [Member]
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	9,261,500	9,261,500
Gulf Power [Member]
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	7,392,717	5,642,717
Mississippi Power [Member]
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	1,130,000	1,130,000
Common stock, shares outstanding (in shares)	1,121,000	1,121,000
Southern Power [Member]
Other intangible assets, accumulated amortization	$ 28,000,000	$ 22,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares outstanding (in shares)	1,000	1,000
Southern Company Gas [Member]
Other intangible assets, accumulated amortization	$ 60,000,000	$ 34,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares outstanding (in shares)	100	100

Introduction

Introduction	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
INTRODUCTION	INTRODUCTION The condensed quarterly financial statements of each registrant included herein have been prepared by such registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets as of December 31, 2016 have been derived from the audited financial statements of each registrant. In the opinion of each registrant's management, the information regarding such registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended March 31, 2017 and 2016 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each registrant believes that the disclosures regarding such registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Southern Company's financial statements reflect its investments in its subsidiaries, including Southern Company Gas as a result of the Merger, on a consolidated basis. Southern Company Gas' results of operations and cash flows for the three months ended March 31, 2017 and financial condition as of March 31, 2017 and December 31, 2016 are reflected within Southern Company's consolidated amounts in these accompanying notes herein. The equity method is used for entities in which Southern Company has significant influence but does not control, including Southern Company Gas' investment in SNG, and for variable interest entities where Southern Company has an equity investment but is not the primary beneficiary. See Note (I) under " Southern Company – Merger with Southern Company Gas " for additional information regarding the Merger. Pursuant to the Merger, Southern Company pushed down the application of the acquisition method of accounting to the consolidated financial statements of Southern Company Gas such that the assets and liabilities are recorded at their respective fair values, and goodwill has been established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the consolidated financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout Southern Company Gas' condensed consolidated financial statements and the accompanying notes herein, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor." Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the results of operations, financial position, or cash flows of any registrant. Recently Issued Accounting Standards In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers , replacing the existing accounting standard and industry specific guidance for revenue recognition with a five-step model for recognizing and measuring revenue from contracts with customers. The underlying principle of the standard is to recognize revenue to depict the transfer of goods or services to customers at the amount expected to be collected. The new standard also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers. While the registrants expect most of their revenue to be included in the scope of ASC 606, they have not fully completed the evaluation of all revenue arrangements. The majority of Southern Company's, the traditional electric operating companies', and Southern Company Gas' revenue, including energy provided to customers, is from tariff offerings that provide electricity or natural gas without a defined contractual term. For such arrangements, the registrants expect that the revenue from contracts with these customers will continue to be equivalent to the electricity or natural gas supplied and billed in that period (including unbilled revenues) and the adoption of ASC 606 will not result in a significant shift in the timing of revenue recognition for such sales. The registrants' ongoing evaluation of other revenue streams and related contracts includes longer term contractual commitments and unregulated sales to customers. Some revenue arrangements, such as certain PPAs and alternative revenue programs, are excluded from the scope of ASC 606 and, therefore, will be accounted for and presented separately from revenues under ASC 606 on the registrants' financial statements. In addition, the power and utilities industry is currently addressing other specific industry issues, including the applicability of ASC 606 to contributions in aid of construction (CIAC). Although final implementation guidance has not been issued, Southern Company, the traditional electric operating companies, and Southern Company Gas expect CIAC to be out of the scope of ASC 606. Given Southern Power's core activities of selling generation capacity and energy to high credit rated customers, Southern Power currently does not expect the new standard to have a significant impact to net income. The new standard is effective for interim and annual reporting periods beginning after December 15, 2017. The registrants must select a transition method to be applied either retrospectively to each prior reporting period presented or retrospectively with a cumulative effect adjustment to retained earnings at the date of initial adoption. As the ultimate impact of the new standard has not yet been determined, the registrants have not elected a transition method. On January 26, 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 removes the requirement to compare the implied fair value of goodwill with the carrying amount as part of Step 2 of the goodwill impairment test. Under the new standard, the goodwill impairment loss will be measured as the excess of a reporting unit's carrying amount over its fair value, not exceeding the total amount of goodwill allocated to that reporting unit, which may increase the frequency of goodwill impairment charges if a future goodwill impairment test does not pass the Step 1 evaluation. ASU 2017-04 is effective prospectively for annual and interim periods beginning on or after December 15, 2019, and early adoption is permitted on testing dates after January 1, 2017. On March 10, 2017, the FASB issued ASU No. 2017-07, Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (ASU 2017-07). ASU 2017-07 requires that an employer report the service cost component in the same line item or items as other compensation costs and requires the other components of net periodic pension and postretirement benefit costs to be separately presented in the income statement outside income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. However, all cost components remain eligible for capitalization under FERC regulations. ASU 2017-07 will be applied retrospectively for the presentation of the service cost component and the other components of net periodic pension and postretirement benefit costs in the income statement. The capitalization of the service cost component of net periodic pension and postretirement benefit costs in assets will be applied on a prospective basis. ASU 2017-07 is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. Southern Company, the traditional electric operating companies, and Southern Company Gas are currently evaluating the new standard. The presentation changes required for net periodic pension and postretirement benefit costs will result in a decrease in Southern Company's , the traditional electric operating companies', and Southern Company Gas' operating income and an increase in other income for 2016 and 2017 and are expected to result in a decrease in operating income and an increase in other income for 2018. The adoption of ASU 2017-07 is not expected to have a material impact on Southern Company's , the traditional electric operating companies', or Southern Company Gas' financial statements. Affiliate Transactions Prior to the completion of Southern Company Gas' acquisition of its 50% equity interest in SNG, SCS (as agent for Alabama Power, Georgia Power, and Southern Power) and Southern Company Gas had entered into long-term interstate natural gas transportation agreements with SNG. The interstate transportation service provided to Alabama Power, Georgia Power, Southern Power, and Southern Company Gas by SNG pursuant to these agreements is governed by the terms and conditions of SNG's natural gas tariff and is subject to FERC regulation. For the three months ended March 31, 2017, transportation costs under these agreements for Alabama Power, Georgia Power, Southern Power, and Southern Company Gas were approximately $1 million , $26 million , $6 million , and $9 million , respectively. SCS, as agent for Southern Power, has agreements with certain subsidiaries of Southern Company Gas to purchase natural gas. For the three months ended March 31, 2017, natural gas purchases made by Southern Power from Southern Company Gas' subsidiaries were approximately $23 million . Goodwill and Other Intangible Assets As of March 31, 2017 and December 31, 2016, goodwill was as follows: Goodwill (in millions) Southern Company $ 6,251 Southern Power $ 2 Southern Company Gas Gas distribution operations $ 4,702 Gas marketing services 1,265 Southern Company Gas total $ 5,967 Goodwill is not amortized, but is subject to an annual impairment test during the fourth quarter of each year, or more frequently if impairment indicators arise. Other intangible assets were as follows: As of March 31, 2017 As of December 31, 2016 Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 268 $ (44 ) $ 224 $ 268 $ (32 ) $ 236 Trade names 158 (8 ) 150 158 (5 ) 153 Patents 4 — 4 4 — 4 Backlog 5 (1 ) 4 5 (1 ) 4 Storage and transportation contracts 64 (15 ) 49 64 (2 ) 62 Software and other 2 (1 ) 1 2 — 2 PPA fair value adjustments 456 (28 ) 428 456 (22 ) 434 Total other intangible assets subject to amortization $ 957 $ (97 ) $ 860 $ 957 $ (62 ) $ 895 Other intangible assets not subject to amortization: Federal Communications Commission licenses $ 75 $ — $ 75 $ 75 $ — $ 75 Total other intangible assets $ 1,032 $ (97 ) $ 935 $ 1,032 $ (62 ) $ 970 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (28 ) $ 428 $ 456 $ (22 ) $ 434 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 221 $ (41 ) $ 180 $ 221 $ (30 ) $ 191 Trade names 115 (4 ) 111 115 (2 ) 113 Wholesale gas services Storage and transportation contracts 64 (15 ) 49 64 (2 ) 62 Total other intangible assets subject to amortization $ 400 $ (60 ) $ 340 $ 400 $ (34 ) $ 366 Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2017 (in millions) Southern Company $ 35 Southern Power $ 6 Southern Company Gas $ 26 See Note 12 to the financial statements of Southern Company under "Southern Power" and Note 2 to the financial statements of Southern Power in Item 8 of the Form 10-K for additional information regarding Southern Power's PPA fair value adjustments related to its business acquisitions. Also see Note (I) under " Southern Company – Acquisition of PowerSecure " and " – Merger with Southern Company Gas " for additional information. Property Damage Reserve See Note 1 to the financial statements of Gulf Power under "Property Damage Reserve" in Item 8 of the Form 10-K for additional information. Gulf Power's cost of repairing damages from major storms and other uninsured property damages, including uninsured damages to transmission and distribution facilities, generation facilities, and other property is charged to Gulf Power's property damage reserve. In accordance with a settlement agreement approved by the Florida PSC on April 4, 2017 (2017 Rate Case Settlement Agreement), Gulf Power suspended further property damage reserve accruals effective April 2017. Gulf Power may make discretionary accruals, but is required to resume accruals of $3.5 million annually if the reserve balance falls below zero . In addition, Gulf Power may initiate a storm surcharge to recover costs associated with any tropical systems named by the National Hurricane Center or other catastrophic storm events that reduce the property damage reserve in the aggregate by approximately $31 million ( 75% of the April 1, 2017 balance) or more. The storm surcharge would begin, on an interim basis, 60 days following the filing of a cost recovery petition, would be limited to $4.00 /month for a 1,000 KWH residential customer unless Gulf Power incurs in excess of $100 million in qualified storm recovery costs in a calendar year, and would replenish the storm reserve to approximately $40 million . See Note (B) under " Regulatory Matters – Gulf Power – Retail Base Rate Cases " for additional details regarding the 2017 Rate Case Settlement Agreement. Natural Gas for Sale Southern Company Gas' natural gas distribution utilities, with the exception of Nicor Gas, carry natural gas inventory on a WACOG basis. Nicor Gas' natural gas inventory is carried at cost on a LIFO basis. Inventory decrements occurring during the year that are restored prior to year end are charged to cost of natural gas at the estimated annual replacement cost. Inventory decrements that are not restored prior to year end are charged to cost of natural gas at the actual LIFO cost of the inventory layers liquidated. Southern Company Gas' inventory decrement at March 31, 2017 is expected to be restored prior to year end. The cost of natural gas, including inventory costs, is recovered from customers under a purchased gas recovery mechanism adjusted for differences between actual costs and amounts billed; therefore, LIFO liquidations have no impact on Southern Company's or Southern Company Gas' net income. Natural gas inventories for Southern Company Gas' non-utility businesses are carried at the lower of weighted average cost or current market price, with cost determined on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Southern Company Gas recorded no LOCOM adjustment in the successor first quarter 2017 and recorded a $3 million LOCOM adjustment in the predecessor first quarter 2016 .

Contingencies and Regulatory Ma

Contingencies and Regulatory Matters	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
CONTINGENCIES AND REGULATORY MATTERS	CONTINGENCIES AND REGULATORY MATTERS See Note 3 to the financial statements of the registrants in Item 8 of the Form 10-K for information relating to various lawsuits, other contingencies, and regulatory matters. General Litigation Matters Each registrant is subject to certain claims and legal actions arising in the ordinary course of business. In addition, the business activities of Southern Company's subsidiaries are subject to extensive governmental regulation related to public health and the environment, such as regulation of air emissions and water discharges. Litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental requirements such as air quality and water standards, has occurred throughout the U.S. This litigation has included claims for damages alleged to have been caused by CO 2 and other emissions, CCR, and alleged exposure to hazardous materials, and/or requests for injunctive relief in connection with such matters. The ultimate outcome of such pending or potential litigation against each registrant and any subsidiaries cannot be predicted at this time; however, for current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on such registrant's financial statements. Southern Company On January 20, 2017, a purported securities class action complaint was filed against Southern Company, certain of its officers, and certain of Mississippi Power's former officers in the U.S. District Court for the Northern District of Georgia, Atlanta Division, by Monroe County Employees' Retirement System on behalf of all persons who purchased shares of Southern Company's common stock between April 25, 2012 and October 29, 2013. The complaint alleges that Southern Company, certain of its officers, and certain of Mississippi Power's former officers made materially false and misleading statements regarding the Kemper IGCC in violation of certain provisions under the Securities Exchange Act of 1934, as amended. The complaint seeks, among other things, compensatory damages and litigation costs and attorneys' fees. Southern Company believes this legal challenge has no merit; however, an adverse outcome in this proceeding could have an impact on Southern Company's results of operations, financial condition, and liquidity. Southern Company will vigorously defend itself in this matter, and the ultimate outcome of this matter cannot be determined at this time. On February 27, 2017, Jean Vineyard filed a shareholder derivative lawsuit in the U.S. District Court for the Northern District of Georgia that names as defendants Southern Company, certain of its directors, certain of its officers, and certain of Mississippi Power's former officers. The complaint alleges that the defendants caused Southern Company to make false or misleading statements regarding the Kemper IGCC cost and schedule. Further, the complaint alleges that the defendants were unjustly enriched and caused the waste of corporate assets. The plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and, on her own behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiff also seeks certain changes to Southern Company's corporate governance and internal processes. On March 27, 2017, the court deferred this lawsuit until 30 days after certain further action in the purported securities class action complaint discussed above. Southern Company believes that this legal challenge has no merit; however, an adverse outcome in this proceeding could have an impact on Southern Company's results of operations, financial condition, and liquidity. Southern Company will vigorously defend itself in this matter, and the ultimate outcome of this matter cannot be determined at this time. Georgia Power In 2011, plaintiffs filed a putative class action against Georgia Power in the Superior Court of Fulton County, Georgia alleging that Georgia Power's collection in rates of municipal franchise fees (all of which are remitted to municipalities) exceeded the amounts allowed in orders of the Georgia PSC and alleging certain state tort law claims. In November 2016, the Georgia Court of Appeals reversed the trial court's previous dismissal of the case and remanded the case to the trial court for further proceedings. Georgia Power has filed a petition for writ of certiorari with the Georgia Supreme Court. Georgia Power believes the plaintiffs' claims have no merit and intends to vigorously defend itself in this matter. The ultimate outcome of this matter cannot be determined at this time. Southern Company Gas Nicor Gas and Nicor Energy Services Company, wholly-owned subsidiaries of Southern Company Gas, and Nicor Inc. were defendants in a putative class action initially filed in 2011 in state court in Cook County, Illinois. The plaintiffs purported to represent a class of the customers who purchased the Gas Line Comfort Guard product from Nicor Energy Services Company and variously alleged that the marketing, sale, and billing of the Gas Line Comfort Guard product violated the Illinois Consumer Fraud and Deceptive Business Practices Act, constituting common law fraud and resulting in unjust enrichment of these entities. The plaintiffs sought, on behalf of the classes they purported to represent, actual and punitive damages, interest, costs, attorney fees, and injunctive relief. On February 8, 2017, the judge denied the plaintiffs' motion for class certification and Southern Company Gas' motion for summary judgment. On March 7, 2017, the parties reached a settlement, which was finalized and effective on April 3, 2017. The settlement did not have a material impact on Southern Company's or Southern Company Gas' financial statements. Environmental Remediation The Southern Company system must comply with environmental laws and regulations that cover the handling and disposal of waste and releases of hazardous substances. Under these various laws and regulations, the Southern Company system could incur substantial costs to clean up affected sites. The traditional electric operating companies and the natural gas distribution utilities in Illinois, New Jersey, Georgia, and Florida have each received authority from their respective state PSCs or other applicable state regulatory agencies to recover approved environmental compliance costs through regulatory mechanisms. These regulatory mechanisms are adjusted annually or as necessary within limits approved by the state PSCs or other applicable state regulatory agencies. Georgia Power's environmental remediation liability as of March 31, 2017 was $13 million . Georgia Power has been designated or identified as a potentially responsible party at sites governed by the Georgia Hazardous Site Response Act and/or by the federal Comprehensive Environmental Response, Compensation, and Liability Act, and assessment and potential cleanup of such sites is expected. Gulf Power's environmental remediation liability includes estimated costs of environmental remediation projects of approximately $52 million as of March 31, 2017 . These estimated costs primarily relate to site closure criteria by the Florida Department of Environmental Protection (FDEP) for potential impacts to soil and groundwater from herbicide applications at Gulf Power's substations. The schedule for completion of the remediation projects is subject to FDEP approval. The projects have been approved by the Florida PSC for recovery through Gulf Power's environmental cost recovery clause; therefore, these liabilities have no impact on net income. Southern Company Gas' environmental remediation liability as of March 31, 2017 was $409 million based on the estimated cost of environmental investigation and remediation associated with known current and former manufactured gas plant operating sites. These environmental remediation expenditures are recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies of the natural gas distribution utilities, with the exception of one site representing $5 million of the total accrued remediation costs. The final outcome of these matters cannot be determined at this time. However, the final disposition of these matters is not expected to have a material impact on the financial statements of Southern Company, Georgia Power, Gulf Power, or Southern Company Gas. FERC Matters Municipal and Rural Associations Tariff See Note 3 to the financial statements of Mississippi Power under "FERC Matters" in Item 8 of the Form 10-K for additional information regarding a settlement agreement entered into by Mississippi Power regarding the establishment of a regulatory asset for Kemper IGCC-related costs. See " Integrated Coal Gasification Combined Cycle " herein for additional information regarding Mississippi Power's construction of the Kemper IGCC. In March 2016, Mississippi Power reached a settlement agreement with its wholesale customers, which was subsequently approved by the FERC, for an increase in wholesale base revenues under the MRA cost-based electric tariff, primarily as a result of placing scrubbers for Plant Daniel Units 1 and 2 in service in 2015. The settlement agreement became effective for services rendered beginning May 1, 2016, resulting in an estimated annual revenue increase of $7 million under the MRA cost-based electric tariff. Additionally, under the settlement agreement, the tariff customers agreed to similar regulatory treatment for MRA tariff ratemaking as the treatment approved for retail ratemaking through an order issued by the Mississippi PSC in December 2015 (In-Service Asset Rate Order). This regulatory treatment primarily includes (i) recovery of the Kemper IGCC assets currently operational and providing service to customers and other related costs, (ii) amortization of the Kemper IGCC-related regulatory assets included in rates under the settlement agreement over the 36 months ending April 30, 2019, (iii) Kemper IGCC-related expenses included in rates under the settlement agreement no longer being deferred and charged to expense, and (iv) removing all of the Kemper IGCC CWIP from rate base with a corresponding increase in accrual of AFUDC. The additional resulting AFUDC is estimated to be approximately $18 million until the end of May 2017 when the Kemper IGCC is projected to be placed in service. Fuel Cost Recovery Mississippi Power has a wholesale MRA and a Market Based (MB) fuel cost recovery factor. At March 31, 2017 , the amount of over-recovered wholesale MRA fuel costs included in the balance sheets was $12 million compared to $13 million at December 31, 2016 . At March 31, 2017 and December 31, 2016 , the amount of over-recovered wholesale MB fuel costs included in the balance sheets was $1 million . See Note 3 to the financial statements of Mississippi Power under "FERC Matters – Fuel Cost Recovery" in Item 8 of the Form 10-K for additional information. Market-Based Rate Authority The traditional electric operating companies and Southern Power have authority from the FERC to sell electricity at market-based rates. Since 2008, that authority, for certain balancing authority areas, has been conditioned on compliance with the requirements of an energy auction, which the FERC found to be tailored mitigation that addresses potential market power concerns. In accordance with FERC regulations governing such authority, the traditional electric operating companies and Southern Power filed a triennial market power analysis in 2014, which included continued reliance on the energy auction as tailored mitigation. In 2015, the FERC issued an order finding that the traditional electric operating companies' and Southern Power's existing tailored mitigation may not effectively mitigate the potential to exert market power in certain areas served by the traditional electric operating companies and in some adjacent areas. The FERC directed the traditional electric operating companies and Southern Power to show why market-based rate authority should not be revoked in these areas or to provide a mitigation plan to further address market power concerns. The traditional electric operating companies and Southern Power filed a request for rehearing and filed their response with the FERC in 2015. In December 2016, the traditional electric operating companies and Southern Power filed an amendment to their market-based rate tariff that proposed certain changes to the energy auction, as well as several non-tariff changes. On February 2, 2017, the FERC issued an order accepting all such changes subject to an additional condition of cost-based price caps for certain sales outside of the energy auction, finding that all of these changes would provide adequate alternative mitigation for the traditional electric operating companies' and Southern Power's potential to exert market power in certain areas served by the traditional electric operating companies and in some adjacent areas. On February 23, 2017, the traditional electric operating companies and Southern Power accepted the terms of the order in a compliance filing. While the FERC's February 2, 2017 order references the market power proceeding discussed above, it remains a separate, ongoing matter. The ultimate outcome of these matters cannot be determined at this time. Regulatory Matters Alabama Power See Note 3 to the financial statements of Southern Company and Alabama Power under "Regulatory Matters – Alabama Power" and "Retail Regulatory Matters," respectively, in Item 8 of the Form 10-K for additional information regarding Alabama Power's recovery of retail costs through various regulatory clauses and accounting orders. The balance of each regulatory clause recovery on the balance sheet follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, 2016 (in millions) Rate CNP Compliance (*) Deferred under recovered regulatory clause revenues $ — $ 9 Rate CNP PPA Over recovered regulatory clause revenues 3 — Deferred under recovered regulatory clause revenues — 142 Retail Energy Cost Recovery Other regulatory liabilities, current 40 76 Natural Disaster Reserve Other regulatory liabilities, deferred 66 69 (*) In accordance with an accounting order issued on February 17, 2017 by the Alabama PSC, Alabama Power reclassified the $23 million under recovered balance for Rate CNP Compliance to a deferred regulatory asset account. Georgia Power Rate Plans See Note 3 to the financial statements of Southern Company and Georgia Power under "Regulatory Matters – Georgia Power – Rate Plans" and "Retail Regulatory Matters – Rate Plans," respectively, in Item 8 of the Form 10-K for additional information. Georgia Power's revenues from regulated retail operations are collected through various rate mechanisms subject to the oversight of the Georgia PSC. Georgia Power currently recovers its costs from the regulated retail business through the 2013 ARP, which includes traditional base tariff rates, Demand-Side Management tariffs, Environmental Compliance Cost Recovery tariffs, and Municipal Franchise Fee tariffs. In addition, financing costs related to the construction of Plant Vogtle Units 3 and 4 are being collected through the NCCR tariff and fuel costs are collected through a separate fuel cost recovery tariff. See " Nuclear Construction " herein and Note 3 to the financial statements of Southern Company under "Regulatory Matters – Georgia Power – Nuclear Construction" and Georgia Power under "Retail Regulatory Matters – Nuclear Construction" in Item 8 of the Form 10-K for additional information regarding the NCCR tariff. Also see " Fuel Cost Recovery " herein and Note 3 to the financial statements of Southern Company under "Regulatory Matters – Georgia Power – Fuel Cost Recovery" and Georgia Power under "Retail Regulatory Matters – Fuel Cost Recovery" in Item 8 of the Form 10-K for additional information regarding fuel cost recovery. Integrated Resource Plan See Note 3 to the financial statements of Southern Company and Georgia Power under "Regulatory Matters – Georgia Power – Integrated Resource Plan" and "Retail Regulatory Matters – Integrated Resource Plan," respectively, in Item 8 of the Form 10-K for additional information regarding Georgia Power's triennial Integrated Resource Plan. On March 7, 2017, the Georgia PSC approved Georgia Power's decision to suspend work at a future generation site in Stewart County, Georgia, due to changing economics, including load forecasts and lower fuel costs. The timing of recovery for costs of approximately $50 million incurred through March 31, 2017 will be determined by the Georgia PSC in a future base rate case. The ultimate outcome of this matter cannot be determined at this time. Fuel Cost Recovery See Note 3 to the financial statements of Southern Company and Georgia Power under "Regulatory Matters – Georgia Power – Fuel Cost Recovery" and "Retail Regulatory Matters – Fuel Cost Recovery," respectively, in Item 8 of the Form 10-K for additional information. As of March 31, 2017 and December 31, 2016 , Georgia Power's over recovered fuel balance totaled $18 million and $84 million , respectively, and is included in other current liabilities on Southern Company's and Georgia Power's condensed balance sheets. Fuel cost recovery revenues are adjusted for differences in actual recoverable fuel costs and amounts billed in current regulated rates. Accordingly, changes in the billing factor will not have a significant effect on Southern Company's or Georgia Power's revenues or net income, but will affect cash flow. Nuclear Construction See Note 3 to the financial statements of Southern Company and Georgia Power under "Regulatory Matters – Georgia Power – Nuclear Construction" and "Retail Regulatory Matters – Nuclear Construction," respectively, in Item 8 of the Form 10-K for additional information regarding Georgia Power's construction of Plant Vogtle Units 3 and 4, Vogtle Construction Monitoring (VCM) reports, the NCCR tariff, the Vogtle Construction Litigation (as defined below), and the Contractor Settlement Agreement (as defined below). Vogtle 3 and 4 Agreement and Contractor Bankruptcy In 2008, Georgia Power, acting for itself and as agent for the Vogtle Owners, entered into an agreement with the Contractor, pursuant to which the Contractor agreed to design, engineer, procure, construct, and test Plant Vogtle Units 3 and 4 (Vogtle 3 and 4 Agreement). Under the terms of the Vogtle 3 and 4 Agreement, the Vogtle Owners agreed to pay a purchase price subject to certain price escalations and adjustments, including fixed escalation amounts and index-based adjustments, as well as adjustments for change orders, and performance bonuses for early completion and unit performance. The Vogtle 3 and 4 Agreement also provides for liquidated damages upon the Contractor's failure to fulfill the schedule and certain performance guarantees, each subject to an aggregate cap of 10% of the contract price, or approximately $920 million . In addition, the Vogtle 3 and 4 Agreement provides for limited cost sharing by the Vogtle Owners for Contractor costs under certain conditions with maximum additional capital costs under this provision attributable to Georgia Power (based on Georgia Power's ownership interest) of approximately $114 million . Each Vogtle Owner is severally (and not jointly) liable for its proportionate share, based on its ownership interest, of all amounts owed to the Contractor under the Vogtle 3 and 4 Agreement. Georgia Power's proportionate share is 45.7% . In the event of a credit rating downgrade below investment grade of any Vogtle Owner, such Vogtle Owner will be required to provide a letter of credit or other credit enhancement. On December 31, 2015, Westinghouse and the Vogtle Owners entered into a definitive settlement agreement (Contractor Settlement Agreement) to resolve disputes between the Vogtle Owners and the Contractor under the Vogtle 3 and 4 Agreement, including litigation that was pending in the U.S. District Court for the Southern District of Georgia (Vogtle Construction Litigation). Among other things, the Contractor Settlement Agreement and the related amendment to the Vogtle 3 and 4 Agreement (i) revised the guaranteed substantial completion dates to June 30, 2019 for Unit 3 and June 30, 2020 for Unit 4; (ii) provided that delay liquidated damages will commence if the nuclear fuel loading date for each unit does not occur by December 31, 2018 for Unit 3 and December 31, 2019 for Unit 4; and (iii) provided that, pursuant to the amendment to the Vogtle 3 and 4 Agreement, Georgia Power, based on its ownership interest, pay to the Contractor and capitalize to the project cost approximately $350 million in settlement of disputed claims. Further, as a consequence of the settlement and Westinghouse's acquisition of WECTEC, Westinghouse engaged Fluor Enterprises, Inc. (Fluor Enterprises), a subsidiary of Fluor Corporation (Fluor), as a new construction subcontractor. Under the terms of the Vogtle 3 and 4 Agreement, the Contractor does not have a right to terminate the Vogtle 3 and 4 Agreement for convenience. The Contractor may terminate the Vogtle 3 and 4 Agreement under certain circumstances, including certain Vogtle Owner suspension or delays of work, action by a governmental authority to permanently stop work, certain breaches of the Vogtle 3 and 4 Agreement by the Vogtle Owners, Vogtle Owner insolvency, and certain other events. In the event of an abandonment of work by the Contractor, the maximum liability of the Contractor under the Vogtle 3 and 4 Agreement is increased to 40% of the contract price (approximately $1.7 billion based on Georgia Power's ownership interest). The Vogtle Owners may terminate the Vogtle 3 and 4 Agreement at any time for convenience, provided that the Vogtle Owners will be required to pay certain termination costs. In addition, the Vogtle Owners may terminate the Vogtle 3 and 4 Agreement for certain Contractor breaches, including abandonment of work by the Contractor. Under the Toshiba Guarantee, Toshiba has guaranteed certain payment obligations of the Contractor, including any liability of the Contractor for abandonment of work. However, due to Toshiba's financial situation described below, substantial risk regarding the Vogtle Owners' ability to fully collect under the Toshiba Guarantee exists. In January 2016, Westinghouse delivered to the Vogtle Owners $920 million of letters of credit from financial institutions (Westinghouse Letters of Credit) to secure a portion of the Contractor's potential obligations under the Vogtle 3 and 4 Agreement. The Westinghouse Letters of Credit are subject to annual renewals through June 30, 2020 and require 60 days' written notice to Georgia Power in the event the Westinghouse Letters of Credit will not be renewed. In the event of such notice, the Vogtle Owners would be able to draw on the entire balance of the Westinghouse Letters of Credit. The Westinghouse Letters of Credit remain in place in accordance with the terms of the Vogtle 3 and 4 Agreement. On March 29, 2017, Westinghouse and WECTEC each filed for bankruptcy protection under Chapter 11 of the U.S. Bankruptcy Code. Georgia Power, acting for itself and as agent for the Vogtle Owners, entered into an interim assessment agreement with the Contractor and WECTEC Staffing Services LLC (WECTEC Staffing), as of March 29, 2017 (Interim Assessment Agreement), to provide for a continuation of work with respect to Plant Vogtle Units 3 and 4. Georgia Power's entry into the Interim Assessment Agreement was conditioned upon South Carolina Electric & Gas Company entering into a similar interim assessment agreement with the Contractor relating to V.C. Summer, which also occurred on March 29, 2017. The provisions in the Interim Assessment Agreement became effective upon approval of the Interim Assessment Agreement by the bankruptcy court on March 30, 2017. The term of the Interim Assessment Agreement was originally scheduled to expire on April 28, 2017. On April 28, 2017, Georgia Power, acting for itself and as agent for the Vogtle Owners, entered into an amendment to the Interim Assessment Agreement with the Contractor and WECTEC Staffing solely to extend the term of the Interim Assessment Agreement through the earlier of (i) May 12, 2017 and (ii) termination of the Interim Assessment Agreement by any party upon five business days' notice (Interim Assessment Period). The Interim Assessment Agreement provides, among other items, that (i) Georgia Power will be obligated to pay, on behalf of the Vogtle Owners, all costs accrued by the Contractor for subcontractors and vendors for services performed or goods provided during the Interim Assessment Period, with these amounts to be paid to the Contractor, except for amounts accrued for Fluor, which will be paid directly to Fluor; (ii) during the Interim Assessment Period, the Contractor shall provide certain engineering, procurement, and management services for Plant Vogtle Units 3 and 4, to the same extent as contemplated by the Vogtle 3 and 4 Agreement, and Georgia Power, on behalf of the Vogtle Owners, will make payments of $5.4 million per week for these services; (iii) Georgia Power will have the right to make payments, on behalf of the Vogtle Owners, directly to subcontractors and vendors who have accounts past due with the Contractor; (iv) during the Interim Assessment Period, the Contractor will use its commercially reasonable efforts to provide information reasonably requested by Georgia Power as is necessary to continue construction and investigate the completion status of Plant Vogtle Units 3 and 4; (v) the Contractor will reject or accept the Vogtle 3 and 4 Agreement by the termination of the Interim Assessment Agreement; and (vi) during the Interim Assessment Period, Georgia Power will not exercise any remedies against Toshiba under the Toshiba Guarantee. Under the Interim Assessment Agreement, all parties expressly reserve all rights and remedies under the Vogtle 3 and 4 Agreement, all related security and collateral, under applicable law. A number of subcontractors to the Contractor, including Fluor Enterprises, have alleged non-payment by the Contractor for amounts owed for work performed on Plant Vogtle Units 3 and 4. Georgia Power, acting for itself and as agent for the Vogtle Owners, has taken, and continues to take, action to remove liens filed by these subcontractors through the posting of surety bonds. Georgia Power estimates the aggregate liability for the Vogtle Owners under the Interim Assessment Agreement and the removal of subcontractor liens to be approximately $470 million , of which Georgia Power's proportionate share would total approximately $215 million . As of March 31, 2017, $245 million of this aggregate liability had been paid or accrued. Georgia Power is evaluating remedies available to the Vogtle Owners for these payments, including draws under the Westinghouse Letters of Credit and enforcement of the Toshiba Guarantee. In February 2017, the Contractor provided Georgia Power with revised forecasted in-service dates of December 2019 and September 2020 for Plant Vogtle Units 3 and 4, respectively. However, based on information subsequently made available during Westinghouse and WECTEC's bankruptcy proceedings and pursuant to the Interim Assessment Agreement, Georgia Power and the Vogtle Owners do not believe the revised in-service dates are achievable. Georgia Power, along with the other Vogtle Owners, is undertaking a comprehensive schedule and cost-to-complete assessment, as well as a cancellation cost assessment. It is reasonably possible these assessments result in estimated incremental costs to complete, including owners' costs, that materially exceed the value of the Toshiba Guarantee. Georgia Power intends to work with the Georgia PSC and the other Vogtle Owners to determine future actions related to Plant Vogtle Units 3 and 4. Georgia Power, for itself and as agent for the other Vogtle Owners, is also negotiating a new service agreement which would, if necessary, engage the Contractor to provide design, engineering, and procurement services to Southern Nuclear, in the event Southern Nuclear assumes control over construction management. In addition, Georgia Power, on behalf of itself and the other Vogtle Owners, intends to take all actions available to it to enforce its rights related to the Vogtle 3 and 4 Agreement, including enforcing the Toshiba Guarantee, subject to the Interim Assessment Agreement, and accessing the Westinghouse Letters of Credit. On April 11, 2017, Toshiba filed its unaudited financial statements as of and for the nine months ended December 31, 2016, which reflected a negative shareholders' equity balance of $1.9 billion , with Japanese regulators. Toshiba also announced that further substantial charges may be required in the quarter ended March 31, 2017 in connection with the bankruptcy filing of Westinghouse and WECTEC and that there are material events and conditions that raise substantial doubt about Toshiba's ability to continue as a going concern. The Contractor's bankruptcy filing is expected to have a material impact on the construction cost and schedule of, as well as the cost recovery for, Plant Vogtle Units 3 and 4 and could have a material impact on Southern Company's and Georgia Power's financial statements. In addition, an inability or other failure by Toshiba to perform its obligations under the Toshiba Guarantee could have a further material impact on the net cost to the Vogtle Owners to complete construction of Plant Vogtle Units 3 and 4 and, therefore, on Southern Company's and Georgia Power's financial statements. The ultimate outcome of these matters also is dependent on the results of the assessments currently underway, as well as the related regulatory treatment, and cannot be determined at this time. Regulatory Matters In 2009, the Georgia PSC voted to certify construction of Plant Vogtle Units 3 and 4 with a certified capital cost of $4.418 billion . In addition, in 2009 the Georgia PSC approved inclusion of the Plant Vogtle Units 3 and 4 related CWIP accounts in rate base, and the State of Georgia enacted the Georgia Nuclear Energy Financing Act, which allows Georgia Power to recover financing costs for nuclear construction projects certified by the Georgia PSC. Financing costs are recovered on all applicable certified costs through annual adjustments to the NCCR tariff by including the related CWIP accounts in rate base during the construction period. On December 20, 2016, the Georgia PSC voted to approve a settlement agreement (Vogtle Cost Settlement Agreement) resolving the following prudence matters: (i) none of the $3.3 billion of costs incurred through December 31, 2015 and reflected in the fourteenth VCM report will be disallowed from rate base on the basis of imprudence; (ii) the Contractor Settlement Agreement is reasonable and prudent and none of the amounts paid or to be paid pursuant to the Contractor Settlement Agreement should be disallowed from rate base on the basis of imprudence; (iii) financing costs on verified and approved capital costs will be deemed prudent provided they are incurred prior to December 31, 2019 and December 31, 2020 for Plant Vogtle Units 3 and 4, respectively; and (iv) (a) the in-service capital cost forecast will be adjusted to $5.680 billion (Revised Forecast), which includes a contingency of $240 million above Georgia Power's then current forecast of $5.440 billion , (b) capital costs incurred up to the Revised Forecast will be presumed to be reasonable and prudent with the burden of proof on any party challenging such costs, and (c) Georgia Power would have the burden to show that any capital costs above the Revised Forecast are reasonable and prudent. Under the terms of the Vogtle Cost Settlement Agreement, the certified in-service capital cost for purposes of calculating the NCCR tariff will remain at $4.418 billion . Construction capital costs above $4.418 billion will accrue AFUDC through the date each unit is placed in service. The ROE used to calculate the NCCR tariff was reduced from 10.95% (the ROE rate setting point authorized by the Georgia PSC in the 2013 ARP) to 10.00% effective January 1, 2016. For purposes of the AFUDC calculation, the ROE on costs between $4.418 billion and $5.440 billion will also be 10.00% and the ROE on any amounts above $5.440 billio

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS As of March 31, 2017 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 274 $ 213 $ — $ — $ 487 Interest rate derivatives — 13 — — 13 Nuclear decommissioning trusts (c) 714 942 — 21 1,677 Cash equivalents 589 — — — 589 Other investments 9 — 1 — 10 Total $ 1,586 $ 1,168 $ 1 $ 21 $ 2,776 Liabilities: Energy-related derivatives (a)(b) $ 303 $ 155 $ — $ — $ 458 Interest rate derivatives — 32 — — 32 Foreign currency derivatives — 62 — — 62 Contingent consideration — — 20 — 20 Total $ 303 $ 249 $ 20 $ — $ 572 Alabama Power Assets: Energy-related derivatives $ — $ 11 $ — $ — $ 11 Nuclear decommissioning trusts: (d) Domestic equity 405 77 — — 482 Foreign equity 52 51 — — 103 U.S. Treasury and government agency securities — 28 — — 28 Corporate bonds 22 143 — — 165 Mortgage and asset backed securities — 18 — — 18 Private Equity — — — 21 21 Other — 7 — — 7 Cash equivalents 555 — — — 555 Total $ 1,034 $ 335 $ — $ 21 $ 1,390 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Georgia Power Assets: Energy-related derivatives $ — $ 24 $ — $ — $ 24 Interest rate derivatives — 2 — — 2 Nuclear decommissioning trusts: (d) (e) Domestic equity 216 1 — — 217 Foreign equity — 137 — — 137 U.S. Treasury and government agency securities — 196 — — 196 Municipal bonds — 70 — — 70 Corporate bonds — 168 — — 168 Mortgage and asset backed securities — 41 — — 41 Other 19 5 — — 24 Cash equivalents — — — — — Total $ 235 $ 644 $ — $ — $ 879 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Interest rate derivatives — 4 — — 4 Total $ — $ 17 $ — $ — $ 17 Gulf Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Cash equivalents 21 — — — 21 Total $ 21 $ 2 $ — $ — $ 23 Liabilities: Energy-related derivatives $ — $ 31 $ — $ — $ 31 Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Interest rate derivatives — 4 — — 4 Total $ — $ 7 $ — $ — $ 7 Liabilities: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Power Assets: Energy-related derivatives $ — $ 15 $ — $ — $ 15 Liabilities: Energy-related derivatives $ — $ 5 $ — $ — $ 5 Foreign currency derivatives — 62 — — 62 Contingent consideration — — 20 — 20 Total $ — $ 67 $ 20 $ — $ 87 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 274 $ 158 $ — $ — $ 432 Liabilities: Energy-related derivatives (a)(b) $ 303 $ 84 $ — $ — $ 387 (a) Excludes $19 million associated with certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $92 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. (e) Includes the investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2017 , approximately $56 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. Southern Company, Alabama Power, and Georgia Power continue to elect the option to fair value investment securities held in the nuclear decommissioning trust funds. The fair value of the funds at Southern Company, including reinvested interest and dividends and excluding the funds' expenses, increased by $63 million and $20 million for the three months ended March 31, 2017 and 2016, respectively. Alabama Power recorded an increase in fair value of $34 million and $11 million for the three months ended March 31, 2017 and 2016, respectively, as a change in regulatory liabilities related to its AROs. Georgia Power recorded an increase in fair value of $29 million and $9 million for the three months ended March 31, 2017 and 2016, respectively, as a change in its regulatory asset related to its AROs. Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (H) for additional information on how these derivatives are used. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. For fair value measurements of the investments within the nuclear decommissioning trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. See Note 1 to the financial statements of Southern Company, Alabama Power, and Georgia Power under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. Southern Power has contingent payment obligations related to certain acquisitions whereby Southern Power is obligated to pay generation-based payments to the seller over a period ranging from 10 to 30 years, beginning at the commercial operation date. The obligation is categorized as Level 3 under Fair Value Measurements as the fair value is determined using significant unobservable inputs for the forecasted facility generation in MW-hours, as well as other inputs such as a fixed dollar amount per MW-hour, and a discount rate, and is evaluated periodically. The fair value of contingent consideration reflects the net present value of expected payments and any periodic change arising from forecasted generation is expected to be immaterial. "Other investments" include investments that are not traded in the open market. The fair value of these investments have been determined based on market factors including comparable multiples and the expectations regarding cash flows and business plan executions. As of March 31, 2017 , the fair value measurements of private equity investments held in the nuclear decommissioning trust that are calculated at net asset value per share (or its equivalent) as a practical expedient, as well as the nature and risks of those investments, were as follows: As of March 31, 2017: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 21 $ 22 Not Applicable Not Applicable Alabama Power $ 21 $ 22 Not Applicable Not Applicable Private equity funds include a fund-of-funds that invests in high-quality private equity funds across several market sectors, a fund that invests in real estate assets, and a fund that acquires companies to create resale value. Private equity funds do not have redemption rights. Distributions from these funds will be received as the underlying investments in the funds are liquidated. Liquidations are expected to occur at various times over the next 10 years . As of March 31, 2017 , other financial instruments for which the carrying amount did not equal fair value were as follows: Carrying Amount Fair Value (in millions) Long-term debt, including securities due within one year: Southern Company $ 45,881 $ 46,828 Alabama Power $ 7,439 $ 7,807 Georgia Power $ 11,362 $ 11,777 Gulf Power $ 1,079 $ 1,110 Mississippi Power $ 2,977 $ 2,909 Southern Power $ 5,648 $ 5,694 Southern Company Gas $ 5,268 $ 5,487 The fair values are determined using Level 2 measurements and are based on quoted market prices for the same or similar issues or on the current rates available to Southern Company, Alabama Power, Georgia Power, Gulf Power, Mississippi Power, Southern Power, and Southern Company Gas.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY Earnings per Share For Southern Company, the only difference in computing basic and diluted earnings per share is attributable to awards outstanding under the stock option and performance share plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on the stock option and performance share plans. The effect of both stock options and performance share award units was determined using the treasury stock method. Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) As reported shares 993 916 Effect of options and performance share award units 7 6 Diluted shares 1,000 922 Stock options and performance share award units that were not included in the diluted earnings per share calculation because they were anti-dilutive were immaterial for the three months ended March 31, 2017 and 2016 . Changes in Stockholders' Equity The following table presents year-to-date changes in stockholders' equity of Southern Company: Number of Common Shares Common Preferred and Preference Stock of Subsidiaries Total Issued Treasury Noncontrolling Interests (*) (in thousands) (in millions) Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — 658 — — 658 Other comprehensive income (loss) — — (9 ) — — (9 ) Stock issued 4,240 — 186 — — 186 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (556 ) — — (556 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (18 ) (18 ) Net income attributable to noncontrolling interests — — — — (4 ) (4 ) Other — (35 ) — — (1 ) (1 ) Balance at March 31, 2017 995,453 (854 ) $ 25,094 $ 609 $ 1,293 $ 26,996 Balance at December 31, 2015 915,073 (3,352 ) $ 20,592 $ 609 $ 781 $ 21,982 Consolidated net income attributable to Southern Company — — 489 — — 489 Other comprehensive income (loss) — — (114 ) — — (114 ) Stock issued 6,572 — 270 — — 270 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (497 ) — — (497 ) Contributions from noncontrolling interests — — — — 129 129 Distributions to noncontrolling interests — — — — (4 ) (4 ) Purchase of membership interests from noncontrolling interests — — — — (129 ) (129 ) Net income attributable to noncontrolling interests — — — — 1 1 Other — (35 ) — — — Balance at March 31, 2016 921,645 (3,387 ) $ 20,797 $ 609 $ 778 $ 22,184 (*) Related to Southern Power Company and excludes redeemable noncontrolling interests. Subsequent to March 31, 2017, approximately $114 million was reclassified from redeemable noncontrolling interests to noncontrolling interests, included in stockholder's equity, due to the expiration of SunPower Corp's option to require Southern Power to purchase its membership interests in one of the solar partnerships. See Note 10 to the financial statements of Southern Power in Item 8 of the Form 10-K for additional information.

Financing

Financing	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
FINANCING	FINANCING Going Concern As of March 31, 2017, Mississippi Power's current liabilities exceeded current assets by approximately $1.2 billion primarily due to a $1.2 billion unsecured term loan that matures on March 30, 2018 and $35 million in senior notes that mature on November 15, 2017, as well as $36 million of short-term notes payable, $40 million of tax-exempt variable rate demand obligations, and $50 million of pollution control bonds that are required to be remarketed over the next 12 months. Mississippi Power expects the funds needed to satisfy maturing debt obligations will exceed amounts available from operating cash flows, lines of credit, and other external sources. Accordingly, Mississippi Power intends to satisfy these obligations through loans and/or equity contributions from Southern Company. Specifically, Mississippi Power has been informed by Southern Company that, in the event sufficient funds are not available from external sources, Southern Company intends to provide Mississippi Power with loans and/or equity contributions sufficient to fund the remaining indebtedness scheduled to mature and other cash needs over the next 12 months. Therefore, Mississippi Power's financial statement presentation contemplates continuation of Mississippi Power as a going concern as a result of Southern Company's anticipated ongoing financial support of Mississippi Power, consistent with GAAP. For additional information, see Notes 1 and 6 to the financial statements of Mississippi Power under "Recently Issued Accounting Standards" and "Going Concern," respectively, in Item 8 of the Form 10-K. DOE Loan Guarantee Borrowings See Note 6 to the financial statements of Southern Company and Georgia Power in Item 8 of the Form 10-K for additional information regarding Georgia Power's loan guarantee agreement (Loan Guarantee Agreement) with the DOE and related multi-advance term loan facility (FFB Credit Facility) with the FFB. Advances may be requested under the FFB Credit Facility on a quarterly basis through 2020. The final maturity date for each advance under the FFB Credit Facility is February 20, 2044. Interest is payable quarterly and principal payments will begin on February 20, 2020. Borrowings under the FFB Credit Facility will bear interest at the applicable U.S. Treasury rate plus a spread equal to 0.375% . Future advances are subject to satisfaction of customary conditions, as well as certification of compliance with the requirements of the Title XVII Loan Guarantee Program, accuracy of project-related representations and warranties, delivery of updated project-related information, absence of liens on Georgia Power's ownership interest in Plant Vogtle Units 3 and 4 other than permitted liens, evidence of compliance with the prevailing wage requirements of the Davis-Bacon Act of 1931, as amended, and certification from the DOE's consulting engineer that proceeds of the advances are used to reimburse Eligible Project Costs. The Contractor's bankruptcy and failure to perform its obligations under the Vogtle 3 and 4 Agreement could impact Georgia Power's ability to make further borrowings under the Loan Guarantee Agreement. Under the Loan Guarantee Agreement, Georgia Power is subject to customary borrower affirmative and negative covenants and events of default. In addition, Georgia Power is subject to project-related reporting requirements and other project-specific covenants and events of default. In the event certain mandatory prepayment events occur, the FFB's commitment to make further advances under the FFB Credit Facility will terminate and Georgia Power will be required to prepay the outstanding principal amount of all borrowings under the FFB Credit Facility over a period of five years (with level principal amortization). Among other things, these mandatory prepayment events include (i) the termination of the Vogtle 3 and 4 Agreement under certain circumstances; (ii) cancellation of Plant Vogtle Units 3 and 4 by the Georgia PSC, or by Georgia Power if authorized by the Georgia PSC; and (iii) cost disallowances by the Georgia PSC that could have a material adverse effect on completion of Plant Vogtle Units 3 and 4 or Georgia Power's ability to repay the outstanding borrowings under the FFB Credit Facility. Under certain circumstances, insurance proceeds and any proceeds from an event of taking must be applied to immediately prepay outstanding borrowings under the FFB Credit Facility. Georgia Power also may voluntarily prepay outstanding borrowings under the FFB Credit Facility. Under the FFB Credit Facility, any prepayment (whether mandatory or optional) will be made with a make-whole premium or discount, as applicable. In connection with any cancellation of Plant Vogtle Units 3 and 4 that results in a mandatory prepayment event, the DOE may elect to continue construction of Plant Vogtle Units 3 and 4. In such an event, the DOE will have the right to assume Georgia Power's rights and obligations under the principal agreements relating to Plant Vogtle Units 3 and 4 and to acquire all or a portion of Georgia Power's ownership interest in Plant Vogtle Units 3 and 4. See Note (B) under " Regulatory Matters – Georgia Power – Nuclear Construction " for additional information regarding Plant Vogtle Units 3 and 4. Bank Credit Arrangements Bank credit arrangements provide liquidity support to the registrants' commercial paper borrowings and the traditional electric operating companies' pollution control revenue bonds. The amount of variable rate pollution control revenue bonds of the traditional electric operating companies outstanding requiring liquidity support as of March 31, 2017 was approximately $1.9 billion (comprised of approximately $890 million at Alabama Power, $868 million at Georgia Power, $82 million at Gulf Power, and $40 million at Mississippi Power). In addition, at March 31, 2017 , the traditional electric operating companies had approximately $386 million (comprised of approximately $250 million at Georgia Power, $86 million at Gulf Power, and $50 million at Mississippi Power) of fixed rate pollution control revenue bonds outstanding that were required to be reoffered within the next 12 months. See Note 6 to the financial statements of each registrant under "Bank Credit Arrangements" in Item 8 of the Form 10-K and " Financing Activities " herein for additional information. The following table outlines the committed credit arrangements by company as of March 31, 2017 : Expires Executable Term Loans Expires Within One Year Company 2017 2018 2020 Total Unused One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ 1,000 $ 1,250 $ 2,250 $ 2,250 $ — $ — $ — $ — Alabama Power 35 500 800 1,335 1,335 — — — 35 Georgia Power — — 1,750 1,750 1,732 — — — — Gulf Power 85 195 — 280 280 45 — 25 70 Mississippi Power 173 — — 173 141 — 13 13 160 Southern Power Company — — 600 600 524 — — — — Southern Company Gas (b) 75 1,925 — 2,000 1,949 — — — 75 Other 55 — — 55 55 20 — 20 35 Southern Company Consolidated $ 423 $ 3,620 $ 4,400 $ 8,443 $ 8,266 $ 65 $ 13 $ 58 $ 375 (a) Represents the Southern Company parent entity. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.3 billion of these arrangements. Southern Company Gas' committed credit arrangements also include $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Subject to applicable market conditions, Southern Company and its subsidiaries expect to renew or replace their bank credit arrangements as needed, prior to expiration. In connection therewith, Southern Company and its subsidiaries may extend the maturity dates and/or increase or decrease the lending commitments thereunder. Financing Activities The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first three months of 2017 : Company (a) Senior Note Issuances Senior Note Maturities and Redemptions Other Long-Term Debt Issuances Other Long-Term Debt Redemptions and Maturities (b) (in millions) Southern Company (c) $ — $ — $ — $ 400 Alabama Power 550 200 — — Georgia Power 850 — — 2 Gulf Power — — 6 — Southern Power — — 3 2 Other — — — 4 Southern Company Consolidated $ 1,400 $ 200 $ 9 $ 408 (a) Mississippi Power and Southern Company Gas did not issue or redeem any long-term debt during the first three months of 2017. (b) Includes reductions in capital lease obligations resulting from cash payments under capital leases. (c) Represents the Southern Company parent entity. Southern Company In March 2017, Southern Company repaid at maturity a $400 million 18 -month floating rate bank loan. Alabama Power In March 2017, Alabama Power issued $550 million aggregate principal amount of Series 2017A 2.45% Senior Notes due March 30, 2022. The proceeds were used to repay Alabama Power's short-term indebtedness and for general corporate purposes, including Alabama Power's continuous construction program. Georgia Power In March 2017, Georgia Power issued $450 million aggregate principal amount of Series 2017A 2.00% Senior Notes due March 30, 2020 and $400 million aggregate principal amount of Series 2017B 3.25% Senior Notes due March 30, 2027. The proceeds were used to repay a portion of Georgia Power's short-term indebtedness and for general corporate purposes, including Georgia Power's continuous construction program. Gulf Power In March 2017, Gulf Power extended the maturity of a $100 million short-term floating rate bank loan bearing interest based on one -month LIBOR from April 2017 to October 2017. Mississippi Power On February 28, 2017, Mississippi Power amended $551 million in promissory notes to Southern Company extending the maturity dates of the notes from December 1, 2017 to July 31, 2018. On March 31, 2017, Mississippi Power issued a $9 million short-term note bearing interest at 5% per annum, which was repaid on April 27, 2017.

Retirement Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS Southern Company has a defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at Southern Company Gas, as discussed below, and PowerSecure. The Southern Company qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No mandatory contributions to the Southern Company qualified pension plan are anticipated for the year ending December 31, 2017 . Southern Company also provides certain defined benefit pension plans for a selected group of management and highly compensated employees. Benefits under these non-qualified pension plans are funded on a cash basis. In addition, Southern Company provides certain medical care and life insurance benefits for retired employees through other postretirement benefit plans. The traditional electric operating companies fund related other postretirement trusts to the extent required by their respective regulatory commissions. In addition, Southern Company Gas has a qualified defined benefit, trusteed, pension plan covering certain eligible employees, which was closed in 2012 to new employees. This qualified pension plan is funded in accordance with requirements of ERISA. No mandatory contributions to the Southern Company Gas qualified pension plan are anticipated for the year ending December 31, 2017 . Southern Company Gas also provides certain non-qualified defined benefit and defined contribution pension plans for a selected group of management and highly compensated employees. Benefits under these non-qualified pension plans are funded on a cash basis. In addition, Southern Company Gas provides certain medical care and life insurance benefits for eligible retired employees through a postretirement benefit plan. Southern Company Gas also has a separate unfunded supplemental retirement health care plan that provides medical care and life insurance benefits to employees of discontinued businesses. See Note 2 to the financial statements of Southern Company, Alabama Power, Georgia Power, Gulf Power, Mississippi Power, and Southern Company Gas in Item 8 of the Form 10-K for additional information. Components of the net periodic benefit costs for the three months ended March 31, 2017 and 2016 are presented in the following tables. Pension Plans Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Three Months Ended March 31, 2017 Service cost $ 73 $ 16 $ 19 $ 3 $ 4 Interest cost 114 24 34 5 5 Expected return on plan assets (224 ) (49 ) (71 ) (10 ) (10 ) Amortization: Prior service costs 3 1 1 — — Net (gain)/loss 40 10 14 2 2 Net periodic pension cost (income) $ 6 $ 2 $ (3 ) $ — $ 1 Three Months Ended March 31, 2016 Service cost $ 62 $ 14 $ 17 $ 3 $ 3 Interest cost 100 24 34 5 5 Expected return on plan assets (187 ) (46 ) (64 ) (9 ) (9 ) Amortization: Prior service costs 4 1 1 — — Net (gain)/loss 38 10 14 2 2 Net periodic pension cost $ 17 $ 3 $ 2 $ 1 $ 1 Pension Plans Southern Company Gas (in millions) Successor – Three Months Ended March 31, 2017 Service cost $ 6 Interest cost 10 Expected return on plan assets (18 ) Amortization: Prior service costs — Net (gain)/loss 5 Net periodic pension cost $ 3 Predecessor – Three Months Ended March 31, 2016 Service cost $ 6 Interest cost 10 Expected return on plan assets (16 ) Amortization: Prior service costs — Net (gain)/loss 6 Net periodic pension cost $ 6 Postretirement Benefits Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Three Months Ended March 31, 2017 Service cost $ 6 $ 1 $ 2 $ — $ — Interest cost 20 5 7 1 1 Expected return on plan assets (16 ) (6 ) (6 ) — — Amortization: Prior service costs 2 1 — — — Net (gain)/loss 2 — 2 — — Net periodic postretirement benefit cost $ 14 $ 1 $ 5 $ 1 $ 1 Three Months Ended March 31, 2016 Service cost $ 5 $ 1 $ 2 $ — $ — Interest cost 18 5 8 1 1 Expected return on plan assets (14 ) (6 ) (6 ) — — Amortization: Prior service costs 2 1 — — — Net (gain)/loss 3 — 2 — — Net periodic postretirement benefit cost $ 14 $ 1 $ 6 $ 1 $ 1 Postretirement Benefits Southern Company Gas (in millions) Successor – Three Months Ended March 31, 2017 Service cost $ 1 Interest cost 3 Expected return on plan assets (2 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 2 Predecessor – Three Months Ended March 31, 2016 Service cost $ 1 Interest cost 3 Expected return on plan assets (2 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 2

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES See Note 5 to the financial statements of each registrant in Item 8 of the Form 10-K for additional tax information. Current and Deferred Income Taxes Tax Credit Carryforwards Southern Company had federal ITC and PTC carryforwards (primarily related to Southern Power) totaling $1.9 billion as of March 31, 2017 compared to $1.8 billion as of December 31, 2016 . The federal ITC carryforwards begin expiring in 2032 but are expected to be fully utilized by 2022. The PTC carryforwards begin expiring in 2036 but are expected to be utilized by 2022. The acquisition of additional renewable projects and carrying back the federal net operating loss, as well as potential tax reform legislation on existing renewable incentives, could further delay existing tax credit carryforwards. The ultimate outcome of these matters cannot be determined at this time. Effective Tax Rate Southern Company Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity, and federal income tax benefits from ITCs and PTCs. Southern Company's effective tax rate was 32.1% for the three months ended March 31, 2017 compared to 30.2% for the corresponding period in 2016 . The effective tax rate increase was primarily due to higher pre-tax earnings resulting from the Merger with Southern Company Gas and decreased tax benefits from ITCs, partially offset by an increase in tax benefits from wind PTCs and state apportionment rate changes. Southern Company recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Company uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income. Mississippi Power Mississippi Power's effective tax (benefit) rate was (58.7)% for the three months ended March 31, 2017 compared to (850.4)% for the corresponding period in 2016 . The effective tax rate increase was primarily due to the estimated probable losses on construction of the Kemper IGCC. Southern Power Southern Power's effective tax (benefit) rate was (385.9)% for the three months ended March 31, 2017 compared to (84.0)% for the corresponding period in 2016 . The effective tax rate decrease was primarily due to additional PTCs arising from Southern Power's wind facility acquisitions, state apportionment rate changes, and lower pre-tax earnings, partially offset by a decrease in tax benefits from ITCs. Southern Power recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Power uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income. Unrecognized Tax Benefits See Note 5 to the financial statements of each registrant under "Unrecognized Tax Benefits" in Item 8 of the Form 10-K for additional information. Changes during the three months ended March 31, 2017 for unrecognized tax benefits were as follows: Mississippi Power Southern Power Southern Company (in millions) Unrecognized tax benefits as of December 31, 2016 $ 465 $ 17 $ 484 Tax positions from current periods 3 1 9 Tax positions from prior periods — — 7 Balance as of March 31, 2017 $ 468 $ 18 $ 500 The tax positions from current and prior periods primarily relate to state tax benefits and charitable contribution carryforwards that will be impacted as a result of the proposed settlement of research and experimental (R&E) expenditures associated with the Kemper IGCC. See " Section 174 Research and Experimental Deduction " herein for additional information. These amounts are presented on a gross basis without considering the related federal or state income tax impact. The impact on the effective tax rate, if recognized, is as follows: As of March 31, 2017 As of December 31, 2016 Mississippi Power Southern Power Southern Company Southern Company (in millions) Tax positions impacting the effective tax rate $ 4 $ 18 $ 36 $ 20 Tax positions not impacting the effective tax rate 464 — 464 464 Balance of unrecognized tax benefits $ 468 $ 18 $ 500 $ 484 The tax positions impacting the effective tax rate primarily relate to federal deferred income tax credits and Southern Company's estimate of the uncertainty related to the amount of those benefits, and state tax benefits and charitable contribution carryforwards that will be impacted as a result of the proposed settlement of R&E expenditures associated with the Kemper IGCC. See " Section 174 Research and Experimental Deduction " herein for additional information. If these tax positions are not able to be recognized due to a federal audit adjustment in the amount that has been estimated, the amount of tax credit carryforwards discussed above would be reduced by approximately $98 million . Accrued interest for all tax positions other than the Section 174 R&E deductions was immaterial for all periods presented. All of the registrants classify interest on tax uncertainties as interest expense. None of the registrants accrued any penalties on uncertain tax positions. It is reasonably possible that the amount of the unrecognized tax benefits could change within 12 months . The settlement of federal and state audits and the U.S. Congress Joint Committee on Taxation approval of the R&E expenditures associated with the Kemper IGCC could impact the balances significantly. At this time, an estimate of the range of reasonably possible outcomes cannot be determined. See " Section 174 Research and Experimental Deduction " herein for more information. The IRS has finalized its audits of Southern Company's consolidated federal income tax returns through 2012. Southern Company has filed its 2013, 2014, and 2015 federal income tax returns and has received partial acceptance letters from the IRS; however, the IRS has not finalized its audits. Southern Company is a participant in the Compliance Assurance Process of the IRS. In addition, the pre-Merger Southern Company Gas 2014 federal tax return is currently under audit. The audits for Southern Company's state income tax returns have either been concluded, or the statute of limitations has expired, for years prior to 2011. Section 174 Research and Experimental Deduction Southern Company reflected deductions for R&E expenditures related to the Kemper IGCC in its federal income tax calculations since 2013 and filed amended federal income tax returns for 2008 through 2013 to also include such deductions. The Kemper IGCC is based on first-of-a-kind technology, and Southern Company and Mississippi Power believe that a significant portion of the plant costs qualify as deductible R&E expenditures under Internal Revenue Code Section 174. In December 2016, Southern Company and the IRS reached a proposed settlement, subject to approval of the U.S. Congress Joint Committee on Taxation, resolving a methodology for these deductions. Due to the uncertainty related to this tax position, Southern Company and Mississippi Power had unrecognized tax benefits associated with these R&E deductions totaling approximately $464 million and associated interest of $32 million as of March 31, 2017 . This matter is expected to be resolved in the next 12 months ; however, the ultimate outcome of this matter cannot be determined at this time.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVES	DERIVATIVES Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' wholesale gas operations use various contracts in its commercial activities that generally meet the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (C) for additional information. In the statements of cash flows, the cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. The cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with classification of the hedged interest or principal, respectively. Energy-Related Derivatives Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which is expected to continue to mitigate price volatility. The Florida PSC extended the moratorium on Gulf Power's fuel-hedging program through January 1, 2021 in connection with the 2017 Rate Case Settlement Agreement. The moratorium does not have an impact on the recovery of existing hedges entered into under the previously-approved hedging program. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in the statements of income. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts which are designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through the respective fuel cost recovery clauses. • Cash Flow Hedges — Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in OCI before being recognized in the statements of income in the same period as the hedged transactions are reflected in earnings. • Not Designated — Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. At March 31, 2017 , the net volume of energy-related derivative contracts for natural gas positions for the Southern Company system, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 503 2021 2024 Alabama Power 71 2020 — Georgia Power 155 2020 — Gulf Power 42 2020 — Mississippi Power 37 2021 — Southern Power 21 2017 2017 Southern Company Gas (*) 177 2019 2024 (*) Southern Company's and Southern Company Gas' derivative instruments include both long and short natural gas positions. A long position is a contract to purchase natural gas and a short position is a contract to sell natural gas. Southern Company Gas' volume represents the net of long natural gas positions of 3.4 billion mmBtu and short natural gas positions of 3.2 billion mmBtu as of March 31, 2017 , which is also included in Southern Company's total volume. In addition to the volumes discussed above, the traditional electric operating companies and Southern Power enter into physical natural gas supply contracts that provide the option to sell back excess gas due to operational constraints. The maximum expected volume of natural gas subject to such a feature is 10 million mmBtu for Southern Company, 4 million mmbtu for Georgia Power, 3 million mmBtu for Southern Power, and 1 million mmBtu for each of Alabama Power, Gulf Power, and Mississippi Power. For cash flow hedges of energy-related derivatives, the amounts expected to be reclassified from accumulated OCI to earnings for the next 12 -month period ending March 31, 2018 are $10 million for Southern Power and immaterial for all other registrants. Interest Rate Derivatives Southern Company and certain subsidiaries may also enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the effective portion of the derivatives' fair value gains or losses is recorded in OCI and is reclassified into earnings at the same time the hedged transactions affect earnings, with any ineffectiveness recorded directly to earnings. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings, providing an offset, with any difference representing ineffectiveness. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. At March 31, 2017 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Gulf Power $ 80 3-month 2.32% December 2026 $ — Cash Flow Hedges of Existing Debt Mississippi Power 900 1-month 0.79% March 2018 4 Fair Value Hedges of Existing Debt Southern Company (*) 250 1.30% 3-month August 2017 — Southern Company (*) 300 2.75% 3-month June 2020 1 Southern Company (*) 1,500 2.35% 1-month July 2021 (21 ) Georgia Power 250 5.40% 3-month June 2018 — Georgia Power 500 1.95% 3-month December 2018 (3 ) Georgia Power 200 4.25% 3-month December 2019 1 Southern Company Consolidated $ 3,980 $ (18 ) (*) Represents the Southern Company parent entity. The estimated pre-tax gains (losses) related to interest rate derivatives expected to be reclassified from accumulated OCI to interest expense for the next 12 -month period ending March 31, 2018 are immaterial for all registrants. Southern Company and certain subsidiaries have deferred gains and losses expected to be amortized into earnings through 2046 . Foreign Currency Derivatives Southern Company and certain subsidiaries may also enter into foreign currency derivatives to hedge exposure to changes in foreign currency exchange rates, such as that arising from the issuance of debt denominated in a currency other than U.S. dollars. Derivatives related to forecasted transactions are accounted for as cash flow hedges where the effective portion of the derivatives' fair value gains or losses is recorded in OCI and is reclassified into earnings at the same time that the hedged transactions affect earnings, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. Any ineffectiveness is recorded directly to earnings. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. At March 31, 2017 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ (35 ) Southern Power 564 3.78% 500 1.85% June 2026 (27 ) Total $ 1,241 € 1,100 $ (62 ) The estimated pre-tax gains (losses) related to foreign currency derivatives that will be reclassified from accumulated OCI to earnings for the next 12 -month period ending March 31, 2018 are $24 million for Southern Company and Southern Power. Derivative Financial Statement Presentation and Amounts Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into derivative contracts that may contain certain provisions that permit intra-contract netting of derivative receivables and payables for routine billing and offsets related to events of default and settlements. Southern Company and certain subsidiaries also utilize master netting agreements to mitigate exposure to counterparty credit risk. These agreements may contain provisions that permit netting across product lines and against cash collateral. The fair value amounts of derivative assets and liabilities on the balance sheet are presented net to the extent that there are netting arrangements or similar agreements with the counterparties. The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 48 $ 30 $ 73 $ 27 Other deferred charges and assets/Other deferred credits and liabilities 6 38 25 33 Total derivatives designated as hedging instruments for regulatory purposes $ 54 $ 68 $ 98 $ 60 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 14 $ 5 $ 23 $ 7 Interest rate derivatives: Other current assets/Liabilities from risk management activities, net of collateral 13 — 12 1 Other deferred charges and assets/Other deferred credits and liabilities — 32 1 28 Foreign currency derivatives: Other current assets/Liabilities from risk management activities, net of collateral — 25 — 25 Other deferred charges and assets/Other deferred credits and liabilities — 37 — 33 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 27 $ 99 $ 36 $ 94 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 306 $ 271 $ 489 $ 483 Other deferred charges and assets/Other deferred credits and liabilities 132 114 66 81 Interest rate derivatives: Other current assets/Liabilities from risk management activities, net of collateral — — 1 — Total derivatives not designated as hedging instruments $ 438 $ 385 $ 556 $ 564 Gross amounts recognized $ 519 $ 552 $ 690 $ 718 Gross amounts offset (*) $ (303 ) $ (395 ) $ (462 ) $ (524 ) Net amounts recognized in the Balance Sheets $ 216 $ 157 $ 228 $ 194 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities $ 9 $ 5 $ 13 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 2 5 7 4 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 10 $ 20 $ 9 Gross amounts recognized $ 11 $ 10 $ 20 $ 9 Gross amounts offset $ (6 ) $ (6 ) $ (8 ) $ (8 ) Net amounts recognized in the Balance Sheets $ 5 $ 4 $ 12 $ 1 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 20 $ 2 $ 30 $ 1 Other deferred charges and assets/Other deferred credits and liabilities 4 11 14 7 Total derivatives designated as hedging instruments for regulatory purposes $ 24 $ 13 $ 44 $ 8 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 2 $ — $ 2 $ — Other deferred charges and assets/Other deferred credits and liabilities — 4 — 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 4 $ 2 $ 3 Gross amounts recognized $ 26 $ 17 $ 46 $ 11 Gross amounts offset $ (6 ) $ (6 ) $ (8 ) $ (8 ) Net amounts recognized in the Balance Sheets $ 20 $ 11 $ 38 $ 3 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities $ 2 $ 14 $ 4 $ 12 Other deferred charges and assets/Other deferred credits and liabilities — 17 1 17 Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 31 $ 5 $ 29 Gross amounts recognized $ 2 $ 31 $ 5 $ 29 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ — $ 29 $ 1 $ 25 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 7 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — 5 2 5 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 12 $ 4 $ 11 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 4 $ — $ 2 $ — Other deferred charges and assets/Other deferred credits and liabilities — — 1 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 4 $ — $ 3 $ — Gross amounts recognized $ 7 $ 12 $ 7 $ 11 Gross amounts offset $ (2 ) $ (2 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 5 $ 10 $ 4 $ 8 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 13 $ 4 $ 18 $ 4 Foreign currency derivatives: Other current assets/Other current liabilities — 25 — 25 Other deferred charges and assets/Other deferred credits and liabilities — 37 — 33 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 13 $ 66 $ 18 $ 62 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 1 $ 3 $ 1 Interest rate derivatives: Other current assets/Other current liabilities — — 1 — Total derivatives not designated as hedging instruments $ 2 $ 1 $ 4 $ 1 Gross amounts recognized $ 15 $ 67 $ 22 $ 63 Gross amounts offset $ (3 ) $ (3 ) $ (5 ) $ (5 ) Net amounts recognized in the Balance Sheets $ 12 $ 64 $ 17 $ 58 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 14 $ 2 $ 24 $ 3 Other deferred charges and assets/Other deferred credits and liabilities — — 1 — Total derivatives designated as hedging instruments for regulatory purposes $ 14 $ 2 $ 25 $ 3 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 1 $ 1 $ 4 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 304 $ 270 $ 486 $ 482 Other deferred charges and assets/Other deferred credits and liabilities 132 114 66 81 Total derivatives not designated as hedging instruments $ 436 $ 384 $ 552 $ 563 Gross amounts of recognized $ 451 $ 387 $ 581 $ 569 Gross amounts offset (*) $ (272 ) $ (364 ) $ (435 ) $ (497 ) Net amounts recognized in the Balance Sheets $ 179 $ 23 $ 146 $ 72 (*) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $92 million and $62 million as of March 31, 2017 and December 31, 2016 , respectively. At March 31, 2017 and December 31, 2016 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at March 31, 2017 Derivative Category and Balance Sheet Location Southern Company (b) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (b) (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (1 ) $ — $ (12 ) $ (5 ) $ (1 ) Other regulatory assets, deferred (32 ) (3 ) (7 ) (17 ) (5 ) — Other regulatory liabilities, current (a) 33 5 18 — 1 9 Total energy-related derivative gains (losses) $ (18 ) $ 1 $ 11 $ (29 ) $ (9 ) $ 8 (a) Georgia Power includes other regulatory liabilities, current in other current liabilities. (b) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $ 4 million at March 31, 2017 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2016 Derivative Category and Balance Sheet Location Southern Company (c) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (c) (in millions) Energy-related derivatives: Other regulatory assets, current $ (16 ) $ (1 ) $ — $ (9 ) $ (5 ) $ (1 ) Other regulatory assets, deferred (19 ) — — (16 ) (3 ) — Other regulatory liabilities, current (a) 56 8 29 1 1 17 Other regulatory liabilities, deferred (b) 12 4 7 — — 1 Total energy-related derivative gains (losses) $ 33 $ 11 $ 36 $ (24 ) $ (7 ) $ 17 (a) Georgia Power includes other regulatory liabilities, current in other current liabilities. (b) Georgia Power includes other regulatory liabilities, deferred in other deferred credits and liabilities. (c) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $ 8 million at December 31, 2016 . For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives, interest rate derivatives, and foreign currency derivatives designated as cash flow hedging instruments were as follows: Derivatives in Cash Flow Hedging Relationships Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Statements of Income Location Amount 2017 2016 2017 2016 (in millions) (in millions) Southern Company Energy-related derivatives $ (11 ) $ — Depreciation and amortization $ (4 ) $ (1 ) Interest rate derivatives 1 (190 ) Interest expense, net of amounts capitalized (5 ) (3 ) Foreign currency derivatives (4 ) — Interest expense, net of amounts capitalized (6 ) — Other income (expense), net (*) 17 — Total $ (14 ) $ (190 ) $ 2 $ (4 ) Gulf Power Energy-related derivatives $ (1 ) $ — Depreciation and amortization $ — $ — Interest rate derivatives — (5 ) Interest expense, net of amounts capitalized — — Total $ (1 ) $ (5 ) $ — $ — Southern Power Energy-related derivatives $ (8 ) $ — Depreciation and amortization $ (4 ) $ (1 ) Foreign currency derivatives (4 ) — Interest expense, net of amounts capitalized (6 ) — Other income (expense), net (*) 17 — Total $ (12 ) $ — $ 7 $ (1 ) (*) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes. For Southern Company Gas, the pre-tax effect of energy related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings for the three months ended March 31, 2017 and the predecessor period of January 1, 2016 through March 31, 2016 were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Successor Predecessor Successor Predecessor Derivatives in Cash Flow Hedging Relationships Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 Statements of Income Location Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives $ (2 ) $ — Cost of natural gas $ — $ — Interest rate derivatives — (45 ) Interest expense, net of amounts capitalized — 1 Total $ (2 ) $ (45 ) $ — $ 1 For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments were immaterial for the other registrants. For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments on the statements of income were as follows: Gain (Loss) Three Months Ended Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2017 2016 (in millions) Southern Company Energy Related derivatives: Natural gas revenues (*) $ 50 $ — Cost of natural gas (3 ) — Total derivatives in non-designated hedging relationships $ 47 $ — (*) Excludes gains (losses) recorded in cost of natural gas associated with weather derivatives of $14 million for the three months ended March 31, 2017 . Gain (Loss) Successor Predecessor Derivatives in Non-Designated Hedging Relationships Statements of Income Location Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) Southern Company Gas Energy Related derivatives: Natural gas revenues (*) $ 50 $ 20 Cost of natural gas (3 ) (1 ) Total derivatives in non-designated hedging relationships $ 47 $ 19 (*) Excludes gains (losses) recorded in cost of natural gas associated with weather derivatives of $14 million for the successor three months ended March 31, 2017 and $3 million for the predecessor three months ended March 31, 2016 . For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were immaterial for the traditional electric operating companies and Southern Power. For the three months ended March 31, 2017 and 2016 , the pre-tax effects of interest rate derivatives designated as fair value hedging instruments were as follows: Derivatives in Fair Value Hedging Relationships Gain (Loss) Three Months Ended March 31, Derivative Category Statements of Income Location 2017 2016 (in millions) Southern Company Interest rate derivatives: Interest expense, net of amounts capitalized $ (8 ) $ 20 Georgia Power Interest rate derivatives: Interest expense, net of amounts capitalized $ (1 ) $ 14 For the three months ended March 31, 2017 and 2016 , the pre-tax effects of interest rate derivatives designated as fair value hedging instruments were offset by changes to the carrying value of long-term debt. There was no material ineffectiveness recorded in earnings for any registrant for any period presented. Contingent Features Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not have any credit arrangements that would require material changes in payment schedules or terminations as a result of a credit rating downgrade. There are certain derivatives that could require collateral, but not accelerated payment, in the event of various credit rating changes of certain Southern Company subsidiaries. At March 31, 2017 , the registrants had no collateral posted with derivative counterparties to satisfy these arrangements. At March 31, 2017 , the fair value of derivative liabilities with contingent features was immaterial for all registrants. The maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, were $11 million for Southern Company, $9 million for the traditional electric operating companies and Southern Power, and $2 million for Southern Company Gas. The maximum potential collateral requirements arising from the credit-risk-related contingent features for the traditional electric operating companies and Southern Power include certain agreements that could require collateral in the event that one or more Southern Company power pool participants has a credit rating change to below investment grade. Generally, collateral may be provided by a Southern Company guaranty, letter of credit, or cash. If collateral is required, fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral are not offset against fair value amounts recognized for derivatives executed with the same counterparty. Alabama Power maintains accounts with certain regional transmission organizations to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Alabama Power may be required to post collateral. At March 31, 2017, cash collateral posted in these accounts was immaterial. Southern Company Gas maintains accounts with brokers or the clearing houses of certain exchanges to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Southern Company Gas may be required to deposit cash into these accounts. At March 31, 2017 , cash collateral held on deposit in broker margin accounts was $92 million . Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to losses related to financial instruments in the event of counterparties' nonperformance. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas only enter into agreements and material transactions with counterparties that have investment grade credit ratings by Moody's and S&P or with counterparties who have posted collateral to cover potential credit exposure. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas have also established risk management policies and controls to determine and monitor the creditworthiness of counterparties in order to mitigate Southern Company's, the traditional electric operating companies', Southern Power's, and Southern Company Gas' exposure to counterparty credit risk. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. In addition, Southern Company Gas conducts credit evaluations and obtains appropriate internal approvals for the counterparty's line of credit before any transaction with the counterparty is executed. In most cases, the counterparty must have an investment grade rating, which includes a minimum long-term debt rating of Baa3 from Moody's and BBB- from S&P. Generally, Southern Company Gas requires credit enhancements by way of a guaranty, cash deposit, or letter of credit for transaction counterparties that do not have investment grade ratings. Southern Company Gas also utilizes master netting agreements whenever possible to mitigate exposure to counterparty credit risk. When Southern Company Gas is engaged in more than one outstanding derivative transaction with the same counterparty and it also has a legally enforceable netting agreement with that counterparty, the "net" mark-to-market exposure represents the netting of the positive and negative exposures with that counterparty and a reasonable measure of Southern Company Gas' credit risk. Southern Company Gas also uses other netting agreements with certain counterparties with whom it conducts significant transactions. Master netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty. Southern Company Gas also nets across product lines and against cash collateral provided the master netting and cash collateral agreements include such provisions. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not anticipate a material adverse effect on the financial statements as a result of counterparty nonperformance.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS Southern Company Merger with Southern Company Gas Southern Company Gas is an energy services holding company whose primary business is the distribution of natural gas through the natural gas distribution utilities. On July 1, 2016, Southern Company completed the Merger for a total purchase price of approximately $8.0 billion and Southern Company Gas became a wholly-owned, direct subsidiary of Southern Company. The Merger was accounted for using the acquisition method of accounting with the assets acquired and liabilities assumed recognized at fair value as of the acquisition date. The following table presents the purchase price allocation: Southern Company Gas Purchase Price (in millions) Current assets $ 1,557 Property, plant, and equipment 10,108 Goodwill 5,967 Intangible assets 400 Regulatory assets 1,118 Other assets 229 Current liabilities (2,201 ) Other liabilities (4,742 ) Long-term debt (4,261 ) Noncontrolling interest (174 ) Total purchase price $ 8,001 The excess of the purchase price over the estimated fair values of the assets acquired and liabilities assumed of $6.0 billion is recognized as goodwill, which is primarily attributable to positioning the Southern Company system to provide natural gas infrastructure to meet customers' growing energy needs and to compete for growth across the energy value chain. Southern Company anticipates that much of the value assigned to goodwill will not be deductible for tax purposes. The valuation of identifiable intangible assets included customer relationships, trade names, and storage and transportation contracts with estimated lives of one to 28 years . The estimated fair value measurements of identifiable intangible assets were primarily based on significant unobservable inputs (Level 3). The results of operations for Southern Company Gas have been included in Southern Company's consolidated financial statements from the date of acquisition and consist of operating revenues of $1.6 billion and net income of $239 million for the three months ended March 31, 2017. The following summarized unaudited pro forma consolidated statement of earnings information assumes that the acquisition of Southern Company Gas was completed on January 1, 2015. The summarized unaudited pro forma consolidated statement of earnings information includes adjustments for (i) intercompany sales, (ii) amortization of intangible assets, (iii) adjustments to interest expense to reflect current interest rates on Southern Company Gas debt and additional interest expense associated with borrowings by Southern Company to fund the Merger, and (iv) the elimination of nonrecurring expenses associated with the Merger. For the Three Months Ended March 31, 2016 Operating revenues (in millions) $ 5,320 Net income attributable to Southern Company (in millions) $ 650 Basic EPS $ 0.70 Diluted EPS $ 0.69 These unaudited pro forma results are for comparative purposes only and may not be indicative of the results that would have occurred had this acquisition been completed on January 1, 2015 or the results that would be attained in the future. Acquisition of PowerSecure On May 9, 2016, Southern Company acquired all of the outstanding stock of PowerSecure, a provider of products and services in the areas of distributed generation, energy efficiency, and utility infrastructure, for $18.75 per common share in cash, resulting in an aggregate purchase price of $429 million . As a result, PowerSecure became a wholly-owned subsidiary of Southern Company. The acquisition of PowerSecure was accounted for using the acquisition method of accounting with the assets acquired and liabilities assumed recognized at fair value as of the acquisition date. The following table presents the purchase price allocation: PowerSecure Purchase Price (in millions) Current assets $ 172 Property, plant, and equipment 46 Intangible assets 101 Goodwill 282 Other assets 4 Current liabilities (114 ) Long-term debt, including current portion (48 ) Deferred credits and other liabilities (14 ) Total purchase price $ 429 The excess of the purchase price over the estimated fair values of the assets acquired and liabilities assumed of $282 million was recognized as goodwill, which is primarily attributable to expected business expansion opportunities for PowerSecure. Southern Company anticipates that the majority of the value assigned to goodwill will not be deductible for tax purposes. The valuation of identifiable intangible assets included customer relationships, trade names, patents, backlog, and software with estimated lives of one to 26 years. The estimated fair value measurements of identifiable intangible assets were primarily based on significant unobservable inputs (Level 3). The results of operations for PowerSecure have been included in Southern Company's consolidated financial statements from the date of acquisition and are immaterial to the consolidated financial results of Southern Company. Pro forma results of operations have not been presented for the acquisition because the effects of the acquisition were immaterial to Southern Company's consolidated financial results for all periods presented. Southern Power See Note 2 to the financial statements of Southern Power and Note 12 to the financial statements of Southern Company under "Southern Power" in Item 8 of the Form 10-K for additional information. Acquisitions During the Three Months Ended March 31, 2017 During the three months ended March 31, 2017, in accordance with Southern Power's overall growth strategy, Southern Renewable Partnerships, LLC (SRP), one of Southern Power's wholly-owned subsidiaries, acquired the Bethel wind facility . Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller; Acquisition Date Approximate Nameplate Capacity ( MW ) Location Southern Power Percentage Ownership Actual COD PPA Contract Period Bethel Wind Invenergy, 276 Castro County, TX 100 % January 2017 12 years The aggregate amount of revenue recognized by Southern Power related to the Bethel facility included in Southern Power's condensed consolidated statements of income during the first quarter 2017 is $4 million . The aggregate amount of net income, excluding impacts from PTCs, recognized by Southern Power during the three months ended March 31, 2017 included in Southern Power's condensed consolidated statements of income was immaterial. The Bethel facility did not have operating revenues or activities prior to completion of construction and the assets being placed in service; therefore, supplemental pro forma information for the comparable 2016 period is not meaningful and has been omitted. In connection with 2016 acquisitions, subsequent to March 31, 2017, allocations of the purchase price to individual assets were finalized with no changes to amounts originally reported for Boulder 1, Grant Plains, Grant Wind, Passadumkeag, and Wake Wind. Construction Projects Completed and in Progress During the three months ended March 31, 2017 , in accordance with its overall growth strategy, Southern Power completed construction of and placed in service, or continued construction of, the projects set forth in the following table. Through March 31, 2017 , total costs of construction incurred for these three projects were $401 million , of which $203 million remained in CWIP for the Lamesa and Mankato facilities acquired in 2016. Total aggregate construction costs, excluding the acquisition costs, are expected to be $530 million to $590 million for these two facilities that were under construction at March 31, 2017 . The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Project Completed During the Three Months Ended March 31, 2017 East Pecos Solar 120 Pecos County, TX March 2017 15 years Projects Under Construction as of March 31, 2017 Lamesa Solar 102 Dawson County, TX April 2017 15 years Mankato Natural Gas 345 Mankato, MN Second quarter 2019 20 years Development Projects In December 2016, as part of Southern Power's renewable development strategy, SRP entered into a joint development agreement with Renewable Energy Systems Americas, Inc. to develop and construct approximately 3,000 MWs of wind projects. Also in December 2016, Southern Power signed agreements and made payments to purchase wind turbine equipment from Siemens Wind Power, Inc. and Vestas-American Wind Technology, Inc. to be used for construction of the facilities. All of the wind turbine equipment was delivered by April 2017, which allows the projects to qualify for 100% PTCs for 10 years following their expected commercial operation dates between 2018 and 2020. The ultimate outcome of these matters cannot be determined at this time.

Joint Ownership Agreements

Joint Ownership Agreements	3 Months Ended
	Mar. 31, 2017
Regulated Operations [Abstract]
Joint Ownership Agreements	JOINT OWNERSHIP AGREEMENTS Southern Company Gas See Note 4 to the financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information. Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2017 and December 31, 2016 and related income from those investments for the successor period ended March 31, 2017 and the predecessor period ended March 31, 2016 were as follows: Balance Sheet Information March 31, 2017 December 31, 2016 (in millions) SNG $ 1,430 $ 1,394 Triton 44 44 Horizon Pipeline 31 30 PennEast Pipeline 30 22 Atlantic Coast Pipeline 42 33 Pivotal JAX LNG, LLC 26 16 Other 1 2 Total $ 1,604 $ 1,541 Successor Predecessor Income Statement Information Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) SNG $ 34 $ — Horizon Pipeline 1 1 PennEast Pipeline 3 — Atlantic Coast Pipeline 1 — Total $ 39 $ 1 Southern Natural Gas In September 2016, Southern Company Gas, through a wholly-owned, indirect subsidiary, acquired a 50% equity interest in SNG, which is accounted for as an equity method investment. On March 31, 2017, Southern Company Gas made an additional $50 million contribution to maintain its 50% equity interest in SNG. See Note 11 to the financial statements of Southern Company Gas under "Investment in SNG" in Item 8 of the Form 10-K for additional information on this investment. Selected financial information of SNG for the first quarter 2017 is as follows: Income Statement Information Three Months Ended March 31, 2017 (in millions) Revenues $ 155 Operating income $ 84 Net income $ 66

Segment and Related Information

Segment and Related Information	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
SEGMENT AND RELATED INFORMATION	SEGMENT AND RELATED INFORMATION Southern Company The primary business of the Southern Company system is electricity sales by the traditional electric operating companies and Southern Power and the distribution of natural gas by Southern Company Gas. The four traditional electric operating companies – Alabama Power, Georgia Power, Gulf Power, and Mississippi Power – are vertically integrated utilities providing electric service in four Southeastern states. Southern Power constructs, acquires, owns, and manages power generation assets, including renewable energy projects, and sells electricity at market-based rates in the wholesale market. Southern Company Gas distributes natural gas through the seven natural gas distribution utilities in seven states and is involved in several other complementary businesses including gas marketing services, wholesale gas services, and gas midstream operations. Southern Company's reportable business segments are the sale of electricity by the four traditional electric operating companies, the sale of electricity in the competitive wholesale market by Southern Power, and the sale of natural gas and other complementary products and services by Southern Company Gas. Revenues from sales by Southern Power to the traditional electric operating companies were $100 million for the three months ended March 31, 2017 and $97 million for the three months ended March 31, 2016 . The "All Other" column includes the Southern Company parent entity, which does not allocate operating expenses to business segments. Also, this category includes segments below the quantitative threshold for separate disclosure. These segments include providing energy technologies and services to electric utilities and large industrial, commercial, institutional, and municipal customers; as well as investments in telecommunications and leveraged lease projects. All other inter-segment revenues are not material. Financial data for business segments and products and services for the three months ended March 31, 2017 and 2016 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) Three Months Ended Operating revenues $ 3,786 $ 450 $ (105 ) $ 4,131 $ 1,560 $ 123 $ (43 ) $ 5,771 Segment net income (loss) (a)(b)(c) 432 70 — 502 239 (84 ) 1 658 Total assets at March 31, 2017 $ 72,692 $ 14,681 $ (306 ) $ 87,067 $ 21,683 $ 2,574 $ (1,564 ) $ 109,760 Three Months Ended Operating revenues $ 3,769 $ 315 $ (103 ) $ 3,981 $ — $ 47 $ (36 ) $ 3,992 Segment net income (loss) (a)(b) 465 50 — 515 — (23 ) (3 ) 489 Total assets at December 31, 2016 $ 72,141 $ 15,169 $ (316 ) $ 86,994 $ 21,853 $ 2,474 $ (1,624 ) $ 109,697 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated probable losses on the Kemper IGCC of $108 million ( $67 million after tax) and $53 million ( $33 million after tax) for the three months ended March 31, 2017 and 2016 , respectively. See Note (B) under " Integrated Coal Gasification Combined Cycle – Kemper IGCC Schedule and Cost Estimate " for additional information. (c) Segment net income (loss) for the traditional electric operating companies also includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) for the three months ended March 31, 2017 . See Note (B) under " Regulatory Matters – Gulf Power – Retail Base Rate Cases " for additional information. Products and Services Electric Utilities' Revenues Period Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2017 $ 3,394 $ 531 $ 206 $ 4,131 Three Months Ended March 31, 2016 3,377 396 208 3,981 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended March 31, 2017 $ 1,132 $ 288 $ 140 $ 1,560 Southern Company Gas Southern Company Gas manages its business through four reportable segments – gas distribution operations, gas marketing services, wholesale gas services, and gas midstream operations. The non-reportable segments are combined and presented as all other. Gas distribution operations is the largest component of Southern Company Gas' business and includes natural gas local distribution utilities that construct, manage, and maintain intrastate natural gas pipelines and gas distribution facilities in seven states. Gas marketing services includes natural gas marketing to end-use customers primarily in Georgia and Illinois. Additionally, gas marketing services provides home equipment protection products and services. Wholesale gas services provides natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. Additionally, wholesale gas services engages in natural gas storage and gas pipeline arbitrage and related activities. Gas midstream operations primarily consists of Southern Company Gas' pipeline investments, with storage and fuel operations also aggregated into this segment. The all other column includes segments below the quantitative threshold for separate disclosure, including the subsidiaries that fall below the quantitative threshold for separate disclosure. After the Merger, Southern Company Gas changed its segment performance measure to net income. In order to properly assess net income by segment, Southern Company Gas executed various intercompany note agreements to revise interest charges to its segments. Since such agreements did not exist in the predecessor period, Southern Company Gas is unable to provide the comparable net income. Business segment financial data for the successor period January 1, 2017 through March 31, 2017 and the predecessor period January 1, 2016 through March 31, 2016 was as follows: Gas Distribution Operations Gas Marketing Services Wholesale Gas Services (*) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Successor – January 1, 2017 Operating revenues $ 1,180 $ 288 $ 131 $ 25 $ 1,624 $ 2 $ (66 ) $ 1,560 Segment net income 117 31 68 15 231 8 — 239 Successor – Total assets at $ 18,201 $ 2,118 $ 1,018 $ 2,363 $ 23,700 $ 10,860 $ (12,877 ) $ 21,683 Predecessor – January 1, 2016 Operating revenues $ 1,028 $ 286 $ 63 $ 15 $ 1,392 $ 2 $ (60 ) $ 1,334 Segment EBIT 235 80 44 (1 ) 358 (5 ) (1 ) 352 Successor – Total assets at $ 19,453 $ 2,084 $ 1,127 $ 2,211 $ 24,875 $ 11,145 $ (14,167 ) $ 21,853 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Successor – January 1, 2017 through March 31, 2017 $ 1,839 $ 136 $ 1,975 $ 1,844 $ 131 Predecessor – January 1, 2016 through March 31, 2016 $ 1,443 $ 81 $ 1,524 $ 1,461 $ 63

Introduction (Policies)

Introduction (Policies)	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	The condensed quarterly financial statements of each registrant included herein have been prepared by such registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets as of December 31, 2016 have been derived from the audited financial statements of each registrant. In the opinion of each registrant's management, the information regarding such registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended March 31, 2017 and 2016 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each registrant believes that the disclosures regarding such registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Southern Company's financial statements reflect its investments in its subsidiaries, including Southern Company Gas as a result of the Merger, on a consolidated basis. Southern Company Gas' results of operations and cash flows for the three months ended March 31, 2017 and financial condition as of March 31, 2017 and December 31, 2016 are reflected within Southern Company's consolidated amounts in these accompanying notes herein. The equity method is used for entities in which Southern Company has significant influence but does not control, including Southern Company Gas' investment in SNG, and for variable interest entities where Southern Company has an equity investment but is not the primary beneficiary. See Note (I) under " Southern Company – Merger with Southern Company Gas " for additional information regarding the Merger. Pursuant to the Merger, Southern Company pushed down the application of the acquisition method of accounting to the consolidated financial statements of Southern Company Gas such that the assets and liabilities are recorded at their respective fair values, and goodwill has been established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the consolidated financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout Southern Company Gas' condensed consolidated financial statements and the accompanying notes herein, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor."
Reclassification	Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the results of operations, financial position, or cash flows of any registrant.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers , replacing the existing accounting standard and industry specific guidance for revenue recognition with a five-step model for recognizing and measuring revenue from contracts with customers. The underlying principle of the standard is to recognize revenue to depict the transfer of goods or services to customers at the amount expected to be collected. The new standard also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers. While the registrants expect most of their revenue to be included in the scope of ASC 606, they have not fully completed the evaluation of all revenue arrangements. The majority of Southern Company's, the traditional electric operating companies', and Southern Company Gas' revenue, including energy provided to customers, is from tariff offerings that provide electricity or natural gas without a defined contractual term. For such arrangements, the registrants expect that the revenue from contracts with these customers will continue to be equivalent to the electricity or natural gas supplied and billed in that period (including unbilled revenues) and the adoption of ASC 606 will not result in a significant shift in the timing of revenue recognition for such sales. The registrants' ongoing evaluation of other revenue streams and related contracts includes longer term contractual commitments and unregulated sales to customers. Some revenue arrangements, such as certain PPAs and alternative revenue programs, are excluded from the scope of ASC 606 and, therefore, will be accounted for and presented separately from revenues under ASC 606 on the registrants' financial statements. In addition, the power and utilities industry is currently addressing other specific industry issues, including the applicability of ASC 606 to contributions in aid of construction (CIAC). Although final implementation guidance has not been issued, Southern Company, the traditional electric operating companies, and Southern Company Gas expect CIAC to be out of the scope of ASC 606. Given Southern Power's core activities of selling generation capacity and energy to high credit rated customers, Southern Power currently does not expect the new standard to have a significant impact to net income. The new standard is effective for interim and annual reporting periods beginning after December 15, 2017. The registrants must select a transition method to be applied either retrospectively to each prior reporting period presented or retrospectively with a cumulative effect adjustment to retained earnings at the date of initial adoption. As the ultimate impact of the new standard has not yet been determined, the registrants have not elected a transition method. On January 26, 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 removes the requirement to compare the implied fair value of goodwill with the carrying amount as part of Step 2 of the goodwill impairment test. Under the new standard, the goodwill impairment loss will be measured as the excess of a reporting unit's carrying amount over its fair value, not exceeding the total amount of goodwill allocated to that reporting unit, which may increase the frequency of goodwill impairment charges if a future goodwill impairment test does not pass the Step 1 evaluation. ASU 2017-04 is effective prospectively for annual and interim periods beginning on or after December 15, 2019, and early adoption is permitted on testing dates after January 1, 2017. On March 10, 2017, the FASB issued ASU No. 2017-07, Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (ASU 2017-07). ASU 2017-07 requires that an employer report the service cost component in the same line item or items as other compensation costs and requires the other components of net periodic pension and postretirement benefit costs to be separately presented in the income statement outside income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. However, all cost components remain eligible for capitalization under FERC regulations. ASU 2017-07 will be applied retrospectively for the presentation of the service cost component and the other components of net periodic pension and postretirement benefit costs in the income statement. The capitalization of the service cost component of net periodic pension and postretirement benefit costs in assets will be applied on a prospective basis. ASU 2017-07 is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. Southern Company, the traditional electric operating companies, and Southern Company Gas are currently evaluating the new standard. The presentation changes required for net periodic pension and postretirement benefit costs will result in a decrease in Southern Company's , the traditional electric operating companies', and Southern Company Gas' operating income and an increase in other income for 2016 and 2017 and are expected to result in a decrease in operating income and an increase in other income for 2018. The adoption of ASU 2017-07 is not expected to have a material impact on Southern Company's , the traditional electric operating companies', or Southern Company Gas' financial statements.
Affiliate Transactions	Affiliate Transactions Prior to the completion of Southern Company Gas' acquisition of its 50% equity interest in SNG, SCS (as agent for Alabama Power, Georgia Power, and Southern Power) and Southern Company Gas had entered into long-term interstate natural gas transportation agreements with SNG. The interstate transportation service provided to Alabama Power, Georgia Power, Southern Power, and Southern Company Gas by SNG pursuant to these agreements is governed by the terms and conditions of SNG's natural gas tariff and is subject to FERC regulation. For the three months ended March 31, 2017, transportation costs under these agreements for Alabama Power, Georgia Power, Southern Power, and Southern Company Gas were approximately $1 million , $26 million , $6 million , and $9 million , respectively. SCS, as agent for Southern Power, has agreements with certain subsidiaries of Southern Company Gas to purchase natural gas. For the three months ended March 31, 2017, natural gas purchases made by Southern Power from Southern Company Gas' subsidiaries were approximately $23 million .
Goodwill and Other Intangible Assets	Goodwill is not amortized, but is subject to an annual impairment test during the fourth quarter of each year, or more frequently if impairment indicators arise.
Property Damage Reserve	Property Damage Reserve See Note 1 to the financial statements of Gulf Power under "Property Damage Reserve" in Item 8 of the Form 10-K for additional information. Gulf Power's cost of repairing damages from major storms and other uninsured property damages, including uninsured damages to transmission and distribution facilities, generation facilities, and other property is charged to Gulf Power's property damage reserve. In accordance with a settlement agreement approved by the Florida PSC on April 4, 2017 (2017 Rate Case Settlement Agreement), Gulf Power suspended further property damage reserve accruals effective April 2017. Gulf Power may make discretionary accruals, but is required to resume accruals of $3.5 million annually if the reserve balance falls below zero . In addition, Gulf Power may initiate a storm surcharge to recover costs associated with any tropical systems named by the National Hurricane Center or other catastrophic storm events that reduce the property damage reserve in the aggregate by approximately $31 million ( 75% of the April 1, 2017 balance) or more. The storm surcharge would begin, on an interim basis, 60 days following the filing of a cost recovery petition, would be limited to $4.00 /month for a 1,000 KWH residential customer unless Gulf Power incurs in excess of $100 million in qualified storm recovery costs in a calendar year, and would replenish the storm reserve to approximately $40 million . See Note (B) under " Regulatory Matters – Gulf Power – Retail Base Rate Cases " for additional details regarding the 2017 Rate Case Settlement Agreement.
Natural Gas For Sale	Natural Gas for Sale Southern Company Gas' natural gas distribution utilities, with the exception of Nicor Gas, carry natural gas inventory on a WACOG basis. Nicor Gas' natural gas inventory is carried at cost on a LIFO basis. Inventory decrements occurring during the year that are restored prior to year end are charged to cost of natural gas at the estimated annual replacement cost. Inventory decrements that are not restored prior to year end are charged to cost of natural gas at the actual LIFO cost of the inventory layers liquidated. Southern Company Gas' inventory decrement at March 31, 2017 is expected to be restored prior to year end. The cost of natural gas, including inventory costs, is recovered from customers under a purchased gas recovery mechanism adjusted for differences between actual costs and amounts billed; therefore, LIFO liquidations have no impact on Southern Company's or Southern Company Gas' net income. Natural gas inventories for Southern Company Gas' non-utility businesses are carried at the lower of weighted average cost or current market price, with cost determined on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Southern Company Gas recorded no LOCOM adjustment in the successor first quarter 2017 and recorded a $3 million LOCOM adjustment in the predecessor first quarter 2016 .
Derivatives	Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' wholesale gas operations use various contracts in its commercial activities that generally meet the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (C) for additional information. In the statements of cash flows, the cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. The cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with classification of the hedged interest or principal, respectively. Energy-Related Derivatives Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which is expected to continue to mitigate price volatility. The Florida PSC extended the moratorium on Gulf Power's fuel-hedging program through January 1, 2021 in connection with the 2017 Rate Case Settlement Agreement. The moratorium does not have an impact on the recovery of existing hedges entered into under the previously-approved hedging program. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in the statements of income. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts which are designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through the respective fuel cost recovery clauses. • Cash Flow Hedges — Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in OCI before being recognized in the statements of income in the same period as the hedged transactions are reflected in earnings. • Not Designated — Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. Interest Rate Derivatives Southern Company and certain subsidiaries may also enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the effective portion of the derivatives' fair value gains or losses is recorded in OCI and is reclassified into earnings at the same time the hedged transactions affect earnings, with any ineffectiveness recorded directly to earnings. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings, providing an offset, with any difference representing ineffectiveness. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred.
Valuation Methodologies	Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (H) for additional information on how these derivatives are used. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. For fair value measurements of the investments within the nuclear decommissioning trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. See Note 1 to the financial statements of Southern Company, Alabama Power, and Georgia Power under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. Southern Power has contingent payment obligations related to certain acquisitions whereby Southern Power is obligated to pay generation-based payments to the seller over a period ranging from 10 to 30 years, beginning at the commercial operation date. The obligation is categorized as Level 3 under Fair Value Measurements as the fair value is determined using significant unobservable inputs for the forecasted facility generation in MW-hours, as well as other inputs such as a fixed dollar amount per MW-hour, and a discount rate, and is evaluated periodically. The fair value of contingent consideration reflects the net present value of expected payments and any periodic change arising from forecasted generation is expected to be immaterial. "Other investments" include investments that are not traded in the open market. The fair value of these investments have been determined based on market factors including comparable multiples and the expectations regarding cash flows and business plan executions.
Earnings per Share	Earnings per Share For Southern Company, the only difference in computing basic and diluted earnings per share is attributable to awards outstanding under the stock option and performance share plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on the stock option and performance share plans. The effect of both stock options and performance share award units was determined using the treasury stock method.

Introduction (Tables)

Introduction (Tables)	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	As of March 31, 2017 and December 31, 2016, goodwill was as follows: Goodwill (in millions) Southern Company $ 6,251 Southern Power $ 2 Southern Company Gas Gas distribution operations $ 4,702 Gas marketing services 1,265 Southern Company Gas total $ 5,967
Schedule of Goodwill and Other Intangible Assets	Other intangible assets were as follows: As of March 31, 2017 As of December 31, 2016 Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 268 $ (44 ) $ 224 $ 268 $ (32 ) $ 236 Trade names 158 (8 ) 150 158 (5 ) 153 Patents 4 — 4 4 — 4 Backlog 5 (1 ) 4 5 (1 ) 4 Storage and transportation contracts 64 (15 ) 49 64 (2 ) 62 Software and other 2 (1 ) 1 2 — 2 PPA fair value adjustments 456 (28 ) 428 456 (22 ) 434 Total other intangible assets subject to amortization $ 957 $ (97 ) $ 860 $ 957 $ (62 ) $ 895 Other intangible assets not subject to amortization: Federal Communications Commission licenses $ 75 $ — $ 75 $ 75 $ — $ 75 Total other intangible assets $ 1,032 $ (97 ) $ 935 $ 1,032 $ (62 ) $ 970 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (28 ) $ 428 $ 456 $ (22 ) $ 434 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 221 $ (41 ) $ 180 $ 221 $ (30 ) $ 191 Trade names 115 (4 ) 111 115 (2 ) 113 Wholesale gas services Storage and transportation contracts 64 (15 ) 49 64 (2 ) 62 Total other intangible assets subject to amortization $ 400 $ (60 ) $ 340 $ 400 $ (34 ) $ 366
Finite-lived Intangible Assets Amortization Expense	Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2017 (in millions) Southern Company $ 35 Southern Power $ 6 Southern Company Gas $ 26

Contingencies and Regulatory 23

Contingencies and Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Recovery Balance of Each Regulatory Clause	The balance of each regulatory clause recovery on the balance sheet follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, 2016 (in millions) Fuel Cost Recovery Other regulatory liabilities, current $ 5 $ 15 Purchased Power Capacity Recovery Under recovered regulatory clause revenues 4 — Environmental Cost Recovery Under recovered regulatory clause revenues 40 13 Energy Conservation Cost Recovery Under recovered regulatory clause revenues 3 4 The balance of each regulatory clause recovery on the balance sheet follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, 2016 (in millions) Rate CNP Compliance (*) Deferred under recovered regulatory clause revenues $ — $ 9 Rate CNP PPA Over recovered regulatory clause revenues 3 — Deferred under recovered regulatory clause revenues — 142 Retail Energy Cost Recovery Other regulatory liabilities, current 40 76 Natural Disaster Reserve Other regulatory liabilities, deferred 66 69 (*) In accordance with an accounting order issued on February 17, 2017 by the Alabama PSC, Alabama Power reclassified the $23 million under recovered balance for Rate CNP Compliance to a deferred regulatory asset account.
Current And Actual Cost Estimate for Kemper IGCC	As of March 31, 2017, in addition to the $2.87 billion of costs above the Mississippi PSC's $2.88 billion cost cap that have been recognized as a charge to income, Mississippi Power had incurred approximately $2.01 billion in costs subject to the cost cap and approximately $1.50 billion in Cost Cap Exceptions related to the construction and start-up of the Kemper IGCC that are not included in current rates. These costs primarily relate to the following: Cost Category Actual Costs (in billions) Gasifiers and Gas Clean-up Facilities $ 1.90 Lignite Mine Facility 0.31 CO 2 Pipeline Facilities 0.11 Combined Cycle and Common Facilities 0.17 AFUDC 0.73 General exceptions 0.07 Plant inventory 0.04 Lignite inventory 0.06 Regulatory and other deferred assets 0.12 Subtotal 3.51 Additional DOE Grants (0.14 ) Total $ 3.37 Mississippi Power's Kemper IGCC 2010 project estimate, current cost estimate (which includes the impacts of the Mississippi Supreme Court's (Court) decision discussed herein under "Rate Recovery of Kemper IGCC Costs – 2013 MPSC Rate Order"), and actual costs incurred as of March 31, 2017 , all of which include 100% of the costs for the Kemper IGCC, are as follows: Cost Category 2010 Project Estimate (a) Current Cost Estimate (b) Actual Costs (in billions) Plant Subject to Cost Cap (c)(e) $ 2.40 $ 5.75 $ 5.57 Lignite Mine and Equipment 0.21 0.23 0.23 CO 2 Pipeline Facilities 0.14 0.12 0.12 AFUDC (d) 0.17 0.83 0.80 Combined Cycle and Related Assets Placed in (e) — 0.05 0.04 General Exceptions 0.05 0.10 0.09 Deferred Costs (e) — 0.22 0.22 Additional DOE Grants (f) — (0.14 ) (0.14 ) Total Kemper IGCC (g) $ 2.97 $ 7.16 $ 6.93 (a) The 2010 Project Estimate is the certificated cost estimate adjusted to include the certificated estimate for the CO 2 pipeline facilities approved in 2011 by the Mississippi PSC, as well as the lignite mine and equipment, AFUDC, and general exceptions. (b) Amounts in the Current Cost Estimate include certain estimated post-in-service costs which are expected to be subject to the cost cap. (c) The 2012 MPSC CPCN Order approved a construction cost cap of up to $2.88 billion , net of the Initial DOE Grants and excluding the cost of the lignite mine and equipment, the cost of the CO 2 pipeline facilities, AFUDC, and certain general exceptions, including change of law, force majeure, and beneficial capital (which exists when Mississippi Power demonstrates that the purpose and effect of the construction cost increase is to produce efficiencies that will result in a neutral or favorable effect on customers relative to the original proposal for the CPCN) (Cost Cap Exceptions). The Current Cost Estimate and the Actual Costs include non-incremental operating and maintenance costs related to the combined cycle and associated common facilities placed in service in August 2014 that are subject to the $2.88 billion cost cap and exclude post-in-service costs for the lignite mine. See " Rate Recovery of Kemper IGCC Costs – 2013 MPSC Rate Order " herein for additional information. (d) Mississippi Power's 2010 Project Estimate included recovery of financing costs during construction rather than the accrual of AFUDC. This approach was not approved by the Mississippi PSC as described in " Rate Recovery of Kemper IGCC Costs – 2013 MPSC Rate Order ." The Current Cost Estimate also reflects the impact of a settlement agreement with the wholesale customers for cost-based rates under FERC's jurisdiction. See " FERC Matters " herein for additional information. (e) Non-capital Kemper IGCC-related costs incurred during construction were initially deferred as regulatory assets. Some of these costs are now included in rates and are being recognized through income; however, such costs continue to be included in the Current Cost Estimate and the Actual Costs at March 31, 2017 . The wholesale portion of debt carrying costs, whether deferred or recognized through income, is not included in the Current Cost Estimate and the Actual Costs at March 31, 2017 . See " Rate Recovery of Kemper IGCC Costs – Regulatory Assets and Liabilities " herein for additional information. (f) On April 8, 2016, Mississippi Power received approximately $137 million in additional grants from the DOE for the Kemper IGCC (Additional DOE Grants), which are expected to be used to reduce future rate impacts for customers. (g) The Current Cost Estimate and the Actual Costs include $2.87 billion that will not be recovered for costs above the cost cap, $0.83 billion of investment costs included in current rates for the combined cycle and related assets in service, and $0.09 billion of costs that were previously expensed for the combined cycle and related assets in service. The Current Cost Estimate and the Actual Costs exclude $0.23 billion of costs not included in current rates for post-June 2013 mine operations, the lignite fuel inventory, and the nitrogen plant capital lease, which will be included in the 2017 Rate Case to be filed by June 3, 2017. See Note 1 and Note 6 to the financial statements of Mississippi Power under "Fuel Inventory" and "Capital Leases," respectively, in Item 8 of the Form 10-K and " Rate Recovery of Kemper IGCC Costs – 2017 Rate Case " herein for additional information.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value on a recurring basis	As of March 31, 2017 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 274 $ 213 $ — $ — $ 487 Interest rate derivatives — 13 — — 13 Nuclear decommissioning trusts (c) 714 942 — 21 1,677 Cash equivalents 589 — — — 589 Other investments 9 — 1 — 10 Total $ 1,586 $ 1,168 $ 1 $ 21 $ 2,776 Liabilities: Energy-related derivatives (a)(b) $ 303 $ 155 $ — $ — $ 458 Interest rate derivatives — 32 — — 32 Foreign currency derivatives — 62 — — 62 Contingent consideration — — 20 — 20 Total $ 303 $ 249 $ 20 $ — $ 572 Alabama Power Assets: Energy-related derivatives $ — $ 11 $ — $ — $ 11 Nuclear decommissioning trusts: (d) Domestic equity 405 77 — — 482 Foreign equity 52 51 — — 103 U.S. Treasury and government agency securities — 28 — — 28 Corporate bonds 22 143 — — 165 Mortgage and asset backed securities — 18 — — 18 Private Equity — — — 21 21 Other — 7 — — 7 Cash equivalents 555 — — — 555 Total $ 1,034 $ 335 $ — $ 21 $ 1,390 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Georgia Power Assets: Energy-related derivatives $ — $ 24 $ — $ — $ 24 Interest rate derivatives — 2 — — 2 Nuclear decommissioning trusts: (d) (e) Domestic equity 216 1 — — 217 Foreign equity — 137 — — 137 U.S. Treasury and government agency securities — 196 — — 196 Municipal bonds — 70 — — 70 Corporate bonds — 168 — — 168 Mortgage and asset backed securities — 41 — — 41 Other 19 5 — — 24 Cash equivalents — — — — — Total $ 235 $ 644 $ — $ — $ 879 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Interest rate derivatives — 4 — — 4 Total $ — $ 17 $ — $ — $ 17 Gulf Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Cash equivalents 21 — — — 21 Total $ 21 $ 2 $ — $ — $ 23 Liabilities: Energy-related derivatives $ — $ 31 $ — $ — $ 31 Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Interest rate derivatives — 4 — — 4 Total $ — $ 7 $ — $ — $ 7 Liabilities: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Fair Value Measurements Using: As of March 31, 2017: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Power Assets: Energy-related derivatives $ — $ 15 $ — $ — $ 15 Liabilities: Energy-related derivatives $ — $ 5 $ — $ — $ 5 Foreign currency derivatives — 62 — — 62 Contingent consideration — — 20 — 20 Total $ — $ 67 $ 20 $ — $ 87 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 274 $ 158 $ — $ — $ 432 Liabilities: Energy-related derivatives (a)(b) $ 303 $ 84 $ — $ — $ 387 (a) Excludes $19 million associated with certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $92 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. (e) Includes the investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2017 , approximately $56 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program.
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments	As of March 31, 2017 , the fair value measurements of private equity investments held in the nuclear decommissioning trust that are calculated at net asset value per share (or its equivalent) as a practical expedient, as well as the nature and risks of those investments, were as follows: As of March 31, 2017: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 21 $ 22 Not Applicable Not Applicable Alabama Power $ 21 $ 22 Not Applicable Not Applicable
Financial instruments for which carrying amount did not equal fair value	As of March 31, 2017 , other financial instruments for which the carrying amount did not equal fair value were as follows: Carrying Amount Fair Value (in millions) Long-term debt, including securities due within one year: Southern Company $ 45,881 $ 46,828 Alabama Power $ 7,439 $ 7,807 Georgia Power $ 11,362 $ 11,777 Gulf Power $ 1,079 $ 1,110 Mississippi Power $ 2,977 $ 2,909 Southern Power $ 5,648 $ 5,694 Southern Company Gas $ 5,268 $ 5,487

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Earnings per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) As reported shares 993 916 Effect of options and performance share award units 7 6 Diluted shares 1,000 922
Changes in Stockholders' Equity	The following table presents year-to-date changes in stockholders' equity of Southern Company: Number of Common Shares Common Preferred and Preference Stock of Subsidiaries Total Issued Treasury Noncontrolling Interests (*) (in thousands) (in millions) Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — 658 — — 658 Other comprehensive income (loss) — — (9 ) — — (9 ) Stock issued 4,240 — 186 — — 186 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (556 ) — — (556 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (18 ) (18 ) Net income attributable to noncontrolling interests — — — — (4 ) (4 ) Other — (35 ) — — (1 ) (1 ) Balance at March 31, 2017 995,453 (854 ) $ 25,094 $ 609 $ 1,293 $ 26,996 Balance at December 31, 2015 915,073 (3,352 ) $ 20,592 $ 609 $ 781 $ 21,982 Consolidated net income attributable to Southern Company — — 489 — — 489 Other comprehensive income (loss) — — (114 ) — — (114 ) Stock issued 6,572 — 270 — — 270 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (497 ) — — (497 ) Contributions from noncontrolling interests — — — — 129 129 Distributions to noncontrolling interests — — — — (4 ) (4 ) Purchase of membership interests from noncontrolling interests — — — — (129 ) (129 ) Net income attributable to noncontrolling interests — — — — 1 1 Other — (35 ) — — — Balance at March 31, 2016 921,645 (3,387 ) $ 20,797 $ 609 $ 778 $ 22,184 (*) Related to Southern Power Company and excludes redeemable noncontrolling interests. Subsequent to March 31, 2017, approximately $114 million was reclassified from redeemable noncontrolling interests to noncontrolling interests, included in stockholder's equity, due to the expiration of SunPower Corp's option to require Southern Power to purchase its membership interests in one of the solar partnerships. See Note 10 to the financial statements of Southern Power in Item 8 of the Form 10-K for additional information.

Financing (Tables)

Financing (Tables)	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Credit arrangements by company	The following table outlines the committed credit arrangements by company as of March 31, 2017 : Expires Executable Term Loans Expires Within One Year Company 2017 2018 2020 Total Unused One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ 1,000 $ 1,250 $ 2,250 $ 2,250 $ — $ — $ — $ — Alabama Power 35 500 800 1,335 1,335 — — — 35 Georgia Power — — 1,750 1,750 1,732 — — — — Gulf Power 85 195 — 280 280 45 — 25 70 Mississippi Power 173 — — 173 141 — 13 13 160 Southern Power Company — — 600 600 524 — — — — Southern Company Gas (b) 75 1,925 — 2,000 1,949 — — — 75 Other 55 — — 55 55 20 — 20 35 Southern Company Consolidated $ 423 $ 3,620 $ 4,400 $ 8,443 $ 8,266 $ 65 $ 13 $ 58 $ 375 (a) Represents the Southern Company parent entity. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.3 billion of these arrangements. Southern Company Gas' committed credit arrangements also include $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas.
Schedule of Long-term Debt Financing Activities	The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first three months of 2017 : Company (a) Senior Note Issuances Senior Note Maturities and Redemptions Other Long-Term Debt Issuances Other Long-Term Debt Redemptions and Maturities (b) (in millions) Southern Company (c) $ — $ — $ — $ 400 Alabama Power 550 200 — — Georgia Power 850 — — 2 Gulf Power — — 6 — Southern Power — — 3 2 Other — — — 4 Southern Company Consolidated $ 1,400 $ 200 $ 9 $ 408 (a) Mississippi Power and Southern Company Gas did not issue or redeem any long-term debt during the first three months of 2017. (b) Includes reductions in capital lease obligations resulting from cash payments under capital leases. (c) Represents the Southern Company parent entity.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three months ended March 31, 2017 and 2016 are presented in the following tables. Pension Plans Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Three Months Ended March 31, 2017 Service cost $ 73 $ 16 $ 19 $ 3 $ 4 Interest cost 114 24 34 5 5 Expected return on plan assets (224 ) (49 ) (71 ) (10 ) (10 ) Amortization: Prior service costs 3 1 1 — — Net (gain)/loss 40 10 14 2 2 Net periodic pension cost (income) $ 6 $ 2 $ (3 ) $ — $ 1 Three Months Ended March 31, 2016 Service cost $ 62 $ 14 $ 17 $ 3 $ 3 Interest cost 100 24 34 5 5 Expected return on plan assets (187 ) (46 ) (64 ) (9 ) (9 ) Amortization: Prior service costs 4 1 1 — — Net (gain)/loss 38 10 14 2 2 Net periodic pension cost $ 17 $ 3 $ 2 $ 1 $ 1 Pension Plans Southern Company Gas (in millions) Successor – Three Months Ended March 31, 2017 Service cost $ 6 Interest cost 10 Expected return on plan assets (18 ) Amortization: Prior service costs — Net (gain)/loss 5 Net periodic pension cost $ 3 Predecessor – Three Months Ended March 31, 2016 Service cost $ 6 Interest cost 10 Expected return on plan assets (16 ) Amortization: Prior service costs — Net (gain)/loss 6 Net periodic pension cost $ 6 Postretirement Benefits Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Three Months Ended March 31, 2017 Service cost $ 6 $ 1 $ 2 $ — $ — Interest cost 20 5 7 1 1 Expected return on plan assets (16 ) (6 ) (6 ) — — Amortization: Prior service costs 2 1 — — — Net (gain)/loss 2 — 2 — — Net periodic postretirement benefit cost $ 14 $ 1 $ 5 $ 1 $ 1 Three Months Ended March 31, 2016 Service cost $ 5 $ 1 $ 2 $ — $ — Interest cost 18 5 8 1 1 Expected return on plan assets (14 ) (6 ) (6 ) — — Amortization: Prior service costs 2 1 — — — Net (gain)/loss 3 — 2 — — Net periodic postretirement benefit cost $ 14 $ 1 $ 6 $ 1 $ 1 Postretirement Benefits Southern Company Gas (in millions) Successor – Three Months Ended March 31, 2017 Service cost $ 1 Interest cost 3 Expected return on plan assets (2 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 2 Predecessor – Three Months Ended March 31, 2016 Service cost $ 1 Interest cost 3 Expected return on plan assets (2 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 2

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Change in Unrecognized Tax Benefits	Changes during the three months ended March 31, 2017 for unrecognized tax benefits were as follows: Mississippi Power Southern Power Southern Company (in millions) Unrecognized tax benefits as of December 31, 2016 $ 465 $ 17 $ 484 Tax positions from current periods 3 1 9 Tax positions from prior periods — — 7 Balance as of March 31, 2017 $ 468 $ 18 $ 500
Impact on Effective Tax Rate, If Recognized	The impact on the effective tax rate, if recognized, is as follows: As of March 31, 2017 As of December 31, 2016 Mississippi Power Southern Power Southern Company Southern Company (in millions) Tax positions impacting the effective tax rate $ 4 $ 18 $ 36 $ 20 Tax positions not impacting the effective tax rate 464 — 464 464 Balance of unrecognized tax benefits $ 468 $ 18 $ 500 $ 484

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of energy-related derivatives	At March 31, 2017 , the net volume of energy-related derivative contracts for natural gas positions for the Southern Company system, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 503 2021 2024 Alabama Power 71 2020 — Georgia Power 155 2020 — Gulf Power 42 2020 — Mississippi Power 37 2021 — Southern Power 21 2017 2017 Southern Company Gas (*) 177 2019 2024 (*) Southern Company's and Southern Company Gas' derivative instruments include both long and short natural gas positions. A long position is a contract to purchase natural gas and a short position is a contract to sell natural gas. Southern Company Gas' volume represents the net of long natural gas positions of 3.4 billion mmBtu and short natural gas positions of 3.2 billion mmBtu as of March 31, 2017 , which is also included in Southern Company's total volume.
Schedule of interest rate derivatives	At March 31, 2017 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Gulf Power $ 80 3-month 2.32% December 2026 $ — Cash Flow Hedges of Existing Debt Mississippi Power 900 1-month 0.79% March 2018 4 Fair Value Hedges of Existing Debt Southern Company (*) 250 1.30% 3-month August 2017 — Southern Company (*) 300 2.75% 3-month June 2020 1 Southern Company (*) 1,500 2.35% 1-month July 2021 (21 ) Georgia Power 250 5.40% 3-month June 2018 — Georgia Power 500 1.95% 3-month December 2018 (3 ) Georgia Power 200 4.25% 3-month December 2019 1 Southern Company Consolidated $ 3,980 $ (18 ) (*) Represents the Southern Company parent entity.
Schedule of foreign currency derivatives	At March 31, 2017 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ (35 ) Southern Power 564 3.78% 500 1.85% June 2026 (27 ) Total $ 1,241 € 1,100 $ (62 )
Fair value of energy-related derivatives and interest rate derivatives	The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 48 $ 30 $ 73 $ 27 Other deferred charges and assets/Other deferred credits and liabilities 6 38 25 33 Total derivatives designated as hedging instruments for regulatory purposes $ 54 $ 68 $ 98 $ 60 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 14 $ 5 $ 23 $ 7 Interest rate derivatives: Other current assets/Liabilities from risk management activities, net of collateral 13 — 12 1 Other deferred charges and assets/Other deferred credits and liabilities — 32 1 28 Foreign currency derivatives: Other current assets/Liabilities from risk management activities, net of collateral — 25 — 25 Other deferred charges and assets/Other deferred credits and liabilities — 37 — 33 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 27 $ 99 $ 36 $ 94 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Liabilities from risk management activities, net of collateral $ 306 $ 271 $ 489 $ 483 Other deferred charges and assets/Other deferred credits and liabilities 132 114 66 81 Interest rate derivatives: Other current assets/Liabilities from risk management activities, net of collateral — — 1 — Total derivatives not designated as hedging instruments $ 438 $ 385 $ 556 $ 564 Gross amounts recognized $ 519 $ 552 $ 690 $ 718 Gross amounts offset (*) $ (303 ) $ (395 ) $ (462 ) $ (524 ) Net amounts recognized in the Balance Sheets $ 216 $ 157 $ 228 $ 194 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities $ 9 $ 5 $ 13 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 2 5 7 4 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 10 $ 20 $ 9 Gross amounts recognized $ 11 $ 10 $ 20 $ 9 Gross amounts offset $ (6 ) $ (6 ) $ (8 ) $ (8 ) Net amounts recognized in the Balance Sheets $ 5 $ 4 $ 12 $ 1 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 20 $ 2 $ 30 $ 1 Other deferred charges and assets/Other deferred credits and liabilities 4 11 14 7 Total derivatives designated as hedging instruments for regulatory purposes $ 24 $ 13 $ 44 $ 8 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 2 $ — $ 2 $ — Other deferred charges and assets/Other deferred credits and liabilities — 4 — 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 4 $ 2 $ 3 Gross amounts recognized $ 26 $ 17 $ 46 $ 11 Gross amounts offset $ (6 ) $ (6 ) $ (8 ) $ (8 ) Net amounts recognized in the Balance Sheets $ 20 $ 11 $ 38 $ 3 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Liabilities from risk management activities $ 2 $ 14 $ 4 $ 12 Other deferred charges and assets/Other deferred credits and liabilities — 17 1 17 Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 31 $ 5 $ 29 Gross amounts recognized $ 2 $ 31 $ 5 $ 29 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ — $ 29 $ 1 $ 25 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 7 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — 5 2 5 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 12 $ 4 $ 11 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ 4 $ — $ 2 $ — Other deferred charges and assets/Other deferred credits and liabilities — — 1 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 4 $ — $ 3 $ — Gross amounts recognized $ 7 $ 12 $ 7 $ 11 Gross amounts offset $ (2 ) $ (2 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 5 $ 10 $ 4 $ 8 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 13 $ 4 $ 18 $ 4 Foreign currency derivatives: Other current assets/Other current liabilities — 25 — 25 Other deferred charges and assets/Other deferred credits and liabilities — 37 — 33 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 13 $ 66 $ 18 $ 62 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 1 $ 3 $ 1 Interest rate derivatives: Other current assets/Other current liabilities — — 1 — Total derivatives not designated as hedging instruments $ 2 $ 1 $ 4 $ 1 Gross amounts recognized $ 15 $ 67 $ 22 $ 63 Gross amounts offset $ (3 ) $ (3 ) $ (5 ) $ (5 ) Net amounts recognized in the Balance Sheets $ 12 $ 64 $ 17 $ 58 As of March 31, 2017 As of December 31, 2016 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 14 $ 2 $ 24 $ 3 Other deferred charges and assets/Other deferred credits and liabilities — — 1 — Total derivatives designated as hedging instruments for regulatory purposes $ 14 $ 2 $ 25 $ 3 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 1 $ 1 $ 4 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 304 $ 270 $ 486 $ 482 Other deferred charges and assets/Other deferred credits and liabilities 132 114 66 81 Total derivatives not designated as hedging instruments $ 436 $ 384 $ 552 $ 563 Gross amounts of recognized $ 451 $ 387 $ 581 $ 569 Gross amounts offset (*) $ (272 ) $ (364 ) $ (435 ) $ (497 ) Net amounts recognized in the Balance Sheets $ 179 $ 23 $ 146 $ 72 (*) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $92 million and $62 million as of March 31, 2017 and December 31, 2016 , respectively.
Pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments	At March 31, 2017 and December 31, 2016 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at March 31, 2017 Derivative Category and Balance Sheet Location Southern Company (b) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (b) (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (1 ) $ — $ (12 ) $ (5 ) $ (1 ) Other regulatory assets, deferred (32 ) (3 ) (7 ) (17 ) (5 ) — Other regulatory liabilities, current (a) 33 5 18 — 1 9 Total energy-related derivative gains (losses) $ (18 ) $ 1 $ 11 $ (29 ) $ (9 ) $ 8 (a) Georgia Power includes other regulatory liabilities, current in other current liabilities. (b) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $ 4 million at March 31, 2017 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2016 Derivative Category and Balance Sheet Location Southern Company (c) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (c) (in millions) Energy-related derivatives: Other regulatory assets, current $ (16 ) $ (1 ) $ — $ (9 ) $ (5 ) $ (1 ) Other regulatory assets, deferred (19 ) — — (16 ) (3 ) — Other regulatory liabilities, current (a) 56 8 29 1 1 17 Other regulatory liabilities, deferred (b) 12 4 7 — — 1 Total energy-related derivative gains (losses) $ 33 $ 11 $ 36 $ (24 ) $ (7 ) $ 17 (a) Georgia Power includes other regulatory liabilities, current in other current liabilities. (b) Georgia Power includes other regulatory liabilities, deferred in other deferred credits and liabilities. (c) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $ 8 million at December 31, 2016 .
Pre-tax effects of interest rate derivatives, designated as cash flow hedging instruments	For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives, interest rate derivatives, and foreign currency derivatives designated as cash flow hedging instruments were as follows: Derivatives in Cash Flow Hedging Relationships Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Statements of Income Location Amount 2017 2016 2017 2016 (in millions) (in millions) Southern Company Energy-related derivatives $ (11 ) $ — Depreciation and amortization $ (4 ) $ (1 ) Interest rate derivatives 1 (190 ) Interest expense, net of amounts capitalized (5 ) (3 ) Foreign currency derivatives (4 ) — Interest expense, net of amounts capitalized (6 ) — Other income (expense), net (*) 17 — Total $ (14 ) $ (190 ) $ 2 $ (4 ) Gulf Power Energy-related derivatives $ (1 ) $ — Depreciation and amortization $ — $ — Interest rate derivatives — (5 ) Interest expense, net of amounts capitalized — — Total $ (1 ) $ (5 ) $ — $ — Southern Power Energy-related derivatives $ (8 ) $ — Depreciation and amortization $ (4 ) $ (1 ) Foreign currency derivatives (4 ) — Interest expense, net of amounts capitalized (6 ) — Other income (expense), net (*) 17 — Total $ (12 ) $ — $ 7 $ (1 ) (*) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes. For Southern Company Gas, the pre-tax effect of energy related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings for the three months ended March 31, 2017 and the predecessor period of January 1, 2016 through March 31, 2016 were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Successor Predecessor Successor Predecessor Derivatives in Cash Flow Hedging Relationships Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 Statements of Income Location Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives $ (2 ) $ — Cost of natural gas $ — $ — Interest rate derivatives — (45 ) Interest expense, net of amounts capitalized — 1 Total $ (2 ) $ (45 ) $ — $ 1
Pre tax effect of interest rate and energy related derivatives	For the three months ended March 31, 2017 and 2016 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments on the statements of income were as follows: Gain (Loss) Three Months Ended Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2017 2016 (in millions) Southern Company Energy Related derivatives: Natural gas revenues (*) $ 50 $ — Cost of natural gas (3 ) — Total derivatives in non-designated hedging relationships $ 47 $ — (*) Excludes gains (losses) recorded in cost of natural gas associated with weather derivatives of $14 million for the three months ended March 31, 2017 . Gain (Loss) Successor Predecessor Derivatives in Non-Designated Hedging Relationships Statements of Income Location Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) Southern Company Gas Energy Related derivatives: Natural gas revenues (*) $ 50 $ 20 Cost of natural gas (3 ) (1 ) Total derivatives in non-designated hedging relationships $ 47 $ 19 (*) Excludes gains (losses) recorded in cost of natural gas associated with weather derivatives of $14 million for the successor three months ended March 31, 2017 and $3 million for the predecessor three months ended March 31, 2016 .
Pre-tax effects of interest rate derivatives, designated as fair value hedging instruments	For the three months ended March 31, 2017 and 2016 , the pre-tax effects of interest rate derivatives designated as fair value hedging instruments were as follows: Derivatives in Fair Value Hedging Relationships Gain (Loss) Three Months Ended March 31, Derivative Category Statements of Income Location 2017 2016 (in millions) Southern Company Interest rate derivatives: Interest expense, net of amounts capitalized $ (8 ) $ 20 Georgia Power Interest rate derivatives: Interest expense, net of amounts capitalized $ (1 ) $ 14

Acquisitions (Tables)

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
Schedule of Business Acquisitions	The following table presents the purchase price allocation: Southern Company Gas Purchase Price (in millions) Current assets $ 1,557 Property, plant, and equipment 10,108 Goodwill 5,967 Intangible assets 400 Regulatory assets 1,118 Other assets 229 Current liabilities (2,201 ) Other liabilities (4,742 ) Long-term debt (4,261 ) Noncontrolling interest (174 ) Total purchase price $ 8,001 The following table presents the purchase price allocation: PowerSecure Purchase Price (in millions) Current assets $ 172 Property, plant, and equipment 46 Intangible assets 101 Goodwill 282 Other assets 4 Current liabilities (114 ) Long-term debt, including current portion (48 ) Deferred credits and other liabilities (14 ) Total purchase price $ 429 During the three months ended March 31, 2017, in accordance with Southern Power's overall growth strategy, Southern Renewable Partnerships, LLC (SRP), one of Southern Power's wholly-owned subsidiaries, acquired the Bethel wind facility . Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller; Acquisition Date Approximate Nameplate Capacity ( MW ) Location Southern Power Percentage Ownership Actual COD PPA Contract Period Bethel Wind Invenergy, 276 Castro County, TX 100 % January 2017 12 years
Business Acquisition, Pro Forma Information	The following summarized unaudited pro forma consolidated statement of earnings information assumes that the acquisition of Southern Company Gas was completed on January 1, 2015. The summarized unaudited pro forma consolidated statement of earnings information includes adjustments for (i) intercompany sales, (ii) amortization of intangible assets, (iii) adjustments to interest expense to reflect current interest rates on Southern Company Gas debt and additional interest expense associated with borrowings by Southern Company to fund the Merger, and (iv) the elimination of nonrecurring expenses associated with the Merger. For the Three Months Ended March 31, 2016 Operating revenues (in millions) $ 5,320 Net income attributable to Southern Company (in millions) $ 650 Basic EPS $ 0.70 Diluted EPS $ 0.69
Schedule of Construction Projects	During the three months ended March 31, 2017 , in accordance with its overall growth strategy, Southern Power completed construction of and placed in service, or continued construction of, the projects set forth in the following table. Through March 31, 2017 , total costs of construction incurred for these three projects were $401 million , of which $203 million remained in CWIP for the Lamesa and Mankato facilities acquired in 2016. Total aggregate construction costs, excluding the acquisition costs, are expected to be $530 million to $590 million for these two facilities that were under construction at March 31, 2017 . The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Project Completed During the Three Months Ended March 31, 2017 East Pecos Solar 120 Pecos County, TX March 2017 15 years Projects Under Construction as of March 31, 2017 Lamesa Solar 102 Dawson County, TX April 2017 15 years Mankato Natural Gas 345 Mankato, MN Second quarter 2019 20 years

Joint Ownership Agreements (Tab

Joint Ownership Agreements (Tables)	3 Months Ended
	Mar. 31, 2017
Regulated Operations [Abstract]
Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2017 and December 31, 2016 and related income from those investments for the successor period ended March 31, 2017 and the predecessor period ended March 31, 2016 were as follows: Balance Sheet Information March 31, 2017 December 31, 2016 (in millions) SNG $ 1,430 $ 1,394 Triton 44 44 Horizon Pipeline 31 30 PennEast Pipeline 30 22 Atlantic Coast Pipeline 42 33 Pivotal JAX LNG, LLC 26 16 Other 1 2 Total $ 1,604 $ 1,541 Selected financial information of SNG for the first quarter 2017 is as follows: Income Statement Information Three Months Ended March 31, 2017 (in millions) Revenues $ 155 Operating income $ 84 Net income $ 66
Schedule of Other Nonoperating Income, by Component	Successor Predecessor Income Statement Information Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 (in millions) (in millions) SNG $ 34 $ — Horizon Pipeline 1 1 PennEast Pipeline 3 — Atlantic Coast Pipeline 1 — Total $ 39 $ 1

Segment and Related Informati32

Segment and Related Information (Tables)	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Financial data for business segments	Financial data for business segments and products and services for the three months ended March 31, 2017 and 2016 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) Three Months Ended Operating revenues $ 3,786 $ 450 $ (105 ) $ 4,131 $ 1,560 $ 123 $ (43 ) $ 5,771 Segment net income (loss) (a)(b)(c) 432 70 — 502 239 (84 ) 1 658 Total assets at March 31, 2017 $ 72,692 $ 14,681 $ (306 ) $ 87,067 $ 21,683 $ 2,574 $ (1,564 ) $ 109,760 Three Months Ended Operating revenues $ 3,769 $ 315 $ (103 ) $ 3,981 $ — $ 47 $ (36 ) $ 3,992 Segment net income (loss) (a)(b) 465 50 — 515 — (23 ) (3 ) 489 Total assets at December 31, 2016 $ 72,141 $ 15,169 $ (316 ) $ 86,994 $ 21,853 $ 2,474 $ (1,624 ) $ 109,697 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated probable losses on the Kemper IGCC of $108 million ( $67 million after tax) and $53 million ( $33 million after tax) for the three months ended March 31, 2017 and 2016 , respectively. See Note (B) under " Integrated Coal Gasification Combined Cycle – Kemper IGCC Schedule and Cost Estimate " for additional information. (c) Segment net income (loss) for the traditional electric operating companies also includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) for the three months ended March 31, 2017 . See Note (B) under " Regulatory Matters – Gulf Power – Retail Base Rate Cases " for additional information. Business segment financial data for the successor period January 1, 2017 through March 31, 2017 and the predecessor period January 1, 2016 through March 31, 2016 was as follows: Gas Distribution Operations Gas Marketing Services Wholesale Gas Services (*) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Successor – January 1, 2017 Operating revenues $ 1,180 $ 288 $ 131 $ 25 $ 1,624 $ 2 $ (66 ) $ 1,560 Segment net income 117 31 68 15 231 8 — 239 Successor – Total assets at $ 18,201 $ 2,118 $ 1,018 $ 2,363 $ 23,700 $ 10,860 $ (12,877 ) $ 21,683 Predecessor – January 1, 2016 Operating revenues $ 1,028 $ 286 $ 63 $ 15 $ 1,392 $ 2 $ (60 ) $ 1,334 Segment EBIT 235 80 44 (1 ) 358 (5 ) (1 ) 352 Successor – Total assets at $ 19,453 $ 2,084 $ 1,127 $ 2,211 $ 24,875 $ 11,145 $ (14,167 ) $ 21,853 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Successor – January 1, 2017 through March 31, 2017 $ 1,839 $ 136 $ 1,975 $ 1,844 $ 131 Predecessor – January 1, 2016 through March 31, 2016 $ 1,443 $ 81 $ 1,524 $ 1,461 $ 63
Financial data for products and services	Products and Services Electric Utilities' Revenues Period Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2017 $ 3,394 $ 531 $ 206 $ 4,131 Three Months Ended March 31, 2016 3,377 396 208 3,981 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended March 31, 2017 $ 1,132 $ 288 $ 140 $ 1,560

Introduction - Narrative (Detai

Introduction - Narrative (Details)	Apr. 30, 2017USD ($)	Apr. 01, 2017USD ($)	Mar. 31, 2017USD ($)kWh	Apr. 04, 2017USD ($)	Mar. 31, 2016USD ($)
Gulf Power [Member]
Related Party Transaction [Line Items]
Number of agreements for renewable generation			$ 40,000,000
Recovery period for natural disaster reserve costs			60 days
Cumulative costs limit under PSC order			$ 100,000,000
Southern Company Gas [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transactions			23,000,000
Southern Natural Gas Company, LLC [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Related party transactions			9,000,000
Southern Natural Gas Company, LLC [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transactions			1,000,000
Southern Natural Gas Company, LLC [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transactions			26,000,000
Southern Natural Gas Company, LLC [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transactions			6,000,000
Subsequent Event [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Property damage reserve, percentage of balance		0.75
Subsequent Event [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Psc approved annual property damage reserve accrual		$ 3,500,000
Number of agreements for renewable generation				$ 0
Increase (decrease) in recoverable property damage costs	$ 31,000,000
Maximum [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Customer surcharge storm recovery costs			$ 4
Customer surcharge storm recovery capacity | kWh			1,000
Wholesale Gas Services [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Inventory valuation reserves			$ 0
Predecessor [Member] | Wholesale Gas Services [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Inventory valuation reserves					$ 3,000,000

Introduction - Goodwill and Int

Introduction - Goodwill and Intangible Assets (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 6,251,000,000	$ 6,251,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	957,000,000	957,000,000
Other intangibles subject to amortization - accumulated amortization	(97,000,000)	(62,000,000)
Other intangibles subject to amortization - net	860,000,000	895,000,000
Total other intangible assets - gross	1,032,000,000	1,032,000,000
Total other intangible assets - net	$ 935,000,000	970,000,000
Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	11 years
Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	26 years
Trade Names [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years
Trade Names [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	28 years
Patents [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	3 years
Patents [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Storage and transportation contracts [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Storage and transportation contracts [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years
Software and other [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Software and other [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	12 years
Southern Company [Member] | FCC Licenses [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	$ 75,000,000	75,000,000
Southern Company [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	268,000,000	268,000,000
Other intangibles subject to amortization - accumulated amortization	(44,000,000)	(32,000,000)
Other intangibles subject to amortization - net	224,000,000	236,000,000
Southern Company [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	158,000,000	158,000,000
Other intangibles subject to amortization - accumulated amortization	(8,000,000)	(5,000,000)
Other intangibles subject to amortization - net	150,000,000	153,000,000
Southern Company [Member] | Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	4,000,000	4,000,000
Other intangibles subject to amortization - accumulated amortization	0	0
Other intangibles subject to amortization - net	4,000,000	4,000,000
Southern Company [Member] | Backlog [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	5,000,000	5,000,000
Other intangibles subject to amortization - accumulated amortization	(1,000,000)	(1,000,000)
Other intangibles subject to amortization - net	4,000,000	4,000,000
Southern Company [Member] | Storage and transportation contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangibles subject to amortization - accumulated amortization	(15,000,000)	(2,000,000)
Other intangibles subject to amortization - net	49,000,000	62,000,000
Southern Company [Member] | Software and other [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	2,000,000	2,000,000
Other intangibles subject to amortization - accumulated amortization	(1,000,000)	0
Other intangibles subject to amortization - net	1,000,000	2,000,000
Southern Company [Member] | PPA fair value adjustments [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Other intangibles subject to amortization - net	$ 428,000,000	434,000,000
Southern Company [Member] | PPA fair value adjustments [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Company [Member] | PPA fair value adjustments [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
Southern Power [Member]
Goodwill [Line Items]
Goodwill	$ 2,000,000	2,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Southern Power [Member] | PPA fair value adjustments [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangibles subject to amortization - accumulated amortization	(28,000,000)	(22,000,000)
Other intangibles subject to amortization - net	$ 428,000,000	434,000,000
Southern Power [Member] | PPA fair value adjustments [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Power [Member] | PPA fair value adjustments [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	20 years
Southern Company Gas [Member]
Goodwill [Line Items]
Goodwill	$ 5,967,000,000	5,967,000,000
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	400,000,000	400,000,000
Other intangibles subject to amortization - accumulated amortization	(60,000,000)	(34,000,000)
Other intangibles subject to amortization - net	340,000,000	366,000,000
Total other intangible assets - net	340,000,000	366,000,000
Southern Company Gas [Member] | Gas Distribution Operations [Member]
Goodwill [Line Items]
Goodwill	4,702,000,000	4,702,000,000
Southern Company Gas [Member] | Gas Marketing Services [Member]
Goodwill [Line Items]
Goodwill	1,265,000,000	1,265,000,000
Southern Company Gas [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	221,000,000	221,000,000
Other intangibles subject to amortization - accumulated amortization	(41,000,000)	(30,000,000)
Other intangibles subject to amortization - net	$ 180,000,000	191,000,000
Southern Company Gas [Member] | Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	11 years
Southern Company Gas [Member] | Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	16 years
Southern Company Gas [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 115,000,000	115,000,000
Other intangibles subject to amortization - accumulated amortization	(4,000,000)	(2,000,000)
Other intangibles subject to amortization - net	$ 111,000,000	113,000,000
Southern Company Gas [Member] | Trade Names [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	10 years
Southern Company Gas [Member] | Trade Names [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	28 years
Southern Company Gas [Member] | Storage and transportation contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 64,000,000	64,000,000
Other intangibles subject to amortization - accumulated amortization	(15,000,000)	(2,000,000)
Other intangibles subject to amortization - net	$ 49,000,000	$ 62,000,000
Southern Company Gas [Member] | Storage and transportation contracts [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	1 year
Southern Company Gas [Member] | Storage and transportation contracts [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - estimated useful life	5 years

Introduction - Intangibles, Amo

Introduction - Intangibles, Amortization (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	$ 957,000,000	$ 957,000,000
Other intangible assets, accumulated amortization	97,000,000	62,000,000
Other intangibles subject to amortization - net	860,000,000	895,000,000
Other intangible assets, net of amortization	935,000,000	970,000,000
Total other intangible assets - gross	1,032,000,000	1,032,000,000
Amortization of intangible assets	35,000,000
Southern Power [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Amortization of intangible assets	6,000,000
Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	400,000,000	400,000,000
Other intangible assets, accumulated amortization	60,000,000	34,000,000
Other intangibles subject to amortization - net	340,000,000	366,000,000
Other intangible assets, net of amortization	340,000,000	366,000,000
Amortization of intangible assets	26,000,000
Customer Relationships [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	268,000,000	268,000,000
Other intangible assets, accumulated amortization	44,000,000	32,000,000
Other intangibles subject to amortization - net	224,000,000	236,000,000
Customer Relationships [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	221,000,000	221,000,000
Other intangible assets, accumulated amortization	41,000,000	30,000,000
Other intangibles subject to amortization - net	180,000,000	191,000,000
Trade Names [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	158,000,000	158,000,000
Other intangible assets, accumulated amortization	8,000,000	5,000,000
Other intangibles subject to amortization - net	150,000,000	153,000,000
Trade Names [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	115,000,000	115,000,000
Other intangible assets, accumulated amortization	4,000,000	2,000,000
Other intangibles subject to amortization - net	111,000,000	113,000,000
Patents [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	4,000,000	4,000,000
Other intangible assets, accumulated amortization	0	0
Other intangibles subject to amortization - net	4,000,000	4,000,000
Backlog [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	5,000,000	5,000,000
Other intangible assets, accumulated amortization	1,000,000	1,000,000
Other intangibles subject to amortization - net	4,000,000	4,000,000
Storage and Transportation Contracts [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangible assets, accumulated amortization	15,000,000	2,000,000
Other intangibles subject to amortization - net	49,000,000	62,000,000
Storage and Transportation Contracts [Member] | Southern Company Gas [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	64,000,000	64,000,000
Other intangible assets, accumulated amortization	15,000,000	2,000,000
Other intangibles subject to amortization - net	49,000,000	62,000,000
Software and other [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	2,000,000	2,000,000
Other intangible assets, accumulated amortization	1,000,000	0
Other intangibles subject to amortization - net	1,000,000	2,000,000
PPA fair value adjustments [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Other intangibles subject to amortization - net	428,000,000	434,000,000
PPA fair value adjustments [Member] | Southern Power [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangibles subject to amortization - gross carrying amount	456,000,000	456,000,000
Other intangible assets, accumulated amortization	28,000,000	22,000,000
Other intangibles subject to amortization - net	428,000,000	434,000,000
FCC Licenses [Member] | Southern Company [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	$ 75,000,000	$ 75,000,000

Contingencies and Regulatory 36

Contingencies and Regulatory Matters - Narrative (Details)	Jul. 01, 2017USD ($)	Apr. 04, 2017intervenor	Mar. 31, 2017USD ($)miMW	Mar. 30, 2017	Mar. 27, 2017	Mar. 10, 2017USD ($)	Feb. 21, 2017USD ($)	Dec. 20, 2016USD ($)	Nov. 17, 2016USD ($)	Jun. 09, 2016USD ($)	Jun. 03, 2016	May 01, 2016USD ($)	Mar. 31, 2016USD ($)	Jan. 01, 2016	Dec. 05, 2015USD ($)	Dec. 03, 2015	Jul. 07, 2015USD ($)	Jun. 03, 2015USD ($)	Jan. 01, 2014USD ($)	Mar. 19, 2013	Jun. 30, 2019USD ($)	Apr. 28, 2017USD ($)	Sep. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Jan. 31, 2016USD ($)	Jan. 31, 2013USD ($)	Mar. 31, 2017USD ($)clausemiMW	Mar. 31, 2016USD ($)	Apr. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)miMW	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2010	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Mar. 31, 2017USD ($)miMW	Dec. 31, 2020USD ($)	Sep. 30, 2016USD ($)	Mar. 31, 2017USD ($)miMW	Jun. 30, 2016USD ($)	Jan. 01, 2121	Apr. 11, 2017USD ($)	Apr. 07, 2017USD ($)	Mar. 17, 2017USD ($)	Nov. 30, 2016USD ($)	Aug. 31, 2016USD ($)	May 20, 2015USD ($)
Loss Contingencies [Line Items]
Lawsuit deferral period					30 days
Maximum borrowing capacity			$ 8,443,000,000																								$ 8,443,000,000							$ 8,443,000,000									$ 8,443,000,000			$ 8,443,000,000
Stockholders' equity, including portion attributable to noncontrolling interest			(26,996,000,000)										$ (22,184,000,000)											$ (22,184,000,000)			(26,996,000,000)	$ (22,184,000,000)		$ (26,612,000,000)				(26,996,000,000)	$ (26,612,000,000)	$ (21,982,000,000)							(26,996,000,000)			(26,996,000,000)
Construction work in progress			9,465,000,000																								9,465,000,000			8,977,000,000				9,465,000,000	8,977,000,000								9,465,000,000			9,465,000,000
Property, plant and equipment, gross			99,774,000,000																								99,774,000,000			98,416,000,000				99,774,000,000	98,416,000,000								99,774,000,000			99,774,000,000
Allowance for equity funds used during construction																											57,000,000	53,000,000
Other regulatory assets, current			560,000,000																								560,000,000			581,000,000				560,000,000	581,000,000								560,000,000			560,000,000
Georgia Power [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			13,000,000																								13,000,000							13,000,000									13,000,000			13,000,000
Cost recovery, new nuclear			50,000,000																								$ 50,000,000							50,000,000									50,000,000			50,000,000
Liquidated damages, percentage																											40.00%															10.00%
Additional construction capital costs								$ 3,300,000,000																						222,000,000																	$ 3,700,000,000
Percentage of proportionate share owed in consortium agreement																																										45.70%
Maximum borrowing capacity			1,750,000,000																								$ 1,750,000,000							1,750,000,000									1,750,000,000			1,750,000,000
Period of notice required for contract termination				5 days
Aggregate liability under contract agreement and removal of liens			215,000,000																								215,000,000							215,000,000									215,000,000			215,000,000
Estimated in-service capital cost																																									$ 4,418,000,000
Estimate of possible loss								$ 240,000,000
Retail rate of return on common equity																																						10.95%
Public utilities, approved return on equity percentage														10.00%
Construction work in progress			5,183,000,000																								5,183,000,000			4,939,000,000				5,183,000,000	4,939,000,000								5,183,000,000			5,183,000,000
Wholesale revenues, non-affiliates																											39,000,000	41,000,000
Property, plant and equipment, gross			34,059,000,000																								34,059,000,000			33,841,000,000				34,059,000,000	33,841,000,000								34,059,000,000			34,059,000,000
Allowance for equity funds used during construction																											13,000,000	14,000,000
Other regulatory assets, current			195,000,000																								195,000,000			193,000,000				195,000,000	193,000,000								195,000,000			195,000,000
Georgia Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Additional construction capital costs																																										$ 114,000,000
Georgia Power [Member] | Other Current Liabilities [Member]
Loss Contingencies [Line Items]
Over recovered fuel balance			18,000,000																								18,000,000							18,000,000									18,000,000			18,000,000
Georgia Power [Member] | Other deferred credits and liabilities [Member]
Loss Contingencies [Line Items]
Over recovered fuel balance																														84,000,000					84,000,000
Gulf Power [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			52,000,000																								52,000,000							52,000,000									52,000,000			52,000,000
Maximum borrowing capacity			$ 280,000,000																								$ 280,000,000							$ 280,000,000									$ 280,000,000			$ 280,000,000
Retail rate of return on common equity			10.25%																								10.25%							10.25%									10.25%			10.25%
Construction work in progress			$ 67,000,000																								$ 67,000,000			51,000,000				$ 67,000,000	51,000,000								$ 67,000,000			$ 67,000,000
Reduction in depreciation expense																											25,500,000								0	$ 20,100,000	$ 8,400,000	$ 62,500,000
Wholesale revenues, non-affiliates																											17,000,000	16,000,000
Loss on Plant Scherer Unit 3																											$ 33,000,000	0
Number of regulatory clauses | clause																											4
Property, plant and equipment, gross			5,110,000,000																								$ 5,110,000,000			5,140,000,000				5,110,000,000	5,140,000,000								5,110,000,000			5,110,000,000
Other regulatory assets, current			$ 50,000,000																								$ 50,000,000			44,000,000				$ 50,000,000	44,000,000								$ 50,000,000			$ 50,000,000
Gulf Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Retail rate of return on common equity			9.25%																								9.25%							9.25%									9.25%			9.25%
Gulf Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Retail rate of return on common equity			11.25%																								11.25%							11.25%									11.25%			11.25%
Southern Company Gas [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			$ 409,000,000																								$ 409,000,000							$ 409,000,000									$ 409,000,000			$ 409,000,000
Maximum borrowing capacity			2,000,000,000																								2,000,000,000							2,000,000,000									2,000,000,000			2,000,000,000
Stockholders' equity, including portion attributable to noncontrolling interest			(9,244,000,000)																								(9,244,000,000)			(9,109,000,000)				(9,244,000,000)	(9,109,000,000)								(9,244,000,000)			(9,244,000,000)
Construction work in progress			625,000,000																								625,000,000			496,000,000				625,000,000	496,000,000								625,000,000			625,000,000
Property, plant and equipment, gross			14,660,000,000																								14,660,000,000			14,508,000,000				14,660,000,000	14,508,000,000								14,660,000,000			14,660,000,000
Other regulatory assets, current			60,000,000																								60,000,000			81,000,000				60,000,000	81,000,000								60,000,000			60,000,000
Mississippi Power [Member]
Loss Contingencies [Line Items]
Increase in base rate under cost based electric tariff due to settlement												$ 7,000,000
Fuel cost recovery			27,000,000																								27,000,000			37,000,000				27,000,000	37,000,000								27,000,000			27,000,000
Maximum borrowing capacity			173,000,000																								173,000,000							173,000,000									173,000,000			173,000,000
Construction work in progress			2,570,000,000																								2,570,000,000			2,545,000,000				2,570,000,000	2,545,000,000								2,570,000,000			2,570,000,000
Wholesale revenues, non-affiliates																											62,000,000	60,000,000
Gain contingency, surcharge revenue																																			5,000,000
PSC retail rate increase (decrease)																																																			$ 2,000,000	$ 1,000,000
Property, plant and equipment, gross			4,963,000,000																								$ 4,963,000,000			4,865,000,000				4,963,000,000	4,865,000,000								4,963,000,000			4,963,000,000
Plant capacity under coal gasification combined cycle technology (in MWs) | MW																											582
Additional DOE grants																																							$ 245,000,000
Maximum cap construction cost																																							2,880,000,000
Reduced percentage interest transferred under asset purchase agreement																				15.00%																				15.00%
Approved rate increase (decrease) percentage																			3.00%
Settlement agreement collection amount to mitigate rate impact year two																			$ 156,000,000
Retail rate recovery																	$ 342,000,000
Carrying costs associated with retail rate recovery																	$ 29,000,000
Allowance for equity funds used during construction																											$ 35,000,000	29,000,000
Other regulatory assets, current			113,000,000																								113,000,000			115,000,000				113,000,000	115,000,000								113,000,000			113,000,000
Regulatory liabilities			8,000,000																								8,000,000							8,000,000									8,000,000			8,000,000
Interest bearing refundable deposit related to assets sale																																																						$ 275,000,000
Promissory note																		$ 301,000,000
Mississippi Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Costs due to extension of in-service date																											25,000,000
Mississippi Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Costs due to extension of in-service date																											35,000,000
Mississippi Power [Member] | Construction in Progress [Member]
Loss Contingencies [Line Items]
Estimate of possible loss			2,950,000,000																								2,950,000,000							$ 2,950,000,000									2,950,000,000			2,950,000,000
Atlanta Gas Light [Member]
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage							10.75%
Approved increase (decrease) in fuel rates amount							$ 20,000,000
Elizabethtown Gas [Member]
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), Amount																							$ 19,000,000
Test year duration																																		12 months
Public utilities, requested return on equity, percentage																							10.25%
Nicor Gas [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity			$ 700,000,000																								700,000,000							$ 700,000,000									700,000,000			700,000,000
Public utilities, requested rate increase (decrease), Amount						$ 208,000,000
Public utilities, requested return on equity, percentage						10.70%
Statutory time limit						11 months
Virginia Natural Gas [Member]
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage			10.25%
Florida City Gas [Member]
Loss Contingencies [Line Items]
Infrastructure replacement program, petitioned investment amount			$ 3,000,000																								3,000,000							3,000,000									3,000,000			3,000,000
Location One [Member] | Southern Company Gas [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			$ 5,000,000																								5,000,000							$ 5,000,000									$ 5,000,000			$ 5,000,000
Kemper Igcc [Member]
Loss Contingencies [Line Items]
Pre-tax charge to income																											108,000,000	53,000,000
After tax charge to income																											$ 67,000,000	$ 33,000,000
Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Period of amortization of regulatory assets													36 months
Pipeline Infrastructure | mi			61																								61							61									61			61
Estimated cost									$ 68,000,000																		$ 5,570,000,000												2,880,000,000
Additional DOE grants																											(140,000,000)
Maximum cap construction cost																											$ 6,930,000,000
Purchase of interest			100.00%																								100.00%							100.00%									100.00%			100.00%
Pre-tax charge to income																											$ 108,000,000																			$ 2,870,000,000
After tax charge to income																											67,000,000																		$ 1,770,000,000
Recoverable cost above maximum cap construction cost																											3,370,000,000
Project improvement costs																														12,000,000					12,000,000
Monthly charge of allowance for equity funds used during construction																											16,000,000																$ 16,000,000
Monthly cost regulatory assets deferred																											3,000,000
Costs subject to cost cap																											2,010,000,000
Cost cap exceptions																											$ 1,500,000,000
Period of commercial operations established by discovery docket																											5 years
Average annual increase (decrease) in operations and maintenance expenses																											$ 105,000,000
Average annual increase (decrease) in maintenance capital																											44,000,000
Allowance for equity funds used during construction																																											445,000,000
Regulatory assets			$ 86,000,000																								86,000,000							$ 86,000,000									86,000,000			86,000,000
Other regulatory assets, current			111,000,000																								$ 111,000,000							111,000,000									111,000,000			111,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Amortization period of regulatory assets and liabilities																											2 years
Kemper Igcc [Member] | Mississippi Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Amortization period of regulatory assets and liabilities																											10 years
Kemper Igcc [Member] | Mississippi Power [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency damages sought										$ 100,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Estimated cost																											$ 3,730,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Other Property And Investments [Member]
Loss Contingencies [Line Items]
Estimated cost																											6,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Fossil Fuel Stock [Member]
Loss Contingencies [Line Items]
Estimated cost																											64,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Materials And Supplies [Member]
Loss Contingencies [Line Items]
Estimated cost																											48,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Other regulatory assets current [Member]
Loss Contingencies [Line Items]
Estimated cost																											24,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Other regulatory assets, deferred [Member]
Loss Contingencies [Line Items]
Estimated cost																											173,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Other current assets [Member]
Loss Contingencies [Line Items]
Estimated cost																											1,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Other deferred charges and assets [Member]
Loss Contingencies [Line Items]
Estimated cost																											17,000,000
Kemper Igcc [Member] | Mississippi Power [Member] | Assets, Current [Member]
Loss Contingencies [Line Items]
Regulatory assets			24,000,000																								24,000,000							24,000,000									24,000,000			24,000,000
Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Liquidated damages, monetary amount																											1,700,000,000															$ 920,000,000
Maximum borrowing capacity																									$ 920,000,000
Construction work in progress			4,100,000,000																								4,100,000,000							4,100,000,000									4,100,000,000			4,100,000,000
Construction financing costs			1,300,000,000
Requested rate increase (decrease) amount																											400,000,000
Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Project settlement cost to be capitalized			350,000,000																								350,000,000							350,000,000									350,000,000			350,000,000
Plant Scherer Unit 3 [Member]
Loss Contingencies [Line Items]
Loss on Plant Scherer Unit 3																											33,000,000
After tax charge to income																											$ 20,000,000
Plant Smith Units 1 and 2 [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Capacity of units included in request for decertification of units | MW																											357
Plant Scherer Unit Three [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Loss on Plant Scherer Unit 3																											$ 32,500,000
Electricity Generation Plant, Non-Nuclear [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated cost																										$ 2,400,000,000													$ 2,400,000,000
Mine [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Term of management fee contract																																								40 years
Subsequent Event [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Weekly payment of services under contract agreement																						$ 5,400,000
Subsequent Event [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
AFUDC cost																													$ 18,000,000
PSC retail rate increase (decrease)																																																		$ 8,000,000
Percentage of PSC retail rate increase																																																		0.85%
Subsequent Event [Member] | Plant Scherer Unit 3 [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Number of Intervenors | intervenor		3
MRA Revenue [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Fuel cost recovery			12,000,000																								12,000,000			13,000,000				12,000,000	13,000,000								12,000,000			12,000,000
MB Revenue [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Fuel cost recovery			1,000,000																								1,000,000			$ 1,000,000				1,000,000	$ 1,000,000								1,000,000			1,000,000
Scenario, Forecast [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Additional construction capital costs																																												$ 5,440,000,000
Stockholders' equity, including portion attributable to noncontrolling interest																																																	$ 1,900,000,000
Amendment to estimated In-service capital cost																																												$ 5,680,000,000
Percent of basis points																																												0.95%				0.30%
Increase (decrease) in basis points																																												$ 8,000,000
Scenario, Forecast [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Overall net customer impact from rate case settlement agreement																																	$ 54,300,000
Increase (decrease) in revenue to be received from base rate change	$ 62,000,000
Wholesale revenues, non-affiliates																																	$ 7,700,000
Retail regulatory equity ratio	0.525
Scenario, Forecast [Member] | Virginia Natural Gas [Member]
Loss Contingencies [Line Items]
Test year duration																																12 months
Scenario, Forecast [Member] | Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Construction financing costs																					$ 30,000,000
Monthly operational readiness costs																					$ 10,000,000
FFB Loan [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity			$ 2,600,000,000																								$ 2,600,000,000							$ 2,600,000,000									$ 2,600,000,000			$ 2,600,000,000
Retirement Of Plant [Member] | Scenario, Forecast [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Regulatory asset, amortization period																															15 years
Plant Scherer Unit Three [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Electric generating units, capacity | MW			205																								205							205									205			205
Regulatory Infrastructure Program [Member] | Nicor Gas [Member]
Loss Contingencies [Line Items]
Program duration period																																					9 years
Property, plant and equipment, gross			$ 24,000,000																								$ 24,000,000							$ 24,000,000									$ 24,000,000			$ 24,000,000
STRIDE [Member] | Atlanta Gas Light [Member]
Loss Contingencies [Line Items]
Approved infrastructure replacement program			38,000,000																								$ 38,000,000							38,000,000									38,000,000			38,000,000
Integrated System Reinforcement Program [Member] | Atlanta Gas Light [Member]
Loss Contingencies [Line Items]
Infrastructure replacement program, petitioned investment amount																																																					$ 177,000,000
Integrated System Reinforcement Program [Member] | Atlanta Gas Light [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Program duration period																											4 years
Aging Infrastructure Replacement Program [Member] | Elizabethtown Gas [Member]
Loss Contingencies [Line Items]
Approved infrastructure replacement program			3,000,000																								$ 3,000,000							3,000,000									3,000,000			3,000,000
SAVE Program [Member] | Virginia Natural Gas [Member]
Loss Contingencies [Line Items]
Regulated operation, allowable cost recovery			13,000,000
Infrastructure replacement program, petitioned investment amount			44,000,000																								44,000,000							44,000,000									44,000,000			44,000,000
Approved infrastructure replacement program			$ 7,000,000																								7,000,000							$ 7,000,000									$ 7,000,000			$ 7,000,000
Cost Estimate Extension [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated cost																											67,000,000
Start-Up Fuel [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated cost																											23,000,000
Outage Work and Operational Maintenance and Improvements [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Estimated cost																											$ 18,000,000
Wholesale [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost, percent																											29.00%
Retail [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost, percent																											71.00%
2017 Accounting Order Request [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Monthly charge of allowance for equity funds used during construction																											$ 12,000,000
Monthly cost, regulatory assets and other																											25,000,000
2017 Rate Case [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Pre-tax charge to income																											80,000,000
Alternate financing																																						$ 1,000,000,000
In-Service Asset Proposal [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage																9.225%
Approved increase (decrease) in fuel rates amount															$ 126,000,000												$ 159,000,000
Public utilities approved equity capital structure percentage																49.733%
Customer refund																								$ 11,000,000
Denbury Onshore, Contractor [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of percentage of carbon dioxide captured from plant			70.00%								100.00%																70.00%							70.00%									70.00%			70.00%
Treetop Midstream Services, LLC, Contractor [Member] | Kemper Igcc [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of percentage of carbon dioxide captured from plant			30.00%																								30.00%							30.00%									30.00%			30.00%
Denbury Onshore, Contractor [Member] | Electricity Generation Plant, Non-Nuclear [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of carbon dioxide term											16 years
Westinghouse [Member] | Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed																									60 days
Vogtle Owners [Member]
Loss Contingencies [Line Items]
Aggregate liability under contract agreement and removal of liens			$ 470,000,000																								$ 470,000,000							$ 470,000,000									$ 470,000,000			$ 470,000,000
Aggregate liability under contract agreement and removal of liens, amount paid or accrued to date			$ 245,000,000																								$ 245,000,000							$ 245,000,000									$ 245,000,000			$ 245,000,000

Contingencies and Regulatory 37

Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Alabama Power (Details) - Alabama Power [Member] - USD ($) $ in Millions	Mar. 31, 2017	Feb. 17, 2017	Dec. 31, 2016
Deferred under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 0		$ 9
Rate CNP PPA	0		142
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Rate CNP PPA	3		0
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Retail Energy Cost Recovery	40		76
Other regulatory liabilities, deferred [Member]
Loss Contingencies [Line Items]
Natural Disaster Reserve	$ 66		$ 69
Regulatory Assets, Deferred [Member]
Loss Contingencies [Line Items]
Over (under) recovered environmental clause		$ 23

Contingencies and Regulatory 38

Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Gulf Power (Details) - Gulf Power [Member] - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 5	$ 15
Environmental Cost Recovery	40	13
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Purchased Power Capacity Recovery	4	0
Energy Conservation Cost Recovery	$ 3	$ 4

Contingencies and Regulatory 39

Contingencies and Regulatory Matters - Current And Actual Cost Estimate (Details) - USD ($) $ in Millions	Nov. 17, 2016	Apr. 08, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2012	Mar. 31, 2017
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Pre-tax charge to income			$ 108	$ 53
Mississippi Power [Member]
Loss Contingencies [Line Items]
Additional DOE grants					$ 245
Total Kemper IGCC, Actual Costs					2,880
Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap	$ 68		5,570		$ 2,880
Lignite Mine and Equipment			230
CO2 Pipeline Facilities			120
AFUDC			800
Combined Cycle and Related Assets Placed in Service – Incremental			40
General Exceptions			90
Deferred Costs			220
Additional DOE grants			(140)
Total Kemper IGCC, Actual Costs			6,930
Government grants received		$ (137)	(140)
Pre-tax charge to income			108			$ 2,870
Recoverable cost above maximum cap construction cost			3,370
Mississippi Power [Member] | Project Estimate [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			2,400
Lignite Mine and Equipment			210
CO2 Pipeline Facilities			140
AFUDC			170
Combined Cycle and Related Assets Placed in Service – Incremental			0
General Exceptions			50
Deferred Costs			0
Additional DOE grants			0
Total Kemper IGCC, Actual Costs			2,970
Mississippi Power [Member] | Current Estimate [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Plant Subject to Cost Cap			5,750
Lignite Mine and Equipment			230
CO2 Pipeline Facilities			120
AFUDC			830
Combined Cycle and Related Assets Placed in Service – Incremental			50
General Exceptions			100
Deferred Costs			220
Additional DOE grants			(140)
Total Kemper IGCC, Actual Costs			7,160
Gasifiers and Gas Clean-up Facilities [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			1,900
Lignite Mine Facility [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			310
CO2 Pipeline Facilities [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			110
Combined Cycle and Common Facilities [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			170
AFUDC [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			730
General Exceptions [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			70
Plant Inventory [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			40
Lignite Inventory [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			60
Regulatory and Other Deferred Assets [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			120
All Costs [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Recoverable cost above maximum cap construction cost			3,510
Investment Costs and Related Assets In Service [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Total Kemper IGCC, Actual Costs			830
Costs Previously Expensed and Related Assets In Service [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Total Kemper IGCC, Actual Costs			90
Post June 2013 Mine Operations, Lignite Fuel Inventory, and Nitrogen Plant Capital Lease [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Total Kemper IGCC, Actual Costs			$ 230

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Assets:
Fair Value	$ 21
Liabilities:
Collateral already posted, aggregate fair value	92
Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	487
Interest rate derivatives	13
Nuclear decommissioning trusts	1,677
Cash equivalents	589
Other investments	10
Total	2,776
Liabilities:
Energy-related derivatives(a)(b)	458
Interest rate derivatives	32
Foreign currency derivatives	62
Contingent consideration	20
Total	572
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	274
Interest rate derivatives	0
Nuclear decommissioning trusts	714
Cash equivalents	589
Other investments	9
Total	1,586
Liabilities:
Energy-related derivatives(a)(b)	303
Interest rate derivatives	0
Foreign currency derivatives	0
Contingent consideration	0
Total	303
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	213
Interest rate derivatives	13
Nuclear decommissioning trusts	942
Cash equivalents	0
Other investments	0
Total	1,168
Liabilities:
Energy-related derivatives(a)(b)	155
Interest rate derivatives	32
Foreign currency derivatives	62
Contingent consideration	0
Total	249
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Interest rate derivatives	0
Nuclear decommissioning trusts	0
Cash equivalents	0
Other investments	1
Total	1
Liabilities:
Energy-related derivatives(a)(b)	0
Interest rate derivatives	0
Foreign currency derivatives	0
Contingent consideration	20
Total	20
Alabama Power [Member]
Assets:
Energy-related derivatives	11	$ 20
Fair Value	21
Liabilities:
Energy-related derivatives(a)(b)	(10)	(9)
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	11
Cash equivalents	555
Total	1,390
Liabilities:
Energy-related derivatives(a)(b)	10
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	482
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	103
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	28
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	165
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	18
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Assets:
Nuclear decommissioning trusts	21
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	7
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0
Cash equivalents	555
Total	1,034
Liabilities:
Energy-related derivatives(a)(b)	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	405
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	52
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	22
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Private Equity Funds [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	11
Cash equivalents	0
Total	335
Liabilities:
Energy-related derivatives(a)(b)	10
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	77
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	51
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	28
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	143
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	18
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Private Equity Funds [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	7
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives(a)(b)	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Private Equity Funds [Member]
Assets:
Nuclear decommissioning trusts	0
Alabama Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member]
Assets:
Energy-related derivatives	26	46
Nuclear decommissioning trusts	56
Liabilities:
Energy-related derivatives(a)(b)	(17)	(11)
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	24
Interest rate derivatives	2
Cash equivalents	0
Total	879
Liabilities:
Energy-related derivatives(a)(b)	13
Interest rate derivatives	4
Total	17
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	217
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	137
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	196
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	70
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	168
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	41
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	24
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0
Interest rate derivatives	0
Cash equivalents	0
Total	235
Liabilities:
Energy-related derivatives(a)(b)	0
Interest rate derivatives	0
Total	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	216
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	19
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	24
Interest rate derivatives	2
Cash equivalents	0
Total	644
Liabilities:
Energy-related derivatives(a)(b)	13
Interest rate derivatives	4
Total	17
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	1
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	137
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	196
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	70
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	168
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	41
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	5
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Interest rate derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives(a)(b)	0
Interest rate derivatives	0
Total	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign equity [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0
Georgia Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	0
Gulf Power [Member]
Assets:
Energy-related derivatives	2	5
Liabilities:
Energy-related derivatives(a)(b)	(31)	(29)
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	2
Cash equivalents	21
Total	23
Liabilities:
Energy-related derivatives(a)(b)	31
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0
Cash equivalents	21
Total	21
Liabilities:
Energy-related derivatives(a)(b)	0
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	2
Cash equivalents	0
Total	2
Liabilities:
Energy-related derivatives(a)(b)	31
Gulf Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives(a)(b)	0
Mississippi Power [Member]
Assets:
Energy-related derivatives	7	7
Liabilities:
Energy-related derivatives(a)(b)	(12)	(11)
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	3
Interest rate derivatives	4
Total	7
Liabilities:
Energy-related derivatives(a)(b)	12
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0
Interest rate derivatives	0
Total	0
Liabilities:
Energy-related derivatives(a)(b)	0
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	3
Interest rate derivatives	4
Total	7
Liabilities:
Energy-related derivatives(a)(b)	12
Mississippi Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Interest rate derivatives	0
Total	0
Liabilities:
Energy-related derivatives(a)(b)	0
Southern Power [Member]
Assets:
Energy-related derivatives	15	22
Liabilities:
Energy-related derivatives(a)(b)	(67)	(63)
Southern Power [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	15
Liabilities:
Energy-related derivatives(a)(b)	5
Foreign currency derivatives	62
Contingent consideration	20
Total	87
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0
Liabilities:
Energy-related derivatives(a)(b)	0
Foreign currency derivatives	0
Contingent consideration	0
Total	0
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	15
Liabilities:
Energy-related derivatives(a)(b)	5
Foreign currency derivatives	62
Contingent consideration	0
Total	67
Southern Power [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Liabilities:
Energy-related derivatives(a)(b)	0
Foreign currency derivatives	0
Contingent consideration	20
Total	20
Southern Company Gas [Member]
Assets:
Energy-related derivatives	451	581
Liabilities:
Energy-related derivatives(a)(b)	(387)	(569)
Collateral already posted, aggregate fair value	92	$ 62
Southern Company Gas [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	432
Liabilities:
Energy-related derivatives(a)(b)	387
Southern Company Gas [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	274
Liabilities:
Energy-related derivatives(a)(b)	303
Southern Company Gas [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	158
Liabilities:
Energy-related derivatives(a)(b)	84
Southern Company Gas [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0
Liabilities:
Energy-related derivatives(a)(b)	0
Nuclear Decommissioning Trusts [Member]
Assets:
Fair Value	21
Nuclear Decommissioning Trusts [Member] | Alabama Power [Member]
Assets:
Fair Value	21
Weather Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Energy-related derivatives	$ 19

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 63	$ 20
Private Equity Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Liquidations term	10 years
Alabama Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 34	11
Georgia Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 29	$ 9
Minimum [Member] | Southern Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Contingent payment obligations, payment period	10 years
Maximum [Member] | Southern Power [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Contingent payment obligations, payment period	30 years

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Measurements Of Investments Calculated At Net Asset Value Per Share (Details) $ in Millions	Mar. 31, 2017USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 21
Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	21
Unfunded Commitments	22
Alabama Power [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	21
Alabama Power [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	21
Unfunded Commitments	$ 22

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Mar. 31, 2017USD ($)
Southern Company [Member]
Long-term debt:
Carrying Amount	$ 45,881
Fair Value	46,828
Alabama Power [Member]
Long-term debt:
Carrying Amount	7,439
Fair Value	7,807
Georgia Power [Member]
Long-term debt:
Carrying Amount	11,362
Fair Value	11,777
Gulf Power [Member]
Long-term debt:
Carrying Amount	1,079
Fair Value	1,110
Mississippi Power [Member]
Long-term debt:
Carrying Amount	2,977
Fair Value	2,909
Southern Power [Member]
Long-term debt:
Carrying Amount	5,648
Fair Value	5,694
Southern Company Gas [Member]
Long-term debt:
Carrying Amount	5,268
Fair Value	$ 5,487

Stockholders' Equity - Earnings

Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Equity [Abstract]
As reported shares (in shares)	993	916
Effect of options and performance share award units (in shares)	7	6
Diluted shares (in shares)	1,000	922
Stock options and performance share award units that were not included in the diluted earnings per share calculation (in shares)	0

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)	(800)
Beginning balance	$ 26,612	$ 21,982
Consolidated net income attributable to Southern Company	658	489
Other comprehensive income (loss)	(9)	(114)
Stock issued	186	270
Stock-based compensation	57	57
Cash dividends on common stock	(556)	(497)
Contributions from noncontrolling interests	71	129
Distributions to noncontrolling interests	(18)	(4)
Purchase of membership interests from noncontrolling interests		(129)
Net income attributable to noncontrolling interests	(4)	1
Other	$ (1)	0
Beginning balance, treasury shares (in shares)	(900)
Ending balance	$ 26,996	$ 22,184
Number of Common shares Issued [Member]
Changes in Stockholders' Equity
Beginning balance (in shares)	991,213	915,073
Stock issued (in shares)	4,240	6,572
Ending balance (in shares)	995,453	921,645
Number of Common shares Treasury [Member]
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)	(819)	(3,352)
Stock issued (in shares)	0
Other (in shares)	(35)	(35)
Beginning balance, treasury shares (in shares)	(854)	(3,387)
Common Stockholders' Equity
Changes in Stockholders' Equity
Beginning balance	$ 24,758	$ 20,592
Consolidated net income attributable to Southern Company	658	489
Other comprehensive income (loss)	(9)	(114)
Stock issued	186	270
Stock-based compensation	57	57
Cash dividends on common stock	(556)	(497)
Other	0
Ending balance	25,094	20,797
Preferred and Preference Stock of Subsidiaries
Changes in Stockholders' Equity
Beginning balance	609	609
Ending balance	609	609
Noncontrolling Interest [Member]
Changes in Stockholders' Equity
Beginning balance	1,245	781
Contributions from noncontrolling interests	71	129
Distributions to noncontrolling interests	(18)	(4)
Purchase of membership interests from noncontrolling interests		(129)
Net income attributable to noncontrolling interests	(4)	1
Other	(1)
Ending balance	1,293	$ 778
SunPower Corp. [Member] | Noncontrolling Interest [Member]
Changes in Stockholders' Equity
Ending balance	$ 114

Financing - Narrative (Details)

Financing - Narrative (Details) - USD ($)	Feb. 28, 2017	Jun. 03, 2015	Feb. 20, 2014	Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Short-term debt				$ 2,818,000,000	$ 2,818,000,000	$ 2,241,000,000
Variable rate pollution control revenue bonds outstanding				1,900,000,000	1,900,000,000
Maximum borrowing capacity				8,443,000,000	8,443,000,000
Senior Note Issuances					1,400,000,000
Mississippi Power [Member]
Debt Instrument [Line Items]
Working capital				1,200,000,000	1,200,000,000
Senior notes, current				35,000,000	35,000,000
Short-term debt				36,000,000	36,000,000	23,000,000
Long-term pollution control bond				50,000,000	50,000,000
Variable rate pollution control revenue bonds outstanding				40,000,000	40,000,000
Fixed rate pollution control revenue bonds outstanding				50,000,000	50,000,000
Maximum borrowing capacity				173,000,000	173,000,000
Promissory note		$ 301,000,000
Mississippi Power [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term debt				36,000,000	36,000,000
Mississippi Power [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Loans payable to bank				1,200,000,000	1,200,000,000
Mississippi Power [Member] | Tax-Exempt Variable Rate Demand Obligations [Member]
Debt Instrument [Line Items]
Short-term debt				40,000,000	40,000,000
Mississippi Power [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt face amount				$ 9,000,000	$ 9,000,000
Debt stated interest rate				5.00%	5.00%
Georgia Power [Member]
Debt Instrument [Line Items]
Short-term debt				$ 0	$ 0	391,000,000
Debt instrument, basis spread on variable rate			0.375%
Amortization period for line of credit facility			5 years
Variable rate pollution control revenue bonds outstanding				868,000,000	868,000,000
Fixed rate pollution control revenue bonds outstanding				250,000,000	250,000,000
Maximum borrowing capacity				1,750,000,000	1,750,000,000
Senior Note Issuances					850,000,000
Georgia Power [Member] | Senior Notes [Member] | Series 2017A [Member]
Debt Instrument [Line Items]
Debt face amount				$ 450,000,000	$ 450,000,000
Debt stated interest rate				2.00%	2.00%
Georgia Power [Member] | Senior Notes [Member] | Series 2017B [Member]
Debt Instrument [Line Items]
Debt face amount				$ 400,000,000	$ 400,000,000
Debt stated interest rate				3.25%	3.25%
Alabama Power [Member]
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				$ 890,000,000	$ 890,000,000
Maximum borrowing capacity				1,335,000,000	1,335,000,000
Senior Note Issuances					550,000,000
Alabama Power [Member] | Senior Notes [Member] | Series 2017A [Member]
Debt Instrument [Line Items]
Debt face amount				$ 550,000,000	$ 550,000,000
Debt stated interest rate				2.45%	2.45%
Gulf Power [Member]
Debt Instrument [Line Items]
Short-term debt				$ 100,000,000	$ 100,000,000	268,000,000
Variable rate pollution control revenue bonds outstanding				82,000,000	82,000,000
Fixed rate pollution control revenue bonds outstanding				86,000,000	86,000,000
Maximum borrowing capacity				280,000,000	280,000,000
Senior Note Issuances					0
Gulf Power [Member] | Bank Loans [Member]
Debt Instrument [Line Items]
Debt face amount				100,000,000	100,000,000
Traditional Operating Companies [Member]
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding				386,000,000	386,000,000
Southern Power [Member]
Debt Instrument [Line Items]
Short-term debt				380,000,000	380,000,000	$ 209,000,000
Maximum borrowing capacity				600,000,000	600,000,000
Senior Note Issuances					0
Southern Company [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				2,250,000,000	2,250,000,000
Senior Note Issuances					$ 0
Southern Company [Member] | Bank Loans [Member]
Debt Instrument [Line Items]
Senior Note Issuances				$ 400,000,000
Debt Instrument, Term				18 months
Southern Company [Member] | Mississippi Power [Member]
Debt Instrument [Line Items]
Promissory note	$ 551,000,000

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2017USD ($)
Line of Credit Facility [Line Items]
Expires, 2017	$ 423,000,000
Expires, 2018	3,620,000,000
Expires, 2020	4,400,000,000
Total	8,443,000,000
Unused	8,266,000,000
Executable Term Loans, One Year	65,000,000
Executable Term Loans, Two Years	13,000,000
Expires Within One Year, Term Out	58,000,000
Expires Within One Year, No Term Out	375,000,000
Southern Company [Member]
Line of Credit Facility [Line Items]
Expires, 2017	0
Expires, 2018	1,000,000,000
Expires, 2020	1,250,000,000
Total	2,250,000,000
Unused	2,250,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Alabama Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	35,000,000
Expires, 2018	500,000,000
Expires, 2020	800,000,000
Total	1,335,000,000
Unused	1,335,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	35,000,000
Georgia Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	0
Expires, 2018	0
Expires, 2020	1,750,000,000
Total	1,750,000,000
Unused	1,732,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Gulf Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	85,000,000
Expires, 2018	195,000,000
Expires, 2020	0
Total	280,000,000
Unused	280,000,000
Executable Term Loans, One Year	45,000,000
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	25,000,000
Expires Within One Year, No Term Out	70,000,000
Mississippi Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	173,000,000
Expires, 2018	0
Expires, 2020	0
Total	173,000,000
Unused	141,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	13,000,000
Expires Within One Year, Term Out	13,000,000
Expires Within One Year, No Term Out	160,000,000
Southern Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	0
Expires, 2018	0
Expires, 2020	600,000,000
Total	600,000,000
Unused	524,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Southern Company Gas [Member]
Line of Credit Facility [Line Items]
Expires, 2017	75,000,000
Expires, 2018	1,925,000,000
Expires, 2020	0
Total	2,000,000,000
Unused	1,949,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	75,000,000
Other [Member]
Line of Credit Facility [Line Items]
Expires, 2017	55,000,000
Expires, 2018	0
Expires, 2020	0
Total	55,000,000
Unused	55,000,000
Executable Term Loans, One Year	20,000,000
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	20,000,000
Expires Within One Year, No Term Out	35,000,000
Southern Company Gas Capital [Member]
Line of Credit Facility [Line Items]
Total	1,300,000,000
Nicor Gas [Member]
Line of Credit Facility [Line Items]
Total	$ 700,000,000

Financing - Schedule of Long-Te

Financing - Schedule of Long-Term Debt Financing Activities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Debt Instrument [Line Items]
Senior Note Issuances	$ 1,400
Senior Note Maturities and Redemptions	200
Other Long-Term Debt Issuances	9
Other Long-Term Debt Redemptions and Maturities	408
Southern Company [Member]
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	400
Alabama Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances	550
Senior Note Maturities and Redemptions	200
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	0
Georgia Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances	850
Senior Note Maturities and Redemptions	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	2
Gulf Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Other Long-Term Debt Issuances	6
Other Long-Term Debt Redemptions and Maturities	0
Southern Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Other Long-Term Debt Issuances	3
Other Long-Term Debt Redemptions and Maturities	2
Other [Member]
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	$ 4

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 0
Pension Plan [Member] | Southern Company Gas [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	0
Pension Plans and Postretirement Plans
Service cost	6,000,000
Interest cost	10,000,000
Expected return on plan assets	(18,000,000)
Amortization:
Prior service costs	0
Net (gain)/loss	5,000,000
Net periodic pension cost (income)	3,000,000
Pension Plan [Member] | Southern Company [Member]
Pension Plans and Postretirement Plans
Service cost	73,000,000	$ 62,000,000
Interest cost	114,000,000	100,000,000
Expected return on plan assets	(224,000,000)	(187,000,000)
Amortization:
Prior service costs	3,000,000	4,000,000
Net (gain)/loss	40,000,000	38,000,000
Net periodic pension cost (income)	6,000,000	17,000,000
Pension Plan [Member] | Alabama Power [Member]
Pension Plans and Postretirement Plans
Service cost	16,000,000	14,000,000
Interest cost	24,000,000	24,000,000
Expected return on plan assets	(49,000,000)	(46,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	10,000,000	10,000,000
Net periodic pension cost (income)	2,000,000	3,000,000
Pension Plan [Member] | Georgia Power [Member]
Pension Plans and Postretirement Plans
Service cost	19,000,000	17,000,000
Interest cost	34,000,000	34,000,000
Expected return on plan assets	(71,000,000)	(64,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	14,000,000	14,000,000
Net periodic pension cost (income)	(3,000,000)	2,000,000
Pension Plan [Member] | Gulf Power [Member]
Pension Plans and Postretirement Plans
Service cost	3,000,000	3,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(9,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	0	1,000,000
Pension Plan [Member] | Mississippi Power [Member]
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(9,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] | Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost	1,000,000
Interest cost	3,000,000
Expected return on plan assets	(2,000,000)
Amortization:
Prior service costs	(1,000,000)
Net (gain)/loss	1,000,000
Net periodic pension cost (income)	2,000,000
Other Postretirement Benefit Plan [Member] | Southern Company [Member]
Pension Plans and Postretirement Plans
Service cost	6,000,000	5,000,000
Interest cost	20,000,000	18,000,000
Expected return on plan assets	(16,000,000)	(14,000,000)
Amortization:
Prior service costs	2,000,000	2,000,000
Net (gain)/loss	2,000,000	3,000,000
Net periodic pension cost (income)	14,000,000	14,000,000
Other Postretirement Benefit Plan [Member] | Alabama Power [Member]
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] | Georgia Power [Member]
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	7,000,000	8,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	5,000,000	6,000,000
Other Postretirement Benefit Plan [Member] | Gulf Power [Member]
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] | Mississippi Power [Member]
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	$ 1,000,000	1,000,000
Predecessor [Member] | Pension Plan [Member] | Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost		6,000,000
Interest cost		10,000,000
Expected return on plan assets		(16,000,000)
Amortization:
Prior service costs		0
Net (gain)/loss		6,000,000
Net periodic pension cost (income)		6,000,000
Predecessor [Member] | Other Postretirement Benefit Plan [Member] | Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost		1,000,000
Interest cost		3,000,000
Expected return on plan assets		(2,000,000)
Amortization:
Prior service costs		(1,000,000)
Net (gain)/loss		1,000,000
Net periodic pension cost (income)		$ 2,000,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective tax rate	32.10%	30.20%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 484
Tax positions from current periods	9
Tax positions from prior periods	7
Balance as of March 31, 2017	500
Tax positions impacting the effective tax rate			$ 36	$ 20
Tax positions not impacting the effective tax rate			464	464
Balance of unrecognized tax benefits	$ 484		500	484
Significantly Increase or Decrease in Amount of Unrecognized Tax Benefits	12 months
Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of March 31, 2017	$ 464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			32
Mississippi Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(58.70%)	(850.40%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 465
Tax positions from current periods	3
Tax positions from prior periods	0
Balance as of March 31, 2017	468
Tax positions impacting the effective tax rate			4
Tax positions not impacting the effective tax rate			464
Balance of unrecognized tax benefits	465		468	465
Mississippi Power [Member] | Kemper IGCC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of March 31, 2017	464
Balance of unrecognized tax benefits	$ 464		464
Unrecognized tax benefit, associated interest			32
Southern Power [Member]
Income Tax Contingency [Line Items]
Effective tax rate	(385.90%)	(84.00%)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of December 31, 2016	$ 17
Tax positions from current periods	1
Tax positions from prior periods	0
Balance as of March 31, 2017	18
Tax positions impacting the effective tax rate			18
Tax positions not impacting the effective tax rate			0
Balance of unrecognized tax benefits	$ 17		18	17
Investment Tax Credit Carryforward [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward, amount			1,900	$ 1,800
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions not impacting the effective tax rate			$ 98

Derivatives - Energy-Related an

Derivatives - Energy-Related and Interest Rate Derivatives (Details) BTU in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)BTU
Interest Rate Contract [Member]
Interest rate derivatives
Notional Amount	$ 3,980
Fair Value Gain (Loss) at March 31, 2017	$ (18)
Southern Company [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	503
Longest Hedge Date	2,021
Longest Non-Hedge Date	2,024
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date August 2017 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	1.30%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date August 2017 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.17%
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date June 2020 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 300
Interest Rate Received	2.75%
Fair Value Gain (Loss) at March 31, 2017	$ 1
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date June 2020 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.92%
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date July 2021 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Fair Value Gain (Loss) at March 31, 2017	$ (21)
Southern Company [Member] | Interest Rate Contract [Member] | Maturity Date July 2021 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.87%
Alabama Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	71
Longest Hedge Date	2,020
Georgia Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	155
Longest Hedge Date	2,020
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date June 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 250
Interest Rate Received	5.40%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date June 2018 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	4.02%
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 500
Interest Rate Received	1.95%
Fair Value Gain (Loss) at March 31, 2017	$ (3)
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2018 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	0.76%
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2019 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 200
Interest Rate Received	4.25%
Fair Value Gain (Loss) at March 31, 2017	$ 1
Georgia Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2019 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivatives
Weighted Average Interest Rate Paid	2.46%
Gulf Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	42
Longest Hedge Date	2,020
Gulf Power [Member] | Interest Rate Contract [Member] | Maturity Date December 2026 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivatives
Notional Amount	$ 80
Weighted Average Interest Rate Paid	2.32%
Fair Value Gain (Loss) at March 31, 2017	$ 0
Mississippi Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	37
Longest Hedge Date	2,021
Mississippi Power [Member] | Interest Rate Contract [Member] | Maturity Date March 2018 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivatives
Notional Amount	$ 900
Weighted Average Interest Rate Paid	0.79%
Fair Value Gain (Loss) at March 31, 2017	$ 4
Southern Power [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	21
Longest Hedge Date	2,017
Longest Non-Hedge Date	2,017
Southern Company Gas [Member] | Energy-related, Natural Gas [Member]
Energy-related derivative contracts
Net Purchased mmBtu | BTU	177
Longest Hedge Date	2,019
Longest Non-Hedge Date	2,024
Southern Company Gas [Member] | Energy-related, Natural Gas [Member] | Long [Member] | Not Designated as Hedging Instrument [Member]
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | BTU	3,400
Southern Company Gas [Member] | Energy-related, Natural Gas [Member] | Short [Member] | Not Designated as Hedging Instrument [Member]
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | BTU	3,200

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) BTU in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)BTU	Dec. 31, 2016USD ($)
Derivative [Line Items]
Collateral already posted, aggregate fair value	$ 92
Maximum potential collateral requirements arising from credit risk related contingent features	$ 11
Southern Company [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	10
Georgia Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	4
Southern Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	3
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 10
Parent Company And Georgia Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	1
Parent Company and Southern Power [Member]
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	$ 24
Southern Company Gas [Member]
Derivative [Line Items]
Collateral already posted, aggregate fair value	92	$ 62
Maximum potential collateral requirements arising from credit risk related contingent features	2
Traditional Operating Companies and Southern Power [Member]
Derivative [Line Items]
Maximum potential collateral requirements arising from credit risk related contingent features	9
Derivative Counterparties [Member] | Registrants [Member]
Derivative [Line Items]
Collateral already posted, aggregate fair value	$ 0

Derivatives - Foreign Currency

Derivatives - Foreign Currency Derivatives (Details) - 3 months ended Mar. 31, 2017 - Cash Flow Hedges Of Existing Debt [Member] - Foreign Exchange Contract [Member] € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) at March 31, 2017	(62)
Southern Power [Member] | Maturity Date June 2022 [Member]
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain (Loss) at March 31, 2017	$ (35)
Southern Power [Member] | Maturity Date June 2026 [Member]
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) at March 31, 2017	$ (27)

Derivatives - Derivative Financ

Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 92
Southern Company [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	519	$ 690
Derivatives, liabilities	552	718
Derivative asset amount offset	(303)	(462)
Derivative liability amount offset	(395)	(524)
Derivative asset	216	228
Derivative liability	157	194
Southern Company [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	438	556
Derivatives, liabilities	385	564
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	306	489
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	66
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	271	483
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	114	81
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	54	98
Derivatives, liabilities	68	60
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	48	73
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	6	25
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	30	27
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	38	33
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	27	36
Derivatives, liabilities	99	94
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	23
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	7
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	12
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	1
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	32	28
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	37	33
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	25	25
Alabama Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	20
Derivatives, liabilities	10	9
Derivative asset amount offset	(6)	(8)
Derivative liability amount offset	(6)	(8)
Derivative asset	5	12
Derivative liability	4	1
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	20
Derivatives, liabilities	10	9
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	13
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	7
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	5
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	4
Georgia Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	26	46
Derivatives, liabilities	17	11
Derivative asset amount offset	(6)	(8)
Derivative liability amount offset	(6)	(8)
Derivative asset	20	38
Derivative liability	11	3
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	24	44
Derivatives, liabilities	13	8
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	20	30
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	14
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	11	7
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	1
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	2
Derivatives, liabilities	4	3
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	2
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	3
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Gulf Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	5
Derivatives, liabilities	31	29
Derivative asset amount offset	(2)	(4)
Derivative liability amount offset	(2)	(4)
Derivative asset	0	1
Derivative liability	29	25
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	5
Derivatives, liabilities	31	29
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	14	12
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	17	17
Mississippi Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	7	7
Derivatives, liabilities	12	11
Derivative asset amount offset	(2)	(3)
Derivative liability amount offset	(2)	(3)
Derivative asset	5	4
Derivative liability	10	8
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	4
Derivatives, liabilities	12	11
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	2
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	2
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	5
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	7	6
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	3
Derivatives, liabilities	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	2
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	15	22
Derivatives, liabilities	67	63
Derivative asset amount offset	(3)	(5)
Derivative liability amount offset	(3)	(5)
Derivative asset	12	17
Derivative liability	64	58
Southern Power [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
Derivatives, liabilities	1	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	3
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	18
Derivatives, liabilities	66	62
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	18
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	4
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	37	33
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	25	25
Southern Company Gas [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	451	581
Derivatives, liabilities	387	569
Derivative asset amount offset	(272)	(435)
Derivative liability amount offset	(364)	(497)
Derivative asset	179	146
Derivative liability	23	72
Collateral already posted, aggregate fair value	92	62
Southern Company Gas [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	4	8
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	436	552
Derivatives, liabilities	384	563
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	66
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	114	81
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	304	486
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	270	482
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	25
Derivatives, liabilities	2	3
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	24
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	3
Southern Company Gas [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	4
Southern Company Gas [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	$ 1	$ 3

Derivatives - Pre-tax Effects o

Derivatives - Pre-tax Effects of Derivatives Designated as Cash Flow Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	$ 92
Southern Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(14)	$ (190)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	2	(4)
Southern Company [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(18)		$ 33
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(11)	0
Southern Company [Member] | Energy Related Derivative [Member] | Amortization [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(4)	(1)
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(19)		(16)
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(32)		(19)
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	33		56
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			12
Southern Company [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	1	(190)
Southern Company [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(5)	(3)
Southern Company [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(4)	0
Southern Company [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6)	0
Southern Company [Member] | Foreign Exchange Contract [Member] | Other Income Expense Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	17	0
Alabama Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	1		11
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(3)		0
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	5		8
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			4
Georgia Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	11		36
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(7)		0
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	18		29
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			7
Gulf Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(1)	(5)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0	0
Gulf Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(29)		(24)
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(1)	0
Gulf Power [Member] | Energy Related Derivative [Member] | Amortization [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0	0
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(12)		(9)
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(17)		(16)
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		1
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			0
Gulf Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	(5)
Gulf Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0	0
Mississippi Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(9)		(7)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(5)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(3)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	1		1
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			0
Southern Company Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	92		62
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(2)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0
Southern Company Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	8		17
Collateral already posted, aggregate fair value	4		8
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(2)
Southern Company Gas [Member] | Energy Related Derivative [Member] | Cost of Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0
Southern Company Gas [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)
Southern Company Gas [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
Southern Company Gas [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	9		17
Southern Company Gas [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			$ 1
Southern Company Gas [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0
Southern Company Gas [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0
Southern Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(12)	0
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	7	(1)
Southern Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(8)	0
Southern Power [Member] | Energy Related Derivative [Member] | Amortization [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(4)	(1)
Southern Power [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(4)	0
Southern Power [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6)	0
Southern Power [Member] | Foreign Exchange Contract [Member] | Other Income Expense Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 17	0
Predecessor [Member] | Southern Company Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(45)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		1
Predecessor [Member] | Southern Company Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		0
Predecessor [Member] | Southern Company Gas [Member] | Energy Related Derivative [Member] | Cost of Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		0
Predecessor [Member] | Southern Company Gas [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(45)
Predecessor [Member] | Southern Company Gas [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		$ 1

Derivatives - Pre-tax Effects56

Derivatives - Pre-tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	$ 81	$ 2
Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	47	0
Energy Related Derivative [Member] | Natural Gas Revenues [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	50	0
Energy Related Derivative [Member] | Cost of Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(3)	0
Southern Company Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	82
Southern Company Gas [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	47
Southern Company Gas [Member] | Energy Related Derivative [Member] | Natural Gas Revenues [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	50
Southern Company Gas [Member] | Energy Related Derivative [Member] | Cost of Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(3)
Southern Company Gas [Member] | Weather Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	14
Southern Company Gas [Member] | Predecessor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net		(5)
Southern Company Gas [Member] | Predecessor [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net		19
Southern Company Gas [Member] | Predecessor [Member] | Energy Related Derivative [Member] | Natural Gas Revenues [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net		20
Southern Company Gas [Member] | Predecessor [Member] | Energy Related Derivative [Member] | Cost of Natural Gas [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net		(1)
Southern Company Gas [Member] | Predecessor [Member] | Weather Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net		$ 3
Southern Company [Member] | Weather Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	$ 14

Derivatives - Pre-tax Effects57

Derivatives - Pre-tax Effects of Derivatives as Fair Value Hedging Relationships (Details) - Interest Rate Contract [Member] - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Southern Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ (8)	$ 20
Georgia Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets, fair value, gross asset	$ (1)	$ 14

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) $ / shares in Units, MW in Thousands, $ in Millions	Jul. 01, 2016USD ($)	May 09, 2016USD ($)$ / shares	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2020	Dec. 31, 2016USD ($)MW
Business Acquisition [Line Items]
Goodwill			$ 6,251			$ 6,251
Revenues			5,771	$ 3,992
Consolidated net income attributable to Southern Company			658	489
Construction work in progress			9,465			8,977
Southern Company Gas [Member]
Business Acquisition [Line Items]
Goodwill			5,967			5,967
Revenues			1,560
Consolidated net income attributable to Southern Company			239
Construction work in progress			625			496
Southern Power [Member]
Business Acquisition [Line Items]
Goodwill			2			2
Revenues			450	315
Consolidated net income attributable to Southern Company			$ 70	$ 50
Number of projects to be placed in service			3
Total costs of construction			$ 401
Construction work in progress			328			$ 398
Southern Company Gas [Member]
Business Acquisition [Line Items]
Aggregate purchase price	$ 8,000
Goodwill			$ 5,967
Southern Company Gas [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated lives of intangible assets			1 year
Southern Company Gas [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated lives of intangible assets			28 years
PowerSecure International, Inc. [Member]
Business Acquisition [Line Items]
Aggregate purchase price		$ 429
Goodwill			$ 282
Acquisition, share price (in dollars per share) | $ / shares		$ 18.75
PowerSecure International, Inc. [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated lives of intangible assets			1 year
PowerSecure International, Inc. [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated lives of intangible assets			26 years
Series of Business Acquisitions [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Revenue of acquirees, actual			$ 4
Series of Construction Projects [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Construction work in progress			203
Series of Construction Projects [Member] | Minimum [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Estimated future construction payments			530
Series of Construction Projects [Member] | Maximum [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Estimated future construction payments			$ 590
Renewable Energy Systems Americas, Inc. [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Approx. nameplate capacity, wind (MW) | MW						3
Wind Generating Facility [Member] | Scenario, Forecast [Member] | Southern Power [Member]
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage					100.00%
Production tax credits, project qualification period					10 years

Acquisitions - Schedule of Acqu

Acquisitions - Schedule of Acquisitions (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	$ 6,251	$ 6,251
Southern Company Gas [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Current assets	1,557
Intangible assets	400
Property, plant, and equipment	10,108
Goodwill	5,967
Regulatory assets	1,118
Other assets	229
Current liabilities	(2,201)
Deferred credits and other liabilities	(4,742)
Long-term debt	(4,261)
Noncontrolling interest	(174)
Total purchase price	8,001
PowerSecure International, Inc. [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Current assets	172
Intangible assets	101
Property, plant, and equipment	46
Goodwill	282
Other assets	4
Current liabilities	(114)
Long-term debt, including current portion	48
Deferred credits and other liabilities	(14)
Total purchase price	429
Southern Power [Member]
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	$ 2	$ 2

Acquisitions - Schedule of Pro

Acquisitions - Schedule of Pro Forma Consolidated Information (Details) - Southern Company Gas [Member] $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)$ / shares
Business Acquisition [Line Items]
Operating revenues | $	$ 5,320
Net income attributable to Southern Company | $	$ 650
Basic EPS (in dollars per share) | $ / shares	$ 0.70
Diluted EPS (in dollars per share) | $ / shares	$ 0.69

Acquisitions - Schedule of Cons

Acquisitions - Schedule of Construction Projects (Details) - Southern Power [Member] - MW	Jan. 06, 2017	Apr. 30, 2017	Mar. 31, 2017	Jun. 30, 2019
Bethel [Member]
Business Acquisition [Line Items]
Approx. nameplate capacity, solar (MW)	276
Noncontrolling interest, ownership percentage by parent	100.00%
PPA Contract Period	12 years
East Pecos [Member]
Business Acquisition [Line Items]
Approx. nameplate capacity, solar (MW)			120
PPA Contract Period			15 years
Subsequent Event [Member] | Lamesa [Member]
Business Acquisition [Line Items]
Approx. nameplate capacity, solar (MW)		102
PPA Contract Period		15 years
Scenario, Forecast [Member] | RE Roserock Holdings, LLC [Member]
Business Acquisition [Line Items]
Approx. nameplate capacity, solar (MW)				345
PPA Contract Period				20 years

Joint Ownership Agreements - Ba

Joint Ownership Agreements - Balance Sheet Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,615	$ 1,549
Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,604	1,541
SNG [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,430	1,394
Triton [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	44	44
Horizon Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	31	30
PennEast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	30	22
Atlantic Coast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	42	33
Pivotal JAX LNG, LLC [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	26	16
Other [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1	$ 2

Joint Ownership Agreements - In

Joint Ownership Agreements - Income Statement Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 39	$ 0
Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	39
Southern Company Gas [Member] | Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		1
Southern Company Gas [Member] | SNG [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	34
Southern Company Gas [Member] | SNG [Member] | Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		0
Southern Company Gas [Member] | Horizon Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1
Southern Company Gas [Member] | Horizon Pipeline [Member] | Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		1
Southern Company Gas [Member] | PennEast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	3
Southern Company Gas [Member] | PennEast Pipeline [Member] | Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		0
Southern Company Gas [Member] | Atlantic Coast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 1
Southern Company Gas [Member] | Atlantic Coast Pipeline [Member] | Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 0

Joint Ownership Agreements - Na

Joint Ownership Agreements - Narrative (Details) - SNG [Member] - Southern Company Gas [Member] - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%
Capital contributions from parent company	$ 50

Joint Ownership Agreements - 65

Joint Ownership Agreements - Investment in SNG (Details) - SNG [Member] $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Revenues	$ 155
Operating income	84
Net income	$ 66

Segment and Related Informati66

Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)statesegment	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4
Operating revenues	$ 5,771	$ 3,992
Segment net income (loss)	658	489
Total assets	109,760		$ 109,697
Kemper IGCC [Member]
Segment Reporting Information [Line Items]
Pre-tax charge to income	108	53
After tax charge to income	67	33
Plant Scherer Unit 3 [Member]
Segment Reporting Information [Line Items]
After tax charge to income	20
Loss on Plant Scherer Unit 3	33
Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,131	3,981
Segment net income (loss)	502	515
Total assets	87,067		86,994
Intersegment Eliminations [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	(105)	(103)
Segment net income (loss)	0	0
Total assets	(306)		(316)
Consolidation Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(43)	(36)
Segment net income (loss)	1	(3)
Total assets	(1,564)		(1,624)
Traditional Operating Companies [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,786	3,769
Segment net income (loss)	432	465
Total assets	72,692		72,141
Southern Power [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	450	315
Segment net income (loss)	70	50
Total assets	14,681		15,169
Southern Company Gas [Member] | Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,560
Segment net income (loss)	239
Total assets	21,683		21,853
All Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	123	47
Segment net income (loss)	(84)	(23)
Total assets	2,574		2,474
Gulf Power [Member]
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	37	21
Operating revenues	350	335
Segment net income (loss)	18	29
Total assets	4,767		4,822
Loss on Plant Scherer Unit 3	$ 33	0
Southern Company Gas [Member]
Segment Reporting Information [Line Items]
Number of reportable segments | segment	7
Operating revenues	$ 1,560
Segment net income (loss)	239
Total assets	21,683		21,853
Southern Company Gas [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,624
Segment net income (loss)	231
Total assets	23,700		24,875
Southern Company Gas [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(66)
Segment net income (loss)	0
Total assets	(12,877)		(14,167)
Southern Company Gas [Member] | Gas Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,180
Segment net income (loss)	117
Total assets	18,201		19,453
Southern Company Gas [Member] | Gas Marketing Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	288
Segment net income (loss)	31
Total assets	2,118		2,084
Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	131
Segment net income (loss)	68
Total assets	1,018		1,127
Cost of Revenue	1,844
Southern Company Gas [Member] | Gas Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	25
Segment net income (loss)	15
Total assets	2,363		2,211
Southern Company Gas [Member] | All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	2
Segment net income (loss)	8
Total assets	10,860		11,145
Southern Power [Member]
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	100	97
Operating revenues	450	315
Segment net income (loss)	70	50
Total assets	14,681		$ 15,169
Predecessor [Member] | Southern Company Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,334
Segment net income (loss)		182
EBIT		352
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,392
EBIT		358
Predecessor [Member] | Southern Company Gas [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues		(60)
EBIT		(1)
Predecessor [Member] | Southern Company Gas [Member] | Gas Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,028
EBIT		235
Predecessor [Member] | Southern Company Gas [Member] | Gas Marketing Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		286
EBIT		80
Predecessor [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		63
EBIT		44
Cost of Revenue		1,461
Predecessor [Member] | Southern Company Gas [Member] | Gas Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		15
EBIT		(1)
Predecessor [Member] | Southern Company Gas [Member] | All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		2
EBIT		(5)
Third Party Gross Revenues [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,839
Third Party Gross Revenues [Member] | Predecessor [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,443
Intercompany Revenues [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	136
Intercompany Revenues [Member] | Predecessor [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		81
Total Gross Revenues [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 1,975
Total Gross Revenues [Member] | Predecessor [Member] | Southern Company Gas [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 1,524

Segment and Related Informati67

Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 4,131	$ 3,981
Gas Revenue	1,560
Retail [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	3,394	3,377
Wholesale [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	531	396
Other [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	206	$ 208
Gas Distribution Operations [Member]
Revenue from External Customer [Line Items]
Gas Revenue	1,132
Gas Marketing Services [Member]
Revenue from External Customer [Line Items]
Gas Revenue	288
Other Gas Revenue [Member]
Revenue from External Customer [Line Items]
Gas Revenue	$ 140

Segment and Related Informati68

Segment and Related Information - Narrative (Details) - Southern Company Gas [Member]	3 Months Ended
	Mar. 31, 2017segment
Segment Reporting Information [Line Items]
Number of Natural Gas Distribution Utilities	7
Number of reportable segments	4