Mississippi Power (MSPWP) 10-Q 8 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2018shares
Document Information [Line Items]
Entity Registrant Name	SOUTHERN CO
Entity Central Index Key	92,122
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	1,014,136,083
ALABAMA POWER CO
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 CO
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 CO
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 CO
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 CO
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 Co GAS
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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Revenues:
Retail electric revenues	$ 3,740	$ 3,777	$ 7,308	$ 7,171
Wholesale electric revenues	611	618	1,230	1,149
Other electric revenues	175	167	339	342
Natural gas revenues (includes alternative revenue programs of $(4), $-, $(27), and $9, respectively)	706	684	2,314	2,214
Alternative revenue programs	(4)	0	(27)	9
Other revenues	395	184	808	326
Total operating revenues	5,627	5,430	11,999	11,202
Operating Expenses:
Fuel	1,103	1,092	2,204	2,088
Purchased power	236	211	503	390
Cost of natural gas	228	232	949	951
Cost of other sales	279	114	568	203
Other operations and maintenance	1,559	1,356	3,008	2,740
Depreciation and amortization	783	754	1,552	1,469
Taxes other than income taxes	316	308	671	638
Estimated loss on plants under construction	1,060	3,012	1,105	3,120
Asset impairment			161	0
Goodwill impairment			42
Total operating expenses	5,564	7,079	10,560	11,599
Operating Income (Loss)	63	(1,649)	1,439	(397)
Other Income and (Expense):
Allowance for equity funds used during construction	32	58	63	115
Earnings from equity method investments	31	28	72	67
Interest expense, net of amounts capitalized	(470)	(424)	(928)	(840)
Other income (expense), net	78	52	138	98
Total other income and (expense)	(329)	(286)	(655)	(560)
Earnings (Loss) Before Income Taxes	(266)	(1,935)	784	(957)
Income taxes (benefit)	(139)	(587)	(25)	(273)
Consolidated Net Income (Loss)	(127)	(1,348)	809	(684)
Less:
Dividends on preferred and preference stock of subsidiaries	4	11	8	22
Net income attributable to noncontrolling interests	23	22	17	17
Net Income (Loss)	$ (154)	$ (1,381)	$ 784	$ (723)
Earnings (loss) per share —
Basic (in dollars per share)	$ (0.15)	$ (1.38)	$ 0.77	$ (0.73)
Diluted (in dollars per share)	$ (0.15)	$ (1.37)	$ 0.77	$ (0.72)
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	1,014	998	1,012	996
Diluted (in shares)	1,014	1,005	1,017	1,003
Cash dividends paid per share of common stock (in dollars per share)	$ 0.60	$ 0.58	$ 1.18	$ 1.14
ALABAMA POWER CO
Operating Revenues:
Retail electric revenues	$ 1,338	$ 1,333	$ 2,624	$ 2,560
Wholesale revenues, non-affiliates	65	68	139	133
Wholesale revenues, affiliates	31	32	82	65
Other revenues	69	51	131	108
Total operating revenues	1,503	1,484	2,976	2,866
Operating Expenses:
Fuel	347	303	672	601
Purchased power, non-affiliates	48	40	113	75
Purchased power, affiliates	43	34	80	62
Other operations and maintenance	402	389	788	772
Depreciation and amortization	189	183	379	364
Taxes other than income taxes	94	95	192	191
Total operating expenses	1,123	1,044	2,224	2,065
Operating Income (Loss)	380	440	752	801
Other Income and (Expense):
Allowance for equity funds used during construction	14	8	27	16
Interest expense, net of amounts capitalized	(80)	(77)	(158)	(153)
Other income (expense), net	12	15	15	25
Total other income and (expense)	(54)	(54)	(116)	(112)
Earnings (Loss) Before Income Taxes	326	386	636	689
Income taxes (benefit)	64	151	145	277
Consolidated Net Income (Loss)	262	235	491	412
Less:
Dividends on preferred and preference stock of subsidiaries	3	5	7	9
Net Income (Loss)	259	230	484	403
GEORGIA POWER CO
Operating Revenues:
Retail electric revenues	1,889	1,904	3,688	3,593
Wholesale revenues, non-affiliates	36	40	80	79
Wholesale revenues, affiliates	3	9	13	17
Other revenues	120	95	227	191
Total operating revenues	2,048	2,048	4,008	3,880
Operating Expenses:
Fuel	378	445	790	815
Purchased power, non-affiliates	111	103	233	191
Purchased power, affiliates	178	138	349	310
Other operations and maintenance	457	417	863	816
Depreciation and amortization	230	223	458	444
Taxes other than income taxes	106	101	214	199
Estimated loss on plants under construction	1,060	0	1,060	0
Total operating expenses	2,520	1,427	3,967	2,775
Operating Income (Loss)	(472)	621	41	1,105
Other Income and (Expense):
Allowance for equity funds used during construction			32	25
Interest expense, net of amounts capitalized	(102)	(104)	(208)	(205)
Other income (expense), net	35	34	73	71
Total other income and (expense)	(67)	(70)	(135)	(134)
Earnings (Loss) Before Income Taxes	(539)	551	(94)	971
Income taxes (benefit)	(143)	199	(50)	355
Consolidated Net Income (Loss)	(396)	352	(44)	616
Less:
Dividends on preferred and preference stock of subsidiaries	0	5	0	9
Net Income (Loss)	(396)	347	(44)	607
GULF POWER CO
Operating Revenues:
Retail electric revenues	301	318	591	596
Wholesale revenues, non-affiliates	13	12	26	30
Wholesale revenues, affiliates	14	10	42	47
Other revenues	16	17	33	34
Total operating revenues	344	357	692	707
Operating Expenses:
Fuel	91	88	173	196
Purchased power, non-affiliates	44	44	90	78
Other operations and maintenance	90	90	166	176
Depreciation and amortization	48	35	95	53
Taxes other than income taxes	28	28	58	55
Loss on Plant Scherer Unit 3	0	0	0	33
Total operating expenses	301	285	582	591
Operating Income (Loss)	43	72	110	116
Other Income and (Expense):
Interest expense, net of amounts capitalized	(13)	(13)	(26)	(24)
Other income (expense), net	1	2	3	3
Total other income and (expense)	(12)	(11)	(23)	(21)
Earnings (Loss) Before Income Taxes	31	61	87	95
Income taxes (benefit)	(11)	24	3	38
Consolidated Net Income (Loss)	42	37	84	57
Less:
Dividends on preferred and preference stock of subsidiaries	0	2	0	4
Net Income (Loss)	42	35	84	53
MISSISSIPPI POWER CO
Operating Revenues:
Retail electric revenues	212	222	406	422
Wholesale revenues, non-affiliates	55	62	118	124
Wholesale revenues, affiliates	19	15	54	20
Other revenues	11	4	20	9
Total operating revenues	297	303	598	575
Operating Expenses:
Fuel	98	102	197	180
Purchased power, non-affiliates	7	6	16	14
Other operations and maintenance	67	72	141	148
Depreciation and amortization	44	41	84	81
Taxes other than income taxes	27	26	54	52
Estimated loss on plants under construction	0	3,012	45	3,120
Total operating expenses	243	3,259	537	3,595
Operating Income (Loss)	54	(2,956)	61	(3,020)
Other Income and (Expense):
Allowance for equity funds used during construction	0	36	0	71
Interest expense, net of amounts capitalized	(21)	(17)	(39)	(37)
Other income (expense), net	27	3	27	5
Total other income and (expense)	6	22	(12)	39
Earnings (Loss) Before Income Taxes	60	(2,934)	49	(2,981)
Income taxes (benefit)	13	(881)	9	(908)
Consolidated Net Income (Loss)	47	(2,053)	40	(2,073)
Less:
Dividends on preferred and preference stock of subsidiaries	1	1	1	1
Net Income (Loss)	46	(2,054)	39	(2,074)
SOUTHERN POWER CO
Operating Revenues:
Wholesale revenues, non-affiliates	443	436	867	783
Wholesale revenues, affiliates	109	90	192	190
Other revenues	3	3	5	6
Total operating revenues	555	529	1,064	979
Operating Expenses:
Fuel	153	139	321	271
Purchased power, non-affiliates	39	40	100	70
Other operations and maintenance	91	97	184	190
Depreciation and amortization	125	129	240	247
Taxes other than income taxes	12	12	24	24
Asset impairment	119	0	119	0
Total operating expenses	539	417	988	802
Operating Income (Loss)	16	112	76	177
Other Income and (Expense):
Interest expense, net of amounts capitalized	(46)	(48)	(93)	(97)
Other income (expense), net	2	2	5	(2)
Total other income and (expense)	(44)	(46)	(88)	(99)
Earnings (Loss) Before Income Taxes	(28)	66	(12)	78
Income taxes (benefit)	(73)	(38)	(172)	(90)
Consolidated Net Income (Loss)	45	104	160	168
Less:
Net income attributable to noncontrolling interests	23	22	17	17
Net Income (Loss)	22	82	143	151
SOUTHERN Co GAS
Operating Revenues:
Natural gas revenues (includes alternative revenue programs of $(4), $-, $(27), and $9, respectively)	710	684	2,341	2,205
Alternative revenue programs	(4)	0	(27)	9
Other revenues	24	32	55	62
Total operating revenues	730	716	2,369	2,276
Operating Expenses:
Cost of natural gas	228	232	949	951
Cost of other sales	5	6	12	13
Other operations and maintenance	238	214	514	470
Depreciation and amortization	126	125	255	244
Taxes other than income taxes	48	44	125	114
Goodwill impairment	0	0	42	0
Loss on disposition	36	0	36	0
Total operating expenses	681	621	1,933	1,792
Operating Income (Loss)	49	95	436	484
Other Income and (Expense):
Earnings from equity method investments	31	29	74	68
Interest expense, net of amounts capitalized	(59)	(48)	(118)	(94)
Other income (expense), net	3	4	15	10
Total other income and (expense)	(25)	(15)	(29)	(16)
Earnings (Loss) Before Income Taxes	24	80	407	468
Income taxes (benefit)	55	31	159	180
Consolidated Net Income (Loss)	(31)	49	248	288
Less:
Net Income (Loss)	$ (31)	$ 49	$ 248	$ 288

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Alternative revenue programs	$ (4)	$ 0	$ (27)	$ 9
SOUTHERN Co GAS
Alternative revenue programs	(4)	0	(27)	9
Excise taxes collected	$ 23	$ 19	$ 74	$ 67

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income (loss)	$ (127)	$ (1,348)	$ 809	$ (684)
Qualifying hedges:
Changes in fair value, net of tax	(54)	38	(8)	29
Reclassification adjustment for amounts included in net income, net of tax	64	(41)	45	(42)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	2	1	4	2
Total other comprehensive income (loss)	12	(2)	41	(11)
Comprehensive Income (Loss)	(115)	(1,350)	850	(695)
Less:
Dividends on preferred and preference stock of subsidiaries	4	11	8	22
Comprehensive income attributable to noncontrolling interests	23	22	17	17
Comprehensive Income (Loss) Attributable to Parent	(142)	(1,383)	825	(734)
ALABAMA POWER CO
Net income (loss)	262	235	491	412
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	1	1	2	2
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1	2	2
Comprehensive Income (Loss)	263	236	493	414
Less:
Dividends on preferred and preference stock of subsidiaries	3	5	7	9
GEORGIA POWER CO
Net income (loss)	(396)	352	(44)	616
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	1	1	2	2
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1	2	2
Comprehensive Income (Loss)	(395)	353	(42)	618
Less:
Dividends on preferred and preference stock of subsidiaries	0	5	0	9
GULF POWER CO
Net income (loss)	42	37	84	57
Qualifying hedges:
Changes in fair value, net of tax	0	(1)	0	(1)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	0	(1)	0	(1)
Comprehensive Income (Loss)	42	36	84	56
Less:
Dividends on preferred and preference stock of subsidiaries	0	2	0	4
MISSISSIPPI POWER CO
Net income (loss)	47	(2,053)	40	(2,073)
Qualifying hedges:
Changes in fair value, net of tax	0	0	(1)	1
Reclassification adjustment for amounts included in net income, net of tax	0	0	1	0
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	0	0	0	1
Comprehensive Income (Loss)	47	(2,053)	40	(2,072)
Less:
Dividends on preferred and preference stock of subsidiaries	1	1	1	1
SOUTHERN POWER CO
Net income (loss)	45	104	160	168
Qualifying hedges:
Changes in fair value, net of tax	(55)	40	(8)	32
Reclassification adjustment for amounts included in net income, net of tax	59	(45)	35	(48)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	0	0	1	0
Total other comprehensive income (loss)	4	(5)	28	(16)
Comprehensive Income (Loss)	49	99	188	152
Less:
Comprehensive income attributable to noncontrolling interests	23	22	17	17
Comprehensive Income (Loss) Attributable to Parent	26	77	171	135
SOUTHERN Co GAS
Net income (loss)	(31)	49	248	288
Qualifying hedges:
Changes in fair value, net of tax	1	(1)	1	(2)
Reclassification adjustment for amounts included in net income, net of tax	0	0	2	0
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	0	0	0	(1)
Total other comprehensive income (loss)	1	(1)	3	(3)
Comprehensive Income (Loss)	$ (30)	$ 48	$ 251	$ 285

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in fair value, tax	$ (18)	$ 23	$ (3)	$ 17
Reclassification adjustment for cash flow hedge, gain (loss), tax	21	(25)	15	(26)
Reclassification adjustment for pension and other post retirement benefit plans, tax	1	1	1	1
ALABAMA POWER CO
Reclassification adjustment for cash flow hedge, gain (loss), tax	0	1	1	1
GEORGIA POWER CO
Reclassification adjustment for cash flow hedge, gain (loss), tax	0	0	1	1
GULF POWER CO
Changes in fair value, tax	0	0	0	(1)
MISSISSIPPI POWER CO
Changes in fair value, tax	0	0	(1)	0
Reclassification adjustment for cash flow hedge, gain (loss), tax	0	0	0	0
SOUTHERN POWER CO
Changes in fair value, tax	(19)	24	(3)	20
Reclassification adjustment for cash flow hedge, gain (loss), tax	20	(27)	12	(30)
Reclassification adjustment for pension and other post retirement benefit plans, tax	0	0	0	0
SOUTHERN Co GAS
Changes in fair value, tax	0	(1)	0	(2)
Reclassification adjustment for cash flow hedge, gain (loss), tax	0	0	1	0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities:
Net income (loss)	$ 809	$ (684)
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	1,750	1,683
Deferred income taxes	(338)	(270)
Allowance for equity funds used during construction	(63)	(115)
Pension, postretirement, and other employee benefits	(74)	(83)
Settlement of asset retirement obligations	(97)	(87)
Stock based compensation expense	83	73
Estimated loss on plants under construction	1,088	3,120
Goodwill impairment	42
Asset impairment	161	0
Other, net	5	(118)
Changes in certain current assets and liabilities —
-Receivables	94	107
-Prepayments	(73)	(61)
-Natural gas for sale, net of temporary LIFO liquidation	295	223
-Other current assets	(40)	(30)
-Accounts payable	(406)	(353)
-Accrued taxes	213	(132)
-Accrued compensation	(284)	(331)
-Retail fuel cost over recovery	10	(187)
-Other current liabilities	125	(14)
Net cash provided from operating activities	3,258	2,741
Investing Activities:
Business acquisitions, net of cash acquired	(64)	(1,046)
Property additions	(3,828)	(3,398)
Nuclear decommissioning trust fund purchases	(571)	(388)
Nuclear decommissioning trust fund sales	566	383
Cost of removal, net of salvage	(128)	(128)
Change in construction payables, net	49	(117)
Investment in unconsolidated subsidiaries	(63)	(116)
Payments pursuant to LTSAs	(103)	(132)
Asset dispositions	500	65
Other investing activities	18	(6)
Net cash used for investing activities	(3,624)	(4,883)
Financing Activities:
Increase (decrease) in notes payable, net	1,442	30
Proceeds —
Long-term debt	1,100	2,958
Short-term borrowings	1,650	1,004
Common stock	222	417
Redemptions and repurchases —
Long-term debt	(3,379)	(1,478)
Preferred and preference stock	0	(150)
Short-term borrowings	(550)	0
Distributions to noncontrolling interests	(42)	(40)
Capital contributions from noncontrolling interests	1,210	73
Payment of common stock dividends	(1,194)	(1,134)
Other financing activities	(223)	(75)
Net cash provided from financing activities	236	1,605
Net Change in Cash, Cash Equivalents, and Restricted Cash	(130)	(537)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	2,147	1,992
Cash, Cash Equivalents, and Restricted Cash at End of Period	2,017	1,455
Cash paid (received) during the period for —
Interest	927	833
Income taxes, net	4	1
Noncash transactions — Accrued property additions at end of period	1,067	629
ALABAMA POWER CO
Operating Activities:
Net income (loss)	491	412
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	452	442
Deferred income taxes	48	192
Allowance for equity funds used during construction	(27)	(16)
Pension, postretirement, and other employee benefits	(28)	(24)
Other, net	(40)	20
Changes in certain current assets and liabilities —
-Receivables	(153)	(58)
-Prepayments	(57)	(56)
-Materials and supplies	(47)	(18)
-Other current assets	29	12
-Accounts payable	(196)	(154)
-Accrued taxes	134	52
-Accrued compensation	(70)	(74)
-Retail fuel cost over recovery	0	(65)
-Other current liabilities	116	7
Net cash provided from operating activities	652	672
Investing Activities:
Property additions	(997)	(738)
Nuclear decommissioning trust fund purchases	(131)	(117)
Nuclear decommissioning trust fund sales	131	117
Cost of removal, net of salvage	(34)	(54)
Change in construction payables, net	(29)	48
Other investing activities	(15)	(15)
Net cash used for investing activities	(1,075)	(759)
Proceeds —
Senior notes	500	550
Capital contributions from parent company	488	327
Redemptions and repurchases —
Senior notes	0	(200)
Payment of common stock dividends	(402)	(357)
Other financing activities	(21)	(14)
Net cash provided from financing activities	565	306
Net Change in Cash, Cash Equivalents, and Restricted Cash	142	219
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	544	420
Cash, Cash Equivalents, and Restricted Cash at End of Period	686	639
Cash paid (received) during the period for —
Interest	143	140
Income taxes, net	17	88
Noncash transactions — Accrued property additions at end of period	216	132
GEORGIA POWER CO
Operating Activities:
Net income (loss)	(44)	616
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	562	543
Deferred income taxes	(256)	159
Allowance for equity funds used during construction	(32)	(25)
Deferred expenses	34	41
Pension, postretirement, and other employee benefits	(47)	(45)
Settlement of asset retirement obligations	(49)	(62)
Other, net	27	(39)
Changes in certain current assets and liabilities —
-Receivables	(103)	(150)
-Fossil fuel stock	38	(32)
-Prepaid income taxes	115	(4)
-Other current assets	25	(18)
-Accounts payable	(87)	(153)
-Accrued taxes	(89)	(194)
-Accrued compensation	(56)	(65)
-Retail fuel cost over recovery	0	(84)
-Other current liabilities	(26)	(6)
Net cash provided from operating activities	1,072	482
Investing Activities:
Property additions	(1,501)	(1,284)
Nuclear decommissioning trust fund purchases	(440)	(271)
Nuclear decommissioning trust fund sales	435	266
Cost of removal, net of salvage	(50)	(32)
Change in construction payables, net of joint owner portion	86	1
Payments pursuant to LTSAs	(46)	(56)
Asset dispositions	134	63
Other investing activities	(11)	(12)
Net cash used for investing activities	(1,393)	(1,325)
Financing Activities:
Increase (decrease) in notes payable, net	480	37
Proceeds —
Senior notes	0	850
Short-term borrowings	0	800
Capital contributions from parent company	1,502	380
Redemptions and repurchases —
Senior notes	(1,000)	(450)
Pollution control revenue bonds	(398)	(27)
Other long-term debt	(100)	0
Short-term borrowings	(150)	0
Payment of common stock dividends	(691)	(640)
Premiums on redemption and repurchases of senior notes	(152)	0
Other financing activities	(11)	(19)
Net cash provided from financing activities	(520)	931
Net Change in Cash, Cash Equivalents, and Restricted Cash	(841)	88
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	852	3
Cash, Cash Equivalents, and Restricted Cash at End of Period	11	91
Cash paid (received) during the period for —
Interest	211	186
Income taxes, net	64	213
Noncash transactions — Accrued property additions at end of period	669	348
GULF POWER CO
Operating Activities:
Net income (loss)	84	57
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	98	56
Deferred income taxes	(21)	19
Loss on Plant Scherer Unit 3	0	33
Other, net	(3)	(3)
Changes in certain current assets and liabilities —
-Receivables	9	(25)
-Other current assets	(2)	14
-Accounts payable	(16)	3
-Accrued taxes	18	7
-Accrued compensation	(15)	(17)
-Over recovered regulatory clause revenues	5	(19)
-Other current liabilities	0	(1)
Net cash provided from operating activities	157	124
Investing Activities:
Property additions	(135)	(97)
Cost of removal, net of salvage	(14)	(9)
Change in construction payables, net	(3)	(14)
Other investing activities	(6)	(3)
Net cash used for investing activities	(158)	(123)
Financing Activities:
Increase (decrease) in notes payable, net	45	(190)
Proceeds —
Senior notes	0	300
Capital contributions from parent company	37	5
Common stock	0	175
Redemptions and repurchases —
Preferred and preference stock	0	(150)
Senior notes	0	(85)
Payment of common stock dividends	(77)	(63)
Other financing activities	(1)	(4)
Net cash provided from financing activities	4	(12)
Net Change in Cash, Cash Equivalents, and Restricted Cash	3	(11)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	28	56
Cash, Cash Equivalents, and Restricted Cash at End of Period	31	45
Cash paid (received) during the period for —
Interest	25	22
Income taxes, net	21	7
Noncash transactions — Accrued property additions at end of period	22	19
MISSISSIPPI POWER CO
Operating Activities:
Net income (loss)	40	(2,073)
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	86	94
Deferred income taxes	289	(860)
Allowance for equity funds used during construction	0	(71)
Estimated loss on plants under construction	28	3,120
Other, net	(13)	(11)
Changes in certain current assets and liabilities —
-Receivables	(51)	(15)
-Fossil fuel stock	(2)	21
-Other current assets	(9)	(10)
-Accounts payable	(15)	(20)
-Accrued taxes	(41)	0
-Accrued compensation	(14)	(17)
-Over recovered regulatory clause revenues	10	(30)
-Other current liabilities	(11)	7
Net cash provided from operating activities	297	135
Investing Activities:
Property additions	(74)	(337)
Change in construction payables, net	(9)	(19)
Payments pursuant to LTSAs	(13)	3
Other investing activities	(12)	(8)
Net cash used for investing activities	(108)	(361)
Financing Activities:
Increase (decrease) in notes payable, net	(4)	(10)
Proceeds —
Senior notes	600	0
Short-term borrowings	300	4
Capital contributions from parent company	1	1,001
Long-term debt to parent company	0	(40)
Redemptions and repurchases —
Other long-term debt	(900)	(300)
Short-term borrowings	(200)	0
Long-term debt to parent company	0	(591)
Other financing activities	(6)	(2)
Net cash provided from financing activities	(209)	142
Net Change in Cash, Cash Equivalents, and Restricted Cash	(20)	(84)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	248	224
Cash, Cash Equivalents, and Restricted Cash at End of Period	228	140
Cash paid (received) during the period for —
Interest	39	26
Income taxes, net	(257)	(93)
Noncash transactions — Accrued property additions at end of period	23	59
SOUTHERN POWER CO
Operating Activities:
Net income (loss)	160	168
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	256	264
Deferred income taxes	(252)	91
Amortization of investment tax credits	(29)	(28)
Deferred revenues	(19)	(34)
Income taxes receivable, non-current	(4)	(58)
Asset impairment	119	0
Other, net	13	(1)
Changes in certain current assets and liabilities —
-Receivables	(30)	(58)
-Prepaid income taxes	(36)	33
-Other current assets	3	20
-Accounts payable	(41)	(45)
-Accrued taxes	15	4
-Other current liabilities	(28)	(8)
Net cash provided from operating activities	127	348
Investing Activities:
Business acquisitions, net of cash acquired	(64)	(1,004)
Property additions	(198)	(145)
Change in construction payables, net	2	(167)
Payments pursuant to LTSAs	(32)	(68)
Other investing activities	15	(3)
Net cash used for investing activities	(277)	(1,387)
Financing Activities:
Increase (decrease) in notes payable, net	(41)	189
Proceeds —
Short-term borrowings	200	0
Capital contributions from parent company	16	0
Redemptions and repurchases —
Return of paid in capital	(250)	0
Senior notes	(350)	0
Other long-term debt	(420)	(3)
Distributions to noncontrolling interests	(42)	(40)
Capital contributions from noncontrolling interests	1,210	73
Payment of common stock dividends	(156)	(158)
Other financing activities	(15)	(18)
Net cash provided from financing activities	152	43
Net Change in Cash, Cash Equivalents, and Restricted Cash	2	(996)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	140	1,112
Cash, Cash Equivalents, and Restricted Cash at End of Period	142	116
Cash paid (received) during the period for —
Interest	109	113
Income taxes, net	109	(117)
Noncash transactions — Accrued property additions at end of period	33	19
SOUTHERN Co GAS
Operating Activities:
Net income (loss)	248	288
Adjustments to reconcile consolidated net income (loss) to net cash provided from operating activities —
Depreciation and amortization, total	255	244
Deferred income taxes	(12)	144
Mark-to-market adjustments	2	(49)
Goodwill impairment	42	0
Loss on disposition	36	0
Other, net	(24)	(34)
Changes in certain current assets and liabilities —
-Receivables	504	418
-Natural gas for sale, net of temporary LIFO liquidation	295	223
-Prepaid income taxes	9	24
-Other current assets	32	(12)
-Accounts payable	(125)	(102)
-Accrued taxes	38	(8)
-Accrued compensation	(6)	(12)
-Other current liabilities	24	25
Net cash provided from operating activities	1,318	1,149
Investing Activities:
Property additions	(679)	(684)
Cost of removal, net of salvage	(18)	(25)
Change in construction payables, net	(6)	23
Investment in unconsolidated subsidiaries	(60)	(111)
Asset dispositions	364	0
Other investing activities	18	18
Net cash used for investing activities	(381)	(779)
Financing Activities:
Increase (decrease) in notes payable, net	(515)	(631)
Proceeds —
Senior notes	0	450
Capital contributions from parent company	10	57
Redemptions and repurchases —
Long-term debt	(200)	0
Payment of common stock dividends	(235)	(221)
Other financing activities	0	(6)
Net cash provided from financing activities	(940)	(351)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(3)	19
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	78	24
Cash, Cash Equivalents, and Restricted Cash at End of Period	75	43
Cash paid (received) during the period for —
Interest	129	105
Income taxes, net	106	20
Noncash transactions — Accrued property additions at end of period	$ 129	$ 84

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Net cash paid for capitalized interest	$ 35	$ 55
ALABAMA POWER CO
Net cash paid for capitalized interest	10	6
GEORGIA POWER CO
Net cash paid for capitalized interest	12	11
GULF POWER CO
Net cash paid for capitalized interest	0	0
MISSISSIPPI POWER CO
Interest paid	39	53
Net cash paid for capitalized interest	0	27
SOUTHERN POWER CO
Net cash paid for capitalized interest	10	4
SOUTHERN Co GAS
Net cash paid for capitalized interest	$ 3	$ 7

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 1,980	$ 2,130
Receivables —
Customer accounts receivable	1,728	1,806
Energy marketing receivables	451	607
Unbilled revenues	769	810
Under recovered fuel clause revenues	159	171
Other accounts and notes receivable	621	698
Accumulated provision for uncollectible accounts	(42)	(44)
Materials and supplies	1,397	1,438
Fossil fuel for generation	462	594
Natural gas for sale	292	595
Prepaid expenses	398	452
Other regulatory assets, current	528	604
Assets held for sale, current	2,704	12
Other current assets	172	199
Total current assets	11,619	10,072
Property, Plant, and Equipment:
In service	99,626	103,542
Less: Accumulated depreciation	30,255	31,457
Plant in service, net of depreciation	69,371	72,085
Nuclear fuel, at amortized cost	874	883
Construction work in progress	6,947	6,904
Total property, plant, and equipment	77,192	79,872
Other Property and Investments:
Goodwill	5,315	6,268
Equity investments in unconsolidated subsidiaries	1,546	1,513
Other intangible assets, net of amortization	702	873
Nuclear decommissioning trusts, at fair value	1,829	1,832
Leveraged leases	788	775
Miscellaneous property and investments	247	249
Total other property and investments	10,427	11,510
Deferred Charges and Other Assets:
Deferred charges related to income taxes	789	825
Unamortized loss on reacquired debt	333	206
Other regulatory assets, deferred	6,302	6,943
Assets held for sale	4,618	0
Other deferred charges and assets	1,497	1,577
Total deferred charges and other assets	13,539	9,551
Total Assets	112,777	111,005
Current Liabilities:
Securities due within one year	2,237	3,892
Notes payable	4,981	2,439
Energy marketing trade payables	485	546
Accounts payable —
Accounts payable	2,162	2,530
Customer deposits	488	542
Accrued taxes —
Accrued taxes	544	636
Accrued interest	469	488
Accrued compensation	646	959
Asset retirement obligations, current	332	351
Other regulatory liabilities, current	508	337
Liabilities held for sale, current	706	0
Other current liabilities	808	874
Total current liabilities	14,366	13,594
Long-term Debt	42,483	44,462
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	5,934	6,842
Deferred credits related to income taxes	6,647	7,256
Accumulated deferred ITCs	2,360	2,267
Employee benefit obligations	2,009	2,256
Asset retirement obligations, deferred	5,836	4,473
Accrued environmental remediation	273	389
Other cost of removal obligations	2,364	2,684
Other regulatory liabilities, deferred	140	239
Liabilities held for sale	2,833	0
Other deferred credits and liabilities	516	691
Total deferred credits and other liabilities	28,912	27,097
Total Liabilities	85,761	85,153
Redeemable Preferred Stock of Subsidiaries	324	324
Common Stockholders' Equity:
Common stock	5,066	5,038
Paid-in capital	10,303	10,469
Treasury, at cost	(39)	(36)
Retained earnings (accumulated deficit)	8,494	8,885
Accumulated other comprehensive income (loss)	(188)	(189)
Total Common Stockholders' Equity	23,636	24,167
Noncontrolling interests	3,056	1,361
Total stockholders' equity	26,692	25,528
Total Liabilities and Stockholders' Equity	112,777	111,005
ALABAMA POWER CO
Current Assets:
Cash and cash equivalents	686	544
Receivables —
Customer accounts receivable	401	355
Unbilled revenues	174	162
Under recovered fuel clause revenues	28	0
Other accounts and notes receivable	41	55
Affiliated	54	43
Accumulated provision for uncollectible accounts	(10)	(9)
Materials and supplies	518	458
Fossil fuel for generation	154	184
Prepaid expenses	90	85
Other regulatory assets, current	146	124
Other current assets	11	5
Total current assets	2,293	2,006
Property, Plant, and Equipment:
In service	29,374	27,326
Less: Accumulated depreciation	9,813	9,563
Plant in service, net of depreciation	19,561	17,763
Nuclear fuel, at amortized cost	337	339
Construction work in progress	1,172	908
Total property, plant, and equipment	21,070	19,010
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	66	67
Nuclear decommissioning trusts, at fair value	906	903
Miscellaneous property and investments	124	124
Total other property and investments	1,096	1,094
Deferred Charges and Other Assets:
Deferred charges related to income taxes	234	239
Deferred under recovered regulatory clause revenues	121	54
Other regulatory assets, deferred	1,244	1,272
Other deferred charges and assets	212	189
Total deferred charges and other assets	1,811	1,754
Total Assets	26,270	23,864
Current Liabilities:
Securities due within one year	200	0
Accounts payable —
Affiliated	298	327
Other	398	585
Customer deposits	95	92
Accrued taxes —
Accrued taxes	137	54
Accrued interest	81	77
Accrued compensation	140	205
Other regulatory liabilities, current	118	1
Other current liabilities	143	59
Total current liabilities	1,610	1,400
Long-term Debt	7,922	7,628
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,829	2,760
Deferred credits related to income taxes	2,061	2,082
Accumulated deferred ITCs	109	112
Employee benefit obligations	275	304
Asset retirement obligations, deferred	3,085	1,702
Other cost of removal obligations	580	609
Other regulatory liabilities, deferred	43	84
Other deferred credits and liabilities	64	63
Total deferred credits and other liabilities	9,046	7,716
Total Liabilities	18,578	16,744
Redeemable Preferred Stock	291	291
Common Stockholders' Equity:
Common stock	1,222	1,222
Paid-in capital	3,480	2,986
Retained earnings (accumulated deficit)	2,729	2,647
Accumulated other comprehensive income (loss)	(30)	(26)
Total Common Stockholders' Equity	7,401	6,829
Total Liabilities and Stockholders' Equity	26,270	23,864
GEORGIA POWER CO
Current Assets:
Cash and cash equivalents	11	852
Receivables —
Customer accounts receivable	631	544
Unbilled revenues	276	255
Under recovered fuel clause revenues	159	165
Joint owner accounts receivable	239	262
Other accounts and notes receivable	81	76
Affiliated	25	24
Accumulated provision for uncollectible accounts	(3)	(3)
Materials and supplies	498	504
Fossil fuel for generation	276	314
Prepaid expenses	91	216
Other regulatory assets, current	206	205
Other current assets	23	14
Total current assets	2,513	3,428
Property, Plant, and Equipment:
In service	35,467	34,861
Less: Accumulated depreciation	11,901	11,704
Plant in service, net of depreciation	23,566	23,157
Nuclear fuel, at amortized cost	536	544
Construction work in progress	4,157	4,613
Total property, plant, and equipment	28,259	28,314
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	52	53
Nuclear decommissioning trusts, at fair value	924	929
Miscellaneous property and investments	61	59
Total other property and investments	1,037	1,041
Deferred Charges and Other Assets:
Deferred charges related to income taxes	518	516
Other regulatory assets, deferred	3,064	2,932
Other deferred charges and assets	570	548
Total deferred charges and other assets	4,152	3,996
Total Assets	35,961	36,779
Current Liabilities:
Securities due within one year	509	857
Notes payable	480	150
Accounts payable —
Affiliated	458	493
Other	885	834
Customer deposits	275	270
Accrued taxes —
Accrued taxes	230	344
Accrued interest	110	123
Accrued compensation	149	219
Asset retirement obligations, current	191	270
Other regulatory liabilities, current	214	191
Other current liabilities	205	198
Total current liabilities	3,706	3,949
Long-term Debt	9,936	11,073
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,925	3,175
Deferred credits related to income taxes	3,218	3,248
Accumulated deferred ITCs	267	248
Employee benefit obligations	636	659
Asset retirement obligations, deferred	2,427	2,368
Other deferred credits and liabilities	144	128
Total deferred credits and other liabilities	9,617	9,826
Total Liabilities	23,259	24,848
Common Stockholders' Equity:
Common stock	398	398
Paid-in capital	8,834	7,328
Retained earnings (accumulated deficit)	3,480	4,215
Accumulated other comprehensive income (loss)	(10)	(10)
Total Common Stockholders' Equity	12,702	11,931
Total Liabilities and Stockholders' Equity	35,961	36,779
GULF POWER CO
Current Assets:
Cash and cash equivalents	31	28
Receivables —
Customer accounts receivable	87	76
Unbilled revenues	71	67
Under recovered fuel clause revenues	3	27
Other accounts and notes receivable	5	7
Affiliated	15	14
Accumulated provision for uncollectible accounts	(1)	(1)
Materials and supplies	61	57
Fossil fuel for generation	63	63
Other regulatory assets, current	49	56
Other current assets	19	21
Total current assets	403	415
Property, Plant, and Equipment:
In service	5,293	5,196
Less: Accumulated depreciation	1,523	1,461
Plant in service, net of depreciation	3,770	3,735
Construction work in progress	116	91
Total property, plant, and equipment	3,886	3,826
Deferred Charges and Other Assets:
Deferred charges related to income taxes	30	31
Other regulatory assets, deferred	486	502
Other deferred charges and assets	36	23
Total deferred charges and other assets	552	556
Total Assets	4,841	4,797
Current Liabilities:
Notes payable	90	45
Accounts payable —
Affiliated	51	52
Other	57	75
Customer deposits	35	35
Accrued taxes —
Accrued taxes	28	10
Accrued interest	8	9
Accrued compensation	24	39
Deferred capacity expense, current	22	22
Asset retirement obligations, current	39	37
Other regulatory liabilities, current	54	0
Other current liabilities	24	27
Total current liabilities	432	351
Long-term Debt	1,285	1,285
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	540	537
Deferred credits related to income taxes	384	458
Employee benefit obligations	98	102
Deferred capacity expense	86	97
Asset retirement obligations, deferred	109	105
Other cost of removal obligations	216	221
Other regulatory liabilities, deferred	52	43
Other deferred credits and liabilities	64	67
Total deferred credits and other liabilities	1,549	1,630
Total Liabilities	3,266	3,266
Common Stockholders' Equity:
Common stock	678	678
Paid-in capital	632	594
Retained earnings (accumulated deficit)	266	259
Accumulated other comprehensive income (loss)	(1)	0
Total Common Stockholders' Equity	1,575	1,531
Total Liabilities and Stockholders' Equity	4,841	4,797
MISSISSIPPI POWER CO
Current Assets:
Cash and cash equivalents	228	248
Receivables —
Customer accounts receivable	37	36
Unbilled revenues	42	41
Income taxes receivable, current	37	4
Other accounts and notes receivable	24	12
Affiliated	21	16
Materials and supplies	50	44
Fossil fuel for generation	19	17
Other regulatory assets, current	121	125
Other current assets	9	9
Total current assets	588	552
Property, Plant, and Equipment:
In service	4,816	4,773
Less: Accumulated depreciation	1,365	1,325
Plant in service, net of depreciation	3,451	3,448
Construction work in progress	88	84
Total property, plant, and equipment	3,539	3,532
Other Property and Investments:
Total other property and investments	25	30
Deferred Charges and Other Assets:
Deferred charges related to income taxes	34	35
Other regulatory assets, deferred	448	437
Accumulated deferred income taxes	0	247
Other deferred charges and assets	19	33
Total deferred charges and other assets	501	752
Total Assets	4,653	4,866
Current Liabilities:
Securities due within one year	257	989
Notes payable	100	4
Accounts payable —
Affiliated	53	59
Other	62	96
Accrued taxes —
Accrued income taxes	0	40
Accrued taxes	51	101
Accrued compensation	25	39
Accrued plant closure costs	42	35
Asset retirement obligations, current	41	37
Other current liabilities	74	63
Total current liabilities	705	1,463
Long-term Debt	1,522	1,097
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	60	0
Deferred credits related to income taxes	415	372
Employee benefit obligations	112	116
Asset retirement obligations, deferred	135	137
Other cost of removal obligations	179	178
Other regulatory liabilities, deferred	78	79
Other deferred credits and liabilities	16	33
Total deferred credits and other liabilities	995	915
Total Liabilities	3,222	3,475
Redeemable Preferred Stock	33	33
Common Stockholders' Equity:
Common stock	38	38
Paid-in capital	4,531	4,529
Retained earnings (accumulated deficit)	(3,166)	(3,205)
Accumulated other comprehensive income (loss)	(5)	(4)
Total Common Stockholders' Equity	1,398	1,358
Total Liabilities and Stockholders' Equity	4,653	4,866
SOUTHERN POWER CO
Current Assets:
Cash and cash equivalents	142	129
Receivables —
Customer accounts receivable	165	117
Other accounts and notes receivable	63	98
Affiliated	60	50
Materials and supplies	213	278
Prepaid income taxes	82	50
Assets held for sale, current	17	1
Other current assets	31	35
Total current assets	773	758
Property, Plant, and Equipment:
In service	13,402	13,755
Less: Accumulated depreciation	1,959	1,910
Plant in service, net of depreciation	11,443	11,845
Construction work in progress	771	511
Total property, plant, and equipment	12,214	12,356
Other Property and Investments:
Intangible assets, net (including goodwill)	398	411
Total other property and investments	398	411
Deferred Charges and Other Assets:
Prepaid LTSAs	93	118
Accumulated deferred income taxes	1,223	925
Income taxes receivable, non-current	81	72
Assets held for sale	183	0
Other deferred charges and assets	463	566
Total deferred charges and other assets	2,043	1,681
Total Assets	15,428	15,206
Current Liabilities:
Securities due within one year	0	770
Notes payable	264	105
Accounts payable —
Affiliated	75	102
Other	84	103
Accrued taxes —
Liabilities held for sale, current	2	0
Other current liabilities	146	152
Total current liabilities	571	1,232
Long-term Debt	5,037	5,071
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	135	199
Accumulated deferred ITCs	1,856	1,884
Other deferred credits and liabilities	255	322
Total deferred credits and other liabilities	2,246	2,405
Total Liabilities	7,854	8,708
Common Stockholders' Equity:
Common stock	0	0
Paid-in capital	3,023	3,662
Retained earnings (accumulated deficit)	1,464	1,478
Accumulated other comprehensive income (loss)	31	(2)
Total Common Stockholders' Equity	4,518	5,138
Noncontrolling interests	3,056	1,360
Total stockholders' equity	7,574	6,498
Total Liabilities and Stockholders' Equity	15,428	15,206
SOUTHERN Co GAS
Current Assets:
Cash and cash equivalents	69	73
Receivables —
Customer accounts receivable	243	400
Energy marketing receivables	451	607
Unbilled revenues	60	285
Other accounts and notes receivable	53	103
Accumulated provision for uncollectible accounts	(26)	(28)
Natural gas for sale	292	595
Prepaid expenses	64	53
Assets from risk management activities, net of collateral	93	135
Other regulatory assets, current	55	94
Assets held for sale, current	2,298	0
Other current assets	42	78
Total current assets	3,694	2,395
Property, Plant, and Equipment:
In service	14,504	15,833
Less: Accumulated depreciation	4,293	4,596
Plant in service, net of depreciation	10,211	11,237
Construction work in progress	571	491
Total property, plant, and equipment	10,782	11,728
Other Property and Investments:
Goodwill	5,015	5,967
Equity investments in unconsolidated subsidiaries	1,507	1,477
Other intangible assets, net of amortization	125	280
Miscellaneous property and investments	20	21
Total other property and investments	6,667	7,745
Deferred Charges and Other Assets:
Other regulatory assets, deferred	742	901
Other deferred charges and assets	227	218
Total deferred charges and other assets	969	1,119
Total Assets	22,112	22,987
Current Liabilities:
Securities due within one year	156	157
Notes payable	1,003	1,518
Energy marketing trade payables	485	546
Accounts payable —
Accounts payable	359	446
Customer deposits	101	128
Accrued taxes —
Accrued income taxes	86	40
Accrued taxes	63	78
Accrued interest	53	51
Accrued compensation	61	74
Liabilities from risk management activities, net of collateral	21	69
Other regulatory liabilities, current	162	135
Liabilities held for sale, current	412	0
Other current liabilities	143	159
Total current liabilities	3,105	3,401
Long-term Debt	5,667	5,891
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,026	1,089
Deferred credits related to income taxes	920	1,063
Employee benefit obligations	389	415
Accrued environmental remediation	273	342
Other cost of removal obligations	1,575	1,646
Other deferred credits and liabilities	96	118
Total deferred credits and other liabilities	4,279	4,673
Total Liabilities	13,051	13,965
Common Stockholders' Equity:
Common stock	0	0
Paid-in capital	9,236	9,214
Retained earnings (accumulated deficit)	(202)	(212)
Accumulated other comprehensive income (loss)	27	20
Total Common Stockholders' Equity	9,061	9,022
Total Liabilities and Stockholders' Equity	$ 22,112	$ 22,987

Condensed Consolidated Balance9

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Other intangible assets, accumulated amortization	$ 205	$ 186
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)	1,000,000,000	1,000,000,000
Treasury shares at cost (in shares)	1,000,000	900,000
ALABAMA POWER CO
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 CO
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 CO
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	7,392,717	7,392,717
MISSISSIPPI POWER CO
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 CO
Other intangible assets, accumulated amortization	$ 60	$ 47
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 Co GAS
Other intangible assets, accumulated amortization	$ 121	$ 120
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	6 Months Ended
	Jun. 30, 2018
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, 2017 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 June 30, 2018 and 2017 . 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. 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 Adopted Accounting Standards See Note 1 to the financial statements of the registrants under "Recently Issued Accounting Standards" in Item 8 of the Form 10-K for additional information. Revenue In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers (ASC 606), 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. ASC 606 became effective on January 1, 2018 and the registrants adopted it using the modified retrospective method applied to open contracts and only to the version of the contracts in effect as of January 1, 2018. In accordance with the modified retrospective method, the registrants' previously issued financial statements have not been restated to comply with ASC 606 and the registrants did not have a cumulative-effect adjustment to retained earnings. The adoption of ASC 606 had no significant impact on the timing of revenue recognition compared to previously reported results; however, it requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers, which are included in Note (C). ASC 606 provided additional clarity on financial statement presentation that resulted in reclassifications into other revenues and other operations and maintenance from other income/(expense), net at Alabama Power and Georgia Power related to certain unregulated sales of products and services. In addition, contract assets related to Southern Company's unregulated distributed generation business have been reclassified from unbilled revenue in accordance with the guidance in ASC 606. These reclassifications did not affect the timing or amount of revenues recognized or cash flows. ASC 606 also provided additional guidance on over-time revenue recognition, resulting in a change in the timing of revenue recognized from guaranteed and fixed billing arrangements at Southern Company Gas. The changes in natural gas revenues recognized in the second quarter and year-to-date 2018 relate primarily to the seasonal nature of natural gas usage. The net impact of accounting for revenue under ASC 606 decreased Southern Company's consolidated net income by $5 million for the three months ended June 30, 2018 and increased Southern Company's consolidated net income by $5 million for the six months ended June 30, 2018 . The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Three Months Ended For the Six Months Ended Condensed Statements of Income As Reported Balances Without Adoption of Effect of Change As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) (in millions) Southern Company Natural gas revenues $ 706 $ 713 $ (7 ) $ 2,314 $ 2,307 $ 7 Other revenues 395 393 2 808 805 3 Other operations and maintenance 1,559 1,546 13 3,008 2,985 23 Operating income 63 81 (18 ) 1,439 1,452 (13 ) Other income (expense), net 78 67 11 138 118 20 Earnings (loss) before income taxes (266 ) (259 ) (7 ) 784 777 7 Income taxes (benefit) (139 ) (137 ) (2 ) (25 ) (27 ) 2 Consolidated net income (loss) (127 ) (122 ) (5 ) 809 804 5 Consolidated net income (loss) attributable to Southern Company (154 ) (149 ) (5 ) 784 779 5 Alabama Power Other revenues $ 69 $ 60 $ 9 $ 131 $ 114 $ 17 Other operations and maintenance 402 391 11 788 767 21 Operating income 380 382 (2 ) 752 756 (4 ) Other income (expense), net 12 10 2 15 11 4 Georgia Power Other revenues $ 120 $ 97 $ 23 $ 227 $ 189 $ 38 Other operations and maintenance 457 437 20 863 828 35 Operating income (loss) (472 ) (475 ) 3 41 38 3 Other income (expense), net 35 38 (3 ) 73 76 (3 ) Southern Company Gas Natural gas revenues $ 710 $ 717 $ (7 ) $ 2,341 $ 2,334 $ 7 Operating income 49 56 (7 ) 436 429 7 Earnings before income taxes 24 31 (7 ) 407 400 7 Income taxes 55 57 (2 ) 159 157 2 Net income (loss) (31 ) (26 ) (5 ) 248 243 5 For the Six Months Ended Condensed Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 809 $ 804 $ 5 Changes in certain current assets and liabilities: Receivables 94 99 (5 ) Other current assets (40 ) (45 ) 5 Accrued taxes 213 215 (2 ) Other current liabilities 125 118 7 Georgia Power Changes in certain current assets and liabilities: Receivables $ (103 ) $ (75 ) $ (28 ) Other current assets 25 (3 ) 28 Southern Company Gas Net income $ 248 $ 243 $ 5 Changes in certain current assets and liabilities: Accrued taxes 38 40 (2 ) Other current liabilities 24 17 7 At June 30, 2018 Condensed Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 769 $ 824 $ (55 ) Other accounts and notes receivable 621 622 (1 ) Other current assets 172 116 56 Accrued taxes 544 542 2 Other current liabilities 808 815 (7 ) Retained earnings 8,494 8,489 5 Southern Company Gas Accrued income taxes $ 86 $ 84 $ 2 Other current liabilities 143 150 (7 ) Accumulated deficit (202 ) (207 ) 5 Other In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18). ASU 2016-18 eliminates the need to reflect transfers between cash and restricted cash in operating, investing, and financing activities in the statements of cash flows. In addition, the net change in cash and cash equivalents during the period includes amounts generally described as restricted cash or restricted cash equivalents. The registrants adopted ASU 2016-18 effective January 1, 2018 with no material impact on their financial statements. Southern Company, Southern Power, and Southern Company Gas retrospectively applied ASU 2016-18 effective January 1, 2018 and have restated prior periods in the statements of cash flows by immaterial amounts. The change in restricted cash in the statements of cash flows was previously disclosed in operating activities for Southern Company and Southern Company Gas and in investing activities for Southern Company and Southern Power. See " Restricted Cash " herein for additional information. In March 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 statements of income outside of income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. The registrants adopted ASU 2017-07 effective January 1, 2018 with no material impact on their financial statements. ASU 2017-07 has been applied retrospectively for the presentation of the service cost component and the other components of net periodic benefit costs in the statements of income for Southern Company, the traditional electric operating companies, and Southern Company Gas. Since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017, no retrospective presentation of Southern Power's net periodic benefits costs is required. The requirement to limit capitalization to the service cost component of net periodic benefit costs has been applied on a prospective basis from the date of adoption for all registrants. The presentation changes resulted in a decrease in operating income and an increase in other income for the three and six months ended June 30, 2018 and 2017 for Southern Company, the traditional electric operating companies, and Southern Company Gas. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12). ASU 2017-12 makes more financial and non-financial hedging strategies eligible for hedge accounting, amends the related presentation and disclosure requirements, and simplifies hedge effectiveness assessment requirements. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The registrants adopted ASU 2017-12 effective January 1, 2018 with no material impact on their financial statements. See Note (I) for disclosures required by ASU 2017-12. On February 14, 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (ASU 2018-02) to address the application of ASC 740, Income Taxes (ASC 740) to certain provisions of the Tax Reform Legislation. ASU 2018-02 specifically addresses the ASC 740 requirement that the effect of a change in tax laws or rates on deferred tax assets and liabilities be included in income from continuing operations, even when the tax effects were initially recognized directly in OCI at the previous rate, which strands the income tax rate differential in accumulated OCI. The amendments in ASU 2018-02 allow a reclassification from accumulated OCI to retained earnings for stranded tax effects resulting from the Tax Reform Legislation. The registrants adopted ASU 2018-02 effective January 1, 2018 with no material impact on their financial statements. Asset Retirement Obligations See Note 1 to the financial statements of Southern Company and the traditional electric operating companies under "Asset Retirement Obligations and Other Costs of Removal" in Item 8 of the Form 10-K for additional information regarding each company's AROs and the EPA's Disposal of Coal Combustion Residuals from Electric Utilities final rule (CCR Rule). As of June 30, 2018 , details of the AROs, including those related to the CCR Rule, included in the condensed balance sheets of Southern Company, Alabama Power, and Mississippi Power were as follows: Southern Company Alabama Power Mississippi Power (in millions) Balance at December 31, 2017 $ 4,824 $ 1,709 $ 174 Liabilities incurred 1 — — Liabilities settled (97 ) (19 ) (15 ) Accretion 95 41 2 Cash flow revisions 1,493 1,451 15 Reclassification to held for sale (148 ) — — Balance at June 30, 2018 $ 6,168 $ 3,182 $ 176 In June 2018, Alabama Power recorded an increase of approximately $1.2 billion to its AROs related to the CCR Rule. The revised cost estimates as of June 30, 2018 are based on information from feasibility studies performed on ash ponds in use at plants operated by Alabama Power, including a plant jointly-owned by Mississippi Power. During the second quarter 2018, Alabama Power's management completed its analysis of these studies which indicated that additional closure costs, primarily related to increases in estimated ash volume, water management requirements, and design revisions, will be required to close these ash ponds under the planned closure-in-place methodology. As a result of these revised cost estimates, in June 2018, Mississippi Power recorded an increase of approximately $11 million to its AROs related to an ash pond at the plant jointly-owned with Alabama Power. Georgia Power continues to perform engineering studies related to its plans to close the ash ponds at all of its generating plants, including one jointly owned with Gulf Power, in compliance with federal and state CCR rules. Georgia Power also continues to refine its closure strategy and cost estimates for each ash pond and is preparing permit applications as required by the State of Georgia CCR rule. While each of Georgia Power and Gulf Power believes its recorded liability for ash pond closures appropriately reflects its obligations under the current closure strategies it has elected, changes to such strategies and cost estimates would likely result in additional closure costs which would increase each of Georgia Power's and Gulf Power's ARO liability. It is not currently possible to determine the magnitude of an increase related to a change in closure strategies nor an increase related to ongoing engineering studies for the current closure strategies, and the timing of future cash outflows are indeterminable at this time. As permit applications advance, engineering studies continue, and the timing of ash pond closures develop further on a plant-by-plant basis during the second half of 2018 and in the future, Georgia Power will record any changes as necessary to its ARO liability, which could be material. Georgia Power expects to continue to periodically update these cost estimates as necessary, which could change further as additional information becomes available. Gulf Power will record any incremental AROs, which could be material, related to its share of Plant Scherer Unit 3, which is co-owned with Georgia Power, once Georgia Power further refines its cost estimate of the impact on its ARO liability. As further analysis is performed and closure details are developed with respect to ash pond closures, the traditional electric operating companies expect to periodically update their cost estimates as necessary. Absent continued recovery of ARO costs through regulated rates, Southern Company's and the traditional electric operating companies' results of operations, cash flows, and financial condition could be materially impacted. The ultimate outcome of this matter cannot be determined at this time. In June 2018, Alabama Power completed an updated decommissioning cost site study for Plant Farley. The estimated cost of decommissioning based on the study resulted in an increase in Southern Company's and Alabama Power's ARO liability of approximately $300 million . See " Nuclear Decommissioning " below for additional information. The reclassification of a portion of the ARO liability to liabilities held for sale by Southern Company represents the AROs related to Gulf Power. See Note (J) under " Southern Company's Sale of Gulf Power " and " Assets Held for Sale " for additional information. Nuclear Decommissioning See Note 1 to the financial statements of Southern Company and Alabama Power under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. In June 2018, Alabama Power completed an updated decommissioning cost site study for Plant Farley. The estimated costs of decommissioning based on the 2018 site study are as follows: Decommissioning periods: Beginning year 2037 Completion year 2076 (in millions) Site study costs: Radiated structures $ 1,621 Non-radiated structures 99 Total site study costs $ 1,720 The decommissioning cost estimates are based on prompt dismantlement and removal of the plant from service. The actual decommissioning costs may vary from the above estimates because of changes in the assumed date of decommissioning, changes in NRC requirements, or changes in the assumptions used in making these estimates. For ratemaking purposes, Alabama Power's decommissioning costs are based on the site study. Significant assumptions used to determine these costs for ratemaking were an inflation rate of 4.5% and a trust earnings rate of 7.0% . The next site study is expected to be completed in 2023 . Amounts previously contributed to the external trust funds are currently projected to be adequate to meet the updated decommissioning obligations. Alabama Power will continue to provide site specific estimates of the decommissioning costs and related projections of funds in the external trust to the Alabama PSC and, if necessary, would seek the Alabama PSC's approval to address any changes in a manner consistent with the NRC and other applicable requirements. Goodwill and Other Intangible Assets The following table presents year-to-date changes in goodwill balances for Southern Company and Southern Company Gas: Goodwill Southern Company Southern Company Gas Gas Distribution Operations Gas Marketing Services Total (in millions) Balance at December 31, 2017 $ 6,268 $ 4,702 $ 1,265 $ 5,967 Impairment (a) (42 ) — (42 ) (42 ) Sale of Pivotal Home Solutions (a) (242 ) — (242 ) (242 ) Reclassification to held for sale (b) (668 ) (668 ) — (668 ) Balance at June 30, 2018 $ 5,315 (c) $ 4,034 $ 981 $ 5,015 (a) On April 11, 2018, Southern Company Gas entered into a stock purchase agreement for the sale of Pivotal Home Solutions. In contemplation of the transaction, a goodwill impairment charge of $42 million was recorded in the first quarter 2018. On June 4, 2018, Southern Company Gas and Pivotal Home Solutions completed this transaction. See Note (J) under " Southern Company Gas " for additional information. (b) Reflects goodwill associated with Elizabethtown Gas, Elkton Gas, and Florida City Gas, which were sold subsequent to June 30, 2018. See Note (J) under " Southern Company Gas " and " Assets Held for Sale " for additional information. (c) Total does not add due to rounding. 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: At June 30, 2018 At December 31, 2017 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 (*) $ 223 $ (79 ) $ 144 $ 288 $ (83 ) $ 205 Trade names (*) 70 (17 ) 53 159 (17 ) 142 Storage and transportation contracts 64 (44 ) 20 64 (34 ) 30 PPA fair value adjustments 456 (60 ) 396 456 (47 ) 409 Other 19 (5 ) 14 17 (5 ) 12 Total other intangible assets subject to amortization $ 832 $ (205 ) $ 627 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 907 $ (205 ) $ 702 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (60 ) $ 396 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services (*) Customer relationships $ 156 $ (71 ) $ 85 $ 221 $ (77 ) $ 144 Trade names 26 (6 ) 20 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (44 ) 20 64 (34 ) 30 Total other intangible assets subject to amortization $ 246 $ (121 ) $ 125 $ 400 $ (120 ) $ 280 (*) Balances as of June 30, 2018 reflect Southern Company Gas' sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. Amortization associated with other intangible assets was as follows: Three Months Ended Six Months Ended June 30, 2018 (in millions) Southern Company $ 23 $ 50 Southern Power $ 6 $ 13 Southern Company Gas $ 14 $ 31 Restricted Cash The registrants adopted ASU 2016-18 as of January 1, 2018. See " Recently Adopted Accounting Standards – Other " herein for additional information. At December 31, 2017 , Southern Power had restricted cash primarily related to certain acquisitions and construction projects. At both June 30, 2018 and December 31, 2017 , Southern Company Gas had restricted cash held as collateral for worker's compensation, life insurance, and long-term disability insurance. The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at June 30, 2018 and/or December 31, 2017 : Southern Company Southern Company Gas (in millions) At June 30, 2018 Cash and cash equivalents $ 1,980 $ 69 Cash and cash equivalents classified as assets held for sale 31 — Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,017 $ 75 Southern Company Southern Power Southern Company Gas (in millions) At December 31, 2017 Cash and cash equivalents $ 2,130 $ 129 $ 73 Restricted cash: Other accounts and notes receivable 5 — 5 Deferred charges and other assets 12 11 — Total cash, cash equivalents, and restricted cash $ 2,147 $ 140 $ 78 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 June 30, 2018 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 had no material LOCOM adjustment in any period presented. Hypothetical Liquidation at Book Value Southern Power has consolidated renewable generation projects that are partially funded by a third-party tax equity investor. The related contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. Therefore, the noncontrolling interest is accounted for under a balance sheet approach utilizing the hypothetical liquidation at book value (HLBV) method. The HLBV method calculates each partner's share of income based on the change in net equity the partner can legally claim in a hypothetical liquidation at the end of the period compared to the beginning of the period.

Contingencies and Regulatory Ma

Contingencies and Regulatory Matters	6 Months Ended
	Jun. 30, 2018
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 laws and regulations governing air, water, land, and protection of natural resources. Litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental laws and regulations 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 In January 2017, a putative securities class action complaint was filed against Southern Company, certain of its officers, and certain former Mississippi Power 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 former Mississippi Power officers made materially false and misleading statements regarding the Kemper County energy facility 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. In June 2017, the plaintiffs filed an amended complaint that provided additional detail about their claims, increased the purported class period by one day, and added certain other former Mississippi Power officers as defendants. In July 2017, the defendants filed a motion to dismiss the plaintiffs' amended complaint with prejudice, to which the plaintiffs filed an opposition in September 2017. On March 29, 2018, the U.S. District Court for the Northern District of Georgia, Atlanta Division, issued an order granting, in part, the defendants' motion to dismiss. The court dismissed certain claims against certain officers of Southern Company and Mississippi Power and dismissed the allegations related to a number of the statements that plaintiffs challenged as being false or misleading. On April 26, 2018, the defendants filed a motion for reconsideration of the court's order, seeking dismissal of the remaining claims in the lawsuit. In February 2017, Jean Vineyard filed a shareholder derivative lawsuit and, in May 2017, Judy Mesirov filed a shareholder derivative lawsuit, each in the U.S. District Court for the Northern District of Georgia. Each of these lawsuits names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. In August 2017, these two shareholder derivative lawsuits were consolidated in the U.S. District Court for the Northern District of Georgia. The complaints allege that the defendants caused Southern Company to make false or misleading statements regarding the Kemper County energy facility cost and schedule. Further, the complaints allege that the defendants were unjustly enriched and caused the waste of corporate assets and also allege that the individual defendants violated their fiduciary duties. Each plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and, on each plaintiff's own behalf, attorneys' fees and costs in bringing the lawsuit. Each plaintiff also seeks certain changes to Southern Company's corporate governance and internal processes. On April 25, 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the putative securities class action. In May 2017, Helen E. Piper Survivor's Trust filed a shareholder derivative lawsuit in the Superior Court of Gwinnett County, State of Georgia that names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. The complaint alleges that the individual defendants, among other things, breached their fiduciary duties in connection with schedule delays and cost overruns associated with the construction of the Kemper County energy facility. The complaint further alleges that the individual defendants authorized or failed to correct false and misleading statements regarding the Kemper County energy facility schedule and cost and failed to implement necessary internal controls to prevent harm to Southern Company. The plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and disgorgement of profits and, on its behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiff also seeks certain unspecified changes to Southern Company's corporate governance and internal processes. The court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the putative securities class action. Southern Company believes these legal challenges have no merit; however, an adverse outcome in any of these proceedings could have an impact on Southern Company's results of operations, financial condition, and liquidity. Southern Company will vigorously defend itself in these matters, the ultimate outcome of which cannot be determined at this time. Alabama Power On March 2, 2018, the Alabama Department of Environmental Management (ADEM) issued proposed administrative orders assessing a penalty of $1.25 million to Alabama Power for unpermitted discharge of fluids and/or pollutants to groundwater at five electric generating plants. The proposed orders also require the submission to the ADEM of a plan with a schedule for implementation of a comprehensive groundwater investigation, including an assessment of corrective measures, a report evaluating any deficiencies at the facilities that may have led to the unpermitted discharges, and quarterly progress reports. Alabama Power is awaiting finalization of the orders. 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 2016, the Georgia Court of Appeals reversed the trial court's previous dismissal of the case and remanded the case to the trial court. Georgia Power filed a petition for writ of certiorari with the Georgia Supreme Court, which was granted in August 2017. On June 18, 2018, the Georgia Supreme Court affirmed the judgment of the Georgia Court of Appeals and the case has been remanded to the trial court for further proceedings. Georgia Power believes the plaintiffs' claims have no merit and intends to vigorously defend itself in this matter. The amount of any possible losses cannot be calculated at this time because, among other factors, it is unknown whether any class will ultimately be certified; the scope of such a class, if certified; and whether any losses would be subject to recovery from any municipalities. The ultimate outcome of this matter cannot be determined at this time. Mississippi Power In 2016, a complaint against Mississippi Power was filed in Harrison County Circuit Court (Circuit Court) by Biloxi Freezing & Processing Inc., Gulfside Casino Partnership, and John Carlton Dean, which was amended and refiled to include, among other things, Southern Company as a defendant. The individual plaintiff alleged that Mississippi Power and Southern Company violated the Mississippi Unfair Trade Practices Act. All plaintiffs alleged that Mississippi Power and Southern Company concealed, falsely represented, and failed to fully disclose important facts concerning the cost and schedule of the Kemper County energy facility and that these alleged breaches unjustly enriched Mississippi Power and Southern Company. The plaintiffs sought unspecified actual damages and punitive damages; asked the Circuit Court to appoint a receiver to oversee, operate, manage, and otherwise control all affairs relating to the Kemper County energy facility; asked the Circuit Court to revoke any licenses or certificates authorizing Mississippi Power or Southern Company to engage in any business related to the Kemper County energy facility in Mississippi; and sought attorney's fees, costs, and interest. The plaintiffs also sought an injunction to prevent any Kemper County energy facility costs from being charged to customers through electric rates. In June 2017, the Circuit Court ruled in favor of motions by Southern Company and Mississippi Power and dismissed the case. In July 2017, the plaintiffs filed notice of an appeal. On July 13, 2018, Mississippi Power and Southern Company reached a settlement agreement with the plaintiffs and the plaintiffs' appeal was dismissed with prejudice. The settlement had no material impact on Southern Company's or Mississippi Power's financial statements. On May 18, 2018, Southern Company and Mississippi Power received a notice of dispute and arbitration demand filed by Martin Product Sales, LLC (Martin) based on two agreements, both related to Kemper IGCC byproducts for which Mississippi Power provided termination notices in September 2017. Martin alleges breach of contract, breach of good faith and fair dealing, fraud and misrepresentation, and civil conspiracy and makes a claim for damages in the amount of approximately $143 million , as well as additional unspecified damages, attorney's fees, costs, and interest. Southern Company and Mississippi Power believe this legal challenge has no merit; however, an adverse outcome in this proceeding could have a material impact on Southern Company's and Mississippi Power's results of operations, financial condition, and liquidity. Southern Company and Mississippi Power will vigorously defend themselves in this matter, the ultimate outcome of which cannot be determined at this time. On May 14, 2018, Mississippi Power's claim for lost revenue resulting from the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 was settled. The settlement proceeds of $18 million , net of expenses and income tax, are included in Southern Company's and Mississippi Power's earnings for the second quarter 2018. Southern Power Southern Power indirectly owns a 51% membership interest in RE Roserock LLC (Roserock), the owner of the Roserock facility in Pecos County, Texas. Prior to the facility being placed in service in November 2016, certain solar panels were damaged during installation by the construction contractor, McCarthy Building Companies, Inc. (McCarthy), and certain solar panels were damaged by a hail event that also occurred during construction. In May 2017, Roserock filed a lawsuit in the state district court in Pecos County, Texas, (State Court lawsuit) against XL Insurance America, Inc. (XL) and North American Elite Insurance Company (North American Elite) seeking recovery from an insurance policy for damages resulting from the hail storm and McCarthy's installation practices. On June 1, 2018, the court in the State Court lawsuit granted Roserock's motion for partial summary judgment, finding that the insurers were in breach of contract and in violation of the Texas Insurance Code for failing to pay any monies owed for the hail claim. Roserock is working to distinguish its damages between those attributable to the hail event versus damages attributable to installation. In addition to the State Court lawsuit, lawsuits were filed between Roserock and McCarthy, as well as other parties, and that litigation has been consolidated in the U.S. District Court for the Western District of Texas. Southern Power intends to vigorously pursue and defend these matters, the ultimate outcome of which cannot be determined at this time. Southern Company Gas Nicor Energy Services Company, doing business as Pivotal Home Solutions, formerly a wholly-owned subsidiary of Southern Company Gas, was a defendant in a putative class action initially filed in 2017 in the state court in Indiana. The plaintiffs purported to represent a class of the customers who purchased products from Nicor Energy Services Company and alleged that the marketing, sale, and billing of the products violated the Indiana Consumer Fraud and Deceptive Business Practices Act, constituting common law fraud and resulting in unjust enrichment of these entities. In 2018, Nicor Energy Services Company was named in a second class action filed in the state court of Ohio asserting nearly identical allegations and legal claims. The plaintiffs sought, on behalf of the classes they purported to represent, actual and punitive damages, interest costs, attorney fees, and injunctive relief. To facilitate the sale of Pivotal Home Solutions, Southern Company Gas retained most of the financial responsibility for these lawsuits following the completion of the sale. On June 12, 2018, the parties settled these claims and Southern Company Gas recorded an $11 million charge, which is reflected in other operations and maintenance expenses on the statements of income. Environmental Matters Environmental Remediation The Southern Company system must comply with environmental laws and regulations governing 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 all 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 was $25 million and $22 million as of June 30, 2018 and December 31, 2017 , respectively. 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 $48 million and $52 million as of June 30, 2018 and December 31, 2017 , respectively. 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. At June 30, 2018 , Southern Company Gas' environmental remediation liability was $305 million based on the estimated cost of environmental investigation and remediation associated with known current and former manufactured gas plant operating sites, with an additional $77 million liability related to Elizabethtown Gas classified as held for sale. At December 31, 2017 , Southern Company Gas' total environmental remediation liability was $388 million , of which $85 million related to Elizabethtown Gas. 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 $2 million of the total accrued remediation costs. See Note (J) under " Southern Company Gas " and " Assets Held for Sale " for additional information. The ultimate outcome of these matters cannot be determined at this time; however, as a result of the regulatory treatment for environmental remediation expenses described above, 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 Market-Based Rate Authority See Note 3 to the financial statements of Southern Company, the traditional electric operating companies, and Southern Power under "FERC Matters" in Item 8 of the Form 10-K for additional information regarding proceedings related to the traditional electric operating companies' and Southern Power's 2014 and 2017 triennial market power analyses. On May 4, 2018, the FERC issued an order terminating both proceedings, finding that the traditional electric operating companies and Southern Power satisfy the FERC's standards for market-based rates. On May 9, 2018, the traditional electric operating companies and Southern Power made the compliance filing required by the order. These proceedings are essentially concluded. Open Access Transmission Tariff On May 10, 2018, the Alabama Municipal Electric Authority and Cooperative Energy filed with the FERC a complaint against SCS and the traditional electric operating companies claiming that the current 11.25% base ROE used in calculating the annual transmission revenue requirements of the traditional electric operating companies' open access transmission tariff is unjust and unreasonable as measured by the applicable FERC standards. The complaint requests that the base ROE be set no higher than 8.65% and that the FERC order refunds for the difference in revenue requirements that results from applying a just and reasonable ROE established in this proceeding upon determining the current ROE is unjust and unreasonable. On June 18, 2018, SCS and the traditional electric operating companies filed their response challenging the adequacy of the showing presented by the complainants and offering support for the current ROE. The ultimate outcome of this matter cannot be determined at this time. Cooperative Energy Power Supply Agreement See Note 3 to the financial statements of Mississippi Power under "FERC Matters – Cooperative Energy Power Supply Agreement" in Item 8 of the Form 10-K for additional information regarding Cooperative Energy's network integration transmission service agreement (NITSA) with SCS. On March 23, 2018, the FERC accepted the amendment to the NITSA between Cooperative Energy and SCS, effective April 1, 2018. 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 June 30, December 31, (in millions) Rate CNP Compliance Deferred under recovered regulatory clause revenues $ 30 $ 17 Rate CNP PPA Deferred under recovered regulatory clause revenues 11 12 Retail Energy Cost Recovery Deferred under recovered regulatory clause revenues 80 25 Under recovered regulatory clause revenues 28 — Natural Disaster Reserve Other regulatory liabilities, deferred 30 38 On May 1, 2018, the Alabama PSC approved modifications to Rate RSE and other commitments designed to position Alabama Power to address the growing pressure on its credit quality resulting from the Tax Reform Legislation, without increasing retail rates under Rate RSE in the near term. Alabama Power plans to reduce growth in total debt by increasing equity, with corresponding reductions in debt issuances, thereby de-leveraging its capital structure. Alabama Power's goal is to achieve an equity ratio of approximately 55% by the end of 2025. At June 30, 2018, Alabama Power's equity ratio was approximately 46.6% . Rate RSE The approved modifications to Rate RSE became effective June 2018 and are applicable for January 2019 billings and thereafter. The modifications include reducing the top of the allowed weighted common equity return (WCER) range from 6.21% to 6.15% and modifications to the refund mechanism applicable to prior year actual results. The modifications to the refund mechanism allow Alabama Power to retain a portion of the revenue that causes the actual WCER for a given year to exceed the allowed range. Generally, if Alabama Power's actual WCER range is between 6.15% and 7.65% , customers will receive 25% of the amount between 6.15% and 6.65% , 40% of the amount between 6.65% and 7.15% , and 75% of the amount between 7.15% and 7.65% . Customers will receive all amounts in excess of an actual WCER of 7.65% . In conjunction with these modifications to Rate RSE, on May 8, 2018, Alabama Power consented to a moratorium on any upward adjustments under Rate RSE for 2019 and 2020. Additionally, Alabama Power will return $50 million to customers through bill credits in 2019. In accordance with an established retail tariff that provides for an interim adjustment to customer billings to recognize the impact of a change in the statutory income tax rate, Alabama Power is returning approximately $257 million to retail customers through bill credits in the second half of 2018 as a result of the change in the federal income tax rate under the Tax Reform Legislation. Rate ECR On May 1, 2018, the Alabama PSC approved an increase to Rate ECR from 2.015 cents per KWH to 2.353 cents per KWH effective July 2018 which is expected to result in additional collections of approximately $100 million through December 31, 2018. The approved increase in the Rate ECR factor will have no significant effect on Alabama Power's net income, but will increase operating cash flows related to fuel cost recovery in 2018. The rate will return to 5.910 cents per KWH in 2019, absent a further order from the Alabama PSC. Accounting Order On May 1, 2018, the Alabama PSC approved an accounting order that authorizes Alabama Power to defer the benefits of federal excess deferred income taxes associated with the Tax Reform Legislation for the year ending December 31, 2018 as a regulatory liability and to use up to $30 million of such deferrals to offset under recovered amounts under Rate ECR. Any remaining amounts will be used for the benefit of customers as determined by the Alabama PSC. As of June 30, 2018, Alabama Power had applied approximately $30 million of such deferrals to offset the under recovered balance under Rate ECR and expects the total deferrals for the year ending December 31, 2018 to be approximately $50 million . See Note 5 to the financial statements of Southern Company and Alabama Power under "Federal Tax Reform Legislation" and of Alabama Power under "Current and Deferred Income Taxes" in Item 8 of the Form 10-K for additional information. Plant Greene County Alabama Power jointly owns Plant Greene County with an affiliate, Mississippi Power. See Note 4 to the financial statements of Alabama Power in Item 8 of the Form 10-K for additional information regarding the joint ownership agreement. On August 6, 2018, Mississippi Power filed its proposed Reserve Margin Plan (RMP) with the Mississippi PSC, which proposes a 4 -year acceleration of the retirement of Plant Greene County Units 1 and 2 to the third quarter 2021 and the third quarter 2022, respectively. Mississippi Power's proposed Plant Greene County unit retirements would require the completion of proposed transmission and system reliability improvements, as well as agreement by Alabama Power. Alabama Power will monitor Mississippi Power's proposed RMP and associated regulatory process as well as the proposed transmission and system reliability improvements. Alabama Power will review all the facts and circumstances and will evaluate all its alternatives prior to reaching a final determination on the ongoing operations of Plant Greene County. The ultimate outcome of this matter cannot be determined at this time. Georgia Power 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 certified construction costs 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 "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. 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 regarding Georgia Power's 2013 ARP and the Georgia PSC's 2018 order related to the Tax Reform Legislation. On April 3, 2018, the Georgia PSC approved a settlement agreement between Georgia Power and the staff of the Georgia PSC regarding the retail rate impact of the Tax Reform Legislation (Georgia Power Tax Reform Settlement Agreement). Pursuant to the Georgia Power Tax Reform Settlement Agreement, to reflect the federal income tax rate reduction impact of the Tax Reform Legislation, Georgia Power will refund to customers a total of $330 million through bill credits of $131 million in October 2018, $96 million in June 2019, and $103 million in February 2020. In addition, Georgia Power is deferring as a regulatory liability (i) the revenue equivalent of the tax expense reduction resulting from legislation lowering the Georgia state income tax rate from 6.00% to 5.75% in 2019 and (ii) the entire benefit of approximately $700 million in federal and state excess accumulated deferred income taxes. The amortization of these regulatory liabilities is expected to be addressed in Georgia Power's next base rate case, which is scheduled to be filed by July 1, 2019. If there is not a base rate case in 2019, customers will receive $185 million in annual bill credits beginning in 2020, with any additional federal and state income tax savings deferred as a regulatory liability, until Georgia Power's next base rate case. To address the negative cash flow and credit metric impacts of the Tax Reform Legislation, the Georgia PSC also approved an increase in Georgia Power's retail equity ratio to the lower of (i) Georgia Power's actual common equity weight in its capital structure or (ii) 55% , until Georgia Power's next base rate case. Benefits from reduced federal income tax rates in excess of the amounts refunded to customers will be retained by Georgia Power to cover the carrying costs of the incremental equity in 2018 and 2019. Fuel Cost Recovery As of June 30, 2018 and December 31, 2017 , Georgia Power's under recovered fuel balance totaled $159 million and $165 million , respectively, and is included as under recovered fuel clause revenues on Southern Company's and Georgia Power's condensed balance sheets. The Georgia PSC will review Georgia Power's cumulative over or under recovered fuel balance no later than September 1, 2018 and evaluate the need to file a fuel case. Georgia Power continues to be allowed to adjust its fuel cost recovery rates under an interim fuel rider prior to the next fuel case if the under or over recovered fuel balance exceeds $200 million . 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. Gulf Power See Note 3 to the financial statements of Gulf Power under "Retail Regulatory Matters" in Item 8 of the Form 10-K for additional information regarding Gulf Power's rates and charges for service to retail customers. Retail Base Rate Case See Note 3 to the financial statements of Southern Company and Gulf Power under "Regulatory Matters – Gulf Power – Retail Base Rate Cases" and "Retail Regulatory Matters – Retail Base Rate Cases," respectively, in Item 8 of the Form 10-K for additional information. As a continuation of a settlement agreement approved by the Florida PSC in April 2017 (2017 Gulf Power Rate Case Settlement Agreement), on March 26, 2018, the Florida PSC approved a stipulation and settlement agreement among Gulf Power and three intervenors addressing the retail revenue requirement effects of the Tax Reform Legislation (Gulf Power Tax Reform Settlement Agreement). The Gulf Power Tax Reform Settlement Agreement results in annual reductions to Gulf Power's revenues of $18.2 million from base rates and $15.6 million from environmental cost recovery rates, implemented April 1, 2018, and also provides for a one-time refund of $69.4 million for the retail portion of unprotected (not subject to normalization) deferred tax liabilities through a reduced fuel cost recovery rate over the remainder of 2018. Through June 30, 2018 , approximately $28 million of this refund has been reflected in customer bills. As a result of the Gulf Power Tax Reform Settlement Agreement, the Florida PSC also approved an increase in Gulf Power's maximum equity ratio from 52.5% to 53.5% for all retail regulatory purposes. As part of the Gulf Power Tax Reform Settlement Agreement, a limited scope proceeding to address protected deferred tax liabilities consistent with IRS normalization principles was initiated on April 30, 2018. Pending resolution of this proceeding, Gulf Power is deferring the related amounts for 2018 as a regulatory liability. Through June 30, 2018 , amounts deferred totaled $5 million . Unless otherwise agreed to by the parties to the Gulf Power Tax Reform Settlement Agreement, amounts recorded in this regulatory liability will be refunded to retail customers in 2019 through Gulf Power's fuel cost recovery rates. The ultimate outcome of this matter cannot be determined at this time. Cost Recovery Clauses See Note 3 to the financial statements of Gulf Power under "Retail Regulatory Matters – Cost Recovery Clauses" in Item 8 of the Form 10-K for additional information regarding Gulf Power's recovery of retail costs through various regulatory clauses and accounting orders, as approved by the Florida PSC. Regulatory clause recovery balances included in the balance sheets are as follows: Regulatory Clause Balance Sheet Line Item June 30, December 31, (in millions) Fuel Cost Recovery Under recovered regulatory clause revenues $ — $ 22 Fuel Cost Recovery Other regulatory liabilities, current 5 — Purchased Power Capacity Recovery Under recovered regulatory clause revenues 2 2 Environmental Cost Recovery (*) Under recovered regulatory clause revenues 1 2 Energy Conservation Cost Recovery Other regulatory liabilities, current 1 — (*) At June 30, 2018 and December 31, 2017 , the unde

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	REVENUE FROM CONTRACTS WITH CUSTOMERS The registrants generate revenues from a variety of sources, some of which are excluded from the scope of ASC 606, such as leases, derivatives, and certain cost recovery mechanisms. See Note (A) under " Recently Adopted Accounting Standards – Revenue " for additional information on the adoption of ASC 606 for revenue from contracts with customers. The majority of the revenues of the traditional electric operating companies and Southern Company Gas are generated from contracts with retail electric and natural gas distribution customers. Revenues from this integrated service to deliver electricity or gas when and if called upon by the customer is recognized as a single performance obligation satisfied over time and is recognized at a tariff rate as electricity or gas is delivered to the customer during the month. The traditional electric operating companies and Southern Company Gas exclude taxes imposed on the customer and collected on behalf of governmental agencies to be remitted to these agencies from the transaction price in determining the revenue related to contracts with a customer. The traditional electric operating companies and Southern Power also have contracts with multiple performance obligations, such as capacity and energy in a wholesale PPA, where the contract's total transaction price is allocated to each performance obligation based on the standalone selling price. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, the registrants recognize revenue as the performance obligations are satisfied over time as electricity or natural gas is delivered to the customer or as generation capacity is available to the customer. At Southern Company Gas, the performance obligations related to wholesale gas services are satisfied, and revenue is recognized, at a point in time when natural gas is delivered to the customer. The registrants generally have a right to consideration in an amount that corresponds directly with the value to the customer of the entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice and has elected to recognize revenue for its sales of electricity, capacity, and natural gas using the invoice practical expedient. In addition, payment for goods and services rendered is typically due in the subsequent month following satisfaction of the registrants' performance obligation. The following tables disaggregate revenue sources for the three and six months ended June 30, 2018 : For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,579 $ 3,118 Commercial 1,315 2,557 Industrial 814 1,569 Other 32 64 Natural gas distribution revenues 642 1,865 Alternative revenue programs (b) (4 ) (27 ) Total retail electric and gas distribution revenues $ 4,378 $ 9,146 Wholesale energy revenues (c)(d) 459 928 Wholesale capacity revenues (d) 152 302 Other natural gas revenues (e) 68 476 Other revenues (f) 570 1,147 Total operating revenues $ 5,627 $ 11,999 (a) Retail electric revenues include $18 million and $36 million of leases for the three and six months ended June 30, 2018 , respectively, and a net increase of $68 million and $101 million for the three and six months ended June 30, 2018 , respectively, from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 3 to the financial statements of Southern Company under "Regulatory Matters" in Item 8 of the Form 10-K for additional information on cost recovery mechanisms. (b) See Note 1 to the financial statements of Southern Company under "Revenues" in Item 8 of the Form 10-K for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (c) Wholesale energy revenues include $61 million and $155 million for the three and six months ended June 30, 2018 , respectively, of revenues accounted for as derivatives, primarily related to physical energy sales in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $118 million and $31 million , respectively, for the three months ended June 30, 2018 and $187 million and $61 million , respectively, for the six months ended June 30, 2018 of PPA contracts accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $1.3 billion and $3.3 billion for the three and six months ended June 30, 2018 , respectively, of which $0.7 billion and $1.8 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (L) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other revenues include $89 million and $183 million for the three and six months ended June 30, 2018 , respectively, of revenues not accounted for under ASC 606. Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) For the Three Months Ended June 30, 2018 Operating revenues Retail revenues (a)(b) Residential $ 557 $ 785 $ 172 $ 65 Commercial 402 749 96 68 Industrial 372 335 31 76 Other 7 20 2 3 Total retail electric revenues $ 1,338 $ 1,889 $ 301 $ 212 Wholesale energy revenues (c) 71 26 21 73 Wholesale capacity revenues 25 13 6 1 Other revenues (b)(d) 69 120 16 11 Total operating revenues $ 1,503 $ 2,048 $ 344 $ 297 For the Six Months Ended June 30, 2018 Operating revenues Retail revenues (a)(b) Residential $ 1,127 $ 1,529 $ 337 $ 125 Commercial 774 1,466 188 130 Industrial 710 650 63 146 Other 13 43 3 5 Total retail electric revenues $ 2,624 $ 3,688 $ 591 $ 406 Wholesale energy revenues (c) 172 66 56 167 Wholesale capacity revenues 49 27 12 5 Other revenues (b)(d) 131 227 33 20 Total operating revenues $ 2,976 $ 4,008 $ 692 $ 598 (a) Retail revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include a net increase or (net reduction) of $78 million , $3 million , $(12) million , and $(1) million , respectively, for the three months ended June 30, 2018 and $125 million , $12 million , $(28) million , and $(8) million , respectively, for the six months ended June 30, 2018 related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 3 to the financial statements of Alabama Power, Georgia Power, Gulf Power, and Mississippi Power under "Retail Regulatory Matters" in Item 8 of the Form 10-K for additional information on cost recovery mechanisms. (b) Retail revenues and other revenues at Georgia Power include $18 million and $33 million , respectively, for the three months ended June 30, 2018 and $36 million and $66 million , respectively, for the six months ended June 30, 2018 of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power and Georgia Power include $4 million and $5 million , respectively, for the three months ended June 30, 2018 and $9 million and $13 million , respectively, for the six months ended June 30, 2018 accounted for as derivatives primarily related to physical energy sales in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power, Georgia Power, and Gulf Power include $26 million , $26 million , and $2 million , respectively, for the three months ended June 30, 2018 and $52 million , $53 million , and $4 million , respectively, for the six months ended June 30, 2018 of revenues not accounted for under ASC 606. For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Power PPA capacity revenues (a) $ 144 $ 282 PPA energy revenues (a) 302 556 Non-PPA revenues (b) 106 221 Other revenues 3 5 Total operating revenues $ 555 $ 1,064 (a) PPA capacity revenues and PPA energy revenues include $47 million and $127 million , respectively, for the three months ended June 30, 2018 and $94 million and $203 million , respectively, for the six months ended June 30, 2018 related to PPAs accounted for as leases. See Note 1 to the financial statements of Southern Power under "Revenues" in Item 8 of the Form 10-K for additional information on capacity revenues accounted for as leases. (b) Non-PPA revenues include $50 million and $129 million for the three and six months ended June 30, 2018 , respectively, of revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. See Note 1 to the financial statements of Southern Power under "Revenues" in Item 8 of the Form 10-K and Note (I) for additional information on energy-related derivative contracts. For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 273 $ 933 Commercial 76 268 Transportation 7 24 Industrial 228 505 Other 58 135 Alternative revenue programs (a) (4 ) (27 ) Total natural gas distribution revenues $ 638 $ 1,838 Gas marketing services (b) 89 359 Wholesale gas services (c) (15 ) 131 Gas midstream operations 18 40 Other revenues — 1 Total operating revenues $ 730 $ 2,369 (a) See Note 1 to the financial statements of Southern Company Gas under "Revenues" in Item 8 of the Form 10-K for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Gas marketing services includes $4 million for the six months ended June 30, 2018 of revenues not accounted for under ASC 606. (c) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $1.3 billion and $3.3 billion for the three and six months ended June 30, 2018 , respectively, of which $0.7 billion and $1.8 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (L) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues and Note (I) for additional information on energy-related derivative contracts. Contract Balances The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers as of June 30, 2018 : Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,785 $ 33 $ 36 Alabama Power 603 — 10 Georgia Power 840 9 9 Gulf Power 169 — 1 Mississippi Power 83 — — Southern Power 136 — 4 Southern Company Gas 570 — 1 As of June 30, 2018 , Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Georgia Power had contract assets primarily related to unregulated service agreements where payment is contingent on project completion. Georgia Power had contract liabilities for outstanding performance obligations primarily related to fixed retail customer bill programs where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one -year contract term. Southern Company's unregulated distributed generation business had $23 million and $16 million of contract assets and contract liabilities, respectively, remaining for outstanding performance obligations. Remaining Performance Obligations The traditional electric operating companies and Southern Power have long-term contracts with customers in which revenues are recognized as performance obligations are satisfied over the contract term. These contracts primarily relate to PPAs whereby the traditional electric operating companies and Southern Power provide electricity and generation capacity to a customer. The revenue recognized for the delivery of electricity is variable; however, certain PPAs include a fixed payment for fixed generation capacity over the term of the contract. Southern Company's unregulated distributed generation business also has partially satisfied performance obligations related to certain fixed price contracts. Revenues from contracts with customers related to these performance obligations remaining at June 30, 2018 are expected to be recognized as follows: 2018 2019 2020 2021 2022 2023 and Thereafter (in millions) Southern Company (*) $ 263 $ 352 $ 322 $ 322 $ 310 $ 1,960 Alabama Power 11 22 22 26 23 161 Georgia Power 20 41 38 40 30 113 Gulf Power 11 22 — — — — Mississippi Power 2 3 3 1 — — Southern Power (*) 211 310 283 277 276 1,809 (*) Excludes amounts related to held for sale assets. See Note (J) under " Southern Company's Sale of Gulf Power " and " Southern Power – Sale of Florida Plants " for additional information.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS As of June 30, 2018 , 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 June 30, 2018: 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) $ 287 $ 166 $ — $ — $ 453 Foreign currency derivatives — 132 — — 132 Nuclear decommissioning trusts (c) 798 998 — 33 1,829 Cash equivalents 1,449 — — — 1,449 Other investments 9 — 1 — 10 Total $ 2,543 $ 1,296 $ 1 $ 33 $ 3,873 Liabilities: Energy-related derivatives (a)(b) $ 422 $ 151 $ — $ — $ 573 Interest rate derivatives — 68 — — 68 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ 422 $ 242 $ 22 $ — $ 686 Alabama Power Assets: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Nuclear decommissioning trusts: (d) Domestic equity 440 86 — — 526 Foreign equity 61 55 — — 116 U.S. Treasury and government agency securities — 18 — — 18 Corporate bonds 28 158 — — 186 Mortgage and asset backed securities — 18 — — 18 Private equity — — — 33 33 Other 7 — — — 7 Cash equivalents 495 — — — 495 Total $ 1,031 $ 343 $ — $ 33 $ 1,407 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Fair Value Measurements Using: As of June 30, 2018: 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 $ — $ 7 $ — $ — $ 7 Nuclear decommissioning trusts: (d) (e) Domestic equity 242 1 — — 243 Foreign equity — 135 — — 135 U.S. Treasury and government agency securities — 239 — — 239 Municipal bonds — 78 — — 78 Corporate bonds — 164 — — 164 Mortgage and asset backed securities — 41 — — 41 Other 19 5 — — 24 Total $ 261 $ 670 $ — $ — $ 931 Liabilities: Energy-related derivatives $ — $ 19 $ — $ — $ 19 Interest rate derivatives — 6 — — 6 Total $ — $ 25 $ — $ — $ 25 Gulf Power Assets: Cash equivalents $ 27 $ — $ — $ — $ 27 Liabilities: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 205 — — — 205 Total $ 205 $ 3 $ — $ — $ 208 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Fair Value Measurements Using: As of June 30, 2018: 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 $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 132 — — 132 Total $ — $ 135 $ — $ — $ 135 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ — $ 26 $ 22 $ — $ 48 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 287 $ 144 $ — $ — $ 431 Cash equivalents 1 — — — 1 Total $ 288 $ 144 $ — $ — $ 432 Liabilities: Energy-related derivatives (a)(b) $ 422 $ 99 $ — $ — $ 521 (a) Excludes $3 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $183 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 June 30, 2018 , approximately $63 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 $14 million and $4 million , respectively, for the three and six months ended June 30, 2018 and increased by $55 million and $118 million , respectively, for the three and six months ended June 30, 2017 . Alabama Power recorded an increase in fair value of $15 million and $10 million , respectively, for the three and six months ended June 30, 2018 and an increase of $28 million and $62 million , respectively, for the three and six months ended June 30, 2017 as a change in regulatory liabilities related to its AROs. Georgia Power recorded a decrease in fair value of $1 million and $6 million , respectively, for the three and six months ended June 30, 2018 and an increase of $27 million and $56 million , respectively, for the three and six months ended June 30, 2017 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 (I) 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 primarily obligated to make generation-based payments to the seller, which commenced at the commercial operation date of the respective facility and continue through 2026. 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. 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 has been determined based on market factors including comparable multiples and the expectations regarding cash flows and business plan executions. As of June 30, 2018 , the fair value measurements of private equity investments held in the nuclear decommissioning trusts 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 June 30, 2018: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 33 $ 33 Not Applicable Not Applicable Alabama Power $ 33 $ 33 Not Applicable Not Applicable Private equity funds include a fund-of-funds that invests in high-quality private equity funds across several market sectors, funds that invest 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 June 30, 2018 , 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 $ 45,806 $ 46,481 Alabama Power 8,119 8,435 Georgia Power 10,294 10,499 Gulf Power 1,285 1,311 Mississippi Power 1,779 1,760 Southern Power 5,037 5,094 Southern Company Gas 5,823 5,957 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	6 Months Ended
	Jun. 30, 2018
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 stock-based compensation plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on stock-based compensation plans. The effect of stock-based compensation plans was determined using the treasury stock method. Shares used to compute diluted earnings per share were as follows: Three Months Ended June 30, 2018 Three Months Ended June 30, 2017 Six Months Ended June 30, 2018 Six Months Ended June 30, 2017 (in millions) As reported shares 1,014 998 1,012 996 Effect of stock-based compensation — 7 5 7 Diluted shares 1,014 1,005 1,017 1,003 Stock-based compensation awards that were not included in the diluted earnings per share calculation because they were anti-dilutive totaled approximately 5.3 million shares for the three months ended June 30, 2018 and were immaterial for the three months ended June 30, 2017 and six months ended June 30, 2018 and 2017 . 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 (a) (in thousands) (in millions) Balance at December 31, 2017 1,008,532 (929 ) $ 24,167 $ — $ 1,361 $ 25,528 Consolidated net income attributable to Southern Company — — 784 — — 784 Other comprehensive income — — 41 — — 41 Stock issued 6,590 — 222 — — 222 Stock-based compensation — — 48 — — 48 Cash dividends on common stock — — (1,194 ) — — (1,194 ) Contributions from noncontrolling interests — — — — 31 31 Distributions to noncontrolling interests — — — — (42 ) (42 ) Net income attributable to noncontrolling interests — — — — 17 17 Sale of SPSH noncontrolling interests (b) — — (407 ) — 1,690 1,283 Other — (57 ) (25 ) — (1 ) (26 ) Balance at June 30, 2018 1,015,122 (986 ) $ 23,636 $ — $ 3,056 $ 26,692 Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — (723 ) — — (723 ) Other comprehensive income (loss) — — (11 ) — — (11 ) Stock issued 9,129 — 417 — — 417 Stock-based compensation — — 72 — — 72 Cash dividends on common stock — — (1,134 ) — — (1,134 ) Preference stock redemption — — — (150 ) — (150 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (40 ) (40 ) Net income attributable to noncontrolling interests — — — — 16 16 Reclassification from redeemable noncontrolling interests — — — — 114 114 Other — (49 ) (7 ) 3 1 (3 ) Balance at June 30, 2017 1,000,342 (868 ) $ 23,372 $ 462 $ 1,407 $ 25,241 (a) Primarily related to Southern Power Company and excludes redeemable noncontrolling interests. See Note 10 to the financial statements of Southern Power in Item 8 of the Form 10-K for additional information. (b) See Note (J) under "Southern Power – Sale of Solar Facility Interests " for additional information.

Financing

Financing	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
FINANCING	FINANCING Bank Credit Arrangements Bank credit arrangements provide liquidity support to the registrants' commercial paper borrowings and the traditional electric operating companies' revenue bonds. The amount of variable rate revenue bonds of the traditional electric operating companies outstanding requiring liquidity support as of June 30, 2018 was approximately $1.5 billion (comprised of approximately $854 million at Alabama Power, $550 million at Georgia Power, $82 million at Gulf Power, and $40 million at Mississippi Power). In addition, at June 30, 2018 , the traditional electric operating companies had approximately $482 million (comprised of approximately $120 million at Alabama Power, $232 million at Georgia Power, $37 million at Gulf Power, and $93 million at Mississippi Power) of revenue bonds outstanding that were required to be remarketed within the next 12 months. Subsequent to June 30, 2018, approximately $43 million of these pollution control revenue bonds of Mississippi Power were purchased and held by Mississippi Power. 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 June 30, 2018 : Expires Executable Term Loans Expires Within One Year Company 2018 2019 2020 2022 Total Unused One Year Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — Alabama Power 2 31 500 800 1,333 1,333 — — 33 Georgia Power — — — 1,750 1,750 1,736 — — — Gulf Power 20 25 235 — 280 280 45 45 — Mississippi Power 100 — — — 100 100 — — 100 Southern Power Company (b) — — — 750 750 728 — — — Southern Company Gas (c) — — — 1,900 1,900 1,895 — — — Other — 30 — — 30 30 — — 30 Southern Company Consolidated $ 122 $ 86 $ 735 $ 7,200 $ 8,143 $ 8,101 $ 45 $ 45 $ 163 (a) Represents the Southern Company parent entity. (b) Does not include Southern Power's $120 million continuing letter of credit facility for standby letters of credit expiring in 2019, of which $23 million remains unused at June 30, 2018 . (c) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.4 billion of these arrangements. Southern Company Gas' committed credit arrangements also include $500 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. DOE Loan Guarantee Borrowings See Note 6 to the financial statements of Southern Company and Georgia Power under "DOE Loan Guarantee Borrowings" in Item 8 of the Form 10-K for additional information regarding Georgia Power's Loan Guarantee Agreement. On July 27, 2017, Georgia Power entered into an amendment to the Loan Guarantee Agreement (LGA Amendment) in connection with the DOE's consent to Georgia Power's entry into the Vogtle Services Agreement and the related intellectual property licenses (IP Licenses). Under the terms of the Loan Guarantee Agreement, upon termination of the Vogtle 3 and 4 Agreement, further advances are conditioned upon the DOE's approval of any agreements entered into in replacement of the Vogtle 3 and 4 Agreement. Under the terms of the LGA Amendment, Georgia Power will not request any advances unless and until certain conditions are satisfied, including (i) receipt of the DOE's approval of the Bechtel Agreement (together with the Vogtle Services Agreement and the IP Licenses, the Replacement EPC Arrangements) and (ii) Georgia Power's entry into a further amendment to the Loan Guarantee Agreement with the DOE to reflect the Replacement EPC Arrangements. In September 2017, the DOE issued a conditional commitment to Georgia Power for up to approximately $1.67 billion in additional guaranteed loans under the Loan Guarantee Agreement. In June 2018, the DOE approved a request by Georgia Power to extend the conditional commitment to September 30, 2018. Any further extension must be approved by the DOE. Final approval and issuance of these additional loan guarantees by the DOE cannot be assured and are subject to the negotiation of definitive agreements, completion of due diligence by the DOE, receipt of any necessary regulatory approvals, and satisfaction of other conditions, including the Vogtle Owners' votes to continue construction. As of June 30, 2018, Georgia Power had $2.6 billion of borrowings outstanding under the multi-advance term loan facility (FFB Credit Facility) among Georgia Power, the DOE, and the FFB. 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 (including any decision not to continue construction of Plant Vogtle Units 3 and 4) 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 Services Agreement or rejection of the Vogtle Services Agreement in bankruptcy if Georgia Power does not maintain access to intellectual property rights under the IP Licenses; (ii) a decision by Georgia Power not to continue construction of Plant Vogtle Units 3 and 4; (iii) cancellation of Plant Vogtle Units 3 and 4 by the Georgia PSC, or by Georgia Power if authorized by the Georgia PSC; and (iv) 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. In addition, if Georgia Power discontinues construction of Plant Vogtle Units 3 and 4, Georgia Power would be obligated to immediately repay a portion of the outstanding borrowings under the FFB Credit Facility to the extent such outstanding borrowings exceed 70% of Eligible Project Costs, net of the proceeds received by Georgia Power under the Guarantee Settlement Agreement. 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. Financing Activities The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first six months of 2018 : Company Senior Note Issuances Senior Note Maturities, Redemptions, and Repurchases Revenue Bond Other Long-Term Debt Redemptions and Maturities (*) (in millions) Alabama Power $ 500 $ — $ — $ — Georgia Power — 1,000 398 104 Mississippi Power 600 — — 900 Southern Power — 350 — 420 Southern Company Gas — — 200 — Other — — — 7 Southern Company Consolidated $ 1,100 $ 1,350 $ 598 $ 1,431 (*) Includes reductions in capital lease obligations resulting from cash payments under capital leases. Southern Company In March 2018, Southern Company entered into a $900 million short-term floating rate bank loan bearing interest based on one -month LIBOR. The proceeds were used for working capital and other general corporate purposes. In April 2018, Southern Company borrowed $250 million pursuant to a short-term uncommitted bank credit arrangement, which bears interest at a rate agreed upon by Southern Company and the bank from time to time and is payable on no less than 30 days' demand by the bank. In June 2018, Southern Company repaid at maturity two $100 million short-term floating rate bank term loans. Alabama Power In June 2018, Alabama Power issued $500 million aggregate principal amount of Series 2018A 4.30% Senior Notes due July 15, 2048. The proceeds were used to repay outstanding commercial paper and for general corporate purposes, including Alabama Power's continuous construction program. Georgia Power In January 2018, Georgia Power repaid its outstanding $150 million and $100 million floating rate bank loans due May 31, 2018 and October 26, 2018, respectively. In March 2018, Georgia Power purchased and held $104.6 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2013 and $173 million aggregate principal amount of Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 2009. Georgia Power may reoffer these bonds to the public at a later date. In April 2018, Georgia Power purchased and held $55 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994. Georgia Power may reoffer these bonds to the public at a later date. Also in April 2018, Georgia Power redeemed all $250 million aggregate principal amount of its Series 2008B 5.40% Senior Notes due June 1, 2018. In May 2018, through cash tender offers, Georgia Power repurchased and retired $89 million of the $250 million aggregate principal amount outstanding of its Series 2007A 5.65% Senior Notes due March 1, 2037, $326 million of the $500 million aggregate principal amount outstanding of its Series 2009A 5.95% Senior Notes due February 1, 2039, and $335 million of the $600 million aggregate principal amount outstanding of its Series 2010B 5.40% Senior Notes due June 1, 2040, for an aggregate purchase price, excluding accrued and unpaid interest, of $902 million . In June 2018, Georgia Power purchased and held $65 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 2008. Georgia Power may reoffer these bonds to the public at a later date. Mississippi Power In March 2018, Mississippi Power issued $300 million aggregate principal amount of Series 2018A Floating Rate Senior Notes due March 27, 2020 bearing interest based on three -month LIBOR and $300 million aggregate principal amount of Series 2018B 3.95% Senior Notes due March 30, 2028. In March 2018, Mississippi Power also entered into a $300 million short-term floating rate bank loan bearing interest based on one -month LIBOR, of which $200 million was repaid in the second quarter 2018 and $50 million was repaid subsequent to June 30, 2018. Mississippi Power used the proceeds from these financings to repay a $900 million unsecured term loan. Southern Power In May 2018, Southern Power entered into two short-term floating rate bank loans, each for an aggregate principal amount of $100 million , which bear interest based on one -month LIBOR. In the second quarter 2018, Southern Power used a portion of the proceeds from the sale of a 33% equity interest in SPSH to repay $420 million aggregate principal amount of long-term floating rate bank loans and $350 million aggregate principal amount of Series 2015A 1.50% Senior Notes due June 1, 2018. See Note (J) under "Southern Power – Sale of Solar Facility Interests " for additional information. Southern Company Gas On January 4, 2018, Southern Company Gas issued a floating rate promissory note to Southern Company in an aggregate principal amount of $100 million bearing interest based on one -month LIBOR. On March 28, 2018, Southern Company Gas repaid this promissory note. In the second quarter 2018, Pivotal Utility Holdings caused $200 million aggregate principal amount of gas facility revenue bonds to be redeemed. Also in the second quarter 2018, Pivotal Utility Holdings, as borrower, and Southern Company Gas, as guarantor, entered into a $181 million short-term delayed draw floating rate bank term loan bearing interest based on one -month LIBOR, which Pivotal Utility Holdings used to repay the gas facility revenue bonds. Subsequent to June 30, 2018, Pivotal Utility Holdings repaid this short-term loan. In May 2018, Southern Company Gas Capital borrowed $95 million pursuant to a short-term uncommitted bank credit arrangement, guaranteed by Southern Company Gas, bearing interest at a rate agreed upon by Southern Company Gas Capital and the bank from time to time and payable on no less than 30 days' demand by the bank. The proceeds of the loan were used to pay down short-term debt. Subsequent to June 30, 2018, Southern Company Gas Capital repaid this loan.

Retirement Benefits

Retirement Benefits	6 Months Ended
	Jun. 30, 2018
Retirement Benefits [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS On January 1, 2018, the qualified defined benefit pension plan of Southern Company Gas was merged into the qualified defined benefit pension plan of Southern Company. Following the plan merger, Southern Company has a qualified defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at PowerSecure. The Southern Company qualified defined benefit 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 defined benefit pension plan are anticipated for the year ending December 31, 2018 . In addition, the Southern Company Gas non-qualified retirement plans were merged into the Southern Company non-qualified retirement plan (defined benefit and defined contribution). Following the non-qualified retirement plan mergers, Southern Company continues to provide certain non-qualified defined benefits for a select group of management and highly compensated employees, which are funded on a cash basis. Furthermore, 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. Southern Company Gas also provides certain medical care and life insurance benefits for eligible retired employees through a postretirement benefit plan. Southern Company Gas has a separate unfunded supplemental retirement health care plan that provides medical care and life insurance benefits to employees of discontinued businesses. As indicated in Note (A), the registrants adopted ASU 2017-07 as of January 1, 2018. ASU 2017-07 requires that an employer report the service cost component of net periodic benefit costs in the same line item or items as other compensation costs and requires the other components of net periodic benefit costs to be separately presented in the statements of income outside of income from operations. The presentation requirements of ASU 2017-07 have been applied retrospectively with the service cost component of net periodic benefit costs included in operations and maintenance and all other components of net periodic benefit costs included in other income (expense), net in the statements of income for the three and six months ended June 30, 2017. With respect to the presentation requirements, the registrants have used the practical expedient provided by ASU 2017-07, which permits an employer to use the amounts disclosed in its retirement benefits footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements to those periods. The amounts of the other components of net periodic benefit costs reclassified for the prior period are presented in the following tables. See Note 2 to the financial statements of each registrant in Item 8 of the Form 10-K for additional information. Components of the net periodic benefit costs for the three and six months ended June 30, 2018 and 2017 are presented in the following tables. Three Months Ended June 30, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 89 $ 20 $ 21 $ 4 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 5 2 9 Expected return on plan assets (235 ) (53 ) (74 ) (10 ) (10 ) (2 ) (17 ) Amortization: Prior service costs 1 1 1 — — — — Regulatory asset — — — — — — 4 Net (gain)/loss 54 13 17 3 2 — 3 Net periodic pension cost (income) $ 25 $ 6 $ — $ 2 $ 1 $ 2 $ 7 Postretirement Benefits Service cost $ 6 $ 2 $ 1 $ 1 $ 1 $ — $ — Interest cost 18 4 7 — 1 — 3 Expected return on plan assets (17 ) (7 ) (7 ) (1 ) (1 ) — (2 ) Amortization: Prior service costs 1 1 1 — — — — Regulatory asset — — — — — — 2 Net (gain)/loss 4 1 2 — — — — Net periodic postretirement benefit cost $ 12 $ 1 $ 4 $ — $ 1 $ — $ 3 Six Months Ended June 30, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 179 $ 39 $ 43 $ 8 $ 8 $ 4 $ 16 Interest cost 232 50 70 10 10 3 19 Expected return on plan assets (471 ) (104 ) (148 ) (20 ) (20 ) (5 ) (35 ) Amortization: Prior service costs 2 1 1 — — — (1 ) Regulatory asset — — — — — — 7 Net (gain)/loss 107 27 34 5 5 1 6 Net periodic pension cost (income) $ 49 $ 13 $ — $ 3 $ 3 $ 3 $ 12 Postretirement Benefits Service cost $ 12 $ 3 $ 3 $ 1 $ 1 $ — $ 1 Interest cost 37 8 14 1 2 — 5 Expected return on plan assets (34 ) (13 ) (13 ) (1 ) (1 ) — (4 ) Amortization: Regulatory asset 3 2 1 — — — 3 Net (gain)/loss 7 1 4 — — — — Net periodic postretirement benefit cost $ 25 $ 1 $ 9 $ 1 $ 2 $ — $ 5 Three Months Ended June 30, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 74 $ 16 $ 18 $ 4 $ 3 $ 5 Interest cost 113 24 35 5 5 10 Expected return on plan assets (225 ) (49 ) (70 ) (9 ) (10 ) (17 ) Amortization: Prior service costs 3 — 1 — 1 (1 ) Net (gain)/loss 41 11 14 1 2 5 Net periodic pension cost (income) $ 6 $ 2 $ (2 ) $ 1 $ 1 $ 2 Postretirement Benefits Service cost $ 6 $ 2 $ 1 $ 1 $ 1 $ — Interest cost 20 4 8 — 1 2 Expected return on plan assets (17 ) (8 ) (6 ) (1 ) (1 ) (1 ) Amortization: Prior service costs 1 1 1 — — — Net (gain)/loss 5 1 1 — — 1 Net periodic postretirement benefit cost $ 15 $ — $ 5 $ — $ 1 $ 2 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017. Six Months Ended June 30, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 147 $ 32 $ 37 $ 7 $ 7 $ 11 Interest cost 227 48 69 10 10 20 Expected return on plan assets (449 ) (98 ) (141 ) (19 ) (20 ) (35 ) Amortization: Prior service costs 6 1 2 — 1 (1 ) Net (gain)/loss 81 21 28 3 4 10 Net periodic pension cost (income) $ 12 $ 4 $ (5 ) $ 1 $ 2 $ 5 Postretirement Benefits Service cost $ 12 $ 3 $ 3 $ 1 $ 1 $ 1 Interest cost 40 9 15 1 2 5 Expected return on plan assets (33 ) (14 ) (12 ) (1 ) (1 ) (3 ) Amortization: Prior service costs 3 2 1 — — (1 ) Net (gain)/loss 7 1 3 — — 2 Net periodic postretirement benefit cost $ 29 $ 1 $ 10 $ 1 $ 2 $ 4 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
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. Federal Tax Reform Legislation Following the enactment of the Tax Reform Legislation, the SEC staff issued Staff Accounting Bulletin 118 – "Income Tax Accounting Implications of the Tax Cuts and Jobs Act" (SAB 118), which provides for a measurement period of up to one year from the enactment date to complete accounting under GAAP for the tax effects of the legislation. Due to the complex and comprehensive nature of the enacted tax law changes, and their application under GAAP, the registrants consider all amounts recorded in the financial statements as a result of the Tax Reform Legislation to be "provisional" as discussed in SAB 118 and subject to revision. Each of the registrants is awaiting additional guidance from industry and income tax authorities in order to finalize its accounting. The ultimate impact of the Tax Reform Legislation on deferred income tax assets and liabilities and the related regulatory assets and liabilities cannot be determined at this time. See Note (B) under " Regulatory Matters " for additional information. Current and Deferred Income Taxes Tax Credit Carryforwards Southern Company had federal ITC and PTC carryforwards (primarily related to Southern Power) totaling $2.3 billion as of June 30, 2018 compared to $2.1 billion as of December 31, 2017 . The federal ITC and PTC carryforwards begin expiring in 2034 and 2032, respectively, but are expected to be fully utilized by 2021. The estimated tax credit utilization reflects the 2018 abandonment loss related to certain Kemper County energy facility expenditures as well as the projected taxable gains on the various sale transactions described in Note (J) and " Legal Entity Reorganizations " herein. The expected utilization of tax credit carryforwards could be further delayed by numerous factors, including the acquisition of additional renewable projects and increased generation at existing wind facilities. The ultimate outcome of these matters cannot be determined at this time. Effective Tax Rate Each registrant's effective tax rate for the six months ended June 30, 2018 varied significantly as compared to the corresponding period in 2017 due to the 14% lower 2018 federal tax rate resulting from the Tax Reform Legislation. 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 benefit rate was (3.2)% for the six months ended June 30, 2018 compared to a benefit rate of (28.6)% for the corresponding period in 2017 . The effective tax rate increase was primarily due to the $3.1 billion pre-tax loss on the Kemper IGCC, net of the non-deductible AFUDC equity portion, recorded in 2017, partially offset by the $1.1 billion pre-tax loss related to Plant Vogtle Units 3 and 4 in 2018, the reduction in the federal corporate income tax rate and the benefit from the flowback of excess deferred income taxes as a result of the Tax Reform Legislation, as well as net state income tax benefits related to changes in state apportionment rates arising from the reorganization of Southern Power's legal entities as discussed further herein. See Note 3 to the financial statements of Southern Company under "Kemper County Energy Facility" in Item 8 of the Form 10-K and Note (B) under " Kemper County Energy Facility " for additional information regarding the Kemper IGCC and Note (B) under " Nuclear Construction " for additional information regarding Plant Vogtle Units 3 and 4. See Note (B) under "Regulatory Matters" for additional information on the flowback of excess deferred income taxes. 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. Alabama Power Alabama Power's effective tax rate was 22.8% for the six months ended June 30, 2018 compared to 40.2% for the corresponding period in 2017 . The effective tax rate decrease was primarily due to the reduction in the federal corporate income tax rate and the benefit from the flowback of excess deferred income taxes as a result of the Tax Reform Legislation. See Note (B) under "Regulatory Matters – Alabama Power" for additional information. Georgia Power Georgia Power's effective tax benefit rate was (53.5)% for the six months ended June 30, 2018 compared to an effective tax rate of 36.6% for the corresponding period in 2017 . The effective tax rate decrease was primarily due to the $1.1 billion pre-tax loss related to the estimated probable loss on Plant Vogtle Units 3 and 4 recorded in 2018, partially offset by the reduction in the federal corporate income tax rate. See Note (B) under " Nuclear Construction " for additional information. Gulf Power Gulf Power's effective tax rate was 3.3% for the six months ended June 30, 2018 compared to 39.8% for the corresponding period in 2017 . The effective tax rate decrease was primarily due to the reduction in the federal corporate income tax rate and the benefit from the flowback of excess deferred income taxes as a result of the Tax Reform Legislation. See Note (B) under "Regulatory Matters – Gulf Power" for additional information. Mississippi Power Mississippi Power's effective tax rate was 18.7% for the six months ended June 30, 2018 compared to a benefit rate of (30.5)% for the corresponding period in 2017 . The effective tax rate increase was primarily due to the $3.1 billion pre-tax loss on the Kemper IGCC, net of the non-deductible AFUDC equity portion, recorded in 2017, partially offset by the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation. See Note (B) under "Regulatory Matters – Mississippi Power" for additional information. Southern Power Southern Power's effective tax benefit rate was (1,386.5)% for the six months ended June 30, 2018 compared to a benefit rate of (114.7)% for the corresponding period in 2017 . The effective tax rate decrease was primarily due to lower earnings before income taxes resulting from a $119 million asset impairment charge related to the sale of Southern Power's equity interests in two natural gas-fired operating facilities, Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) described in Note (J) under "Southern Power – Sale of Florida Plants ," as well as the reduction in the federal corporate income tax rate and the net state income tax benefits related to certain changes in apportionment rates arising from the reorganization of Southern Power's legal entities as described below. 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. Southern Company Gas Southern Company Gas' effective tax rate was 39.1% for the six months ended June 30, 2018 compared to 38.5% for the corresponding period in 2017 . This increase was primarily related to income taxes recorded related to the sale of Pivotal Home Solutions, including the reduction in deferred tax expense as a result of treating the sale as an asset sale for tax purposes, partially offset by the reduction in the federal corporate income tax rate and the benefit from the flowback of excess deferred income taxes as a result of the Tax Reform Legislation. See Note (B) under "Regulatory Matters – Southern Company Gas" and Note (J) under "Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. Legal Entity Reorganizations In March 2018, Southern Power substantially completed a legal entity reorganization of various direct and indirect subsidiaries that own and operate substantially all of its solar facilities, including certain subsidiaries owned in partnership with various third parties. The reorganization resulted in net state tax benefits related to certain changes in apportionment rates totaling approximately $50 million , which were recorded in the first quarter 2018. In April 2018, Southern Power completed the final stage of the reorganization resulting in additional net state tax benefits of approximately $4 million . Southern Power is pursuing the sale of a noncontrolling interest in a portfolio of eight operating wind facilities through the use of third-party tax equity, which, if successful, is expected to close in the fourth quarter 2018. In the third quarter 2018, various direct and indirect subsidiaries of Southern Power that own and operate these wind facilities are expected to be reorganized under a new holding company in which the tax equity partner would invest. The reorganization is expected to result in estimated net state tax benefits totaling approximately $10 million related to certain changes in apportionment rates. The ultimate outcome of this matter cannot be determined at this time. 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. The registrants had no unrecognized tax benefits as of June 30, 2018 . It is reasonably possible that the amount of the unrecognized tax benefits could change within 12 months . The settlement of federal and state audits could impact the balances significantly. At this time, an estimate of the range of reasonably possible outcomes cannot be determined. The IRS has finalized its audits of Southern Company's consolidated income tax returns through 2016, as well as the pre-Merger Southern Company Gas tax returns. Southern Company is a participant in the Compliance Assurance Process of the IRS. 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.

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2018
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 (D) 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. The registrants adopted ASU 2017-12 as of January 1, 2018. See Note (A) under " Recently Adopted Accounting Standards – Other " for additional information. 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 approved a moratorium on Gulf Power's fuel-hedging program until January 1, 2021. 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 operating revenues. 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 and in the same income statement line item as the earnings effect of the hedged transactions. • 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 June 30, 2018 , 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 (*) 701 2022 2029 Alabama Power 82 2022 — Georgia Power 174 2022 — Gulf Power 13 2020 — Mississippi Power 66 2022 — Southern Power 14 2020 — Southern Company Gas (*) 352 2020 2029 (*) 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 3.9 billion mmBtu and short natural gas positions of 3.6 billion mmBtu as of June 30, 2018 , 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 17 million mmBtu for Southern Company, 3 million mmBtu for Alabama Power, 6 million mmBtu for Georgia Power, 1 million mmBtu for Gulf Power, 2 million mmBtu for Mississippi Power, and 5 million mmBtu for Southern 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 June 30, 2019 are immaterial for all 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 derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. 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 on the same income statement line item. 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 June 30, 2018 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value Gain (Loss) at June 30, 2018 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month June 2020 $ (6 ) Southern Company (*) 1,500 2.35% 1-month July 2021 (57 ) Georgia Power 500 1.95% 3-month December 2018 (3 ) Georgia Power 200 4.25% 3-month December 2019 (3 ) Southern Company Consolidated $ 2,500 $ (69 ) (*) 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 June 30, 2019 are $(18) million for Southern Company and immaterial for all other 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 derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and on the same income statement line as the earnings effect of the hedged transactions, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. At June 30, 2018 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at June 30, 2018 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 54 Southern Power 564 3.78% 500 1.85% June 2026 55 Total $ 1,241 € 1,100 $ 109 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 June 30, 2019 are $(23) 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 June 30, 2018 As of December 31, 2017 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/Other current liabilities $ 16 $ 12 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 5 27 7 24 Assets held for sale, current/Liabilities held for sale, current — 8 — — Assets held for sale/Liabilities held for sale — 4 — — Total derivatives designated as hedging instruments for regulatory purposes $ 21 $ 51 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 3 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Interest rate derivatives: Other current assets/Other current liabilities — 15 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 53 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 132 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 135 $ 95 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 239 $ 272 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 189 246 170 215 Total derivatives not designated as hedging instruments $ 428 $ 518 $ 550 $ 652 Gross amounts recognized $ 584 $ 664 $ 700 $ 794 Gross amounts offset (a) $ (306 ) $ (489 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 278 $ 175 $ 295 $ 196 As of June 30, 2018 As of December 31, 2017 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/Other current liabilities $ 6 $ 3 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 2 6 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 8 $ 9 $ 4 $ 10 Gross amounts recognized $ 8 $ 9 $ 4 $ 10 Gross amounts offset $ (4 ) $ (4 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 4 $ 5 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 5 $ 5 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 2 14 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 7 $ 19 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 5 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 6 $ — $ 5 Gross amounts recognized $ 7 $ 25 $ 6 $ 24 Gross amounts offset $ (7 ) $ (7 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 18 $ — $ 18 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ — $ 8 $ — $ 14 Other deferred charges and assets/Other deferred credits and liabilities — 4 — 7 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 12 $ — $ 21 Gross amounts recognized $ — $ 12 $ — $ 21 Gross amounts offset $ — $ — $ — $ — Net amounts recognized in the Balance Sheets $ — $ 12 $ — $ 21 As of June 30, 2018 As of December 31, 2017 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 $ 2 $ 3 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 6 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 9 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ — $ 1 $ — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ — $ 1 $ — Gross amounts recognized $ 3 $ 9 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ 1 $ 7 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 132 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 135 $ 26 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Gross amounts recognized $ 135 $ 26 $ 132 $ 36 Gross amounts offset $ (2 ) $ (2 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 133 $ 24 $ 129 $ 33 As of June 30, 2018 As of December 31, 2017 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 $ 3 $ 1 $ 5 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — — Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 2 $ 5 $ 8 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 $ — $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 239 $ 272 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 189 246 170 215 Total derivatives not designated as hedging instruments $ 428 $ 518 $ 549 $ 649 Gross amounts of recognized $ 431 $ 521 $ 554 $ 660 Gross amounts offset (a) $ (291 ) $ (474 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 140 $ 47 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $183 million and $193 million as of June 30, 2018 and December 31, 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $3 million and $11 million as of June 30, 2018 and December 31, 2017 , respectively. At June 30, 2018 and December 31, 2017 , 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 June 30, 2018 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (4 ) $ (1 ) $ (1 ) $ (8 ) $ (1 ) $ (1 ) Other regulatory assets, deferred (20 ) (4 ) (11 ) (4 ) (5 ) — Assets held for sale, current (8 ) — — — — — Assets held for sale (4 ) — — — — — Other regulatory liabilities, current 8 4 — — — 4 Total energy-related derivative gains (losses) $ (28 ) $ (1 ) $ (12 ) $ (12 ) $ (6 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $2 million at June 30, 2018 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2017 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (34 ) $ (4 ) $ (7 ) $ (14 ) $ (5 ) $ (4 ) Other regulatory assets, deferred (18 ) (3 ) (6 ) (7 ) (2 ) — Other regulatory liabilities, current 7 — — — — 7 Other regulatory liabilities, deferred 1 1 — — — — Total energy-related derivative gains (losses) $ (44 ) $ (6 ) $ (13 ) $ (21 ) $ (7 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $6 million at December 31, 2017 . For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives $ — $ (9 ) $ 12 $ (20 ) Interest rate derivatives — (1 ) (2 ) (1 ) Foreign currency derivatives (73 ) 71 (21 ) 67 Total $ (73 ) $ 61 $ (11 ) $ 46 Southern Power Energy-related derivatives $ (1 ) $ (7 ) $ 10 $ (15 ) Foreign currency derivatives (73 ) 71 (21 ) 67 Total $ (74 ) $ 64 $ (11 ) $ 52 Southern Company Gas Energy-related derivatives $ 1 $ (2 ) $ 2 $ (4 ) For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments on accumulated OCI were immaterial for the other registrants. For the three and six months ended June 30, 2017 , there was no material ineffectiveness recorded in earnings for any registrant. Upon the adoption of ASU 2017-12, beginning in 2018, ineffectiveness was no longer separately measured and recorded in earnings. See Note (A) for additional information. For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Company Depreciation and amortization $ 783 $ 754 $ 1,552 $ 1,469 Gain (loss) on cash flow hedges (a) Energy-related derivatives 1 (2 ) 2 (6 ) Interest expense, net of amounts capitalized (470 ) (424 ) (928 ) (840 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (6 ) (5 ) (11 ) (10 ) Foreign currency derivatives (7 ) (5 ) (12 ) (12 ) Gain (loss) on fair value hedges (b) Interest rate derivatives (7 ) 7 (31 ) (1 ) Other income (expense), net 78 52 138 98 Gain (loss) on cash flow hedges (a)(c) Foreign currency derivatives (73 ) 79 (37 ) 96 Cost of natural gas 228 232 949 951 Gain (loss) on cash flow hedges (a) Energy-related derivatives — — (2 ) — Alabama Power Interest expense, net of amounts capitalized $ (80 ) $ (77 ) $ (158 ) $ (153 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (1 ) (2 ) (3 ) (3 ) Georgia Power Interest expense, net of amounts capitalized $ (102 ) $ (104 ) $ (208 ) $ (205 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (2 ) (1 ) (3 ) (3 ) Gain (loss) on fair value hedges (b) Interest rate derivatives 2 — (1 ) (1 ) Mississippi Power Interest expense, net of amounts capitalized $ (21 ) $ (17 ) $ (39 ) $ (37 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (1 ) — (1 ) (1 ) Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Power Depreciation and amortization $ 125 $ 129 $ 240 $ 247 Gain (loss) on cash flow hedges (a) Energy-related derivatives 1 (2 ) 2 (6 ) Interest expense, net of amounts capitalized (46 ) (48 ) (93 ) (97 ) Gain (loss) on cash flow hedges (a) Foreign currency derivatives (7 ) (5 ) (12 ) (12 ) Other income (expense), net 2 2 5 (2 ) Gain (loss) on cash flow hedges (a)(c) Foreign currency derivatives (73 ) 79 (37 ) 96 Southern Company Gas Cost of natural gas $ 228 $ 232 $ 949 $ 951 Gain (loss) on cash flow hedges (a) Energy-related derivatives — — (2 ) — (a) Amounts reflect gains or losses on cash flow hedges that were reclassified from accumulated OCI into income. (b) For fair value hedges presented above, generally changes in the fair value of the derivative contracts are equal to changes in the fair value of the underlying debt and have no material impact on income. (c) 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 the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of cash flow hedge accounting on income for interest rate derivatives were immaterial for Gulf Power and Southern Company Gas. As of June 30, 2018 and December 31, 2017, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items As of June 30, 2018 As of December 31, 2017 As of June 30, 2018 As of December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (497 ) $ (746 ) $ 3 $ 3 Long-term Debt (2,528 ) (2,553 ) 63 35 Georgia Power Securities due within one year $ (497 ) $ (746 ) $ 3 $ 3 Long-term Debt (497 ) (498 ) 3 1 For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income were as follows: Gain (Loss) Three Months Ended June 30, Six Months Ended June 30, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives: Natural gas revenues (*) $ (28 ) $ 16 $ (43 ) $ 65 Cost of natural gas 2 (2 ) 4 (4 ) Total derivatives in non-designated hedging relationships $ (26 ) $ 14 $ (39 ) $ 61 Southern Company Gas Energy-related derivatives: Natural gas revenues (*) $ (28 ) $ 16 $ (43 ) $ 65 Cost of natural gas 2 (2 ) 4 (4 ) Total derivatives in non-designated hedging relationships $ (26 ) $ 14 $ (39 ) $ 61 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of $15 million for the six months ended June 30, 2017 and immaterial amounts for all other periods presented. For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were immaterial f or the traditional electric operating companies and Southern Power. 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 June 30, 2018 , the registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the registrants with interest rate derivatives at June 30, 2018 , the fair value of interest rate derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, was immaterial. At June 30, 2018 , the fair value of energy-related derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, were immaterial for all registrants. 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 and Southern Power maintain 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 and Southern Power may be required to post collateral. At June 30, 2018 , 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 June 30, 2018 , cash collateral held on deposit in broker margin accounts was $183 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 Sout

Acquisitions and Dispositions

Acquisitions and Dispositions	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS Southern Company's Sale of Gulf Power On May 20, 2018, Southern Company entered into a stock purchase agreement (Gulf Power SPA) with NextEra Energy and its wholly-owned subsidiary 700 Universe, LLC, which provides for the sale of all of the capital stock of Gulf Power for an aggregate cash purchase price of $5.75 billion (less the amount of indebtedness assumed at closing, which is currently estimated at approximately $1.4 billion ), subject to (i) customary adjustments for indebtedness and working capital and (ii) reduction by the amount (if any) by which Gulf Power fails to meet a specified capital expenditure target. The Gulf Power SPA contains customary representations, warranties, and covenants of Southern Company, 700 Universe, LLC, and NextEra Energy. These covenants include, among others, an obligation of Southern Company to cause Gulf Power to operate its business in the ordinary course until the sale is consummated and an obligation for each of the parties to use reasonable best efforts to obtain the governmental and regulatory approvals described below. The completion of the sale is subject to the satisfaction or waiver of certain closing conditions, including, among others, (i) the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act (HSR Act), (ii) approval by the FERC and the Federal Communications Commission, (iii) the entry into certain ancillary agreements, including transmission-related agreements and a transition services agreement, among the parties and their affiliates, and (iv) other customary closing conditions. The Gulf Power SPA may be terminated by either Southern Company or 700 Universe, LLC under certain circumstances, including if the sale is not consummated by June 28, 2019 (subject to extension to December 31, 2019, if all of the conditions to closing, other than the conditions related to obtaining regulatory approvals, have been satisfied). The Gulf Power SPA further provides that, upon the termination thereof, (i) under certain specified circumstances, 700 Universe, LLC will be required to pay Southern Company a termination fee of $100 million or $200 million (such amount depending on the specific circumstances of such termination) and (ii) upon certain other specified circumstances Southern Company will be required to pay 700 Universe, LLC a termination fee of $100 million . The sale of Gulf Power is expected to occur in the first half of 2019. The assets and liabilities of Gulf Power are classified as assets held for sale and liabilities held for sale on Southern Company's balance sheet as of June 30, 2018 . See " Assets Held for Sale " below for additional information. The ultimate outcome of this matter cannot be determined at this time. Southern Power See Note 11 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 Six Months Ended June 30, 2018 During the six months ended June 30, 2018, one of Southern Power's wholly-owned subsidiaries acquired and completed construction of the Gaskell West 1 solar 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 Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC January 26, 2018 20 Kern County, CA 100% of Class B (*) March 2018 20 years (*) Southern Power owns 100% of the class B membership interests under a tax equity partnership agreement. The Gaskell West 1 facility did not have operating revenues or activities prior to completion of construction and the assets being placed in service during March 2018. Construction Projects Completed and in Progress During the six months ended June 30, 2018 , Southern Power started or continued construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $520 million and $590 million for the Cactus Flats, Mankato, and Wild Horse Mountain facilities. At June 30, 2018 , construction costs included in CWIP related to these projects totaled $353 million . 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 Projects Under Construction as of June 30, 2018 Cactus Flats (a) Wind 148 Concho County, TX July 2018 12-15 years Mankato Natural Gas 345 Mankato, MN First half 2019 20 years Wild Horse Mountain (b) Wind 100 Pushmataha County, OK Fourth quarter 2019 20 years (a) In July 2017, Southern Power purchased 100% of the Cactus Flats facility and commenced construction. Subsequent to June 30, 2018, the facility was placed in service and Southern Power expects to close on a tax equity partnership agreement, which would result in Southern Power owning 100% of the class B membership interests. (b) In May 2018, Southern Power purchased 100% of the Wild Horse Mountain facility and commenced construction. Southern Power may enter into a tax equity partnership agreement, in which case it would then own 100% of the class B membership interests. Development Projects During 2017, as part of its renewable development strategy, Southern Power purchased wind turbine equipment from Siemens Gamesa Renewable Energy Inc. and Vestas-American Wind Technology, Inc. to be used for various development and construction projects. Any wind projects reaching commercial operation by 2021 are expected to qualify for 80% PTCs. During 2016, Southern Power entered into a joint development agreement with Renewable Energy Systems Americas, Inc. to develop and construct wind projects. In addition, in 2016, Southern Power purchased wind turbine equipment from Siemens Wind Power, Inc. and Vestas-American Wind Technology, Inc. to be used for construction of the facilities. Any wind projects reaching commercial operation by 2020 are expected to qualify for 100% PTCs. In response to the previously disclosed decrease of planned expenditures for plant acquisitions and placeholder growth, Southern Power continues to refine the deployment of wind turbine equipment to projects and the amount of MW capacity to be constructed. While the expectation is that the majority of the equipment will be deployed in a manner to qualify for the 100% and 80% PTCs, Southern Power may consider other strategies, such as selling equipment or interests in projects. The ultimate outcome of these matters cannot be determined at this time. Sale of Solar Facility Interests In May 2018, Southern Power sold a 33% equity interest in SPSH, a newly-formed limited partnership indirectly owning substantially all of Southern Power's solar facilities, to Global Atlantic Financial Group Limited (Global Atlantic) for approximately $1.2 billion , subject to customary working capital adjustments. The proceeds were used to repay $770 million of existing indebtedness, to return capital of $250 million to Southern Company, and for other general corporate purposes, including working capital. Since Southern Power retains control of the limited partnership through its wholly-owned general partner, the sale was recorded as an equity transaction and Southern Power will continue to consolidate the results of SPSH. On the date of the transaction, the noncontrolling interest was increased by $511 million to reflect 33% of the carrying value of the partnership. This difference, partially offset by the tax impact and other related transaction charges, also resulted in a $407 million decrease to Southern Power's common stockholder's equity. Sale of Florida Plants In May 2018, Southern Power entered into an equity interest purchase agreement with NextEra Energy to sell all of its equity interests in the Florida Plants, for an aggregate purchase price of $195 million , subject to customary working capital and timing adjustments. The sale is subject to certain closing and timing conditions and approvals, including, but not limited to, the expiration or termination of the waiting period under the HSR Act and approval by the FERC. The ultimate purchase price will decrease $110,000 per day for each day after December 31, 2018 through the closing of the transaction. Conversely, the ultimate purchase price will increase $110,000 per day for each day the closing occurs prior to December 31, 2018. The transaction is currently expected to occur in the first half of 2019. As a result of this pending transaction, Southern Power recorded an asset impairment charge of approximately $119 million ( $89 million after tax) in the second quarter 2018. The assets and liabilities of the Florida Plants are classified as assets held for sale and liabilities held for sale on Southern Company's and Southern Power's balance sheets as of June 30, 2018 . See " Assets Held for Sale " below for additional information. The ultimate outcome of this matter cannot be determined at this time. Assets Subject to Lien Under the terms of the PPA and the expansion PPA for the Mankato project, approximately $475 million of assets, primarily related to property, plant, and equipment, are subject to lien at June 30, 2018. Southern Company Gas Sale of Pivotal Home Solutions On June 4, 2018, Southern Company Gas completed the stock sale of Pivotal Home Solutions to American Water Enterprises LLC for a total cash purchase price of $358 million and an additional $6 million for working capital. This disposition resulted in a net loss of $76 million , which included $40 million of income tax expense. In contemplation of the transaction, a goodwill impairment charge of $42 million was recorded during the first quarter 2018. The after-tax loss included income tax expense on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Additionally, this disposition is subject to a final working capital adjustment that may impact the cash proceeds from disposition, but not the loss recorded. Southern Company Gas and American Water Enterprises LLC entered into a transition services agreement whereby Southern Company Gas will provide certain administrative and operational services through no later than February 3, 2019. Sale of Elizabethtown Gas and Elkton Gas On July 1, 2018, a Southern Company Gas subsidiary, Pivotal Utility Holdings, completed the sales of the assets of two of its natural gas distribution utilities, Elizabethtown Gas and Elkton Gas, to South Jersey Industries, Inc. for a total cash purchase price of $1.7 billion and an additional $40 million for working capital. This disposition resulted in an estimated pre-tax gain of approximately $235 million and an after-tax gain of approximately $12 million , which will be recorded in the third quarter 2018. The after-tax gain included income tax expense on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Additionally, this disposition is subject to a final working capital adjustment that may impact the cash proceeds from disposition, but not the gain that will be recorded in the third quarter 2018. Southern Company Gas and South Jersey Industries, Inc. entered into transition services agreements whereby Southern Company Gas will provide certain administrative and operational services through no later than January 31, 2020. The assets and liabilities of Elizabethtown Gas and Elkton Gas are classified as assets held for sale and liabilities held for sale on Southern Company's and Southern Company Gas' balance sheets at June 30, 2018 . See " Assets Held for Sale " below for additional information. Sale of Florida City Gas On July 29, 2018, Southern Company Gas and its wholly-owned direct subsidiary, NUI Corporation, completed the stock sale of Pivotal Utility Holdings, which primarily consisted of Florida City Gas, to NextEra Energy for a total cash purchase price of $530 million (less $3 million of indebtedness assumed at closing for customer deposits) and an additional $60 million for cash and other working capital. This disposition resulted in an estimated pre-tax gain of approximately $126 million and an after-tax gain of approximately $4 million , which will be recorded in the third quarter 2018. The after-tax gain included income tax expense on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Additionally, this disposition is subject to a final working capital adjustment that may impact the cash proceeds from disposition, but not the gain that will be recorded in the third quarter 2018. Southern Company Gas and NextEra Energy entered into a transition services agreement whereby Southern Company Gas will provide certain administrative and operational services through no later than July 29, 2020. The assets and liabilities of Florida City Gas are classified as assets held for sale and liabilities held for sale on Southern Company's and Southern Company Gas' balance sheets at June 30, 2018 . See " Assets Held for Sale " below for additional information. Assets Held for Sale As discussed above, Southern Company, Southern Power, and Southern Company Gas each have assets and liabilities held for sale on their balance sheets at June 30, 2018 . Assets and liabilities held for sale have been classified separately on each company's balance sheet at the lower of carrying value or fair value less costs to sell at the time the criteria for held-for-sale classification were met. For assets and liabilities held for sale recorded at fair value on a nonrecurring basis, the fair value of assets held for sale is based primarily on unobservable inputs (Level 3), which includes the agreed upon sales prices in executed sales agreements. Upon classification as held for sale in May 2018, Southern Power ceased recognizing depreciation on the Florida Plants' property, plant, and equipment to be sold. Since the depreciation of the assets to be sold in the Gulf Power transaction continues to be reflected in customer rates and will be reflected in the carryover basis of the assets when sold, Southern Company will continue to record depreciation on those assets through the date the transaction closes. Likewise, since the depreciation of the assets sold in the Elizabethtown Gas, Elkton Gas, and Florida City Gas transactions continued to be reflected in customer rates and was reflected in the carryover basis of the assets when sold, Southern Company Gas continued to record depreciation on those assets through the respective date that each transaction closed. The following table provides each company's major classes of assets and liabilities classified as held for sale at June 30, 2018 : Southern Company Southern Power Southern Company Gas (in millions) Assets Held for Sale: Current assets $ 487 $ 17 $ 81 Total property, plant, and equipment 5,462 168 1,408 Goodwill and other intangible assets 668 — 668 Other non-current assets 705 15 141 Total Assets Held for Sale $ 7,322 $ 200 $ 2,298 Liabilities Held for Sale: Current liabilities $ 354 $ 2 $ 61 Long-term debt 1,285 — — Accumulated deferred income taxes 566 — 26 Other non-current liabilities 1,334 — 325 Total Liabilities Held for Sale $ 3,539 $ 2 $ 412 Southern Company, Southern Power, and Southern Company Gas each concluded that the sale of these assets, both individually and combined, did not represent a strategic shift in operations that has, or is expected to have, a major effect on its operations and financial results; therefore, none of these assets held for sale have been classified as discontinued operations for any of the periods presented. Gulf Power and the Florida Plants represent individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax profit for these components for the three and six months ended June 30, 2018 and 2017 is presented below: For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Earnings before income taxes: Gulf Power $ 31 $ 61 $ 87 $ 95 Southern Power's Florida Plants (*) $ 14 $ 11 $ 24 $ 20 (*) Excludes any allocation of interest from Southern Power's corporate debt.

Variable Interest Entity and Eq

Variable Interest Entity and Equity Method Investments	6 Months Ended
	Jun. 30, 2018
Regulated Operations [Abstract]
VARIABLE INTEREST ENTITY AND EQUITY METHOD INVESTMENTS	VARIABLE INTEREST ENTITY AND EQUITY METHOD INVESTMENTS Southern Power In May 2018, Southern Power sold a 33% equity interest in SPSH to Global Atlantic. See Note (J) under "Southern Power" for additional information. A wholly-owned subsidiary of Southern Power is the general partner and holds a 1% ownership interest in SPSH and another wholly-owned subsidiary of Southern Power owns the remaining 66% ownership in SPSH. SPSH is a variable interest entity (VIE) because the arrangement is structured as a limited partnership and the 33% limited partner does not have substantive kick-out rights against the general partner. Southern Power previously consolidated SPSH and will continue to do so as the primary beneficiary of the VIE because it controls the most significant activities of the partnership, including operating and maintaining its assets. At June 30, 2018, SPSH had total assets of $6.5 billion , total liabilities of $0.1 billion , and noncontrolling interests related to other partners' interests of $1.2 billion . Cash distributions from SPSH are allocated 67% to Southern Power and 33% to Global Atlantic in accordance with their membership interests and the limited partnership agreement. Transfers and sales of the assets in the VIE are subject to limited partner consent and the liabilities do not have recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. 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 June 30, 2018 and December 31, 2017 and related income from those investments for the three and six -month periods ended June 30, 2018 and June 30, 2017 were as follows: Investment Balance June 30, 2018 December 31, 2017 (in millions) SNG $ 1,258 $ 1,262 Atlantic Coast Pipeline 56 41 PennEast Pipeline 67 57 Triton 42 42 Pivotal JAX LNG, LLC 52 44 Horizon Pipeline 31 30 Other 1 1 Total $ 1,507 $ 1,477 Earnings from Equity Method Investments Three Months Ended Three Months Ended Six Months Ended Six Months (in millions) SNG $ 27 $ 24 $ 66 $ 58 PennEast Pipeline 1 1 2 4 Atlantic Coast Pipeline 1 2 3 3 Triton 1 2 2 2 Horizon Pipeline 1 — 1 1 Total $ 31 $ 29 $ 74 $ 68 Southern Natural Gas Selected financial information of SNG for the three and six months ended June 30, 2018 and June 30, 2017 is as follows: Income Statement Information Three Months Ended June 30, 2018 Three Months Ended June 30, 2017 Six Months Ended June 30, 2018 Six Months Ended June 30, 2017 (in millions) Revenues $ 146 $ 143 $ 306 $ 298 Operating income $ 60 $ 63 $ 159 $ 147 Net income $ 54 $ 48 $ 132 $ 114

Segment and Related Information

Segment and Related Information	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
SEGMENT AND RELATED INFORMATION	SEGMENT AND RELATED INFORMATION Southern Company The primary businesses of the Southern Company system are 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 develops, 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 its natural gas distribution utilities in four states and is involved in several other complementary businesses including gas marketing services, wholesale gas services, and gas midstream operations. Through June 30, 2018, Southern Company Gas had seven natural gas distribution utilities in seven states. Subsequent to June 30, 2018, Southern Company Gas completed sales of three of its natural gas distribution utilities. See Note (J) under "Southern Company Gas" for additional information. 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 $109 million and $192 million for the three and six months ended June 30, 2018 , respectively, and $90 million and $190 million for the three and six months ended June 30, 2017 , respectively. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies were $8 million for both the three and six months ended June 30, 2018 and $10 million for both the three and six months ended June 30, 2017 . Revenues from sales of natural gas from Southern Company Gas to Southern Power were $22 million and $58 million for the three and six months ended June 30, 2018 , respectively, and $33 million and $56 million for the three and six months ended June 30, 2017 , respectively. 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 and six months ended June 30, 2018 and 2017 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 June 30, 2018: Operating revenues $ 4,124 $ 555 $ (114 ) $ 4,565 $ 730 $ 381 $ (49 ) $ 5,627 Segment net income (loss) (a)(b)(c) (48 ) 22 — (26 ) (31 ) (100 ) 3 (154 ) Six Months Ended June 30, 2018: Operating revenues $ 8,104 $ 1,064 $ (220 ) $ 8,948 $ 2,369 $ 782 $ (100 ) $ 11,999 Segment net income (loss) (a)(b)(c)(d) 563 143 — 706 248 (174 ) 4 784 At June 30, 2018: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 298 $ — $ 5,315 Total assets 73,634 15,428 (313 ) 88,749 22,112 3,707 (1,791 ) 112,777 Three Months Ended June 30, 2017: Operating revenues $ 4,157 $ 529 $ (101 ) $ 4,585 $ 716 $ 166 $ (37 ) $ 5,430 Segment net income (loss) (a)(b) (1,442 ) 82 — (1,360 ) 49 (68 ) (2 ) (1,381 ) Six Months Ended June 30, 2017: Operating revenues $ 7,943 $ 979 $ (206 ) $ 8,716 $ 2,276 $ 289 $ (79 ) $ 11,202 Segment net income (loss) (a)(b)(e) (1,010 ) 151 — (859 ) 288 (152 ) — (723 ) At December 31, 2017: Goodwill $ — $ 2 $ — $ 2 $ 5,967 $ 299 $ — $ 6,268 Total assets 72,204 15,206 (325 ) 87,085 22,987 2,552 (1,619 ) 111,005 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $1.1 billion ( $0.8 billion after tax) and $3.0 billion ( $2.1 billion after tax) for the three months ended June 30, 2018 and 2017 , respectively, and $1.1 billion ( $0.8 billion after tax) and $3.1 billion ( $2.2 billion after tax) for the six months ended June 30, 2018 and 2017 , respectively. See Note 3 to the financial statements of Southern Company under "Kemper County Energy Facility" in Item 8 of the Form 10-K and Note (B) under " Nuclear Construction " and " Kemper County Energy Facility " for additional information. (c) Segment net income (loss) for Southern Power includes a pre-tax impairment charge of $119 million ( $89 million after tax) for the three and six months ended June 30, 2018 related to the pending sale of Southern Power's Florida Plants. See Note (J) under "Southern Power – Sale of Florida Plants " for additional information. (d) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the six months ended June 30, 2018 related to the sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. (e) Segment net income (loss) for the traditional electric operating companies 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 six months ended June 30, 2017. See Note 3 to the financial statements of Southern Company under "Regulatory Matters – Gulf Power – Retail Base Rate Cases" in Item 8 of the Form 10-K for additional information. Products and Services Electric Utilities' Revenues Period Retail Wholesale Other Total (in millions) Three Months Ended June 30, 2018 $ 3,740 $ 611 $ 214 $ 4,565 Three Months Ended June 30, 2017 3,777 618 190 4,585 Six Months Ended June 30, 2018 $ 7,308 $ 1,230 $ 410 $ 8,948 Six Months Ended June 30, 2017 7,171 1,149 396 8,716 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended June 30, 2018 $ 638 $ 89 $ 3 $ 730 Three Months Ended June 30, 2017 557 166 (7 ) 716 Six Months Ended June 30, 2018 $ 1,838 $ 359 $ 172 $ 2,369 Six Months Ended June 30, 2017 1,689 454 133 2,276 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. Subsequent to June 30, 2018, Southern Company Gas sold three of its natural gas distribution utilities, Elizabethtown Gas, Elkton Gas, and Florida City Gas. See Note (J) under "Southern Company Gas" for additional information. Gas marketing services includes natural gas marketing to end-use customers primarily in Georgia and Illinois. On June 4, 2018, Southern Company Gas sold Pivotal Home Solutions. See Note (J) under "Southern Company Gas" for additional information. 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. Business segment financial data for the three and six months ended June 30, 2018 and 2017 was as follows: Gas Distribution Operations (a) Gas Marketing Services (b)(c) Wholesale Gas Services (d) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Three Months Ended June 30, 2018: Operating revenues $ 643 $ 89 $ (16 ) $ 18 $ 734 $ 1 $ (5 ) $ 730 Segment net income 68 (76 ) (21 ) 14 (15 ) (16 ) — (31 ) Six Months Ended June 30, 2018: Operating revenues 1,856 359 150 40 2,405 2 (38 ) 2,369 Segment net income 216 (63 ) 83 38 274 (26 ) — 248 Total assets at June 30, 2018: 18,654 1,610 818 2,269 23,351 11,544 (12,783 ) 22,112 Three Months Ended June 30, 2017: Operating revenues $ 603 $ 166 $ (12 ) $ 12 $ 769 $ 3 $ (56 ) $ 716 Segment net income 54 4 (17 ) 9 50 (1 ) — 49 Six Months Ended June 30, 2017: Operating revenues 1,783 454 119 37 2,393 5 (122 ) 2,276 Segment net income 171 35 51 25 282 6 — 288 Total assets at December 31, 2017: 19,358 2,147 1,096 2,241 24,842 12,184 (14,039 ) 22,987 (a) Operating revenues for the three gas distribution operations dispositions were $70 million and $66 million for the three months ended June 30, 2018 and 2017 , respectively, and $237 million and $224 million for the six months ended June 30, 2018 and 2017 , respectively. See Note (J) under " Southern Company Gas " for additional information. (b) Operating revenues for the gas marketing services disposition were $24 million and $32 million for the three months ended June 30, 2018 and 2017 , respectively, and $55 million and $63 million for the six months ended June 30, 2018 and 2017 , respectively. See Note (J) under " Southern Company Gas " for additional information. (c) Segment net income for gas marketing services includes a loss on disposition of $36 million for the three and six months ended June 30, 2018 and a goodwill impairment charge of $42 million for the six months ended June 30, 2018 recorded in contemplation of the sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas " for additional information. (d) 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) Three Months Ended June 30, 2018 $ 1,336 $ 102 $ 1,438 $ 1,454 $ (16 ) Three Months Ended June 30, 2017 1,531 123 1,654 1,666 (12 ) Six Months Ended June 30, 2018 $ 3,274 $ 269 $ 3,543 $ 3,393 $ 150 Six Months Ended June 30, 2017 3,370 259 3,629 3,510 119

Introduction (Policies)

Introduction (Policies)	6 Months Ended
	Jun. 30, 2018
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, 2017 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 June 30, 2018 and 2017 . 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.
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 Adopted Accounting Standards	Recently Adopted Accounting Standards See Note 1 to the financial statements of the registrants under "Recently Issued Accounting Standards" in Item 8 of the Form 10-K for additional information. Revenue In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers (ASC 606), 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. ASC 606 became effective on January 1, 2018 and the registrants adopted it using the modified retrospective method applied to open contracts and only to the version of the contracts in effect as of January 1, 2018. In accordance with the modified retrospective method, the registrants' previously issued financial statements have not been restated to comply with ASC 606 and the registrants did not have a cumulative-effect adjustment to retained earnings. The adoption of ASC 606 had no significant impact on the timing of revenue recognition compared to previously reported results; however, it requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers, which are included in Note (C). ASC 606 provided additional clarity on financial statement presentation that resulted in reclassifications into other revenues and other operations and maintenance from other income/(expense), net at Alabama Power and Georgia Power related to certain unregulated sales of products and services. In addition, contract assets related to Southern Company's unregulated distributed generation business have been reclassified from unbilled revenue in accordance with the guidance in ASC 606. These reclassifications did not affect the timing or amount of revenues recognized or cash flows. ASC 606 also provided additional guidance on over-time revenue recognition, resulting in a change in the timing of revenue recognized from guaranteed and fixed billing arrangements at Southern Company Gas. The changes in natural gas revenues recognized in the second quarter and year-to-date 2018 relate primarily to the seasonal nature of natural gas usage. The net impact of accounting for revenue under ASC 606 decreased Southern Company's consolidated net income by $5 million for the three months ended June 30, 2018 and increased Southern Company's consolidated net income by $5 million for the six months ended June 30, 2018 . The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Three Months Ended For the Six Months Ended Condensed Statements of Income As Reported Balances Without Adoption of Effect of Change As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) (in millions) Southern Company Natural gas revenues $ 706 $ 713 $ (7 ) $ 2,314 $ 2,307 $ 7 Other revenues 395 393 2 808 805 3 Other operations and maintenance 1,559 1,546 13 3,008 2,985 23 Operating income 63 81 (18 ) 1,439 1,452 (13 ) Other income (expense), net 78 67 11 138 118 20 Earnings (loss) before income taxes (266 ) (259 ) (7 ) 784 777 7 Income taxes (benefit) (139 ) (137 ) (2 ) (25 ) (27 ) 2 Consolidated net income (loss) (127 ) (122 ) (5 ) 809 804 5 Consolidated net income (loss) attributable to Southern Company (154 ) (149 ) (5 ) 784 779 5 Alabama Power Other revenues $ 69 $ 60 $ 9 $ 131 $ 114 $ 17 Other operations and maintenance 402 391 11 788 767 21 Operating income 380 382 (2 ) 752 756 (4 ) Other income (expense), net 12 10 2 15 11 4 Georgia Power Other revenues $ 120 $ 97 $ 23 $ 227 $ 189 $ 38 Other operations and maintenance 457 437 20 863 828 35 Operating income (loss) (472 ) (475 ) 3 41 38 3 Other income (expense), net 35 38 (3 ) 73 76 (3 ) Southern Company Gas Natural gas revenues $ 710 $ 717 $ (7 ) $ 2,341 $ 2,334 $ 7 Operating income 49 56 (7 ) 436 429 7 Earnings before income taxes 24 31 (7 ) 407 400 7 Income taxes 55 57 (2 ) 159 157 2 Net income (loss) (31 ) (26 ) (5 ) 248 243 5 For the Six Months Ended Condensed Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 809 $ 804 $ 5 Changes in certain current assets and liabilities: Receivables 94 99 (5 ) Other current assets (40 ) (45 ) 5 Accrued taxes 213 215 (2 ) Other current liabilities 125 118 7 Georgia Power Changes in certain current assets and liabilities: Receivables $ (103 ) $ (75 ) $ (28 ) Other current assets 25 (3 ) 28 Southern Company Gas Net income $ 248 $ 243 $ 5 Changes in certain current assets and liabilities: Accrued taxes 38 40 (2 ) Other current liabilities 24 17 7 At June 30, 2018 Condensed Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 769 $ 824 $ (55 ) Other accounts and notes receivable 621 622 (1 ) Other current assets 172 116 56 Accrued taxes 544 542 2 Other current liabilities 808 815 (7 ) Retained earnings 8,494 8,489 5 Southern Company Gas Accrued income taxes $ 86 $ 84 $ 2 Other current liabilities 143 150 (7 ) Accumulated deficit (202 ) (207 ) 5 Other In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18). ASU 2016-18 eliminates the need to reflect transfers between cash and restricted cash in operating, investing, and financing activities in the statements of cash flows. In addition, the net change in cash and cash equivalents during the period includes amounts generally described as restricted cash or restricted cash equivalents. The registrants adopted ASU 2016-18 effective January 1, 2018 with no material impact on their financial statements. Southern Company, Southern Power, and Southern Company Gas retrospectively applied ASU 2016-18 effective January 1, 2018 and have restated prior periods in the statements of cash flows by immaterial amounts. The change in restricted cash in the statements of cash flows was previously disclosed in operating activities for Southern Company and Southern Company Gas and in investing activities for Southern Company and Southern Power. See " Restricted Cash " herein for additional information. In March 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 statements of income outside of income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. The registrants adopted ASU 2017-07 effective January 1, 2018 with no material impact on their financial statements. ASU 2017-07 has been applied retrospectively for the presentation of the service cost component and the other components of net periodic benefit costs in the statements of income for Southern Company, the traditional electric operating companies, and Southern Company Gas. Since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017, no retrospective presentation of Southern Power's net periodic benefits costs is required. The requirement to limit capitalization to the service cost component of net periodic benefit costs has been applied on a prospective basis from the date of adoption for all registrants. The presentation changes resulted in a decrease in operating income and an increase in other income for the three and six months ended June 30, 2018 and 2017 for Southern Company, the traditional electric operating companies, and Southern Company Gas. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12). ASU 2017-12 makes more financial and non-financial hedging strategies eligible for hedge accounting, amends the related presentation and disclosure requirements, and simplifies hedge effectiveness assessment requirements. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The registrants adopted ASU 2017-12 effective January 1, 2018 with no material impact on their financial statements. See Note (I) for disclosures required by ASU 2017-12. On February 14, 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (ASU 2018-02) to address the application of ASC 740, Income Taxes (ASC 740) to certain provisions of the Tax Reform Legislation. ASU 2018-02 specifically addresses the ASC 740 requirement that the effect of a change in tax laws or rates on deferred tax assets and liabilities be included in income from continuing operations, even when the tax effects were initially recognized directly in OCI at the previous rate, which strands the income tax rate differential in accumulated OCI. The amendments in ASU 2018-02 allow a reclassification from accumulated OCI to retained earnings for stranded tax effects resulting from the Tax Reform Legislation. The registrants adopted ASU 2018-02 effective January 1, 2018 with no material impact on their financial statements.
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.
Restricted Cash	Restricted Cash The registrants adopted ASU 2016-18 as of January 1, 2018. See " Recently Adopted Accounting Standards – Other " herein for additional information. At December 31, 2017 , Southern Power had restricted cash primarily related to certain acquisitions and construction projects. At both June 30, 2018 and December 31, 2017 , Southern Company Gas had restricted cash held as collateral for worker's compensation, life insurance, and long-term disability insurance.
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 June 30, 2018 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.
Hypothetical Liquidation at Book Value	Hypothetical Liquidation at Book Value Southern Power has consolidated renewable generation projects that are partially funded by a third-party tax equity investor. The related contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. Therefore, the noncontrolling interest is accounted for under a balance sheet approach utilizing the hypothetical liquidation at book value (HLBV) method. The HLBV method calculates each partner's share of income based on the change in net equity the partner can legally claim in a hypothetical liquidation at the end of the period compared to the beginning of the period.
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 (I) 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 primarily obligated to make generation-based payments to the seller, which commenced at the commercial operation date of the respective facility and continue through 2026. 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. 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 has 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 stock-based compensation plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on stock-based compensation plans. The effect of stock-based compensation plans was determined using the treasury stock method.
Derivatives	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 derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. 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 on the same income statement line item. 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. 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 (D) 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. The registrants adopted ASU 2017-12 as of January 1, 2018. See Note (A) under " Recently Adopted Accounting Standards – Other " for additional information. 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 approved a moratorium on Gulf Power's fuel-hedging program until January 1, 2021. 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 operating revenues. 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 and in the same income statement line item as the earnings effect of the hedged transactions. • 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.

Introduction (Tables)

Introduction (Tables)	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Three Months Ended For the Six Months Ended Condensed Statements of Income As Reported Balances Without Adoption of Effect of Change As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) (in millions) Southern Company Natural gas revenues $ 706 $ 713 $ (7 ) $ 2,314 $ 2,307 $ 7 Other revenues 395 393 2 808 805 3 Other operations and maintenance 1,559 1,546 13 3,008 2,985 23 Operating income 63 81 (18 ) 1,439 1,452 (13 ) Other income (expense), net 78 67 11 138 118 20 Earnings (loss) before income taxes (266 ) (259 ) (7 ) 784 777 7 Income taxes (benefit) (139 ) (137 ) (2 ) (25 ) (27 ) 2 Consolidated net income (loss) (127 ) (122 ) (5 ) 809 804 5 Consolidated net income (loss) attributable to Southern Company (154 ) (149 ) (5 ) 784 779 5 Alabama Power Other revenues $ 69 $ 60 $ 9 $ 131 $ 114 $ 17 Other operations and maintenance 402 391 11 788 767 21 Operating income 380 382 (2 ) 752 756 (4 ) Other income (expense), net 12 10 2 15 11 4 Georgia Power Other revenues $ 120 $ 97 $ 23 $ 227 $ 189 $ 38 Other operations and maintenance 457 437 20 863 828 35 Operating income (loss) (472 ) (475 ) 3 41 38 3 Other income (expense), net 35 38 (3 ) 73 76 (3 ) Southern Company Gas Natural gas revenues $ 710 $ 717 $ (7 ) $ 2,341 $ 2,334 $ 7 Operating income 49 56 (7 ) 436 429 7 Earnings before income taxes 24 31 (7 ) 407 400 7 Income taxes 55 57 (2 ) 159 157 2 Net income (loss) (31 ) (26 ) (5 ) 248 243 5 For the Six Months Ended Condensed Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 809 $ 804 $ 5 Changes in certain current assets and liabilities: Receivables 94 99 (5 ) Other current assets (40 ) (45 ) 5 Accrued taxes 213 215 (2 ) Other current liabilities 125 118 7 Georgia Power Changes in certain current assets and liabilities: Receivables $ (103 ) $ (75 ) $ (28 ) Other current assets 25 (3 ) 28 Southern Company Gas Net income $ 248 $ 243 $ 5 Changes in certain current assets and liabilities: Accrued taxes 38 40 (2 ) Other current liabilities 24 17 7 At June 30, 2018 Condensed Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 769 $ 824 $ (55 ) Other accounts and notes receivable 621 622 (1 ) Other current assets 172 116 56 Accrued taxes 544 542 2 Other current liabilities 808 815 (7 ) Retained earnings 8,494 8,489 5 Southern Company Gas Accrued income taxes $ 86 $ 84 $ 2 Other current liabilities 143 150 (7 ) Accumulated deficit (202 ) (207 ) 5
Schedule of Change in Asset Retirement Obligation	As of June 30, 2018 , details of the AROs, including those related to the CCR Rule, included in the condensed balance sheets of Southern Company, Alabama Power, and Mississippi Power were as follows: Southern Company Alabama Power Mississippi Power (in millions) Balance at December 31, 2017 $ 4,824 $ 1,709 $ 174 Liabilities incurred 1 — — Liabilities settled (97 ) (19 ) (15 ) Accretion 95 41 2 Cash flow revisions 1,493 1,451 15 Reclassification to held for sale (148 ) — — Balance at June 30, 2018 $ 6,168 $ 3,182 $ 176
Estimated Cost Of Decommissioning	In June 2018, Alabama Power completed an updated decommissioning cost site study for Plant Farley. The estimated costs of decommissioning based on the 2018 site study are as follows: Decommissioning periods: Beginning year 2037 Completion year 2076 (in millions) Site study costs: Radiated structures $ 1,621 Non-radiated structures 99 Total site study costs $ 1,720
Schedule of Goodwill	The following table presents year-to-date changes in goodwill balances for Southern Company and Southern Company Gas: Goodwill Southern Company Southern Company Gas Gas Distribution Operations Gas Marketing Services Total (in millions) Balance at December 31, 2017 $ 6,268 $ 4,702 $ 1,265 $ 5,967 Impairment (a) (42 ) — (42 ) (42 ) Sale of Pivotal Home Solutions (a) (242 ) — (242 ) (242 ) Reclassification to held for sale (b) (668 ) (668 ) — (668 ) Balance at June 30, 2018 $ 5,315 (c) $ 4,034 $ 981 $ 5,015 (a) On April 11, 2018, Southern Company Gas entered into a stock purchase agreement for the sale of Pivotal Home Solutions. In contemplation of the transaction, a goodwill impairment charge of $42 million was recorded in the first quarter 2018. On June 4, 2018, Southern Company Gas and Pivotal Home Solutions completed this transaction. See Note (J) under " Southern Company Gas " for additional information. (b) Reflects goodwill associated with Elizabethtown Gas, Elkton Gas, and Florida City Gas, which were sold subsequent to June 30, 2018. See Note (J) under " Southern Company Gas " and " Assets Held for Sale " for additional information. (c) Total does not add due to rounding.
Schedule of Goodwill and Other Intangible Assets	Other intangible assets were as follows: At June 30, 2018 At December 31, 2017 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 (*) $ 223 $ (79 ) $ 144 $ 288 $ (83 ) $ 205 Trade names (*) 70 (17 ) 53 159 (17 ) 142 Storage and transportation contracts 64 (44 ) 20 64 (34 ) 30 PPA fair value adjustments 456 (60 ) 396 456 (47 ) 409 Other 19 (5 ) 14 17 (5 ) 12 Total other intangible assets subject to amortization $ 832 $ (205 ) $ 627 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 907 $ (205 ) $ 702 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (60 ) $ 396 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services (*) Customer relationships $ 156 $ (71 ) $ 85 $ 221 $ (77 ) $ 144 Trade names 26 (6 ) 20 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (44 ) 20 64 (34 ) 30 Total other intangible assets subject to amortization $ 246 $ (121 ) $ 125 $ 400 $ (120 ) $ 280 (*) Balances as of June 30, 2018 reflect Southern Company Gas' sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information.
Finite-lived Intangible Assets Amortization Expense	Amortization associated with other intangible assets was as follows: Three Months Ended Six Months Ended June 30, 2018 (in millions) Southern Company $ 23 $ 50 Southern Power $ 6 $ 13 Southern Company Gas $ 14 $ 31
Schedule of Cash and Cash Equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at June 30, 2018 and/or December 31, 2017 : Southern Company Southern Company Gas (in millions) At June 30, 2018 Cash and cash equivalents $ 1,980 $ 69 Cash and cash equivalents classified as assets held for sale 31 — Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,017 $ 75 Southern Company Southern Power Southern Company Gas (in millions) At December 31, 2017 Cash and cash equivalents $ 2,130 $ 129 $ 73 Restricted cash: Other accounts and notes receivable 5 — 5 Deferred charges and other assets 12 11 — Total cash, cash equivalents, and restricted cash $ 2,147 $ 140 $ 78
Restrictions on Cash and Cash Equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at June 30, 2018 and/or December 31, 2017 : Southern Company Southern Company Gas (in millions) At June 30, 2018 Cash and cash equivalents $ 1,980 $ 69 Cash and cash equivalents classified as assets held for sale 31 — Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,017 $ 75 Southern Company Southern Power Southern Company Gas (in millions) At December 31, 2017 Cash and cash equivalents $ 2,130 $ 129 $ 73 Restricted cash: Other accounts and notes receivable 5 — 5 Deferred charges and other assets 12 11 — Total cash, cash equivalents, and restricted cash $ 2,147 $ 140 $ 78

Contingencies and Regulatory 24

Contingencies and Regulatory Matters - (Tables)	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Cost Recovery Clauses	The balance of each regulatory clause recovery on the balance sheet follows: Regulatory Clause Balance Sheet Line Item June 30, December 31, (in millions) Rate CNP Compliance Deferred under recovered regulatory clause revenues $ 30 $ 17 Rate CNP PPA Deferred under recovered regulatory clause revenues 11 12 Retail Energy Cost Recovery Deferred under recovered regulatory clause revenues 80 25 Under recovered regulatory clause revenues 28 — Natural Disaster Reserve Other regulatory liabilities, deferred 30 38 Regulatory clause recovery balances included in the balance sheets are as follows: Regulatory Clause Balance Sheet Line Item June 30, December 31, (in millions) Fuel Cost Recovery Under recovered regulatory clause revenues $ — $ 22 Fuel Cost Recovery Other regulatory liabilities, current 5 — Purchased Power Capacity Recovery Under recovered regulatory clause revenues 2 2 Environmental Cost Recovery (*) Under recovered regulatory clause revenues 1 2 Energy Conservation Cost Recovery Other regulatory liabilities, current 1 — (*) At June 30, 2018 and December 31, 2017 , the under recovered balance included in the balance sheets represents the current portion of the regulatory assets associated with projected environmental expenditures of approximately $11 million and $13 million , respectively, partially offset by the over recovered environmental cost recovery balance of approximately $10 million and $11 million , respectively.
Revised Cost and Schedule	Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4 by the expected in-service dates of November 2021 and November 2022, respectively, is as follows: (in billions) Base project capital cost forecast (a)(b) $ 8.0 Construction contingency estimate 0.4 Total project capital cost forecast (a)(b) 8.4 Net investment as of June 30, 2018 (b) (4.0 ) Remaining estimate to complete (a) $ 4.4 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $350 million . (b) Net of $1.7 billion received from Toshiba in 2017 under the Guarantee Settlement Agreement and $188 million in Customer Refunds recognized as a regulatory liability in 2017.

Revenue from Contracts with C25

Revenue from Contracts with Customers (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following tables disaggregate revenue sources for the three and six months ended June 30, 2018 : For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,579 $ 3,118 Commercial 1,315 2,557 Industrial 814 1,569 Other 32 64 Natural gas distribution revenues 642 1,865 Alternative revenue programs (b) (4 ) (27 ) Total retail electric and gas distribution revenues $ 4,378 $ 9,146 Wholesale energy revenues (c)(d) 459 928 Wholesale capacity revenues (d) 152 302 Other natural gas revenues (e) 68 476 Other revenues (f) 570 1,147 Total operating revenues $ 5,627 $ 11,999 (a) Retail electric revenues include $18 million and $36 million of leases for the three and six months ended June 30, 2018 , respectively, and a net increase of $68 million and $101 million for the three and six months ended June 30, 2018 , respectively, from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 3 to the financial statements of Southern Company under "Regulatory Matters" in Item 8 of the Form 10-K for additional information on cost recovery mechanisms. (b) See Note 1 to the financial statements of Southern Company under "Revenues" in Item 8 of the Form 10-K for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (c) Wholesale energy revenues include $61 million and $155 million for the three and six months ended June 30, 2018 , respectively, of revenues accounted for as derivatives, primarily related to physical energy sales in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $118 million and $31 million , respectively, for the three months ended June 30, 2018 and $187 million and $61 million , respectively, for the six months ended June 30, 2018 of PPA contracts accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $1.3 billion and $3.3 billion for the three and six months ended June 30, 2018 , respectively, of which $0.7 billion and $1.8 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (L) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other revenues include $89 million and $183 million for the three and six months ended June 30, 2018 , respectively, of revenues not accounted for under ASC 606. Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) For the Three Months Ended June 30, 2018 Operating revenues Retail revenues (a)(b) Residential $ 557 $ 785 $ 172 $ 65 Commercial 402 749 96 68 Industrial 372 335 31 76 Other 7 20 2 3 Total retail electric revenues $ 1,338 $ 1,889 $ 301 $ 212 Wholesale energy revenues (c) 71 26 21 73 Wholesale capacity revenues 25 13 6 1 Other revenues (b)(d) 69 120 16 11 Total operating revenues $ 1,503 $ 2,048 $ 344 $ 297 For the Six Months Ended June 30, 2018 Operating revenues Retail revenues (a)(b) Residential $ 1,127 $ 1,529 $ 337 $ 125 Commercial 774 1,466 188 130 Industrial 710 650 63 146 Other 13 43 3 5 Total retail electric revenues $ 2,624 $ 3,688 $ 591 $ 406 Wholesale energy revenues (c) 172 66 56 167 Wholesale capacity revenues 49 27 12 5 Other revenues (b)(d) 131 227 33 20 Total operating revenues $ 2,976 $ 4,008 $ 692 $ 598 (a) Retail revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include a net increase or (net reduction) of $78 million , $3 million , $(12) million , and $(1) million , respectively, for the three months ended June 30, 2018 and $125 million , $12 million , $(28) million , and $(8) million , respectively, for the six months ended June 30, 2018 related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 3 to the financial statements of Alabama Power, Georgia Power, Gulf Power, and Mississippi Power under "Retail Regulatory Matters" in Item 8 of the Form 10-K for additional information on cost recovery mechanisms. (b) Retail revenues and other revenues at Georgia Power include $18 million and $33 million , respectively, for the three months ended June 30, 2018 and $36 million and $66 million , respectively, for the six months ended June 30, 2018 of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power and Georgia Power include $4 million and $5 million , respectively, for the three months ended June 30, 2018 and $9 million and $13 million , respectively, for the six months ended June 30, 2018 accounted for as derivatives primarily related to physical energy sales in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power, Georgia Power, and Gulf Power include $26 million , $26 million , and $2 million , respectively, for the three months ended June 30, 2018 and $52 million , $53 million , and $4 million , respectively, for the six months ended June 30, 2018 of revenues not accounted for under ASC 606. For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Power PPA capacity revenues (a) $ 144 $ 282 PPA energy revenues (a) 302 556 Non-PPA revenues (b) 106 221 Other revenues 3 5 Total operating revenues $ 555 $ 1,064 (a) PPA capacity revenues and PPA energy revenues include $47 million and $127 million , respectively, for the three months ended June 30, 2018 and $94 million and $203 million , respectively, for the six months ended June 30, 2018 related to PPAs accounted for as leases. See Note 1 to the financial statements of Southern Power under "Revenues" in Item 8 of the Form 10-K for additional information on capacity revenues accounted for as leases. (b) Non-PPA revenues include $50 million and $129 million for the three and six months ended June 30, 2018 , respectively, of revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. See Note 1 to the financial statements of Southern Power under "Revenues" in Item 8 of the Form 10-K and Note (I) for additional information on energy-related derivative contracts. For the Three Months Ended June 30, 2018 For the Six Months Ended June 30, 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 273 $ 933 Commercial 76 268 Transportation 7 24 Industrial 228 505 Other 58 135 Alternative revenue programs (a) (4 ) (27 ) Total natural gas distribution revenues $ 638 $ 1,838 Gas marketing services (b) 89 359 Wholesale gas services (c) (15 ) 131 Gas midstream operations 18 40 Other revenues — 1 Total operating revenues $ 730 $ 2,369 (a) See Note 1 to the financial statements of Southern Company Gas under "Revenues" in Item 8 of the Form 10-K for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Gas marketing services includes $4 million for the six months ended June 30, 2018 of revenues not accounted for under ASC 606. (c) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $1.3 billion and $3.3 billion for the three and six months ended June 30, 2018 , respectively, of which $0.7 billion and $1.8 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (L) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues and Note (I) for additional information on energy-related derivative contracts.
Contract with Customer, Asset and Liability	The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers as of June 30, 2018 : Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,785 $ 33 $ 36 Alabama Power 603 — 10 Georgia Power 840 9 9 Gulf Power 169 — 1 Mississippi Power 83 — — Southern Power 136 — 4 Southern Company Gas 570 — 1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	Revenues from contracts with customers related to these performance obligations remaining at June 30, 2018 are expected to be recognized as follows: 2018 2019 2020 2021 2022 2023 and Thereafter (in millions) Southern Company (*) $ 263 $ 352 $ 322 $ 322 $ 310 $ 1,960 Alabama Power 11 22 22 26 23 161 Georgia Power 20 41 38 40 30 113 Gulf Power 11 22 — — — — Mississippi Power 2 3 3 1 — — Southern Power (*) 211 310 283 277 276 1,809 (*) Excludes amounts related to held for sale assets. See Note (J) under " Southern Company's Sale of Gulf Power " and " Southern Power – Sale of Florida Plants " for additional information.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on a Recurring Basis	As of June 30, 2018 , 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 June 30, 2018: 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) $ 287 $ 166 $ — $ — $ 453 Foreign currency derivatives — 132 — — 132 Nuclear decommissioning trusts (c) 798 998 — 33 1,829 Cash equivalents 1,449 — — — 1,449 Other investments 9 — 1 — 10 Total $ 2,543 $ 1,296 $ 1 $ 33 $ 3,873 Liabilities: Energy-related derivatives (a)(b) $ 422 $ 151 $ — $ — $ 573 Interest rate derivatives — 68 — — 68 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ 422 $ 242 $ 22 $ — $ 686 Alabama Power Assets: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Nuclear decommissioning trusts: (d) Domestic equity 440 86 — — 526 Foreign equity 61 55 — — 116 U.S. Treasury and government agency securities — 18 — — 18 Corporate bonds 28 158 — — 186 Mortgage and asset backed securities — 18 — — 18 Private equity — — — 33 33 Other 7 — — — 7 Cash equivalents 495 — — — 495 Total $ 1,031 $ 343 $ — $ 33 $ 1,407 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Fair Value Measurements Using: As of June 30, 2018: 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 $ — $ 7 $ — $ — $ 7 Nuclear decommissioning trusts: (d) (e) Domestic equity 242 1 — — 243 Foreign equity — 135 — — 135 U.S. Treasury and government agency securities — 239 — — 239 Municipal bonds — 78 — — 78 Corporate bonds — 164 — — 164 Mortgage and asset backed securities — 41 — — 41 Other 19 5 — — 24 Total $ 261 $ 670 $ — $ — $ 931 Liabilities: Energy-related derivatives $ — $ 19 $ — $ — $ 19 Interest rate derivatives — 6 — — 6 Total $ — $ 25 $ — $ — $ 25 Gulf Power Assets: Cash equivalents $ 27 $ — $ — $ — $ 27 Liabilities: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 205 — — — 205 Total $ 205 $ 3 $ — $ — $ 208 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Fair Value Measurements Using: As of June 30, 2018: 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 $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 132 — — 132 Total $ — $ 135 $ — $ — $ 135 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ — $ 26 $ 22 $ — $ 48 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 287 $ 144 $ — $ — $ 431 Cash equivalents 1 — — — 1 Total $ 288 $ 144 $ — $ — $ 432 Liabilities: Energy-related derivatives (a)(b) $ 422 $ 99 $ — $ — $ 521 (a) Excludes $3 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $183 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 June 30, 2018 , approximately $63 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 June 30, 2018 , the fair value measurements of private equity investments held in the nuclear decommissioning trusts 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 June 30, 2018: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 33 $ 33 Not Applicable Not Applicable Alabama Power $ 33 $ 33 Not Applicable Not Applicable
Financial Instruments for Which Carrying Amount Did Not Equal Fair Value	As of June 30, 2018 , 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 $ 45,806 $ 46,481 Alabama Power 8,119 8,435 Georgia Power 10,294 10,499 Gulf Power 1,285 1,311 Mississippi Power 1,779 1,760 Southern Power 5,037 5,094 Southern Company Gas 5,823 5,957

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Earnings per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended June 30, 2018 Three Months Ended June 30, 2017 Six Months Ended June 30, 2018 Six Months Ended June 30, 2017 (in millions) As reported shares 1,014 998 1,012 996 Effect of stock-based compensation — 7 5 7 Diluted shares 1,014 1,005 1,017 1,003
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 (a) (in thousands) (in millions) Balance at December 31, 2017 1,008,532 (929 ) $ 24,167 $ — $ 1,361 $ 25,528 Consolidated net income attributable to Southern Company — — 784 — — 784 Other comprehensive income — — 41 — — 41 Stock issued 6,590 — 222 — — 222 Stock-based compensation — — 48 — — 48 Cash dividends on common stock — — (1,194 ) — — (1,194 ) Contributions from noncontrolling interests — — — — 31 31 Distributions to noncontrolling interests — — — — (42 ) (42 ) Net income attributable to noncontrolling interests — — — — 17 17 Sale of SPSH noncontrolling interests (b) — — (407 ) — 1,690 1,283 Other — (57 ) (25 ) — (1 ) (26 ) Balance at June 30, 2018 1,015,122 (986 ) $ 23,636 $ — $ 3,056 $ 26,692 Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — (723 ) — — (723 ) Other comprehensive income (loss) — — (11 ) — — (11 ) Stock issued 9,129 — 417 — — 417 Stock-based compensation — — 72 — — 72 Cash dividends on common stock — — (1,134 ) — — (1,134 ) Preference stock redemption — — — (150 ) — (150 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (40 ) (40 ) Net income attributable to noncontrolling interests — — — — 16 16 Reclassification from redeemable noncontrolling interests — — — — 114 114 Other — (49 ) (7 ) 3 1 (3 ) Balance at June 30, 2017 1,000,342 (868 ) $ 23,372 $ 462 $ 1,407 $ 25,241 (a) Primarily related to Southern Power Company and excludes redeemable noncontrolling interests. See Note 10 to the financial statements of Southern Power in Item 8 of the Form 10-K for additional information. (b) See Note (J) under "Southern Power – Sale of Solar Facility Interests " for additional information.

Financing (Tables)

Financing (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Credit Arrangements by Company	The following table outlines the committed credit arrangements by company as of June 30, 2018 : Expires Executable Term Loans Expires Within One Year Company 2018 2019 2020 2022 Total Unused One Year Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — Alabama Power 2 31 500 800 1,333 1,333 — — 33 Georgia Power — — — 1,750 1,750 1,736 — — — Gulf Power 20 25 235 — 280 280 45 45 — Mississippi Power 100 — — — 100 100 — — 100 Southern Power Company (b) — — — 750 750 728 — — — Southern Company Gas (c) — — — 1,900 1,900 1,895 — — — Other — 30 — — 30 30 — — 30 Southern Company Consolidated $ 122 $ 86 $ 735 $ 7,200 $ 8,143 $ 8,101 $ 45 $ 45 $ 163 (a) Represents the Southern Company parent entity. (b) Does not include Southern Power's $120 million continuing letter of credit facility for standby letters of credit expiring in 2019, of which $23 million remains unused at June 30, 2018 . (c) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.4 billion of these arrangements. Southern Company Gas' committed credit arrangements also include $500 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 six months of 2018 : Company Senior Note Issuances Senior Note Maturities, Redemptions, and Repurchases Revenue Bond Other Long-Term Debt Redemptions and Maturities (*) (in millions) Alabama Power $ 500 $ — $ — $ — Georgia Power — 1,000 398 104 Mississippi Power 600 — — 900 Southern Power — 350 — 420 Southern Company Gas — — 200 — Other — — — 7 Southern Company Consolidated $ 1,100 $ 1,350 $ 598 $ 1,431 (*) Includes reductions in capital lease obligations resulting from cash payments under capital leases.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2018
Retirement Benefits [Abstract]
Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three and six months ended June 30, 2018 and 2017 are presented in the following tables. Three Months Ended June 30, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 89 $ 20 $ 21 $ 4 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 5 2 9 Expected return on plan assets (235 ) (53 ) (74 ) (10 ) (10 ) (2 ) (17 ) Amortization: Prior service costs 1 1 1 — — — — Regulatory asset — — — — — — 4 Net (gain)/loss 54 13 17 3 2 — 3 Net periodic pension cost (income) $ 25 $ 6 $ — $ 2 $ 1 $ 2 $ 7 Postretirement Benefits Service cost $ 6 $ 2 $ 1 $ 1 $ 1 $ — $ — Interest cost 18 4 7 — 1 — 3 Expected return on plan assets (17 ) (7 ) (7 ) (1 ) (1 ) — (2 ) Amortization: Prior service costs 1 1 1 — — — — Regulatory asset — — — — — — 2 Net (gain)/loss 4 1 2 — — — — Net periodic postretirement benefit cost $ 12 $ 1 $ 4 $ — $ 1 $ — $ 3 Six Months Ended June 30, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 179 $ 39 $ 43 $ 8 $ 8 $ 4 $ 16 Interest cost 232 50 70 10 10 3 19 Expected return on plan assets (471 ) (104 ) (148 ) (20 ) (20 ) (5 ) (35 ) Amortization: Prior service costs 2 1 1 — — — (1 ) Regulatory asset — — — — — — 7 Net (gain)/loss 107 27 34 5 5 1 6 Net periodic pension cost (income) $ 49 $ 13 $ — $ 3 $ 3 $ 3 $ 12 Postretirement Benefits Service cost $ 12 $ 3 $ 3 $ 1 $ 1 $ — $ 1 Interest cost 37 8 14 1 2 — 5 Expected return on plan assets (34 ) (13 ) (13 ) (1 ) (1 ) — (4 ) Amortization: Regulatory asset 3 2 1 — — — 3 Net (gain)/loss 7 1 4 — — — — Net periodic postretirement benefit cost $ 25 $ 1 $ 9 $ 1 $ 2 $ — $ 5 Three Months Ended June 30, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 74 $ 16 $ 18 $ 4 $ 3 $ 5 Interest cost 113 24 35 5 5 10 Expected return on plan assets (225 ) (49 ) (70 ) (9 ) (10 ) (17 ) Amortization: Prior service costs 3 — 1 — 1 (1 ) Net (gain)/loss 41 11 14 1 2 5 Net periodic pension cost (income) $ 6 $ 2 $ (2 ) $ 1 $ 1 $ 2 Postretirement Benefits Service cost $ 6 $ 2 $ 1 $ 1 $ 1 $ — Interest cost 20 4 8 — 1 2 Expected return on plan assets (17 ) (8 ) (6 ) (1 ) (1 ) (1 ) Amortization: Prior service costs 1 1 1 — — — Net (gain)/loss 5 1 1 — — 1 Net periodic postretirement benefit cost $ 15 $ — $ 5 $ — $ 1 $ 2 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017. Six Months Ended June 30, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 147 $ 32 $ 37 $ 7 $ 7 $ 11 Interest cost 227 48 69 10 10 20 Expected return on plan assets (449 ) (98 ) (141 ) (19 ) (20 ) (35 ) Amortization: Prior service costs 6 1 2 — 1 (1 ) Net (gain)/loss 81 21 28 3 4 10 Net periodic pension cost (income) $ 12 $ 4 $ (5 ) $ 1 $ 2 $ 5 Postretirement Benefits Service cost $ 12 $ 3 $ 3 $ 1 $ 1 $ 1 Interest cost 40 9 15 1 2 5 Expected return on plan assets (33 ) (14 ) (12 ) (1 ) (1 ) (3 ) Amortization: Prior service costs 3 2 1 — — (1 ) Net (gain)/loss 7 1 3 — — 2 Net periodic postretirement benefit cost $ 29 $ 1 $ 10 $ 1 $ 2 $ 4 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.

Derivatives (Tables)

Derivatives (Tables)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Energy-Related Derivatives	At June 30, 2018 , 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 (*) 701 2022 2029 Alabama Power 82 2022 — Georgia Power 174 2022 — Gulf Power 13 2020 — Mississippi Power 66 2022 — Southern Power 14 2020 — Southern Company Gas (*) 352 2020 2029 (*) 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 3.9 billion mmBtu and short natural gas positions of 3.6 billion mmBtu as of June 30, 2018 , which is also included in Southern Company's total volume.
Schedule of Interest Rate Derivatives	At June 30, 2018 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value Gain (Loss) at June 30, 2018 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month June 2020 $ (6 ) Southern Company (*) 1,500 2.35% 1-month July 2021 (57 ) Georgia Power 500 1.95% 3-month December 2018 (3 ) Georgia Power 200 4.25% 3-month December 2019 (3 ) Southern Company Consolidated $ 2,500 $ (69 ) (*) Represents the Southern Company parent entity.
Schedule of Foreign Currency Derivatives	At June 30, 2018 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at June 30, 2018 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 54 Southern Power 564 3.78% 500 1.85% June 2026 55 Total $ 1,241 € 1,100 $ 109
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 June 30, 2018 As of December 31, 2017 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/Other current liabilities $ 16 $ 12 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 5 27 7 24 Assets held for sale, current/Liabilities held for sale, current — 8 — — Assets held for sale/Liabilities held for sale — 4 — — Total derivatives designated as hedging instruments for regulatory purposes $ 21 $ 51 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 3 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Interest rate derivatives: Other current assets/Other current liabilities — 15 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 53 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 132 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 135 $ 95 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 239 $ 272 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 189 246 170 215 Total derivatives not designated as hedging instruments $ 428 $ 518 $ 550 $ 652 Gross amounts recognized $ 584 $ 664 $ 700 $ 794 Gross amounts offset (a) $ (306 ) $ (489 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 278 $ 175 $ 295 $ 196 As of June 30, 2018 As of December 31, 2017 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/Other current liabilities $ 6 $ 3 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 2 6 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 8 $ 9 $ 4 $ 10 Gross amounts recognized $ 8 $ 9 $ 4 $ 10 Gross amounts offset $ (4 ) $ (4 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 4 $ 5 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 5 $ 5 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 2 14 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 7 $ 19 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 5 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 6 $ — $ 5 Gross amounts recognized $ 7 $ 25 $ 6 $ 24 Gross amounts offset $ (7 ) $ (7 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 18 $ — $ 18 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ — $ 8 $ — $ 14 Other deferred charges and assets/Other deferred credits and liabilities — 4 — 7 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 12 $ — $ 21 Gross amounts recognized $ — $ 12 $ — $ 21 Gross amounts offset $ — $ — $ — $ — Net amounts recognized in the Balance Sheets $ — $ 12 $ — $ 21 As of June 30, 2018 As of December 31, 2017 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 $ 2 $ 3 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 6 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 9 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ — $ 1 $ — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ — $ 1 $ — Gross amounts recognized $ 3 $ 9 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ 1 $ 7 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 132 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 135 $ 26 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Gross amounts recognized $ 135 $ 26 $ 132 $ 36 Gross amounts offset $ (2 ) $ (2 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 133 $ 24 $ 129 $ 33 As of June 30, 2018 As of December 31, 2017 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 $ 3 $ 1 $ 5 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — — Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 2 $ 5 $ 8 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 $ — $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 239 $ 272 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 189 246 170 215 Total derivatives not designated as hedging instruments $ 428 $ 518 $ 549 $ 649 Gross amounts of recognized $ 431 $ 521 $ 554 $ 660 Gross amounts offset (a) $ (291 ) $ (474 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 140 $ 47 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $183 million and $193 million as of June 30, 2018 and December 31, 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $3 million and $11 million as of June 30, 2018 and December 31, 2017 , respectively.
Pre-tax Effects of Unrealized Derivative Gains (Losses) Arising from Energy-Related Derivative Instruments	At June 30, 2018 and December 31, 2017 , 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 June 30, 2018 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (4 ) $ (1 ) $ (1 ) $ (8 ) $ (1 ) $ (1 ) Other regulatory assets, deferred (20 ) (4 ) (11 ) (4 ) (5 ) — Assets held for sale, current (8 ) — — — — — Assets held for sale (4 ) — — — — — Other regulatory liabilities, current 8 4 — — — 4 Total energy-related derivative gains (losses) $ (28 ) $ (1 ) $ (12 ) $ (12 ) $ (6 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $2 million at June 30, 2018 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2017 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (34 ) $ (4 ) $ (7 ) $ (14 ) $ (5 ) $ (4 ) Other regulatory assets, deferred (18 ) (3 ) (6 ) (7 ) (2 ) — Other regulatory liabilities, current 7 — — — — 7 Other regulatory liabilities, deferred 1 1 — — — — Total energy-related derivative gains (losses) $ (44 ) $ (6 ) $ (13 ) $ (21 ) $ (7 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $6 million at December 31, 2017 .
Pre-tax Effects of Interest Rate Derivatives, Designated as Cash Flow Hedging Instruments	For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives $ — $ (9 ) $ 12 $ (20 ) Interest rate derivatives — (1 ) (2 ) (1 ) Foreign currency derivatives (73 ) 71 (21 ) 67 Total $ (73 ) $ 61 $ (11 ) $ 46 Southern Power Energy-related derivatives $ (1 ) $ (7 ) $ 10 $ (15 ) Foreign currency derivatives (73 ) 71 (21 ) 67 Total $ (74 ) $ 64 $ (11 ) $ 52 Southern Company Gas Energy-related derivatives $ 1 $ (2 ) $ 2 $ (4 )
Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location	For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Company Depreciation and amortization $ 783 $ 754 $ 1,552 $ 1,469 Gain (loss) on cash flow hedges (a) Energy-related derivatives 1 (2 ) 2 (6 ) Interest expense, net of amounts capitalized (470 ) (424 ) (928 ) (840 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (6 ) (5 ) (11 ) (10 ) Foreign currency derivatives (7 ) (5 ) (12 ) (12 ) Gain (loss) on fair value hedges (b) Interest rate derivatives (7 ) 7 (31 ) (1 ) Other income (expense), net 78 52 138 98 Gain (loss) on cash flow hedges (a)(c) Foreign currency derivatives (73 ) 79 (37 ) 96 Cost of natural gas 228 232 949 951 Gain (loss) on cash flow hedges (a) Energy-related derivatives — — (2 ) — Alabama Power Interest expense, net of amounts capitalized $ (80 ) $ (77 ) $ (158 ) $ (153 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (1 ) (2 ) (3 ) (3 ) Georgia Power Interest expense, net of amounts capitalized $ (102 ) $ (104 ) $ (208 ) $ (205 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (2 ) (1 ) (3 ) (3 ) Gain (loss) on fair value hedges (b) Interest rate derivatives 2 — (1 ) (1 ) Mississippi Power Interest expense, net of amounts capitalized $ (21 ) $ (17 ) $ (39 ) $ (37 ) Gain (loss) on cash flow hedges (a) Interest rate derivatives (1 ) — (1 ) (1 ) Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Southern Power Depreciation and amortization $ 125 $ 129 $ 240 $ 247 Gain (loss) on cash flow hedges (a) Energy-related derivatives 1 (2 ) 2 (6 ) Interest expense, net of amounts capitalized (46 ) (48 ) (93 ) (97 ) Gain (loss) on cash flow hedges (a) Foreign currency derivatives (7 ) (5 ) (12 ) (12 ) Other income (expense), net 2 2 5 (2 ) Gain (loss) on cash flow hedges (a)(c) Foreign currency derivatives (73 ) 79 (37 ) 96 Southern Company Gas Cost of natural gas $ 228 $ 232 $ 949 $ 951 Gain (loss) on cash flow hedges (a) Energy-related derivatives — — (2 ) — (a) Amounts reflect gains or losses on cash flow hedges that were reclassified from accumulated OCI into income. (b) For fair value hedges presented above, generally changes in the fair value of the derivative contracts are equal to changes in the fair value of the underlying debt and have no material impact on income. (c) 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.
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location	As of June 30, 2018 and December 31, 2017, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items As of June 30, 2018 As of December 31, 2017 As of June 30, 2018 As of December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (497 ) $ (746 ) $ 3 $ 3 Long-term Debt (2,528 ) (2,553 ) 63 35 Georgia Power Securities due within one year $ (497 ) $ (746 ) $ 3 $ 3 Long-term Debt (497 ) (498 ) 3 1
Pre-tax Effect of Interest Rate and Energy Related Derivatives	For the three and six months ended June 30, 2018 and 2017 , the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income were as follows: Gain (Loss) Three Months Ended June 30, Six Months Ended June 30, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives: Natural gas revenues (*) $ (28 ) $ 16 $ (43 ) $ 65 Cost of natural gas 2 (2 ) 4 (4 ) Total derivatives in non-designated hedging relationships $ (26 ) $ 14 $ (39 ) $ 61 Southern Company Gas Energy-related derivatives: Natural gas revenues (*) $ (28 ) $ 16 $ (43 ) $ 65 Cost of natural gas 2 (2 ) 4 (4 ) Total derivatives in non-designated hedging relationships $ (26 ) $ 14 $ (39 ) $ 61 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of $15 million for the six months ended June 30, 2017 and immaterial amounts for all other periods presented.

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions	Project Facility Resource Seller; Acquisition Date Approximate Nameplate Capacity ( MW ) Location Southern Power Percentage Ownership Actual COD PPA Contract Period Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC January 26, 2018 20 Kern County, CA 100% of Class B (*) March 2018 20 years (*) Southern Power owns 100% of the class B membership interests under a tax equity partnership agreement.
Schedule of Construction Projects	Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Under Construction as of June 30, 2018 Cactus Flats (a) Wind 148 Concho County, TX July 2018 12-15 years Mankato Natural Gas 345 Mankato, MN First half 2019 20 years Wild Horse Mountain (b) Wind 100 Pushmataha County, OK Fourth quarter 2019 20 years (a) In July 2017, Southern Power purchased 100% of the Cactus Flats facility and commenced construction. Subsequent to June 30, 2018, the facility was placed in service and Southern Power expects to close on a tax equity partnership agreement, which would result in Southern Power owning 100% of the class B membership interests. (b) In May 2018, Southern Power purchased 100% of the Wild Horse Mountain facility and commenced construction. Southern Power may enter into a tax equity partnership agreement, in which case it would then own 100% of the class B membership interests.
Disposal Groups, Including Discontinued Operations	The following table provides each company's major classes of assets and liabilities classified as held for sale at June 30, 2018 : Southern Company Southern Power Southern Company Gas (in millions) Assets Held for Sale: Current assets $ 487 $ 17 $ 81 Total property, plant, and equipment 5,462 168 1,408 Goodwill and other intangible assets 668 — 668 Other non-current assets 705 15 141 Total Assets Held for Sale $ 7,322 $ 200 $ 2,298 Liabilities Held for Sale: Current liabilities $ 354 $ 2 $ 61 Long-term debt 1,285 — — Accumulated deferred income taxes 566 — 26 Other non-current liabilities 1,334 — 325 Total Liabilities Held for Sale $ 3,539 $ 2 $ 412 Gulf Power and the Florida Plants represent individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax profit for these components for the three and six months ended June 30, 2018 and 2017 is presented below: For the Three Months For the Six Months 2018 2017 2018 2017 (in millions) (in millions) Earnings before income taxes: Gulf Power $ 31 $ 61 $ 87 $ 95 Southern Power's Florida Plants (*) $ 14 $ 11 $ 24 $ 20 (*) Excludes any allocation of interest from Southern Power's corporate debt.

Variable Interest Entity and 32

Variable Interest Entity and Equity Method Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Regulated Operations [Abstract]
Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments as of June 30, 2018 and December 31, 2017 and related income from those investments for the three and six -month periods ended June 30, 2018 and June 30, 2017 were as follows: Investment Balance June 30, 2018 December 31, 2017 (in millions) SNG $ 1,258 $ 1,262 Atlantic Coast Pipeline 56 41 PennEast Pipeline 67 57 Triton 42 42 Pivotal JAX LNG, LLC 52 44 Horizon Pipeline 31 30 Other 1 1 Total $ 1,507 $ 1,477 Selected financial information of SNG for the three and six months ended June 30, 2018 and June 30, 2017 is as follows: Income Statement Information Three Months Ended June 30, 2018 Three Months Ended June 30, 2017 Six Months Ended June 30, 2018 Six Months Ended June 30, 2017 (in millions) Revenues $ 146 $ 143 $ 306 $ 298 Operating income $ 60 $ 63 $ 159 $ 147 Net income $ 54 $ 48 $ 132 $ 114
Schedule of Other Nonoperating Income, by Component	Earnings from Equity Method Investments Three Months Ended Three Months Ended Six Months Ended Six Months (in millions) SNG $ 27 $ 24 $ 66 $ 58 PennEast Pipeline 1 1 2 4 Atlantic Coast Pipeline 1 2 3 3 Triton 1 2 2 2 Horizon Pipeline 1 — 1 1 Total $ 31 $ 29 $ 74 $ 68

Segment and Related Informati33

Segment and Related Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Financial Data for Business Segments	Financial data for business segments and products and services for the three and six months ended June 30, 2018 and 2017 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 June 30, 2018: Operating revenues $ 4,124 $ 555 $ (114 ) $ 4,565 $ 730 $ 381 $ (49 ) $ 5,627 Segment net income (loss) (a)(b)(c) (48 ) 22 — (26 ) (31 ) (100 ) 3 (154 ) Six Months Ended June 30, 2018: Operating revenues $ 8,104 $ 1,064 $ (220 ) $ 8,948 $ 2,369 $ 782 $ (100 ) $ 11,999 Segment net income (loss) (a)(b)(c)(d) 563 143 — 706 248 (174 ) 4 784 At June 30, 2018: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 298 $ — $ 5,315 Total assets 73,634 15,428 (313 ) 88,749 22,112 3,707 (1,791 ) 112,777 Three Months Ended June 30, 2017: Operating revenues $ 4,157 $ 529 $ (101 ) $ 4,585 $ 716 $ 166 $ (37 ) $ 5,430 Segment net income (loss) (a)(b) (1,442 ) 82 — (1,360 ) 49 (68 ) (2 ) (1,381 ) Six Months Ended June 30, 2017: Operating revenues $ 7,943 $ 979 $ (206 ) $ 8,716 $ 2,276 $ 289 $ (79 ) $ 11,202 Segment net income (loss) (a)(b)(e) (1,010 ) 151 — (859 ) 288 (152 ) — (723 ) At December 31, 2017: Goodwill $ — $ 2 $ — $ 2 $ 5,967 $ 299 $ — $ 6,268 Total assets 72,204 15,206 (325 ) 87,085 22,987 2,552 (1,619 ) 111,005 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $1.1 billion ( $0.8 billion after tax) and $3.0 billion ( $2.1 billion after tax) for the three months ended June 30, 2018 and 2017 , respectively, and $1.1 billion ( $0.8 billion after tax) and $3.1 billion ( $2.2 billion after tax) for the six months ended June 30, 2018 and 2017 , respectively. See Note 3 to the financial statements of Southern Company under "Kemper County Energy Facility" in Item 8 of the Form 10-K and Note (B) under " Nuclear Construction " and " Kemper County Energy Facility " for additional information. (c) Segment net income (loss) for Southern Power includes a pre-tax impairment charge of $119 million ( $89 million after tax) for the three and six months ended June 30, 2018 related to the pending sale of Southern Power's Florida Plants. See Note (J) under "Southern Power – Sale of Florida Plants " for additional information. (d) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the six months ended June 30, 2018 related to the sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. (e) Segment net income (loss) for the traditional electric operating companies 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 six months ended June 30, 2017. See Note 3 to the financial statements of Southern Company under "Regulatory Matters – Gulf Power – Retail Base Rate Cases" in Item 8 of the Form 10-K for additional information. Business segment financial data for the three and six months ended June 30, 2018 and 2017 was as follows: Gas Distribution Operations (a) Gas Marketing Services (b)(c) Wholesale Gas Services (d) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Three Months Ended June 30, 2018: Operating revenues $ 643 $ 89 $ (16 ) $ 18 $ 734 $ 1 $ (5 ) $ 730 Segment net income 68 (76 ) (21 ) 14 (15 ) (16 ) — (31 ) Six Months Ended June 30, 2018: Operating revenues 1,856 359 150 40 2,405 2 (38 ) 2,369 Segment net income 216 (63 ) 83 38 274 (26 ) — 248 Total assets at June 30, 2018: 18,654 1,610 818 2,269 23,351 11,544 (12,783 ) 22,112 Three Months Ended June 30, 2017: Operating revenues $ 603 $ 166 $ (12 ) $ 12 $ 769 $ 3 $ (56 ) $ 716 Segment net income 54 4 (17 ) 9 50 (1 ) — 49 Six Months Ended June 30, 2017: Operating revenues 1,783 454 119 37 2,393 5 (122 ) 2,276 Segment net income 171 35 51 25 282 6 — 288 Total assets at December 31, 2017: 19,358 2,147 1,096 2,241 24,842 12,184 (14,039 ) 22,987 (a) Operating revenues for the three gas distribution operations dispositions were $70 million and $66 million for the three months ended June 30, 2018 and 2017 , respectively, and $237 million and $224 million for the six months ended June 30, 2018 and 2017 , respectively. See Note (J) under " Southern Company Gas " for additional information. (b) Operating revenues for the gas marketing services disposition were $24 million and $32 million for the three months ended June 30, 2018 and 2017 , respectively, and $55 million and $63 million for the six months ended June 30, 2018 and 2017 , respectively. See Note (J) under " Southern Company Gas " for additional information. (c) Segment net income for gas marketing services includes a loss on disposition of $36 million for the three and six months ended June 30, 2018 and a goodwill impairment charge of $42 million for the six months ended June 30, 2018 recorded in contemplation of the sale of Pivotal Home Solutions. See Note (J) under " Southern Company Gas " for additional information. (d) 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) Three Months Ended June 30, 2018 $ 1,336 $ 102 $ 1,438 $ 1,454 $ (16 ) Three Months Ended June 30, 2017 1,531 123 1,654 1,666 (12 ) Six Months Ended June 30, 2018 $ 3,274 $ 269 $ 3,543 $ 3,393 $ 150 Six Months Ended June 30, 2017 3,370 259 3,629 3,510 119
Financial Data for Products and Services	Products and Services Electric Utilities' Revenues Period Retail Wholesale Other Total (in millions) Three Months Ended June 30, 2018 $ 3,740 $ 611 $ 214 $ 4,565 Three Months Ended June 30, 2017 3,777 618 190 4,585 Six Months Ended June 30, 2018 $ 7,308 $ 1,230 $ 410 $ 8,948 Six Months Ended June 30, 2017 7,171 1,149 396 8,716 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended June 30, 2018 $ 638 $ 89 $ 3 $ 730 Three Months Ended June 30, 2017 557 166 (7 ) 716 Six Months Ended June 30, 2018 $ 1,838 $ 359 $ 172 $ 2,369 Six Months Ended June 30, 2017 1,689 454 133 2,276

Introduction - Narrative (Detai

Introduction - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Net income (loss)		$ (127)	$ (1,348)	$ 809	$ (684)
Accretion				95
ALABAMA POWER CO
Related Party Transaction [Line Items]
Net income (loss)		262	235	491	412
Increase in ARO due to new CCR rule	$ 1,200
Accretion				$ 41
Inflation rate assumption				4.50%
Trust earnings rate assumption				7.00%
MISSISSIPPI POWER CO
Related Party Transaction [Line Items]
Net income (loss)		47	(2,053)	$ 40	(2,073)
Increase in ARO due to new CCR rule	11
Accretion				2
GEORGIA POWER CO
Related Party Transaction [Line Items]
Net income (loss)		(396)	352	(44)	616
SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income (loss)		(31)	49	248	288
Wholesale Gas Services | SOUTHERN Co GAS
Related Party Transaction [Line Items]
Inventory write-down		0	$ 0	0	$ 0
Accounting Standards Update 2014-09 | Effect of Change
Related Party Transaction [Line Items]
Net income (loss)		(5)		5
Accounting Standards Update 2014-09 | Effect of Change | SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income (loss)		$ (5)		$ 5
Plant Farley | ALABAMA POWER CO
Related Party Transaction [Line Items]
Increase in ARO	$ 300

Introduction - ASC 606 (Details

Introduction - ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Condensed Statements of Income
Natural gas revenues	$ 706	$ 684	$ 2,314	$ 2,214
Other revenues	395	184	808	326
Other operations and maintenance	1,559	1,356	3,008	2,740
Operating income (loss)	63	(1,649)	1,439	(397)
Other income (expense), net	78	52	138	98
Earnings (loss) before income taxes	(266)	(1,935)	784	(957)
Income taxes (benefit)	(139)	(587)	(25)	(273)
Net income (loss)	(127)	(1,348)	809	(684)
Consolidated net income attributable to Southern Company	(154)	(1,381)	784	(723)
Condensed Statements of Cash Flows
Net income (loss)	(127)	(1,348)	809	(684)
Changes in certain current assets and liabilities:
Receivables			94	107
Other current assets			(40)	(30)
Accrued taxes			213	(132)
Other current liabilities			125	(14)
Condensed Balance Sheets
Unbilled revenues	769		769		$ 810
Other accounts and notes receivable	621		621		698
Other current assets	172		172		199
Other current liabilities	808		808		874
Retained earnings	8,494		8,494		8,885
Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues	713		2,307
Other revenues	393		805
Other operations and maintenance	1,546		2,985
Operating income (loss)	81		1,452
Other income (expense), net	67		118
Earnings (loss) before income taxes	(259)		777
Income taxes (benefit)	(137)		(27)
Net income (loss)	(122)		804
Consolidated net income attributable to Southern Company	(149)		779
Condensed Statements of Cash Flows
Net income (loss)	(122)		804
Changes in certain current assets and liabilities:
Receivables			99
Other current assets			(45)
Accrued taxes			215
Other current liabilities			118
Condensed Balance Sheets
Unbilled revenues	824		824
Other accounts and notes receivable	622		622
Other current assets	116		116
Accrued taxes	542		542
Other current liabilities	815		815
Retained earnings	8,489		8,489
ALABAMA POWER CO
Condensed Statements of Income
Other revenues	69	51	131	108
Other operations and maintenance	402	389	788	772
Operating income (loss)	380	440	752	801
Other income (expense), net	12	15	15	25
Earnings (loss) before income taxes	326	386	636	689
Income taxes (benefit)	64	151	145	277
Net income (loss)	262	235	491	412
Consolidated net income attributable to Southern Company	259	230	484	403
Condensed Statements of Cash Flows
Net income (loss)	262	235	491	412
Changes in certain current assets and liabilities:
Receivables			(153)	(58)
Other current assets			29	12
Accrued taxes			134	52
Other current liabilities			116	7
Condensed Balance Sheets
Unbilled revenues	174		174		162
Other accounts and notes receivable	41		41		55
Other current assets	11		11		5
Other current liabilities	143		143		59
Retained earnings	2,729		2,729		2,647
ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	60		114
Other operations and maintenance	391		767
Operating income (loss)	382		756
Other income (expense), net	10		11
GEORGIA POWER CO
Condensed Statements of Income
Other revenues	120	95	227	191
Other operations and maintenance	457	417	863	816
Operating income (loss)	(472)	621	41	1,105
Other income (expense), net	35	34	73	71
Earnings (loss) before income taxes	(539)	551	(94)	971
Income taxes (benefit)	(143)	199	(50)	355
Net income (loss)	(396)	352	(44)	616
Consolidated net income attributable to Southern Company	(396)	347	(44)	607
Condensed Statements of Cash Flows
Net income (loss)	(396)	352	(44)	616
Changes in certain current assets and liabilities:
Receivables			(103)	(150)
Other current assets			25	(18)
Accrued taxes			(89)	(194)
Other current liabilities			(26)	(6)
Condensed Balance Sheets
Unbilled revenues	276		276		255
Other accounts and notes receivable	81		81		76
Other current assets	23		23		14
Accrued taxes	230		230		344
Other current liabilities	205		205		198
Retained earnings	3,480		3,480		4,215
GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	97		189
Other operations and maintenance	437		828
Operating income (loss)	(475)		38
Other income (expense), net	38		76
Changes in certain current assets and liabilities:
Receivables			(75)
Other current assets			(3)
SOUTHERN Co GAS
Condensed Statements of Income
Natural gas revenues	710	684	2,341	2,205
Other revenues	24	32	55	62
Other operations and maintenance	238	214	514	470
Operating income (loss)	49	95	436	484
Other income (expense), net	3	4	15	10
Earnings (loss) before income taxes	24	80	407	468
Income taxes (benefit)	55	31	159	180
Net income (loss)	(31)	49	248	288
Consolidated net income attributable to Southern Company	(31)	49	248	288
Condensed Statements of Cash Flows
Net income (loss)	(31)	$ 49	248	288
Changes in certain current assets and liabilities:
Receivables			504	418
Other current assets			32	(12)
Accrued taxes			38	(8)
Other current liabilities			24	$ 25
Condensed Balance Sheets
Unbilled revenues	60		60		285
Other accounts and notes receivable	53		53		103
Other current assets	42		42		78
Accrued taxes	63		63		78
Accrued income taxes	86		86		40
Other current liabilities	143		143		159
Retained earnings	(202)		(202)		$ (212)
SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues	717		2,334
Operating income (loss)	56		429
Earnings (loss) before income taxes	31		400
Income taxes (benefit)	57		157
Net income (loss)	(26)		243
Condensed Statements of Cash Flows
Net income (loss)	(26)		243
Changes in certain current assets and liabilities:
Accrued taxes			40
Other current liabilities			17
Condensed Balance Sheets
Accrued income taxes	84		84
Other current liabilities	150		150
Retained earnings	(207)		(207)
Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Natural gas revenues	(7)		7
Other revenues	2		3
Other operations and maintenance	13		23
Operating income (loss)	(18)		(13)
Other income (expense), net	11		20
Earnings (loss) before income taxes	(7)		7
Income taxes (benefit)	(2)		2
Net income (loss)	(5)		5
Consolidated net income attributable to Southern Company	(5)		5
Condensed Statements of Cash Flows
Net income (loss)	(5)		5
Changes in certain current assets and liabilities:
Receivables			(5)
Other current assets			5
Accrued taxes			(2)
Other current liabilities			7
Condensed Balance Sheets
Unbilled revenues	(55)		(55)
Other accounts and notes receivable	(1)		(1)
Other current assets	56		56
Accrued taxes	2		2
Other current liabilities	(7)		(7)
Retained earnings	5		5
Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	9		17
Other operations and maintenance	11		21
Operating income (loss)	(2)		(4)
Other income (expense), net	2		4
Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	23		38
Other operations and maintenance	20		35
Operating income (loss)	3		3
Other income (expense), net	(3)		(3)
Changes in certain current assets and liabilities:
Receivables			(28)
Other current assets			28
Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Natural gas revenues	(7)		7
Operating income (loss)	(7)		7
Earnings (loss) before income taxes	(7)		7
Income taxes (benefit)	(2)		2
Net income (loss)	(5)		5
Condensed Statements of Cash Flows
Net income (loss)	(5)		5
Changes in certain current assets and liabilities:
Accrued taxes			(2)
Other current liabilities			7
Condensed Balance Sheets
Accrued income taxes	2		2
Other current liabilities	(7)		(7)
Retained earnings	$ 5		$ 5

Introduction - Asset Retirement

Introduction - Asset Retirement Obligation (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at December 31, 2017	$ 4,824
Liabilities incurred	1
Liabilities settled	(97)
Accretion	95
Cash flow revisions	1,493
Reclassification to held for sale	(148)
Balance at June 30, 2018	6,168
ALABAMA POWER CO
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at December 31, 2017	1,709
Liabilities incurred	0
Liabilities settled	(19)
Accretion	41
Cash flow revisions	1,451
Reclassification to held for sale	0
Balance at June 30, 2018	3,182
MISSISSIPPI POWER CO
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at December 31, 2017	174
Liabilities incurred	0
Liabilities settled	(15)
Accretion	2
Cash flow revisions	15
Reclassification to held for sale	0
Balance at June 30, 2018	$ 176

Introduction - Nuclear Decommis

Introduction - Nuclear Decommissioning (Details) - ALABAMA POWER CO - Plant Farley $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Public Utility, Property, Plant and Equipment [Line Items]
Beginning year	2,037
Completion year	2,076
Site study costs	$ 1,720
Radiated structures
Public Utility, Property, Plant and Equipment [Line Items]
Site study costs	1,621
Non-radiated structures
Public Utility, Property, Plant and Equipment [Line Items]
Site study costs	$ 99

Introduction - Goodwill (Detail

Introduction - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill [Roll Forward]
Balance at December 31, 2017		$ 6,268		$ 6,268
Impairment				(42)
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				(668)
Balance at June 30, 2018	$ 5,315			5,315
SOUTHERN Co GAS
Goodwill [Roll Forward]
Balance at December 31, 2017		5,967		5,967
Impairment	0	(42)	$ 0	(42)	$ 0
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				(668)
Balance at June 30, 2018	5,015			5,015
SOUTHERN Co GAS | Gas Distribution Operations
Goodwill [Roll Forward]
Balance at December 31, 2017		4,702		4,702
Impairment				0
Sale of Pivotal Home Solutions				0
Reclassification to held for sale				(668)
Balance at June 30, 2018	4,034			4,034
SOUTHERN Co GAS | Gas Marketing Services
Goodwill [Roll Forward]
Balance at December 31, 2017		$ 1,265		1,265
Impairment				(42)
Sale of Pivotal Home Solutions				(242)
Reclassification to held for sale				0
Balance at June 30, 2018	$ 981			$ 981

Introduction - Other Intangible

Introduction - Other Intangibles (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (205)	$ (186)
Total other intangible assets - net	702	873
Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	832	984
Accumulated Amortization	(205)	(186)
Other Intangible Assets, Net	627	798
Total other intangible assets - gross	907	1,059
Total other intangible assets - net	702	873
Customer relationships | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	223	288
Accumulated Amortization	(79)	(83)
Other Intangible Assets, Net	144	205
Trade names | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	70	159
Accumulated Amortization	(17)	(17)
Other Intangible Assets, Net	53	142
Storage and transportation contracts | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(44)	(34)
Other Intangible Assets, Net	20	30
PPA fair value adjustments | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(60)	(47)
Other Intangible Assets, Net	396	409
Other | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	19	17
Accumulated Amortization	(5)	(5)
Other Intangible Assets, Net	14	12
Federal Communications Commission licenses | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets not subject to amortization	75	75
SOUTHERN POWER CO
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(60)	(47)
SOUTHERN POWER CO | PPA fair value adjustments
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(60)	(47)
Other Intangible Assets, Net	396	409
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	246	400
Accumulated Amortization	(121)	(120)
Other Intangible Assets, Net	125	280
Total other intangible assets - net	125	280
SOUTHERN Co GAS | Customer relationships
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	156	221
Accumulated Amortization	(71)	(77)
Other Intangible Assets, Net	85	144
SOUTHERN Co GAS | Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	26	115
Accumulated Amortization	(6)	(9)
Other Intangible Assets, Net	20	106
SOUTHERN Co GAS | Storage and transportation contracts
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(44)	(34)
Other Intangible Assets, Net	$ 20	$ 30

Introduction - Intangibles, Amo

Introduction - Intangibles, Amortization (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 23	$ 50
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	6	13
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 14	$ 31

Introduction - Restricted Cash

Introduction - Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,980	$ 2,130
Restricted cash:
Total cash, cash equivalents, and restricted cash	2,017	2,147	$ 1,455	$ 1,992
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	69	73
Cash and cash equivalents classified as assets held for sale	0
Restricted cash:
Other accounts and notes receivable	6	5
Deferred charges and other assets		0
Total cash, cash equivalents, and restricted cash	75	78	43	24
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	142	129
Restricted cash:
Other accounts and notes receivable		0
Deferred charges and other assets		11
Total cash, cash equivalents, and restricted cash	142	140	$ 116	$ 1,112
Southern Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	1,980	2,130
Cash and cash equivalents classified as assets held for sale	31
Restricted cash:
Other accounts and notes receivable	6	5
Deferred charges and other assets		12
Total cash, cash equivalents, and restricted cash	$ 2,017	$ 2,147

Contingencies and Regulatory 42

Contingencies and Regulatory Matters - General (Details) $ in Thousands	Jun. 12, 2018USD ($)	May 18, 2018USD ($)	May 14, 2018USD ($)	Mar. 02, 2018USD ($)generating_plant	Feb. 07, 2018	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)
ALABAMA POWER CO
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage						46.60%
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage					9.33%
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability						$ 25,000	$ 22,000
GULF POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability						48,000	52,000
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability						$ 305,000	388,000
RE Roserock, LLC | SOUTHERN POWER CO
Loss Contingencies [Line Items]
Ownership percentage by parent						51.00%
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability						$ 2,000
Location One | SOUTHERN Co GAS | Elizabethtown Gas
Loss Contingencies [Line Items]
Environmental remediation liability						$ 77,000	$ 85,000
Alabama Department of Environmental Management (ADEM) | ALABAMA POWER CO
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party				$ 1,250
Number of electric generating plants | generating_plant				5
Deepwater Horizon Oil Spill Litigation Case | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Litigation settlement awarded from other party			$ 18,000
Martin Product Sales, LLC Litigation | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Damages sought by litigation		$ 143,000
Nicor Energy Services Company Litigation | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Litigation amount awarded to other party	$ 11,000
Open Access Transmission Tariff
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage						11.25%
Public utilities, requested return on equity, percentage						8.65%

Contingencies and Regulatory 43

Contingencies and Regulatory Matters - Alabama Power (Details) - USD ($) $ in Millions	Aug. 06, 2018	Jun. 30, 2018	Dec. 31, 2017
ALABAMA POWER CO | Deferred under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Rate CNP Compliance		$ 30	$ 17
Rate CNP PPA		11	12
Retail Energy Cost Recovery		80	25
ALABAMA POWER CO | Under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Retail Energy Cost Recovery		28	0
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Natural Disaster Reserve		$ 30	$ 38
Plant Greene County Units 1 and 2 | Reserve Margin Plan | Subsequent Event | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Accelerated retirement period	4 years

Contingencies and Regulatory 44

Contingencies and Regulatory Matters - Alabama Power Narrative (Details) - ALABAMA POWER CO $ in Millions	Jan. 01, 2019$ / KWH_Kilowatt_hour	May 01, 2018USD ($)$ / KWH_Kilowatt_hour	Apr. 30, 2018$ / KWH_Kilowatt_hour	Jun. 30, 2018USD ($)	Dec. 31, 2025	Dec. 31, 2018USD ($)	May 08, 2018USD ($)
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage				46.60%
Public utilities, allowed weighted common equity return, percentage		6.15%	6.21%
Customer refundable fees, refund payments, tranche one, percentage				25.00%
Customer refundable fees, refund payments, tranche two, percentage				40.00%
Customer refundable fees, refund payments, tranche three, percentage				75.00%
Customer refund liability, noncurrent							$ 50
Customer refund liability, current							$ 257
Current billing rates under rate ecr in terms of per units | $ / KWH_Kilowatt_hour		2.353	2.015
Approved increase (decrease) in fuel rates amount		$ 100
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit, maximum amount used to offset under recovered amounts		$ 30
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit				$ 30
Minimum
Loss Contingencies [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage				6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one				6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two				6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three				7.15%
Maximum
Loss Contingencies [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage				7.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one				6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two				7.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three				7.65%
Customer refundable fees, refund payments, percentage				7.65%
Scenario, Forecast
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage					55.00%
Current billing rates under rate ecr in terms of per units | $ / KWH_Kilowatt_hour	5.910
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit						$ 50

Contingencies and Regulatory 45

Contingencies and Regulatory Matters - Georgia Power (Details) $ in Millions	Apr. 03, 2018USD ($)	Feb. 29, 2020USD ($)	Jun. 30, 2019USD ($)	Oct. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2019	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Effective tax rate					(3.20%)	(28.60%)
Deferred income tax expense (benefit)					$ (338)	$ (270)
GEORGIA POWER CO
Loss Contingencies [Line Items]
Customer refund	$ 330
Effective tax rate					(53.50%)	36.60%
Deferred income tax expense (benefit)	(700)				$ (256)	$ 159
Customer refund liability in absence of base rate case	$ 185
Under recovered fuel balance, threshold for interim fuel rider					200
GEORGIA POWER CO | Maximum
Loss Contingencies [Line Items]
Retail regulatory equity ratio	0.55
GEORGIA POWER CO | Other current liabilities
Loss Contingencies [Line Items]
Over (under) recovered fuel balance					$ (159)			$ (165)
State and Local Jurisdiction | GEORGIA POWER CO
Loss Contingencies [Line Items]
Effective tax rate	6.00%
Scenario, Forecast | GEORGIA POWER CO
Loss Contingencies [Line Items]
Customer refundable fees, refund payments		$ 103	$ 96	$ 131
Scenario, Forecast | State and Local Jurisdiction | GEORGIA POWER CO
Loss Contingencies [Line Items]
Effective tax rate							5.75%

Contingencies and Regulatory 46

Contingencies and Regulatory Matters - Gulf Power (Details) - GULF POWER CO $ in Millions	Mar. 26, 2018USD ($)	Mar. 25, 2018	Jun. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Tax reform settlement agreement, annual reduction of revenue from base rates	$ 18.2
Tax reform settlement agreement, annual reduction of revenue from environmental cost recovery rates	15.6
Tax reform settlement agreement, refund	$ 69.4
Customer refundable fees, refund payments			$ 28
Retail regulatory equity ratio	0.535	0.525
Environmental Cost Recovery			10	$ 10		$ 11
Projected environmental expenditures				11	$ 13
Property Basis Differences
Loss Contingencies [Line Items]
Deferred tax asset, regulatory liability			5	5
Under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery			0	0		22
Purchased Power Capacity Recovery			2	2		2
Environmental Cost Recovery			1	1		2
Other regulatory liabilities, current
Loss Contingencies [Line Items]
Fuel Cost Recovery			5	5		0
Energy Conservation Cost Recovery			$ 1	$ 1		$ 0

Contingencies and Regulatory 47

Contingencies and Regulatory Matters - Mississippi Power (Details) - USD ($)

Jul. 27, 2018

May 08, 2018

Mar. 22, 2018

Feb. 07, 2018

Sep. 30, 2018

Jun. 30, 2018

Jun. 30, 2017

Jun. 30, 2018

Jun. 30, 2017

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Dec. 31, 2013

Aug. 03, 2018

Loss Contingencies [Line Items]

Retail electric revenues

$ 3,740,000,000

$ 3,777,000,000

$ 7,308,000,000

$ 7,171,000,000

MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Performance evaluation plan, prior year lookback, surcharge (refund)

$ 0

$ 5,000,000

$ 5,000,000

$ 0

$ 0

Public utilities, interim rate increase (decrease), percentage

4.00%

0.00%

0.00%

Public utilities, interim rate

$ 38,000,000

Public utilities, requested revenue requirement increase (decrease), amount

$ 26,000,000

Public utilities, requested return on equity, percentage

9.33%

Performance evaluation plan, equity ratio

55.00%

Retail electric revenues

$ 212,000,000

$ 222,000,000

$ 406,000,000

$ 422,000,000

Increase retail base rate, annual base revenue

$ 3,000,000

Ad valorem tax adjustment, annual rate increase, percentage

0.80%

Ad valorem tax adjustment, annual rate increase, amount

$ 7,000,000

PEP Settlement Agreement | MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Public utilities, approved return on equity percentage

43.50%

Subsequent Event | MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Environmental compliance overview plan, maximum annual increase in revenue, amount

$ 17,000,000

Subsequent Event | PEP Settlement Agreement

Loss Contingencies [Line Items]

Public utilities, requested revenue requirement increase (decrease), compensation costs, amount

$ 5,500,000

Subsequent Event | PEP Settlement Agreement | MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Public utilities, approved revenue requirement increase (decrease), amount

$ 21,600,000

Public utilities, performance-adjusted allowed return on equity percentage

9.31%

Deferred income taxes

$ 44,000,000

Equity ratio, variance threshold

1.00%

Subsequent Event | Scenario, Forecast | PEP Settlement Agreement | MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Retail electric revenues

$ 5,000,000

Maximum | Subsequent Event | PEP Settlement Agreement | MISSISSIPPI POWER CO

Loss Contingencies [Line Items]

Public utilities, approved return on equity percentage

50.00%

Contingencies and Regulatory 48

Contingencies and Regulatory Matters - Southern Company Gas (Details) - USD ($) $ in Millions	Jun. 22, 2018	May 15, 2018	May 02, 2018	Mar. 28, 2018	Mar. 26, 2018	Feb. 23, 2018	Feb. 15, 2018	Oct. 31, 2017	Mar. 31, 2018
Florida City Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount								$ (19)
Public utilities, interim rate								$ 5
Public utilities, requested rate increase (decrease), amended, amount					$ 11.5
Public utilities, requested return on equity, percentage					10.19%
Public utilities, interim rate increase (decrease), percentage		4.00%
Public utilities, approved return on equity percentage		55.00%
Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount						$ 16
Customer credit		$ 8
Atlanta Gas Light | Pipeline Replacement Program
Loss Contingencies [Line Items]
Litigation settlement awarded from other party									$ 7
Nicor Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount			$ (44)
Public utilities, approved return on equity percentage			9.80%
Chattanooga Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount							$ (7)
Public utilities, requested return on equity, percentage							11.25%
Elizabeth Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount	$ (12)
Elkton Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount				$ (0.1)
Minimum | Florida City Gas
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage						10.55%
Maximum | Florida City Gas
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage		10.95%

Contingencies and Regulatory 49

Contingencies and Regulatory Matters - Nuclear Construction (Details) - GEORGIA POWER CO $ in Millions

Jan. 01, 2021

Jan. 01, 2020

Aug. 31, 2018USD ($)

Apr. 03, 2018USD ($)

Feb. 28, 2018USD ($)

Jan. 11, 2018USD ($)

Jan. 01, 2016

Jun. 30, 2018USD ($)subcontractor

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2009USD ($)utilityMW

Dec. 31, 2022USD ($)

Jun. 30, 2017USD ($)

Jun. 01, 2021

Sep. 30, 2017USD ($)

Dec. 31, 2013

Loss Contingencies [Line Items]

Number of construction units approved | utility

2

Electric generating capacity in mega watts under consortium agreement | MW

1,100

Estimated in-service capital cost

$ 4,418

Financing costs collected, net of tax

$ 1,700

Additional construction capital costs

$ 3,300

Amendment to estimated in-service capital cost

$ 5,680

Retail rate of return on common equity

10.95%

Customer refund

$ 330

Eligible project costs to be reimbursed

3,460

Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Construction financing costs

1,700

Increase in base project capital cost forecast

700

Estimated project costs

1,100

Increase in expected costs

800

Base project capital cost forecast, monthly

50

Monthly AFUDC

$ 12

Percentage of ownership interest required for voting for continuing construction

90.00%

Public utilities, increase in construction budget

$ 1,000

Extension in project schedule

1 year

Percentage of approval required to change primary construction contractor

90.00%

Percentage of approval required for material amendments

67.00%

Cost settlement agreement revised forecast, net of payments

$ 7,300

Additional construction capital costs

$ 448

$ 4,400

Public utilities, approved return on equity percentage

10.00%

Return on equity reduction, negative impact on earnings

$ 25

Guarantor obligations

1,700

Customer refund

$ 188

Scenario, Forecast | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Construction financing costs

$ 3,200

Public utilities, approved return on equity percentage

5.30%

8.30%

Monthly reduction of ROE to calculate NCRR tariff

0.10%

Return on equity reduction, negative impact on earnings

$ 100

$ 585

Requested capital construction costs

$ 578

Vogtle Owners | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Period of notice required in the event letters of credit are not renewed

30 days

FFB Loan

Loss Contingencies [Line Items]

Long-term line of credit

$ 2,600

Conditional borrowing commitment

$ 1,670

Minimum | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Number of subcontractors | subcontractor

60

Contingencies and Regulatory 50

Contingencies and Regulatory Matters - Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - USD ($) $ in Millions	Apr. 03, 2018	Jun. 30, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Customer refund	$ 330
Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Base project capital cost forecast		$ 8,000
Construction contingency estimate		400
Project capital cost forecast		8,400
Net investment as of June 30, 2018		(4,000)
Remaining estimate to complete		4,400
Expected capitalized costs		$ 350
Guarantor obligations			$ 1,700
Customer refund			$ 188

Contingencies and Regulatory 51

Contingencies and Regulatory Matters - Kemper County Energy Facility (Details) - MISSISSIPPI POWER CO - USD ($) $ in Millions	Aug. 06, 2018	Jun. 30, 2018	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Loss Contingencies [Line Items]
Accrued plant closure costs		$ 42		$ 42			$ 35
Kemper County Energy Facility
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment		0		45
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment after tax				33
Accrued plant closure costs		$ 25		$ 25
Scenario, Forecast | Kemper County Energy Facility
Loss Contingencies [Line Items]
Production costs, period cost			$ 4		$ 4	$ 7
Subsequent Event | Reserve Margin Plan | Plant Watson, Unit 4
Loss Contingencies [Line Items]
Accelerated retirement period	2 years
Subsequent Event | Reserve Margin Plan | Plant Watson, Unit 5
Loss Contingencies [Line Items]
Accelerated retirement period	7 years
Subsequent Event | Reserve Margin Plan | Plant Greene County Units 1 and 2
Loss Contingencies [Line Items]
Accelerated retirement period	4 years

Contingencies and Regulatory 52

Contingencies and Regulatory Matters - Other Matters (Details)	6 Months Ended
	Jun. 30, 2018USD ($)
Southern Company Holdings Subsidiary
Loss Contingencies [Line Items]
Leveraged leases, balance sheet, investment in leveraged leases	$ 86,000,000
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Impairment of long-lived assets	0
Natural Gas Storage
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, net	$ 111,000,000
Natural Gas Storage - Salt Dome Caverns
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, percentage of total	20.00%

Revenue from Contracts with C53

Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 5,627	$ 5,430	$ 11,999	$ 11,202
Other Income	89		183
Retail electric revenues
Disaggregation of Revenue [Line Items]
Lease income	18		36
Increase (decrease) in revenue from cost recovery mechanisms	68		101
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,579		3,118
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,315		2,557
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	814		1,569
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	32		64
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	642		1,865
Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(4)		(27)
Total retail electric and gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4,378		9,146
Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	459		928
Revenue from transactions accounted for as derivatives	61		155
Lease income from PPA contracts	118		187
Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	152		302
Lease income from PPA contracts	31		61
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	68		476
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	570		1,147
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	730	716	2,369	2,276
SOUTHERN Co GAS | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	638		1,838
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	273		933
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	76		268
SOUTHERN Co GAS | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	7		24
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	228		505
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	58		135
SOUTHERN Co GAS | Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(4)		(27)
SOUTHERN Co GAS | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0		1
SOUTHERN Co GAS | Gas Marketing Services
Disaggregation of Revenue [Line Items]
Total operating revenues	89		359
Other Income			4
SOUTHERN Co GAS | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	(15)		131
SOUTHERN Co GAS | Gas midstream operations
Disaggregation of Revenue [Line Items]
Total operating revenues	18		40
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,503	1,484	2,976	2,866
Other Income	26		52
ALABAMA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,338		2,624
Increase (decrease) in revenue from cost recovery mechanisms	78		125
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	557		1,127
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	402		774
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	372		710
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	7		13
ALABAMA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	71		172
Revenue from transactions accounted for as derivatives	4		9
ALABAMA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	25		49
ALABAMA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	69		131
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	2,048	2,048	4,008	3,880
Other Income	26		53
GEORGIA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,889		3,688
Lease income	18		36
Increase (decrease) in revenue from cost recovery mechanisms	3		12
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	785		1,529
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	749		1,466
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	335		650
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	20		43
GEORGIA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	26		66
Revenue from transactions accounted for as derivatives	5		13
GEORGIA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	13		27
GEORGIA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	120		227
Lease income	33		66
GULF POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	344	357	692	707
Other Income	2		4
GULF POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	301		591
Increase (decrease) in revenue from cost recovery mechanisms	(12)		(28)
GULF POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	172		337
GULF POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	96		188
GULF POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	31		63
GULF POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	2		3
GULF POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	21		56
GULF POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	6		12
GULF POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	16		33
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	297	303	598	575
MISSISSIPPI POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	212		406
Increase (decrease) in revenue from cost recovery mechanisms	(1)		(8)
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	65		125
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	68		130
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	76		146
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	3		5
MISSISSIPPI POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	73		167
MISSISSIPPI POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1		5
MISSISSIPPI POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	11		20
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	555	529	1,064	979
SOUTHERN POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	3		5
SOUTHERN POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	144		282
Lease income from PPA contracts	47		94
SOUTHERN POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	302		556
Revenue from transactions accounted for as derivatives	50		129
Lease income from PPA contracts	127		203
SOUTHERN POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	106		221
Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	734	769	2,405	2,393
Wholesale gas services | Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	(16)	(12)	150	119
Wholesale gas services | Third Party Gross Revenues | Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,336	$ 1,531	3,274	$ 3,370
Revenue from transactions accounted for as derivatives	$ 700		$ 1,800

Revenue from Contracts with C54

Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,785
Contract Assets	33
Contract Liabilities	36
ALABAMA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	603
Contract Assets	0
Contract Liabilities	10
GEORGIA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	840
Contract Assets	9
Contract Liabilities	$ 9
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 169
Contract Assets	0
Contract Liabilities	1
MISSISSIPPI POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	83
Contract Assets	0
Contract Liabilities	0
SOUTHERN POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	136
Contract Assets	0
Contract Liabilities	4
SOUTHERN Co GAS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	570
Contract Assets	0
Contract Liabilities	1
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	23
Contract Liabilities	$ 16

Revenue from Contracts with C55

Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 263
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 352
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 322
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 322
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 310
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 1,960
Performance obligation, expected timing of satisfaction
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 11
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 26
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 23
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 161
Performance obligation, expected timing of satisfaction
GEORGIA POWER CO
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 20
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 41
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 38
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 40
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 30
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 113
Performance obligation, expected timing of satisfaction
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 11
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 3
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 3
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 1
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 211
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 310
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 283
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 277
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 276
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 1,809
Performance obligation, expected timing of satisfaction

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets:
Fair Value	$ 33
Liabilities:
Collateral already posted, aggregate fair value	183
Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	453
Foreign currency derivatives	132
Nuclear decommissioning trusts	1,829
Cash equivalents	1,449
Other investments	10
Total	3,873
Liabilities:
Energy-related derivatives	573
Interest rate derivatives	68
Foreign currency derivatives	23
Contingent consideration	22
Total	686
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	287
Foreign currency derivatives	0
Nuclear decommissioning trusts	798
Cash equivalents	1,449
Other investments	9
Total	2,543
Liabilities:
Energy-related derivatives	422
Interest rate derivatives	0
Foreign currency derivatives	0
Contingent consideration	0
Total	422
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	166
Foreign currency derivatives	132
Nuclear decommissioning trusts	998
Cash equivalents	0
Other investments	0
Total	1,296
Liabilities:
Energy-related derivatives	151
Interest rate derivatives	68
Foreign currency derivatives	23
Contingent consideration	0
Total	242
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Foreign currency derivatives	0
Nuclear decommissioning trusts	0
Cash equivalents	0
Other investments	1
Total	1
Liabilities:
Energy-related derivatives	0
Interest rate derivatives	0
Foreign currency derivatives	0
Contingent consideration	22
Total	22
ALABAMA POWER CO
Assets:
Energy-related derivatives	8	$ 4
Fair Value	33
Liabilities:
Energy-related derivatives	9	10
ALABAMA POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	8
Cash equivalents	495
Total	1,407
Liabilities:
Energy-related derivatives	9
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Domestic equity
Assets:
Nuclear decommissioning trusts	526
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Foreign equity
Assets:
Nuclear decommissioning trusts	116
ALABAMA POWER CO | Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	18
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Nuclear decommissioning trusts	186
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	18
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Private equity
Assets:
Nuclear decommissioning trusts	33
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Other
Assets:
Nuclear decommissioning trusts	7
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Cash equivalents	495
Total	1,031
Liabilities:
Energy-related derivatives	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Assets:
Nuclear decommissioning trusts	440
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Assets:
Nuclear decommissioning trusts	61
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Assets:
Nuclear decommissioning trusts	28
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Assets:
Nuclear decommissioning trusts	7
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	8
Cash equivalents	0
Total	343
Liabilities:
Energy-related derivatives	9
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Assets:
Nuclear decommissioning trusts	86
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Assets:
Nuclear decommissioning trusts	55
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	18
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Nuclear decommissioning trusts	158
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	18
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Private equity
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Private equity
Assets:
Nuclear decommissioning trusts	0
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO
Assets:
Energy-related derivatives	7	6
Nuclear decommissioning trusts	63
Liabilities:
Energy-related derivatives	25	24
GEORGIA POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	7
Total	931
Liabilities:
Energy-related derivatives	19
Interest rate derivatives	6
Total	25
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Domestic equity
Assets:
Nuclear decommissioning trusts	243
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Foreign equity
Assets:
Nuclear decommissioning trusts	135
GEORGIA POWER CO | Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	239
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Municipal bonds
Assets:
Nuclear decommissioning trusts	78
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Nuclear decommissioning trusts	164
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	41
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Other
Assets:
Nuclear decommissioning trusts	24
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Total	261
Liabilities:
Energy-related derivatives	0
Interest rate derivatives	0
Total	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Assets:
Nuclear decommissioning trusts	242
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Assets:
Nuclear decommissioning trusts	19
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	7
Total	670
Liabilities:
Energy-related derivatives	19
Interest rate derivatives	6
Total	25
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Assets:
Nuclear decommissioning trusts	1
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Assets:
Nuclear decommissioning trusts	135
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	239
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Assets:
Nuclear decommissioning trusts	78
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Nuclear decommissioning trusts	164
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	41
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other
Assets:
Nuclear decommissioning trusts	5
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Total	0
Liabilities:
Energy-related derivatives	0
Interest rate derivatives	0
Total	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	0
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other
Assets:
Nuclear decommissioning trusts	0
GULF POWER CO
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	12	21
GULF POWER CO | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	27
Liabilities:
Energy-related derivatives	12
GULF POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	27
Liabilities:
Energy-related derivatives	0
GULF POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Liabilities:
Energy-related derivatives	12
GULF POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Liabilities:
Energy-related derivatives	0
MISSISSIPPI POWER CO
Assets:
Energy-related derivatives	3	3
Liabilities:
Energy-related derivatives	9	9
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	3
Cash equivalents	205
Total	208
Liabilities:
Energy-related derivatives	9
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Cash equivalents	205
Total	205
Liabilities:
Energy-related derivatives	0
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	3
Cash equivalents	0
Total	3
Liabilities:
Energy-related derivatives	9
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives	0
SOUTHERN POWER CO
Assets:
Energy-related derivatives	135	132
Liabilities:
Energy-related derivatives	26	36
SOUTHERN POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	3
Foreign currency derivatives	132
Total	135
Liabilities:
Energy-related derivatives	3
Foreign currency derivatives	23
Contingent consideration	22
Total	48
SOUTHERN POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Foreign currency derivatives	0
Total	0
Liabilities:
Energy-related derivatives	0
Foreign currency derivatives	0
Contingent consideration	0
Total	0
SOUTHERN POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	3
Foreign currency derivatives	132
Total	135
Liabilities:
Energy-related derivatives	3
Foreign currency derivatives	23
Contingent consideration	0
Total	26
SOUTHERN POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Foreign currency derivatives	0
Total	0
Liabilities:
Energy-related derivatives	0
Foreign currency derivatives	0
Contingent consideration	22
Total	22
SOUTHERN Co GAS
Assets:
Energy-related derivatives	431	554
Liabilities:
Energy-related derivatives	521	660
Collateral already posted, aggregate fair value	183	$ 193
SOUTHERN Co GAS | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	431
Cash equivalents	1
Total	432
Liabilities:
Energy-related derivatives	521
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	287
Cash equivalents	1
Total	288
Liabilities:
Energy-related derivatives	422
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	144
Cash equivalents	0
Total	144
Liabilities:
Energy-related derivatives	99
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Cash equivalents	0
Total	0
Liabilities:
Energy-related derivatives	0
Nuclear Decommissioning Trusts
Assets:
Fair Value	33
Nuclear Decommissioning Trusts | ALABAMA POWER CO
Assets:
Fair Value	33
Weather Derivative | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	$ 3

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 14	$ 55	$ 4	$ 118
Private equity
Fair Value, Option, Quantitative Disclosures [Line Items]
Liquidations term			10 years
ALABAMA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	15	28	$ 10	62
GEORGIA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ (1)	$ 27	$ (6)	$ 56

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Measurements Of Investments Calculated At Net Asset Value Per Share (Details) $ in Millions	Jun. 30, 2018USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 33
Private equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	33
Unfunded Commitments	33
ALABAMA POWER CO
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	33
ALABAMA POWER CO | Private equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	33
Unfunded Commitments	$ 33

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Jun. 30, 2018USD ($)
Southern Company
Long-term debt, including securities due within one year:
Carrying Amount	$ 45,806
Fair Value	46,481
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying Amount	8,119
Fair Value	8,435
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying Amount	10,294
Fair Value	10,499
GULF POWER CO
Long-term debt, including securities due within one year:
Carrying Amount	1,285
Fair Value	1,311
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying Amount	1,779
Fair Value	1,760
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying Amount	5,037
Fair Value	5,094
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying Amount	5,823
Fair Value	$ 5,957

Stockholders' Equity - Earnings

Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
As reported shares (in shares)	1,014	998	1,012	996
Effect of stock-based compensation (in shares)	0	7	5	7
Diluted shares (in shares)	1,014	1,005	1,017	1,003
Stock options and performance share award units that were not included in the diluted earnings per share calculation (in shares)	5.3	0	0	0

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)			(900)
Beginning balance			$ 25,528	$ 26,612
Consolidated net income attributable to Southern Company	$ (154)	$ (1,381)	784	(723)
Other comprehensive income			41	(11)
Stock issued			222	417
Stock-based compensation			48	72
Cash dividends on common stock			(1,194)	(1,134)
Preference stock redemption				(150)
Contributions from noncontrolling interests			31	71
Distributions to noncontrolling interests			(42)	(40)
Net income attributable to noncontrolling interests			17	16
Sale of SPSH noncontrolling interests			1,283
Reclassification from redeemable noncontrolling interests				114
Other			$ (26)	(3)
Ending balance, treasury shares (in shares)	(1,000)		(1,000)
Ending balance	$ 26,692	$ 25,241	$ 26,692	$ 25,241
Number of Common Shares Issued
Changes in Stockholders' Equity
Beginning balance (in shares)			1,008,532	991,213
Stock issued (in shares)			6,590	9,129
Other (in shares)			0
Ending balance (in shares)	1,015,122	1,000,342	1,015,122	1,000,342
Number of Common Shares Treasury Issued
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)			(929)	(819)
Stock issued (in shares)			0	0
Other (in shares)			(57)	(49)
Ending balance, treasury shares (in shares)	(986)	(868)	(986)	(868)
Common Stockholders' Equity
Changes in Stockholders' Equity
Beginning balance			$ 24,167	$ 24,758
Consolidated net income attributable to Southern Company			784	(723)
Other comprehensive income			41	(11)
Stock issued			222	417
Stock-based compensation			48	72
Cash dividends on common stock			(1,194)	(1,134)
Sale of SPSH noncontrolling interests			(407)
Other			(25)	(7)
Ending balance	$ 23,636	$ 23,372	23,636	23,372
Preferred and Preference Stock of Subsidiaries
Changes in Stockholders' Equity
Beginning balance			0	609
Preference stock redemption				(150)
Other			0	3
Ending balance	0	462	0	462
Noncontrolling Interest
Changes in Stockholders' Equity
Beginning balance			1,361	1,245
Contributions from noncontrolling interests			31	71
Distributions to noncontrolling interests			(42)	(40)
Net income attributable to noncontrolling interests			17	16
Sale of SPSH noncontrolling interests			1,690
Reclassification from redeemable noncontrolling interests				114
Other			(1)	1
Ending balance	$ 3,056	$ 1,407	$ 3,056	$ 1,407

Financing - Narrative (Details)

Financing - Narrative (Details)	Aug. 07, 2018USD ($)	May 20, 2018	Jun. 30, 2018USD ($)agreement	May 31, 2018USD ($)agreement	Apr. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Jan. 31, 2018USD ($)	Jan. 04, 2018USD ($)	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			$ 1,500,000,000				$ 1,500,000,000	$ 1,500,000,000
Maximum borrowing capacity			8,143,000,000				8,143,000,000	8,143,000,000
Floating rate Promissory Note Due July 2018
Debt Instrument [Line Items]
Debt face amount										$ 100,000,000
Southern Company
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 2,000,000,000				2,000,000,000	2,000,000,000
Southern Company | Floating Rate Bank Term Loan Agreement 1 | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount						$ 900,000,000
Southern Company | Uncommitted Bank Credit Arrangement | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount					$ 250,000,000
Debt instrument, payable by demand from bank, term					30 days
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 1
Debt Instrument [Line Items]
Number of loan agreements | agreement			2
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 4
Debt Instrument [Line Items]
Debt face amount			$ 100,000,000				100,000,000	100,000,000
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 5
Debt Instrument [Line Items]
Debt face amount			100,000,000				100,000,000	100,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			854,000,000				854,000,000	854,000,000
Fixed rate pollution control revenue bonds outstanding			120,000,000				120,000,000	120,000,000
Maximum borrowing capacity			1,333,000,000				1,333,000,000	1,333,000,000
ALABAMA POWER CO | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Instrument [Line Items]
Debt face amount			$ 500,000,000				$ 500,000,000	$ 500,000,000
Debt stated interest rate			4.30%				4.30%	4.30%
ALABAMA POWER CO | Senior Notes | Series 2008B 5.40% Senior Notes due June 1, 2018
Debt Instrument [Line Items]
Debt stated interest rate					5.40%
Repurchased face amount					$ 250,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			$ 550,000,000				$ 550,000,000	$ 550,000,000
Fixed rate pollution control revenue bonds outstanding			232,000,000				232,000,000	232,000,000
Maximum borrowing capacity			1,750,000,000				1,750,000,000	$ 1,750,000,000
Amortization period for line of credit facility								5 years
Percent of eligible project costs to be reimbursed								70.00%
GEORGIA POWER CO | Loan Guarantee Agreement
Debt Instrument [Line Items]
Conditional borrowing commitment											$ 1,670,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 2
Debt Instrument [Line Items]
Debt face amount									$ 150,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 3
Debt Instrument [Line Items]
Debt face amount									$ 100,000,000
GEORGIA POWER CO | Senior Notes
Debt Instrument [Line Items]
Repayments of debt				$ 902,000,000
GEORGIA POWER CO | Senior Notes | Series 2007A 5.65% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				89,000,000
Debt face amount				$ 250,000,000
Debt stated interest rate				5.65%
GEORGIA POWER CO | Senior Notes | Series 2009A 5.95% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				$ 326,000,000
Debt face amount				$ 500,000,000
Debt stated interest rate				5.95%
GEORGIA POWER CO | Senior Notes | Series 2010B 5.40% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				$ 335,000,000
Debt face amount				$ 600,000,000
Debt stated interest rate				5.40%
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1995
Debt Instrument [Line Items]
Debt face amount						104,600,000
GEORGIA POWER CO | Municipal Bonds | Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 1997
Debt Instrument [Line Items]
Debt face amount						173,000,000
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994
Debt Instrument [Line Items]
Debt face amount					$ 55,000,000
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 2008
Debt Instrument [Line Items]
Debt face amount			65,000,000				65,000,000	$ 65,000,000
GULF POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			82,000,000				82,000,000	82,000,000
Fixed rate pollution control revenue bonds outstanding			37,000,000				37,000,000	37,000,000
Maximum borrowing capacity			280,000,000				280,000,000	280,000,000
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			40,000,000				40,000,000	40,000,000
Fixed rate pollution control revenue bonds outstanding			93,000,000				93,000,000	93,000,000
Maximum borrowing capacity			100,000,000				100,000,000	100,000,000
MISSISSIPPI POWER CO | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount						300,000,000
MISSISSIPPI POWER CO | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Instrument [Line Items]
Debt face amount						300,000,000
MISSISSIPPI POWER CO | Senior Notes | Series 2018B 3.95% Senior Notes
Debt Instrument [Line Items]
Debt face amount						$ 300,000,000
Debt stated interest rate						3.95%
MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Repayments of debt							200,000,000
MISSISSIPPI POWER CO | Unsecured Debt | Unsecured Term Loan
Debt Instrument [Line Items]
Repayments of debt						$ 900,000,000
Traditional Electric Operating Companies
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding			482,000,000				482,000,000	482,000,000
SOUTHERN POWER CO
Debt Instrument [Line Items]
Repayments of debt				$ 770,000,000
Maximum borrowing capacity			750,000,000				750,000,000	750,000,000
SOUTHERN POWER CO | Floating Rate Bank Term Loan Agreement 1 | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount				$ 100,000,000
Number of loan agreements | agreement				2
Repurchased face amount			$ 420,000,000				$ 420,000,000	$ 420,000,000
SOUTHERN POWER CO | Senior Notes | Series 2015A 1.50% Senior Notes
Debt Instrument [Line Items]
Debt stated interest rate			1.50%				1.50%	1.50%
Repurchased face amount			$ 350,000,000				$ 350,000,000	$ 350,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Maximum borrowing capacity			1,900,000,000				1,900,000,000	1,900,000,000
SOUTHERN Co GAS | Uncommitted Bank Credit Arrangement | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount				$ 95,000,000
Debt instrument, payable by demand from bank, term				30 days
SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount			200,000,000				200,000,000	200,000,000
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity			500,000,000				500,000,000	500,000,000
Nicor Gas | Collateralized Mortgage Backed Securities | First Mortgage Bonds
Debt Instrument [Line Items]
Debt face amount			181,000,000				$ 181,000,000	181,000,000
Subsequent Event | MISSISSIPPI POWER CO | Municipal Bonds | Pollution Control Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, repurchase amount	$ 43,000,000
Subsequent Event | MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Repayments of debt	$ 50,000,000
SP Solar Holdings I, LP | SOUTHERN POWER CO
Debt Instrument [Line Items]
Limited liability company or limited partnership, members or limited partners, ownership interest		33.00%		33.00%			33.00%
FFB Loan | GEORGIA POWER CO
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 2,600,000,000				$ 2,600,000,000	$ 2,600,000,000
Conditional borrowing commitment											$ 1,670,000,000

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details)	Jun. 30, 2018USD ($)
Line of Credit Facility [Line Items]
Expires, 2018	$ 122,000,000
Expires, 2019	86,000,000
Expires, 2020	735,000,000
Expires, 2022	7,200,000,000
Total	8,143,000,000
Unused	8,101,000,000
Executable Term Loans, One Year	45,000,000
Expires Within One Year, Term Out	45,000,000
Expires Within One Year, No Term Out	163,000,000
Southern Company
Line of Credit Facility [Line Items]
Expires, 2018	0
Expires, 2019	0
Expires, 2020	0
Expires, 2022	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
ALABAMA POWER CO
Line of Credit Facility [Line Items]
Expires, 2018	2,000,000
Expires, 2019	31,000,000
Expires, 2020	500,000,000
Expires, 2022	800,000,000
Total	1,333,000,000
Unused	1,333,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	33,000,000
GEORGIA POWER CO
Line of Credit Facility [Line Items]
Expires, 2018	0
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,750,000,000
Total	1,750,000,000
Unused	1,736,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
GULF POWER CO
Line of Credit Facility [Line Items]
Expires, 2018	20,000,000
Expires, 2019	25,000,000
Expires, 2020	235,000,000
Expires, 2022	0
Total	280,000,000
Unused	280,000,000
Executable Term Loans, One Year	45,000,000
Expires Within One Year, Term Out	45,000,000
Expires Within One Year, No Term Out	0
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
Expires, 2018	100,000,000
Expires, 2019	0
Expires, 2020	0
Expires, 2022	0
Total	100,000,000
Unused	100,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	100,000,000
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2018	0
Expires, 2019	0
Expires, 2020	0
Expires, 2022	750,000,000
Total	750,000,000
Unused	728,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
Expires, 2018	0
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,900,000,000
Total	1,900,000,000
Unused	1,895,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Other
Line of Credit Facility [Line Items]
Expires, 2018	0
Expires, 2019	30,000,000
Expires, 2020	0
Expires, 2022	0
Total	30,000,000
Unused	30,000,000
Executable Term Loans, One Year	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,400,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	500,000,000
Standby Letters of Credit | SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	$ 23,000,000

Financing - Schedule of Long-Te

Financing - Schedule of Long-Term Debt Financing Activities (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Debt Instrument [Line Items]
Senior Note Issuances	$ 1,100
Senior Note Maturities, Redemptions, and Repurchases	1,350
Revenue Bond Maturities, Redemptions, and Repurchases	598
Other Long-Term Debt Redemptions and Maturities	1,431
ALABAMA POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	500
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	0
GEORGIA POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities, Redemptions, and Repurchases	1,000
Revenue Bond Maturities, Redemptions, and Repurchases	398
Other Long-Term Debt Redemptions and Maturities	104
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	600
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	900
SOUTHERN POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities, Redemptions, and Repurchases	350
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	420
SOUTHERN Co GAS
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Maturities, Redemptions, and Repurchases	200
Other Long-Term Debt Redemptions and Maturities	0
Other
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	$ 7

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Amortization:
Net (gain)/loss
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0		$ 0
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	20,000,000	16,000,000	39,000,000	$ 32,000,000
Interest cost	25,000,000	24,000,000	50,000,000	48,000,000
Expected return on plan assets	(53,000,000)	(49,000,000)	(104,000,000)	(98,000,000)
Amortization:
Prior service costs	1,000,000	0	1,000,000	1,000,000
Regulatory asset	0		0
Net (gain)/loss	13,000,000	11,000,000	27,000,000	21,000,000
Net periodic pension cost (income)	6,000,000	2,000,000	13,000,000	4,000,000
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	21,000,000	18,000,000	43,000,000	37,000,000
Interest cost	35,000,000	35,000,000	70,000,000	69,000,000
Expected return on plan assets	(74,000,000)	(70,000,000)	(148,000,000)	(141,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	1,000,000	2,000,000
Regulatory asset	0		0
Net (gain)/loss	17,000,000	14,000,000	34,000,000	28,000,000
Net periodic pension cost (income)	0	(2,000,000)	0	(5,000,000)
Pension Plans | GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	4,000,000	8,000,000	7,000,000
Interest cost	5,000,000	5,000,000	10,000,000	10,000,000
Expected return on plan assets	(10,000,000)	(9,000,000)	(20,000,000)	(19,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0		0
Net (gain)/loss	3,000,000	1,000,000	5,000,000	3,000,000
Net periodic pension cost (income)	2,000,000	1,000,000	3,000,000	1,000,000
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000	8,000,000	7,000,000
Interest cost	5,000,000	5,000,000	10,000,000	10,000,000
Expected return on plan assets	(10,000,000)	(10,000,000)	(20,000,000)	(20,000,000)
Amortization:
Prior service costs	0	1,000,000	0	1,000,000
Regulatory asset	0		0
Net (gain)/loss	2,000,000	2,000,000	5,000,000	4,000,000
Net periodic pension cost (income)	1,000,000	1,000,000	3,000,000	2,000,000
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000		4,000,000
Interest cost	2,000,000		3,000,000
Expected return on plan assets	(2,000,000)		(5,000,000)
Amortization:
Prior service costs	0		0
Regulatory asset	0		0
Net (gain)/loss	0		1,000,000
Net periodic pension cost (income)	2,000,000		3,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	8,000,000	5,000,000	16,000,000	11,000,000
Interest cost	9,000,000	10,000,000	19,000,000	20,000,000
Expected return on plan assets	(17,000,000)	(17,000,000)	(35,000,000)	(35,000,000)
Amortization:
Prior service costs	0	(1,000,000)	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000		7,000,000
Net (gain)/loss	3,000,000	5,000,000	6,000,000	10,000,000
Net periodic pension cost (income)	7,000,000	2,000,000	12,000,000	5,000,000
Pension Plans | Southern Company
Pension Plans and Postretirement Plans
Service cost	89,000,000	74,000,000	179,000,000	147,000,000
Interest cost	116,000,000	113,000,000	232,000,000	227,000,000
Expected return on plan assets	(235,000,000)	(225,000,000)	(471,000,000)	(449,000,000)
Amortization:
Prior service costs	1,000,000	3,000,000	2,000,000	6,000,000
Regulatory asset	0		0
Net (gain)/loss	54,000,000	41,000,000	107,000,000	81,000,000
Net periodic pension cost (income)	25,000,000	6,000,000	49,000,000	12,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000	3,000,000	3,000,000
Interest cost	4,000,000	4,000,000	8,000,000	9,000,000
Expected return on plan assets	(7,000,000)	(8,000,000)	(13,000,000)	(14,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000		2,000,000
Regulatory asset	0		2,000,000
Net (gain)/loss	1,000,000	1,000,000	1,000,000	1,000,000
Net periodic pension cost (income)	1,000,000	0	1,000,000	1,000,000
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	3,000,000	3,000,000
Interest cost	7,000,000	8,000,000	14,000,000	15,000,000
Expected return on plan assets	(7,000,000)	(6,000,000)	(13,000,000)	(12,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000		1,000,000
Regulatory asset	0		1,000,000
Net (gain)/loss	2,000,000	1,000,000	4,000,000	3,000,000
Net periodic pension cost (income)	4,000,000	5,000,000	9,000,000	10,000,000
Postretirement Benefits | GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	1,000,000
Interest cost	0	0	1,000,000	1,000,000
Expected return on plan assets	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Amortization:
Prior service costs	0	0		0
Regulatory asset	0		0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	0	1,000,000	1,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	1,000,000
Interest cost	1,000,000	1,000,000	2,000,000	2,000,000
Expected return on plan assets	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Amortization:
Prior service costs	0	0		0
Regulatory asset	0		0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	1,000,000	1,000,000	2,000,000	2,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0		0
Interest cost	0		0
Expected return on plan assets	0		0
Amortization:
Prior service costs	0
Regulatory asset	0		0
Net (gain)/loss	0		0
Net periodic pension cost (income)	0		0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0	0	1,000,000	1,000,000
Interest cost	3,000,000	2,000,000	5,000,000	5,000,000
Expected return on plan assets	(2,000,000)	(1,000,000)	(4,000,000)	(3,000,000)
Amortization:
Prior service costs	0	0		(1,000,000)
Regulatory asset	2,000,000		3,000,000
Net (gain)/loss	0	1,000,000	0	2,000,000
Net periodic pension cost (income)	3,000,000	2,000,000	5,000,000	4,000,000
Postretirement Benefits | Southern Company
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000	12,000,000	12,000,000
Interest cost	18,000,000	20,000,000	37,000,000	40,000,000
Expected return on plan assets	(17,000,000)	(17,000,000)	(34,000,000)	(33,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000		3,000,000
Regulatory asset	0		3,000,000
Net (gain)/loss	4,000,000	5,000,000	7,000,000	7,000,000
Net periodic pension cost (income)	$ 12,000,000	$ 15,000,000	$ 25,000,000	$ 29,000,000

Income Taxes (Details)

Income Taxes (Details)	1 Months Ended		3 Months Ended				6 Months Ended
	Apr. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018operating_facility	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)operating_facility	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)operating_facility	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Income Tax Contingency [Line Items]
Effective tax rate							(3.20%)	(28.60%)
Increase in effective tax rate due to loss on Kemper IGCC							$ 3,100,000,000
Income taxes (benefit)					$ (139,000,000)	$ (587,000,000)	(25,000,000)	$ (273,000,000)
Unrecognized tax benefits					0		$ 0
Significantly increase (decrease) in amount of unrecognized tax benefits							12 months
ALABAMA POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							22.80%	40.20%
Income taxes (benefit)					64,000,000	151,000,000	$ 145,000,000	$ 277,000,000
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							(53.50%)	36.60%
Income taxes (benefit)					(143,000,000)	199,000,000	$ (50,000,000)	$ 355,000,000
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Income Tax Contingency [Line Items]
Estimated project costs							$ 1,100,000,000
GULF POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							3.30%	39.80%
Income taxes (benefit)					(11,000,000)	24,000,000	$ 3,000,000	$ 38,000,000
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							18.70%	(30.50%)
Increase in effective tax rate due to loss on Kemper IGCC							$ 3,100,000,000
Income taxes (benefit)					13,000,000	(881,000,000)	$ 9,000,000	$ (908,000,000)
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax rate							39.10%	38.50%
Income taxes (benefit)					55,000,000	31,000,000	$ 159,000,000	$ 180,000,000
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax rate							(1386.50%)	(114.70%)
Income taxes (benefit)	$ (4,000,000)	$ (50,000,000)			(73,000,000)	$ (38,000,000)	$ (172,000,000)	$ (90,000,000)
SOUTHERN POWER CO | Florida Plants | Disposal Group, Held-for-sale, Not Discontinued Operations
Income Tax Contingency [Line Items]
Pre-tax impairment charge					$ 119,000,000		$ 119,000,000
Number of natural gas-fired operating facilities disposed | operating_facility					2		2
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Tax credit carryforward, amount					$ 2,300,000,000		$ 2,300,000,000		$ 2,100,000,000
Scenario, Forecast | SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Income taxes (benefit)				$ (10,000,000)
Number of operating wind facilities | operating_facility			8

Derivatives - Energy-Related an

Derivatives - Energy-Related and Interest Rate Derivatives (Details) MMBTU in Millions	6 Months Ended
	Jun. 30, 2018USD ($)MMBTU
Interest rate derivatives
Interest rate derivatives
Notional Amount	$ 2,500,000,000
Fair Value Gain (Loss) at June 30, 2018	$ (69,000,000)
Southern Company | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	701
Longest Hedge Date	2,022
Longest Non-Hedge Date	2,029
Southern Company | Interest rate derivatives | 2020-06-15 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 300,000,000
Interest Rate Received	2.75%
Fair Value Gain (Loss) at June 30, 2018	$ (6,000,000)
Southern Company | Interest rate derivatives | 2020-06-15 | London Interbank Offered Rate (LIBOR) | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.92%
Southern Company | Interest rate derivatives | 7/1/2021 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 1,500,000,000
Interest Rate Received	2.35%
Fair Value Gain (Loss) at June 30, 2018	$ (57,000,000)
Southern Company | Interest rate derivatives | 7/1/2021 | London Interbank Offered Rate (LIBOR) | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.87%
ALABAMA POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	82
Longest Hedge Date	2,022
GEORGIA POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	174
Longest Hedge Date	2,022
GEORGIA POWER CO | Interest rate derivatives | 12/1/2018 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 500,000,000
Interest Rate Received	1.95%
Fair Value Gain (Loss) at June 30, 2018	$ (3,000,000)
GEORGIA POWER CO | Interest rate derivatives | 12/1/2018 | London Interbank Offered Rate (LIBOR) | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.76%
GEORGIA POWER CO | Interest rate derivatives | 12/1/2019 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 200,000,000
Interest Rate Received	4.25%
Fair Value Gain (Loss) at June 30, 2018	$ (3,000,000)
GEORGIA POWER CO | Interest rate derivatives | 12/1/2019 | London Interbank Offered Rate (LIBOR) | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	2.46%
GULF POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	13
Longest Hedge Date	2,020
MISSISSIPPI POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	66
Longest Hedge Date	2,022
SOUTHERN POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	14
Longest Hedge Date	2,020
SOUTHERN Co GAS | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	352
Longest Hedge Date	2,020
Longest Non-Hedge Date	2,029
SOUTHERN Co GAS | Energy-related, Natural Gas | Long | Derivatives not designated as hedging instruments
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,900
SOUTHERN Co GAS | Energy-related, Natural Gas | Short | Derivatives not designated as hedging instruments
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,600

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Millions	6 Months Ended
	Jun. 30, 2018USD ($)MMBTU	Dec. 31, 2017USD ($)
Derivative [Line Items]
Collateral already posted, aggregate fair value | $	$ 183,000,000
Southern Company
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	17
Cash flow hedge gain (loss) to be reclassified within twelve months | $	$ (18,000,000)
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	3
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	6
Gulf Power and Mississippi Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	1
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	2
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	5
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ (23,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, aggregate fair value | $	183,000,000	$ 193,000,000
Derivative Counterparties | Registrants
Derivative [Line Items]
Collateral already posted, aggregate fair value | $	$ 0

Derivatives - Foreign Currency

Derivatives - Foreign Currency Derivatives (Details) - 6 months ended Jun. 30, 2018 - Cash Flow Hedges of Existing Debt - Foreign currency derivatives € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) at June 30, 2018	109
SOUTHERN POWER CO | June 2022
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain (Loss) at June 30, 2018	$ 54
SOUTHERN POWER CO | June 2026
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) at June 30, 2018	$ 55

Derivatives - Derivative Financ

Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 183
Southern Company
Derivatives, Fair Value [Line Items]
Derivatives, assets	584	$ 700
Derivatives, liabilities	664	794
Derivative asset amount offset	(306)	(405)
Derivative liability amount offset	(489)	(598)
Derivative asset	278	295
Derivative liability	175	196
Southern Company | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives, assets	428	550
Derivatives, liabilities	518	652
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	239	380
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	189	170
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	272	437
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	246	215
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	21	17
Derivatives, liabilities	51	67
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	16	10
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	7
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	12	43
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	27	24
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets held for sale, noncurrent
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities held for sale, noncurrent
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	0
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities held for sale, current
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	8	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	135	133
Derivatives, liabilities	95	75
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	3
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	3	14
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	15	4
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	53	34
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	129
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	23	23
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	8	4
Derivatives, liabilities	9	10
Derivative asset amount offset	(4)	(4)
Derivative liability amount offset	(4)	(4)
Derivative asset	4	0
Derivative liability	5	6
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	8	4
Derivatives, liabilities	9	10
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	6	2
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	2
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	3	6
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	6	4
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	7	6
Derivatives, liabilities	25	24
Derivative asset amount offset	(7)	(6)
Derivative liability amount offset	(7)	(6)
Derivative asset	0	0
Derivative liability	18	18
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	7	6
Derivatives, liabilities	19	19
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	2
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	9
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	14	10
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	6	5
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	4
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
GULF POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	12	21
Derivative asset amount offset	0	0
Derivative liability amount offset	0	0
Derivative asset	0	0
Derivative liability	12	21
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	12	21
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	8	14
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	7
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
Derivatives, liabilities	9	9
Derivative asset amount offset	(2)	(2)
Derivative liability amount offset	(2)	(2)
Derivative asset	1	1
Derivative liability	7	7
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	2
Derivatives, liabilities	9	9
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	1
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	1
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	3	6
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	6	3
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Derivatives, liabilities	0	0
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	135	132
Derivatives, liabilities	26	36
Derivative asset amount offset	(2)	(3)
Derivative liability amount offset	(2)	(3)
Derivative asset	133	129
Derivative liability	24	33
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	2
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	135	132
Derivatives, liabilities	26	34
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	3
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	11
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	129
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	23	23
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivatives, assets	431	554
Derivatives, liabilities	521	660
Derivative asset amount offset	(291)	(390)
Derivative liability amount offset	(474)	(583)
Derivative asset	140	164
Derivative liability	47	77
Collateral already posted, aggregate fair value	183	193
Weather derivative premium	3	11
SOUTHERN Co GAS | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	2	6
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	428	549
Derivatives, liabilities	518	649
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	189	170
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	246	215
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	239	379
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	272	434
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	5
Derivatives, liabilities	2	8
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	5
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	8
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Energy-related derivatives | Liabilities from risk management activities
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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	$ 183		$ 183
Gain (Loss) Recognized in OCI on Derivative	(73)	$ 61	(11)	$ 46
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(28)		(28)		$ (44)
Gain (Loss) Recognized in OCI on Derivative	0	(9)	12	(20)
Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(4)		(4)		(34)
Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(20)		(20)		(18)
Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(8)		(8)
Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(4)		(4)
Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	8		8		7
Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					1
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	0	(1)	(2)	(1)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(73)	71	(21)	67
ALABAMA POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(6)
ALABAMA POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(4)
ALABAMA POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(4)		(4)		(3)
ALABAMA POWER CO | Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
ALABAMA POWER CO | Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
ALABAMA POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	4		4		0
ALABAMA POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					1
GEORGIA POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(12)		(12)		(13)
GEORGIA POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(7)
GEORGIA POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(11)		(11)		(6)
GEORGIA POWER CO | Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
GEORGIA POWER CO | Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
GEORGIA POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
GEORGIA POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					0
GULF POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(12)		(12)		(21)
GULF POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(8)		(8)		(14)
GULF POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(4)		(4)		(7)
GULF POWER CO | Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
GULF POWER CO | Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
GULF POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
GULF POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					0
MISSISSIPPI POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(6)		(6)		(7)
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(5)
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(5)		(2)
MISSISSIPPI POWER CO | Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
MISSISSIPPI POWER CO | Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					0
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	183		183		193
SOUTHERN Co GAS | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	3		3		3
Collateral already posted, aggregate fair value	2		2		6
Gain (Loss) Recognized in OCI on Derivative	1	(2)	2	(4)
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(4)
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
SOUTHERN Co GAS | Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
SOUTHERN Co GAS | Energy-related derivatives | Assets held for sale, noncurrent
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	4		4		7
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					$ 0
SOUTHERN POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(74)	64	(11)	52
SOUTHERN POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(1)	(7)	10	(15)
SOUTHERN POWER CO | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (73)	$ 71	$ (21)	$ 67

Derivatives - Location and Amou

Derivatives - Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Depreciation and amortization	$ 783	$ 754	$ 1,552	$ 1,469
Interest expense, net of amounts capitalized	(470)	(424)	(928)	(840)
Other income (expense), net	78	52	138	98
Cost of natural gas	228	232	949	951
Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(73)	79	(37)	96
Cash Flow Hedging | Depreciation and amortization | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	1	(2)	2	(6)
Cash Flow Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(6)	(5)	(11)	(10)
Cash Flow Hedging | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	(5)	(12)	(12)
Cash Flow Hedging | Cost of natural gas | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	0	0	(2)	0
Fair Value Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	7	(31)	(1)
ALABAMA POWER CO
Derivative [Line Items]
Depreciation and amortization	189	183	379	364
Interest expense, net of amounts capitalized	(80)	(77)	(158)	(153)
Other income (expense), net	12	15	15	25
ALABAMA POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(1)	(2)	(3)	(3)
GEORGIA POWER CO
Derivative [Line Items]
Depreciation and amortization	230	223	458	444
Interest expense, net of amounts capitalized	(102)	(104)	(208)	(205)
Other income (expense), net	35	34	73	71
GEORGIA POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(2)	(1)	(3)	(3)
GEORGIA POWER CO | Fair Value Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	2	0	(1)	(1)
MISSISSIPPI POWER CO
Derivative [Line Items]
Depreciation and amortization	44	41	84	81
Interest expense, net of amounts capitalized	(21)	(17)	(39)	(37)
Other income (expense), net	27	3	27	5
MISSISSIPPI POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(1)	0	(1)	(1)
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	125	129	240	247
Interest expense, net of amounts capitalized	(46)	(48)	(93)	(97)
Other income (expense), net	2	2	5	(2)
SOUTHERN POWER CO | Cash Flow Hedging | Depreciation and amortization | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	1	(2)	2	(6)
SOUTHERN POWER CO | Cash Flow Hedging | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	(5)	(12)	(12)
SOUTHERN POWER CO | Cash Flow Hedging | Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(73)	79	(37)	96
SOUTHERN Co GAS
Derivative [Line Items]
Depreciation and amortization	126	125	255	244
Interest expense, net of amounts capitalized	(59)	(48)	(118)	(94)
Other income (expense), net	3	4	15	10
Cost of natural gas	228	232	949	951
SOUTHERN Co GAS | Cost of natural gas | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	$ 0	$ 0	$ (2)	$ 0

Derivatives - Cumulative Basis

Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (497)	$ (746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	3	3
Securities due within one year | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(497)	(746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	3	3
Long-term Debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(2,528)	(2,553)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	63	35
Long-term Debt | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(497)	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 3	$ 1

Derivatives - Pre-tax Effects74

Derivatives - Pre-tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Energy-related derivatives | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ (26)	$ 14	$ (39)	$ 61
Energy-related derivatives | Natural gas revenues | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(28)	16	(43)	65
Energy-related derivatives | Cost of natural gas | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	2	(2)	4	(4)
Southern Company | Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	0	0	0	15
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net			(2)	49
SOUTHERN Co GAS | Energy-related derivatives | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(26)	14	(39)	61
SOUTHERN Co GAS | Energy-related derivatives | Natural gas revenues | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(28)	16	(43)	65
SOUTHERN Co GAS | Energy-related derivatives | Cost of natural gas | Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 2	$ (2)	$ 4	$ (4)

Acquisitions and Dispositions -

Acquisitions and Dispositions - Southern Company (Details) - Scenario, Forecast - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 28, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock purchase agreement, contract termination fees		$ 100
Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses, net of cash divested	$ 5,750
Amount of indebtedness assumed at closing	$ 1,400
700 Universe, LLC | Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock purchase agreement, contract termination fees		100
700 Universe, LLC | Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock purchase agreement, contract termination fees		$ 200

Acquisitions and Dispositions76

Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended		3 Months Ended
	Jul. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Jun. 30, 2019	Aug. 07, 2018	Jun. 30, 2018	May 31, 2018	Jul. 31, 2017
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)						20
PPA Contract Period		20 years
Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership								100.00%
Wildhorse
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	148
Scenario, Forecast | Mankato
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				345
PPA Contract Period				20 years
Scenario, Forecast | Wildhorse
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			100
PPA Contract Period			20 years
Minimum | Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	12 years
Maximum | Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	15 years
Common Class B | Gaskell West 1
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Class B Membership Interest | Gaskell West 1
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Class B Membership Interest | Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Subsequent Event | Class B Membership Interest | Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership					100.00%

Acquisitions and Dispositions77

Acquisitions and Dispositions - Southern Power Narrative (Details) - USD ($) $ in Thousands	May 25, 2018	May 20, 2018	May 31, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Business Acquisition [Line Items]
Construction work in progress				$ 6,947,000	$ 6,947,000				$ 6,904,000
Sale of SPSH noncontrolling interests					1,283,000
Assets subject to lien				112,777,000	112,777,000				111,005,000
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress				771,000	771,000				511,000
Sale of SPSH noncontrolling interests			$ 511,000
Repayments of debt			770,000
Repayments of capital			250,000		250,000	$ 0
Assets subject to lien				15,428,000	15,428,000				$ 15,206,000
SOUTHERN POWER CO | Series of Construction Projects
Business Acquisition [Line Items]
Construction work in progress				353,000	353,000
SOUTHERN POWER CO | Minimum | Series of Construction Projects
Business Acquisition [Line Items]
Estimated future construction payments				520,000	520,000
SOUTHERN POWER CO | Maximum | Series of Construction Projects
Business Acquisition [Line Items]
Estimated future construction payments				590,000	590,000
Wind Generating Facility | Scenario, Forecast | SOUTHERN POWER CO
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage							80.00%	100.00%
Disposal Group, Held-for-sale, Not Discontinued Operations | Florida Plants | SOUTHERN POWER CO
Business Acquisition [Line Items]
Proceeds from sale of equity method investments			195,000
Decrease in consideration per day between end of fiscal year and closing			110
Increase in consideration per day if closing is prior to end of fiscal year			$ 110
Pre-tax impairment charge				119,000	119,000
After tax impairment charge				$ 89,000	88,000
SP Solar Holdings I, LP | SOUTHERN POWER CO
Business Acquisition [Line Items]
Limited liability company or limited partnership, members or limited partners, ownership interest		33.00%	33.00%	33.00%
Proceeds from sale of equity method investments	$ 1,200,000
Common Stockholders' Equity
Business Acquisition [Line Items]
Sale of SPSH noncontrolling interests					(407,000)
Senior Lien [Member] | SOUTHERN POWER CO | Mankato
Business Acquisition [Line Items]
Assets subject to lien				$ 475,000	$ 475,000

Acquisitions and Dispositions78

Acquisitions and Dispositions - Southern Company Gas (Details) $ in Millions	Jul. 29, 2018USD ($)	Jul. 01, 2018USD ($)utility	Jun. 04, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Aug. 07, 2018utility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment							$ 42
SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill impairment				$ 0	$ 42	$ 0	42	$ 0
Gain (loss) on disposition of business				(36)		$ 0	(36)	$ 0
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price on sale of business			$ 358
Working capital adjustment			6
Gain (loss) on disposition of business, after tax			(76)
Tax on gain (loss) on disposition of business			$ 40
Goodwill impairment					$ 42		42
Florida City Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term debt				$ 3			$ 3
Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of natural gas distribution utilities disposed | utility									3
Subsequent Event | Elizabethtown Gas and Elkton Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price on sale of business		$ 1,700
Working capital adjustment		40
Gain (loss) on disposition of business, after tax		$ (12)
Number of natural gas distribution utilities disposed | utility		2
Gain (loss) on disposition of business		$ 235
Subsequent Event | Florida City Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash purchase price on sale of business	$ 530
Gain (loss) on disposition of business, after tax	4
Gain (loss) on disposition of business	126
Additional cash amount	$ 60

Acquisitions and Dispositions79

Acquisitions and Dispositions - Held for Sale (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets Held for Sale:
Current assets	$ 2,704	$ 12
Liabilities Held for Sale:
Current liabilities	706	0
Other non-current liabilities	2,833	0
SOUTHERN POWER CO
Assets Held for Sale:
Current assets	17	1
Liabilities Held for Sale:
Current liabilities	2	0
SOUTHERN Co GAS
Assets Held for Sale:
Current assets	2,298	0
Liabilities Held for Sale:
Current liabilities	412	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets Held for Sale:
Current assets	487
Total property, plant, and equipment	5,462
Goodwill and other intangible assets	668
Other non-current assets	705
Total Assets Held for Sale	7,322
Liabilities Held for Sale:
Current liabilities	354
Long-term debt	1,285
Accumulated deferred income taxes	566
Other non-current liabilities	1,334
Total Liabilities Held for Sale	3,539
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN POWER CO
Assets Held for Sale:
Current assets	17
Total property, plant, and equipment	168
Goodwill and other intangible assets	0
Other non-current assets	15
Total Assets Held for Sale	200
Liabilities Held for Sale:
Current liabilities	2
Long-term debt	0
Accumulated deferred income taxes	0
Other non-current liabilities	0
Total Liabilities Held for Sale	2
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN Co GAS
Assets Held for Sale:
Current assets	81
Total property, plant, and equipment	1,408
Goodwill and other intangible assets	668
Other non-current assets	141
Total Assets Held for Sale	2,298
Liabilities Held for Sale:
Current liabilities	61
Long-term debt	0
Accumulated deferred income taxes	26
Other non-current liabilities	325
Total Liabilities Held for Sale	$ 412

Acquisitions and Dispositions80

Acquisitions and Dispositions - Pre-tax Profit (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes:	$ 31	$ 61	$ 87	$ 95
Florida Plants | SOUTHERN POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes:	$ 14	$ 11	$ 24	$ 20

Variable Interest Entity and 81

Variable Interest Entity and Equity Method Investments - Narrative (Details) - USD ($) $ in Billions	May 20, 2018	May 31, 2018	Jun. 30, 2018	Jun. 30, 2018
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage				67.00%
Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage				33.00%
SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Limited liability company or limited partnership, members or limited partners, ownership interest	33.00%	33.00%	33.00%
Wholly Owned Subsidiary Of Southern Power | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Limited liability company (llc) or limited partnership (lp), managing member or general partner, ownership interest	66.00%
Variable Interest Entity, Primary Beneficiary | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets			$ 6.5	$ 6.5
Liabilities			0.1	0.1
Noncontrolling Interest in Variable Interest Entity			$ 1.2	$ 1.2
General Partner | Wholly Owned Subsidiary Of Southern Power | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Limited liability company (llc) or limited partnership (lp), managing member or general partner, ownership interest	1.00%

Variable Interest Entity and 82

Variable Interest Entity and Equity Method Investments - Balance Sheet Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,546	$ 1,513
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,507	1,477
SNG | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,258	1,262
Atlantic Coast Pipeline | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	56	41
PennEast Pipeline | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	67	57
Triton | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	42	42
Pivotal JAX LNG, LLC | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	52	44
Horizon Pipeline | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	31	30
Other | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1	$ 1

Variable Interest Entity and 83

Variable Interest Entity and Equity Method Investments - Income Statement Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 31	$ 28	$ 72	$ 67
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	31	29	74	68
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	27	24	66	58
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	1	2	4
SOUTHERN Co GAS | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	2	3	3
SOUTHERN Co GAS | Triton
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	2	2	2
SOUTHERN Co GAS | Horizon Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 1	$ 0	$ 1	$ 1

Variable Interest Entity and 84

Variable Interest Entity and Equity Method Investments - Investment in SNG (Details) - SNG - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Revenues	$ 146	$ 143	$ 306	$ 298
Operating income	60	63	159	147
Net income	$ 54	$ 48	$ 132	$ 114

Segment and Related Informati85

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)utilitystate	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)utilitystatesegment	Jun. 30, 2017USD ($)	Aug. 07, 2018utilitystate
Segment Reporting Information [Line Items]
Number of reportable segments | segment			4
Number of states in which entity operates | state	4		4
Natural gas revenues	$ 706	$ 684	$ 2,314	$ 2,214
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of reportable segments | segment			4
Number of states in which entity operates | state	7		7
Number of natural gas distribution utilities | utility	7		7
Natural gas revenues	$ 710	684	$ 2,341	2,205
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	109	90	192	190
Traditional Electric Operating Companies | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Natural gas revenues	8	10	8	10
Southern Company | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Natural gas revenues	$ 22	$ 33	$ 58	$ 56
Subsequent Event | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state					4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Subsequent Event | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities disposed | utility					3

Segment and Related Informati86

Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018USD ($)utility	Mar. 31, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)utility	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Operating revenues	$ 5,627		$ 5,430	$ 11,999	$ 11,202
Segment net income	(154)		(1,381)	784	(723)
Goodwill	5,315			5,315		$ 6,268
Total assets	112,777			112,777		111,005
Goodwill impairment				42
Plant Scherer Unit 3
Segment Reporting Information [Line Items]
After tax charge to income					20
Loss on Plant Scherer Unit 3					33
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(49)		(37)	(100)	(79)
Segment net income	3		(2)	4	0
Goodwill	0			0		0
Total assets	(1,791)			(1,791)		(1,619)
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,565		4,585	8,948	8,716
Segment net income	(26)		(1,360)	706	(859)
Goodwill	2			2		2
Total assets	88,749			88,749		87,085
SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	730		716	2,369	2,276
Segment net income	(31)		49	248	288
Goodwill	5,015			5,015		5,967
Total assets	22,112			22,112		22,987
All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	381		166	782	289
Segment net income	(100)		(68)	(174)	(152)
Goodwill	298			298		299
Total assets	3,707			3,707		2,552
GEORGIA POWER AND MISSISSIPPI POWER CO | Kemper County Energy Facility
Segment Reporting Information [Line Items]
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment	1,060		3,000	1,100	3,100
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment after tax	800		2,100	800	2,200
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	555		529	1,064	979
Segment net income	22		82	143	151
Total assets	15,428			15,428		15,206
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	730		716	2,369	2,276
Segment net income	(31)		49	248	288
Goodwill	5,015			5,015		5,967
Total assets	22,112			22,112		22,987
Goodwill impairment	0	$ 42	0	42	0
Loss on disposition	36		0	36	0
SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	734		769	2,405	2,393
Segment net income	(15)		50	274	282
Total assets	23,351			23,351		24,842
SOUTHERN Co GAS | Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(5)		(56)	(38)	(122)
Segment net income	0		0	0	0
Total assets	(12,783)			(12,783)		(14,039)
SOUTHERN Co GAS | All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1		3	2	5
Segment net income	(16)		(1)	(26)	6
Total assets	11,544			11,544		12,184
SOUTHERN Co GAS | Gas Distribution Operations
Segment Reporting Information [Line Items]
Goodwill	4,034			4,034		4,702
Goodwill impairment				0
SOUTHERN Co GAS | Gas Distribution Operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	643		603	1,856	1,783
Segment net income	68		54	216	171
Total assets	18,654			18,654		19,358
Revenue on disposition	70		66
Net income on disposition				237	224
SOUTHERN Co GAS | Gas Marketing Services
Segment Reporting Information [Line Items]
Goodwill	981			981		1,265
Goodwill impairment				42
SOUTHERN Co GAS | Gas Marketing Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	89		166	359	454
Segment net income	(76)		4	(63)	35
Total assets	1,610			1,610		2,147
Revenue on disposition	24		32
Net income on disposition				55	63
Loss on disposition	36			36
SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	(16)		(12)	150	119
Segment net income	(21)		(17)	83	51
Total assets	818			818		1,096
Less Gross Gas Costs	1,454		1,666	3,393	3,510
SOUTHERN Co GAS | Gas Midstream Operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	18		12	40	37
Segment net income	14		9	38	25
Total assets	2,269			2,269		2,241
Third Party Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,336		1,531	3,274	3,370
Intercompany Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	102		123	269	259
Total Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,438		1,654	3,543	3,629
Reportable Subsegments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,124		4,157	8,104	7,943
Segment net income	(48)		(1,442)	563	(1,010)
Goodwill	0			0		0
Total assets	73,634			73,634		72,204
Reportable Subsegments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	555		529	1,064	979
Segment net income	22		82	143	151
Goodwill	2			2		2
Total assets	15,428			15,428		15,206
Intersubsegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(114)		(101)	(220)	(206)
Segment net income	0		$ 0	0	$ 0
Goodwill	0			0		0
Total assets	(313)			(313)		$ (325)
Disposal Group, Held-for-sale, Not Discontinued Operations | Florida Plants | SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Pre-tax impairment charge	119			119
After tax impairment charge	$ 89			$ 88
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOUTHERN Co GAS | Gas Distribution Operations | Operating Segments
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities disposed | utility	3			3
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Pivotal Home Solutions | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill impairment		$ 42		$ 42

Segment and Related Informati87

Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 4,565	$ 4,585	$ 8,948	$ 8,716
Southern Company Gas' Revenues	730	716	2,369	2,276
Retail
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	3,740	3,777	7,308	7,171
Wholesale
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	611	618	1,230	1,149
Other
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	214	190	410	396
Gas Distribution Operations
Revenue from External Customer [Line Items]
Southern Company Gas' Revenues	638	557	1,838	1,689
Gas Marketing Services
Revenue from External Customer [Line Items]
Southern Company Gas' Revenues	89	166	359	454
Other
Revenue from External Customer [Line Items]
Southern Company Gas' Revenues	$ 3	$ (7)	$ 172	$ 133