The Southern Company (SO) 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2018shares
Document Information [Line Items]
Entity Registrant Name	SOUTHERN CO
Entity Central Index Key	92,122
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)	1,011,624,620
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
	Mar. 31, 2018	Mar. 31, 2017
Operating Revenues:
Retail electric revenues	$ 3,568	$ 3,394
Wholesale electric revenues	619	531
Other electric revenues	165	175
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,607	1,530
Alternative revenue programs	24	(9)
Other revenues	413	141
Total operating revenues	6,372	5,771
Operating Expenses:
Fuel	1,101	996
Purchased power	267	179
Cost of natural gas	720	719
Cost of other sales	289	88
Other operations and maintenance	1,451	1,383
Depreciation and amortization	769	716
Taxes other than income taxes	355	330
Estimated loss on Kemper IGCC	44	108
Total operating expenses	4,996	4,519
Operating Income	1,376	1,252
Other Income and (Expense):
Allowance for equity funds used during construction	30	57
Earnings from equity method investments	41	39
Interest expense, net of amounts capitalized	(458)	(416)
Other income (expense), net	60	48
Total other income and (expense)	(327)	(272)
Earnings Before Income Taxes	1,049	980
Income taxes	113	315
Consolidated Net Income	936	665
Less:
Dividends on preferred and preference stock of subsidiaries	4	11
Net loss attributable to noncontrolling interests	(6)	(4)
Net Income	$ 938	$ 658
Earnings per share —
Basic (in dollars per share)	$ 0.93	$ 0.66
Diluted (in dollars per share)	$ 0.92	$ 0.66
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	1,011	993
Diluted (in shares)	1,016	1,000
Cash dividends paid per share of common stock (in dollars per share)	$ 0.58	$ 0.56
ALABAMA POWER CO
Operating Revenues:
Retail electric revenues	$ 1,285	$ 1,227
Wholesale revenues, non-affiliates	74	66
Wholesale revenues, affiliates	51	33
Other revenues	63	56
Total operating revenues	1,473	1,382
Operating Expenses:
Fuel	326	298
Purchased power, non-affiliates	64	34
Purchased power, affiliates	37	28
Other operations and maintenance	387	384
Depreciation and amortization	189	181
Taxes other than income taxes	98	96
Total operating expenses	1,101	1,021
Operating Income	372	361
Other Income and (Expense):
Allowance for equity funds used during construction	13	8
Interest expense, net of amounts capitalized	(79)	(75)
Other income (expense), net	5	10
Total other income and (expense)	(61)	(57)
Earnings Before Income Taxes	311	304
Income taxes	82	126
Consolidated Net Income	229	178
Less:
Dividends on preferred and preference stock of subsidiaries	4	4
Net Income	225	174
GEORGIA POWER CO
Operating Revenues:
Retail electric revenues	1,798	1,689
Wholesale revenues, non-affiliates	44	39
Wholesale revenues, affiliates	10	8
Other revenues	109	96
Total operating revenues	1,961	1,832
Operating Expenses:
Fuel	412	371
Purchased power, non-affiliates	121	88
Purchased power, affiliates	171	172
Other operations and maintenance	408	399
Depreciation and amortization	228	221
Taxes other than income taxes	108	98
Total operating expenses	1,448	1,349
Operating Income	513	483
Other Income and (Expense):
Interest expense, net of amounts capitalized	(106)	(101)
Other income (expense), net	38	38
Total other income and (expense)	(68)	(63)
Earnings Before Income Taxes	445	420
Income taxes	93	156
Consolidated Net Income	352	264
Less:
Dividends on preferred and preference stock of subsidiaries	0	4
Net Income	352	260
GULF POWER CO
Operating Revenues:
Retail electric revenues	290	279
Wholesale revenues, non-affiliates	13	17
Wholesale revenues, affiliates	28	37
Other revenues	17	17
Total operating revenues	348	350
Operating Expenses:
Fuel	82	108
Purchased power, non-affiliates	46	34
Other operations and maintenance	76	86
Depreciation and amortization	47	18
Taxes other than income taxes	30	27
Loss on Plant Scherer Unit 3	0	33
Total operating expenses	281	306
Operating Income	67	44
Other Income and (Expense):
Interest expense, net of amounts capitalized	(13)	(12)
Other income (expense), net	1	2
Total other income and (expense)	(12)	(10)
Earnings Before Income Taxes	55	34
Income taxes	13	14
Consolidated Net Income	42	20
Less:
Dividends on preferred and preference stock of subsidiaries	0	2
Net Income	42	18
MISSISSIPPI POWER CO
Operating Revenues:
Retail electric revenues	194	200
Wholesale revenues, non-affiliates	63	62
Wholesale revenues, affiliates	34	5
Other revenues	11	5
Total operating revenues	302	272
Operating Expenses:
Fuel	98	78
Purchased power, non-affiliates	9	8
Other operations and maintenance	75	76
Depreciation and amortization	41	40
Taxes other than income taxes	28	26
Estimated loss on Kemper IGCC	44	108
Total operating expenses	295	336
Operating Income	7	(64)
Other Income and (Expense):
Allowance for equity funds used during construction	0	35
Interest expense, net of amounts capitalized	(19)	(19)
Other income (expense), net	1	1
Total other income and (expense)	(18)	17
Earnings Before Income Taxes	(11)	(47)
Income taxes	(4)	(27)
Consolidated Net Income	(7)	(20)
Less:
Dividends on preferred and preference stock of subsidiaries	0	0
Net Income	(7)	(20)
SOUTHERN POWER CO
Operating Revenues:
Wholesale revenues, non-affiliates	424	347
Wholesale revenues, affiliates	83	100
Other revenues	2	3
Total operating revenues	509	450
Operating Expenses:
Fuel	169	132
Purchased power, non-affiliates	61	30
Other operations and maintenance	93	92
Depreciation and amortization	114	119
Taxes other than income taxes	12	12
Total operating expenses	449	385
Operating Income	60	65
Other Income and (Expense):
Interest expense, net of amounts capitalized	(47)	(50)
Other income (expense), net	3	(1)
Total other income and (expense)	(44)	(51)
Earnings Before Income Taxes	16	14
Income taxes	(99)	(52)
Consolidated Net Income	115	66
Less:
Net loss attributable to noncontrolling interests	(6)	(4)
Net Income	121	70
SOUTHERN Co GAS
Operating Revenues:
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,631	1,521
Alternative revenue programs	(24)	9
Other revenues	32	30
Total operating revenues	1,639	1,560
Operating Expenses:
Cost of natural gas	720	719
Cost of other sales	7	7
Other operations and maintenance	276	255
Depreciation and amortization	129	120
Taxes other than income taxes	77	70
Goodwill impairment	42	0
Total operating expenses	1,251	1,171
Operating Income	388	389
Other Income and (Expense):
Earnings from equity method investments	42	39
Interest expense, net of amounts capitalized	(59)	(46)
Other income (expense), net	12	7
Total other income and (expense)	(5)	0
Earnings Before Income Taxes	383	389
Income taxes	104	150
Consolidated Net Income	279	239
Less:
Net Income	$ 279	$ 239

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Income (Unaudited) - Parenthetical - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Alternative revenue programs	$ (24)	$ 9
SOUTHERN Co GAS
Alternative revenue programs	24	(9)
Excise taxes collected	$ 51	$ 48

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 936	$ 665
Qualifying hedges:
Changes in fair value, net of tax	47	(9)
Reclassification adjustment for amounts included in net income, net of tax	19	1
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	2	1
Total other comprehensive income (loss)	30	(9)
Comprehensive Income	966	656
Less:
Dividends on preferred and preference stock of subsidiaries	4	11
Comprehensive loss attributable to noncontrolling interests	(6)	(4)
Comprehensive Income (Loss) Attributable to Parent	968	649
ALABAMA POWER CO
Net income	229	178
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	(1)	(1)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1
Comprehensive Income	230	179
Less:
Dividends on preferred and preference stock of subsidiaries	4	4
GEORGIA POWER CO
Net income	352	264
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	(1)	(1)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1
Comprehensive Income	353	265
Less:
Dividends on preferred and preference stock of subsidiaries	0	4
GULF POWER CO
Net income	42	20
Qualifying hedges:
Changes in fair value, net of tax	0	(1)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	0	(1)
Comprehensive Income	42	19
Less:
Dividends on preferred and preference stock of subsidiaries	0	2
MISSISSIPPI POWER CO
Net income	(7)	(20)
Qualifying hedges:
Changes in fair value, net of tax	(1)	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	(1)	1
Comprehensive Income	(8)	(19)
Less:
Dividends on preferred and preference stock of subsidiaries	0	0
SOUTHERN POWER CO
Net income	115	66
Qualifying hedges:
Changes in fair value, net of tax	48	(8)
Reclassification adjustment for amounts included in net income, net of tax	24	4
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	24	(12)
Comprehensive Income	139	54
Less:
Comprehensive loss attributable to noncontrolling interests	(6)	(4)
Comprehensive Income (Loss) Attributable to Parent	145	58
SOUTHERN Co GAS
Net income	279	239
Qualifying hedges:
Changes in fair value, net of tax	1	(1)
Reclassification adjustment for amounts included in net income, net of tax	(2)	0
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	(1)	(1)
Total other comprehensive income (loss)	2	(2)
Comprehensive Income	$ 281	$ 237

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in fair value, tax	$ 16	$ (5)
Reclassification adjustment for cash flow hedge, gain (loss), tax	(6)	(1)
Reclassification adjustment for pension and other post retirement benefit plans, tax	0	0
ALABAMA POWER CO
Changes in fair value, tax	0	0
Reclassification adjustment for cash flow hedge, gain (loss), tax	1	1
GULF POWER CO
Changes in fair value, tax	0	0
MISSISSIPPI POWER CO
Changes in fair value, tax	(1)	0
SOUTHERN POWER CO
Changes in fair value, tax	16	(4)
Reclassification adjustment for cash flow hedge, gain (loss), tax	(8)	(3)
SOUTHERN Co GAS
Changes in fair value, tax	0	(1)
Reclassification adjustment for cash flow hedge, gain (loss), tax	1	0
Reclassification adjustment for pension and other post retirement benefit plans, tax	$ 0	$ (1)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net income	$ 936	$ 665
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	873	823
Deferred income taxes	34	161
Allowance for equity funds used during construction	(30)	(57)
Stock based compensation expense	69	61
Estimated loss on Kemper IGCC	37	108
Mark-to-market adjustments	(60)	(81)
Other, net	6	(10)
Changes in certain current assets and liabilities —
-Receivables	197	310
-Prepayments	(82)	(111)
-Natural gas for sale, net of temporary LIFO liquidation	413	411
-Other current assets	7	(31)
-Accounts payable	(425)	(533)
-Accrued taxes	(79)	(212)
-Accrued compensation	(471)	(438)
-Retail fuel cost over recovery	3	(122)
-Other current liabilities	81	(48)
Net cash provided from operating activities	1,509	896
Investing Activities:
Business acquisitions, net of cash acquired	(46)	(1,004)
Property additions	(1,781)	(1,488)
Nuclear decommissioning trust fund purchases	(306)	(224)
Nuclear decommissioning trust fund sales	301	218
Cost of removal, net of salvage	(79)	(61)
Change in construction payables, net	(112)	(170)
Investment in unconsolidated subsidiaries	(30)	(81)
Payments pursuant to LTSAs	(73)	(55)
Asset dispositions	135	64
Other investing activities	(4)	4
Net cash used for investing activities	(1,995)	(2,797)
Financing Activities:
Increase (decrease) in notes payable, net	782	573
Proceeds —
Long-term debt	600	1,409
Common stock	113	186
Short-term borrowings	1,200	4
Redemptions and repurchases —
Long-term debt	(1,283)	(608)
Short-term borrowings	(150)	0
Distributions to noncontrolling interests	(13)	(18)
Capital contributions from noncontrolling interests	8	71
Payment of common stock dividends	(586)	(556)
Other financing activities	(42)	(36)
Net cash provided from financing activities	629	1,025
Net Change in Cash, Cash Equivalents, and Restricted Cash	143	(876)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	2,147	1,992
Cash, Cash Equivalents, and Restricted Cash at End of Period	2,290	1,116
Cash paid (received) during the period for —
Interest	499	461
Income taxes, net	(1)	(6)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	894	578
ALABAMA POWER CO
Operating Activities:
Net income	229	178
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	228	219
Deferred income taxes	32	59
Allowance for equity funds used during construction	(13)	(8)
Other, net	(22)	(3)
Changes in certain current assets and liabilities —
-Prepayments	(82)	(76)
-Materials and supplies	27	10
-Other current assets	19	39
-Accounts payable	(216)	(214)
-Accrued taxes	57	77
-Accrued compensation	(108)	(96)
-Retail fuel cost over recovery		(36)
-Other current liabilities	45	(9)
Net cash provided from operating activities	155	128
Investing Activities:
Property additions	(490)	(306)
Nuclear decommissioning trust fund purchases	(50)	(63)
Nuclear decommissioning trust fund sales	51	63
Cost of removal, net of salvage	(19)	(26)
Change in construction payables, net	(50)	5
Other investing activities	(6)	(2)
Net cash used for investing activities	(564)	(329)
Financing Activities:
Increase (decrease) in notes payable, net	245	0
Proceeds —
Senior notes	0	550
Capital contributions from parent company	484	314
Redemptions and repurchases —
Redemptions — Senior notes	0	(200)
Payment of common stock dividends	(202)	(179)
Other financing activities	(9)	(8)
Net cash provided from financing activities	518	477
Net Change in Cash, Cash Equivalents, and Restricted Cash	109	276
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	544	420
Cash, Cash Equivalents, and Restricted Cash at End of Period	653	696
Cash paid (received) during the period for —
Interest	84	84
Income taxes, net	9	0
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	195	90
GEORGIA POWER CO
Operating Activities:
Net income	352	264
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	280	271
Deferred income taxes	(38)	71
Deferred expenses	35	38
Pension, postretirement, and other employee benefits	(19)	(21)
Settlement of asset retirement obligations	(23)	(22)
Other, net	(7)	(42)
Changes in certain current assets and liabilities —
-Receivables	135	142
-Fossil fuel stock	24	(38)
-Prepaid income taxes	84	5
-Other current assets	9	(16)
-Accounts payable	(180)	(155)
-Accrued taxes	(191)	(235)
-Accrued compensation	(85)	(87)
-Retail fuel cost over recovery	0	(66)
-Other current liabilities	(3)	2
Net cash provided from operating activities	373	111
Investing Activities:
Property additions	(681)	(556)
Nuclear decommissioning trust fund purchases	(255)	(161)
Nuclear decommissioning trust fund sales	250	155
Cost of removal, net of salvage	(26)	(17)
Change in construction payables, net of joint owner portion	(47)	(36)
Payments pursuant to LTSAs	(43)	(22)
Asset dispositions	134	63
Other investing activities	0	8
Net cash used for investing activities	(668)	(566)
Financing Activities:
Increase (decrease) in notes payable, net	0	(391)
Proceeds —
Senior notes	0	850
Capital contributions from parent company	1,474	345
Redemptions and repurchases —
Pollution control revenue bonds	(278)	0
Short-term borrowings	(150)	0
Redemptions — Other long-term debt	(100)	0
Payment of common stock dividends	(339)	(320)
Other financing activities	(6)	(11)
Net cash provided from financing activities	601	473
Net Change in Cash, Cash Equivalents, and Restricted Cash	306	18
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	852	3
Cash, Cash Equivalents, and Restricted Cash at End of Period	1,158	21
Cash paid (received) during the period for —
Interest	115	88
Income taxes, net	0	(5)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	525	320
GULF POWER CO
Operating Activities:
Net income	42	20
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	49	20
Loss on Plant Scherer Unit 3	0	33
Other, net	1	3
Changes in certain current assets and liabilities —
-Receivables	46	(1)
-Fossil fuel stock	(14)	12
-Other current assets	5	6
-Accounts payable	(28)	(8)
-Accrued taxes	12	(4)
-Accrued compensation	(21)	(23)
-Over recovered regulatory clause revenues	(1)	(18)
-Other current liabilities	13	10
Net cash provided from operating activities	104	50
Investing Activities:
Property additions	(70)	(46)
Cost of removal, net of salvage	(11)	(2)
Change in construction payables, net	12	(7)
Other investing activities	(2)	(2)
Net cash used for investing activities	(71)	(57)
Financing Activities:
Increase (decrease) in notes payable, net	16	(168)
Proceeds —
Capital contributions from parent company	2	4
Common stock	0	175
Redemptions and repurchases —
Payment of common stock dividends	(39)	(31)
Other financing activities	(1)	3
Net cash provided from financing activities	(22)	(17)
Net Change in Cash, Cash Equivalents, and Restricted Cash	11	(24)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	28	56
Cash, Cash Equivalents, and Restricted Cash at End of Period	39	32
Cash paid (received) during the period for —
Interest	1	2
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	38	26
MISSISSIPPI POWER CO
Operating Activities:
Net income	(7)	(20)
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	44	49
Deferred income taxes	155	(47)
Allowance for equity funds used during construction	0	(35)
Estimated loss on Kemper IGCC	37	108
Other, net	3	(3)
Changes in certain current assets and liabilities —
-Receivables	(129)	5
-Other current assets	(12)	13
-Accounts payable	(21)	(35)
-Accrued taxes	(110)	(46)
-Accrued compensation	(22)	(22)
-Over recovered regulatory clause revenues	9	(12)
-Other current liabilities	(9)	5
Net cash provided from operating activities	(62)	(40)
Investing Activities:
Property additions	(33)	(186)
Payments pursuant to LTSAs	(9)	1
Other investing activities	(10)	(5)
Net cash used for investing activities	(52)	(190)
Financing Activities:
Increase (decrease) in notes payable, net	(4)	9
Proceeds —
Senior notes	600	0
Short-term borrowings	300	4
Redemptions and repurchases —
Redemptions — Other long-term debt	(900)	0
Other financing activities	(5)	(1)
Net cash provided from financing activities	(9)	12
Net Change in Cash, Cash Equivalents, and Restricted Cash	(123)	(218)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	248	224
Cash, Cash Equivalents, and Restricted Cash at End of Period	125	6
Cash paid (received) during the period for —
Interest	21	13
Income taxes, net	19	0
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	30	78
SOUTHERN POWER CO
Operating Activities:
Net income	115	66
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	122	127
Deferred income taxes	(50)	36
Amortization of investment tax credits	(14)	(14)
Deferred revenues	14	27
Other, net	15	5
Changes in certain current assets and liabilities —
-Receivables	48	(7)
-Prepaid income taxes	(32)	(21)
-Other current assets	5	(6)
-Accounts payable	(43)	(38)
-Accrued taxes	9	(40)
-Other current liabilities	(12)	15
Net cash provided from operating activities	149	96
Investing Activities:
Business acquisitions, net of cash acquired	(46)	(1,004)
Property additions	(121)	(69)
Change in construction payables, net	25	(125)
Payments pursuant to LTSAs	(18)	(31)
Other investing activities	7	(2)
Net cash used for investing activities	(153)	(1,231)
Financing Activities:
Increase (decrease) in notes payable, net	29	171
Redemptions and repurchases —
Distributions to noncontrolling interests	(13)	(18)
Capital contributions from noncontrolling interests	8	71
Payment of common stock dividends	(78)	(79)
Other financing activities	0	(12)
Net cash provided from financing activities	(54)	133
Net Change in Cash, Cash Equivalents, and Restricted Cash	(58)	(1,002)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	140	1,112
Cash, Cash Equivalents, and Restricted Cash at End of Period	82	110
Cash paid (received) during the period for —
Interest	29	28
Income taxes, net	(39)	(1)
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	57	53
SOUTHERN Co GAS
Operating Activities:
Net income	279	239
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	129	120
Deferred income taxes	47	46
Mark-to-market adjustments	(59)	(82)
Goodwill impairment	42	0
Other, net	(2)	26
Changes in certain current assets and liabilities —
-Receivables	175	115
-Natural gas for sale, net of temporary LIFO liquidation	413	411
-Prepaid income taxes	21	24
-Other current assets	14	19
-Accounts payable	(119)	(216)
-Accrued taxes	28	19
-Accrued compensation	(38)	(14)
-Other current liabilities	48	49
Net cash provided from operating activities	978	756
Investing Activities:
Property additions	(268)	(301)
Cost of removal, net of salvage	(14)	(11)
Change in construction payables, net	(46)	(12)
Investment in unconsolidated subsidiaries	(29)	(81)
Other investing activities	(4)	2
Net cash used for investing activities	(361)	(403)
Financing Activities:
Increase (decrease) in notes payable, net	(483)	(234)
Redemptions and repurchases —
Payment of common stock dividends	(118)	(111)
Other financing activities	6	1
Net cash provided from financing activities	(595)	(344)
Net Change in Cash, Cash Equivalents, and Restricted Cash	22	9
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	78	24
Cash, Cash Equivalents, and Restricted Cash at End of Period	100	33
Cash paid (received) during the period for —
Interest	52	41
Noncash Investing and Financing Items [Abstract]
Noncash transactions — Accrued property additions at end of period	$ 89	$ 53

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net cash paid for capitalized interest	$ 17	$ 25
ALABAMA POWER CO
Net cash paid for capitalized interest	5	3
GEORGIA POWER CO
Net cash paid for capitalized interest	6	5
GULF POWER CO
Net cash paid for capitalized interest	0	0
MISSISSIPPI POWER CO
Interest paid	21	25
Net cash paid for capitalized interest	0	12
SOUTHERN POWER CO
Net cash paid for capitalized interest	5	2
SOUTHERN Co GAS
Net cash paid for capitalized interest	$ 1	$ 3

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 2,284	$ 2,130
Receivables —
Customer accounts receivable	1,683	1,806
Energy marketing receivables	448	607
Unbilled revenues	777	810
Under recovered fuel clause revenues	156	171
Other accounts and notes receivable	703	698
Accumulated provision for uncollectible accounts	(54)	(44)
Materials and supplies	1,430	1,438
Fossil fuel for generation	565	594
Natural gas for sale	235	595
Prepaid expenses	432	452
Other regulatory assets, current	579	604
Other current assets	286	211
Total current assets	9,524	10,072
Property, Plant, and Equipment:
In service	104,499	103,542
Less: Accumulated depreciation	31,920	31,457
Plant in service, net of depreciation	72,579	72,085
Nuclear fuel, at amortized cost	908	883
Construction work in progress	7,460	6,904
Total property, plant, and equipment	80,947	79,872
Other Property and Investments:
Goodwill	6,226	6,268
Equity investments in unconsolidated subsidiaries	1,542	1,513
Other intangible assets, net of amortization	848	873
Nuclear decommissioning trusts, at fair value	1,827	1,832
Leveraged leases	781	775
Miscellaneous property and investments	250	249
Total other property and investments	11,474	11,510
Deferred Charges and Other Assets:
Deferred charges related to income taxes	818	825
Unamortized loss on reacquired debt	203	206
Other regulatory assets, deferred	6,948	6,943
Other deferred charges and assets	1,653	1,577
Total deferred charges and other assets	9,622	9,551
Total Assets	111,567	111,005
Current Liabilities:
Securities due within one year	3,235	3,892
Notes payable	4,271	2,439
Energy marketing trade payables	437	546
Accounts payable —
Accounts payable	2,089	2,530
Customer deposits	530	542
Accrued taxes —
Unrecognized tax benefits	0
Accrued taxes	368	636
Accrued interest	432	488
Accrued compensation	493	959
Asset retirement obligations, current	301	351
Other regulatory liabilities, current	551	337
Other current liabilities	923	874
Total current liabilities	13,630	13,594
Long-term Debt	44,446	44,462
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	6,930	6,842
Deferred credits related to income taxes	7,179	7,256
Accumulated deferred ITCs	2,362	2,267
Employee benefit obligations	2,206	2,256
Asset retirement obligations, deferred	4,536	4,473
Accrued environmental remediation	378	389
Other cost of removal obligations	2,667	2,684
Other regulatory liabilities, deferred	224	239
Other deferred credits and liabilities	660	691
Total deferred credits and other liabilities	27,142	27,097
Total Liabilities	85,218	85,153
Redeemable Preferred Stock of Subsidiaries	324	324
Common Stockholders' Equity:
Par value	5,054	5,038
Paid-in capital	10,603	10,469
Treasury, at cost	(38)	(36)
Retained earnings (accumulated deficit)	9,257	8,885
Accumulated other comprehensive income (loss)	(200)	(189)
Total Common Stockholders' Equity	24,676	24,167
Noncontrolling Interests	1,349	1,361
Total Stockholders' Equity	26,025	25,528
Total Liabilities and Stockholders' Equity	111,567	111,005
ALABAMA POWER CO
Current Assets:
Cash and cash equivalents	653	544
Receivables —
Customer accounts receivable	345	355
Unbilled revenues	131	162
Other accounts and notes receivable	36	55
Affiliated	57	43
Accumulated provision for uncollectible accounts	(10)	(9)
Materials and supplies	492	458
Fossil fuel for generation	165	184
Prepaid expenses	133	85
Other regulatory assets, current	131	124
Other current assets	3	5
Total current assets	2,136	2,006
Property, Plant, and Equipment:
In service	27,520	27,326
Less: Accumulated depreciation	9,693	9,563
Plant in service, net of depreciation	17,827	17,763
Nuclear fuel, at amortized cost	358	339
Construction work in progress	1,126	908
Total property, plant, and equipment	19,311	19,010
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	66	67
Nuclear decommissioning trusts, at fair value	897	903
Miscellaneous property and investments	123	124
Total other property and investments	1,086	1,094
Deferred Charges and Other Assets:
Deferred charges related to income taxes	233	239
Deferred under recovered regulatory clause revenues	101	54
Other regulatory assets, deferred	1,257	1,272
Other deferred charges and assets	193	189
Total deferred charges and other assets	1,784	1,754
Total Assets	24,317	23,864
Current Liabilities:
Securities due within one year	200	0
Notes payable	248	3
Accounts payable —
Affiliated	251	327
Other	398	585
Customer deposits	94	92
Accrued taxes —
Accrued taxes	77	54
Accrued interest	65	77
Accrued compensation	96	205
Other regulatory liabilities, current	59	1
Other current liabilities	57	56
Total current liabilities	1,545	1,400
Long-term Debt	7,429	7,628
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,792	2,760
Deferred credits related to income taxes	2,067	2,082
Accumulated deferred ITCs	111	112
Employee benefit obligations	297	304
Asset retirement obligations, deferred	1,709	1,702
Other cost of removal obligations	596	609
Other regulatory liabilities, deferred	75	84
Other deferred credits and liabilities	70	63
Total deferred credits and other liabilities	7,717	7,716
Total Liabilities	16,691	16,744
Redeemable Preferred Stock	291	291
Common Stockholders' Equity:
Par value	1,222	1,222
Paid-in capital	3,474	2,986
Retained earnings (accumulated deficit)	2,670	2,647
Accumulated other comprehensive income (loss)	(31)	(26)
Total Common Stockholders' Equity	7,335	6,829
Total Liabilities and Stockholders' Equity	24,317	23,864
GEORGIA POWER CO
Current Assets:
Cash and cash equivalents	1,158	852
Receivables —
Customer accounts receivable	471	544
Unbilled revenues	189	255
Under recovered fuel clause revenues	156	165
Joint owner accounts receivable	226	262
Other accounts and notes receivable	77	76
Affiliated	24	24
Accumulated provision for uncollectible accounts	(2)	(3)
Materials and supplies	499	504
Fossil fuel for generation	290	314
Prepaid expenses	117	216
Other regulatory assets, current	198	205
Other current assets	39	14
Total current assets	3,442	3,428
Property, Plant, and Equipment:
In service	35,177	34,861
Less: Accumulated depreciation	11,818	11,704
Plant in service, net of depreciation	23,359	23,157
Nuclear fuel, at amortized cost	550	544
Construction work in progress	4,800	4,613
Total property, plant, and equipment	28,709	28,314
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	52	53
Nuclear decommissioning trusts, at fair value	930	929
Miscellaneous property and investments	59	59
Total other property and investments	1,041	1,041
Deferred Charges and Other Assets:
Deferred charges related to income taxes	517	516
Other regulatory assets, deferred	2,940	2,932
Other deferred charges and assets	550	548
Total deferred charges and other assets	4,007	3,996
Total Assets	37,199	36,779
Current Liabilities:
Securities due within one year	757	857
Notes payable	0	150
Accounts payable —
Affiliated	349	493
Other	742	834
Customer deposits	273	270
Accrued taxes —
Accrued income taxes	129	344
Accrued interest	110	123
Accrued compensation	110	219
Asset retirement obligations, current	213	270
Other regulatory liabilities, current	232	191
Other current liabilities	215	198
Total current liabilities	3,130	3,949
Long-term Debt	10,797	11,073
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,140	3,175
Deferred credits related to income taxes	3,219	3,248
Accumulated deferred ITCs	269	248
Employee benefit obligations	651	659
Asset retirement obligations, deferred	2,425	2,368
Other deferred credits and liabilities	148	128
Total deferred credits and other liabilities	9,852	9,826
Total Liabilities	23,779	24,848
Common Stockholders' Equity:
Par value	398	398
Paid-in capital	8,805	7,328
Retained earnings (accumulated deficit)	4,228	4,215
Accumulated other comprehensive income (loss)	(11)	(10)
Total Common Stockholders' Equity	13,420	11,931
Total Liabilities and Stockholders' Equity	37,199	36,779
GULF POWER CO
Current Assets:
Cash and cash equivalents	39	28
Receivables —
Customer accounts receivable	72	76
Unbilled revenues	53	67
Under recovered fuel clause revenues	10	27
Other accounts and notes receivable	5	7
Affiliated	6	14
Accumulated provision for uncollectible accounts	(1)	(1)
Materials and supplies	59	57
Fossil fuel for generation	77	63
Other regulatory assets, current	53	56
Other current assets	12	21
Total current assets	385	415
Property, Plant, and Equipment:
In service	5,227	5,196
Less: Accumulated depreciation	1,494	1,461
Plant in service, net of depreciation	3,733	3,735
Construction work in progress	123	91
Total property, plant, and equipment	3,856	3,826
Deferred Charges and Other Assets:
Deferred charges related to income taxes	30	31
Other regulatory assets, deferred	493	502
Other deferred charges and assets	26	23
Total deferred charges and other assets	549	556
Total Assets	4,790	4,797
Current Liabilities:
Notes payable	61	45
Accounts payable —
Affiliated	45	52
Other	66	75
Customer deposits	35	35
Accrued taxes —
Accrued taxes	22	10
Accrued interest	20	9
Accrued compensation	17	39
Deferred capacity expense, current	22	22
Asset retirement obligations, current	39	37
Other regulatory liabilities, current	72	0
Other current liabilities	26	27
Total current liabilities	425	351
Long-term Debt	1,285	1,285
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	536	537
Deferred credits related to income taxes	386	458
Employee benefit obligations	100	102
Deferred capacity expense	92	97
Asset retirement obligations, deferred	105	105
Other cost of removal obligations	215	221
Other regulatory liabilities, deferred	42	43
Other deferred credits and liabilities	68	67
Total deferred credits and other liabilities	1,544	1,630
Total Liabilities	3,254	3,266
Common Stockholders' Equity:
Par value	678	678
Paid-in capital	597	594
Retained earnings (accumulated deficit)	262	259
Accumulated other comprehensive income (loss)	(1)	0
Total Common Stockholders' Equity	1,536	1,531
Total Liabilities and Stockholders' Equity	4,790	4,797
MISSISSIPPI POWER CO
Current Assets:
Cash and cash equivalents	125	248
Receivables —
Customer accounts receivable	26	36
Unbilled revenues	35	41
Income taxes receivable, current	144	4
Other accounts and notes receivable	9	12
Affiliated	25	16
Materials and supplies	51	44
Fossil fuel for generation	21	17
Other regulatory assets, current	123	125
Other current assets	2	9
Total current assets	561	552
Property, Plant, and Equipment:
In service	4,780	4,773
Less: Accumulated depreciation	1,344	1,325
Plant in service, net of depreciation	3,436	3,448
Construction work in progress	93	84
Total property, plant, and equipment	3,529	3,532
Other Property and Investments:
Total other property and investments	30	30
Deferred Charges and Other Assets:
Deferred charges related to income taxes	35	35
Other regulatory assets, deferred	449	437
Accumulated deferred income taxes	98	247
Other deferred charges and assets	10	33
Total deferred charges and other assets	592	752
Total Assets	4,712	4,866
Current Liabilities:
Securities due within one year	214	989
Notes payable	300	4
Accounts payable —
Affiliated	47	59
Other	78	96
Accrued taxes —
Accrued income taxes	0	40
Accrued taxes	31	101
Accrued compensation	18	39
Accrued plant closure costs	61	35
Asset retirement obligations, current	36	37
Other current liabilities	67	63
Total current liabilities	852	1,463
Long-term Debt	1,567	1,097
Deferred Credits and Other Liabilities:
Deferred credits related to income taxes	391	372
Employee benefit obligations	115	116
Asset retirement obligations, deferred	134	137
Other cost of removal obligations	177	178
Other regulatory liabilities, deferred	78	79
Other deferred credits and liabilities	14	33
Total deferred credits and other liabilities	909	915
Total Liabilities	3,328	3,475
Redeemable Preferred Stock	33	33
Common Stockholders' Equity:
Par value	38	38
Paid-in capital	4,531	4,529
Retained earnings (accumulated deficit)	(3,213)	(3,205)
Accumulated other comprehensive income (loss)	(5)	(4)
Total Common Stockholders' Equity	1,351	1,358
Total Liabilities and Stockholders' Equity	4,712	4,866
SOUTHERN POWER CO
Current Assets:
Cash and cash equivalents	82	129
Receivables —
Customer accounts receivable	126	117
Other accounts and notes receivable	69	98
Affiliated	28	50
Materials and supplies	218	278
Prepaid income taxes	82	50
Other current assets	35	36
Total current assets	640	758
Property, Plant, and Equipment:
In service	13,803	13,755
Less: Accumulated depreciation	1,989	1,910
Plant in service, net of depreciation	11,814	11,845
Construction work in progress	634	511
Total property, plant, and equipment	12,448	12,356
Other Property and Investments:
Goodwill	2	2
Intangible assets, net (including goodwill)	404	411
Total other property and investments	404	411
Deferred Charges and Other Assets:
Prepaid LTSAs	103	118
Accumulated deferred income taxes	911	925
Income taxes receivable, non-current	76	72
Other deferred charges and assets	600	566
Total deferred charges and other assets	1,690	1,681
Total Assets	15,182	15,206
Current Liabilities:
Securities due within one year	770	770
Notes payable	134	105
Accounts payable —
Affiliated	56	102
Other	130	103
Accrued taxes —
Other current liabilities	145	152
Total current liabilities	1,235	1,232
Long-term Debt	5,108	5,071
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	142	199
Accumulated deferred ITCs	1,872	1,884
Other deferred credits and liabilities	267	322
Total deferred credits and other liabilities	2,281	2,405
Total Liabilities	8,624	8,708
Common Stockholders' Equity:
Par value	0	0
Paid-in capital	3,663	3,662
Retained earnings (accumulated deficit)	1,519	1,478
Accumulated other comprehensive income (loss)	27	(2)
Total Common Stockholders' Equity	5,209	5,138
Noncontrolling interests	1,349	1,360
Total Stockholders' Equity	6,558	6,498
Total Liabilities and Stockholders' Equity	15,182	15,206
SOUTHERN Co GAS
Current Assets:
Cash and cash equivalents	94	73
Receivables —
Customer accounts receivable	509	400
Energy marketing receivables	448	607
Unbilled revenues	210	285
Other accounts and notes receivable	51	103
Accumulated provision for uncollectible accounts	(36)	(28)
Natural gas for sale	235	595
Prepaid expenses	66	53
Assets from risk management activities, net of collateral	145	135
Other regulatory assets, current	75	94
Other current assets	51	78
Total current assets	1,848	2,395
Property, Plant, and Equipment:
In service	16,056	15,833
Less: Accumulated depreciation	4,670	4,596
Plant in service, net of depreciation	11,386	11,237
Construction work in progress	511	491
Total property, plant, and equipment	11,897	11,728
Other Property and Investments:
Goodwill	5,925	5,967
Equity investments in unconsolidated subsidiaries	1,504	1,477
Other intangible assets, net of amortization	264	280
Miscellaneous property and investments	20	21
Total other property and investments	7,713	7,745
Deferred Charges and Other Assets:
Other regulatory assets, deferred	878	901
Other deferred charges and assets	232	218
Total deferred charges and other assets	1,110	1,119
Total Assets	22,568	22,987
Current Liabilities:
Securities due within one year	177	157
Notes payable	1,035	1,518
Energy marketing trade payables	437	546
Accounts payable —
Accounts payable	392	446
Customer deposits	112	128
Accrued taxes —
Accrued income taxes	77	40
Accrued taxes	76	78
Accrued interest	65	51
Accrued compensation	55	74
Liabilities from risk management activities, net of collateral	18	69
Other regulatory liabilities, current	179	135
Temporary LIFO liquidation	54	0
Other current liabilities	143	159
Total current liabilities	2,820	3,401
Long-term Debt	5,859	5,891
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,104	1,089
Deferred credits related to income taxes	1,083	1,063
Employee benefit obligations	413	415
Accrued environmental remediation	333	342
Other cost of removal obligations	1,650	1,646
Other deferred credits and liabilities	107	118
Total deferred credits and other liabilities	4,690	4,673
Total Liabilities	13,369	13,965
Common Stockholders' Equity:
Par value	0	0
Paid-in capital	9,228	9,214
Retained earnings (accumulated deficit)	(55)	(212)
Accumulated other comprehensive income (loss)	26	20
Total Stockholders' Equity	9,199	9,022
Total Liabilities and Stockholders' Equity	$ 22,568	$ 22,987

Condensed Consolidated Balance9

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other intangible assets, accumulated amortization	$ 212	$ 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	$ 54	$ 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	$ 136	$ 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	3 Months Ended
	Mar. 31, 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 March 31, 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 certain fixed retail revenues and pole attachment revenues at Georgia Power have been reclassified from unbilled revenue and other accounts and notes receivable, respectively, in accordance with the guidance in ASC 606. Neither of these changes resulted in an adjustment to the timing or amount of the recognition of revenues 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 increase in natural gas revenues recognized in the first quarter 2018 relates primarily to the seasonal nature of natural gas usage and is expected to be offset by decreases in natural gas revenue recognized in future periods during 2018. The net impact of accounting for revenue under ASC 606 increased Southern Company's consolidated net income and net income per share by $10 million and $0.01 per basic share, respectively, for the three months ended March 31, 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 as of and for the three months ended March 31, 2018 compared to previously recognized guidance is shown below. As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Condensed Consolidated Statements of Income Natural gas revenues $ 1,607 $ 1,593 $ 14 Other revenues 413 412 1 Other operations and maintenance 1,451 1,441 10 Operating income 1,376 1,371 5 Other income (expense), net 60 51 9 Earnings before income taxes 1,049 1,035 14 Income taxes 113 109 4 Consolidated net income 936 926 10 Consolidated net income attributable to Southern Company 938 928 10 Basic earnings per share $ 0.93 $ 0.92 $ 0.01 Diluted earnings per share $ 0.92 $ 0.91 $ 0.01 Condensed Consolidated Statements of Cash Flow Consolidated net income $ 936 $ 926 $ 10 Changes in certain current assets and liabilities: Receivables 197 211 (14 ) Other current assets 7 (7 ) 14 Accrued taxes (79 ) (75 ) (4 ) Other current liabilities 81 67 14 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Condensed Consolidated Balance Sheet Unbilled revenues $ 777 $ 822 $ (45 ) Other accounts and notes receivable 703 709 (6 ) Other current assets 286 235 51 Accrued taxes 368 364 4 Other current liabilities 923 937 (14 ) Retained earnings 9,257 9,247 10 Alabama Power Condensed Statements of Income Other revenues $ 63 $ 55 $ 8 Other operations and maintenance 387 377 10 Operating income 372 374 (2 ) Other income (expense), net 5 3 2 Georgia Power Condensed Statements of Income Other revenues $ 109 $ 94 $ 15 Other operations and maintenance 408 394 14 Operating income 513 512 1 Other income (expense), net 38 39 (1 ) Condensed Statements of Cash Flows Changes in certain current assets and liabilities: Receivables $ 135 $ 145 $ (10 ) Other current assets 9 (1 ) 10 Condensed Balance Sheet Unbilled revenues $ 189 $ 202 $ (13 ) Other accounts and notes receivable 77 83 (6 ) Other current assets 39 20 19 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Gas Condensed Statements of Income Natural gas revenues $ 1,631 $ 1,617 $ 14 Operating income 388 374 14 Earnings before income taxes 383 369 14 Income taxes 104 100 4 Net income 279 269 10 Condensed Statements of Cash Flows Net income $ 279 $ 269 $ 10 Changes in certain current assets and liabilities: Accrued taxes 28 32 (4 ) Other current liabilities 48 34 14 Condensed Consolidated Balance Sheet Accrued income taxes $ 77 $ 73 $ 4 Other current liabilities 143 157 (14 ) Accumulated deficit (55 ) (65 ) 10 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 months ended March 31, 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 At March 31, 2018 and December 31, 2017 , goodwill was as follows: Goodwill At March 31, 2018 At December 31, 2017 (in millions) Southern Company $ 6,226 $ 6,268 Southern Power $ 2 $ 2 Southern Company Gas Gas distribution operations $ 4,702 $ 4,702 Gas marketing services 1,223 1,265 Southern Company Gas total $ 5,925 $ 5,967 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 as of March 31, 2018. See Note (J) under "Southern Company Gas" for additional information. 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 March 31, 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 $ 288 $ (93 ) $ 195 $ 288 $ (83 ) $ 205 Trade names 159 (19 ) 140 159 (17 ) 142 Storage and transportation contracts 64 (40 ) 24 64 (34 ) 30 PPA fair value adjustments 456 (54 ) 402 456 (47 ) 409 Other 18 (6 ) 12 17 (5 ) 12 Total other intangible assets subject to amortization $ 985 $ (212 ) $ 773 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 1,060 $ (212 ) $ 848 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (54 ) $ 402 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 221 $ (86 ) $ 135 $ 221 $ (77 ) $ 144 Trade names 115 (10 ) 105 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (40 ) 24 64 (34 ) 30 Total other intangible assets subject to amortization $ 400 $ (136 ) $ 264 $ 400 $ (120 ) $ 280 Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2018 (in millions) Southern Company $ 26 Southern Power $ 7 Southern Company Gas $ 16 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 March 31, 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 March 31, 2018 and/or December 31, 2017: Southern Company Southern Company Gas (in millions) At March 31, 2018 Cash and cash equivalents $ 2,284 $ 94 Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,290 $ 100 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 March 31, 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 financed 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	3 Months Ended
	Mar. 31, 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 regulation of air emissions and water discharges. Litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental requirements such as air quality and water standards, has occurred throughout the U.S. This litigation has included claims for damages alleged to have been caused by CO 2 and other emissions, CCR, and alleged exposure to hazardous materials, and/or requests for injunctive relief in connection with such matters. The ultimate outcome of such pending or potential litigation against each registrant and any subsidiaries cannot be predicted at this time; however, for current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on such registrant's financial statements. 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. Southern Company In January 2017, a purported 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 the 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 and the court has deferred the consolidated case until after certain further action in the purported securities class action complaint discussed above. 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. 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 has deferred the lawsuit until after certain further action in the purported securities class action complaint discussed above. 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. 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 for further proceedings. Georgia Power filed a petition for writ of certiorari with the Georgia Supreme Court, which was granted in August 2017. A decision from the Georgia Supreme Court is expected in late 2018. Georgia Power believes the plaintiffs' claims have no merit and intends to vigorously defend itself in this matter. The ultimate outcome of this matter cannot be determined at this time. 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 alleges that Mississippi Power and Southern Company violated the Mississippi Unfair Trade Practices Act. All plaintiffs have 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 have unjustly enriched Mississippi Power and Southern Company. The plaintiffs seek unspecified actual damages and punitive damages; ask the Circuit Court to appoint a receiver to oversee, operate, manage, and otherwise control all affairs relating to the Kemper County energy facility; ask 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 seek attorney's fees, costs, and interest. The plaintiffs also seek 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. 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 itself in this matter, the ultimate outcome of which cannot be determined at this time. Southern Power During 2015, Southern Power indirectly acquired a 51% membership interest in RE Roserock LLC (Roserock), the owner of the Roserock facility in Pecos County, Texas, which was under construction by Recurrent Energy, LLC and was subsequently placed in service in November 2016. Prior to placing the facility in service, certain solar panels were damaged during installation. While the facility currently is generating energy consistent with operational expectations and PPA obligations, Southern Power is pursuing remedies under its insurance policies and other contracts to repair or replace these solar panels. In connection therewith, Southern Power is withholding payments of approximately $26 million from the construction contractor, who has placed a lien on the Roserock facility for the same amount. The amounts withheld are included in other accounts and notes payable and other current liabilities on Southern Company's consolidated balance sheets and other accounts payable and other current liabilities on Southern Power's consolidated balance sheets. In May 2017, Roserock filed a lawsuit in the state district court in Pecos County, Texas, 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 a hail storm and certain installation practices by the construction contractor, McCarthy Building Companies, Inc. (McCarthy). Also in May 2017, Roserock filed a separate lawsuit against McCarthy in the state district court in Travis County, Texas alleging breach of contract and breach of warranty for the damages sustained at the Roserock facility, which has since been moved to the U.S. District Court for the Western District of Texas. Additionally in May 2017, McCarthy filed a counter lawsuit against Roserock, Array Technologies, Inc., Canadian Solar (USA), Inc., XL, and North American Elite in the U.S. District Court for the Western District of Texas alleging, among other things, breach of contract, and requesting foreclosure of mechanic's liens against Roserock. In July 2017, the U.S. District Court for the Western District of Texas consolidated the two pending lawsuits. In December 2017, the U.S. District Court for the Western District of Texas dismissed McCarthy's claims against Canadian Solar (USA), Inc. and dismissed cross-claims that XL and North American Elite had sought to bring against Roserock. Southern Power intends to vigorously pursue and defend these matters, the ultimate outcome of which cannot be determined at this time. 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 $22 million as of both March 31, 2018 and December 31, 2017 . 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 $49 million and $52 million as of March 31, 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. Southern Company Gas' environmental remediation liability was $369 million and $388 million as of March 31, 2018 and December 31, 2017 , respectively, based on the estimated cost of environmental investigation and remediation associated with known current and former manufactured gas plant operating sites. These environmental remediation expenditures are recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies of the natural gas distribution utilities, with the exception of one site representing $2 million of the total accrued remediation costs. 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 The traditional electric operating companies and Southern Power have authority from the FERC to sell electricity at market-based rates. Since 2008, that authority, for certain balancing authority areas, has been conditioned on compliance with the requirements of an energy auction, which the FERC found to be tailored mitigation that addresses potential market power concerns. In accordance with FERC regulations governing such authority, the traditional electric operating companies and Southern Power filed a triennial market power analysis in 2014, which included continued reliance on the energy auction as tailored mitigation. In 2015, the FERC issued an order finding that the traditional electric operating companies' and Southern Power's existing tailored mitigation may not effectively mitigate the potential to exert market power in certain areas served by the traditional electric operating companies and in some adjacent areas. The FERC directed the traditional electric operating companies and Southern Power to show why market-based rate authority should not be revoked in these areas or to provide a mitigation plan to further address market power concerns. The traditional electric operating companies and Southern Power filed a request for rehearing and filed their response with the FERC in 2015. In 2016, the traditional electric operating companies and Southern Power filed an amendment to their market-based rate tariff that proposed certain changes to the energy auction, as well as several non-tariff changes. In February 2017, the FERC issued an order accepting all such changes subject to an additional condition of cost-based price caps for certain sales outside of the energy auction, finding that all of these changes would provide adequate alternative mitigation for the traditional electric operating companies' and Southern Power's potential to exert market power in certain areas served by the traditional electric operating companies and in some adjacent areas. In May 2017, the FERC accepted the traditional electric operating companies' and Southern Power's compliance filing accepting the terms of the order. While the FERC's February 2017 order references the market power proceeding discussed above, it remains a separate, ongoing matter. In October 2017, the FERC issued an order in response to the traditional electric operating companies' and Southern Power's June 29, 2017 triennial updated market power analysis. The FERC directed the traditional electric operating companies and Southern Power to show cause within 60 days why market-based rate authority should not be revoked in certain areas adjacent to the area presently under mitigation in accordance with the February 2017 order or to provide a mitigation plan to further address market power concerns. In November 2017, the traditional electric operating companies and Southern Power responded to the FERC and proposed to resolve matters by applying the alternative mitigation authorized by the February 2017 order to the adjacent areas made the subject of the October 2017 order. The ultimate outcome of these matters 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 March 31, December 31, (in millions) Rate CNP Compliance Deferred under recovered regulatory clause revenues $ 15 $ 17 Rate CNP PPA Deferred under recovered regulatory clause revenues 8 12 Retail Energy Cost Recovery Deferred under recovered regulatory clause revenues 78 25 Natural Disaster Reserve Other regulatory liabilities, deferred 38 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. Rate RSE The approved modifications to Rate RSE are effective June 2018 and 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, Alabama Power committed 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. Alabama Power typically has three to five business days to indicate its acceptance of the Alabama PSC's actions following issuance of the related Alabama PSC order. The ultimate outcome of this matter cannot be determined at this time. 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 will also return 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. Alabama Power typically has three to five business days to indicate its acceptance of the Alabama PSC's actions following issuance of the related Alabama PSC order. The ultimate outcome of this matter cannot be determined at this time. 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. Up to $30 million of such deferrals may be used to offset under-recovered amounts under Rate ECR, with any remaining amounts to be used for the benefit of customers as determined by the Alabama PSC. Alabama Power expects the benefits deferred to total approximately $30 million to $50 million . The ultimate outcome of this matter cannot be determined at this time. 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. 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 March 31, 2018 and December 31, 2017 , Georgia Power's under recovered fuel balance totaled $156 million and $165 million , respectively, and is included in current assets 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 Gulf Power's fuel cost recovery rate over the remainder of 2018. 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. 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 March 31, December 31, (in millions) Fuel Cost Recovery Under recovered regulatory clause revenues $ 4 $ 22 Purchased Power Capacity Recovery Under recovered regulatory clause revenues 4 2 Environmental Cost Recovery (*) Under recovered regulatory clause revenues 2 2 (*) At March 31, 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 $12 million and $13 million , respectively, partially offset by the over recovered environmental cost recovery balance of approximately $10 million and $11 million , respectively. Mississippi Power See Note 3 to the financial statements of Mississippi Power under "Retail Regulatory Matters" in Item 8 of the Form 10-K for additional information. On April 10, 2018, the Mississippi PSC stated its intent to begin an operations review process for investor-owned utilities in Mississippi and instructed its legal staff and the Mississippi Public Utilities Staff to prepare an order and request for proposals for a review of Mississippi Power. Mississippi Power expects that the review will include its cost recovery framework and an analysis of potential participation in a regional transmission organization. The ultimate outcome of this matter cannot be determined at this time. Performance Evaluation Plan In 2014, 2015, 2016, and 2017, Mississippi Power submitted its annual PEP lookback filings for the prior years, which for 2013 and 2014 each indicated no surcharge or refund and for each of 2015 and 2016 indicated a $5 million surcharge. Additionally, in July 2016, in November 2016, and on November 15, 2017, Mississippi Power submitted its annual projected PEP filings for 2016, 2017, and 2018, respectively, which for 2016 and 2017 indicated no change in rates and for 2018 indicated a rate increase of 4% , or $38 million in annual revenues. The Mississippi PSC suspended each of these filings to allow more time for review. On February 7, 2018, Mississippi Power revised its annual projected PEP filing for 2018 to reflect the impacts of the Tax Reform Legislation. The revised filing requests an increase of $26 million in annual revenues, based on a performance adjusted ROE of 9.33% and an increased equity ratio of 55% . The Mississippi

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS As of March 31, 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 March 31, 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) $ 360 $ 172 $ — $ — $ 532 Foreign currency derivatives — 182 — — 182 Nuclear decommissioning trusts (c) 776 1,019 — 32 1,827 Cash equivalents 1,664 — — — 1,664 Other investments 9 — 1 — 10 Total $ 2,809 $ 1,373 $ 1 $ 32 $ 4,215 Liabilities: Energy-related derivatives (a)(b) $ 506 $ 136 $ — $ — $ 642 Interest rate derivatives — 61 — — 61 Foreign currency derivatives — 22 — — 22 Contingent consideration — — 22 — 22 Total $ 506 $ 219 $ 22 $ — $ 747 Alabama Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Nuclear decommissioning trusts: (d) Domestic equity 437 83 — — 520 Foreign equity 63 58 — — 121 U.S. Treasury and government agency securities — 19 — — 19 Corporate bonds 21 162 — — 183 Mortgage and asset backed securities — 17 — — 17 Private Equity — — — 32 32 Other 6 — — — 6 Cash equivalents 459 — — — 459 Total $ 986 $ 342 $ — $ 32 $ 1,360 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 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 $ — $ 5 $ — $ — $ 5 Nuclear decommissioning trusts: (d) (e) Domestic equity 238 1 — — 239 Foreign equity — 141 — — 141 U.S. Treasury and government agency securities — 241 — — 241 Municipal bonds — 76 — — 76 Corporate bonds — 168 — — 168 Mortgage and asset backed securities — 40 — — 40 Other 11 14 — — 25 Cash equivalents 1,055 — — — 1,055 Total $ 1,304 $ 686 $ — $ — $ 1,990 Liabilities: Energy-related derivatives $ — $ 18 $ — $ — $ 18 Interest rate derivatives — 8 — — 8 Total $ — $ 26 $ — $ — $ 26 Gulf Power Assets: Cash equivalents $ 27 $ — $ — $ — $ 27 Liabilities: Energy-related derivatives $ — $ 17 $ — $ — $ 17 Mississippi Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Cash equivalents 103 — — — 103 Total $ 103 $ 2 $ — $ — $ 105 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 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 $ — $ 4 $ — $ — $ 4 Foreign currency derivatives — 182 — — 182 Total $ — $ 186 $ — $ — $ 186 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 22 — — 22 Contingent consideration — — 22 — 22 Total $ — $ 25 $ 22 $ — $ 47 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 360 $ 158 $ — $ — $ 518 Liabilities: Energy-related derivatives (a)(b) $ 506 $ 82 $ — $ — $ 588 (a) Excludes $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $223 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. (e) Includes the investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2018 , approximately $76 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, decreased by $11 million and increased by $63 million for the three months ended March 31, 2018 and 2017 , respectively. Alabama Power recorded a decrease in fair value of $5 million and an increase of $34 million for the three months ended March 31, 2018 and 2017 , respectively, as a change in regulatory liabilities related to its AROs. Georgia Power recorded a decrease in fair value of $6 million and an increase of $29 million for the three months ended March 31, 2018 and 2017 , respectively, as a change in its regulatory asset related to its AROs. Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (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 March 31, 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 March 31, 2018: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 32 $ 19 Not Applicable Not Applicable Alabama Power $ 32 $ 19 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 March 31, 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 $ 47,479 $ 48,836 Alabama Power 7,626 8,093 Georgia Power 11,402 11,851 Gulf Power 1,285 1,317 Mississippi Power 1,781 1,790 Southern Power 5,878 6,006 Southern Company Gas 6,036 6,276 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.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 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 months ended March 31, 2018 : For the Three Months Ended March 31, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,539 Commercial 1,243 Industrial 756 Other 30 Natural gas distribution revenues 1,224 Alternative revenue programs (b) (24 ) Total retail electric and gas distribution revenues $ 4,768 Wholesale energy revenues (c)(d) 468 Wholesale capacity revenues (d) 151 Other natural gas revenues (e) 407 Other revenues (f) 578 Total operating revenues $ 6,372 (a) Retail electric revenues include $18 million of leases and a net increase of $117 million 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 $93 million of revenues accounted for as derivatives, primarily related to revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $69 million and $30 million , respectively, 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 $1.9 billion , of which $1.1 billion 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 $90 million of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2018 Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Operating revenues Retail revenues (a)(b) Residential $ 570 $ 744 $ 165 $ 60 Commercial 371 717 92 62 Industrial 338 316 32 70 Other 6 21 1 2 Total retail electric revenues $ 1,285 $ 1,798 $ 290 $ 194 Wholesale energy revenues (c) 101 40 35 93 Wholesale capacity revenues 24 14 6 4 Other revenues (b)(d) 63 109 17 11 Total operating revenues $ 1,473 $ 1,961 $ 348 $ 302 (a) Retail revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include a net increase or (net reduction) of $47 million , $10 million , $(16) million , and $76 million , respectively, 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, of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include $5 million , $7 million , $1 million , and $1 million , respectively, accounted for as derivatives primarily related to physical energy sales in the forward and spot markets. See Note (I) for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power, Georgia Power, and Gulf Power include $25 million , $26 million , and $2 million , respectively, of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2018 (in millions) Southern Power PPA capacity revenues (a) $ 138 PPA energy revenues (a) 254 Non-PPA revenues (b) 115 Other revenues 2 Total operating revenues $ 509 (a) PPA capacity revenues and PPA energy revenues include $47 million and $76 million , respectively, 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 $79 million 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 March 31, 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 660 Commercial 192 Transportation 277 Industrial 17 Other 78 Alternative revenue programs (a) (24 ) Total natural gas distribution revenues $ 1,200 Gas marketing services (b) 271 Wholesale gas services (c) 146 Gas midstream operations 22 Total operating revenues $ 1,639 (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 $3 million and $1 million of revenues accounted for as derivatives and leases, respectively. See Note (I) for additional information on energy-related derivative contracts. (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 $1.9 billion , of which $1.1 billion 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 March 31, 2018: Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,607 $ 60 $ 52 Alabama Power 507 — 11 Georgia Power 600 29 5 Gulf Power 129 — 1 Mississippi Power 64 — — Southern Power 78 — 4 Southern Company Gas 948 — 15 As of March 31, 2018 , Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Georgia Power had contract assets 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, as well as unregulated service agreements where payment is contingent on project completion. Southern Company Gas' contract liability relates to collections from customers received in advance of the satisfaction of related performance obligations, primarily associated with maintenance and warranty contracts for residential and commercial appliances. Southern Company's unregulated distributed generation business had $31 million and $20 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 March 31, 2018 are expected to be recognized as follows: 2018 2019 2020 2021 2022 2023 and Thereafter (in millions) Southern Company $ 458 $ 403 $ 369 $ 358 $ 345 $ 2,161 Alabama Power 16 21 22 26 22 161 Georgia Power 31 41 38 40 30 113 Gulf Power 16 22 — — — — Mississippi Power 2 3 3 1 — — Southern Power 384 350 330 313 312 2,010

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 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 the stock option and performance share plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on the stock option and performance share plans. The effect of both stock options and performance share award units was determined using the treasury stock method. Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) As reported shares 1,011 993 Effect of options and performance share award units 5 7 Diluted shares 1,016 1,000 Stock options and performance share award units that were not included in the diluted earnings per share calculation because they were anti-dilutive were immaterial for the three months ended March 31, 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 (*) (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 — — 938 — — 938 Other comprehensive income — — 30 — — 30 Stock issued 4,055 — 113 — — 113 Stock-based compensation — — 36 — — 36 Cash dividends on common stock — — (586 ) — — (586 ) Contributions from noncontrolling interests — — — — 9 9 Distributions to noncontrolling interests — — — — (13 ) (13 ) Net income (loss) attributable to noncontrolling interests — — — — (6 ) (6 ) Other — (33 ) (22 ) — (2 ) (24 ) Balance at March 31, 2018 1,012,587 (962 ) $ 24,676 $ — $ 1,349 $ 26,025 Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — 658 — — 658 Other comprehensive income (loss) — — (9 ) — — (9 ) Stock issued 4,240 — 186 — — 186 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (556 ) — — (556 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (18 ) (18 ) Net income (loss) attributable to noncontrolling interests — — — — (4 ) (4 ) Other — (35 ) — — (1 ) (1 ) Balance at March 31, 2017 995,453 (854 ) $ 25,094 $ 609 $ 1,293 $ 26,996 (*) 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.

Financing

Financing	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
FINANCING	FINANCING 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. 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 March 31, 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 March 31, 2018 , the traditional electric operating companies had approximately $437 million (comprised of approximately $120 million at Alabama Power, $192 million at Georgia Power, $75 million at Gulf Power, and $50 million at Mississippi Power) of revenue bonds outstanding that were required to be remarketed within the next 12 months. Subsequent to March 31, 2018, $55 million of these pollution control revenue bonds of Georgia Power were purchased and held by Georgia 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 March 31, 2018 : Expires Executable Term Loans Expires Within One Year Company 2018 2019 2020 2022 Total Unused One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — $ — Alabama Power 35 — 500 800 1,335 1,335 — — — 35 Georgia Power — — — 1,750 1,750 1,736 — — — — Gulf Power 20 25 235 — 280 280 45 — 20 — Mississippi Power 100 — — — 100 100 — — — 100 Southern Power Company (b) — — — 750 750 728 — — — — Southern Company Gas (c) — — — 1,900 1,900 1,890 — — — — Other 30 — — — 30 30 20 — 20 10 Southern Company Consolidated $ 185 $ 25 $ 735 $ 7,200 $ 8,145 $ 8,098 $ 65 $ — $ 40 $ 145 (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 $21 million remains unused at March 31, 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. Financing Activities The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first three months of 2018 : Company Senior Note Issuances Revenue Bond Other Long-Term Debt Redemptions and Maturities (*) (in millions) Georgia Power $ — $ 278 $ 102 Mississippi Power 600 — 900 Other — — 3 Southern Company Consolidated $ 600 $ 278 $ 1,005 (*) 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. 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. 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 $125 million was repaid subsequent to March 31, 2018. Mississippi Power used the proceeds from these financings to repay the entire $900 million principal amount of its unsecured term loan. 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. Subsequent to March 31, 2018, Pivotal Utility Holdings caused $20 million aggregate principal amount of gas facility revenue bonds to be redeemed and provided notice of its intent to cause, on May 23, 2018, the remaining $180 million aggregate principal amount of gas facility revenue bonds issued for its benefit to be redeemed. Subsequent to March 31, 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 agreement. Pivotal Utility Holdings has the right to borrow up to $181 million on or before May 31, 2018, upon satisfaction of certain customary conditions. Pivotal Utility Holdings expects the proceeds to be used to repay the remaining $180 million of gas facility revenue bonds.

Retirement Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 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 months ended March 31, 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 months ended March 31, 2018 and 2017 are presented in the following tables. Three Months Ended March 31, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 90 $ 19 $ 22 $ 4 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 5 1 10 Expected return on plan assets (236 ) (51 ) (74 ) (10 ) (10 ) (3 ) (18 ) Amortization: Prior service costs 1 — — — — — (1 ) Regulatory asset — — — — — — 3 Net (gain)/loss 53 14 17 2 3 1 3 Net periodic pension cost (income) $ 24 $ 7 $ — $ 1 $ 2 $ 1 $ 5 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ — $ 1 Interest cost 19 4 7 1 1 — 2 Expected return on plan assets (17 ) (6 ) (6 ) — — — (2 ) Amortization: Prior service costs 2 1 — — — — — Regulatory asset — — — — — — 1 Net (gain)/loss 3 — 2 — — — — Net periodic postretirement benefit cost $ 13 $ — $ 5 $ 1 $ 1 $ — $ 2 Three Months Ended March 31, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 73 $ 16 $ 19 $ 3 $ 4 $ 6 Interest cost 114 24 34 5 5 10 Expected return on plan assets (224 ) (49 ) (71 ) (10 ) (10 ) (18 ) Amortization: Prior service costs 3 1 1 — — — Net (gain)/loss 40 10 14 2 2 5 Net periodic pension cost (income) $ 6 $ 2 $ (3 ) $ — $ 1 $ 3 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ 1 Interest cost 20 5 7 1 1 3 Expected return on plan assets (16 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 2 1 — — — (1 ) Net (gain)/loss 2 — 2 — — 1 Net periodic postretirement benefit cost $ 14 $ 1 $ 5 $ 1 $ 1 $ 2 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 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 are 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 March 31, 2018 compared to $2.1 billion as of December 31, 2017 . The federal ITC carryforwards begin expiring in 2034 but are expected to be fully utilized by 2027. The PTC carryforwards begin expiring in 2032 but are expected to be utilized by 2027. The estimated tax credit utilization reflects a 2018 abandonment loss related to certain Kemper County energy facility expenditures. 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 three months ended March 31, 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 rate was 10.8% for the three months ended March 31, 2018 compared to 32.1% for the corresponding period in 2017 . The effective tax rate decrease was primarily due to the lower federal tax rate in 2018 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. Southern Company recognizes PTCs when wind energy is generated and sold (using the prescribed KWH rate in applicable federal and state statutes), which may differ significantly from amounts computed on a quarterly basis using an overall estimated annual effective income tax rate. Southern Company uses this method of recognition since the amount of PTCs can be significantly impacted by wind generation. This method can significantly affect the effective income tax rate for the period depending on the amount of pretax income. Mississippi Power Mississippi Power's effective tax (benefit) rate was (34.7)% for the three months ended March 31, 2018 compared to (58.7)% for the corresponding period in 2017 . In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate increase was primarily due to lower estimated losses on the Kemper IGCC for the three months ended March 31, 2018 compared to the corresponding period in 2017, partially offset by non-deductible AFUDC equity in 2017. Southern Power Southern Power's effective tax (benefit) rate was (647.0)% for the three months ended March 31, 2018 compared to (385.9)% for the corresponding period in 2017 . In addition to the reduction in the federal corporate income tax rate as a result of the Tax Reform Legislation, the effective tax rate decrease was primarily due to 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. Legal Entity Reorganization 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 . 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 March 31, 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.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 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 extended the moratorium on Gulf Power's fuel-hedging program until January 1, 2021 in connection with the 2017 Gulf Power Rate Case Settlement Agreement. The moratorium does not have an impact on the recovery of existing hedges entered into under the previously-approved hedging program. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in the statements of income. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts which are designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through the respective fuel cost recovery clauses. • Cash Flow Hedges — Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in OCI before being recognized in the statements of income in the same period 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 March 31, 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 (*) 670 2021 2026 Alabama Power 74 2021 — Georgia Power 167 2021 — Gulf Power 17 2020 — Mississippi Power 59 2021 — Southern Power 14 2020 2018 Southern Company Gas (*) 339 2020 2026 (*) 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 3.6 billion mmBtu and short natural gas positions of 3.3 billion mmBtu as of March 31, 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 31 million mmBtu for Southern Company, 5 million mmBtu for Alabama Power, 9 million mmBtu for Georgia Power, 3 million mmBtu for Gulf Power, 4 million mmBtu for Mississippi Power, and 10 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 March 31, 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 March 31, 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 March 31, 2018 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month June 2020 $ (5 ) Southern Company (*) 1,500 2.35% 1-month July 2021 (50 ) Georgia Power 250 5.40% 3-month June 2018 (1 ) Georgia Power 500 1.95% 3-month December 2018 (4 ) Georgia Power 200 4.25% 3-month December 2019 (2 ) Southern Company Consolidated $ 2,750 $ (62 ) (*) Represents the Southern Company parent entity. The estimated pre-tax gains (losses) related to interest rate derivatives expected to be reclassified from accumulated OCI to interest expense for the next 12 -month period ending March 31, 2019 are $(20) 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 March 31, 2018 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2018 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 83 Southern Power 564 3.78% 500 1.85% June 2026 77 Total $ 1,241 € 1,100 $ 160 The estimated pre-tax gains (losses) related to foreign currency derivatives that will be reclassified from accumulated OCI to earnings for the next 12 -month period ending March 31, 2019 are $(22) million for Southern Company and Southern Power. Derivative Financial Statement Presentation and Amounts Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into derivative contracts that may contain certain provisions that permit intra-contract netting of derivative receivables and payables for routine billing and offsets related to events of default and settlements. Southern Company and certain subsidiaries also utilize master netting agreements to mitigate exposure to counterparty credit risk. These agreements may contain provisions that permit netting across product lines and against cash collateral. The fair value amounts of derivative assets and liabilities on the balance sheet are presented net to the extent that there are netting arrangements or similar agreements with the counterparties. The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 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 $ 7 $ 28 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 4 27 7 24 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 55 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 3 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Interest rate derivatives: Other current assets/Other current liabilities — 14 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 47 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 22 — 23 Other deferred charges and assets/Other deferred credits and liabilities 182 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 186 $ 87 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 283 $ 299 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 234 284 170 215 Total derivatives not designated as hedging instruments $ 517 $ 583 $ 550 $ 652 Gross amounts recognized $ 714 $ 725 $ 700 $ 794 Gross amounts offset (a) $ (336 ) $ (559 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 378 $ 166 $ 295 $ 196 As of March 31, 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 $ 2 $ 3 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 5 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 8 $ 4 $ 10 Gross amounts recognized $ 3 $ 8 $ 4 $ 10 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 1 $ 6 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 6 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 2 12 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 5 $ 18 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 6 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — 2 — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 8 $ — $ 5 Gross amounts recognized $ 5 $ 26 $ 6 $ 24 Gross amounts offset $ (5 ) $ (5 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 21 $ — $ 18 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ — $ 11 $ — $ 14 Other deferred charges and assets/Other deferred credits and liabilities — 6 — 7 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 17 $ — $ 21 Gross amounts recognized $ — $ 17 $ — $ 21 Gross amounts offset $ — $ — $ — $ — Net amounts recognized in the Balance Sheets $ — $ 17 $ — $ 21 As of March 31, 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 $ 1 $ 4 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 4 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 8 $ 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 $ 2 $ 8 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 6 $ 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 $ 3 $ 2 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Foreign currency derivatives: Other current assets/Other current liabilities — 22 — 23 Other deferred charges and assets/Other deferred credits and liabilities 182 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 186 $ 25 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Gross amounts recognized $ 186 $ 25 $ 132 $ 36 Gross amounts offset $ (1 ) $ (1 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 185 $ 24 $ 129 $ 33 As of March 31, 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 $ 1 $ 4 $ 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 $ 283 $ 299 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 234 284 170 215 Total derivatives not designated as hedging instruments $ 517 $ 583 $ 549 $ 649 Gross amounts of recognized $ 518 $ 588 $ 554 $ 660 Gross amounts offset (a) $ (325 ) $ (548 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 193 $ 40 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $223 million and $193 million as of March 31, 2018 and December 31, 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $4 million and $11 million as of March 31, 2018 and December 31, 2017 , respectively. At March 31, 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 March 31, 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 $ (20 ) $ (1 ) $ (3 ) $ (11 ) $ (3 ) $ (2 ) Other regulatory assets, deferred (23 ) (4 ) (10 ) (6 ) (3 ) — Other regulatory liabilities, current 7 — — — — 7 Total energy-related derivative gains (losses) $ (36 ) $ (5 ) $ (13 ) $ (17 ) $ (6 ) $ 5 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $8 million at March 31, 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 months ended March 31, 2018 and 2017 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Derivatives in Cash Flow Hedging Relationships Gain (Loss) Recognized in OCI on Derivative Gain (Loss) Reclassified from Accumulated OCI into Income Statements of Income Location Amount 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives $ 12 $ (11 ) Depreciation and amortization $ 1 $ (4 ) Cost of natural gas (2 ) — Interest rate derivatives (2 ) 1 Interest expense, net of amounts capitalized (5 ) (5 ) Foreign currency derivatives 53 (4 ) Interest expense, net of amounts capitalized (5 ) (6 ) Other income (expense), net (*) 36 17 Total $ 63 $ (14 ) $ 25 $ 2 Southern Power Energy-related derivatives $ 11 $ (8 ) Depreciation and amortization $ 1 $ (4 ) Foreign currency derivatives 53 (4 ) Interest expense, net of amounts capitalized (5 ) (6 ) Other income (expense), net (*) 36 17 Total $ 64 $ (12 ) $ 32 $ 7 (*) 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 months ended March 31, 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 months ended March 31, 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 months ended March 31, 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 2018 2017 (in millions) Southern Company Depreciation and amortization $ 769 $ 716 Gain (loss) on cash flow hedges Energy-related derivatives 1 (4 ) Interest expense, net of amounts capitalized (458 ) (416 ) Gain (loss) on cash flow hedges Interest rate derivatives (5 ) (5 ) Foreign currency derivatives (5 ) (6 ) Gain (loss) on fair value hedges (a) Interest rate derivatives (24 ) (8 ) Other income (expense), net 60 48 Gain (loss) on cash flow hedges (b) Foreign currency derivatives 36 17 Southern Power Depreciation and amortization $ 114 $ 119 Gain (loss) on cash flow hedges Energy-related derivatives 1 (4 ) Interest expense, net of amounts capitalized (47 ) (50 ) Gain (loss) on cash flow hedges Foreign currency derivatives (5 ) (6 ) Other income (expense), net 3 (1 ) Gain (loss) on cash flow hedges (b) Foreign currency derivatives 36 17 (a) For fair value hedges presented above, changes in the fair value of the derivative contracts are equal to changes in the fair value of the underlying debt and have no impact on income. (b) 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 months ended March 31, 2018 and 2017 , the pre-tax effects of cash flow and fair value hedge accounting on income for energy-related derivatives and interest rate derivatives were immaterial for the traditional electric operating companies and Southern Company Gas. As of March 31, 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 March 31, 2018 As of December 31, 2017 As of March 31, 2018 As of December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (745 ) $ (746 ) $ 4 $ 3 Long-term Debt (2,533 ) (2,553 ) 57 35 Georgia Power Securities due within one year $ (745 ) $ (746 ) $ 4 $ 3 Long-term Debt (497 ) (498 ) 2 1 For the three months ended March 31, 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 March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 (in millions) Southern Company Energy-related derivatives: Natural gas revenues (*) $ (15 ) $ 50 Cost of natural gas 2 (3 ) Total derivatives in non-designated hedging relationships $ (13 ) $ 47 Southern Company Gas Energy-related derivatives: Natural gas revenues (*) $ (15 ) $ 50 Cost of natural gas 2 (3 ) Total derivatives in non-designated hedging relationships $ (13 ) $ 47 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of an immaterial amount and $14 million for the three months ended March 31, 2018 and 2017 , respectively. For the three months ended March 31, 2018 and 2017 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were i mmaterial for 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 March 31, 2018 , the registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the registrants with interest rate derivatives at March 31, 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 March 31, 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 March 31, 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 March 31, 2018 , cash collateral held on deposit in broker margin accounts was $223 million . Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to losses related to financial instruments in the event of counterparties' nonperformance. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas only enter into agreements and material transactions with counterparties that have investment grade credit ratings by Moody's and S&P or with counterparties who have posted collateral to cover potential credit exposure. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas have also established risk management policies and controls to determine and monitor the creditworthiness of counterparties in order to mitigate Southern Company's, the traditional electric operating companies', Southern Power's, and Southern Company Gas' exposure to counterparty credit risk. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. In addition, Southern Company Gas conducts credit evaluations and obtains appropriate internal approvals for the counterparty's line of credit before any transaction with the counterparty is executed. In most cases, the counterparty must have an investment grade rating, which includes a minimum long-term debt rating of Baa3 from Moody's and BBB- from S&P. Generally, Southern Company Gas requires credit enhancements by way of a guaranty, cash deposit, or letter of credit for transaction counterparties that do not have investment grade ratings. Southern Company Gas also utilizes master netting agreements whenever possible to mitigate exposure to counterparty credit risk. When Southern Company Gas is engaged in more than one outstanding derivative transaction with the same counterparty and it also has a legally enforceable netting agreement with that counterparty, the "net" mark-to-market exposure represents the netting of the positive and negative exposures with that counterparty and a reasonable measure of Southern Company Gas' credit risk. Southern Company Gas also uses other netting agreements with certain counterparties with whom it conducts significant transactions. Master netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty. Southern Company Gas also nets across product lines and against cash collateral provided the master netting and cash collateral agreements include such provisions. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not anticipate a material adverse effect on the financial statements as a result of counterparty nonperformance.

Acquisitions and Dispositions

Acquisitions and Dispositions	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS 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 Three Months Ended March 31, 2018 During the three months ended March 31, 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 three months ended March 31, 2018 , Southern Power continued construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $370 million and $415 million for the Mankato and Cactus Flats facilities. At March 31, 2018 , construction costs included in CWIP related to these projects totaled $273 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 March 31, 2018 Cactus Flats (*) Wind 148 Concho County, TX Third quarter 2018 12-15 years Mankato Natural Gas 345 Mankato, MN Second quarter 2019 20 years (*) In July 2017, Southern Power purchased 100% of the Cactus Flats facility and commenced construction. Upon placing the facility in service, Southern Power expects to close on a tax equity partnership agreement, subject to various customary conditions at closing, and will 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. The ultimate outcome of these matters cannot be determined at this time. Southern Company Gas Proposed Sale of Elizabethtown Gas and Elkton Gas In October 2017, a Southern Company Gas subsidiary, Pivotal Utility Holdings, entered into agreements for the sale 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 . The completion of each asset sale is subject to the satisfaction or waiver of certain conditions, including, among other customary closing conditions, the receipt of required regulatory approvals, including the FERC, the New Jersey BPU, and, with respect to the sale of Elkton Gas, the Maryland PSC. Southern Company Gas and South Jersey Industries, Inc. made joint filings in December 2017 and on January 16, 2018 with the New Jersey BPU and the Maryland PSC, respectively, requesting regulatory approval. The asset sales are expected to be completed by the end of the third quarter 2018. The ultimate outcome of these matters cannot be determined at this time. Proposed Sale of Pivotal Home Solutions On April 11, 2018, Southern Company Gas and its subsidiary Pivotal Home Solutions entered into a stock purchase agreement with American Water Enterprises LLC for the sale of Pivotal Home Solutions for a purchase price of approximately $365 million , including estimated working capital. In contemplation of the transaction, a goodwill impairment charge of $42 million was recorded as of March 31, 2018. The remaining goodwill of $242 million is not deductible for tax purposes and, as a result, a deferred tax liability has not been provided. The completion of this transaction is subject to the satisfaction or waiver of certain conditions, including, among other customary closing conditions, approval from the Florida Office of Insurance Regulation and the expiration or termination of any applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. The transaction is expected to be completed by the end of the second quarter 2018. The ultimate outcome of this matter cannot be determined at this time.

Joint Ownership Agreements

Joint Ownership Agreements	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
JOINT OWNERSHIP AGREEMENTS	JOINT OWNERSHIP AGREEMENTS Southern Company Gas See Note 4 to the financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information. Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2018 and December 31, 2017 and related income from those investments for the three -month periods ended March 31, 2018 and March 31, 2017 were as follows: Balance Sheet Information March 31, 2018 December 31, 2017 (in millions) SNG $ 1,274 $ 1,262 Atlantic Coast Pipeline 49 41 PennEast Pipeline 62 57 Triton 42 42 Pivotal JAX LNG, LLC 45 44 Horizon Pipeline 31 30 Other 1 1 Total $ 1,504 $ 1,477 Income Statement Information Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) SNG $ 39 $ 34 PennEast Pipeline 1 3 Atlantic Coast Pipeline 1 1 Triton 1 — Horizon Pipeline — 1 Total $ 42 $ 39 Southern Natural Gas Selected financial information of SNG for the three months ended March 31, 2018 and March 31, 2017 is as follows: Income Statement Information Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) Revenues $ 160 $ 155 Operating income $ 99 $ 84 Net income $ 78 $ 66

Segment and Related Information

Segment and Related Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
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 the seven natural gas distribution utilities in seven states and is involved in several other complementary businesses including gas marketing services, wholesale gas services, and gas midstream operations. Southern Company's reportable business segments are the sale of electricity by the four traditional electric operating companies, the sale of electricity in the competitive wholesale market by Southern Power, and the sale of natural gas and other complementary products and services by Southern Company Gas. Revenues from sales by Southern Power to the traditional electric operating companies were $83 million and $100 million for the three months ended March 31, 2018 and 2017 , respectively. Revenues from sales of natural gas from Southern Company Gas to Southern Power were $36 million and $23 million for the three months ended March 31, 2018 and 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 months ended March 31, 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 March 31, 2018: Operating revenues $ 3,979 $ 509 $ (106 ) $ 4,382 $ 1,639 $ 401 $ (50 ) $ 6,372 Segment net income (loss) (a)(b)(c) 612 121 — 733 279 (74 ) — 938 Total assets at March 31, 2018 $ 72,893 $ 15,182 $ (262 ) $ 87,813 $ 22,568 $ 2,733 $ (1,547 ) $ 111,567 Three Months Ended March 31, 2017: Operating revenues $ 3,786 $ 450 $ (105 ) $ 4,131 $ 1,560 $ 123 $ (43 ) $ 5,771 Segment net income (loss) (a)(b)(d) 432 70 — 502 239 (84 ) 1 658 Total assets at December 31, 2017 $ 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 the Kemper IGCC of $44 million ( $33 million after tax) and $108 million ( $67 million after tax) for the three months ended March 31, 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 "Kemper County Energy Facility" for additional information. (c) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 in contemplation of the sale of Pivotal Home Solutions. See Note (J) under "Southern Company Gas – Proposed Sale of Pivotal Home Solutions" for additional information. (d) Segment net income (loss) for the traditional electric operating companies also includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) for the three months ended March 31, 2017. See Note 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 March 31, 2018 $ 3,568 $ 619 $ 195 $ 4,382 Three Months Ended March 31, 2017 3,394 531 206 4,131 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended March 31, 2018 $ 1,200 $ 271 $ 168 $ 1,639 Three Months Ended March 31, 2017 1,132 288 140 1,560 Southern Company Gas Southern Company Gas manages its business through four reportable segments – gas distribution operations, gas marketing services, wholesale gas services, and gas midstream operations. The non-reportable segments are combined and presented as all other. Gas distribution operations is the largest component of Southern Company Gas' business and includes natural gas local distribution utilities that construct, manage, and maintain intrastate natural gas pipelines and gas distribution facilities in seven states. Gas marketing services includes natural gas marketing to end-use customers primarily in Georgia and Illinois. Additionally, gas marketing services provides home equipment protection products and services. Wholesale gas services provides natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. Additionally, wholesale gas services engages in natural gas storage and gas pipeline arbitrage and related activities. Gas midstream operations primarily consists of Southern Company Gas' pipeline investments, with storage and fuel operations also aggregated into this segment. The all other column includes segments below the quantitative threshold for separate disclosure, including the subsidiaries that fall below the quantitative threshold for separate disclosure. Business segment financial data for the three months ended March 31, 2018 and 2017 was as follows: Gas Distribution Operations Gas Marketing Services (a) Wholesale Gas Services (b) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2018: Operating revenues $ 1,212 $ 271 $ 166 $ 22 $ 1,671 $ 1 $ (33 ) $ 1,639 Segment net income 149 13 104 23 289 (10 ) — 279 Total assets at March 31, 2018: 18,332 2,144 903 2,263 23,642 11,839 (12,913 ) 22,568 Three Months Ended March 31, 2017: Operating revenues $ 1,180 $ 288 $ 131 $ 25 $ 1,624 $ 2 $ (66 ) $ 1,560 Segment net income 117 31 68 15 231 8 — 239 Total assets at December 31, 2017: 19,358 2,147 1,096 2,241 24,842 12,184 (14,039 ) 22,987 (a) Segment net income for gas marketing services includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 in contemplation of the sale of Pivotal Home Solutions. See Note (J) under "Southern Company Gas – Proposed Sale of Pivotal Home Solutions" for additional information. (b) 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 March 31, 2018 $ 1,938 $ 167 $ 2,105 $ 1,939 $ 166 Three Months Ended March 31, 2017 $ 1,839 $ 136 $ 1,975 $ 1,844 $ 131

Introduction (Policies)

Introduction (Policies)	3 Months Ended
	Mar. 31, 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 March 31, 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 certain fixed retail revenues and pole attachment revenues at Georgia Power have been reclassified from unbilled revenue and other accounts and notes receivable, respectively, in accordance with the guidance in ASC 606. Neither of these changes resulted in an adjustment to the timing or amount of the recognition of revenues 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 increase in natural gas revenues recognized in the first quarter 2018 relates primarily to the seasonal nature of natural gas usage and is expected to be offset by decreases in natural gas revenue recognized in future periods during 2018. The net impact of accounting for revenue under ASC 606 increased Southern Company's consolidated net income and net income per share by $10 million and $0.01 per basic share, respectively, for the three months ended March 31, 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 as of and for the three months ended March 31, 2018 compared to previously recognized guidance is shown below. As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Condensed Consolidated Statements of Income Natural gas revenues $ 1,607 $ 1,593 $ 14 Other revenues 413 412 1 Other operations and maintenance 1,451 1,441 10 Operating income 1,376 1,371 5 Other income (expense), net 60 51 9 Earnings before income taxes 1,049 1,035 14 Income taxes 113 109 4 Consolidated net income 936 926 10 Consolidated net income attributable to Southern Company 938 928 10 Basic earnings per share $ 0.93 $ 0.92 $ 0.01 Diluted earnings per share $ 0.92 $ 0.91 $ 0.01 Condensed Consolidated Statements of Cash Flow Consolidated net income $ 936 $ 926 $ 10 Changes in certain current assets and liabilities: Receivables 197 211 (14 ) Other current assets 7 (7 ) 14 Accrued taxes (79 ) (75 ) (4 ) Other current liabilities 81 67 14 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Condensed Consolidated Balance Sheet Unbilled revenues $ 777 $ 822 $ (45 ) Other accounts and notes receivable 703 709 (6 ) Other current assets 286 235 51 Accrued taxes 368 364 4 Other current liabilities 923 937 (14 ) Retained earnings 9,257 9,247 10 Alabama Power Condensed Statements of Income Other revenues $ 63 $ 55 $ 8 Other operations and maintenance 387 377 10 Operating income 372 374 (2 ) Other income (expense), net 5 3 2 Georgia Power Condensed Statements of Income Other revenues $ 109 $ 94 $ 15 Other operations and maintenance 408 394 14 Operating income 513 512 1 Other income (expense), net 38 39 (1 ) Condensed Statements of Cash Flows Changes in certain current assets and liabilities: Receivables $ 135 $ 145 $ (10 ) Other current assets 9 (1 ) 10 Condensed Balance Sheet Unbilled revenues $ 189 $ 202 $ (13 ) Other accounts and notes receivable 77 83 (6 ) Other current assets 39 20 19 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Gas Condensed Statements of Income Natural gas revenues $ 1,631 $ 1,617 $ 14 Operating income 388 374 14 Earnings before income taxes 383 369 14 Income taxes 104 100 4 Net income 279 269 10 Condensed Statements of Cash Flows Net income $ 279 $ 269 $ 10 Changes in certain current assets and liabilities: Accrued taxes 28 32 (4 ) Other current liabilities 48 34 14 Condensed Consolidated Balance Sheet Accrued income taxes $ 77 $ 73 $ 4 Other current liabilities 143 157 (14 ) Accumulated deficit (55 ) (65 ) 10 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 months ended March 31, 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 March 31, 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 March 31, 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	Hypothetical Liquidation at Book Value Southern Power has consolidated renewable generation projects that are partially financed 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 the stock option and performance share plans. See Note 8 to the financial statements of Southern Company in Item 8 of the Form 10-K for information on the stock option and performance share plans. The effect of both stock options and performance share award units was determined using the treasury stock method.
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 extended the moratorium on Gulf Power's fuel-hedging program until January 1, 2021 in connection with the 2017 Gulf Power Rate Case Settlement Agreement. The moratorium does not have an impact on the recovery of existing hedges entered into under the previously-approved hedging program. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in the statements of income. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts which are designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through the respective fuel cost recovery clauses. • Cash Flow Hedges — Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in OCI before being recognized in the statements of income in the same period 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)	3 Months Ended
	Mar. 31, 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 as of and for the three months ended March 31, 2018 compared to previously recognized guidance is shown below. As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Condensed Consolidated Statements of Income Natural gas revenues $ 1,607 $ 1,593 $ 14 Other revenues 413 412 1 Other operations and maintenance 1,451 1,441 10 Operating income 1,376 1,371 5 Other income (expense), net 60 51 9 Earnings before income taxes 1,049 1,035 14 Income taxes 113 109 4 Consolidated net income 936 926 10 Consolidated net income attributable to Southern Company 938 928 10 Basic earnings per share $ 0.93 $ 0.92 $ 0.01 Diluted earnings per share $ 0.92 $ 0.91 $ 0.01 Condensed Consolidated Statements of Cash Flow Consolidated net income $ 936 $ 926 $ 10 Changes in certain current assets and liabilities: Receivables 197 211 (14 ) Other current assets 7 (7 ) 14 Accrued taxes (79 ) (75 ) (4 ) Other current liabilities 81 67 14 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Condensed Consolidated Balance Sheet Unbilled revenues $ 777 $ 822 $ (45 ) Other accounts and notes receivable 703 709 (6 ) Other current assets 286 235 51 Accrued taxes 368 364 4 Other current liabilities 923 937 (14 ) Retained earnings 9,257 9,247 10 Alabama Power Condensed Statements of Income Other revenues $ 63 $ 55 $ 8 Other operations and maintenance 387 377 10 Operating income 372 374 (2 ) Other income (expense), net 5 3 2 Georgia Power Condensed Statements of Income Other revenues $ 109 $ 94 $ 15 Other operations and maintenance 408 394 14 Operating income 513 512 1 Other income (expense), net 38 39 (1 ) Condensed Statements of Cash Flows Changes in certain current assets and liabilities: Receivables $ 135 $ 145 $ (10 ) Other current assets 9 (1 ) 10 Condensed Balance Sheet Unbilled revenues $ 189 $ 202 $ (13 ) Other accounts and notes receivable 77 83 (6 ) Other current assets 39 20 19 As of and for the Three Months Ended March 31, 2018 As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Gas Condensed Statements of Income Natural gas revenues $ 1,631 $ 1,617 $ 14 Operating income 388 374 14 Earnings before income taxes 383 369 14 Income taxes 104 100 4 Net income 279 269 10 Condensed Statements of Cash Flows Net income $ 279 $ 269 $ 10 Changes in certain current assets and liabilities: Accrued taxes 28 32 (4 ) Other current liabilities 48 34 14 Condensed Consolidated Balance Sheet Accrued income taxes $ 77 $ 73 $ 4 Other current liabilities 143 157 (14 ) Accumulated deficit (55 ) (65 ) 10
Schedule of Goodwill	At March 31, 2018 and December 31, 2017 , goodwill was as follows: Goodwill At March 31, 2018 At December 31, 2017 (in millions) Southern Company $ 6,226 $ 6,268 Southern Power $ 2 $ 2 Southern Company Gas Gas distribution operations $ 4,702 $ 4,702 Gas marketing services 1,223 1,265 Southern Company Gas total $ 5,925 $ 5,967
Schedule of Goodwill and Other Intangible Assets	Other intangible assets were as follows: At March 31, 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 $ 288 $ (93 ) $ 195 $ 288 $ (83 ) $ 205 Trade names 159 (19 ) 140 159 (17 ) 142 Storage and transportation contracts 64 (40 ) 24 64 (34 ) 30 PPA fair value adjustments 456 (54 ) 402 456 (47 ) 409 Other 18 (6 ) 12 17 (5 ) 12 Total other intangible assets subject to amortization $ 985 $ (212 ) $ 773 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 1,060 $ (212 ) $ 848 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 456 $ (54 ) $ 402 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 221 $ (86 ) $ 135 $ 221 $ (77 ) $ 144 Trade names 115 (10 ) 105 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (40 ) 24 64 (34 ) 30 Total other intangible assets subject to amortization $ 400 $ (136 ) $ 264 $ 400 $ (120 ) $ 280
Finite-lived Intangible Assets Amortization Expense	Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2018 (in millions) Southern Company $ 26 Southern Power $ 7 Southern Company Gas $ 16
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 March 31, 2018 and/or December 31, 2017: Southern Company Southern Company Gas (in millions) At March 31, 2018 Cash and cash equivalents $ 2,284 $ 94 Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,290 $ 100 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 March 31, 2018 and/or December 31, 2017: Southern Company Southern Company Gas (in millions) At March 31, 2018 Cash and cash equivalents $ 2,284 $ 94 Restricted cash: Other accounts and notes receivable 6 6 Total cash, cash equivalents, and restricted cash $ 2,290 $ 100 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)	3 Months Ended
	Mar. 31, 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 March 31, December 31, (in millions) Rate CNP Compliance Deferred under recovered regulatory clause revenues $ 15 $ 17 Rate CNP PPA Deferred under recovered regulatory clause revenues 8 12 Retail Energy Cost Recovery Deferred under recovered regulatory clause revenues 78 25 Natural Disaster Reserve Other regulatory liabilities, deferred 38 38 Regulatory clause recovery balances included in the balance sheets are as follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, (in millions) Fuel Cost Recovery Under recovered regulatory clause revenues $ 4 $ 22 Purchased Power Capacity Recovery Under recovered regulatory clause revenues 4 2 Environmental Cost Recovery (*) Under recovered regulatory clause revenues 2 2 (*) At March 31, 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 $12 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 with in-service dates of November 2021 and November 2022, respectively, is as follows: (in billions) Project capital cost forecast $ 7.3 Net investment as of March 31, 2018 (3.7 ) Remaining estimate to complete $ 3.6 Note: Excludes financing costs capitalized through AFUDC and is 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.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on a Recurring Basis	As of March 31, 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 March 31, 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) $ 360 $ 172 $ — $ — $ 532 Foreign currency derivatives — 182 — — 182 Nuclear decommissioning trusts (c) 776 1,019 — 32 1,827 Cash equivalents 1,664 — — — 1,664 Other investments 9 — 1 — 10 Total $ 2,809 $ 1,373 $ 1 $ 32 $ 4,215 Liabilities: Energy-related derivatives (a)(b) $ 506 $ 136 $ — $ — $ 642 Interest rate derivatives — 61 — — 61 Foreign currency derivatives — 22 — — 22 Contingent consideration — — 22 — 22 Total $ 506 $ 219 $ 22 $ — $ 747 Alabama Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Nuclear decommissioning trusts: (d) Domestic equity 437 83 — — 520 Foreign equity 63 58 — — 121 U.S. Treasury and government agency securities — 19 — — 19 Corporate bonds 21 162 — — 183 Mortgage and asset backed securities — 17 — — 17 Private Equity — — — 32 32 Other 6 — — — 6 Cash equivalents 459 — — — 459 Total $ 986 $ 342 $ — $ 32 $ 1,360 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 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 $ — $ 5 $ — $ — $ 5 Nuclear decommissioning trusts: (d) (e) Domestic equity 238 1 — — 239 Foreign equity — 141 — — 141 U.S. Treasury and government agency securities — 241 — — 241 Municipal bonds — 76 — — 76 Corporate bonds — 168 — — 168 Mortgage and asset backed securities — 40 — — 40 Other 11 14 — — 25 Cash equivalents 1,055 — — — 1,055 Total $ 1,304 $ 686 $ — $ — $ 1,990 Liabilities: Energy-related derivatives $ — $ 18 $ — $ — $ 18 Interest rate derivatives — 8 — — 8 Total $ — $ 26 $ — $ — $ 26 Gulf Power Assets: Cash equivalents $ 27 $ — $ — $ — $ 27 Liabilities: Energy-related derivatives $ — $ 17 $ — $ — $ 17 Mississippi Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Cash equivalents 103 — — — 103 Total $ 103 $ 2 $ — $ — $ 105 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 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 $ — $ 4 $ — $ — $ 4 Foreign currency derivatives — 182 — — 182 Total $ — $ 186 $ — $ — $ 186 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 22 — — 22 Contingent consideration — — 22 — 22 Total $ — $ 25 $ 22 $ — $ 47 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 360 $ 158 $ — $ — $ 518 Liabilities: Energy-related derivatives (a)(b) $ 506 $ 82 $ — $ — $ 588 (a) Excludes $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $223 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. (e) Includes the investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2018 , approximately $76 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program.
Fair Value Measurements of Investments Calculated at Net Asset Value per Share as Well as the Nature and Risk of Those Investments	As of March 31, 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 March 31, 2018: Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period (in millions) Southern Company $ 32 $ 19 Not Applicable Not Applicable Alabama Power $ 32 $ 19 Not Applicable Not Applicable
Financial Instruments for Which Carrying Amount Did Not Equal Fair Value	As of March 31, 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 $ 47,479 $ 48,836 Alabama Power 7,626 8,093 Georgia Power 11,402 11,851 Gulf Power 1,285 1,317 Mississippi Power 1,781 1,790 Southern Power 5,878 6,006 Southern Company Gas 6,036 6,276

Revenue from Contracts with C26

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following tables disaggregate revenue sources for the three months ended March 31, 2018 : For the Three Months Ended March 31, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,539 Commercial 1,243 Industrial 756 Other 30 Natural gas distribution revenues 1,224 Alternative revenue programs (b) (24 ) Total retail electric and gas distribution revenues $ 4,768 Wholesale energy revenues (c)(d) 468 Wholesale capacity revenues (d) 151 Other natural gas revenues (e) 407 Other revenues (f) 578 Total operating revenues $ 6,372 (a) Retail electric revenues include $18 million of leases and a net increase of $117 million 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 $93 million of revenues accounted for as derivatives, primarily related to revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. See Note (I) for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $69 million and $30 million , respectively, 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 $1.9 billion , of which $1.1 billion 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 $90 million of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2018 Alabama Power Georgia Power Gulf Power Mississippi Power (in millions) Operating revenues Retail revenues (a)(b) Residential $ 570 $ 744 $ 165 $ 60 Commercial 371 717 92 62 Industrial 338 316 32 70 Other 6 21 1 2 Total retail electric revenues $ 1,285 $ 1,798 $ 290 $ 194 Wholesale energy revenues (c) 101 40 35 93 Wholesale capacity revenues 24 14 6 4 Other revenues (b)(d) 63 109 17 11 Total operating revenues $ 1,473 $ 1,961 $ 348 $ 302 (a) Retail revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include a net increase or (net reduction) of $47 million , $10 million , $(16) million , and $76 million , respectively, 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, of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, Gulf Power, and Mississippi Power include $5 million , $7 million , $1 million , and $1 million , respectively, accounted for as derivatives primarily related to physical energy sales in the forward and spot markets. See Note (I) for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power, Georgia Power, and Gulf Power include $25 million , $26 million , and $2 million , respectively, of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2018 (in millions) Southern Power PPA capacity revenues (a) $ 138 PPA energy revenues (a) 254 Non-PPA revenues (b) 115 Other revenues 2 Total operating revenues $ 509 (a) PPA capacity revenues and PPA energy revenues include $47 million and $76 million , respectively, 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 $79 million 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 March 31, 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 660 Commercial 192 Transportation 277 Industrial 17 Other 78 Alternative revenue programs (a) (24 ) Total natural gas distribution revenues $ 1,200 Gas marketing services (b) 271 Wholesale gas services (c) 146 Gas midstream operations 22 Total operating revenues $ 1,639 (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 $3 million and $1 million of revenues accounted for as derivatives and leases, respectively. See Note (I) for additional information on energy-related derivative contracts. (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 $1.9 billion , of which $1.1 billion 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 March 31, 2018: Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,607 $ 60 $ 52 Alabama Power 507 — 11 Georgia Power 600 29 5 Gulf Power 129 — 1 Mississippi Power 64 — — Southern Power 78 — 4 Southern Company Gas 948 — 15
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	Revenues from contracts with customers related to these performance obligations remaining at March 31, 2018 are expected to be recognized as follows: 2018 2019 2020 2021 2022 2023 and Thereafter (in millions) Southern Company $ 458 $ 403 $ 369 $ 358 $ 345 $ 2,161 Alabama Power 16 21 22 26 22 161 Georgia Power 31 41 38 40 30 113 Gulf Power 16 22 — — — — Mississippi Power 2 3 3 1 — — Southern Power 384 350 330 313 312 2,010

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Earnings per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) As reported shares 1,011 993 Effect of options and performance share award units 5 7 Diluted shares 1,016 1,000
Changes in Stockholders' Equity	The following table presents year-to-date changes in stockholders' equity of Southern Company: Number of Common Shares Common Preferred and Preference Stock of Subsidiaries Total Issued Treasury Noncontrolling Interests (*) (in thousands) (in millions) Balance at December 31, 2017 1,008,532 (929 ) $ 24,167 $ — $ 1,361 $ 25,528 Consolidated net income attributable to Southern Company — — 938 — — 938 Other comprehensive income — — 30 — — 30 Stock issued 4,055 — 113 — — 113 Stock-based compensation — — 36 — — 36 Cash dividends on common stock — — (586 ) — — (586 ) Contributions from noncontrolling interests — — — — 9 9 Distributions to noncontrolling interests — — — — (13 ) (13 ) Net income (loss) attributable to noncontrolling interests — — — — (6 ) (6 ) Other — (33 ) (22 ) — (2 ) (24 ) Balance at March 31, 2018 1,012,587 (962 ) $ 24,676 $ — $ 1,349 $ 26,025 Balance at December 31, 2016 991,213 (819 ) $ 24,758 $ 609 $ 1,245 $ 26,612 Consolidated net income attributable to Southern Company — — 658 — — 658 Other comprehensive income (loss) — — (9 ) — — (9 ) Stock issued 4,240 — 186 — — 186 Stock-based compensation — — 57 — — 57 Cash dividends on common stock — — (556 ) — — (556 ) Contributions from noncontrolling interests — — — — 71 71 Distributions to noncontrolling interests — — — — (18 ) (18 ) Net income (loss) attributable to noncontrolling interests — — — — (4 ) (4 ) Other — (35 ) — — (1 ) (1 ) Balance at March 31, 2017 995,453 (854 ) $ 25,094 $ 609 $ 1,293 $ 26,996 (*) 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.

Financing (Tables)

Financing (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Credit Arrangements by Company	The following table outlines the committed credit arrangements by company as of March 31, 2018 : Expires Executable Term Loans Expires Within One Year Company 2018 2019 2020 2022 Total Unused One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — $ — Alabama Power 35 — 500 800 1,335 1,335 — — — 35 Georgia Power — — — 1,750 1,750 1,736 — — — — Gulf Power 20 25 235 — 280 280 45 — 20 — Mississippi Power 100 — — — 100 100 — — — 100 Southern Power Company (b) — — — 750 750 728 — — — — Southern Company Gas (c) — — — 1,900 1,900 1,890 — — — — Other 30 — — — 30 30 20 — 20 10 Southern Company Consolidated $ 185 $ 25 $ 735 $ 7,200 $ 8,145 $ 8,098 $ 65 $ — $ 40 $ 145 (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 $21 million remains unused at March 31, 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 three months of 2018 : Company Senior Note Issuances Revenue Bond Other Long-Term Debt Redemptions and Maturities (*) (in millions) Georgia Power $ — $ 278 $ 102 Mississippi Power 600 — 900 Other — — 3 Southern Company Consolidated $ 600 $ 278 $ 1,005 (*) Includes reductions in capital lease obligations resulting from cash payments under capital leases.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three months ended March 31, 2018 and 2017 are presented in the following tables. Three Months Ended March 31, 2018 Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 90 $ 19 $ 22 $ 4 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 5 1 10 Expected return on plan assets (236 ) (51 ) (74 ) (10 ) (10 ) (3 ) (18 ) Amortization: Prior service costs 1 — — — — — (1 ) Regulatory asset — — — — — — 3 Net (gain)/loss 53 14 17 2 3 1 3 Net periodic pension cost (income) $ 24 $ 7 $ — $ 1 $ 2 $ 1 $ 5 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ — $ 1 Interest cost 19 4 7 1 1 — 2 Expected return on plan assets (17 ) (6 ) (6 ) — — — (2 ) Amortization: Prior service costs 2 1 — — — — — Regulatory asset — — — — — — 1 Net (gain)/loss 3 — 2 — — — — Net periodic postretirement benefit cost $ 13 $ — $ 5 $ 1 $ 1 $ — $ 2 Three Months Ended March 31, 2017 (*) Southern Company Alabama Power Georgia Power Gulf Power Mississippi Power Southern Company Gas (in millions) Pension Plans Service cost $ 73 $ 16 $ 19 $ 3 $ 4 $ 6 Interest cost 114 24 34 5 5 10 Expected return on plan assets (224 ) (49 ) (71 ) (10 ) (10 ) (18 ) Amortization: Prior service costs 3 1 1 — — — Net (gain)/loss 40 10 14 2 2 5 Net periodic pension cost (income) $ 6 $ 2 $ (3 ) $ — $ 1 $ 3 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ 1 Interest cost 20 5 7 1 1 3 Expected return on plan assets (16 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 2 1 — — — (1 ) Net (gain)/loss 2 — 2 — — 1 Net periodic postretirement benefit cost $ 14 $ 1 $ 5 $ 1 $ 1 $ 2 (*) Excludes Southern Power since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017.

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Energy-Related Derivatives	At March 31, 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 (*) 670 2021 2026 Alabama Power 74 2021 — Georgia Power 167 2021 — Gulf Power 17 2020 — Mississippi Power 59 2021 — Southern Power 14 2020 2018 Southern Company Gas (*) 339 2020 2026 (*) 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 3.6 billion mmBtu and short natural gas positions of 3.3 billion mmBtu as of March 31, 2018 , which is also included in Southern Company's total volume.
Schedule of Interest Rate Derivatives	At March 31, 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 March 31, 2018 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month June 2020 $ (5 ) Southern Company (*) 1,500 2.35% 1-month July 2021 (50 ) Georgia Power 250 5.40% 3-month June 2018 (1 ) Georgia Power 500 1.95% 3-month December 2018 (4 ) Georgia Power 200 4.25% 3-month December 2019 (2 ) Southern Company Consolidated $ 2,750 $ (62 ) (*) Represents the Southern Company parent entity.
Schedule of Foreign Currency Derivatives	At March 31, 2018 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2018 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 83 Southern Power 564 3.78% 500 1.85% June 2026 77 Total $ 1,241 € 1,100 $ 160
Fair Value of Energy-Related Derivatives and Interest Rate Derivatives	The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 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 $ 7 $ 28 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 4 27 7 24 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 55 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 3 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Interest rate derivatives: Other current assets/Other current liabilities — 14 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 47 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 22 — 23 Other deferred charges and assets/Other deferred credits and liabilities 182 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 186 $ 87 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 283 $ 299 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 234 284 170 215 Total derivatives not designated as hedging instruments $ 517 $ 583 $ 550 $ 652 Gross amounts recognized $ 714 $ 725 $ 700 $ 794 Gross amounts offset (a) $ (336 ) $ (559 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 378 $ 166 $ 295 $ 196 As of March 31, 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 $ 2 $ 3 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 5 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 8 $ 4 $ 10 Gross amounts recognized $ 3 $ 8 $ 4 $ 10 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 1 $ 6 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 6 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 2 12 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 5 $ 18 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 6 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — 2 — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 8 $ — $ 5 Gross amounts recognized $ 5 $ 26 $ 6 $ 24 Gross amounts offset $ (5 ) $ (5 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 21 $ — $ 18 Gulf Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ — $ 11 $ — $ 14 Other deferred charges and assets/Other deferred credits and liabilities — 6 — 7 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 17 $ — $ 21 Gross amounts recognized $ — $ 17 $ — $ 21 Gross amounts offset $ — $ — $ — $ — Net amounts recognized in the Balance Sheets $ — $ 17 $ — $ 21 As of March 31, 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 $ 1 $ 4 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 1 4 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 8 $ 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 $ 2 $ 8 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 6 $ 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 $ 3 $ 2 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 1 — — Foreign currency derivatives: Other current assets/Other current liabilities — 22 — 23 Other deferred charges and assets/Other deferred credits and liabilities 182 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 186 $ 25 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Gross amounts recognized $ 186 $ 25 $ 132 $ 36 Gross amounts offset $ (1 ) $ (1 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 185 $ 24 $ 129 $ 33 As of March 31, 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 $ 1 $ 4 $ 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 $ 283 $ 299 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 234 284 170 215 Total derivatives not designated as hedging instruments $ 517 $ 583 $ 549 $ 649 Gross amounts of recognized $ 518 $ 588 $ 554 $ 660 Gross amounts offset (a) $ (325 ) $ (548 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 193 $ 40 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $223 million and $193 million as of March 31, 2018 and December 31, 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $4 million and $11 million as of March 31, 2018 and December 31, 2017 , respectively.
Pre-tax Effects of Unrealized Derivative Gains (Losses) Arising from Energy-Related Derivative Instruments	At March 31, 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 March 31, 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 $ (20 ) $ (1 ) $ (3 ) $ (11 ) $ (3 ) $ (2 ) Other regulatory assets, deferred (23 ) (4 ) (10 ) (6 ) (3 ) — Other regulatory liabilities, current 7 — — — — 7 Total energy-related derivative gains (losses) $ (36 ) $ (5 ) $ (13 ) $ (17 ) $ (6 ) $ 5 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $8 million at March 31, 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 months ended March 31, 2018 and 2017 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Derivatives in Cash Flow Hedging Relationships Gain (Loss) Recognized in OCI on Derivative Gain (Loss) Reclassified from Accumulated OCI into Income Statements of Income Location Amount 2018 2017 2018 2017 (in millions) (in millions) Southern Company Energy-related derivatives $ 12 $ (11 ) Depreciation and amortization $ 1 $ (4 ) Cost of natural gas (2 ) — Interest rate derivatives (2 ) 1 Interest expense, net of amounts capitalized (5 ) (5 ) Foreign currency derivatives 53 (4 ) Interest expense, net of amounts capitalized (5 ) (6 ) Other income (expense), net (*) 36 17 Total $ 63 $ (14 ) $ 25 $ 2 Southern Power Energy-related derivatives $ 11 $ (8 ) Depreciation and amortization $ 1 $ (4 ) Foreign currency derivatives 53 (4 ) Interest expense, net of amounts capitalized (5 ) (6 ) Other income (expense), net (*) 36 17 Total $ 64 $ (12 ) $ 32 $ 7 (*) 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 Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location	For the three months ended March 31, 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 2018 2017 (in millions) Southern Company Depreciation and amortization $ 769 $ 716 Gain (loss) on cash flow hedges Energy-related derivatives 1 (4 ) Interest expense, net of amounts capitalized (458 ) (416 ) Gain (loss) on cash flow hedges Interest rate derivatives (5 ) (5 ) Foreign currency derivatives (5 ) (6 ) Gain (loss) on fair value hedges (a) Interest rate derivatives (24 ) (8 ) Other income (expense), net 60 48 Gain (loss) on cash flow hedges (b) Foreign currency derivatives 36 17 Southern Power Depreciation and amortization $ 114 $ 119 Gain (loss) on cash flow hedges Energy-related derivatives 1 (4 ) Interest expense, net of amounts capitalized (47 ) (50 ) Gain (loss) on cash flow hedges Foreign currency derivatives (5 ) (6 ) Other income (expense), net 3 (1 ) Gain (loss) on cash flow hedges (b) Foreign currency derivatives 36 17 (a) For fair value hedges presented above, changes in the fair value of the derivative contracts are equal to changes in the fair value of the underlying debt and have no impact on income. (b) 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 March 31, 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 March 31, 2018 As of December 31, 2017 As of March 31, 2018 As of December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (745 ) $ (746 ) $ 4 $ 3 Long-term Debt (2,533 ) (2,553 ) 57 35 Georgia Power Securities due within one year $ (745 ) $ (746 ) $ 4 $ 3 Long-term Debt (497 ) (498 ) 2 1
Pre-tax Effect of Interest Rate and Energy Related Derivatives	For the three months ended March 31, 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 March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 (in millions) Southern Company Energy-related derivatives: Natural gas revenues (*) $ (15 ) $ 50 Cost of natural gas 2 (3 ) Total derivatives in non-designated hedging relationships $ (13 ) $ 47 Southern Company Gas Energy-related derivatives: Natural gas revenues (*) $ (15 ) $ 50 Cost of natural gas 2 (3 ) Total derivatives in non-designated hedging relationships $ (13 ) $ 47 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of an immaterial amount and $14 million for the three months ended March 31, 2018 and 2017 , respectively.

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions	During the three months ended March 31, 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.
Schedule of Construction Projects	During the three months ended March 31, 2018 , Southern Power continued construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $370 million and $415 million for the Mankato and Cactus Flats facilities. At March 31, 2018 , construction costs included in CWIP related to these projects totaled $273 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 March 31, 2018 Cactus Flats (*) Wind 148 Concho County, TX Third quarter 2018 12-15 years Mankato Natural Gas 345 Mankato, MN Second quarter 2019 20 years (*) In July 2017, Southern Power purchased 100% of the Cactus Flats facility and commenced construction. Upon placing the facility in service, Southern Power expects to close on a tax equity partnership agreement, subject to various customary conditions at closing, and will then own 100% of the class B membership interests.

Joint Ownership Agreements (Tab

Joint Ownership Agreements (Tables)	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2018 and December 31, 2017 and related income from those investments for the three -month periods ended March 31, 2018 and March 31, 2017 were as follows: Balance Sheet Information March 31, 2018 December 31, 2017 (in millions) SNG $ 1,274 $ 1,262 Atlantic Coast Pipeline 49 41 PennEast Pipeline 62 57 Triton 42 42 Pivotal JAX LNG, LLC 45 44 Horizon Pipeline 31 30 Other 1 1 Total $ 1,504 $ 1,477 Selected financial information of SNG for the three months ended March 31, 2018 and March 31, 2017 is as follows: Income Statement Information Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) Revenues $ 160 $ 155 Operating income $ 99 $ 84 Net income $ 78 $ 66
Schedule of Other Nonoperating Income, by Component	Income Statement Information Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 (in millions) SNG $ 39 $ 34 PennEast Pipeline 1 3 Atlantic Coast Pipeline 1 1 Triton 1 — Horizon Pipeline — 1 Total $ 42 $ 39

Segment and Related Informati33

Segment and Related Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Financial Data for Business Segments	Financial data for business segments and products and services for the three months ended March 31, 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 March 31, 2018: Operating revenues $ 3,979 $ 509 $ (106 ) $ 4,382 $ 1,639 $ 401 $ (50 ) $ 6,372 Segment net income (loss) (a)(b)(c) 612 121 — 733 279 (74 ) — 938 Total assets at March 31, 2018 $ 72,893 $ 15,182 $ (262 ) $ 87,813 $ 22,568 $ 2,733 $ (1,547 ) $ 111,567 Three Months Ended March 31, 2017: Operating revenues $ 3,786 $ 450 $ (105 ) $ 4,131 $ 1,560 $ 123 $ (43 ) $ 5,771 Segment net income (loss) (a)(b)(d) 432 70 — 502 239 (84 ) 1 658 Total assets at December 31, 2017 $ 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 the Kemper IGCC of $44 million ( $33 million after tax) and $108 million ( $67 million after tax) for the three months ended March 31, 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 "Kemper County Energy Facility" for additional information. (c) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 in contemplation of the sale of Pivotal Home Solutions. See Note (J) under "Southern Company Gas – Proposed Sale of Pivotal Home Solutions" for additional information. (d) Segment net income (loss) for the traditional electric operating companies also includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) for the three months ended March 31, 2017. See Note 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 months ended March 31, 2018 and 2017 was as follows: Gas Distribution Operations Gas Marketing Services (a) Wholesale Gas Services (b) Gas Midstream Operations Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2018: Operating revenues $ 1,212 $ 271 $ 166 $ 22 $ 1,671 $ 1 $ (33 ) $ 1,639 Segment net income 149 13 104 23 289 (10 ) — 279 Total assets at March 31, 2018: 18,332 2,144 903 2,263 23,642 11,839 (12,913 ) 22,568 Three Months Ended March 31, 2017: Operating revenues $ 1,180 $ 288 $ 131 $ 25 $ 1,624 $ 2 $ (66 ) $ 1,560 Segment net income 117 31 68 15 231 8 — 239 Total assets at December 31, 2017: 19,358 2,147 1,096 2,241 24,842 12,184 (14,039 ) 22,987 (a) Segment net income for gas marketing services includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 in contemplation of the sale of Pivotal Home Solutions. See Note (J) under "Southern Company Gas – Proposed Sale of Pivotal Home Solutions" for additional information. (b) 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 March 31, 2018 $ 1,938 $ 167 $ 2,105 $ 1,939 $ 166 Three Months Ended March 31, 2017 $ 1,839 $ 136 $ 1,975 $ 1,844 $ 131
Financial Data for Products and Services	Products and Services Electric Utilities' Revenues Period Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2018 $ 3,568 $ 619 $ 195 $ 4,382 Three Months Ended March 31, 2017 3,394 531 206 4,131 Southern Company Gas' Revenues Period Gas Gas Other Total (in millions) Three Months Ended March 31, 2018 $ 1,200 $ 271 $ 168 $ 1,639 Three Months Ended March 31, 2017 1,132 288 140 1,560

Introduction - Narrative (Detai

Introduction - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Related Party Transaction [Line Items]
Net income	$ 936	$ 665
Basic earnings per share (in dollars per share)	$ 0.93	$ 0.66
SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income	$ 279	$ 239
Goodwill impairment	42	0
ALABAMA POWER CO
Related Party Transaction [Line Items]
Net income	229	178
GEORGIA POWER CO
Related Party Transaction [Line Items]
Net income	352	264
SOUTHERN POWER CO
Related Party Transaction [Line Items]
Net income	115	66
Wholesale Gas Services | SOUTHERN Co GAS
Related Party Transaction [Line Items]
Inventory write-down	$ 0	$ 0

Introduction - ASC 606 (Details

Introduction - ASC 606 (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	$ 1,607	$ 1,530
Other revenues	413	141
Other operations and maintenance	1,451	1,383
Operating income	1,376	1,252
Other income (expense), net	60	48
Earnings before income taxes	1,049	980
Income taxes	113	315
Net income	936	665
Consolidated net income attributable to Southern Company	$ 938	$ 658
Basic earnings per share (in dollars per share)	$ 0.93	$ 0.66
Diluted earnings per share (in dollars per share)	$ 0.92	$ 0.66
Condensed Consolidated Statements of Cash Flow
Net income	$ 936	$ 665
Changes in certain current assets and liabilities:
Receivables	197	310
Other current assets	7	(31)
Accrued taxes	(79)	(212)
Other current liabilities	81	(48)
Condensed Balance Sheet
Unbilled revenues	777		$ 810
Other accounts and notes receivable	703		698
Other current assets	286		211
Accrued taxes	368		636
Other current liabilities	923		874
Retained earnings	9,257		8,885
Balances Without Adoption of ASC 606
Condensed Statements of Income
Net income	$ 926
Basic earnings per share (in dollars per share)	$ 0.92
Diluted earnings per share (in dollars per share)	$ 0.91
Condensed Consolidated Statements of Cash Flow
Net income	$ 926
Changes in certain current assets and liabilities:
Receivables	211
Other current assets	7
Accrued taxes	(75)
Other current liabilities	67
Condensed Balance Sheet
Unbilled revenues	822
Other accounts and notes receivable	709
Other current assets	235
Accrued taxes	364
Other current liabilities	937
Retained earnings	9,247
ALABAMA POWER CO
Condensed Statements of Income
Other revenues	63	56
Other operations and maintenance	387	384
Operating income	372	361
Other income (expense), net	5	10
Earnings before income taxes	311	304
Income taxes	82	126
Net income	229	178
Consolidated net income attributable to Southern Company	225	174
Condensed Consolidated Statements of Cash Flow
Net income	229	178
Changes in certain current assets and liabilities:
Other current assets	19	39
Accrued taxes	57	77
Other current liabilities	45	(9)
Condensed Balance Sheet
Unbilled revenues	131		162
Other accounts and notes receivable	36		55
Other current assets	3		5
Accrued taxes	77		54
Other current liabilities	57		56
Retained earnings	2,670		2,647
ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	55
Other operations and maintenance	377
Operating income	374
Other income (expense), net	3
GEORGIA POWER CO
Condensed Statements of Income
Other revenues	109	96
Other operations and maintenance	408	399
Operating income	513	483
Other income (expense), net	38	38
Earnings before income taxes	445	420
Income taxes	93	156
Net income	352	264
Consolidated net income attributable to Southern Company	352	260
Condensed Consolidated Statements of Cash Flow
Net income	352	264
Changes in certain current assets and liabilities:
Receivables	135	142
Other current assets	9	(16)
Accrued taxes	(191)	(235)
Other current liabilities	(3)	2
Condensed Balance Sheet
Unbilled revenues	189		255
Other accounts and notes receivable	77		76
Other current assets	39		14
Other current liabilities	215		198
Retained earnings	4,228		4,215
Accrued income taxes	129		344
GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	94
Other operations and maintenance	394
Operating income	512
Other income (expense), net	39
Changes in certain current assets and liabilities:
Receivables	145
Other current assets	(1)
Condensed Balance Sheet
Unbilled revenues	202
Other accounts and notes receivable	83
Other current assets	20
SOUTHERN Co GAS
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,631	1,521
Other revenues	32	30
Other operations and maintenance	276	255
Operating income	388	389
Other income (expense), net	12	7
Earnings before income taxes	383	389
Income taxes	104	150
Net income	279	239
Consolidated net income attributable to Southern Company	279	239
Condensed Consolidated Statements of Cash Flow
Net income	279	239
Changes in certain current assets and liabilities:
Receivables	175	115
Other current assets	14	19
Accrued taxes	28	19
Other current liabilities	48	49
Condensed Balance Sheet
Unbilled revenues	210		285
Other accounts and notes receivable	51		103
Other current assets	51		78
Accrued taxes	76		78
Other current liabilities	143		159
Retained earnings	(55)		(212)
Accrued income taxes	77		$ 40
SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,617
Operating income	374
Earnings before income taxes	369
Income taxes	100
Net income	269
Condensed Consolidated Statements of Cash Flow
Net income	269
Changes in certain current assets and liabilities:
Accrued taxes	32
Other current liabilities	34
Condensed Balance Sheet
Other current liabilities	157
Retained earnings	(65)
Accrued income taxes	73
Operating Segments | SOUTHERN Co GAS
Condensed Statements of Income
Consolidated net income attributable to Southern Company	289	$ 231
SOUTHERN Co GAS | Operating Segments | SOUTHERN Co GAS
Condensed Statements of Income
Consolidated net income attributable to Southern Company	279
Southern Company
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,607
Other revenues	413
Southern Company | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,593
Other revenues	412
Other operations and maintenance	1,441
Operating income	1,371
Other income (expense), net	51
Earnings before income taxes	1,035
Income taxes	109
Net income	926
Consolidated net income attributable to Southern Company	928
Condensed Consolidated Statements of Cash Flow
Net income	926
Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Net income	$ 10
Basic earnings per share (in dollars per share)	$ 0.01
Diluted earnings per share (in dollars per share)	$ 0.01
Condensed Consolidated Statements of Cash Flow
Net income	$ 10
Changes in certain current assets and liabilities:
Receivables	(14)
Other current assets	(14)
Accrued taxes	(4)
Other current liabilities	14
Condensed Balance Sheet
Unbilled revenues	(45)
Other accounts and notes receivable	(6)
Other current assets	51
Accrued taxes	4
Other current liabilities	(14)
Retained earnings	10
Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	8
Other operations and maintenance	10
Operating income	(2)
Other income (expense), net	2
Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	15
Other operations and maintenance	14
Operating income	1
Other income (expense), net	(1)
Changes in certain current assets and liabilities:
Receivables	(10)
Other current assets	10
Condensed Balance Sheet
Unbilled revenues	(13)
Other accounts and notes receivable	(6)
Other current assets	19
Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	14
Operating income	14
Earnings before income taxes	14
Income taxes	4
Net income	10
Condensed Consolidated Statements of Cash Flow
Net income	10
Changes in certain current assets and liabilities:
Accrued taxes	(4)
Other current liabilities	14
Condensed Balance Sheet
Other current liabilities	(14)
Retained earnings	10
Accrued income taxes	4
Accounting Standards Update 2014-09 | Southern Company | Effect of Change
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	14
Other revenues	1
Other operations and maintenance	10
Operating income	5
Other income (expense), net	9
Earnings before income taxes	14
Income taxes	4
Net income	10
Consolidated net income attributable to Southern Company	10
Condensed Consolidated Statements of Cash Flow
Net income	$ 10

Introduction - Goodwill (Detail

Introduction - Goodwill (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 6,226	$ 6,268
SOUTHERN POWER CO
Goodwill [Line Items]
Goodwill	2	2
SOUTHERN Co GAS
Goodwill [Line Items]
Goodwill	5,925	5,967
SOUTHERN Co GAS | Gas distribution operations
Goodwill [Line Items]
Goodwill	4,702	4,702
SOUTHERN Co GAS | Gas marketing services
Goodwill [Line Items]
Goodwill	$ 1,223	$ 1,265

Introduction - Other Intangible

Introduction - Other Intangibles (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 985	$ 984
Accumulated Amortization	(212)	(186)
Other Intangible Assets, Net	773	798
Total other intangible assets - gross	1,060	1,059
Total other intangible assets - net	848	873
Customer relationships | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	288	288
Accumulated Amortization	(93)	(83)
Other Intangible Assets, Net	195	205
Trade names | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	159	159
Accumulated Amortization	(19)	(17)
Other Intangible Assets, Net	140	142
Storage and transportation contracts | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(40)	(34)
Other Intangible Assets, Net	24	30
PPA fair value adjustments | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(54)	(47)
Other Intangible Assets, Net	402	409
Other | Southern Company
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	18	17
Accumulated Amortization	(6)	(5)
Other Intangible Assets, Net	12	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	(54)	(47)
SOUTHERN POWER CO | PPA fair value adjustments
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	456	456
Accumulated Amortization	(54)	(47)
Other Intangible Assets, Net	402	409
SOUTHERN Co GAS
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	400	400
Accumulated Amortization	(136)	(120)
Other Intangible Assets, Net	264	280
Total other intangible assets - net	264	280
SOUTHERN Co GAS | Customer relationships
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	221	221
Accumulated Amortization	(86)	(77)
Other Intangible Assets, Net	135	144
SOUTHERN Co GAS | Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	115	115
Accumulated Amortization	(10)	(9)
Other Intangible Assets, Net	105	106
SOUTHERN Co GAS | Storage and transportation contracts
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(40)	(34)
Other Intangible Assets, Net	$ 24	$ 30

Introduction - Intangibles, Amo

Introduction - Intangibles, Amortization (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 26
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	7
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 16

Introduction - Restricted Cash

Introduction - Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 2,284	$ 2,130
Restricted cash:
Total cash, cash equivalents, and restricted cash	2,290	2,147	$ 1,116	$ 1,992
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	94	73
Restricted cash:
Other accounts and notes receivable	6	5
Deferred charges and other assets		0
Total cash, cash equivalents, and restricted cash	100	78	33	24
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	82	129
Restricted cash:
Other accounts and notes receivable		0
Deferred charges and other assets		11
Total cash, cash equivalents, and restricted cash	82	140	$ 110	$ 1,112
Southern Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	2,284
Restricted cash:
Other accounts and notes receivable	6	5
Deferred charges and other assets		12
Total cash, cash equivalents, and restricted cash	$ 2,290	$ 2,147

Contingencies and Regulatory 40

Contingencies and Regulatory Matters - General (Details) $ in Thousands	Mar. 02, 2018USD ($)generating_plant	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability		$ 22,000	$ 22,000
GULF POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability		49,000	52,000
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability		369,000	$ 388,000
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Fuel Cost Recovery				$ 3,000	$ 6,000
RE Roserock, LLC | SOUTHERN POWER CO
Loss Contingencies [Line Items]
Ownership percentage by parent						51.00%
Loss contingency, payments		26,000
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability		$ 2,000
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

Contingencies and Regulatory 41

Contingencies and Regulatory Matters - Alabama Power (Details) - ALABAMA POWER CO - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Deferred under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 15	$ 17
Rate CNP PPA	8	12
Retail Energy Cost Recovery	78	25
Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Natural Disaster Reserve	$ 38	$ 38

Contingencies and Regulatory 42

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	Mar. 31, 2018	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
Loss Contingencies [Line Items]
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%
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%
Subsequent Event
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage		55.00%
Public utilities, allowed weighted common equity return, percentage		6.15%	6.21%
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
Subsequent Event | Minimum
Loss Contingencies [Line Items]
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit		30
Subsequent Event | Maximum
Loss Contingencies [Line Items]
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit		$ 50
Scenario, Forecast
Loss Contingencies [Line Items]
Customer refundable fees, refund payments					$ 257	$ 50
Current billing rates under rate ecr in terms of per units | $ / KWH_Kilowatt_hour	5.910
Rate RSE | Subsequent Event | Minimum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		3 days
Rate RSE | Subsequent Event | Maximum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		5 days
Rate ECR | Subsequent Event | Minimum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		3 days
Rate ECR | Subsequent Event | Maximum
Loss Contingencies [Line Items]
Public utilities, public service commission, days to accept issuance		5 days

Contingencies and Regulatory 43

Contingencies and Regulatory Matters - Georgia Power (Details) $ in Millions	Apr. 03, 2018USD ($)	Feb. 29, 2020USD ($)	Jun. 30, 2019USD ($)	Oct. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2019	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Effective tax rate					10.80%	32.10%
Deferred income tax expense (benefit)					$ 34	$ 161
GEORGIA POWER CO
Loss Contingencies [Line Items]
Deferred income tax expense (benefit)					(38)	$ 71
Under recovered fuel balance, threshold for interim fuel rider					200
GEORGIA POWER CO | Other current liabilities
Loss Contingencies [Line Items]
Over recovered fuel balance					$ 156			$ 165
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%
Subsequent Event | GEORGIA POWER CO
Loss Contingencies [Line Items]
Customer refund	$ 330
Deferred income tax expense (benefit)	(700)
Customer refund liability in absence of base rate case	$ 185
Subsequent Event | GEORGIA POWER CO | Maximum
Loss Contingencies [Line Items]
Retail regulatory equity ratio	0.55
Subsequent Event | State and Local Jurisdiction | GEORGIA POWER CO
Loss Contingencies [Line Items]
Effective tax rate	6.00%

Contingencies and Regulatory 44

Contingencies and Regulatory Matters - Gulf Power (Details) - GULF POWER CO $ in Millions	Mar. 26, 2018USD ($)	Jul. 01, 2017	Mar. 31, 2018USD ($)	Mar. 31, 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
Retail regulatory equity ratio	0.535	0.525
Environmental Cost Recovery			$ 10		$ 11
Projected environmental expenditures			12	$ 13
Under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery			4		22
Purchased Power Capacity Recovery			4		2
Environmental Cost Recovery			$ 2		$ 2

Contingencies and Regulatory 45

Contingencies and Regulatory Matters - Mississippi Power (Details) - MISSISSIPPI POWER CO - USD ($)	Mar. 22, 2018	Feb. 07, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 23, 2018	Feb. 14, 2018	Sep. 30, 2017
Loss Contingencies [Line Items]
Performance evaluation plan, increase (decrease) in requested annual revenue		$ 26,000,000
Public utilities, requested return on equity, percentage		9.33%
Performance evaluation plan, equity ratio		55.00%
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
Environmental compliance overview plan, maximum annual increase in revenue, percentage										2.00%
Environmental compliance overview plan, maximum annual increase in revenue, amount										$ 17,000,000
Deferred revenue										$ 13,000,000
Fuel Cost Recovery					$ 6,000,000						$ 3,000,000
Ad valorem tax adjustment, annual rate increase, percentage									0.80%
Ad valorem tax adjustment, annual rate increase, amount									$ 7,000,000

Contingencies and Regulatory 46

Contingencies and Regulatory Matters - Southern Company Gas (Details) - USD ($) $ in Millions	Dec. 02, 2019	Dec. 01, 2019	Jun. 01, 2019	Apr. 12, 2018	Mar. 26, 2018	Feb. 23, 2018	Feb. 15, 2018	Feb. 02, 2018	Dec. 31, 2017	Oct. 31, 2017	Dec. 31, 2019
Chattanooga Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount							$ 7
Public utilities, requested return on equity, percentage							11.25%
Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount						$ 16			$ 22
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%	54.00%
Public utilities, interim rate increase (decrease), percentage						3.00%
Nicor Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amended, amount								$ 44
Public utilities, requested return on equity, percentage								9.80%
Scenario, Forecast | Florida City Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amended, amount	$ 3.8	$ 1.3	$ 2.5
Public utilities, requested return on equity, percentage											56.00%
Public utilities, interim rate increase (decrease), percentage											2.00%
Subsequent Event | Elizabeth Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount				$ 11
Subsequent Event | 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 47

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

Jan. 01, 2021

Jan. 01, 2020

Mar. 31, 2018USD ($)

Feb. 28, 2018USD ($)

Jan. 30, 2018USD ($)

Jun. 09, 2017USD ($)

Dec. 20, 2016USD ($)

Jan. 01, 2016

Feb. 20, 2014USD ($)

Mar. 31, 2018USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2009USD ($)utilityMW

Dec. 31, 2008

Dec. 31, 2022USD ($)

Dec. 31, 2020USD ($)

Jun. 30, 2016USD ($)

Sep. 28, 2017USD ($)

Dec. 31, 2013

Loss Contingencies [Line Items]

Construction work in progress

$ 7,460

$ 7,460

$ 6,904

GEORGIA POWER CO

Loss Contingencies [Line Items]

Number of construction units approved | utility

2

Electric generating capacity in mega watts under consortium agreement | MW

1,100

Percentage of proportionate share owed in consortium agreement

45.70%

Construction work in progress

4,800

4,800

4,613

Estimated in-service capital cost

$ 4,418

Financing costs collected, net of tax

1,600

Additional construction capital costs

$ 3,300

Retail rate of return on common equity

10.95%

Eligible project costs to be reimbursed

$ 3,460

Plant Vogtle Units 3 And 4 | GEORGIA POWER CO

Loss Contingencies [Line Items]

Cost settlement agreement revised forecast

8,800

8,800

Cost settlement agreement revised forecast, net of payments

7,300

7,300

Guarantor obligations

$ 1,700

Customer refund

$ 188

Construction work in progress

3,600

$ 3,600

Construction financing costs

$ 1,600

Percentage of ownership interest required for voting for continuing construction

90.00%

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%

90.00%

Percentage of approval required for material amendments

67.00%

67.00%

Increase (decrease) in tariff

$ 50

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

Requested rate increase (decrease) amount

$ (500)

Scenario, Forecast | GEORGIA POWER CO

Loss Contingencies [Line Items]

Amendment to estimated in-service capital cost

$ 5,680

Scenario, Forecast | Plant Vogtle Units 3 And 4 | GEORGIA POWER CO

Loss Contingencies [Line Items]

Construction financing costs

$ 3,100

Public utilities, approved return on equity percentage

5.30%

8.30%

Return on equity reduction, negative impact on earnings

$ 100

$ 585

Vogtle Owners | Plant Vogtle Units 3 And 4 | GEORGIA POWER CO

Loss Contingencies [Line Items]

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

30 days

FFB Loan | GEORGIA POWER CO

Loss Contingencies [Line Items]

Long-term line of credit

$ 2,600

$ 2,600

Conditional borrowing commitment

$ 1,670

Contingencies and Regulatory 48

Contingencies and Regulatory Matters - Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 $ in Billions	Mar. 31, 2018USD ($)
Loss Contingencies [Line Items]
Estimated cost to complete	$ 7.3
Net investment as of March 31, 2018	(3.7)
Remaining estimate to complete	$ (3.6)

Contingencies and Regulatory 49

Contingencies and Regulatory Matters - Kemper County Energy Facility (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Loss Contingencies [Line Items]
Estimated loss on Kemper IGCC	$ 44	$ 108
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Estimated loss on Kemper IGCC	44	$ 108
Accrued plant closure costs	61					$ 35
Kemper County Energy Facility | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment	44
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment after tax	33
Accrued plant closure costs	$ 50
Kemper County Energy Facility | Scenario, Forecast | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Production costs, period Cost			$ 4	$ 1	$ 4

Contingencies and Regulatory 50

Contingencies and Regulatory Matters - Other Matters (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Southern Company Holdings Subsidiary
Loss Contingencies [Line Items]
Leveraged leases, balance sheet, investment in leveraged leases	$ 86
Natural Gas Storage
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, net	$ 111
Natural Gas Storage - Salt Dome Caverns
Loss Contingencies [Line Items]
Public utilities, property, plant and equipment, percentage of total	20.00%

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Fair Value	$ 32
Liabilities:
Collateral already posted, aggregate fair value	223
Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	532
Foreign currency derivatives	182
Nuclear decommissioning trusts	1,827
Cash equivalents	1,664
Other investments	10
Total	4,215
Liabilities:
Energy-related derivatives	642
Interest rate derivatives	61
Foreign currency derivatives	22
Contingent consideration	22
Total	747
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	360
Foreign currency derivatives	0
Nuclear decommissioning trusts	776
Cash equivalents	1,664
Other investments	9
Total	2,809
Liabilities:
Energy-related derivatives	506
Interest rate derivatives	0
Foreign currency derivatives	0
Contingent consideration	0
Total	506
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	172
Foreign currency derivatives	182
Nuclear decommissioning trusts	1,019
Cash equivalents	0
Other investments	0
Total	1,373
Liabilities:
Energy-related derivatives	136
Interest rate derivatives	61
Foreign currency derivatives	22
Contingent consideration	0
Total	219
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	3	$ 4
Fair Value	32
Liabilities:
Energy-related derivatives	8	10
ALABAMA POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	3
Cash equivalents	459
Total	1,360
Liabilities:
Energy-related derivatives	8
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Domestic equity
Assets:
Nuclear decommissioning trusts	520
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Foreign equity
Assets:
Nuclear decommissioning trusts	121
ALABAMA POWER CO | Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	19
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Nuclear decommissioning trusts	183
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	17
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Private Equity
Assets:
Nuclear decommissioning trusts	32
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Other
Assets:
Nuclear decommissioning trusts	6
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Cash equivalents	459
Total	986
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	437
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Assets:
Nuclear decommissioning trusts	63
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	21
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	6
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	3
Cash equivalents	0
Total	342
Liabilities:
Energy-related derivatives	8
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Assets:
Nuclear decommissioning trusts	83
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Assets:
Nuclear decommissioning trusts	58
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	19
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Nuclear decommissioning trusts	162
ALABAMA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	17
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	5	6
Nuclear decommissioning trusts	76
Liabilities:
Energy-related derivatives	26	24
GEORGIA POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	5
Cash equivalents	1,055
Total	1,990
Liabilities:
Energy-related derivatives	18
Interest rate derivatives	8
Total	26
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Domestic equity
Assets:
Nuclear decommissioning trusts	239
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Foreign equity
Assets:
Nuclear decommissioning trusts	141
GEORGIA POWER CO | Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	241
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Nuclear decommissioning trusts	168
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	40
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Other
Assets:
Nuclear decommissioning trusts	25
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Municipal bonds
Assets:
Nuclear decommissioning trusts	76
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Cash equivalents	1,055
Total	1,304
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	238
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) | 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	11
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 | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	5
Cash equivalents	0
Total	686
Liabilities:
Energy-related derivatives	18
Interest rate derivatives	8
Total	26
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	141
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Assets:
Nuclear decommissioning trusts	241
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Nuclear decommissioning trusts	168
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage and asset backed securities
Assets:
Nuclear decommissioning trusts	40
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other
Assets:
Nuclear decommissioning trusts	14
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Assets:
Nuclear decommissioning trusts	76
GEORGIA 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
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) | 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
GEORGIA POWER CO | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds
Assets:
Nuclear decommissioning trusts	0
GULF POWER CO
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	17	21
GULF POWER CO | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	27
Liabilities:
Energy-related derivatives	17
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	17
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	2	3
Liabilities:
Energy-related derivatives	8	9
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	2
Cash equivalents	103
Total	105
Liabilities:
Energy-related derivatives	8
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	0
Cash equivalents	103
Total	103
Liabilities:
Energy-related derivatives	0
MISSISSIPPI POWER CO | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	2
Cash equivalents	0
Total	2
Liabilities:
Energy-related derivatives	8
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	186	132
Liabilities:
Energy-related derivatives	25	36
SOUTHERN POWER CO | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	4
Foreign currency derivatives	182
Total	186
Liabilities:
Energy-related derivatives	3
Foreign currency derivatives	22
Contingent consideration	22
Total	47
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	4
Foreign currency derivatives	182
Total	186
Liabilities:
Energy-related derivatives	3
Foreign currency derivatives	22
Contingent consideration	0
Total	25
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	518	554
Liabilities:
Energy-related derivatives	588	660
Collateral already posted, aggregate fair value	223	$ 193
SOUTHERN Co GAS | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	518
Liabilities:
Energy-related derivatives	588
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Energy-related derivatives	360
Liabilities:
Energy-related derivatives	506
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Energy-related derivatives	158
Liabilities:
Energy-related derivatives	82
SOUTHERN Co GAS | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Energy-related derivatives	0
Liabilities:
Energy-related derivatives	0
Nuclear Decommissioning Trusts
Assets:
Fair Value	32
Nuclear Decommissioning Trusts | ALABAMA POWER CO
Assets:
Fair Value	32
Weather Derivative | Fair Value, Measurements, Recurring
Assets:
Energy-related derivatives	$ 4

Revenue from Contracts with C52

Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 6,372	$ 5,771
Other Income	90
Retail electric revenues
Disaggregation of Revenue [Line Items]
Lease income	18
Increase (decrease) in revenue from cost recovery mechanisms	117
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,539
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,243
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	756
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	30
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,224
Alternative revenue programs(b)
Disaggregation of Revenue [Line Items]
Total operating revenues	(24)
Total retail electric and gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4,768
Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	468
Revenue from transactions accounted for as derivatives	93
Lease income from PPA contracts	69
Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	151
Lease income from PPA contracts	30
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	407
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	578
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,639	1,560
SOUTHERN Co GAS | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,200
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	660
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	192
SOUTHERN Co GAS | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	277
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	17
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	78
SOUTHERN Co GAS | Alternative revenue programs(b)
Disaggregation of Revenue [Line Items]
Total operating revenues	(24)
SOUTHERN Co GAS | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	271
Lease income	1
Revenue from transactions accounted for as derivatives	3
SOUTHERN Co GAS | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	146
SOUTHERN Co GAS | Gas midstream operations
Disaggregation of Revenue [Line Items]
Total operating revenues	22
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,473	1,382
Other Income	25
ALABAMA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,285
Increase (decrease) in revenue from cost recovery mechanisms	47
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	570
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	371
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	338
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	6
ALABAMA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	101
Revenue from transactions accounted for as derivatives	5
ALABAMA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	24
ALABAMA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	63
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,961	1,832
Other Income	26
GEORGIA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,798
Lease income	18
Increase (decrease) in revenue from cost recovery mechanisms	10
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	744
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	717
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	316
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	21
GEORGIA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	40
Revenue from transactions accounted for as derivatives	7
GEORGIA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	14
GEORGIA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	109
Lease income	33
GULF POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	348	350
Other Income	2
GULF POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	290
Increase (decrease) in revenue from cost recovery mechanisms	(16)
GULF POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	165
GULF POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	92
GULF POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	32
GULF POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	1
GULF POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	35
Revenue from transactions accounted for as derivatives	1
GULF POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	6
GULF POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	17
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	302	272
MISSISSIPPI POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	194
Increase (decrease) in revenue from cost recovery mechanisms	76
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	60
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	62
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	70
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	2
MISSISSIPPI POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	93
Revenue from transactions accounted for as derivatives	1
MISSISSIPPI POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4
MISSISSIPPI POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	11
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	509	450
SOUTHERN POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2
SOUTHERN POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	138
Lease income from PPA contracts	47
SOUTHERN POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	254
Revenue from transactions accounted for as derivatives	79
Lease income from PPA contracts	76
SOUTHERN POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	115
Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,671	1,624
Wholesale gas services | Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	166	131
Wholesale gas services | Third Party Gross Revenues | Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,938	$ 1,839
Revenue from transactions accounted for as derivatives	$ 1,100

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 11	$ (63)
Private Equity
Fair Value, Option, Quantitative Disclosures [Line Items]
Liquidations term	10 years
ALABAMA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt	$ 7,626
Increase (decrease) in fair value of funds	5	(34)
GEORGIA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt	11,402
Increase (decrease) in fair value of funds	6	$ (29)
SOUTHERN POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt	5,878
SOUTHERN Co GAS
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term Debt	$ 6,036

Revenue from Contracts with C54

Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,607
Contract Assets	60
Contract Liabilities	52
ALABAMA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	507
Contract Assets	0
Contract Liabilities	11
GEORGIA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	600
Contract Assets	29
Contract Liabilities	$ 5
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 129
Contract Assets	0
Contract Liabilities	1
MISSISSIPPI POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	64
Contract Assets	0
Contract Liabilities	0
SOUTHERN POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	78
Contract Assets	0
Contract Liabilities	4
SOUTHERN Co GAS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	948
Contract Assets	0
Contract Liabilities	15
Unregulated Distributed Generation [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	31
Contract Liabilities	$ 20

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Measurements Of Investments Calculated At Net Asset Value Per Share (Details) $ in Millions	Mar. 31, 2018USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 32
Private Equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	32
Unfunded Commitments	19
ALABAMA POWER CO
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	32
ALABAMA POWER CO | Private Equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	32
Unfunded Commitments	$ 19

Revenue from Contracts with C56

Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	3 Months Ended
	Mar. 31, 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	$ 458
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	$ 403
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	$ 369
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	$ 358
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	$ 345
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	$ 2,161
Performance obligation, expected timing of satisfaction	13 years
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	$ 16
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	$ 21
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	$ 22
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	13 years
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	$ 31
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	13 years
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	$ 16
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	13 years
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	13 years
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	$ 384
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	$ 350
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	$ 330
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	$ 313
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	$ 312
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	$ 2,010
Performance obligation, expected timing of satisfaction	13 years

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Long-term debt:
Long-term Debt	$ 44,446	$ 44,462
Southern Company
Long-term debt:
Carrying Amount	47,479
Fair Value	48,836
ALABAMA POWER CO
Long-term debt:
Carrying Amount	7,626
Fair Value	8,093
Long-term Debt	7,429	7,628
GEORGIA POWER CO
Long-term debt:
Carrying Amount	11,402
Fair Value	11,851
Long-term Debt	10,797	11,073
GULF POWER CO
Long-term debt:
Carrying Amount	1,285
Fair Value	1,317
Long-term Debt	1,285	1,285
MISSISSIPPI POWER CO
Long-term debt:
Carrying Amount	1,781
Fair Value	1,790
Long-term Debt	1,567	1,097
SOUTHERN POWER CO
Long-term debt:
Carrying Amount	5,878
Fair Value	6,006
Long-term Debt	5,108	5,071
SOUTHERN Co GAS
Long-term debt:
Carrying Amount	6,036
Fair Value	6,276
Long-term Debt	$ 5,859	$ 5,891

Stockholders' Equity - Earnings

Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
As reported shares (in shares)	1,011	993
Effect of options and performance share award units (in shares)	5	7
Diluted shares (in shares)	1,016	1,000
Stock options and performance share award units that were not included in the diluted earnings per share calculation (in shares)	0	0

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	938	658
Other comprehensive income	30	(9)
Stock issued	113	186
Stock-based compensation	36	57
Cash dividends on common stock	(586)	(556)
Contributions from noncontrolling interests	9	71
Distributions to noncontrolling interests	(13)	(18)
Net income (loss) attributable to noncontrolling interests	(6)	(4)
Other	$ (24)	(1)
Ending balance, treasury shares (in shares)	(1,000)
Ending balance	$ 26,025	$ 26,996
Number of Common Shares Issued
Changes in Stockholders' Equity
Beginning balance (in shares)	1,008,532	991,213
Stock issued (in shares)	4,055	4,240
Other (in shares)	0
Ending balance (in shares)	1,012,587	995,453
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)	(33)	(35)
Ending balance, treasury shares (in shares)	(962)	(854)
Common Stockholders' Equity
Changes in Stockholders' Equity
Beginning balance	$ 24,167	$ 24,758
Consolidated net income attributable to Southern Company	938	658
Other comprehensive income	30	(9)
Stock issued	113	186
Stock-based compensation	36	57
Cash dividends on common stock	(586)	(556)
Other	(22)	0
Ending balance	24,676	25,094
Preferred and Preference Stock of Subsidiaries
Changes in Stockholders' Equity
Beginning balance	0	609
Other	0
Ending balance	0	609
Noncontrolling Interest
Changes in Stockholders' Equity
Beginning balance	1,361	1,245
Contributions from noncontrolling interests	9	71
Distributions to noncontrolling interests	(13)	(18)
Net income (loss) attributable to noncontrolling interests	(6)	(4)
Other	(2)
Ending balance	$ 1,349	$ 1,293

Financing - Narrative (Details)

Financing - Narrative (Details) - USD ($)	May 02, 2018	Mar. 31, 2018	May 23, 2018	Jan. 31, 2018	Jan. 04, 2018	Jul. 31, 2017
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		$ 1,500,000,000
Maximum borrowing capacity		8,145,000,000
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
Southern Company | Floating Rate Bank Term Loan Agreement 1 | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount		900,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		854,000,000
Fixed rate pollution control revenue bonds outstanding		120,000,000
Maximum borrowing capacity		1,335,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		550,000,000
Fixed rate pollution control revenue bonds outstanding		192,000,000
Maximum borrowing capacity		1,750,000,000
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 | 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
GULF POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		82,000,000
Fixed rate pollution control revenue bonds outstanding		75,000,000
Maximum borrowing capacity		280,000,000
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		40,000,000
Fixed rate pollution control revenue bonds outstanding		50,000,000
Maximum borrowing capacity		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 | 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		437,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Maximum borrowing capacity		1,900,000,000
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity		500,000,000
Nicor Gas | Collateralized Mortgage Backed Securities [Member] | First Mortgage Bonds
Debt Instrument [Line Items]
Debt face amount						$ 181,000,000
Maximum borrowing capacity		$ 181,000,000
Subsequent Event | GEORGIA POWER CO | Municipal Bonds | Pollution Control Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, repurchase amount	$ 55,000,000
Subsequent Event | MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	125,000,000
Subsequent Event | SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount	$ 20,000,000
Scenario, Forecast | SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount			$ 180,000,000

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2018USD ($)
Line of Credit Facility [Line Items]
Expires, 2018	$ 185,000,000
Expires, 2019	25,000,000
Expires, 2020	735,000,000
Expires, 2022	7,200,000,000
Total	8,145,000,000
Unused	8,098,000,000
Executable Term Loans, One Year	65,000,000
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	40,000,000
Expires Within One Year, No Term Out	145,000,000
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
Executable Term Loans, Two Years	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	35,000,000
Expires, 2019	0
Expires, 2020	500,000,000
Expires, 2022	800,000,000
Total	1,335,000,000
Unused	1,335,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	35,000,000
GEORGIA POWER 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
Executable Term Loans, Two Years	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
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	20,000,000
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
Executable Term Loans, Two Years	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
Executable Term Loans, Two Years	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	1,890,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Other
Line of Credit Facility [Line Items]
Expires, 2018	30,000,000
Expires, 2019	0
Expires, 2020	0
Expires, 2022	0
Total	30,000,000
Unused	30,000,000
Executable Term Loans, One Year	20,000,000
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	20,000,000
Expires Within One Year, No Term Out	10,000,000
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	$ 21,000,000

Financing - Schedule of Long-Te

Financing - Schedule of Long-Term Debt Financing Activities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Debt Instrument [Line Items]
Senior Note Issuances	$ 600
Revenue Bond Maturities, Redemptions, and Repurchases	278
Other Long-Term Debt Redemptions and Maturities	1,005
GEORGIA POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	0
Revenue Bond Maturities, Redemptions, and Repurchases	278
Other Long-Term Debt Redemptions and Maturities	102
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	600
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	900
Other
Debt Instrument [Line Items]
Senior Note Issuances	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Redemptions and Maturities	$ 3

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	19,000,000	16,000,000
Interest cost	25,000,000	24,000,000
Expected return on plan assets	(51,000,000)	(49,000,000)
Amortization:
Prior service costs	0	1,000,000
Regulatory asset	0
Net (gain)/loss	14,000,000	10,000,000
Net periodic pension cost (income)	7,000,000	2,000,000
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	22,000,000	19,000,000
Interest cost	35,000,000	34,000,000
Expected return on plan assets	(74,000,000)	(71,000,000)
Amortization:
Prior service costs	0	1,000,000
Regulatory asset	0
Net (gain)/loss	17,000,000	14,000,000
Net periodic pension cost (income)	0	(3,000,000)
Pension Plans | GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(10,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	1,000,000	0
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	4,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(10,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0
Net (gain)/loss	3,000,000	2,000,000
Net periodic pension cost (income)	2,000,000	1,000,000
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000
Interest cost	1,000,000
Expected return on plan assets	(3,000,000)
Amortization:
Prior service costs	0
Regulatory asset	0
Net (gain)/loss	1,000,000
Net periodic pension cost (income)	1,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	8,000,000	6,000,000
Interest cost	10,000,000	10,000,000
Expected return on plan assets	(18,000,000)	(18,000,000)
Amortization:
Prior service costs	(1,000,000)	0
Regulatory asset	3,000,000
Net (gain)/loss	3,000,000	5,000,000
Net periodic pension cost (income)	5,000,000	3,000,000
Pension Plans | Southern Company
Pension Plans and Postretirement Plans
Service cost	90,000,000	73,000,000
Interest cost	116,000,000	114,000,000
Expected return on plan assets	(236,000,000)	(224,000,000)
Amortization:
Prior service costs	1,000,000	3,000,000
Regulatory asset	0
Net (gain)/loss	53,000,000	40,000,000
Net periodic pension cost (income)	24,000,000	6,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	4,000,000	5,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Regulatory asset	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	0	1,000,000
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	7,000,000	7,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	5,000,000	5,000,000
Postretirement Benefits | GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Regulatory asset	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Regulatory asset	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0
Interest cost	0
Expected return on plan assets	0
Amortization:
Prior service costs	0
Regulatory asset	0
Net (gain)/loss	0
Net periodic pension cost (income)	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	2,000,000	3,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)
Amortization:
Prior service costs	0	(1,000,000)
Regulatory asset	1,000,000
Net (gain)/loss	0	1,000,000
Net periodic pension cost (income)	2,000,000	2,000,000
Postretirement Benefits | Southern Company
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000
Interest cost	19,000,000	20,000,000
Expected return on plan assets	(17,000,000)	(16,000,000)
Amortization:
Prior service costs	2,000,000	2,000,000
Regulatory asset	0
Net (gain)/loss	3,000,000	2,000,000
Net periodic pension cost (income)	$ 13,000,000	$ 14,000,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Apr. 30, 2018	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Contingency [Line Items]
Effective tax rate			10.80%	32.10%
Income benefit			$ (113)	$ (315)
Unrecognized tax benefits		$ 0	$ 0
Significantly increase (decrease) in amount of unrecognized tax benefits			12 months
ALABAMA POWER CO
Income Tax Contingency [Line Items]
Income benefit			$ (82)	(126)
GEORGIA POWER CO
Income Tax Contingency [Line Items]
Income benefit			(93)	(156)
GULF POWER CO
Income Tax Contingency [Line Items]
Income benefit			$ (13)	$ (14)
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax rate			(34.70%)	(58.70%)
Income benefit			$ 4	$ 27
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax rate			(647.00%)	(385.90%)
Income benefit		50	$ 99	$ 52
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Income benefit			(104)	$ (150)
Investment Tax Credit Carryforward
Income Tax Contingency [Line Items]
Tax credit carryforward, amount		$ 2,300	$ 2,300		$ 2,100
Subsequent Event | SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Income benefit	$ 4

Derivatives - Energy-Related an

Derivatives - Energy-Related and Interest Rate Derivatives (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2018USD ($)MMBTU
Interest rate derivatives
Interest rate derivatives
Notional Amount	$ 2,750,000,000
Fair Value Gain (Loss) at March 31, 2018	$ (62,000,000)
Southern Company | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	670
Longest Hedge Date	2,021
Longest Non-Hedge Date	2,026
Southern Company | Interest rate derivatives | 2020-06-01 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 300,000,000
Interest Rate Received	2.75%
Fair Value Gain (Loss) at March 31, 2018	$ (5,000,000)
Southern Company | Interest rate derivatives | 2020-06-01 | 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 | 7/31/2021 | 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 March 31, 2018	$ (50,000,000)
Southern Company | Interest rate derivatives | 7/31/2021 | 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	74
Longest Hedge Date	2,021
GEORGIA POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	167
Longest Hedge Date	2,021
GEORGIA POWER CO | Interest rate derivatives | 6/1/2018 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount	$ 250,000,000
Interest Rate Received	5.40%
Fair Value Gain (Loss) at March 31, 2018	$ (1,000,000)
GEORGIA POWER CO | Interest rate derivatives | 6/1/2018 | London Interbank Offered Rate (LIBOR) | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	4.02%
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 March 31, 2018	$ (4,000,000)
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 March 31, 2018	$ (2,000,000)
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	17
Longest Hedge Date	2,020
MISSISSIPPI POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	59
Longest Hedge Date	2,021
SOUTHERN POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	14
Longest Hedge Date	2,020
Longest Non-Hedge Date	2,018
SOUTHERN Co GAS | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	339
Longest Hedge Date	2,020
Longest Non-Hedge Date	2,026
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	3,600
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	3,300

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2018USD ($)MMBTU	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Derivative [Line Items]
Derivative, gain (loss) on derivative, net	$ 60,000,000	$ 81,000,000
Collateral already posted, aggregate fair value	$ 223,000,000
Southern Company
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	31
Cash flow hedge gain (loss) to be reclassified within twelve months	$ (20,000,000)
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	9
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5
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 | MMBTU	3
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	4
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	10
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	$ (22,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Derivative, gain (loss) on derivative, net	59,000,000	82,000,000
Collateral already posted, aggregate fair value	223,000,000		$ 193,000,000
Weather derivative premium	4,000,000		11,000,000
Derivative Counterparties | Registrants
Derivative [Line Items]
Collateral already posted, aggregate fair value	0
Energy-related derivatives | SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, aggregate fair value	8,000,000		$ 6,000,000
Weather Derivatives | Southern Company
Derivative [Line Items]
Derivative, gain (loss) on derivative, net	$ 14,000,000	$ 14,000,000
Long | Derivatives not designated as hedging instruments | Energy-related, Natural Gas | SOUTHERN Co GAS
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,600
Short | Derivatives not designated as hedging instruments | Energy-related, Natural Gas | SOUTHERN Co GAS
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,300

Derivatives - Foreign Currency

Derivatives - Foreign Currency Derivatives (Details) - 3 months ended Mar. 31, 2018 - Cash Flow Hedges of Existing Debt - Foreign Exchange Contract € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) at March 31, 2018	160
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 March 31, 2018	$ 83
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 March 31, 2018	$ 77

Derivatives - Derivative Financ

Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 223
Southern Company
Derivatives, Fair Value [Line Items]
Derivatives, assets	714	$ 700
Derivatives, liabilities	725	794
Derivative asset amount offset	(336)	(405)
Derivative liability amount offset	(559)	(598)
Derivative asset	378	295
Derivative liability	166	196
Southern Company | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives, assets	517	550
Derivatives, liabilities	583	652
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	283	380
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	234	170
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	284	215
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	299	437
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	11	17
Derivatives, liabilities	55	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	7	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	4	7
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 | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	28	43
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	186	133
Derivatives, liabilities	87	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	3	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
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
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 | 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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	47	34
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	14	4
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	182	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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	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 current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	22	23
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	4
Derivatives, liabilities	8	10
Derivative asset amount offset	(2)	(4)
Derivative liability amount offset	(2)	(4)
Derivative asset	1	0
Derivative liability	6	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	3	4
Derivatives, liabilities	8	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	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 deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	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 credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	4
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
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	6
Derivatives, liabilities	26	24
Derivative asset amount offset	(5)	(6)
Derivative liability amount offset	(5)	(6)
Derivative asset	0	0
Derivative liability	21	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	5	6
Derivatives, liabilities	18	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	3	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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	12	10
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	6	9
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	8	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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	1
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	6	4
GULF POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	17	21
Derivative asset amount offset	0	0
Derivative liability amount offset	0	0
Derivative asset	0	0
Derivative liability	17	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	17	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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	6	7
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	11	14
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	3
Derivatives, liabilities	8	9
Derivative asset amount offset	(2)	(2)
Derivative liability amount offset	(2)	(2)
Derivative asset	0	1
Derivative liability	6	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	2	2
Derivatives, liabilities	8	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	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 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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	3
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	4	6
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	186	132
Derivatives, liabilities	25	36
Derivative asset amount offset	(1)	(3)
Derivative liability amount offset	(1)	(3)
Derivative asset	185	129
Derivative liability	24	33
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and 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	186	132
Derivatives, liabilities	25	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	3	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 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 | 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 | 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	182	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 deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	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 current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	22	23
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivatives, assets	518	554
Derivatives, liabilities	588	660
Derivative asset amount offset	(325)	(390)
Derivative liability amount offset	(548)	(583)
Derivative asset	193	164
Derivative liability	40	77
Collateral already posted, aggregate fair value	223	193
Weather derivative premium	4	11
SOUTHERN Co GAS | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	8	6
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	517	549
Derivatives, liabilities	583	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	234	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	284	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	283	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	299	434
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	1	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	4	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
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	$ 223
Southern Company
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	63	$ (14)
Gain (Loss) Reclassified from Accumulated OCI into Income	25	2
Southern Company | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(458)	(416)
Southern Company | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(36)		$ (44)
Gain (Loss) Recognized in OCI on Derivative	12	(11)
Southern Company | Energy-related derivatives | Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(2)	0
Southern Company | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(20)		(34)
Southern Company | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(23)		(18)
Southern Company | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	7		7
Southern Company | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet			1
Southern Company | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(2)	1
Southern Company | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	53	(4)
Southern Company | Foreign Exchange Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	36	17
Southern Company | Foreign Exchange Contract | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	36	17
ALABAMA POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(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)		(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)		(3)
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	0		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	(13)		(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	(3)		(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	(10)		(6)
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
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	(17)		(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	(11)		(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	(6)		(7)
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
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)		(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	(3)		(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	(3)		(2)
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
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	223		193
SOUTHERN Co GAS | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	5		3
Collateral already posted, aggregate fair value	8		6
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	(2)		(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
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	7		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	64	(12)
Gain (Loss) Reclassified from Accumulated OCI into Income	32	7
SOUTHERN POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	11	(8)
SOUTHERN POWER CO | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	53	(4)
Cash Flow Hedging | Southern Company | Energy-related derivatives | Depreciation and amortization
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	1	(4)
Cash Flow Hedging | Southern Company | Interest rate derivatives | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(5)
Cash Flow Hedging | Southern Company | Foreign Exchange Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(6)
Cash Flow Hedging | SOUTHERN POWER CO | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(47)	(50)
Cash Flow Hedging | SOUTHERN POWER CO | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	3	(1)
Cash Flow Hedging | SOUTHERN POWER CO | Energy-related derivatives | Depreciation and amortization
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	1	(4)
Cash Flow Hedging | SOUTHERN POWER CO | Foreign Exchange Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(6)
Cash Flow Hedging | SOUTHERN POWER CO | Foreign Exchange Contract | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	$ 36	$ 17

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
	Mar. 31, 2018	Mar. 31, 2017
Southern Company
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	$ 25	$ 2
Southern Company | Depreciation and amortization
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	769	716
Southern Company | Interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(458)	(416)
Southern Company | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	36	17
Southern Company | Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	36	17
Cash Flow Hedging | Southern Company | Amortization | Energy-related derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	1	(4)
Cash Flow Hedging | Southern Company | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(5)
Cash Flow Hedging | Southern Company | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(6)
Fair Value Hedging | Southern Company | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(24)	(8)
Fair Value Hedging | Southern Company | Other income (expense), net
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	60	48
SOUTHERN POWER CO
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	32	7
SOUTHERN POWER CO | Depreciation and amortization
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	114	119
SOUTHERN POWER CO | Cash Flow Hedging | Amortization | Energy-related derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	1	(4)
SOUTHERN POWER CO | Cash Flow Hedging | Interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(47)	(50)
SOUTHERN POWER CO | Cash Flow Hedging | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	(5)	(6)
SOUTHERN POWER CO | Cash Flow Hedging | Other income (expense), net
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	3	(1)
SOUTHERN POWER CO | Cash Flow Hedging | Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income	$ 36	$ 17

Derivatives - Cumulative Basis

Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (745)	$ (746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	4	3
Securities due within one year | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(745)	(746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	4	3
Long-term Debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(2,533)	(2,553)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	57	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	$ 2	$ 1

Derivatives - Pre-tax Effects72

Derivatives - Pre-tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	$ 60	$ 81
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	(13)	47
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	(15)	50
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	(3)
Southern Company | Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	14	14
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	59	82
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	(13)	47
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	(15)	50
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	$ (3)

Acquisitions and Dispositions -

Acquisitions and Dispositions - Narrative (Details) - USD ($) $ in Millions	Apr. 11, 2018	Oct. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Business Acquisition [Line Items]
Construction work in progress			$ 7,460				$ 6,904
Goodwill			6,226				6,268
SOUTHERN Co GAS
Business Acquisition [Line Items]
Construction work in progress			511				491
Goodwill impairment			42	$ 0
Goodwill			5,925				5,967
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			634				511
Goodwill			2				$ 2
Series of Construction Projects | SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			273
Series of Construction Projects | Minimum | SOUTHERN POWER CO
Business Acquisition [Line Items]
Estimated future construction payments			370
Series of Construction Projects | Maximum | SOUTHERN POWER CO
Business Acquisition [Line Items]
Estimated future construction payments			$ 415
Elizabethtown Gas and Elkton Gas | SOUTHERN Co GAS
Business Acquisition [Line Items]
Aggregate purchase price		$ 1,700
Wind Generating Facility | Scenario, Forecast | SOUTHERN POWER CO
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage					80.00%	100.00%
Pivotal Home Solutions | Subsequent Event | SOUTHERN Co GAS
Business Acquisition [Line Items]
Proceeds from divestiture of businesses	$ 365
Goodwill	$ 242

Acquisitions and Dispositions74

Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Jun. 30, 2019	Sep. 30, 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%
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
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 [Member] | 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%

Joint Ownership Agreements - Ba

Joint Ownership Agreements - Balance Sheet Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,542	$ 1,513
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,504	1,477
SNG | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,274	1,262
Atlantic Coast Pipeline | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	49	41
PennEast Pipeline | SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	62	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	45	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

Joint Ownership Agreements - In

Joint Ownership Agreements - Income Statement Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 41	$ 39
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	42	39
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	39	34
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	3
SOUTHERN Co GAS | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	1
SOUTHERN Co GAS | Triton
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1	0
SOUTHERN Co GAS | Horizon Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 0	$ 1

Joint Ownership Agreements - 77

Joint Ownership Agreements - Investment in SNG (Details) - SNG - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Revenues	$ 160	$ 155
Operating income	99	84
Net income	$ 78	$ 66

Segment and Related Informati78

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)statesegment	Mar. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	$ 1,607	$ 1,530
Number of reportable segments | segment	4
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	7
Number of natural gas distribution utilities | segment	7
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	$ 1,631	1,521
Number of reportable segments | segment	4
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	$ 83	100
Southern Company [Member] | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	$ 36	$ 23

Segment and Related Informati79

Segment and Related Information - Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 6,372	$ 5,771
Segment net income	938	658
Total assets	111,567		$ 111,005
Kemper IGCC
Segment Reporting Information [Line Items]
Pre-tax charge to income	44	108
After tax charge to income	33	67
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	(50)	(43)
Segment net income	0	1
Total assets	(1,547)		(1,619)
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,382	4,131
Segment net income	733	502
Total assets	87,813		87,085
SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Total assets	22,568		22,987
All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	401	123
Segment net income	(74)	(84)
Total assets	2,733		2,552
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	509	450
Segment net income	121	70
Total assets	15,182		15,206
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,639	1,560
Segment net income	279	239
Total assets	22,568		22,987
Goodwill impairment	42	0
SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,671	1,624
Segment net income	289	231
Total assets	23,642		24,842
SOUTHERN Co GAS | Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(33)	(66)
Segment net income	0	0
Total assets	(12,913)		(14,039)
SOUTHERN Co GAS | SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Segment net income	279
SOUTHERN Co GAS | All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1	2
Segment net income	(10)	8
Total assets	11,839		12,184
SOUTHERN Co GAS | Gas distribution operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,212	1,180
Segment net income	149	117
Total assets	18,332		19,358
SOUTHERN Co GAS | Gas marketing services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	271	288
Segment net income	13	31
Total assets	2,144		2,147
SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	166	131
Segment net income	104	68
Total assets	903		1,096
Less Gross Gas Costs	1,939	1,844
SOUTHERN Co GAS | Gas Midstream Operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	22	25
Segment net income	23	15
Total assets	2,263		2,241
Third Party Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,938	1,839
Intercompany Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	167	136
Total Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	2,105	1,975
Reportable Subsegments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	3,979	3,786
Segment net income	612	432
Total assets	72,893		72,204
Reportable Subsegments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	509	450
Segment net income	121	70
Total assets	15,182		15,206
Intersubsegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(106)	(105)
Segment net income	0	$ 0
Total assets	$ (262)		$ (325)

Segment and Related Informati80

Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 4,382	$ 4,131
Gas Revenue	1,639	1,560
Retail
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	3,568	3,394
Wholesale
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	619	531
Other
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	195	206
Gas distribution operations
Revenue from External Customer [Line Items]
Gas Revenue	1,200	1,132
Gas marketing services
Revenue from External Customer [Line Items]
Gas Revenue	271	288
Other
Revenue from External Customer [Line Items]
Gas Revenue	$ 168	$ 140