Mississippi Power (MSPWP) 10-Q 29 Apr 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page	3 Months Ended
	Mar. 31, 2021shares
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-3526
Entity Registrant Name	The Southern Company
Entity Tax Identification Number	58-0690070
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	30 Ivan Allen Jr. Boulevard, N.W.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,058,630,385
Entity Central Index Key	0000092122
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Common Stock, par value $5 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $5 per share
Trading Symbol	SO
Security Exchange Name	NYSE
Series 2016A 5.25% Junior Subordinated Notes due 2076
Document Information [Line Items]
Title of 12(b) Security	Series 2016A 5.25% Junior Subordinated Notes due 2076
Trading Symbol	SOJB
Security Exchange Name	NYSE
Series 2017B 5.25% Junior Subordinated Notes due 2077
Document Information [Line Items]
Title of 12(b) Security	Series 2017B 5.25% Junior Subordinated Notes due 2077
Trading Symbol	SOJC
Security Exchange Name	NYSE
2019 Series A Corporate Units
Document Information [Line Items]
Title of 12(b) Security	2019 Series A Corporate Units
Trading Symbol	SOLN
Security Exchange Name	NYSE
Series 2020A 4.95% Junior Subordinated Notes due 2080
Document Information [Line Items]
Title of 12(b) Security	Series 2020A 4.95% Junior Subordinated Notes due 2080
Trading Symbol	SOJD
Security Exchange Name	NYSE
Series 2020C 4.20% Junior Subordinated Notes due 2060
Document Information [Line Items]
Title of 12(b) Security	Series 2020C 4.20% Junior Subordinated Notes due 2060
Trading Symbol	SOJE
Security Exchange Name	NYSE
ALABAMA POWER CO
Document Information [Line Items]
Entity File Number	1-3164
Entity Registrant Name	Alabama Power Company
Entity Tax Identification Number	63-0004250
Entity Incorporation, State or Country Code	AL
Entity Address, Address Line One	600 North 18th Street
Entity Address, City or Town	Birmingham
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35203
City Area Code	205
Local Phone Number	257-1000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	30,537,500
Entity Central Index Key	0000003153
ALABAMA POWER CO | 5.00% Series Class A Preferred Stock
Document Information [Line Items]
Title of 12(b) Security	5.00% Series Class A Preferred Stock
Trading Symbol	ALP PR Q
Security Exchange Name	NYSE
GEORGIA POWER CO
Document Information [Line Items]
Entity File Number	1-6468
Entity Registrant Name	Georgia Power Company
Entity Tax Identification Number	58-0257110
Entity Incorporation, State or Country Code	GA
Entity Address, Address Line One	241 Ralph McGill Boulevard, N.E.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-6526
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	9,261,500
Entity Central Index Key	0000041091
GEORGIA POWER CO | Series 2017A 5.00% Junior Subordinated Notes due 2077
Document Information [Line Items]
Title of 12(b) Security	Series 2017A 5.00% Junior Subordinated Notes due 2077
Trading Symbol	GPJA
Security Exchange Name	NYSE
MISSISSIPPI POWER CO
Document Information [Line Items]
Entity File Number	001-11229
Entity Registrant Name	Mississippi Power Company
Entity Tax Identification Number	64-0205820
Entity Incorporation, State or Country Code	MS
Entity Address, Address Line One	2992 West Beach Boulevard
Entity Address, City or Town	Gulfport
Entity Address, State or Province	MS
Entity Address, Postal Zip Code	39501
City Area Code	228
Local Phone Number	864-1211
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,121,000
Entity Central Index Key	0000066904
SOUTHERN POWER CO
Document Information [Line Items]
Entity File Number	001-37803
Entity Registrant Name	Southern Power Company
Entity Tax Identification Number	58-2598670
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	30 Ivan Allen Jr. Boulevard, N.W.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30308
City Area Code	404
Local Phone Number	506-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	1,000
Entity Central Index Key	0001160661
SOUTHERN POWER CO | Series 2016A 1.000% Senior Notes due 2022
Document Information [Line Items]
Title of 12(b) Security	Series 2016A 1.000% Senior Notes due 2022
Trading Symbol	SO/22B
Security Exchange Name	NYSE
SOUTHERN POWER CO | Series 2016B 1.850% Senior Notes due 2026
Document Information [Line Items]
Title of 12(b) Security	Series 2016B 1.850% Senior Notes due 2026
Trading Symbol	SO/26A
Security Exchange Name	NYSE
SOUTHERN Co GAS
Document Information [Line Items]
Entity File Number	1-14174
Entity Registrant Name	Southern Company Gas
Entity Tax Identification Number	58-2210952
Entity Incorporation, State or Country Code	GA
Entity Address, Address Line One	Ten Peachtree Place, N.E.
Entity Address, City or Town	Atlanta
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30309
City Area Code	404
Local Phone Number	584-4000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	100
Entity Central Index Key	0001004155

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Revenues:
Operating revenues	$ 5,910	$ 5,018
Operating Expenses:
Total cost of sales	583	439
Other operations and maintenance	1,372	1,296
Depreciation and amortization	871	857
Taxes other than income taxes	345	330
Estimated loss on Plant Vogtle Units 3 and 4	48	0
(Gain) loss on dispositions, net	(44)	(39)
Total operating expenses	4,312	3,755
Operating Income	1,598	1,263
Other Income and (Expense):
Allowance for equity funds used during construction	46	34
Earnings from equity method investments	45	42
Interest expense, net of amounts capitalized	(450)	(456)
Other income (expense), net	58	103
Total other income and (expense)	(301)	(277)
Earnings Before Income Taxes	1,297	986
Income taxes (benefit)	190	145
Comprehensive Income	1,135	794
Consolidated Net Income	1,107	841
Dividends on preferred stock of subsidiaries	4	4
Net loss attributable to noncontrolling interests	(32)	(31)
Net Income	$ 1,135	$ 868
Earnings per share -
Basic (in dollars per share)	$ 1.07	$ 0.82
Diluted (in dollars per share)	$ 1.06	$ 0.81
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	1,060	1,057
Diluted (in shares)	1,066	1,067
Retail electric revenues
Operating Revenues:
Operating revenues	$ 3,342	$ 3,078
Wholesale electric revenues
Operating Revenues:
Operating revenues	545	418
Other electric revenues
Operating Revenues:
Operating revenues	170	151
Natural gas
Operating Revenues:
Operating revenues	1,694	1,249
Operating Expenses:
Total cost of sales	583	439
Other
Operating Revenues:
Operating revenues	159	122
Operating Expenses:
Total cost of sales	82	55
Fuel
Operating Expenses:
Total cost of sales	848	636
Purchased power
Operating Expenses:
Total cost of sales	207	181
Alternative revenue programs
Operating Revenues:
Operating revenues	2	9
ALABAMA POWER CO
Operating Revenues:
Operating revenues	1,559	1,351
Operating Expenses:
Other operations and maintenance	361	350
Depreciation and amortization	211	200
Taxes other than income taxes	103	106
Total operating expenses	1,046	929
Operating Income	513	422
Other Income and (Expense):
Allowance for equity funds used during construction	12	10
Interest expense, net of amounts capitalized	(84)	(88)
Other income (expense), net	32	24
Total other income and (expense)	(40)	(54)
Earnings Before Income Taxes	473	368
Income taxes (benefit)	110	84
Comprehensive Income	364	285
Consolidated Net Income	363	284
Dividends on preferred stock of subsidiaries	4	4
Net Income	359	280
ALABAMA POWER CO | Retail electric revenues
Operating Revenues:
Operating revenues	1,352	1,205
ALABAMA POWER CO | Wholesale electric revenues
Operating Revenues:
Operating revenues	92	56
ALABAMA POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	32	19
ALABAMA POWER CO | Other
Operating Revenues:
Operating revenues	83	71
ALABAMA POWER CO | Fuel
Operating Expenses:
Total cost of sales	291	215
ALABAMA POWER CO | Purchased power
Operating Expenses:
Total cost of sales	50	40
ALABAMA POWER CO | Purchased power, affiliates
Operating Expenses:
Total cost of sales	30	18
GEORGIA POWER CO
Operating Revenues:
Operating revenues	1,970	1,825
Operating Expenses:
Other operations and maintenance	474	465
Depreciation and amortization	338	352
Taxes other than income taxes	116	113
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Total operating expenses	1,569	1,419
Operating Income	401	406
Other Income and (Expense):
Interest expense, net of amounts capitalized	(104)	(111)
Other income (expense), net	72	52
Total other income and (expense)	(32)	(59)
Earnings Before Income Taxes	369	347
Income taxes (benefit)	18	16
Comprehensive Income	353	330
Consolidated Net Income	351	331
GEORGIA POWER CO | Retail electric revenues
Operating Revenues:
Operating revenues	1,787	1,675
GEORGIA POWER CO | Wholesale electric revenues
Operating Revenues:
Operating revenues	43	26
GEORGIA POWER CO | Other
Operating Revenues:
Operating revenues	140	124
GEORGIA POWER CO | Fuel
Operating Expenses:
Total cost of sales	313	231
GEORGIA POWER CO | Purchased power
Operating Expenses:
Total cost of sales	144	129
GEORGIA POWER CO | Purchased power, affiliates
Operating Expenses:
Total cost of sales	136	129
MISSISSIPPI POWER CO
Operating Revenues:
Operating revenues	307	277
Operating Expenses:
Other operations and maintenance	68	76
Depreciation and amortization	47	42
Taxes other than income taxes	31	29
Total operating expenses	252	231
Operating Income	55	46
Other Income and (Expense):
Interest expense, net of amounts capitalized	(14)	(16)
Other income (expense), net	8	8
Total other income and (expense)	(6)	(8)
Earnings Before Income Taxes	49	38
Income taxes (benefit)	4	6
Comprehensive Income	45	32
Consolidated Net Income	45	32
MISSISSIPPI POWER CO | Retail electric revenues
Operating Revenues:
Operating revenues	204	199
MISSISSIPPI POWER CO | Wholesale electric revenues
Operating Revenues:
Operating revenues	63	51
MISSISSIPPI POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	33	21
MISSISSIPPI POWER CO | Other
Operating Revenues:
Operating revenues	7	6
MISSISSIPPI POWER CO | Fuel
Operating Expenses:
Total cost of sales	101	79
MISSISSIPPI POWER CO | Purchased power
Operating Expenses:
Total cost of sales	5	5
SOUTHERN POWER CO
Operating Revenues:
Operating revenues	440	375
Operating Expenses:
Other operations and maintenance	101	79
Depreciation and amortization	119	117
Taxes other than income taxes	12	9
(Gain) loss on dispositions, net	(39)	(39)
Total operating expenses	354	287
Operating Income	86	88
Other Income and (Expense):
Interest expense, net of amounts capitalized	(38)	(39)
Other income (expense), net	7	2
Total other income and (expense)	(31)	(37)
Earnings Before Income Taxes	55	51
Income taxes (benefit)	(10)	7
Comprehensive Income	81	11
Consolidated Net Income	65	44
Net loss attributable to noncontrolling interests	(32)	(31)
Net Income	97	75
SOUTHERN POWER CO | Wholesale electric revenues
Operating Revenues:
Operating revenues	355	286
SOUTHERN POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Operating revenues	81	86
SOUTHERN POWER CO | Other
Operating Revenues:
Operating revenues	4	3
SOUTHERN POWER CO | Fuel
Operating Expenses:
Total cost of sales	141	107
SOUTHERN POWER CO | Purchased power
Operating Expenses:
Total cost of sales	20	14
SOUTHERN Co GAS
Operating Revenues:
Operating revenues	$ 1,694	$ 1,249
Operating Expenses:
Cost, Product and Service [Extensible List]	Natural gas	Natural gas
Other operations and maintenance	$ 299	$ 258
Depreciation and amortization	130	120
Taxes other than income taxes	81	72
Total operating expenses	1,093	889
Operating Income	601	360
Other Income and (Expense):
Earnings from equity method investments	41	43
Interest expense, net of amounts capitalized	(60)	(58)
Other income (expense), net	(63)	9
Total other income and (expense)	(82)	(6)
Earnings Before Income Taxes	519	354
Income taxes (benefit)	121	79
Comprehensive Income	402	260
Consolidated Net Income	398	275
Net Income	398	275
SOUTHERN Co GAS | Natural gas
Operating Revenues:
Operating revenues	1,692	1,240
Operating Expenses:
Total cost of sales	583	439
SOUTHERN Co GAS | Alternative revenue programs
Operating Revenues:
Operating revenues	$ 2	$ 9

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating revenues	$ 5,910	$ 5,018
Alternative revenue programs
Operating revenues	2	9
SOUTHERN Co GAS
Operating revenues	1,694	1,249
Revenue taxes collected	54	47
SOUTHERN Co GAS | Alternative revenue programs
Operating revenues	$ 2	$ 9

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net income	$ 1,107	$ 841
Qualifying hedges:
Changes in fair value, net of tax	(30)	(86)
Reclassification adjustment for amounts included in net income, net of tax	55	38
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	3	1
Total other comprehensive income (loss)	28	(47)
Comprehensive Income	1,135	794
Dividends on preferred stock of subsidiaries	4	4
Comprehensive loss attributable to noncontrolling interests	(32)	(31)
Comprehensive Income (Loss) Attributable to Parent	1,163	821
ALABAMA POWER CO
Net income	363	284
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	364	285
Dividends on preferred stock of subsidiaries	4	4
GEORGIA POWER CO
Net income	351	331
Qualifying hedges:
Changes in fair value, net of tax	0	(2)
Reclassification adjustment for amounts included in net income, net of tax	2	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	2	(1)
Comprehensive Income	353	330
MISSISSIPPI POWER CO
Net income	45	32
Pension and other postretirement benefit plans:
Comprehensive Income	45	32
SOUTHERN POWER CO
Net income	65	44
Qualifying hedges:
Changes in fair value, net of tax	(33)	(62)
Reclassification adjustment for amounts included in net income, net of tax	48	28
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	1	1
Total other comprehensive income (loss)	16	(33)
Comprehensive Income	81	11
Comprehensive loss attributable to noncontrolling interests	(32)	(31)
Comprehensive Income (Loss) Attributable to Parent	113	42
SOUTHERN Co GAS
Net income	398	275
Qualifying hedges:
Changes in fair value, net of tax	1	(20)
Reclassification adjustment for amounts included in net income, net of tax	3	5
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	4	(15)
Comprehensive Income	$ 402	$ 260

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Qualifying hedges:
Changes in fair value, tax	$ (10)	$ (30)
Reclassification adjustment for amounts included in net income, tax	18	13
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	1	2
ALABAMA POWER CO
Qualifying hedges:
Reclassification adjustment for amounts included in net income, tax	0	0
GEORGIA POWER CO
Qualifying hedges:
Changes in fair value, tax	0	(1)
Reclassification adjustment for amounts included in net income, tax	0	1
SOUTHERN POWER CO
Qualifying hedges:
Changes in fair value, tax	(11)	(21)
Reclassification adjustment for amounts included in net income, tax	15	10
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	0	0
SOUTHERN Co GAS
Qualifying hedges:
Changes in fair value, tax	0	(7)
Reclassification adjustment for amounts included in net income, tax	$ 1	$ 2

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Activities:
Net income	$ 1,107	$ 841
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	964	949
Deferred income taxes	140	(58)
Allowance for equity funds used during construction	(46)	(34)
Pension, postretirement, and other employee benefits	(78)	(67)
Settlement of asset retirement obligations	(109)	(86)
Stock based compensation expense	83	72
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Storm damage accruals	54	56
(Gain) loss on dispositions, net	(41)	(38)
Natural gas cost under recovery – long-term	(185)	0
Other, net	114	55
Changes in certain current assets and liabilities —
-Receivables	308	317
-Prepayments	(98)	(110)
-Natural gas for sale, net of temporary LIFO liquidation	456	246
-Natural gas cost under recovery	(487)	0
-Other current assets	63	(67)
-Accounts payable	(216)	(504)
-Accrued taxes	(212)	(102)
-Accrued compensation	(417)	(473)
-Accrued interest	(90)	(60)
-Customer refunds	0	(103)
-Other current liabilities	(116)	60
Net cash provided from operating activities	1,242	894
Investing Activities:
Business acquisitions, net of cash acquired	(345)	0
Property additions	(1,678)	(1,560)
Nuclear decommissioning trust fund purchases	(550)	(254)
Nuclear decommissioning trust fund sales	546	249
Proceeds from dispositions	20	982
Cost of removal, net of salvage	(85)	(69)
Change in construction payables, net	(116)	(141)
Payments pursuant to LTSAs	(60)	(26)
Other investing activities	25	(70)
Net cash used for investing activities	(2,243)	(889)
Financing Activities:
Increase in notes payable, net	182
Decrease in notes payable, net		(685)
Proceeds —
Long-term debt	2,150	2,653
Common stock	14	52
Short-term borrowings	325	565
Redemptions and repurchases —
Long-term debt	(384)	(1,481)
Short-term borrowings	(25)	(100)
Capital contributions from noncontrolling interests	313	16
Distributions to noncontrolling interests	(46)	(48)
Payment of common stock dividends	(678)	(655)
Other financing activities	(117)	(132)
Net cash provided from financing activities	1,734	185
Net Change in Cash, Cash Equivalents, and Restricted Cash	733	190
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	1,068	1,978
Cash, Cash Equivalents, and Restricted Cash at End of Period	1,801	2,168
Cash paid (received) during the period for —
Interest, net of amounts capitalized	519	490
Income taxes, net	(51)	(16)
Noncash transactions —
Accrued property additions at end of period	872	733
Contributions from noncontrolling interests	89	0
Contributions of wind turbine equipment	82	17
Right-of-use assets obtained under finance leases	76	28
Interest capitalized	21	20
ALABAMA POWER CO
Operating Activities:
Net income	363	284
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	248	241
Deferred income taxes	33	10
Allowance for equity funds used during construction	(12)	(10)
Pension, postretirement, and other employee benefits	(29)	(25)
Settlement of asset retirement obligations	(49)	(46)
Other, net	(15)	10
Changes in certain current assets and liabilities —
-Receivables	40	93
-Fossil fuel stock	38	(15)
-Prepayments	(73)	(80)
-Materials and supplies	(4)	(22)
-Other current assets	(11)	(14)
-Accounts payable	(299)	(305)
-Accrued taxes	104	100
-Accrued compensation	(105)	(111)
-Retail fuel cost over recovery	(18)	47
-Other current liabilities	(9)	(12)
Net cash provided from operating activities	214	155
Investing Activities:
Property additions	(466)	(340)
Nuclear decommissioning trust fund purchases	(310)	(81)
Nuclear decommissioning trust fund sales	310	81
Cost of removal, net of salvage	(23)	(15)
Change in construction payables, net	32	(65)
Other investing activities	(9)	(4)
Net cash used for investing activities	(466)	(424)
Redemptions and repurchases —
Pollution control revenue bonds	0	(87)
Capital contributions from parent company	600	610
Payment of common stock dividends	(246)	(239)
Other financing activities	(13)	(11)
Net cash provided from financing activities	341	273
Net Change in Cash, Cash Equivalents, and Restricted Cash	89	4
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	530	894
Cash, Cash Equivalents, and Restricted Cash at End of Period	619	898
Cash paid (received) during the period for —
Interest, net of amounts capitalized	93	92
Noncash transactions —
Accrued property additions at end of period	198	135
Right-of-use assets obtained under leases	1	3
Interest capitalized	3	3
GEORGIA POWER CO
Operating Activities:
Net income	351	331
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	384	396
Deferred income taxes	(86)	(73)
Pension, postretirement, and other employee benefits	(43)	(40)
Settlement of asset retirement obligations	(49)	(33)
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Storm damage accruals	53	53
Retail fuel cost over recovery – long-term	0	90
Other, net	(19)	(52)
Changes in certain current assets and liabilities —
-Receivables	176	22
-Fossil fuel stock	10	(42)
-Other current assets	(7)	(15)
-Accounts payable	(74)	(69)
-Accrued taxes	(110)	(156)
-Accrued compensation	(68)	(87)
-Customer refunds	0	(107)
-Other current liabilities	(77)	(5)
Net cash provided from operating activities	489	213
Investing Activities:
Property additions	(775)	(849)
Nuclear decommissioning trust fund purchases	(241)	(173)
Nuclear decommissioning trust fund sales	236	167
Proceeds from dispositions	1	142
Cost of removal, net of salvage	(40)	(34)
Change in construction payables, net	(103)	(46)
Other investing activities	9	(2)
Net cash used for investing activities	(913)	(795)
Financing Activities:
Increase in notes payable, net	145	11
Proceeds —
Senior notes	750	1,500
Pollution control revenue bonds	0	53
Short-term borrowings	0	200
Redemptions and repurchases —
Pollution control revenue bonds	0	(148)
Senior notes	(325)	(950)
FFB loan	(25)	(16)
Capital contributions from parent company	330	500
Payment of common stock dividends	(412)	(385)
Other financing activities	(19)	(23)
Net cash provided from financing activities	444	742
Net Change in Cash, Cash Equivalents, and Restricted Cash	20	160
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	9	52
Cash, Cash Equivalents, and Restricted Cash at End of Period	29	212
Cash paid (received) during the period for —
Interest, net of amounts capitalized	128	122
Noncash transactions —
Accrued property additions at end of period	445	472
Right-of-use assets obtained under operating leases	3	10
Interest capitalized	15	11
MISSISSIPPI POWER CO
Operating Activities:
Net income	45	32
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	53	44
Other, net	(10)	(3)
Changes in certain current assets and liabilities —
-Receivables	7	14
-Other current assets	1	(10)
-Accounts payable	(30)	(24)
-Accrued taxes	(75)	(54)
-Accrued compensation	(16)	(19)
-Other current liabilities	(13)	3
Net cash provided from operating activities	(38)	(17)
Investing Activities:
Property additions	(45)	(50)
Change in construction payables, net	(8)	(10)
Payments pursuant to LTSAs	(7)	(5)
Other investing activities	(7)	(6)
Net cash used for investing activities	(67)	(71)
Financing Activities:
Increase in notes payable, net	29	0
Proceeds —
Short-term borrowings	0	40
Other long-term debt	0	100
Redemptions and repurchases —
Senior notes	0	(275)
Capital contributions from parent company	100	75
Return of capital to parent company	0	(37)
Payment of common stock dividends	(39)	0
Other financing activities	0	(1)
Net cash provided from financing activities	90	(98)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(15)	(186)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	39	286
Cash, Cash Equivalents, and Restricted Cash at End of Period	24	100
Cash paid (received) during the period for —
Interest, net of amounts capitalized	16	18
Noncash transactions —
Accrued property additions at end of period	26	25
Interest capitalized	0	0
SOUTHERN POWER CO
Operating Activities:
Net income	65	44
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	125	123
Deferred income taxes	(8)	(36)
Amortization of investment tax credits	(15)	(14)
(Gain) loss on dispositions, net	(39)	(39)
Other, net	(4)	(10)
Changes in certain current assets and liabilities —
-Receivables	23	5
-Prepaid income taxes	16	51
-Other current assets	3	(2)
-Accounts payable	19	(34)
-Accrued taxes	5	8
-Other current liabilities	(3)	(13)
Net cash provided from operating activities	187	83
Investing Activities:
Business acquisitions, net of cash acquired	(345)	0
Property additions	(147)	(47)
Proceeds from dispositions	17	660
Change in construction payables, net	(7)	(15)
Payments pursuant to LTSAs	(27)	(15)
Other investing activities	5	17
Net cash used for investing activities	(504)	600
Financing Activities:
Increase in notes payable, net	140
Decrease in notes payable, net		(449)
Proceeds —
Senior notes	400	0
Redemptions and repurchases —
Short-term borrowings	0	(100)
Return of capital to parent company	(271)	0
Capital contributions from noncontrolling interests	313	16
Distributions to noncontrolling interests	(46)	(48)
Payment of common stock dividends	(51)	(50)
Other financing activities	(7)	(1)
Net cash provided from financing activities	478	(632)
Net Change in Cash, Cash Equivalents, and Restricted Cash	161	51
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	182	279
Cash, Cash Equivalents, and Restricted Cash at End of Period	343	330
Cash paid (received) during the period for —
Interest, net of amounts capitalized	26	28
Income taxes, net	(2)	(5)
Noncash transactions —
Accrued property additions at end of period	60	27
Contributions from noncontrolling interests	89	0
Contributions of wind turbine equipment	82	17
Right-of-use assets obtained under operating leases	65	0
Interest capitalized	1	4
SOUTHERN Co GAS
Operating Activities:
Net income	398	275
Adjustments to reconcile net income to net cash provided from operating activities —
Depreciation and amortization, total	130	120
Deferred income taxes	160	22
Mark-to-market adjustments	64	13
Natural gas cost under recovery – long-term	(185)	0
Other, net	5	(19)
Changes in certain current assets and liabilities —
-Receivables	74	112
-Natural gas for sale, net of temporary LIFO liquidation	456	246
-Natural gas cost under recovery	(487)	0
-Other current assets	(34)	33
-Accounts payable	(7)	(185)
-Accrued taxes	10	27
-Accrued compensation	0	(42)
-Other current liabilities	(34)	41
Net cash provided from operating activities	550	643
Investing Activities:
Property additions	(251)	(261)
Proceeds from dispositions	0	178
Cost of removal, net of salvage	(16)	(15)
Change in construction payables, net	(47)	(18)
Investment in unconsolidated subsidiaries	(1)	(77)
Other investing activities	7	0
Net cash used for investing activities	(308)	(193)
Financing Activities:
Decrease in notes payable, net	(127)	(39)
Proceeds —
Short-term borrowings	300	0
Redemptions and repurchases —
Redemptions — Medium-term notes	(30)	0
Capital contributions from parent company	39	0
Payment of common stock dividends	(132)	(133)
Other financing activities	0	(13)
Net cash provided from financing activities	50	(185)
Net Change in Cash, Cash Equivalents, and Restricted Cash	292	265
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	19	49
Cash, Cash Equivalents, and Restricted Cash at End of Period	311	314
Cash paid (received) during the period for —
Interest, net of amounts capitalized	52	49
Income taxes, net	(1)	(12)
Noncash transactions —
Accrued property additions at end of period	95	104
Interest capitalized	$ 2	$ 2

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest capitalized	$ 21	$ 20
ALABAMA POWER CO
Interest capitalized	3	3
GEORGIA POWER CO
Interest capitalized	15	11
MISSISSIPPI POWER CO
Interest capitalized	0	0
SOUTHERN POWER CO
Interest capitalized	1	4
SOUTHERN Co GAS
Interest capitalized	$ 2	$ 2

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 1,770	$ 1,065
Receivables —
Customer accounts	1,716	1,753
Energy marketing	412	516
Unbilled revenues	544	672
Other accounts and notes	478	512
Accumulated provision for uncollectible accounts	(124)	(118)
Materials and supplies	1,504	1,478
Fossil fuel for generation	494	550
Natural gas for sale	197	460
Prepaid expenses	657	276
Assets from risk management activities, net of collateral	100	147
Regulatory assets – asset retirement obligations	214	214
Natural gas cost under recovery	487	0
Other regulatory assets	788	810
Other current assets	232	282
Total current assets	9,469	8,617
Property, Plant, and Equipment:
In service	111,579	110,516
Less: Accumulated depreciation	32,887	32,397
Plant in service, net of depreciation	78,692	78,119
Nuclear fuel, at amortized cost	820	818
Construction work in progress	9,525	8,697
Total property, plant, and equipment	89,037	87,634
Other Property and Investments:
Goodwill	5,280	5,280
Nuclear decommissioning trusts, at fair value	2,346	2,303
Equity investments in unconsolidated subsidiaries	1,368	1,362
Other intangible assets, net of amortization	477	487
Leveraged leases	562	556
Miscellaneous property and investments	463	398
Total other property and investments	10,496	10,386
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,821	1,802
Deferred charges related to income taxes	803	796
Unamortized loss on reacquired debt	274	280
Regulatory assets – asset retirement obligations, deferred	4,966	4,934
Other regulatory assets, deferred	7,263	7,198
Other deferred charges and assets	1,264	1,288
Total deferred charges and other assets	16,391	16,298
Total Assets	125,393	122,935
Current Liabilities:
Securities due within one year	3,535	3,507
Notes payable	1,092	609
Energy marketing trade payables	475	494
Accounts payable —
Accounts payable	2,058	2,312
Customer deposits	470	487
Accrued taxes —
Accrued income taxes	71	130
Other accrued taxes	412	699
Accrued interest	423	513
Accrued compensation	584	1,025
Asset retirement obligations	642	585
Operating lease obligations	244	241
Other regulatory liabilities	462	509
Other current liabilities	1,118	968
Total current liabilities	11,586	12,079
Long-term Debt	46,727	45,073
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	8,839	8,175
Deferred credits related to income taxes	5,676	5,767
Accumulated deferred ITCs	2,214	2,235
Employee benefit obligations	2,091	2,213
Operating lease obligations, deferred	1,652	1,611
Asset retirement obligations, deferred	10,043	10,099
Accrued environmental remediation	208	216
Other cost of removal obligations	2,215	2,211
Other regulatory liabilities, deferred	226	251
Other deferred credits and liabilities	557	480
Total deferred credits and other liabilities	33,721	33,258
Total Liabilities	92,034	90,410
Redeemable Preferred Stock of Subsidiaries	291	291
Common Stockholder's Equity (See accompanying statements)	33,068	32,234
Total Liabilities and Stockholders' Equity	125,393	122,935
ALABAMA POWER CO
Current Assets:
Cash and cash equivalents	619	530
Receivables —
Customer accounts	394	429
Unbilled revenues	124	152
Affiliated	35	31
Other accounts and notes	71	66
Accumulated provision for uncollectible accounts	(33)	(43)
Materials and supplies	550	546
Fossil fuel for generation	197	235
Prepaid expenses	114	42
Other regulatory assets	224	226
Other current assets	43	33
Total current assets	2,338	2,247
Property, Plant, and Equipment:
In service	32,015	31,816
Less: Accumulated depreciation	10,123	10,009
Plant in service, net of depreciation	21,892	21,807
Nuclear fuel, at amortized cost	268	270
Construction work in progress	1,052	866
Total property, plant, and equipment	23,212	22,943
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,198	1,157
Equity investments in unconsolidated subsidiaries	63	63
Miscellaneous property and investments	128	131
Total other property and investments	1,389	1,351
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	140	151
Deferred charges related to income taxes	237	235
Regulatory assets – asset retirement obligations, deferred	1,446	1,441
Other regulatory assets, deferred	2,161	2,162
Other deferred charges and assets	282	273
Total deferred charges and other assets	4,266	4,262
Total Assets	31,205	30,803
Current Liabilities:
Securities due within one year	815	311
Accounts payable —
Affiliated	220	316
Other	392	545
Customer deposits	105	104
Accrued taxes —
Accrued taxes	257	152
Accrued interest	75	90
Accrued compensation	113	212
Asset retirement obligations	275	254
Other regulatory liabilities	98	108
Other current liabilities	108	107
Total current liabilities	2,458	2,199
Long-term Debt	8,055	8,558
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,318	3,273
Deferred credits related to income taxes	2,006	2,016
Accumulated deferred ITCs	92	94
Employee benefit obligations	187	214
Operating lease obligations, deferred	112	119
Asset retirement obligations, deferred	3,688	3,720
Other cost of removal obligations	320	335
Other regulatory liabilities, deferred	98	124
Other deferred credits and liabilities	54	50
Total deferred credits and other liabilities	9,875	9,945
Total Liabilities	20,388	20,702
Redeemable Preferred Stock	291	291
Common Stockholder's Equity (See accompanying statements)	10,526	9,810
Total Liabilities and Stockholders' Equity	31,205	30,803
GEORGIA POWER CO
Current Assets:
Cash and cash equivalents	29	9
Receivables —
Customer accounts	532	621
Unbilled revenues	196	233
Joint owner accounts	124	123
Affiliated	22	21
Other accounts and notes	35	67
Accumulated provision for uncollectible accounts	(26)	(26)
Materials and supplies	610	592
Fossil fuel for generation	268	278
Regulatory assets – storm damage	213	213
Regulatory assets – asset retirement obligations	175	166
Other regulatory assets	250	248
Other current assets	114	143
Total current assets	2,542	2,688
Property, Plant, and Equipment:
In service	39,857	39,682
Less: Accumulated depreciation	12,421	12,251
Plant in service, net of depreciation	27,436	27,431
Nuclear fuel, at amortized cost	553	548
Construction work in progress	7,394	6,857
Total property, plant, and equipment	35,383	34,836
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,149	1,145
Equity investments in unconsolidated subsidiaries	51	51
Miscellaneous property and investments	66	63
Total other property and investments	1,266	1,259
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,273	1,308
Deferred charges related to income taxes	532	527
Regulatory assets – asset retirement obligations, deferred	3,310	3,291
Other regulatory assets, deferred	2,609	2,692
Other deferred charges and assets	434	479
Total deferred charges and other assets	8,158	8,297
Total Assets	47,349	47,080
Current Liabilities:
Securities due within one year	87	542
Notes payable	205	60
Accounts payable —
Affiliated	472	597
Other	732	753
Customer deposits	272	276
Accrued taxes —
Accrued taxes	239	407
Accrued interest	96	130
Accrued compensation	123	233
Asset retirement obligations	304	287
Operating lease obligations	151	151
Other regulatory liabilities	235	228
Over recovered fuel clause revenues	83	113
Other current liabilities	242	254
Total current liabilities	3,241	4,031
Long-term Debt	13,278	12,428
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,303	3,272
Deferred credits related to income taxes	2,517	2,588
Accumulated deferred ITCs	271	273
Employee benefit obligations	539	586
Operating lease obligations, deferred	1,149	1,156
Asset retirement obligations, deferred	5,971	5,978
Other deferred credits and liabilities	306	267
Total deferred credits and other liabilities	14,056	14,120
Total Liabilities	30,575	30,579
Common Stockholder's Equity (See accompanying statements)	16,774	16,501
Total Liabilities and Stockholders' Equity	47,349	47,080
MISSISSIPPI POWER CO
Current Assets:
Cash and cash equivalents	24	39
Receivables —
Customer accounts	50	34
Unbilled revenues	33	38
Affiliated	17	32
Other accounts and notes	29	32
Materials and supplies	67	65
Fossil fuel for generation	17	24
Other regulatory assets	49	60
Other current assets	20	20
Total current assets	306	344
Property, Plant, and Equipment:
In service	5,037	5,011
Less: Accumulated depreciation	1,579	1,545
Plant in service, net of depreciation	3,458	3,466
Construction work in progress	163	146
Total property, plant, and equipment	3,621	3,612
Other Property and Investments:
Total other property and investments	149	151
Deferred Charges and Other Assets:
Deferred charges related to income taxes	32	32
Regulatory assets – asset retirement obligations, deferred	211	201
Other regulatory assets, deferred	386	388
Accumulated deferred income taxes	126	129
Other deferred charges and assets	64	55
Total deferred charges and other assets	819	805
Total Assets	4,895	4,912
Current Liabilities:
Securities due within one year	421	406
Notes payable	54	25
Accounts payable —
Affiliated	50	63
Other	84	109
Accrued taxes —
Accrued taxes	39	114
Accrued interest	14	15
Accrued compensation	18	34
Asset retirement obligations	40	27
Other regulatory liabilities	36	49
Over recovered fuel clause revenues	26	34
Other current liabilities	38	40
Total current liabilities	820	916
Long-term Debt	996	1,013
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	463	447
Deferred credits related to income taxes	285	287
Employee benefit obligations	107	113
Asset retirement obligations, deferred	134	150
Other cost of removal obligations	194	194
Other regulatory liabilities, deferred	14	15
Other deferred credits and liabilities	34	35
Total deferred credits and other liabilities	1,231	1,241
Total Liabilities	3,047	3,170
Common Stockholder's Equity (See accompanying statements)	1,848	1,742
Total Liabilities and Stockholders' Equity	4,895	4,912
SOUTHERN POWER CO
Current Assets:
Cash and cash equivalents	314	182
Receivables —
Customer accounts	123	125
Affiliated	17	37
Other accounts and notes	18	27
Materials and supplies	157	157
Prepaid income taxes	368	11
Other current assets	31	36
Total current assets	1,028	575
Property, Plant, and Equipment:
In service	14,313	13,904
Less: Accumulated depreciation	2,916	2,842
Plant in service, net of depreciation	11,397	11,062
Construction work in progress	219	127
Total property, plant, and equipment	11,616	11,189
Other Property and Investments:
Intangible assets, net of amortization	297	302
Equity investments in unconsolidated subsidiaries	84	19
Miscellaneous property and investments	84	19
Total other property and investments	381	321
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	478	415
Prepaid LTSAs	178	155
Accumulated deferred income taxes	0	262
Income taxes receivable, non-current	28	25
Other deferred charges and assets	286	293
Total deferred charges and other assets	970	1,150
Total Assets	13,995	13,235
Current Liabilities:
Securities due within one year	300	299
Notes payable	315	175
Accounts payable —
Affiliated	44	65
Other	127	92
Accrued taxes —
Accrued income taxes	10	8
Other accrued taxes	15	22
Accrued interest	35	32
Other current liabilities	132	132
Total current liabilities	978	825
Long-term Debt	3,730	3,393
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	230	123
Accumulated deferred ITCs	1,658	1,672
Operating lease obligations, deferred	487	426
Other deferred credits and liabilities	168	165
Total deferred credits and other liabilities	2,543	2,386
Total Liabilities	7,251	6,604
Common Stockholder's Equity (See accompanying statements)	6,744	6,631
Total Liabilities and Stockholders' Equity	13,995	13,235
SOUTHERN Co GAS
Current Assets:
Cash and cash equivalents	309	17
Receivables —
Customer accounts	452	353
Energy marketing	412	516
Unbilled revenues	161	219
Affiliated	2	4
Other accounts and notes	43	51
Accumulated provision for uncollectible accounts	(51)	(40)
Natural gas for sale	197	460
Prepaid expenses	97	48
Assets from risk management activities, net of collateral	68	118
Natural gas cost under recovery	487	0
Other regulatory assets	84	102
Other current assets	39	38
Total current assets	2,300	1,886
Property, Plant, and Equipment:
In service	17,866	17,611
Less: Accumulated depreciation	4,893	4,821
Plant in service, net of depreciation	12,973	12,790
Construction work in progress	636	648
Total property, plant, and equipment	13,609	13,438
Other Property and Investments:
Goodwill	5,015	5,015
Equity investments in unconsolidated subsidiaries	1,290	1,290
Other intangible assets, net of amortization	47	51
Miscellaneous property and investments	20	19
Total other property and investments	6,372	6,375
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	80	81
Other regulatory assets, deferred	786	615
Other deferred charges and assets	230	235
Total deferred charges and other assets	1,096	931
Total Assets	23,377	22,630
Current Liabilities:
Securities due within one year	302	333
Notes payable	497	324
Energy marketing trade payables	475	494
Accounts payable —
Affiliated	49	56
Other	346	373
Customer deposits	76	90
Accrued taxes —
Accrued taxes	94	83
Accrued interest	68	58
Accrued compensation	107	106
Other regulatory liabilities	92	122
Temporary LIFO liquidation	194	0
Other current liabilities	166	150
Total current liabilities	2,466	2,189
Long-term Debt	6,286	6,293
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,427	1,265
Deferred credits related to income taxes	839	847
Employee benefit obligations	273	283
Operating lease obligations, deferred	65	67
Accrued environmental remediation	208	216
Other cost of removal obligations	1,668	1,649
Other deferred credits and liabilities	51	54
Total deferred credits and other liabilities	4,531	4,381
Total Liabilities	13,283	12,863
Common Stockholder's Equity (See accompanying statements)	10,094	9,767
Total Liabilities and Stockholders' Equity	$ 23,377	$ 22,630

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Other intangible assets, amortization	$ 339	$ 328
SOUTHERN POWER CO
Other intangible assets, amortization	94	89
SOUTHERN Co GAS
Other intangible assets, amortization	$ 199	$ 195

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	ALABAMA POWER CO	ALABAMA POWER COCommon Stock	ALABAMA POWER COPaid-In Capital	ALABAMA POWER CORetained Earnings (Accumulated Deficit)	ALABAMA POWER COAccumulated Other Comprehensive Income (Loss)	GEORGIA POWER CO	GEORGIA POWER COCommon Stock	GEORGIA POWER COPaid-In Capital	GEORGIA POWER CORetained Earnings (Accumulated Deficit)	GEORGIA POWER COAccumulated Other Comprehensive Income (Loss)	MISSISSIPPI POWER CO	MISSISSIPPI POWER COCommon Stock	MISSISSIPPI POWER COPaid-In Capital	MISSISSIPPI POWER CORetained Earnings (Accumulated Deficit)	MISSISSIPPI POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO	SOUTHERN POWER COTotal Common Stockholders' Equity	SOUTHERN POWER COPaid-In Capital	SOUTHERN POWER CORetained Earnings (Accumulated Deficit)	SOUTHERN POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CONoncontrolling Interests	SOUTHERN Co GAS	SOUTHERN Co GASPaid-In Capital	SOUTHERN Co GASRetained Earnings (Accumulated Deficit)	SOUTHERN Co GASAccumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2019		1,054	1						31					9					1
Beginning balance at Dec. 31, 2019	$ 31,759	$ 5,257	$ (42)	$ 11,734	$ 10,877	$ (321)	$ 4,254	$ 8,955	$ 1,222	$ 4,755	$ 3,001	$ (23)	$ 15,065	$ 398	$ 10,962	$ 3,756	$ (51)	$ 1,652	$ 38	$ 4,449	$ (2,832)	$ (3)	$ 6,622	$ 2,368	$ 909	$ 1,485	$ (26)	$ 4,254	$ 9,506	$ 9,697	$ (198)	$ 7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	837				868		(31)
Net income (loss)	841							284					331			331		32			32		44	75		75		(31)	275		275
Net income after dividends on preferred stock	868							280			280												75						275
Capital contributions from parent company								612		612			502		502			76		76
Return of capital to parent company																		(37)		(37)									(2)	(2)
Other comprehensive income (loss)	(47)					(47)		1				1	(1)				(1)						(33)	(33)			(33)		(15)			(15)
Stock issued (in shares)		3
Stock issued	52	$ 9		43
Stock-based compensation	5			5
Cash dividends on common stock	(655)				(655)			(239)			(239)		(385)			(385)							(50)	(50)		(50)			(133)		(133)
Capital contributions from noncontrolling interests	16						16																16					16
Distributions to noncontrolling interests	(48)						(48)																(48)					(48)
Other	(3)		$ (2)		(2)	1												(1)		(1)
Ending balance (in shares) at Mar. 31, 2020		1,057	1						31					9					1
Ending balance at Mar. 31, 2020	31,916	$ 5,266	$ (44)	11,782	11,088	(367)	4,191	9,609	$ 1,222	5,367	3,042	(22)	15,512	$ 398	11,464	3,702	(52)	1,722	$ 38	4,487	(2,800)	(3)	6,551	2,360	909	1,510	(59)	4,191	9,631	9,695	(56)	(8)
Beginning balance (in shares) at Dec. 31, 2020		1,058	1						31					9					1
Beginning balance at Dec. 31, 2020	32,234	$ 5,268	$ (46)	11,834	11,311	(395)	4,262	9,810	$ 1,222	5,413	3,194	(19)	16,501	$ 398	12,361	3,789	(47)	1,742	$ 38	4,460	(2,754)	(2)	6,631	2,369	914	1,522	(67)	4,262	9,767	9,930	(141)	(22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	1,103				1,135		(32)
Net income (loss)	1,107							363					351			351		45			45		65	97		97		(32)	398		398
Net income after dividends on preferred stock	1,135							359			359												97						398
Capital contributions from parent company								602		602			332		332			100		100									57	57
Return of capital to parent company																							(271)	(271)	(271)
Other comprehensive income (loss)	28					28		1				1	2				2						16	16			16		4			4
Stock issued (in shares)		2
Stock issued	14	$ 5		9
Stock-based compensation	9			9
Cash dividends on common stock	(678)				(678)			(246)			(246)		(412)			(412)		(39)			(39)		(51)	(51)		(51)			(132)		(132)
Capital contributions from noncontrolling interests	403						403																403					403
Distributions to noncontrolling interests	(46)						(46)																(46)					(46)
Other	1			2			(1)																(3)	(2)	(2)	1	(1)	(1)
Ending balance (in shares) at Mar. 31, 2021		1,060	1						31					9					1
Ending balance at Mar. 31, 2021	$ 33,068	$ 5,273	$ (46)	$ 11,854	$ 11,768	$ (367)	$ 4,586	$ 10,526	$ 1,222	$ 6,015	$ 3,307	$ (18)	$ 16,774	$ 398	$ 12,693	$ 3,728	$ (45)	$ 1,848	$ 38	$ 4,560	$ (2,748)	$ (2)	$ 6,744	$ 2,158	$ 641	$ 1,569	$ (52)	$ 4,586	$ 10,094	$ 9,987	$ 125	$ (18)

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 0.64	$ 0.62

Introduction

Introduction	3 Months Ended
	Mar. 31, 2021
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, 2020 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, 2021 and 2020. 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 and other factors, including the impacts of the COVID-19 pandemic, 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 overall results of operations, financial position, or cash flows of any Registrant. Goodwill and Other Intangible Assets Goodwill at March 31, 2021 and December 31, 2020 was as follows: Goodwill (in millions) Southern Company $ 5,280 Southern Company Gas: Gas distribution operations $ 4,034 Gas marketing services 981 Southern Company Gas total $ 5,015 Goodwill is not amortized but is subject to an annual impairment test in the fourth quarter of the year and on an interim basis as events and changes in circumstances occur. Other intangible assets were as follows: At March 31, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (139) $ 73 $ 212 $ (135) $ 77 Trade names 64 (33) 31 64 (31) 33 Storage and transportation contracts 64 (64) — 64 (64) — PPA fair value adjustments 390 (94) 296 390 (89) 301 Other 11 (9) 2 10 (9) 1 Total other intangible assets subject to amortization $ 741 $ (339) $ 402 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 816 $ (339) $ 477 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (94) $ 296 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (122) $ 34 $ 156 $ (119) $ 37 Trade names 26 (13) 13 26 (12) 14 Wholesale gas services Storage and transportation contracts 64 (64) — 64 (64) — Total other intangible assets subject to amortization $ 246 $ (199) $ 47 $ 246 $ (195) $ 51 Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2021 (in millions) Southern Company (a) $ 11 Southern Power (b) 5 Southern Company Gas (c) 4 (a) Includes $5 million recorded as a reduction to operating revenues. (b) Recorded as a reduction to operating revenues. (c) Relates to gas marketing services. Restricted Cash The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the Registrants that had restricted cash at March 31, 2021 and/or December 31, 2020: Southern Southern Power Southern March 31, 2021 December 31, 2020 March 31, 2021 March 31, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 1,770 $ 1,065 $ 314 $ 309 $ 17 Restricted cash (a) : Other current assets 2 2 — 2 2 Other deferred charges and assets 29 — 29 — — Total cash, cash equivalents, and restricted cash $ 1,801 $ 1,068 (b) $ 343 $ 311 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total does not add due to rounding. Natural Gas for Sale With the exception of Nicor Gas, Southern Company Gas' natural gas distribution utilities record natural gas inventories 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. 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 recorded no material adjustments to natural gas inventories for either period presented. Nicor Gas' inventory decrement at March 31, 2021 is expected to be restored prior to year end.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Regulatory Matters	REGULATORY MATTERS See Note 2 to the financial statements in Item 8 of the Form 10-K for additional information relating to regulatory matters. The recovery balances for certain retail regulatory clauses of the traditional electric operating companies and Southern Company Gas at March 31, 2021 and December 31, 2020 were as follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, 2020 (in millions) Alabama Power Rate CNP Compliance Other regulatory liabilities, current $ 33 $ 28 Rate CNP PPA Other regulatory assets, deferred 58 58 Retail Energy Cost Recovery Other regulatory liabilities, current — 18 Other regulatory assets, deferred 15 — Natural Disaster Reserve Other regulatory liabilities, deferred 52 77 Georgia Power Fuel Cost Recovery Over recovered fuel clause revenues $ 83 $ 113 Mississippi Power Fuel Cost Recovery Over recovered regulatory clause liabilities $ 18 $ 24 Ad Valorem Tax Other regulatory assets, current 12 11 Other regulatory assets, deferred 45 41 Property Damage Reserve Other regulatory liabilities, deferred — 4 Other regulatory assets, deferred 1 — Southern Company Gas Natural Gas Cost Recovery (*) Other regulatory liabilities $ 12 $ 88 Natural gas cost under recovery 487 — Other regulatory assets, deferred 185 — (*) The significant change during the three months ended March 31, 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri. Alabama Power Certificate of Convenience and Necessity Energy Alabama, Gasp, Inc., and the Sierra Club filed requests for reconsideration and rehearing with the Alabama PSC regarding the certificate of convenience and necessity (CCN) issued to Alabama Power in August 2020, which authorized, among other things, the construction of Plant Barry Unit 8 and the acquisition of the Central Alabama Generating Station. In December 2020, the Alabama PSC issued an order denying the requests. On January 7, 2021, Energy Alabama and Gasp, Inc. filed judicial appeals regarding both the Alabama PSC's August 2020 CCN order and the December 2020 order denying reconsideration and rehearing. On February 23, 2021, Alabama Power filed a motion to intervene in the appeal and, on March 9, 2021, the Circuit Court of Montgomery County, Alabama granted the motion. At March 31, 2021, expenditures associated with the construction of Plant Barry Unit 8 included in CWIP totaled approximately $161 million. The ultimate outcome of this matter cannot be determined at this time. Plant Greene County Alabama Power jointly owns Plant Greene County with an affiliate, Mississippi Power. See Note 5 under "Joint Ownership Agreements" in Item 8 of the Form 10-K for additional information. On April 15, 2021, Mississippi Power filed its 2021 IRP with the Mississippi PSC, which includes a schedule to retire its 40% ownership interest in Plant Greene County Units 1 and 2 in December 2025 and 2026, respectively, consistent with each unit's remaining useful life. Mississippi Power's IRP is subject to a review period during which the Mississippi PSC may note any deficiencies which could require re-evaluation or resubmission of the IRP. If no deficiencies are noted, the Mississippi PSC's review will conclude on August 13, 2021. The Plant Greene County unit retirements identified by Mississippi Power require the completion of transmission and system reliability improvements, as well as agreement by Alabama Power. Alabama Power will continue to monitor the status of Mississippi Power's IRP and associated regulatory processes, as well as the transmission and system reliability improvements. Currently, Alabama Power plans to retire Plant Greene County Units 1 and 2 at the dates indicated. The ultimate outcome of this matter cannot be determined at this time. Georgia Power Rate Plan Effective January 1, 2021, Georgia Power reduced its amortization of costs associated with CCR AROs by approximately $90 million as approved by the Georgia PSC in conjunction with Georgia Power's annual compliance filings. In February 2020, the Georgia PSC denied a motion for reconsideration filed by the Sierra Club regarding the Georgia PSC's decision in the 2019 ARP allowing Georgia Power to recover compliance costs for CCR AROs, and, in December 2020, the Superior Court of Fulton County affirmed the decision of the Georgia PSC. On January 5, 2021, the Sierra Club filed a notice of appeal with the Georgia Court of Appeals. The ultimate outcome of this matter cannot be determined at this time. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information regarding Georgia Power's AROs. Nuclear Construction In 2009, the Georgia PSC certified construction of Plant Vogtle Units 3 and 4, in which Georgia Power holds a 45.7% ownership interest. In 2012, the NRC issued the related combined construction and operating licenses, which allowed full construction of the two AP1000 nuclear units (with electric generating capacity of approximately 1,100 MWs each) and related facilities to begin. Until March 2017, construction on Plant Vogtle Units 3 and 4 continued under the Vogtle 3 and 4 Agreement, which was a substantially fixed price agreement. In connection with the EPC Contractor's bankruptcy filing in March 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into several transitional arrangements to allow construction to continue. In July 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into the Vogtle Services Agreement, whereby Westinghouse provides facility design and engineering services, procurement and technical support, and staff augmentation on a time and materials cost basis. The Vogtle Services Agreement provides that it will continue until the start-up and testing of Plant Vogtle Units 3 and 4 are complete and electricity is generated and sold from both units. The Vogtle Services Agreement is terminable by the Vogtle Owners upon 30 days' written notice. In October 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, executed the Bechtel Agreement, a cost reimbursable plus fee arrangement, whereby Bechtel is reimbursed for actual costs plus a base fee and an at-risk fee, which is subject to adjustment based on Bechtel's performance against cost and schedule targets. Each Vogtle Owner is severally (not jointly) liable for its proportionate share, based on its ownership interest, of all amounts owed to Bechtel under the Bechtel Agreement. The Vogtle Owners may terminate the Bechtel Agreement at any time for their convenience, provided that the Vogtle Owners will be required to pay amounts related to work performed prior to the termination (including the applicable portion of the base fee), certain termination-related costs, and, at certain stages of the work, the applicable portion of the at-risk fee. Bechtel may terminate the Bechtel Agreement under certain circumstances, including certain Vogtle Owner suspensions of work, certain breaches of the Bechtel Agreement by the Vogtle Owners, Vogtle Owner insolvency, and certain other events. See Note 8 to the financial statements under "Long-term Debt – DOE Loan Guarantee Borrowings" in Item 8 of the Form 10-K for information on the Amended and Restated Loan Guarantee Agreement, including applicable covenants, events of default, mandatory prepayment events, and conditions to borrowing. Cost and Schedule Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4 by December 2021 and November 2022, respectively, is as follows: (in millions) Base project capital cost forecast (a)(b) $ 8,619 Construction contingency estimate 136 Total project capital cost forecast (a)(b) 8,755 Net investment as of March 31, 2021 (b) (7,560) Remaining estimate to complete (a) $ 1,195 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $250 million, of which $118 million had been accrued through March 31, 2021. (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds. Georgia Power estimates that its financing costs for construction of Plant Vogtle Units 3 and 4 will total approximately $3.0 billion, of which $2.7 billion had been incurred through March 31, 2021. As part of its ongoing processes, Southern Nuclear continues to evaluate cost and schedule forecasts on a regular basis to incorporate current information available, particularly in the areas of engineering support, commodity installation, system turnovers and related test results, and workforce statistics. Southern Nuclear establishes aggressive target values for monthly construction production and system turnover activities as part of a strategy that was designed to maintain margin to the regulatory-approved in-service dates of November 2021 for Unit 3 and November 2022 for Unit 4. In mid-March 2020, Southern Nuclear began implementing policies and procedures designed to mitigate the risk of transmission of COVID-19 at the construction site, including worker distancing measures, isolating individuals who have tested positive for COVID-19, are showing symptoms consistent with COVID-19, are being tested for COVID-19, or have been in close contact with such persons, requiring self-quarantine, and adopting additional precautionary measures. Since March 2020, the number of active cases at the site has fluctuated and impacted productivity levels and pace of activity completion. The lower productivity levels and slower pace of activity completion contributed to a backlog to the aggressive site work plan established at the beginning of 2020. Georgia Power estimates the productivity impacts of the COVID-19 pandemic have consumed approximately three Following the January 2021 milestone extensions, Southern Nuclear has been performing additional construction remediation work, primarily related to electrical commodity installations, necessary to ensure quality and design standards are met as system turnovers are completed to support hot functional testing and fuel load for Unit 3. Hot functional testing commenced in late April 2021 and the site work plan currently targets fuel load for Unit 3 in the third quarter 2021 and an in-service date of December 2021. As the site work plan includes minimal margin to these milestone dates, any delay could result in an in-service date in the first quarter 2022 for Unit 3. Achievement of the extended milestone dates established in January 2021 for Unit 4, which are expected to support a regulatory-approved in-service date of November 2022, primarily depends on overall construction productivity and production levels significantly improving as well as appropriate levels of craft laborers, particularly electrical and pipefitter craft labor, being added and maintained. Considering the factors above, during the first quarter 2021, approximately $84 million of the construction contingency established in the fourth quarter 2020 was assigned to the base capital cost forecast for costs primarily associated with the schedule extension for Unit 3 to December 2021, construction productivity, support resources, and construction remediation work. Georgia Power increased its total capital cost forecast as of March 31, 2021 by adding $48 million to the remaining construction contingency. After considering the significant level of uncertainty that exists regarding the future recoverability of these costs since the ultimate outcome of these matters is subject to the outcome of future assessments by management, as well as Georgia PSC decisions in future regulatory proceedings, Georgia Power recorded a pre-tax charge to income of $48 million ($36 million after tax) for the increase in the total project capital cost forecast as of March 31, 2021. As and when these amounts are spent, Georgia Power may request the Georgia PSC to evaluate those expenditures for rate recovery. In addition, the continuing effects of the COVID-19 pandemic could further disrupt or delay construction and testing activities at Plant Vogtle Units 3 and 4. Georgia Power's proportionate share of the estimated incremental cost associated with COVID-19 mitigation actions and impacts on construction productivity is currently estimated to be between $150 million and $190 million and is included in the total project capital cost forecast. Estimated costs associated with near-term COVID-19 mitigation actions and related impacts on construction productivity are also included in the total project capital cost forecast described above. As construction, including subcontract work, continues and testing and system turnover activities increase, challenges with management of contractors and vendors; subcontractor performance; supervision of craft labor and related productivity, particularly in the installation of electrical, mechanical, and instrumentation and controls commodities, ability to attract and retain craft labor, and/or related cost escalation; procurement, fabrication, delivery, assembly, installation, system turnover, and the initial testing and start-up, including any required engineering changes or any remediation related thereto, of plant systems, structures, or components (some of which are based on new technology that only within the last few years began initial operation in the global nuclear industry at this scale), any of which may require additional labor and/or materials; or other issues could arise and change the projected schedule and estimated cost. There have been technical and procedural challenges to the construction and licensing of Plant Vogtle Units 3 and 4 at the federal and state level and additional challenges may arise. Processes are in place that are designed to assure compliance with the requirements specified in the Westinghouse Design Control Document and the combined construction and operating licenses, including inspections by Southern Nuclear and the NRC that occur throughout construction. In connection with the additional construction remediation work described above, Southern Nuclear reviewed the project's construction quality programs and, where needed, is implementing improvement plans consistent with these processes. Findings resulting from such inspections could require additional remediation and/or further NRC oversight. In addition, certain license amendment requests have been filed and approved or are pending before the NRC. On March 15, 2021, the NRC issued an appealable order denying the Blue Ridge Environmental Defense League's (BREDL) December 2020 motion to reopen proceedings on BREDL's petition challenging a license amendment request. The staff of the NRC has issued the requested amendment. In September 2020, Southern Nuclear notified the NRC of its intent to load fuel for Unit 3 in 2021. Various design and other licensing-based compliance matters, including the timely submittal by Southern Nuclear of the ITAAC documentation for each unit and the related reviews and approvals by the NRC necessary to support NRC authorization to load fuel, may arise, which may result in additional license amendments or require other resolution. If any license amendment requests or other licensing-based compliance issues, including inspections and ITAACs, are not resolved in a timely manner, there may be delays in the project schedule that could result in increased costs. The ultimate outcome of these matters cannot be determined at this time. However, any extension of the in-service date beyond December 2021 for Unit 3 or November 2022 for Unit 4 is currently estimated to result in additional base capital costs for Georgia Power of approximately $25 million per month for Unit 3 and approximately $15 million per month for Unit 4, as well as the related AFUDC. While Georgia Power is not precluded from seeking recovery of any future capital cost forecast increase, management will ultimately determine whether or not to seek recovery. Any further changes to the capital cost forecast that are not expected to be recoverable through regulated rates will be required to be charged to income and such charges could be material. Joint Owner Contracts In November 2017, the Vogtle Owners entered into an amendment to their joint ownership agreements for Plant Vogtle Units 3 and 4 to provide for, among other conditions, additional Vogtle Owner approval requirements. Effective in August 2018, the Vogtle Owners further amended the joint ownership agreements to clarify and provide procedures for certain provisions of the joint ownership agreements related to adverse events that require the vote of the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 to continue construction (as amended, and together with the November 2017 amendment, the Vogtle Joint Ownership Agreements). The Vogtle Joint Ownership Agreements also confirm that the Vogtle Owners' sole recourse against Georgia Power or Southern Nuclear for any action or inaction in connection with their performance as agent for the Vogtle Owners is limited to removal of Georgia Power and/or Southern Nuclear as agent, except in cases of willful misconduct. As a result of an increase in the total project capital cost forecast and Georgia Power's decision not to seek rate recovery of the increase in the base capital costs in conjunction with the nineteenth VCM report in 2018, the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 were required to vote to continue construction. In September 2018, the Vogtle Owners unanimously voted to continue construction of Plant Vogtle Units 3 and 4. Amendments to the Vogtle Joint Ownership Agreements In connection with the vote to continue construction, Georgia Power entered into (i) a binding term sheet (Vogtle Owner Term Sheet) with the other Vogtle Owners and MEAG Power's wholly-owned subsidiaries MEAG Power SPVJ, LLC (MEAG SPVJ), MEAG Power SPVM, LLC (MEAG SPVM), and MEAG Power SPVP, LLC (MEAG SPVP) to take certain actions which partially mitigate potential financial exposure for the other Vogtle Owners, including additional amendments to the Vogtle Joint Ownership Agreements and the purchase of PTCs from the other Vogtle Owners at pre-established prices, and (ii) a term sheet (MEAG Term Sheet) with MEAG Power and MEAG SPVJ to provide up to $300 million of funding with respect to MEAG SPVJ's ownership interest in Plant Vogtle Units 3 and 4 under certain circumstances. In January 2019, Georgia Power, MEAG Power, and MEAG SPVJ entered into an agreement to implement the provisions of the MEAG Term Sheet. In February 2019, Georgia Power, the other Vogtle Owners, and MEAG Power's wholly-owned subsidiaries MEAG SPVJ, MEAG SPVM, and MEAG SPVP entered into certain amendments to the Vogtle Joint Ownership Agreements to implement the provisions of the Vogtle Owner Term Sheet (Global Amendments). As previously disclosed, pursuant to the Global Amendments: (i) each Vogtle Owner must pay its proportionate share of qualifying construction costs for Plant Vogtle Units 3 and 4 based on its ownership percentage up to the estimated cost at completion (EAC) for Plant Vogtle Units 3 and 4 which formed the basis of Georgia Power's forecast of $8.4 billion in the nineteenth VCM plus $800 million; (ii) Georgia Power will be responsible for 55.7% of actual qualifying construction costs between $800 million and $1.6 billion over the EAC in the nineteenth VCM (resulting in $80 million of potential additional costs to Georgia Power), with the remaining Vogtle Owners responsible for 44.3% of such costs pro rata in accordance with their respective ownership interests; and (iii) Georgia Power will be responsible for 65.7% of qualifying construction costs between $1.6 billion and $2.1 billion over the EAC in the nineteenth VCM (resulting in a further $100 million of potential additional costs to Georgia Power), with the remaining Vogtle Owners responsible for 34.3% of such costs pro rata in accordance with their respective ownership interests. If the EAC is revised and exceeds the EAC in the nineteenth VCM by more than $2.1 billion, each of the other Vogtle Owners will have a one-time option at the time the project budget forecast is so revised to tender a portion of its ownership interest to Georgia Power in exchange for Georgia Power's agreement to pay 100% of such Vogtle Owner's remaining share of total construction costs in excess of the EAC in the nineteenth VCM plus $2.1 billion. In addition, pursuant to the Global Amendments, the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 must vote to continue construction if certain adverse events occur, including, among other events: (i) the bankruptcy of Toshiba; (ii) the termination or rejection in bankruptcy of certain agreements, including the Vogtle Services Agreement, the Bechtel Agreement, or the agency agreement with Southern Nuclear; (iii) Georgia Power's public announcement of its intention not to submit for rate recovery any portion of its investment in Plant Vogtle Units 3 and 4 or the Georgia PSC determines that any of Georgia Power's costs relating to the construction of Plant Vogtle Units 3 and 4 will not be recovered in retail rates, excluding any additional amounts paid by Georgia Power on behalf of the other Vogtle Owners pursuant to the Global Amendments described above and the first 6% of costs during any six-month VCM reporting period that are disallowed by the Georgia PSC for recovery, or for which Georgia Power elects not to seek cost recovery, through retail rates; and (iv) an incremental extension of one year or more over the most recently approved schedule. The ultimate outcome of these matters cannot be determined at this time. Regulatory Matters In 2009, the Georgia PSC voted to certify construction of Plant Vogtle Units 3 and 4 with a certified capital cost of $4.418 billion. In addition, in 2009 the Georgia PSC approved inclusion of the Plant Vogtle Units 3 and 4 related CWIP accounts in rate base, and the State of Georgia enacted the Georgia Nuclear Energy Financing Act, which allows Georgia Power to recover financing costs for Plant Vogtle Units 3 and 4. Financing costs are recovered on all applicable certified costs through annual adjustments to the NCCR tariff up to the certified capital cost of $4.418 billion. At March 31, 2021, Georgia Power had recovered approximately $2.6 billion of financing costs. Financing costs related to capital costs above $4.418 billion are being recognized through AFUDC and are expected to be recovered through retail rates over the life of Plant Vogtle Units 3 and 4; however, Georgia Power will not record AFUDC related to any capital costs in excess of the total deemed reasonable by the Georgia PSC (currently $7.3 billion) and not requested for rate recovery. In November 2020, the Georgia PSC approved Georgia Power's request to decrease the NCCR tariff by $142 million annually, effective January 1, 2021. Georgia Power is required to file semi-annual VCM reports with the Georgia PSC by February 28 and August 31 of each year. In 2013, in connection with the eighth VCM report, the Georgia PSC approved a stipulation between Georgia Power and the staff of the Georgia PSC to waive the requirement to amend the Plant Vogtle Units 3 and 4 certificate in accordance with the 2009 certification order until the completion of Plant Vogtle Unit 3, or earlier if deemed appropriate by the Georgia PSC and Georgia Power. In 2016, the Georgia PSC voted to approve a settlement agreement (Vogtle Cost Settlement Agreement) resolving certain prudency matters in connection with the fifteenth VCM report. In December 2017, the Georgia PSC voted to approve (and issued its related order on January 11, 2018) Georgia Power's seventeenth VCM report and modified the Vogtle Cost Settlement Agreement. The Vogtle Cost Settlement Agreement, as modified by the January 11, 2018 order, resolved the following regulatory matters related to Plant Vogtle Units 3 and 4: (i) none of the $3.3 billion of costs incurred through December 31, 2015 and reflected in the fourteenth VCM report should be disallowed from rate base on the basis of imprudence; (ii) the Contractor Settlement Agreement was reasonable and prudent and none of the $0.3 billion paid pursuant to the Contractor Settlement Agreement should be disallowed from rate base on the basis of imprudence; (iii) (a) capital costs incurred up to $5.68 billion would be presumed to be reasonable and prudent with the burden of proof on any party challenging such costs, (b) Georgia Power would have the burden to show that any capital costs above $5.68 billion were prudent, and (c) a revised capital cost forecast of $7.3 billion (after reflecting the impact of payments received under the Guarantee Settlement Agreement and related customer refunds) was found reasonable; (iv) construction of Plant Vogtle Units 3 and 4 should be completed, with Southern Nuclear serving as project manager and Bechtel as primary contractor; (v) approved and deemed reasonable Georgia Power's revised schedule placing Plant Vogtle Units 3 and 4 in service in November 2021 and November 2022, respectively; (vi) confirmed that the revised cost forecast does not represent a cost cap and that prudence decisions on cost recovery will be made at a later date, consistent with applicable Georgia law; (vii) reduced the ROE used to calculate the NCCR tariff (a) from 10.95% (the ROE rate setting point authorized by the Georgia PSC in the 2013 alternate rate plan) to 10.00% effective January 1, 2016, (b) from 10.00% to 8.30%, effective January 1, 2020, and (c) from 8.30% to 5.30%, effective January 1, 2021 (provided that the ROE in no case will be less than Georgia Power's average cost of long-term debt); (viii) reduced the ROE used for AFUDC equity for Plant Vogtle Units 3 and 4 from 10.00% to Georgia Power's average cost of long-term debt, effective January 1, 2018; and (ix) agreed that upon Unit 3 reaching commercial operation, retail base rates would be adjusted to include the costs related to Unit 3 and common facilities deemed prudent in the Vogtle Cost Settlement Agreement. The January 11, 2018 order also stated that if Plant Vogtle Units 3 and 4 are not commercially operational by June 1, 2021 and June 1, 2022, respectively, the ROE used to calculate the NCCR tariff will be further reduced by 10 basis points each month (but not lower than Georgia Power's average cost of long-term debt) until the respective Unit is commercially operational. The ROE reductions negatively impacted earnings by approximately $150 million in 2020 and are estimated to have negative earnings impacts of approximately $265 million and $200 million in 2021 and 2022, respectively. In its January 11, 2018 order, the Georgia PSC also stated if other conditions change and assumptions upon which Georgia Power's seventeenth VCM report are based do not materialize, the Georgia PSC reserved the right to reconsider the decision to continue construction. The Georgia PSC has approved 23 VCM reports covering periods through June 30, 2020, including total construction capital costs incurred through that date of $8.1 billion (before $1.7 billion of payments received under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds). The Georgia PSC's order approving the twenty-third VCM report also instructed Georgia Power and the staff of the Georgia PSC to develop a mutually-agreeable recommendation to the Georgia PSC by the end of March 2021 regarding the procedure for and the timing, form, and substance of the rate adjustment filing related to the Unit 3 and common facility costs. On March 31, 2021, the staff of the Georgia PSC, on behalf of itself and Georgia Power, requested an extension through April 30, 2021. Georgia Power filed its twenty-fourth VCM report with the Georgia PSC on February 18, 2021, covering the period from July 1, 2020 through December 31, 2020, requesting approval of $670 million of construction capital costs incurred during that period. The ultimate outcome of these matters cannot be determined at this time. Mississippi Power Performance Evaluation Plan On March 15, 2021, Mississippi Power submitted its annual retail PEP filing for 2021 to the Mississippi PSC, which requested a 1.8%, or approximately $16 million, annual increase in revenues, primarily due to increased investment and amortization and lower sales. In accordance with the PEP rate schedule, the rate increase became effective with the first billing cycle of April 2021, subject to refund. The ultimate outcome of this matter cannot be determined at this time. Integrated Resource Plan In December 2020, the Mississippi PSC issued an order in the Reserve Margin Plan docket requiring Mississippi Power to incorporate into its 2021 IRP a schedule reflecting the retirement of 950 MWs of fossil-steam generation by year-end 2027 to reduce Mississippi Power's excess reserve margin. On April 15, 2021, Mississippi Power filed its 2021 IRP with the Mississippi PSC. The filing includes a schedule to retire Plant Watson Unit 4 (268 MWs) and Mississippi Power's 40% ownership interest in Plant Greene County Units 1 and 2 (103 MWs each) in December 2023, 2025, and 2026, respectively, consistent with each unit's remaining useful life in the most recent approved depreciation studies. In addition, the schedule reflects the early retirement of Mississippi Power's 50% undivided ownership interest in Plant Daniel Units 1 and 2 (502 MWs) by the end of 2027. The Plant Greene County unit retirements require the completion by Alabama Power of transmission and system reliability improvements, as well as agreement by Alabama Power. The remaining net book value of Plant Daniel Units 1 and 2 was approximately $531 million at March 31, 2021. Mississippi Power expects to reclassify the net book value remaining at retirement to a regulatory asset to be amortized over a period to be determined by the Mississippi PSC in future proceedings, consistent with the December 2020 order. The Plant Watson and Greene County units are expected to be fully depreciated upon retirement. The 2021 IRP is subject to a review period during which the Mississippi PSC may note any deficiencies which could require re-evaluation or resubmission of the IRP. If no deficiencies are noted, the Mississippi PSC's review will conclude on August 13, 2021. The ultimate outcome of this matter cannot be determined at this time. Ad Valorem Tax Adjustment On April 6, 2021, the Mississippi PSC approved Mississippi Power's annual ad valorem tax adjustment filing for 2021, which requested an annual increase in revenues of approximately $28 million, including approximately $19 million of ad valorem taxes previously recovered through PEP in accordance with the Mississippi Power Rate Case Settlement Agreement. The rate became effective with the first billing cycle of May 2021. Southern Company Gas Infrastructure Replacement Programs and Capital Projects Capital expenditures incurred under specific infrastructure replacement programs during the first three months of 2021 were as follows: Utility Program Three Months Ended (in millions) Nicor Gas Investing in Illinois $ 45 Virginia Natural Gas Steps to Advance Virginia's Energy 9 Total $ 54 Atlanta Gas Light On April 28, 2021, Atlanta Gas Light filed its first Integrated Capacity and Delivery Plan (i-CDP) with the Georgia PSC, which includes a series of ongoing and proposed pipeline safety, reliability, and growth programs for the next 10 years (2022 through 2031), as well as the required capital investments and related costs to implement the programs. The i-CDP reflects capital investments totaling approximately $0.5 billion to $0.6 billion annually. Recovery of the related revenue requirements will be included in either subsequent annual GRAM filings or the new System Reinforcement Rider for authorized large pressure improvement and system reliability projects. The i-CDP is subject to a five-month review period, which may be extended. The ultimate outcome of this matter cannot be determined at this time. Virginia Natural Gas On April 6, 2021, the Virginia State Corporation Commission approved a motion filed by Virginia Natural Gas to withdraw the application for its 9.5-mile interconnect project due to a change in the capacity needs of one of the project's customers. No further action is necessary and this matter is now concluded. Deferral of Incremental COVID-19 Costs Nicor Gas On March 18, 2021, the Illi

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies	CONTINGENCIESSee Note 3 to the financial statements in Item 8 of the Form 10-K for information relating to various lawsuits and other contingencies. General Litigation Matters The Registrants are involved in various matters being litigated and regulatory matters. The ultimate outcome of such pending or potential litigation or regulatory matters against each Registrant and any subsidiaries cannot be determined 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. The Registrants believe the pending legal challenges discussed below have no merit; however, the ultimate outcome of these matters cannot be determined at this time. Southern Company In February 2017, Jean Vineyard and Judy Mesirov each filed a shareholder derivative lawsuit 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 current and former officers, and certain former Mississippi Power officers. In 2017, these two shareholder derivative lawsuits were consolidated in the U.S. District Court for the Northern District of Georgia. The complaints allege that the defendants caused Southern Company to make false or misleading statements regarding the Kemper County energy facility cost and schedule. Further, the complaints allege that the defendants were unjustly enriched and caused the waste of corporate assets and also allege that the individual defendants violated their fiduciary duties. In May 2017, Helen E. Piper Survivor's Trust filed a shareholder derivative lawsuit in the Superior Court of Gwinnett County, Georgia that names as defendants Southern Company, certain of its directors, certain of its current and former 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. In August 2019, the court granted a motion filed by the plaintiff in July 2019 to substitute a new named plaintiff, Martin J. Kobuck, in place of Helen E. Piper Survivor's Trust. The plaintiffs in each of these cases seek 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. The plaintiffs also seek certain changes to Southern Company's corporate governance and internal processes. In 2018, the court in each case entered an order staying each lawsuit until 30 days after the settlement of a securities class action filed in January 2017 against Southern Company, certain of its current and former officers, and certain former Mississippi Power officers. In September 2020, the plaintiffs in each case filed a status report noting the settlement of the securities class action and informing the court that the parties had scheduled mediation, which occurred in November 2020. The parties in each case did not reach settlement but continue to explore possible resolution. Each case is stayed while the parties discuss potential resolution. 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 amounts for municipal franchise fees (which fees are paid to municipalities) exceeded the amounts allowed in orders of the Georgia PSC and alleging certain state law claims. This case has been ruled upon and appealed numerous times over the last several years. In one recent appeal, the Georgia Supreme Court remanded the case and noted that the trial court could refer the matter to the Georgia PSC to interpret its tariffs. Following a motion by Georgia Power, in February 2019, the Superior Court of Fulton County ordered the parties to submit petitions to the Georgia PSC for a declaratory ruling and also conditionally certified the proposed class. In March 2019, Georgia Power and the plaintiffs filed petitions with the Georgia PSC seeking confirmation of the proper application of the municipal franchise fee schedule pursuant to the Georgia PSC's orders. Also in March 2019, Georgia Power appealed the class certification decision to the Georgia Court of Appeals. In October 2019, the Georgia PSC issued an order that found Georgia Power has appropriately implemented the municipal franchise fee schedule. In March 2020, the Georgia Court of Appeals vacated the Superior Court of Fulton County's February 2019 order granting conditional class certification and remanded the case to the Superior Court of Fulton County for further proceedings. In September 2020, the plaintiffs and Georgia Power each filed motions for summary judgment and the plaintiffs renewed their motion for class certification. On March 16, 2021, the Superior Court of Fulton County granted class certification and Georgia Power's motion for summary judgment. On March 22, 2021, the plaintiffs filed a notice of appeal, and, on April 2, 2021, Georgia Power filed a notice of cross appeal on the issue of class certification. The amount of any possible losses cannot be estimated at this time because, among other factors, it is unknown whether any losses would be subject to recovery from any municipalities. In July 2020, a group of individual plaintiffs filed a complaint in the Superior Court of Fulton County, Georgia against Georgia Power alleging that releases from Plant Scherer have impacted groundwater, surface water, and air, resulting in alleged personal injuries and property damage. The plaintiffs seek an unspecified amount of monetary damages including punitive damages, a medical monitoring fund, and injunctive relief. In September 2020, Georgia Power filed a motion to dismiss. The amount of any possible losses cannot be estimated at this time. Mississippi Power In 2018, Ray C. Turnage and 10 other individual plaintiffs filed a putative class action complaint against Mississippi Power and the three then-serving members of the Mississippi PSC in the U.S. District Court for the Southern District of Mississippi. Mississippi Power received Mississippi PSC approval in 2013 to charge a mirror CWIP rate premised upon including in its rate base pre-construction and construction costs for the Kemper IGCC prior to placing the Kemper IGCC into service. The Mississippi Supreme Court reversed that approval and ordered Mississippi Power to refund the amounts paid by customers under the previously-approved mirror CWIP rate. The plaintiffs allege that the initial approval process, and the amount approved, were improper. They also allege that Mississippi Power underpaid customers by up to $23.5 million in the refund process by applying an incorrect interest rate. The plaintiffs seek to recover, on behalf of themselves and their putative class, actual damages, punitive damages, pre-judgment interest, post-judgment interest, attorney's fees, and costs. In response to Mississippi Power and the Mississippi PSC each filing a motion to dismiss, the plaintiffs filed an amended complaint in March 2019. The amended complaint included four additional plaintiffs and additional claims for gross negligence, reckless conduct, and intentional wrongdoing. Mississippi Power and the Mississippi PSC each filed a motion to dismiss the amended complaint, which occurred in May 2020 and March 2020, respectively. Also in March 2020, the plaintiffs filed a motion seeking to name the new members of the Mississippi PSC, the Mississippi Development Authority, and Southern Company as additional defendants and add a cause of action against all defendants based on a dormant commerce clause theory under the U.S. Constitution. In July 2020, the plaintiffs filed a motion for leave to file a third amended complaint, which included the same federal claims as the proposed second amended complaint, as well as several additional state law claims based on the allegation that Mississippi Power failed to disclose the annual percentage rate of interest applicable to refunds. In November 2020, the court denied each of the plaintiffs' pending motions and entered final judgment in favor of Mississippi Power. On January 22, 2021, the court denied further motions by the plaintiffs to vacate the judgment and to file a revised second amended complaint. On February 19, 2021, the plaintiffs filed a notice of appeal with the U.S. Court of Appeals for the Fifth Circuit. An adverse outcome in this proceeding could have a material impact on Mississippi Power's financial statements. See Note 3 to the financial statements under "Other Matters – Mississippi Power – Kemper County Energy Facility" in Item 8 of the Form 10-K for additional information. 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 and Georgia have each received authority from their respective state PSCs or other applicable state regulatory agencies to recover approved environmental remediation 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 $16 million and $15 million at March 31, 2021 and December 31, 2020, respectively. Georgia Power has been designated or identified as a potentially responsible party at sites governed by the Georgia Hazardous Site Response Act and/or by the federal Comprehensive Environmental Response, Compensation, and Liability Act, and assessment and potential cleanup of such sites is expected. Southern Company Gas' environmental remediation liability was $240 million and $245 million as of March 31, 2021 and December 31, 2020, respectively, based on the estimated cost of environmental investigation and remediation associated with known former manufactured gas plant operating sites. 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 the applicable Registrants. Southern Company Gas PennEast Pipeline Project Work continues with state and federal agencies to obtain the required permits to begin construction of the PennEast Pipeline. Expected project costs for Southern Company Gas total approximately $300 million, excluding financing costs. The ultimate outcome of the PennEast Pipeline construction project cannot be determined at this time; however, any work delays, whether caused by judicial or regulatory action, abnormal weather, or other conditions, may result in additional cost or schedule modifications or, ultimately, in project cancellation, any of which could result in impairment of Southern Company Gas' investment ($93 million at March 31, 2021) and could have a significant impact on Southern Company's financial statements and a material impact on Southern Company Gas' financial statements. See Note (E) under "Southern Company Gas" for additional information. SNG As a 50% equity investor in SNG, Southern Company Gas is required to make additional capital contributions as necessary pursuant to the terms of its operating agreement with SNG. SNG has $300 million of debt maturing in June 2021 that it anticipates refinancing prior to its maturity. If SNG is unable to refinance or otherwise satisfy this debt obligation, Southern Company Gas has committed to fund up to $150 million as a contingent capital contribution. See Note (E) under "Southern Company Gas" for additional information.

Revenue from Contracts with Cus

Revenue from Contracts with Customers and Lease Income	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers and Lease Income	REVENUE FROM CONTRACTS WITH CUSTOMERS AND LEASE INCOME Revenue from Contracts with Customers The Registrants generate revenues from a variety of sources, some of which are not accounted for as revenue from contracts with customers, such as leases, derivatives, and certain cost recovery mechanisms. See Note 1 to the financial statements under "Revenues" in Item 8 of the Form 10-K for additional information on the revenue policies of the Registrants. See "Lease Income" herein and Note (J) for additional information on revenue accounted for under lease and derivative accounting guidance, respectively. The following table disaggregates revenue from contracts with customers for the three months ended March 31, 2021 and 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended March 31, 2021 Operating revenues Retail electric revenues Residential $ 1,468 $ 628 $ 776 $ 64 $ — $ — Commercial 1,117 372 686 59 — — Industrial 668 320 284 64 — — Other 24 5 17 2 — — Total retail electric revenues 3,277 1,325 1,763 189 — — Natural gas distribution revenues Residential 614 — — — — 614 Commercial 170 — — — — 170 Transportation 288 — — — — 288 Industrial 16 — — — — 16 Other 97 — — — — 97 Total natural gas distribution revenues 1,185 — — — — 1,185 Wholesale electric revenues PPA energy revenues 212 43 13 4 156 — PPA capacity revenues 119 29 13 3 75 — Non-PPA revenues 67 32 9 88 61 — Total wholesale electric revenues 398 104 35 95 292 — Other natural gas revenues Wholesale gas services 1,590 — — — — 1,590 Gas marketing services 194 — — — — 194 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 1,791 — — — — 1,791 Other revenues 249 46 113 8 4 — Total revenue from contracts with customers 6,900 1,475 1,911 292 296 2,976 Other revenue sources (a) 1,306 84 59 15 144 1,014 Other adjustments (b) (2,296) — — — — (2,296) Total operating revenues $ 5,910 $ 1,559 $ 1,970 $ 307 $ 440 $ 1,694 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended March 31, 2020 Operating revenues Retail electric revenues Residential $ 1,370 $ 553 $ 760 $ 57 $ — $ — Commercial 1,146 364 720 62 — — Industrial 680 321 281 78 — — Other 23 5 16 2 — — Total retail electric revenues 3,219 1,243 1,777 199 — — Natural gas distribution revenues Residential 496 — — — — 496 Commercial 130 — — — — 130 Transportation 264 — — — — 264 Industrial 12 — — — — 12 Other 97 — — — — 97 Total natural gas distribution revenues 999 — — — — 999 Wholesale electric revenues PPA energy revenues 159 27 9 2 125 — PPA capacity revenues 105 27 12 1 66 — Non-PPA revenues 51 19 2 69 58 — Total wholesale electric revenues 315 73 23 72 249 — Other natural gas revenues Wholesale gas services 396 — — — — 396 Gas marketing services 163 — — — — 163 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 566 — — — — 566 Other revenues 192 37 95 5 3 — Total revenue from contracts with customers 5,291 1,353 1,895 276 252 1,565 Other revenue sources (a) 868 (2) (70) 1 123 825 Other adjustments (b) (1,141) — — — — (1,141) Total operating revenues $ 5,018 $ 1,351 $ 1,825 $ 277 $ 375 $ 1,249 (a) Other revenue sources relate to revenues from customers accounted for as derivatives and leases, alternative revenue programs at Southern Company Gas, and cost recovery mechanisms and revenues that meet other scope exceptions for revenues from contracts with customers at the traditional electric operating companies. (b) Other adjustments relate to the cost of Southern Company Gas' energy and risk management activities. Wholesale gas services revenues are presented net of the related costs of those activities on the statement of income. See Note (L) under "Southern Company Gas" for additional information on the components of wholesale gas services' operating revenues. Contract Balances The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at March 31, 2021 and December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivable As of March 31, 2021 $ 2,375 $ 567 $ 679 $ 87 $ 85 $ 778 As of December 31, 2020 2,614 632 806 77 112 788 Contract Assets As of March 31, 2021 $ 106 $ 1 $ 47 $ — $ — $ — As of December 31, 2020 158 2 71 — — — Contract Liabilities As of March 31, 2021 $ 75 $ 4 $ 34 $ 1 $ 1 $ 1 As of December 31, 2020 61 6 27 1 1 1 As of March 31, 2021 and December 31, 2020, Georgia Power had contract assets primarily related to unregulated service agreements, where payment is contingent on project completion, and 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 a one-year contract term. Contract liabilities for Georgia Power relate to cash collections recognized in advance of revenue for certain unregulated service agreements. Alabama Power had contract liabilities for outstanding performance obligations primarily related to pole attachment and extended service agreements. Southern Company's unregulated distributed generation business had $55 million and $81 million of contract assets and $34 million and $27 million of contract liabilities at March 31, 2021 and December 31, 2020, respectively, for outstanding performance obligations. Revenues recognized in the three months ended March 31, 2021, which were included in contract liabilities at December 31, 2020, were immaterial for all Registrants. 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, 2021 are expected to be recognized as follows: 2021 (remaining) 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 485 $ 408 $ 340 $ 327 $ 307 $ 2,666 Alabama Power 24 31 24 7 5 — Georgia Power 57 51 36 24 21 41 Southern Power 213 287 280 296 280 2,644 Revenue expected to be recognized for performance obligations remaining at March 31, 2021 w as immaterial for Mississippi Power and Southern Company Gas. Lease Income Lease income for the three months ended March 31, 2021 and 2020 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) For the Three Months Ended March 31, 2021 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 55 21 10 — 21 9 Variable lease income 84 — — — 90 — Total lease income $ 142 $ 21 $ 10 $ 3 $ 111 $ 9 For the Three Months Ended March 31, 2020 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 51 6 16 — 24 9 Variable lease income 74 — — — 80 — Total lease income $ 128 $ 6 $ 16 $ 3 $ 104 $ 9 Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Lease income for Alabama Power and Southern Power is included in wholesale revenues.

Consolidated Entities and Equit

Consolidated Entities and Equity Method Investments	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Consolidated Entities and Equity Method Investments	CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTSSee Note 7 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Power Variable Interest Entities Southern Power has certain subsidiaries that are determined to be VIEs. Southern Power is considered the primary beneficiary of these VIEs because it controls the most significant activities of the VIEs, including operating and maintaining the respective assets, and has the obligation to absorb expected losses of these VIEs to the extent of its equity interests. SP Solar and SP Wind At March 31, 2021 and December 31, 2020, SP Solar had total assets of $6.1 billion, total liabilities of $377 million and $387 million, respectively, and noncontrolling interests of $1.1 billion. Cash distributions from SP Solar are allocated 67% to Southern Power and 33% to Global Atlantic in accordance with their partnership interest percentage. Under the terms of the limited partnership agreement, distributions without limited partner consent are limited to available cash and SP Solar is obligated to distribute all such available cash to its partners each quarter. Available cash includes all cash generated in the quarter subject to the maintenance of appropriate operating reserves. At March 31, 2021 and December 31, 2020, SP Wind had total assets of $2.4 billion, total liabilities of $171 million and $138 million, respectively, and noncontrolling interests of $42 million and $43 million, respectively. Under the terms of the limited liability agreement, distributions without Class A member consent are limited to available cash and SP Wind is obligated to distribute all such available cash to its members each quarter. Available cash includes all cash generated in the quarter subject to the maintenance of appropriate operating reserves. Cash distributions from SP Wind are generally allocated 60% to Southern Power and 40% to the three financial investors in accordance with the limited liability agreement. Southern Power consolidates both SP Solar and SP Wind, as the primary beneficiary, since it controls the most significant activities of each entity, including operating and maintaining their assets. Certain transfers and sales of the assets in the VIEs are subject to partner consent and the liabilities are non-recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. Other Variable Interest Entities Southern Power has other consolidated VIEs that relate to certain subsidiaries that have either sold noncontrolling interests to tax-equity investors or acquired less than a 100% interest from facility developers. These entities are considered VIEs because the arrangements are structured similar to a limited partnership and the noncontrolling members do not have substantive kick-out rights. At March 31, 2021 and December 31, 2020, the other VIEs had total assets of $1.9 billion and $1.1 billion, respectively, total liabilities of $260 million and $110 million, respectively, and noncontrolling interests of $926 million and $454 million, respectively. Under the terms of the partnership agreements, distributions of all available cash are required each month or quarter and additional distributions require partner consent. Equity Method Investments At March 31, 2021 and December 31, 2020, Southern Power had equity method investments in wind and battery storage projects totaling $84 million and $19 million, respectively. Southern Company Gas Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2021 and December 31, 2020 and related income from those investments for the three months ended March 31, 2021 and 2020 were as follows: Investment Balance March 31, 2021 December 31, 2020 (in millions) SNG $ 1,164 $ 1,167 PennEast Pipeline (*) 93 91 Other 33 32 Total $ 1,290 $ 1,290 (*) See Note (C) under "Other Matters – Southern Company Gas" for additional information. Earnings from Equity Method Investments Three Months Ended Three Months Ended (in millions) SNG $ 38 $ 37 PennEast Pipeline (a) 2 2 Other (a)(b) 1 4 Total $ 41 $ 43 (a) Earnings primarily result from AFUDC equity recorded by the project entity. (b) On March 24, 2020, Southern Company Gas completed the sale of its interests in Atlantic Coast Pipeline and Pivotal LNG. See Note 15 to the financial statements under "Southern Company Gas" in Item 8 of the Form 10-K for additional information.

Financing

Financing	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Financing	FINANCING Bank Credit Arrangements See Note 8 to the financial statements under "Bank Credit Arrangements" in Item 8 of the Form 10-K for additional information. At March 31, 2021, committed credit arrangements with banks were as follows: Expires Company 2021 2022 2023 2024 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power 3 525 — 800 1,328 1,328 3 Georgia Power — — — 1,750 1,750 1,728 — Mississippi Power — 150 125 — 275 250 — Southern Power (a) — — — 600 600 568 — Southern Company Gas (b) — — — 1,750 1,750 1,745 — SEGCO 30 — — — 30 30 30 Southern Company $ 33 $ 675 $ 125 $ 6,900 $ 7,733 $ 7,648 $ 33 (a) Does not include Southern Power Company's $75 million and $60 million continuing letter of credit facilities for standby letters of credit expiring in 2023, of which $12 million and $1 million, respectively, was unused at March 31, 2021. Southern Power's subsidiaries are not parties to its bank credit arrangements or letter of credit facilities. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.05 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to this multi-year credit arrangement, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted. 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. These bank credit arrangements, as well as the term loan arrangements of the Registrants, Nicor Gas, and SEGCO, contain covenants that limit debt levels and contain cross-acceleration or, in the case of Southern Power, cross-default provisions to other indebtedness (including guarantee obligations) that are restricted only to the indebtedness of the individual company. Such cross-default provisions to other indebtedness would trigger an event of default if Southern Power defaulted on indebtedness or guarantee obligations over a specified threshold. Such cross-acceleration provisions to other indebtedness would trigger an event of default if the applicable borrower defaulted on indebtedness, the payment of which was then accelerated. At March 31, 2021, the Registrants, Nicor Gas, and SEGCO were in compliance with all such covenants. None of the bank credit arrangements contain material adverse change clauses at the time of borrowings. A portion of the unused credit with banks is allocated to provide liquidity support to the revenue bonds of the traditional electric operating companies and the commercial paper programs of the Registrants and Nicor Gas. The amount of variable rate revenue bonds of the traditional electric operating companies outstanding requiring liquidity support at March 31, 2021 was approximately $1.4 billion (comprised of approximately $854 million at Alabama Power, $550 million at Georgia Power, and $34 million at Mississippi Power). In addition, at March 31, 2021, Georgia Power and Mississippi Power had approximately $174 million and $50 million, respectively, of fixed rate revenue bonds outstanding that are required to be remarketed within the next 12 months. Earnings per Share For Southern Company, the only differences in computing basic and diluted earnings per share are attributable to awards outstanding under stock-based compensation plans and the equity units issued in 2019. Earnings per share dilution resulting from stock-based compensation plans and the equity units issuance is determined using the treasury stock method. See Note 8 to the financial statements under "Equity Units" in Item 8 of the Form 10-K for information on the equity units and Note 12 to the financial statements in Item 8 of the Form 10-K for information on stock-based compensation plans. Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2021 Three Months Ended March 31, 2020 (in millions) As reported shares 1,060 1,057 Effect of stock-based compensation 6 7 Effect of equity units — 3 Diluted shares 1,066 1,067 An immaterial number of stock-based compensation awards was not included in the diluted earnings per share calculation because the awards were anti-dilutive for the three months ended March 31, 2021 and 2020.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES See Note 10 to the financial statements in Item 8 of the Form 10-K for additional tax information. Current and Deferred Income Taxes Tax Credit and Net Operating Loss Carryforwards The utilization of each Registrant's estimated tax credit and state net operating loss carryforwards and related valuation allowances could be impacted by numerous factors, including the acquisition of additional renewable projects, the purchase of rights to additional PTCs of Plant Vogtle Units 3 and 4 pursuant to certain joint ownership agreements, potential impacts of the COVID-19 pandemic, changes in taxable income projections, and potential income tax rate changes. See Note (B) and Note 2 to the financial statements in Item 8 of the Form 10-K under "Georgia Power – Nuclear Construction" for additional information on Plant Vogtle Units 3 and 4. Effective Tax Rate Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity at the traditional electric operating companies, flowback of excess deferred income taxes at the regulated utilities, and federal income tax benefits from ITCs and PTCs primarily at Southern Power. Details of significant changes in the effective tax rate for the applicable Registrants are provided herein. Mississippi Power Mississippi Power's effective tax rate was 8.4% for the three months ended March 31, 2021 compared to 16.2% for the corresponding period in 2020. The effective tax rate decrease was primarily due to an increase in the flowback of excess deferred income taxes beginning in April 2020 as authorized in the Mississippi Power Rate Case Settlement Agreement. See Note 2 to the financial statements under "Mississippi Power – 2019 Base Rate Case" in Item 8 of the Form 10-K for additional information. Southern Power Southern Power's effective tax benefit rate was (17.3)% for the three months ended March 31, 2021 compared to an effective tax rate of 13.5% for the corresponding period in 2020. The effective tax rate decrease was primarily due to changes in state apportionment methodology resulting from tax legislation enacted by the State of Alabama in February 2021, as well as the tax impact from the sale of Plant Mankato in January 2020. See Note 15 to the financial statements under "Southern Power" in Item 8 of the Form 10-K for additional information.

Retirement Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Retirement Benefits	RETIREMENT BENEFITS The Southern Company system has a qualified defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at PowerSecure. The qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 2021. The Southern Company system also provides certain non-qualified defined benefits for a select group of management and highly compensated employees, which are funded on a cash basis. In addition, the Southern Company system provides certain medical care and life insurance benefits for retired employees through other postretirement benefit plans. The traditional electric operating companies fund other postretirement trusts to the extent required by their respective regulatory commissions. 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. See Note 11 to the financial statements in Item 8 of the Form 10-K for additional information. On each Registrant's condensed statements of income, the service cost component of net periodic benefit costs is included in other operations and maintenance expenses and all other components of net periodic benefit costs are included in other income (expense), net. Components of the net periodic benefit costs for the three months ended March 31, 2021 and 2020 are presented in the following tables. Three Months Ended Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 109 $ 26 $ 28 $ 4 $ 2 $ 9 Interest cost 87 20 26 4 1 6 Expected return on plan assets (298) (72) (94) (14) (3) (21) Amortization: Prior service costs — — — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 78 21 25 4 1 3 Net periodic pension cost (income) $ (24) $ (5) $ (15) $ (2) $ 1 $ — Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ — Interest cost 8 2 3 — — 1 Expected return on plan assets (19) (7) (7) — — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ (4) $ (4) $ (1) $ — $ — $ — Three Months Ended Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 94 $ 22 $ 24 $ 4 $ 2 $ 8 Interest cost 108 25 33 5 1 8 Expected return on plan assets (275) (66) (87) (13) (3) (19) Amortization: Prior service costs 1 — — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 67 18 22 3 1 2 Net periodic pension cost (income) $ (5) $ (1) $ (8) $ (1) $ 1 $ 2 Postretirement Benefits Service cost $ 5 $ 2 $ 1 $ — $ — $ — Interest cost 13 3 5 — — 2 Expected return on plan assets (18) (7) (7) — — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ 1 $ (2) $ — $ — $ — $ 1

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS As of March 31, 2021, 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, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 372 $ 179 $ 34 $ — $ 585 Interest rate derivatives — 10 — — 10 Foreign currency derivatives — 41 — — 41 Investments in trusts: (b)(c) Domestic equity 782 214 — — 996 Foreign equity 145 197 — — 342 U.S. Treasury and government agency securities — 325 — — 325 Municipal bonds — 45 — — 45 Pooled funds – fixed income — 18 — — 18 Corporate bonds 5 436 — — 441 Mortgage and asset backed securities — 81 — — 81 Private equity — — — 83 83 Other 50 7 — — 57 Cash equivalents 1,121 11 — — 1,132 Other investments 9 33 — — 42 Total $ 2,484 $ 1,597 $ 34 $ 83 $ 4,198 Liabilities: Energy-related derivatives (a) $ 359 $ 158 $ 6 $ — $ 523 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 16 — 16 Total $ 359 $ 181 $ 22 $ — $ 562 Fair Value Measurements Using: As of March 31, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Nuclear decommissioning trusts: (b) Domestic equity 448 205 — — 653 Foreign equity 145 15 — — 160 U.S. Treasury and government agency securities — 20 — — 20 Municipal bonds — 1 — — 1 Corporate bonds 5 235 — — 240 Mortgage and asset backed securities — 26 — — 26 Private equity — — — 83 83 Other 27 — — — 27 Cash equivalents 401 11 — — 412 Other investments — 33 — — 33 Total $ 1,026 $ 558 $ — $ 83 $ 1,667 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Georgia Power Assets: Energy-related derivatives $ — $ 17 $ — $ — $ 17 Nuclear decommissioning trusts: (b)(c) Domestic equity 334 1 — — 335 Foreign equity — 179 — — 179 U.S. Treasury and government agency securities — 305 — — 305 Municipal bonds — 44 — — 44 Corporate bonds — 201 — — 201 Mortgage and asset backed securities — 55 — — 55 Other 23 7 — — 30 Total $ 357 $ 809 $ — $ — $ 1,166 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 11 $ — $ — $ 11 Liabilities: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Southern Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 41 — — 41 Cash equivalents 115 — — — 115 Total $ 115 $ 42 $ — $ — $ 157 Liabilities: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 16 — 16 Total $ — $ 24 $ 16 $ — $ 40 Southern Company Gas Assets: Energy-related derivatives (a) $ 372 $ 138 $ 34 $ — $ 544 Non-qualified deferred compensation trusts: Domestic equity — 8 — — 8 Foreign equity — 3 — — 3 Pooled funds – fixed income — 18 — — 18 Cash equivalents and restricted cash 284 — — — 284 Total $ 656 $ 167 $ 34 $ — $ 857 Liabilities: Energy-related derivatives (a) $ 359 $ 139 $ 6 $ — $ 504 (a) Excludes cash collateral of $27 million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2021, approximately $34 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. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. 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, including reinvested interest and dividends and excluding the funds' expenses, increased (decreased) by the amounts shown in the table below for the three months ended March 31, 2021 and 2020. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Fair value increases (decreases) Three Months Ended Three Months Ended (in millions) Southern Company $ 39 $ (247) Alabama Power 41 (167) Georgia Power (2) (80) 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 (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation 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. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements 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 it is primarily obligated to make generation-based payments to the seller, which commenced at the commercial operation of the respective facility and continue through 2026. The obligations are 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 traded in the open market that have maturities greater than 90 days, which are categorized as Level 2 under Fair Value Measurements and are comprised of corporate bonds, bank certificates of deposit, treasury bonds, and/or agency bonds. At March 31, 2021, the fair value measurements of private equity investments held in Alabama Power's nuclear decommissioning trusts that are calculated at net asset value per share (or its equivalent) as a practical expedient totaled $83 million and unfunded commitments related to the private equity investments totaled $68 million. Private equity investments include high-quality private equity funds across several market sectors and funds that invest in real estate assets. Private equity funds do not have redemption rights. Distributions from these funds will be received as the underlying investments in the funds are liquidated. At March 31, 2021, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) Long-term debt, including securities due within one year: Carrying amount $ 50,035 $ 8,866 $ 13,220 $ 1,398 $ 4,030 $ 6,588 Fair value 54,113 9,821 14,291 1,507 4,347 7,264 (*) The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the 2016 merger with Southern Company. Southern Company Gas amortizes the fair value adjustments over the remaining lives of the respective bonds, the latest being through 2043. 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 the Registrants. Commodity Contracts with Level 3 Valuation Inputs As of March 31, 2021, the fair value of Southern Company Gas' Level 3 physical natural gas forward contracts was $28 million. Since commodity contracts classified as Level 3 typically include a combination of observable and unobservable components, the changes in fair value may include amounts due in part to observable market factors, or changes to assumptions on the unobservable components. The following table includes transfers to Level 3, which represent the fair value of Southern Company Gas' commodity derivative contracts that include a significant unobservable component for the first time during the period. Three Months Ended March 31, 2021 (in millions) Beginning balance $ 28 Instruments realized or otherwise settled during period (2) Changes in fair value 2 Ending balance $ 28 Changes in fair value of Level 3 instruments represent changes in gains and losses for the periods that are reported on Southern Company Gas' statements of income in natural gas revenues. The valuation of certain commodity contracts requires the use of certain unobservable inputs. All forward pricing used in the valuation of such contracts is directly based on third-party market data, such as broker quotes and exchange settlements, when that data is available. If third-party market data is not available, then industry standard

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2021
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 (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with the classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. Energy-Related Derivatives 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 are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges – Energy-related derivative contracts 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 an approved cost recovery mechanism. • 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 accumulated 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, 2021, the net volume of energy-related derivative contracts for natural gas positions, 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 Longest Longest (in millions) Southern Company (*) 907 2030 2031 Alabama Power 73 2024 — Georgia Power 125 2024 — Mississippi Power 85 2024 — Southern Power 9 2030 2021 Southern Company Gas (*) 615 2023 2031 (*) 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 4.4 billion mmBtu and short natural gas positions of 3.8 billion mmBtu as of March 31, 2021, 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 natural gas due to operational constraints. The maximum expected volume of natural gas subject to such a feature is 39 million mmBtu for Southern Company, which includes 10 million mmBtu for Alabama Power, 12 million mmBtu for Georgia Power, 5 million mmBtu for Mississippi Power, and 12 million mmBtu for Southern Power. For cash flow hedges of energy-related derivatives, the estimated pre-tax gains (losses) expected to be reclassified from accumulated OCI to earnings for the 12-month period ending March 31, 2022 are immaterial for all Registrants. Interest Rate Derivatives Southern Company and certain subsidiaries may 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, 2021, the following interest rate derivatives were outstanding: Notional Interest Weighted Hedge Fair Value Gain (Loss) at March 31, 2021 (in millions) (in millions) Cash Flow Hedges of Existing Debt Mississippi Power $ 60 1-month LIBOR 0.58% December 2021 $ — Fair Value Hedges of Existing Debt Southern Company parent 1,500 2.35% 1-month LIBOR + 0.87% July 2021 10 Southern Company $ 1,560 $ 10 For cash flow hedge interest rate derivatives, the estimated pre-tax gains (losses) expected to be reclassified from accumulated OCI to interest expense for the 12-month period ending March 31, 2022 total $(25) million for Southern Company and are immaterial for all other Registrants. Deferred gains and losses related to interest rate derivatives are expected to be amortized into earnings through 2046 for the Southern Company parent entity, 2035 for Alabama Power, 2044 for Georgia Power, 2028 for Mississippi Power, and 2046 for Southern Company Gas. Foreign Currency Derivatives Southern Company and certain subsidiaries, including Southern Power, may 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, 2021, the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2021 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 9 Southern Power 564 3.78% 500 1.85% June 2026 9 Total $ 1,241 € 1,100 $ 18 The estimated pre-tax gains (losses) related to Southern Power's foreign currency derivatives expected to be reclassified from accumulated OCI to earnings for the 12-month period ending March 31, 2022 are $2 million. 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, 2021 As of December 31, 2020 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: Assets from risk management activities/Other current liabilities $ 30 $ 4 $ 24 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 16 15 18 19 Total derivatives designated as hedging instruments for regulatory purposes $ 46 $ 19 $ 42 $ 30 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 2 $ 1 $ 3 $ 5 Interest rate derivatives: Assets from risk management activities/Other current liabilities 10 — 20 — Foreign currency derivatives: Assets from risk management activities/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 41 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 53 $ 24 $ 110 $ 28 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 265 $ 265 $ 388 $ 331 Other deferred charges and assets/Other deferred credits and liabilities 272 237 270 232 Total derivatives not designated as hedging instruments $ 537 $ 502 $ 658 $ 563 Gross amounts recognized $ 636 $ 545 $ 810 $ 621 Gross amounts offset (a) (450) (477) (529) (557) Net amounts recognized in the Balance Sheets (b) $ 186 $ 68 $ 281 $ 64 As of March 31, 2021 As of December 31, 2020 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 $ 7 $ — $ 7 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 5 4 5 5 Total derivatives designated as hedging instruments for regulatory purposes $ 12 $ 4 $ 12 $ 7 Gross amounts recognized $ 12 $ 4 $ 12 $ 7 Gross amounts offset (4) (4) (7) (7) Net amounts recognized in the Balance Sheets $ 8 $ — $ 5 $ — Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 11 $ 2 $ 7 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 6 6 8 8 Total derivatives designated as hedging instruments for regulatory purposes $ 17 $ 8 $ 15 $ 13 Gross amounts recognized $ 17 $ 8 $ 15 $ 13 Gross amounts offset (7) (7) (12) (12) Net amounts recognized in the Balance Sheets $ 10 $ 1 $ 3 $ 1 Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 6 $ 1 $ 4 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 5 5 5 6 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 6 $ 9 $ 9 Gross amounts recognized $ 11 $ 6 $ 9 $ 9 Gross amounts offset (5) (5) (7) (7) Net amounts recognized in the Balance Sheets $ 6 $ 1 $ 2 $ 2 As of March 31, 2021 As of December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ — $ 2 $ 2 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 41 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 42 $ 23 $ 89 $ 25 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 1 Total derivatives not designated as hedging instruments $ — $ — $ — $ 1 Net amounts recognized in the Balance Sheets $ 42 $ 23 $ 89 $ 26 Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 6 $ 1 $ 6 $ 1 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 1 $ 6 $ 1 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 1 $ 1 $ 1 $ 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 1 $ 1 $ 1 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 265 $ 265 $ 388 $ 330 Other deferred charges and assets/Other deferred credits and liabilities 272 237 270 232 Total derivatives not designated as hedging instruments $ 537 $ 502 $ 658 $ 562 Gross amounts of recognized $ 544 $ 504 $ 665 $ 566 Gross amounts offset (a) (434) (461) (503) (531) Net amounts recognized in the Balance Sheets (b) $ 110 $ 43 $ 162 $ 35 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $27 million and $28 million as of March 31, 2021 and December 31, 2020, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for both periods presented. The traditional electric operating companies had immaterial energy-related derivatives not designated as hedging instruments at March 31, 2021 and no such instruments at December 31, 2020. At March 31, 2021 and December 31, 2020, 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 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) At March 31, 2021: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 24 7 9 5 3 Other regulatory liabilities, deferred 3 1 1 1 — Total energy-related derivative gains (losses) $ 25 $ 8 $ 9 $ 5 $ 3 At December 31, 2020: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 12 5 2 1 4 Other regulatory liabilities, deferred 2 1 1 — — Total energy-related derivative gains (losses) $ 12 $ 6 $ 2 $ — $ 4 For the three months ended March 31, 2021 and 2020, the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months Ended March 31, 2021 2020 (in millions) Southern Company Energy-related derivatives $ 5 $ (4) Interest rate derivatives 3 (26) Foreign currency derivatives (47) (83) Total $ (39) $ (113) Southern Power Energy-related derivatives $ 4 $ — Foreign currency derivatives (47) (83) Total $ (43) $ (83) Southern Company Gas Energy-related derivatives $ 1 $ (4) Interest rate derivatives — (23) Total $ 1 $ (27) For the three months ended March 31, 2021 and 2020, 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, 2021 and 2020, 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 Ended March 31, 2021 2020 (in millions) Southern Company Total cost of natural gas $ 583 $ 439 Gain (loss) on energy-related cash flow hedges (a) (3) (7) Total depreciation and amortization 871 857 Gain (loss) on energy-related cash flow hedges (a) 3 (1) Total interest expense, net of amounts capitalized (450) (456) Gain (loss) on interest rate cash flow hedges (a) (7) (6) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) Gain (loss) on interest rate fair value hedges (b) (10) 29 Total other income (expense), net 58 103 Gain (loss) on foreign currency cash flow hedges (a)(c) (60) (31) Southern Power Total depreciation and amortization $ 119 $ 117 Gain (loss) on energy-related cash flow hedges (a) 3 (1) Total interest expense, net of amounts capitalized (38) (39) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) Total other income (expense), net 7 2 Gain (loss) on foreign currency cash flow hedges (a)(c) (60) (31) (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes. For the three months ended March 31, 2021 and 2020, 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, 2021 and December 31, 2020, 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, 2021 As of December 31, 2020 As of March 31, 2021 As of December 31, 2020 (in millions) (in millions) Southern Company Securities due within one year $ (1,505) $ (1,509) $ (5) $ (10) For the three months ended March 31, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2021 2020 (in millions) Energy-related derivatives: Natural gas revenues (*) $ (17) $ 70 Cost of natural gas 7 7 Total derivatives in non-designated hedging relationships $ (10) $ 77 (*) Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for all periods presented. For the three months ended March 31, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments were immaterial for all other Registrants. 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, 2021, the Registrants had no collateral posted with derivative counterparties to satisfy these arrangements. At March 31, 2021, the Registrants had no interest rate derivative liabilities with contingent features. At March 31, 2021, 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. Following the sale of Gulf Power to NextEra Energy, Inc., Gulf Power is continuing to participate in the Southern Company power pool for a defined transition period that, subject to certain potential adjustments, is scheduled to end on January 1, 2024. 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 and they may be required to post collateral based on the value of the positions in these accounts and the associated margin requirements. At March 31, 2021, 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, 2021, cash collateral held on deposit in broker margin accounts was $27 million. The Registrants are exposed to losses related to financial instruments in the event of counterparties' nonperformance. The Registrants 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. The Registrants have also established risk management policies and controls to determine and monitor the creditworthiness of counterparties in order to mitigate their exposure to counterparty credit risk. Southern Company Gas uses established credit policies to determine and monitor the creditworthiness of counterparties, including requirements to post collateral or other credit security, as well as the quality of pledged collateral. Collateral or credit security is most often in the form of cash or letters of credit from an investment-grade financial institution, but may also include cash or U.S. government securities held by a trustee. Prior to entering a physical transaction, Southern Company Gas assigns its counterparties an internal credit rating and credit limit based on the counterparties' Moody's, S&P, and Fitch ratings, commercially available credit reports, and audited financial statements. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. Southern Company Gas utilizes netting agreements whenever possible to mitigate exposure to counterparty credit risk. Netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty across product lines and against cash collateral, provided the netting and cash collateral agreements include such provisions. While the amounts due from, or owed to, counterparties are settled net, they are recorded on a gross basis on the balance sheet as energy marketing receivables and energy marketing payables. The Registrants do not anticipate a material adverse effect on their respective financial statements as a result of counterparty nonperformance.

Acquisitions and Dispositions

Acquisitions and Dispositions	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Acquisitions and Dispositions	ACQUISITIONS AND DISPOSITIONSSee Note 15 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Company The following table provides Southern Company's major classes of assets classified as held for sale at March 31, 2021 and December 31, 2020: Southern Company At March 31, At December 31, 2021 2020 (in millions) Assets Held for Sale: Total property, plant, and equipment $ 7 $ 8 Leveraged leases 52 52 Total Assets Held for Sale $ 59 $ 60 Southern Company's asset sales, both individually and combined, do not represent a strategic shift in operations that has, or is expected to have, a major effect on operations and financial results; therefore, none of the assets have been classified as discontinued operations for any of the periods presented. Southern Power Asset Acquisition During the three months ended March 31, 2021, Southern Power acquired a controlling membership interest in the wind facility listed below. Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Deuel Harvest (*) Wind Invenergy Renewables, LLC 300 Deuel County, SD 100% of Class B February 2021 25 years and 15 years (*) On March 26, 2021, Southern Power acquired a controlling interest in the facility and consolidates the project's operating results in its financial statements. On March 30, 2021, Southern Power completed a tax equity transaction whereby it received $220 million. The tax equity partner, which is the Class A member, and Invenergy Renewables, LLC each own a noncontrolling interest. Construction Projects During the three months ended March 31, 2021, Southern Power continued construction of the Garland and Tranquillity battery energy storage facilities and the Glass Sands wind facility. Total aggregate construction costs, excluding acquisition costs, are expected to be between $392 million and $460 million for the facilities under construction. At March 31, 2021, total costs of construction incurred for these projects were $158 million and are included in CWIP. 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 at March 31, 2021 Garland Solar Storage (a) Battery energy storage system 88 Kern County, CA Third quarter 2021 20 years Tranquillity Solar Storage (a) Battery energy storage system 72 Fresno County, CA Fourth quarter 2021 20 years Glass Sands (b) Wind 118 Murray County, OK Fourth quarter 2021 12 years (a) In December 2020, Southern Power restructured its ownership of the project by contributing the Class A membership interests to an existing partnership and selling 100% of the Class B membership interests while retaining the controlling interest. Prior to commercial operation, Southern Power may restructure the project ownership again and enter into additional partnerships, but expects to retain the controlling interest. The ultimate outcome of this matter cannot be determined at this time. (b) In December 2020, Southern Power purchased 100% of the membership interests of the Glass Sands facility. Development Projects Southern Power continues to evaluate and refine the deployment of the remaining wind turbine equipment purchased in 2016 and 2017 to development and construction projects. During the three months ended March 31, 2021, gains on wind turbine equipment contributed to various equity method investments totaled approximately $37 million. Southern Company Gas Sale of Sequent On April 28, 2021, certain affiliates of Southern Company Gas entered into an agreement for the sale of Sequent for a purchase price of $50 million, plus working capital and certain other adjustments. The net book value of Sequent at March 31, 2021, excluding working capital, was $46 million; however, any potential gain or loss on the sale will be based, in large part, on the fair value of the open derivative positions as of the date of closing. See Notes (I) and (J) for information on fair value and derivatives outstanding at March 31, 2021. Southern Company Gas has existing agreements in place in which it guarantees the payment performance of Sequent. Southern Company Gas will continue to guarantee payment performance for Sequent after the transaction closes for a period of time as the buyer obtains releases from these obligations. As of March 31, 2021, the obligations subject to the payment performance guarantee totaled $279 million. Changes in the price of natural gas, market conditions, and the number of open contracts will change the amount that Southern Company Gas is required to guarantee for Sequent each month. The maximum potential exposure over the period of the payment performance guarantee generally is capped at $1 billion. At closing, the buyer (an investment-grade entity) will issue a payment performance guarantee to Southern Company Gas, equal to the outstanding guarantee obligation throughout this period. Further, Southern Company Gas will retain responsibility for certain potential obligations that may arise from transactions during Winter Storm Uri. The completion of the transaction is subject to the satisfaction or waiver of certain conditions, including, among other customary closing conditions, 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 during the third quarter 2021; however, the ultimate outcome of this matter cannot be determined at this time. Sale of Pivotal LNG In connection with its March 2020 sale of Pivotal LNG, Southern Company Gas was entitled to two $5 million payments contingent upon Dominion Modular LNG Holdings, Inc. meeting certain milestones related to Pivotal LNG. Southern Company Gas received the first payment on April 22, 2021 and expects to receive the second payment in August 2021.

Segment and Related Information

Segment and Related Information	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segment and Related Information	SEGMENT AND RELATED INFORMATION Southern Company The primary businesses of the Southern Company system are electricity sales by the traditional electric operating companies and Southern Power and the distribution of natural gas by Southern Company Gas. The traditional electric operating companies – Alabama Power, Georgia Power, and Mississippi Power – are vertically integrated utilities providing electric service in three Southeastern states. Southern Power develops, constructs, acquires, owns, and manages power generation assets, including renewable energy and battery energy storage projects, and sells electricity at market-based rates in the wholesale market. Southern Company Gas distributes natural gas through its natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. Southern Company's reportable business segments are the sale of electricity by the 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 $81 million for the three months ended March 31, 2021 and $86 million for the three months ended March 31, 2020. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies were immaterial for the three months ended March 31, 2021 and 2020. Revenues from sales of natural gas from Southern Company Gas to Southern Power were $12 million for the three months ended March 31, 2021 and $10 million for the three months ended March 31, 2020. 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 solutions to electric utilities and their customers in the areas of distributed generation, energy storage and renewables, and energy efficiency, 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, 2021 and 2020 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) Three Months Ended March 31, 2021 Operating revenues $ 3,764 $ 440 $ (87) $ 4,117 $ 1,694 $ 134 $ (35) $ 5,910 Segment net income (loss) (a)(b)(c) 756 97 — 853 398 (108) (8) 1,135 At March 31, 2021 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Total assets 86,053 13,995 (637) 99,411 23,377 3,392 (787) 125,393 Three Months Ended March 31, 2020 Operating revenues $ 3,407 $ 375 $ (87) $ 3,695 $ 1,249 $ 114 $ (40) $ 5,018 Segment net income (loss) (a)(d) 642 75 — 717 275 (121) (3) 868 At December 31, 2020 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 (a) Attributable to Southern Company. (b) For the traditional electric operating companies, includes a $48 million pre-tax charge ($36 million after tax) at Georgia Power for estimated loss on Plant Vogtle Units 3 and 4. See Note (B) under "Georgia Power – Nuclear Construction" for additional information. (c) For Southern Power, includes gains on wind turbine equipment contributed to various equity method investments totaling approximately $37 million pre-tax ($28 million after tax). See Notes (E) and (K) under "Southern Power" for additional information. (d) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Power" for additional information. Products and Services Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2021 $ 3,342 $ 545 $ 230 $ 4,117 Three Months Ended March 31, 2020 3,078 418 199 3,695 Southern Company Gas' Revenues Gas Wholesale Gas Services (*) Gas Other Total (in millions) Three Months Ended March 31, 2021 $ 1,192 $ 298 $ 195 $ 9 $ 1,694 Three Months Ended March 31, 2020 1,013 51 177 8 1,249 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. See "Southern Company Gas" herein for additional information. Southern Company Gas Southern Company Gas manages its business through four reportable segments – gas distribution operations, gas pipeline investments, wholesale gas services, and gas marketing services. The non-reportable segments are combined and presented as all other. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information on the disposition activities described herein. 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 four states. Gas pipeline investments consists of joint ventures in natural gas pipeline investments including a 50% interest in SNG, a 20% ownership interest in the PennEast Pipeline project, and a 50% joint ownership interest in the Dalton Pipeline. These natural gas pipelines enable the provision of diverse sources of natural gas supplies to the customers of Southern Company Gas. Gas pipeline investments also included a 5% ownership interest in the Atlantic Coast Pipeline construction project prior to its sale on March 24, 2020. 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. The Virginia Natural Gas asset management agreement ended on March 31, 2021 and was not extended. Additionally, wholesale gas services engages in natural gas storage and gas pipeline arbitrage and related activities. See Note (K) under "Southern Company Gas" for information regarding the sale of Sequent, which is expected to be completed during the third quarter 2021. Gas marketing services provides natural gas marketing to end-use customers primarily in Georgia and Illinois through SouthStar. The all other column includes segments and subsidiaries that fall below the quantitative threshold for separate disclosure, including storage and fuels operations. The all other column included Jefferson Island through its sale on December 1, 2020 and Pivotal LNG through its sale on March 24, 2020. Business segment financial data for the three months ended March 31, 2021 and 2020 was as follows: Gas Distribution Operations Gas Pipeline Investments Wholesale Gas Services (*) Gas Marketing Services Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2021 Operating revenues $ 1,200 $ 8 $ 298 $ 195 $ 1,701 $ 7 $ (14) $ 1,694 Segment net income (loss) 183 29 126 56 394 4 — 398 Total assets at March 31, 2021 20,161 1,596 939 1,553 24,249 11,477 (12,349) 23,377 Three Months Ended March 31, 2020 Operating revenues $ 1,020 $ 8 $ 51 $ 177 $ 1,256 $ 8 $ (15) $ 1,249 Segment net income (loss) 164 30 23 57 274 1 — 275 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 (*) 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, 2021 $ 2,588 $ 63 $ 2,651 $ 2,353 $ 298 Three Months Ended March 31, 2020 1,185 29 1,214 1,163 51

Introduction (Policies)

Introduction (Policies)	3 Months Ended
	Mar. 31, 2021
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, 2020 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, 2021 and 2020. 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 and other factors, including the impacts of the COVID-19 pandemic, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year.
Reclassifications	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 overall results of operations, financial position, or cash flows of any Registrant.
Goodwill	Goodwill is not amortized but is subject to an annual impairment test in the fourth quarter of the year and on an interim basis as events and changes in circumstances occur.
Natural Gas for Sale	Natural Gas for Sale With the exception of Nicor Gas, Southern Company Gas' natural gas distribution utilities record natural gas inventories 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. 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.
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 (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation 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. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information.
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 (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with the classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. Energy-Related Derivatives 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 are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges – Energy-related derivative contracts 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 an approved cost recovery mechanism. • 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 accumulated 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. Interest Rate Derivatives Southern Company and certain subsidiaries may 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 Foreign Currency Derivatives Southern Company and certain subsidiaries, including Southern Power, may 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.

Introduction (Tables)

Introduction (Tables)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	Goodwill at March 31, 2021 and December 31, 2020 was as follows: Goodwill (in millions) Southern Company $ 5,280 Southern Company Gas: Gas distribution operations $ 4,034 Gas marketing services 981 Southern Company Gas total $ 5,015
Schedule of Other Intangible Assets, Indefinite-Lived	Other intangible assets were as follows: At March 31, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (139) $ 73 $ 212 $ (135) $ 77 Trade names 64 (33) 31 64 (31) 33 Storage and transportation contracts 64 (64) — 64 (64) — PPA fair value adjustments 390 (94) 296 390 (89) 301 Other 11 (9) 2 10 (9) 1 Total other intangible assets subject to amortization $ 741 $ (339) $ 402 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 816 $ (339) $ 477 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (94) $ 296 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (122) $ 34 $ 156 $ (119) $ 37 Trade names 26 (13) 13 26 (12) 14 Wholesale gas services Storage and transportation contracts 64 (64) — 64 (64) — Total other intangible assets subject to amortization $ 246 $ (199) $ 47 $ 246 $ (195) $ 51
Schedule of Other Intangible Assets, Finite-Lived	Other intangible assets were as follows: At March 31, 2021 At December 31, 2020 Gross Carrying Amount Accumulated Amortization Other Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 212 $ (139) $ 73 $ 212 $ (135) $ 77 Trade names 64 (33) 31 64 (31) 33 Storage and transportation contracts 64 (64) — 64 (64) — PPA fair value adjustments 390 (94) 296 390 (89) 301 Other 11 (9) 2 10 (9) 1 Total other intangible assets subject to amortization $ 741 $ (339) $ 402 $ 740 $ (328) $ 412 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 816 $ (339) $ 477 $ 815 $ (328) $ 487 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (94) $ 296 $ 390 $ (89) $ 301 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (122) $ 34 $ 156 $ (119) $ 37 Trade names 26 (13) 13 26 (12) 14 Wholesale gas services Storage and transportation contracts 64 (64) — 64 (64) — Total other intangible assets subject to amortization $ 246 $ (199) $ 47 $ 246 $ (195) $ 51
Schedule of Amortization of Other Intangible Assets	Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2021 (in millions) Southern Company (a) $ 11 Southern Power (b) 5 Southern Company Gas (c) 4 (a) Includes $5 million recorded as a reduction to operating revenues. (b) Recorded as a reduction to operating revenues. (c) Relates to gas marketing services.
Schedule of Restrictions on Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the Registrants that had restricted cash at March 31, 2021 and/or December 31, 2020: Southern Southern Power Southern March 31, 2021 December 31, 2020 March 31, 2021 March 31, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 1,770 $ 1,065 $ 314 $ 309 $ 17 Restricted cash (a) : Other current assets 2 2 — 2 2 Other deferred charges and assets 29 — 29 — — Total cash, cash equivalents, and restricted cash $ 1,801 $ 1,068 (b) $ 343 $ 311 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total does not add due to rounding.
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amount shown in the condensed statements of cash flows for the Registrants that had restricted cash at March 31, 2021 and/or December 31, 2020: Southern Southern Power Southern March 31, 2021 December 31, 2020 March 31, 2021 March 31, 2021 December 31, 2020 (in millions) (in millions) (in millions) Cash and cash equivalents $ 1,770 $ 1,065 $ 314 $ 309 $ 17 Restricted cash (a) : Other current assets 2 2 — 2 2 Other deferred charges and assets 29 — 29 — — Total cash, cash equivalents, and restricted cash $ 1,801 $ 1,068 (b) $ 343 $ 311 $ 19 (a) For Southern Company Gas, reflects restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance. For Southern Power, reflects restricted cash held for construction payables. (b) Total does not add due to rounding.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Schedule of Cost Recovery Clauses	The recovery balances for certain retail regulatory clauses of the traditional electric operating companies and Southern Company Gas at March 31, 2021 and December 31, 2020 were as follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, 2020 (in millions) Alabama Power Rate CNP Compliance Other regulatory liabilities, current $ 33 $ 28 Rate CNP PPA Other regulatory assets, deferred 58 58 Retail Energy Cost Recovery Other regulatory liabilities, current — 18 Other regulatory assets, deferred 15 — Natural Disaster Reserve Other regulatory liabilities, deferred 52 77 Georgia Power Fuel Cost Recovery Over recovered fuel clause revenues $ 83 $ 113 Mississippi Power Fuel Cost Recovery Over recovered regulatory clause liabilities $ 18 $ 24 Ad Valorem Tax Other regulatory assets, current 12 11 Other regulatory assets, deferred 45 41 Property Damage Reserve Other regulatory liabilities, deferred — 4 Other regulatory assets, deferred 1 — Southern Company Gas Natural Gas Cost Recovery (*) Other regulatory liabilities $ 12 $ 88 Natural gas cost under recovery 487 — Other regulatory assets, deferred 185 — (*) The significant change during the three months ended March 31, 2021 was primarily driven by an increase in the cost of gas purchased in February 2021 resulting from Winter Storm Uri.
Nuclear Construction Cost and Schedule	Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4 by December 2021 and November 2022, respectively, is as follows: (in millions) Base project capital cost forecast (a)(b) $ 8,619 Construction contingency estimate 136 Total project capital cost forecast (a)(b) 8,755 Net investment as of March 31, 2021 (b) (7,560) Remaining estimate to complete (a) $ 1,195 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $250 million, of which $118 million had been accrued through March 31, 2021. (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds.
Schedule of Infrastructure Replacement Programs and Capital Projects	Capital expenditures incurred under specific infrastructure replacement programs during the first three months of 2021 were as follows: Utility Program Three Months Ended (in millions) Nicor Gas Investing in Illinois $ 45 Virginia Natural Gas Steps to Advance Virginia's Energy 9 Total $ 54

Revenue from Contracts with C_2

Revenue from Contracts with Customers and Lease Income (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following table disaggregates revenue from contracts with customers for the three months ended March 31, 2021 and 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended March 31, 2021 Operating revenues Retail electric revenues Residential $ 1,468 $ 628 $ 776 $ 64 $ — $ — Commercial 1,117 372 686 59 — — Industrial 668 320 284 64 — — Other 24 5 17 2 — — Total retail electric revenues 3,277 1,325 1,763 189 — — Natural gas distribution revenues Residential 614 — — — — 614 Commercial 170 — — — — 170 Transportation 288 — — — — 288 Industrial 16 — — — — 16 Other 97 — — — — 97 Total natural gas distribution revenues 1,185 — — — — 1,185 Wholesale electric revenues PPA energy revenues 212 43 13 4 156 — PPA capacity revenues 119 29 13 3 75 — Non-PPA revenues 67 32 9 88 61 — Total wholesale electric revenues 398 104 35 95 292 — Other natural gas revenues Wholesale gas services 1,590 — — — — 1,590 Gas marketing services 194 — — — — 194 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 1,791 — — — — 1,791 Other revenues 249 46 113 8 4 — Total revenue from contracts with customers 6,900 1,475 1,911 292 296 2,976 Other revenue sources (a) 1,306 84 59 15 144 1,014 Other adjustments (b) (2,296) — — — — (2,296) Total operating revenues $ 5,910 $ 1,559 $ 1,970 $ 307 $ 440 $ 1,694 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Three Months Ended March 31, 2020 Operating revenues Retail electric revenues Residential $ 1,370 $ 553 $ 760 $ 57 $ — $ — Commercial 1,146 364 720 62 — — Industrial 680 321 281 78 — — Other 23 5 16 2 — — Total retail electric revenues 3,219 1,243 1,777 199 — — Natural gas distribution revenues Residential 496 — — — — 496 Commercial 130 — — — — 130 Transportation 264 — — — — 264 Industrial 12 — — — — 12 Other 97 — — — — 97 Total natural gas distribution revenues 999 — — — — 999 Wholesale electric revenues PPA energy revenues 159 27 9 2 125 — PPA capacity revenues 105 27 12 1 66 — Non-PPA revenues 51 19 2 69 58 — Total wholesale electric revenues 315 73 23 72 249 — Other natural gas revenues Wholesale gas services 396 — — — — 396 Gas marketing services 163 — — — — 163 Other natural gas revenues 7 — — — — 7 Total natural gas revenues 566 — — — — 566 Other revenues 192 37 95 5 3 — Total revenue from contracts with customers 5,291 1,353 1,895 276 252 1,565 Other revenue sources (a) 868 (2) (70) 1 123 825 Other adjustments (b) (1,141) — — — — (1,141) Total operating revenues $ 5,018 $ 1,351 $ 1,825 $ 277 $ 375 $ 1,249 (a) Other revenue sources relate to revenues from customers accounted for as derivatives and leases, alternative revenue programs at Southern Company Gas, and cost recovery mechanisms and revenues that meet other scope exceptions for revenues from contracts with customers at the traditional electric operating companies. (b) Other adjustments relate to the cost of Southern Company Gas' energy and risk management activities. Wholesale gas services revenues are presented net of the related costs of those activities on the statement of income. See Note (L) under "Southern Company Gas" for additional information on the components of wholesale gas services' operating revenues.
Schedule of Contract Balances	The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at March 31, 2021 and December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivable As of March 31, 2021 $ 2,375 $ 567 $ 679 $ 87 $ 85 $ 778 As of December 31, 2020 2,614 632 806 77 112 788 Contract Assets As of March 31, 2021 $ 106 $ 1 $ 47 $ — $ — $ — As of December 31, 2020 158 2 71 — — — Contract Liabilities As of March 31, 2021 $ 75 $ 4 $ 34 $ 1 $ 1 $ 1 As of December 31, 2020 61 6 27 1 1 1
Schedule of Remaining Performance Obligations	Revenues from contracts with customers related to these performance obligations remaining at March 31, 2021 are expected to be recognized as follows: 2021 (remaining) 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 485 $ 408 $ 340 $ 327 $ 307 $ 2,666 Alabama Power 24 31 24 7 5 — Georgia Power 57 51 36 24 21 41 Southern Power 213 287 280 296 280 2,644
Schedule of Lease Income	Lease income for the three months ended March 31, 2021 and 2020 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) For the Three Months Ended March 31, 2021 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 55 21 10 — 21 9 Variable lease income 84 — — — 90 — Total lease income $ 142 $ 21 $ 10 $ 3 $ 111 $ 9 For the Three Months Ended March 31, 2020 Lease income - interest income on sales-type leases $ 3 $ — $ — $ 3 $ — $ — Lease income - operating leases 51 6 16 — 24 9 Variable lease income 74 — — — 80 — Total lease income $ 128 $ 6 $ 16 $ 3 $ 104 $ 9

Consolidated Entities and Equ_2

Consolidated Entities and Equity Method Investments (Tables)	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Schedule of Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2021 and December 31, 2020 and related income from those investments for the three months ended March 31, 2021 and 2020 were as follows: Investment Balance March 31, 2021 December 31, 2020 (in millions) SNG $ 1,164 $ 1,167 PennEast Pipeline (*) 93 91 Other 33 32 Total $ 1,290 $ 1,290 (*) See Note (C) under "Other Matters – Southern Company Gas" for additional information.
Schedule of Earnings from Equity Method Investments	Earnings from Equity Method Investments Three Months Ended Three Months Ended (in millions) SNG $ 38 $ 37 PennEast Pipeline (a) 2 2 Other (a)(b) 1 4 Total $ 41 $ 43 (a) Earnings primarily result from AFUDC equity recorded by the project entity. (b) On March 24, 2020, Southern Company Gas completed the sale of its interests in Atlantic Coast Pipeline and Pivotal LNG. See Note 15 to the financial statements under "Southern Company Gas" in Item 8 of the Form 10-K for additional information.

Financing (Tables)

Financing (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Credit Arrangements	At March 31, 2021, committed credit arrangements with banks were as follows: Expires Company 2021 2022 2023 2024 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power 3 525 — 800 1,328 1,328 3 Georgia Power — — — 1,750 1,750 1,728 — Mississippi Power — 150 125 — 275 250 — Southern Power (a) — — — 600 600 568 — Southern Company Gas (b) — — — 1,750 1,750 1,745 — SEGCO 30 — — — 30 30 30 Southern Company $ 33 $ 675 $ 125 $ 6,900 $ 7,733 $ 7,648 $ 33 (a) Does not include Southern Power Company's $75 million and $60 million continuing letter of credit facilities for standby letters of credit expiring in 2023, of which $12 million and $1 million, respectively, was unused at March 31, 2021. Southern Power's subsidiaries are not parties to its bank credit arrangements or letter of credit facilities. (b) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.05 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $700 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to this multi-year credit arrangement, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted.
Schedule of Shares Used to Compute Diluted Earnings Per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2021 Three Months Ended March 31, 2020 (in millions) As reported shares 1,060 1,057 Effect of stock-based compensation 6 7 Effect of equity units — 3 Diluted shares 1,066 1,067

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Schedule of Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three months ended March 31, 2021 and 2020 are presented in the following tables. Three Months Ended Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 109 $ 26 $ 28 $ 4 $ 2 $ 9 Interest cost 87 20 26 4 1 6 Expected return on plan assets (298) (72) (94) (14) (3) (21) Amortization: Prior service costs — — — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 78 21 25 4 1 3 Net periodic pension cost (income) $ (24) $ (5) $ (15) $ (2) $ 1 $ — Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ — Interest cost 8 2 3 — — 1 Expected return on plan assets (19) (7) (7) — — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ (4) $ (4) $ (1) $ — $ — $ — Three Months Ended Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 94 $ 22 $ 24 $ 4 $ 2 $ 8 Interest cost 108 25 33 5 1 8 Expected return on plan assets (275) (66) (87) (13) (3) (19) Amortization: Prior service costs 1 — — — — (1) Regulatory asset — — — — — 4 Net (gain)/loss 67 18 22 3 1 2 Net periodic pension cost (income) $ (5) $ (1) $ (8) $ (1) $ 1 $ 2 Postretirement Benefits Service cost $ 5 $ 2 $ 1 $ — $ — $ — Interest cost 13 3 5 — — 2 Expected return on plan assets (18) (7) (7) — — (2) Amortization: Regulatory asset — — — — — 2 Net (gain)/loss 1 — 1 — — (1) Net periodic postretirement benefit cost (income) $ 1 $ (2) $ — $ — $ — $ 1

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	As of March 31, 2021, 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, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 372 $ 179 $ 34 $ — $ 585 Interest rate derivatives — 10 — — 10 Foreign currency derivatives — 41 — — 41 Investments in trusts: (b)(c) Domestic equity 782 214 — — 996 Foreign equity 145 197 — — 342 U.S. Treasury and government agency securities — 325 — — 325 Municipal bonds — 45 — — 45 Pooled funds – fixed income — 18 — — 18 Corporate bonds 5 436 — — 441 Mortgage and asset backed securities — 81 — — 81 Private equity — — — 83 83 Other 50 7 — — 57 Cash equivalents 1,121 11 — — 1,132 Other investments 9 33 — — 42 Total $ 2,484 $ 1,597 $ 34 $ 83 $ 4,198 Liabilities: Energy-related derivatives (a) $ 359 $ 158 $ 6 $ — $ 523 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 16 — 16 Total $ 359 $ 181 $ 22 $ — $ 562 Fair Value Measurements Using: As of March 31, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Nuclear decommissioning trusts: (b) Domestic equity 448 205 — — 653 Foreign equity 145 15 — — 160 U.S. Treasury and government agency securities — 20 — — 20 Municipal bonds — 1 — — 1 Corporate bonds 5 235 — — 240 Mortgage and asset backed securities — 26 — — 26 Private equity — — — 83 83 Other 27 — — — 27 Cash equivalents 401 11 — — 412 Other investments — 33 — — 33 Total $ 1,026 $ 558 $ — $ 83 $ 1,667 Liabilities: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Georgia Power Assets: Energy-related derivatives $ — $ 17 $ — $ — $ 17 Nuclear decommissioning trusts: (b)(c) Domestic equity 334 1 — — 335 Foreign equity — 179 — — 179 U.S. Treasury and government agency securities — 305 — — 305 Municipal bonds — 44 — — 44 Corporate bonds — 201 — — 201 Mortgage and asset backed securities — 55 — — 55 Other 23 7 — — 30 Total $ 357 $ 809 $ — $ — $ 1,166 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Fair Value Measurements Using: As of March 31, 2021: Quoted Prices Significant Significant Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 11 $ — $ — $ 11 Liabilities: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Southern Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 41 — — 41 Cash equivalents 115 — — — 115 Total $ 115 $ 42 $ — $ — $ 157 Liabilities: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 16 — 16 Total $ — $ 24 $ 16 $ — $ 40 Southern Company Gas Assets: Energy-related derivatives (a) $ 372 $ 138 $ 34 $ — $ 544 Non-qualified deferred compensation trusts: Domestic equity — 8 — — 8 Foreign equity — 3 — — 3 Pooled funds – fixed income — 18 — — 18 Cash equivalents and restricted cash 284 — — — 284 Total $ 656 $ 167 $ 34 $ — $ 857 Liabilities: Energy-related derivatives (a) $ 359 $ 139 $ 6 $ — $ 504 (a) Excludes cash collateral of $27 million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2021, approximately $34 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. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information.
Schedule of Increase (Decrease) In Fair Value Of Funds	The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased (decreased) by the amounts shown in the table below for the three months ended March 31, 2021 and 2020. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Fair value increases (decreases) Three Months Ended Three Months Ended (in millions) Southern Company $ 39 $ (247) Alabama Power 41 (167) Georgia Power (2) (80)
Schedule of Financial Instruments for which Carrying Amount Did Not Equal Fair Value	At March 31, 2021, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) Long-term debt, including securities due within one year: Carrying amount $ 50,035 $ 8,866 $ 13,220 $ 1,398 $ 4,030 $ 6,588 Fair value 54,113 9,821 14,291 1,507 4,347 7,264 (*) The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the 2016 merger with Southern Company. Southern Company Gas amortizes the fair value adjustments over the remaining lives of the respective bonds, the latest being through 2043.
Schedule of Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component	The following table includes transfers to Level 3, which represent the fair value of Southern Company Gas' commodity derivative contracts that include a significant unobservable component for the first time during the period. Three Months Ended March 31, 2021 (in millions) Beginning balance $ 28 Instruments realized or otherwise settled during period (2) Changes in fair value 2 Ending balance $ 28

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Energy-Related Derivatives	At March 31, 2021, the net volume of energy-related derivative contracts for natural gas positions, 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 Longest Longest (in millions) Southern Company (*) 907 2030 2031 Alabama Power 73 2024 — Georgia Power 125 2024 — Mississippi Power 85 2024 — Southern Power 9 2030 2021 Southern Company Gas (*) 615 2023 2031 (*) 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 4.4 billion mmBtu and short natural gas positions of 3.8 billion mmBtu as of March 31, 2021, which is also included in Southern Company's total volume.
Schedule of Interest Rate Derivatives	At March 31, 2021, the following interest rate derivatives were outstanding: Notional Interest Weighted Hedge Fair Value Gain (Loss) at March 31, 2021 (in millions) (in millions) Cash Flow Hedges of Existing Debt Mississippi Power $ 60 1-month LIBOR 0.58% December 2021 $ — Fair Value Hedges of Existing Debt Southern Company parent 1,500 2.35% 1-month LIBOR + 0.87% July 2021 10 Southern Company $ 1,560 $ 10
Schedule of Foreign Currency Derivatives	At March 31, 2021, the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2021 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 9 Southern Power 564 3.78% 500 1.85% June 2026 9 Total $ 1,241 € 1,100 $ 18
Schedule of Derivative Category and Balance Sheet Location	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, 2021 As of December 31, 2020 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: Assets from risk management activities/Other current liabilities $ 30 $ 4 $ 24 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 16 15 18 19 Total derivatives designated as hedging instruments for regulatory purposes $ 46 $ 19 $ 42 $ 30 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 2 $ 1 $ 3 $ 5 Interest rate derivatives: Assets from risk management activities/Other current liabilities 10 — 20 — Foreign currency derivatives: Assets from risk management activities/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 41 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 53 $ 24 $ 110 $ 28 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 265 $ 265 $ 388 $ 331 Other deferred charges and assets/Other deferred credits and liabilities 272 237 270 232 Total derivatives not designated as hedging instruments $ 537 $ 502 $ 658 $ 563 Gross amounts recognized $ 636 $ 545 $ 810 $ 621 Gross amounts offset (a) (450) (477) (529) (557) Net amounts recognized in the Balance Sheets (b) $ 186 $ 68 $ 281 $ 64 As of March 31, 2021 As of December 31, 2020 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 $ 7 $ — $ 7 $ 2 Other deferred charges and assets/Other deferred credits and liabilities 5 4 5 5 Total derivatives designated as hedging instruments for regulatory purposes $ 12 $ 4 $ 12 $ 7 Gross amounts recognized $ 12 $ 4 $ 12 $ 7 Gross amounts offset (4) (4) (7) (7) Net amounts recognized in the Balance Sheets $ 8 $ — $ 5 $ — Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 11 $ 2 $ 7 $ 5 Other deferred charges and assets/Other deferred credits and liabilities 6 6 8 8 Total derivatives designated as hedging instruments for regulatory purposes $ 17 $ 8 $ 15 $ 13 Gross amounts recognized $ 17 $ 8 $ 15 $ 13 Gross amounts offset (7) (7) (12) (12) Net amounts recognized in the Balance Sheets $ 10 $ 1 $ 3 $ 1 Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 6 $ 1 $ 4 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 5 5 5 6 Total derivatives designated as hedging instruments for regulatory purposes $ 11 $ 6 $ 9 $ 9 Gross amounts recognized $ 11 $ 6 $ 9 $ 9 Gross amounts offset (5) (5) (7) (7) Net amounts recognized in the Balance Sheets $ 6 $ 1 $ 2 $ 2 As of March 31, 2021 As of December 31, 2020 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ — $ 2 $ 2 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 41 — 87 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 42 $ 23 $ 89 $ 25 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 1 Total derivatives not designated as hedging instruments $ — $ — $ — $ 1 Net amounts recognized in the Balance Sheets $ 42 $ 23 $ 89 $ 26 Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 6 $ 1 $ 6 $ 1 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 1 $ 6 $ 1 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 1 $ 1 $ 1 $ 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 1 $ 1 $ 1 $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 265 $ 265 $ 388 $ 330 Other deferred charges and assets/Other deferred credits and liabilities 272 237 270 232 Total derivatives not designated as hedging instruments $ 537 $ 502 $ 658 $ 562 Gross amounts of recognized $ 544 $ 504 $ 665 $ 566 Gross amounts offset (a) (434) (461) (503) (531) Net amounts recognized in the Balance Sheets (b) $ 110 $ 43 $ 162 $ 35 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $27 million and $28 million as of March 31, 2021 and December 31, 2020, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for both periods presented.
Schedule of Pre-tax Effects of Unrealized Derivative Gains (Losses)	At March 31, 2021 and December 31, 2020, 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 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) At March 31, 2021: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 24 7 9 5 3 Other regulatory liabilities, deferred 3 1 1 1 — Total energy-related derivative gains (losses) $ 25 $ 8 $ 9 $ 5 $ 3 At December 31, 2020: Energy-related derivatives: Other regulatory assets, deferred $ (2) $ — $ (1) $ (1) $ — Other regulatory liabilities, current 12 5 2 1 4 Other regulatory liabilities, deferred 2 1 1 — — Total energy-related derivative gains (losses) $ 12 $ 6 $ 2 $ — $ 4
Schedule of Pre-Tax Effects of Cash Flow Hedging on AOCI	For the three months ended March 31, 2021 and 2020, the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months Ended March 31, 2021 2020 (in millions) Southern Company Energy-related derivatives $ 5 $ (4) Interest rate derivatives 3 (26) Foreign currency derivatives (47) (83) Total $ (39) $ (113) Southern Power Energy-related derivatives $ 4 $ — Foreign currency derivatives (47) (83) Total $ (43) $ (83) Southern Company Gas Energy-related derivatives $ 1 $ (4) Interest rate derivatives — (23) Total $ 1 $ (27)
Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income	For the three months ended March 31, 2021 and 2020, 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 Ended March 31, 2021 2020 (in millions) Southern Company Total cost of natural gas $ 583 $ 439 Gain (loss) on energy-related cash flow hedges (a) (3) (7) Total depreciation and amortization 871 857 Gain (loss) on energy-related cash flow hedges (a) 3 (1) Total interest expense, net of amounts capitalized (450) (456) Gain (loss) on interest rate cash flow hedges (a) (7) (6) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) Gain (loss) on interest rate fair value hedges (b) (10) 29 Total other income (expense), net 58 103 Gain (loss) on foreign currency cash flow hedges (a)(c) (60) (31) Southern Power Total depreciation and amortization $ 119 $ 117 Gain (loss) on energy-related cash flow hedges (a) 3 (1) Total interest expense, net of amounts capitalized (38) (39) Gain (loss) on foreign currency cash flow hedges (a) (6) (6) Total other income (expense), net 7 2 Gain (loss) on foreign currency cash flow hedges (a)(c) (60) (31) (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes.
Schedule of Cumulative Basis Adjustments for Fair Value Hedges	As of March 31, 2021 and December 31, 2020, 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, 2021 As of December 31, 2020 As of March 31, 2021 As of December 31, 2020 (in millions) (in millions) Southern Company Securities due within one year $ (1,505) $ (1,509) $ (5) $ (10)
Schedule of Pre-tax Effect of Interest Rate and Energy Related Derivatives on Income	For the three months ended March 31, 2021 and 2020, the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2021 2020 (in millions) Energy-related derivatives: Natural gas revenues (*) $ (17) $ 70 Cost of natural gas 7 7 Total derivatives in non-designated hedging relationships $ (10) $ 77 (*) Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for all periods presented.

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Schedule of Assets Held for Sale	The following table provides Southern Company's major classes of assets classified as held for sale at March 31, 2021 and December 31, 2020: Southern Company At March 31, At December 31, 2021 2020 (in millions) Assets Held for Sale: Total property, plant, and equipment $ 7 $ 8 Leveraged leases 52 52 Total Assets Held for Sale $ 59 $ 60
Schedule of Asset Acquisitions	During the three months ended March 31, 2021, Southern Power acquired a controlling membership interest in the wind facility listed below. Acquisition-related costs were expensed as incurred and were not material. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Deuel Harvest (*) Wind Invenergy Renewables, LLC 300 Deuel County, SD 100% of Class B February 2021 25 years and 15 years (*) On March 26, 2021, Southern Power acquired a controlling interest in the facility and consolidates the project's operating results in its financial statements. On March 30, 2021, Southern Power completed a tax equity transaction whereby it received $220 million. The tax equity partner, which is the Class A member, and Invenergy Renewables, LLC each own a noncontrolling interest.
Schedule of Construction Projects	Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Under Construction at March 31, 2021 Garland Solar Storage (a) Battery energy storage system 88 Kern County, CA Third quarter 2021 20 years Tranquillity Solar Storage (a) Battery energy storage system 72 Fresno County, CA Fourth quarter 2021 20 years Glass Sands (b) Wind 118 Murray County, OK Fourth quarter 2021 12 years (a) In December 2020, Southern Power restructured its ownership of the project by contributing the Class A membership interests to an existing partnership and selling 100% of the Class B membership interests while retaining the controlling interest. Prior to commercial operation, Southern Power may restructure the project ownership again and enter into additional partnerships, but expects to retain the controlling interest. The ultimate outcome of this matter cannot be determined at this time. (b) In December 2020, Southern Power purchased 100% of the membership interests of the Glass Sands facility.

Segment and Related Informati_2

Segment and Related Information (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Financial Data for Business Segments	Financial data for business segments and products and services for the three months ended March 31, 2021 and 2020 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) Three Months Ended March 31, 2021 Operating revenues $ 3,764 $ 440 $ (87) $ 4,117 $ 1,694 $ 134 $ (35) $ 5,910 Segment net income (loss) (a)(b)(c) 756 97 — 853 398 (108) (8) 1,135 At March 31, 2021 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Total assets 86,053 13,995 (637) 99,411 23,377 3,392 (787) 125,393 Three Months Ended March 31, 2020 Operating revenues $ 3,407 $ 375 $ (87) $ 3,695 $ 1,249 $ 114 $ (40) $ 5,018 Segment net income (loss) (a)(d) 642 75 — 717 275 (121) (3) 868 At December 31, 2020 Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 263 $ — $ 5,280 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 (a) Attributable to Southern Company. (b) For the traditional electric operating companies, includes a $48 million pre-tax charge ($36 million after tax) at Georgia Power for estimated loss on Plant Vogtle Units 3 and 4. See Note (B) under "Georgia Power – Nuclear Construction" for additional information. (c) For Southern Power, includes gains on wind turbine equipment contributed to various equity method investments totaling approximately $37 million pre-tax ($28 million after tax). See Notes (E) and (K) under "Southern Power" for additional information. (d) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Power" for additional information. Business segment financial data for the three months ended March 31, 2021 and 2020 was as follows: Gas Distribution Operations Gas Pipeline Investments Wholesale Gas Services (*) Gas Marketing Services Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2021 Operating revenues $ 1,200 $ 8 $ 298 $ 195 $ 1,701 $ 7 $ (14) $ 1,694 Segment net income (loss) 183 29 126 56 394 4 — 398 Total assets at March 31, 2021 20,161 1,596 939 1,553 24,249 11,477 (12,349) 23,377 Three Months Ended March 31, 2020 Operating revenues $ 1,020 $ 8 $ 51 $ 177 $ 1,256 $ 8 $ (15) $ 1,249 Segment net income (loss) 164 30 23 57 274 1 — 275 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 (*) 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, 2021 $ 2,588 $ 63 $ 2,651 $ 2,353 $ 298 Three Months Ended March 31, 2020 1,185 29 1,214 1,163 51
Schedule of Financial Data for Products and Services	Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2021 $ 3,342 $ 545 $ 230 $ 4,117 Three Months Ended March 31, 2020 3,078 418 199 3,695 Southern Company Gas' Revenues Gas Wholesale Gas Services (*) Gas Other Total (in millions) Three Months Ended March 31, 2021 $ 1,192 $ 298 $ 195 $ 9 $ 1,694 Three Months Ended March 31, 2020 1,013 51 177 8 1,249 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. See "Southern Company Gas" herein for additional information.

Introduction - Schedule of Good

Introduction - Schedule of Goodwill (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill	$ 5,280	$ 5,280
SOUTHERN Co GAS
Goodwill [Line Items]
Goodwill	5,015	5,015
SOUTHERN Co GAS | Gas distribution operations
Goodwill [Line Items]
Goodwill	4,034	4,034
SOUTHERN Co GAS | Gas marketing services
Goodwill [Line Items]
Goodwill	$ 981	$ 981

Introduction - Schedule of Othe

Introduction - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 741	$ 740
Accumulated Amortization	(339)	(328)
Other Intangible Assets, Net	402	412
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	816	815
Accumulated Amortization	(339)	(328)
Other Intangible Assets, Net	477	487
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	212	212
Accumulated Amortization	(139)	(135)
Other Intangible Assets, Net	73	77
Total other intangible assets
Accumulated Amortization	(139)	(135)
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(33)	(31)
Other Intangible Assets, Net	31	33
Total other intangible assets
Accumulated Amortization	(33)	(31)
Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	(64)	(64)
PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(94)	(89)
Other Intangible Assets, Net	296	301
Total other intangible assets
Accumulated Amortization	(94)	(89)
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	11	10
Accumulated Amortization	(9)	(9)
Other Intangible Assets, Net	2	1
Total other intangible assets
Accumulated Amortization	(9)	(9)
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(94)	(89)
Total other intangible assets
Accumulated Amortization	(94)	(89)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	390	390
Accumulated Amortization	(94)	(89)
Other Intangible Assets, Net	296	301
Total other intangible assets
Accumulated Amortization	(94)	(89)
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	246	246
Accumulated Amortization	(199)	(195)
Other Intangible Assets, Net	47	51
Total other intangible assets
Accumulated Amortization	(199)	(195)
Other Intangible Assets, Net	47	51
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(122)	(119)
Other Intangible Assets, Net	34	37
Total other intangible assets
Accumulated Amortization	(122)	(119)
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(13)	(12)
Other Intangible Assets, Net	13	14
Total other intangible assets
Accumulated Amortization	(13)	(12)
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(64)
Other Intangible Assets, Net	0	0
Total other intangible assets
Accumulated Amortization	$ (64)	$ (64)

Introduction - Schedule of Amor

Introduction - Schedule of Amortization of Other Intangible Assets (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 11
Decrease in operating revenues	5
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	5
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 4

Introduction - Schedule of Rest

Introduction - Schedule of Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,770	$ 1,065
Restricted cash:
Total cash, cash equivalents, and restricted cash	1,801	1,068	$ 2,168	$ 1,978
Other current assets
Restricted cash:
Restricted cash	2	2
Other deferred charges and assets
Restricted cash:
Restricted cash	29	0
SOUTHERN POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	314	182
Restricted cash:
Total cash, cash equivalents, and restricted cash	343	182	330	279
SOUTHERN POWER CO | Other current assets
Restricted cash:
Restricted cash	0
SOUTHERN POWER CO | Other deferred charges and assets
Restricted cash:
Restricted cash	29
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	309	17
Restricted cash:
Total cash, cash equivalents, and restricted cash	311	19	$ 314	$ 49
SOUTHERN Co GAS | Other current assets
Restricted cash:
Restricted cash	2	2
SOUTHERN Co GAS | Other deferred charges and assets
Restricted cash:
Restricted cash	$ 0	$ 0

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Cost Recovery Clauses (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 487	$ 0
ALABAMA POWER CO | Other regulatory liabilities, current
Loss Contingencies [Line Items]
Rate CNP Compliance	33	28
Retail Energy Cost Recovery	0	18
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Natural Disaster Reserve	52	77
ALABAMA POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Rate CNP PPA	58	58
Retail Energy Cost Recovery	15	0
GEORGIA POWER CO | Over recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery	83	113
MISSISSIPPI POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Property Damage Reserve	0	4
MISSISSIPPI POWER CO | Over recovered regulatory clause liabilities
Loss Contingencies [Line Items]
Fuel Cost Recovery	18	24
MISSISSIPPI POWER CO | Other regulatory assets, current
Loss Contingencies [Line Items]
Ad Valorem Tax	12	11
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Ad Valorem Tax	45	41
Property Damage Reserve	1	0
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Natural gas cost under recovery	487	0
SOUTHERN Co GAS | Other regulatory liabilities
Loss Contingencies [Line Items]
Natural gas cost under recovery	12	88
SOUTHERN Co GAS | Other regulatory assets, current
Loss Contingencies [Line Items]
Natural gas cost under recovery	487	0
SOUTHERN Co GAS | Other regulatory assets, deferred
Loss Contingencies [Line Items]
Natural gas cost under recovery	$ 185	$ 0

Regulatory Matters - APC (Detai

Regulatory Matters - APC (Details) - USD ($) $ in Millions	Apr. 15, 2021	Mar. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Construction work in progress		$ 9,525	$ 8,697
ALABAMA POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress		1,052	866
ALABAMA POWER CO | Plant Barry Unit 8
Public Utilities, General Disclosures [Line Items]
Construction work in progress		161
MISSISSIPPI POWER CO
Public Utilities, General Disclosures [Line Items]
Construction work in progress		$ 163	$ 146
MISSISSIPPI POWER CO | Plant Greene County Units 1 and 2 | ALABAMA POWER CO | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Proportionate ownership share	40.00%

Regulatory Matters - GPC Rate P

Regulatory Matters - GPC Rate Plan (Details) $ in Millions	Jan. 01, 2021USD ($)
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Public Utilities, General Disclosures [Line Items]
Approved reduction in amortization of CCR ARO costs	$ 90

Regulatory Matters - GPC Nuclea

Regulatory Matters - GPC Nuclear Construction (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2012utilityMW	Aug. 31, 2018
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	$ 48	$ 0
GEORGIA POWER CO
Loss Contingencies [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4	48	$ 0
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	$ 36
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Proportionate ownership share	45.70%
Number of construction units approved | utility			2
Electric generating capacity in mega watts under consortium agreement | MW			1,100
Estimated cost to complete, construction contingency estimate, financing costs	$ 3,000
Estimated cost to complete, construction contingency estimate, financing costs, incurred to date	2,700
Construction contingency estimate	84
Construction contingency estimate, additional amount	48
Base project capital cost forecast, monthly	25
Monthly AFUDC	$ 15
Percentage of ownership interest required for voting for continuing construction				90.00%
GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | Vogtle Owners
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed	30 days
Minimum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term	3 months
Estimate of possible loss	$ 150
Maximum | GEORGIA POWER CO | Plant Vogtle Units 3 And 4 | COVID-19
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss, loss of productivity, term	4 months
Estimate of possible loss	$ 190

Regulatory Matters - GPC Nucl_2

Regulatory Matters - GPC Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Jun. 30, 2020
Loss Contingencies [Line Items]
Base project capital cost forecast	$ 8,619
Construction contingency estimate	136
Total project capital cost forecast	8,755
Net investment as of March 31, 2021	(7,560)
Remaining estimate to complete	1,195
Expected capitalized costs	250
Capitalized interest accrued	118
Twenty Third Vogtle Construction Monitoring Report
Loss Contingencies [Line Items]
Guarantor obligations	1,700	$ 1,700
Customer refund	$ 188	$ 188

Regulatory Matters - GPC Amendm

Regulatory Matters - GPC Amendments to the Vogtle Joint Ownership Agreements (Details) - Plant Vogtle Units 3 And 4 - Georgia Power - USD ($) $ in Millions	Jan. 11, 2018	Mar. 31, 2021	Aug. 31, 2018
Public Utilities, General Disclosures [Line Items]
Production tax credits, aggregate purchase price, maximum		$ 300
Preliminary estimated cost to complete		$ 8,755
Additional construction capital costs	$ 3,300
Remaining share of construction costs, agreement to pay, percentage		100.00%
Percentage of ownership interest required for voting for continuing construction			90.00%
Percentage of costs, disallowed for recovery		6.00%
Costs disallowed for recovery, period		6 months
Public utilities, extension project schedule, term		1 year
Category I
Public Utilities, General Disclosures [Line Items]
Preliminary estimated cost to complete		$ 8,400
Additional construction capital costs, threshold		$ 800
Category II
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		55.70%
Additional construction capital costs		$ 80
Category II | Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		44.30%
Category II | Minimum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 800
Category II | Maximum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 1,600
Category III
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		65.70%
Additional construction capital costs		$ 100
Category III | Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs, responsibility to pay		34.30%
Category III | Maximum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold		$ 2,100

Regulatory Matters - GPC Nucl_3

Regulatory Matters - GPC Nuclear Construction Regulatory Matters (Details) - Plant Vogtle Units 3 And 4 - Georgia Power $ in Millions

Jan. 01, 2021

Aug. 31, 2020USD ($)

Jan. 01, 2020

Jan. 11, 2018USD ($)

Jan. 01, 2016

Nov. 30, 2020USD ($)

Mar. 31, 2021USD ($)

Jun. 30, 2020USD ($)

Dec. 31, 2022USD ($)

Dec. 31, 2021USD ($)

Dec. 31, 2020USD ($)report

Dec. 31, 2009USD ($)

Dec. 31, 2013

Public Utilities, General Disclosures [Line Items]

Estimated in-service capital cost

$ 4,418

Financing costs collected, net of tax

$ 2,600

Cost settlement agreement revised forecast, net of payments

$ 7,300

Requested decrease in NCCR tariff

$ 142

Additional construction capital costs

3,300

Payments for contractor settlement agreement

300

Amendment to estimated in-service capital cost

$ 5,680

Retail rate of return on common equity

10.95%

Public utilities, approved return on equity percentage

5.30%

8.30%

10.00%

Public utilities, approved return on equity, monthly percentage decrease

0.10%

Return on equity reduction, negative impact on earnings

$ 150

Twenty Third Vogtle Construction Monitoring Report

Public Utilities, General Disclosures [Line Items]

Number of approved construction management reports | report

23

Requested capital construction costs

$ 8,100

Guarantor obligations

$ 1,700

1,700

Customer refund

$ 188

$ 188

Twenty Fourth Vogtle Construction Monitoring Report

Public Utilities, General Disclosures [Line Items]

Requested capital construction costs

$ 670

Scenario, Forecast

Public Utilities, General Disclosures [Line Items]

Return on equity reduction, negative impact on earnings

$ 200

$ 265

Regulatory Matters - MPC (Detai

Regulatory Matters - MPC (Details) - MISSISSIPPI POWER CO $ in Millions	Apr. 06, 2021USD ($)	Mar. 15, 2021USD ($)	Apr. 15, 2021MW	Mar. 31, 2021USD ($)	Dec. 31, 2020MW
Loss Contingencies [Line Items]
Requested revenues increase percentage		1.80%
Requested revenues increase amount | $		$ 16
Required fossil-stream generation retirements (in MWs) | MW					950
Plant Daniel Units 1 and 2
Loss Contingencies [Line Items]
Remaining net book value | $				$ 531
Subsequent Event
Loss Contingencies [Line Items]
Requested revenues increase amount | $	$ 28
Public utilities, valorem taxes previously recovered, amount | $	$ 19
Subsequent Event | Plant Watson Unit 4
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) | MW			268
Subsequent Event | Plant Greene County Units 1 and 2
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) | MW			103
Subsequent Event | Plant Greene County Units 1 and 2 | ALABAMA POWER CO
Loss Contingencies [Line Items]
Proportionate ownership share			40.00%
Subsequent Event | Plant Daniel Units 1 and 2
Loss Contingencies [Line Items]
Required fossil-stream generation retirements (in MWs) | MW			502
Proportionate ownership share			50.00%

Regulatory Matters - GAS Narrat

Regulatory Matters - GAS Narrative (Details) - Subsequent Event $ in Billions	Apr. 28, 2021USD ($)	Apr. 06, 2021mi
Virginia Natural Gas
Loss Contingencies [Line Items]
Motion filed to withdraw project application, header improvement project, scope of project | mi		9.5
Atlanta Gas Light
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital budgets and related operations and maintenance spending, term	10 years
Integrated capacity delivery plan, review period	5 months
Atlanta Gas Light | Minimum
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital forecast plan, amount, years one through three	$ 0.5
Atlanta Gas Light | Maximum
Loss Contingencies [Line Items]
Integrated capacity delivery plan, capital forecast plan, amount, years one through three	$ 0.6

Regulatory Matters - GAS Schedu

Regulatory Matters - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - SOUTHERN Co GAS $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 54
Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures	45
Steps to Advance Virginia's Energy
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 9

Contingencies - General Litigat

Contingencies - General Litigation Matters (Details) - Pending Litigation $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019plaintiff	Dec. 31, 2018USD ($)plaintiffdefendant	Dec. 31, 2017claim
Shareholder Derivative Lawsuits
Loss Contingencies [Line Items]
Pending number of claims | claim			2
Stay period		30 days
MISSISSIPPI POWER CO | Purported Violations of Mississippi Consumer Protection Act
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff	4	10
Number of defendants | defendant		3
Underpayment of refunds | $		$ 23.5

Contingencies - Environmental R

Contingencies - Environmental Remediation (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 16	$ 15
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 240	$ 245

Contingencies - Other Matters (

Contingencies - Other Matters (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,368	$ 1,362
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Equity investments in unconsolidated subsidiaries	1,290	1,290
SOUTHERN Co GAS | PennEast Pipeline
Loss Contingencies [Line Items]
Construction contingency estimate	300
Equity investments in unconsolidated subsidiaries	93	91
SOUTHERN Co GAS | SNG
Loss Contingencies [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,164	$ 1,167
Ownership percentage, equity method investment	50.00%
Commitment to fund contingent capital contribution	$ 150
SNG
Loss Contingencies [Line Items]
Debt maturing in June 2021	$ 300

Revenue from Contracts with C_3

Revenue from Contracts with Customers and Lease Income - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 6,900	$ 5,291
Total operating revenues	5,910	5,018
Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,277	3,219
Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,468	1,370
Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,117	1,146
Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	668	680
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	24	23
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,185	999
Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	614	496
Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	170	130
Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	288	264
Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	16	12
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	97	97
Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	398	315
PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	212	159
PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	119	105
Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	67	51
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,791	566
Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,590	396
Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	194	163
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	7	7
Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	249	192
Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	1,306	868
Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	(2,296)	(1,141)
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,475	1,353
Total operating revenues	1,559	1,351
ALABAMA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,325	1,243
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	628	553
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	372	364
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	320	321
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	5	5
ALABAMA POWER CO | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	104	73
ALABAMA POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	43	27
ALABAMA POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	29	27
ALABAMA POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	32	19
ALABAMA POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
ALABAMA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	46	37
ALABAMA POWER CO | Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	84	(2)
ALABAMA POWER CO | Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	0	0
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,911	1,895
Total operating revenues	1,970	1,825
GEORGIA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,763	1,777
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	776	760
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	686	720
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	284	281
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	17	16
GEORGIA POWER CO | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	35	23
GEORGIA POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	13	9
GEORGIA POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	13	12
GEORGIA POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	9	2
GEORGIA POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
GEORGIA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	113	95
GEORGIA POWER CO | Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	59	(70)
GEORGIA POWER CO | Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	0	0
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	292	276
Total operating revenues	307	277
MISSISSIPPI POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	189	199
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	64	57
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	59	62
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	64	78
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	2
MISSISSIPPI POWER CO | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	95	72
MISSISSIPPI POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	2
MISSISSIPPI POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3	1
MISSISSIPPI POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	88	69
MISSISSIPPI POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
MISSISSIPPI POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	8	5
MISSISSIPPI POWER CO | Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	15	1
MISSISSIPPI POWER CO | Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	0	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	296	252
Total operating revenues	440	375
SOUTHERN POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	292	249
SOUTHERN POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	156	125
SOUTHERN POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	75	66
SOUTHERN POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	61	58
SOUTHERN POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	3
SOUTHERN POWER CO | Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	144	123
SOUTHERN POWER CO | Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	0	0
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,976	1,565
Total operating revenues	1,694	1,249
SOUTHERN Co GAS | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,185	999
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	614	496
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	170	130
SOUTHERN Co GAS | Transportation
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	288	264
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	16	12
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	97	97
SOUTHERN Co GAS | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,791	566
SOUTHERN Co GAS | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,590	396
SOUTHERN Co GAS | Gas marketing services
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	194	163
SOUTHERN Co GAS | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	7	7
SOUTHERN Co GAS | Other revenues
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
SOUTHERN Co GAS | Other revenue sources
Disaggregation of Revenue [Line Items]
Other revenues	1,014	825
SOUTHERN Co GAS | Other adjustments
Disaggregation of Revenue [Line Items]
Other revenues	$ (2,296)	$ (1,141)

Revenue from Contracts with C_4

Revenue from Contracts with Customers and Lease Income - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Accounts Receivable	$ 2,375	$ 2,614
Contract Assets	106	158
Contract Liabilities	75	61
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	567	632
Contract Assets	1	2
Contract Liabilities	4	6
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	679	806
Contract Assets	47	71
Contract Liabilities	34	27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	87	77
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	85	112
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivable	778	788
Contract Assets	0	0
Contract Liabilities	$ 1	$ 1

Revenue from Contracts with C_5

Revenue from Contracts with Customers and Lease Income - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contract assets	$ 106	$ 158
Contract liabilities	75	61
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	55	81
Contract liabilities	34	27
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Contract assets	47	71
Contract liabilities	$ 34	$ 27

Revenue from Contracts with C_6

Revenue from Contracts with Customers and Lease Income - Schedule of Remaining Performance Obligations (Details) $ in Millions	Mar. 31, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 485
Performance obligation, expected timing of satisfaction	9 months
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	$ 408
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	$ 340
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 327
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 307
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,666
Performance obligation, expected timing of satisfaction
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 24
Performance obligation, expected timing of satisfaction	9 months
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	$ 31
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	$ 24
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 7
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 5
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 57
Performance obligation, expected timing of satisfaction	9 months
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	$ 51
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	$ 36
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 24
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 21
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 41
Performance obligation, expected timing of satisfaction
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 213
Performance obligation, expected timing of satisfaction	9 months
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	$ 287
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	$ 280
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 296
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 280
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,644
Performance obligation, expected timing of satisfaction

Revenue from Contracts with C_7

Revenue from Contracts with Customers and Lease Income - Schedule of Lease Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 3	$ 3
Lease income - operating leases	55	51
Variable lease income	84	74
Total lease income	142	128
ALABAMA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	21	6
Variable lease income	0	0
Total lease income	21	6
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	10	16
Variable lease income	0	0
Total lease income	10	16
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	3	3
Lease income - operating leases	0	0
Variable lease income	0	0
Total lease income	3	3
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	21	24
Variable lease income	90	80
Total lease income	111	104
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	9	9
Variable lease income	0	0
Total lease income	$ 9	$ 9

Consolidated Entities and Equ_3

Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)investor	Dec. 31, 2020USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 125,393	$ 122,935
Liabilities	92,034	90,410
Equity method investments	463	398
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	13,995	13,235
Liabilities	7,251	6,604
Equity method investments	$ 84	19
SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	67.00%
SP Solar Holdings I, LP | Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	33.00%
Variable Interest Entity, Primary Beneficiary | SP Solar Holdings I, LP | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 6,100
Liabilities	377	387
Noncontrolling interests related to other partners' interests	1,100	1,100
Variable Interest Entity, Primary Beneficiary | SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	2,400
Liabilities	171	138
Noncontrolling interests related to other partners' interests	$ 42	43
Distribution made to limited partner, cash distributions paid, percentage	60.00%
Number of financial investors | investor	3
Variable Interest Entity, Primary Beneficiary | SP Wind | Financial Investors
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	40.00%
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 1,900	1,100
Liabilities	260	110
Noncontrolling interests related to other partners' interests	$ 926	$ 454

Consolidated Entities and Equ_4

Consolidated Entities and Equity Method Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 1,368	$ 1,362
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,290	1,290
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,164	1,167
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Investment Balance	93	91
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 33	$ 32

Consolidated Entities and Equ_5

Consolidated Entities and Equity Method Investments - Schedule of Earnings from Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	$ 45	$ 42
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	41	43
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	38	37
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	2	2
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	$ 1	$ 4

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2021USD ($)
Line of Credit Facility [Line Items]
Expires, 2021	$ 33,000,000
Expires, 2022	675,000,000
Expires, 2023	125,000,000
Expires, 2024	6,900,000,000
Total	7,733,000,000
Unused	7,648,000,000
Due within One Year	33,000,000
Southern Company parent
Line of Credit Facility [Line Items]
Expires, 2021	0
Expires, 2022	0
Expires, 2023	0
Expires, 2024	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Due within One Year	0
ALABAMA POWER CO
Line of Credit Facility [Line Items]
Expires, 2021	3,000,000
Expires, 2022	525,000,000
Expires, 2023	0
Expires, 2024	800,000,000
Total	1,328,000,000
Unused	1,328,000,000
Due within One Year	3,000,000
GEORGIA POWER CO
Line of Credit Facility [Line Items]
Expires, 2021	0
Expires, 2022	0
Expires, 2023	0
Expires, 2024	1,750,000,000
Total	1,750,000,000
Unused	1,728,000,000
Due within One Year	0
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
Expires, 2021	0
Expires, 2022	150,000,000
Expires, 2023	125,000,000
Expires, 2024	0
Total	275,000,000
Unused	250,000,000
Due within One Year	0
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2021	0
Expires, 2022	0
Expires, 2023	0
Expires, 2024	600,000,000
Total	600,000,000
Unused	568,000,000
Due within One Year	0
SOUTHERN POWER CO | Continuing Letter of Credit Facility A
Line of Credit Facility [Line Items]
Expires, 2023	75,000,000
Unused	12,000,000
SOUTHERN POWER CO | Continuing Letter of Credit Facility B
Line of Credit Facility [Line Items]
Expires, 2023	60,000,000
Unused	1,000,000
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
Expires, 2021	0
Expires, 2022	0
Expires, 2023	0
Expires, 2024	1,750,000,000
Total	1,750,000,000
Unused	1,745,000,000
Due within One Year	0
SEGCO
Line of Credit Facility [Line Items]
Expires, 2021	30,000,000
Expires, 2022	0
Expires, 2023	0
Expires, 2024	0
Total	30,000,000
Unused	30,000,000
Due within One Year	30,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,050,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 700,000,000

Financing - Narrative (Details)

Financing - Narrative (Details) $ in Millions	Mar. 31, 2021USD ($)
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	$ 1,400
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	854
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	550
Fixed rate pollution control revenue bonds outstanding	174
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	34
Fixed rate pollution control revenue bonds outstanding	$ 50

Financing - Schedule of Shares

Financing - Schedule of Shares Used to Compute Diluted Earnings Per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Disclosure [Abstract]
As reported shares (in shares)	1,060	1,057
Effect of stock-based compensation (in shares)	6	7
Effect of equity units (in shares)	0	3
Diluted shares (in shares)	1,066	1,067

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	8.40%	16.20%
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	(17.30%)	13.50%

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0
Pension Plans and Postretirement Plans
Service cost	109,000,000	$ 94,000,000
Interest cost	87,000,000	108,000,000
Expected return on plan assets	(298,000,000)	(275,000,000)
Amortization:
Prior service costs	0	1,000,000
Regulatory asset	0	0
Net (gain)/loss	78,000,000	67,000,000
Net periodic pension cost (income)	(24,000,000)	(5,000,000)
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	26,000,000	22,000,000
Interest cost	20,000,000	25,000,000
Expected return on plan assets	(72,000,000)	(66,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	21,000,000	18,000,000
Net periodic pension cost (income)	(5,000,000)	(1,000,000)
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	28,000,000	24,000,000
Interest cost	26,000,000	33,000,000
Expected return on plan assets	(94,000,000)	(87,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	25,000,000	22,000,000
Net periodic pension cost (income)	(15,000,000)	(8,000,000)
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	4,000,000
Interest cost	4,000,000	5,000,000
Expected return on plan assets	(14,000,000)	(13,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	4,000,000	3,000,000
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	2,000,000
Interest cost	1,000,000	1,000,000
Expected return on plan assets	(3,000,000)	(3,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	1,000,000	1,000,000
Net periodic pension cost (income)	1,000,000	1,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	9,000,000	8,000,000
Interest cost	6,000,000	8,000,000
Expected return on plan assets	(21,000,000)	(19,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000	4,000,000
Net (gain)/loss	3,000,000	2,000,000
Net periodic pension cost (income)	0	2,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	6,000,000	5,000,000
Interest cost	8,000,000	13,000,000
Expected return on plan assets	(19,000,000)	(18,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss	1,000,000	1,000,000
Net periodic pension cost (income)	(4,000,000)	1,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	2,000,000
Interest cost	2,000,000	3,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	(4,000,000)	(2,000,000)
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	1,000,000
Interest cost	3,000,000	5,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss	1,000,000	1,000,000
Net periodic pension cost (income)	(1,000,000)	0
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization:
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	0	0
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization:
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	0	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	2,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)
Amortization:
Regulatory asset	2,000,000	2,000,000
Net (gain)/loss	(1,000,000)	(1,000,000)
Net periodic pension cost (income)	$ 0	$ 1,000,000

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets:
Derivatives	$ 186	$ 281
Liabilities:
Derivatives	68	64
Collateral already posted, assets, aggregate fair value	27
ALABAMA POWER CO
Assets:
Derivatives	8	5
Liabilities:
Derivatives	0	0
GEORGIA POWER CO
Assets:
Derivatives	10	3
Investments in trusts	34
Liabilities:
Derivatives	1	1
MISSISSIPPI POWER CO
Assets:
Derivatives	6	2
Liabilities:
Derivatives	1	2
SOUTHERN POWER CO
Assets:
Derivatives	42	89
Liabilities:
Derivatives	23	26
SOUTHERN Co GAS
Assets:
Derivatives	110	162
Liabilities:
Derivatives	43	35
Collateral already posted, assets, aggregate fair value	27	$ 28
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	1,132
Other investments	42
Total	4,198
Liabilities:
Contingent consideration	16
Total	562
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	1,121
Other investments	9
Total	2,484
Liabilities:
Contingent consideration	0
Total	359
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	11
Other investments	33
Total	1,597
Liabilities:
Contingent consideration	0
Total	181
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	34
Liabilities:
Contingent consideration	16
Total	22
Fair Value, Measurements, Recurring | Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	83
Fair Value, Measurements, Recurring | Energy-related derivatives
Assets:
Derivatives	585
Liabilities:
Derivatives	523
Fair Value, Measurements, Recurring | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	372
Liabilities:
Derivatives	359
Fair Value, Measurements, Recurring | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	179
Liabilities:
Derivatives	158
Fair Value, Measurements, Recurring | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	34
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | Interest rate derivatives
Assets:
Derivatives	10
Fair Value, Measurements, Recurring | Interest rate derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Fair Value, Measurements, Recurring | Interest rate derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	10
Fair Value, Measurements, Recurring | Interest rate derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Fair Value, Measurements, Recurring | Foreign currency derivatives
Assets:
Derivatives	41
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Foreign currency derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	41
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | Foreign currency derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Domestic equity
Assets:
Investments in trusts	996
Fair Value, Measurements, Recurring | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	782
Fair Value, Measurements, Recurring | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	214
Fair Value, Measurements, Recurring | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Foreign equity
Assets:
Investments in trusts	342
Fair Value, Measurements, Recurring | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	145
Fair Value, Measurements, Recurring | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	197
Fair Value, Measurements, Recurring | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Investments in trusts	325
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	325
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Municipal bonds
Assets:
Investments in trusts	45
Fair Value, Measurements, Recurring | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	45
Fair Value, Measurements, Recurring | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Pooled funds – fixed income
Assets:
Investments in trusts	18
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	18
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Investments in trusts	441
Fair Value, Measurements, Recurring | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	436
Fair Value, Measurements, Recurring | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Investments in trusts	81
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	81
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity
Assets:
Investments in trusts	83
Fair Value, Measurements, Recurring | Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	83
Fair Value, Measurements, Recurring | Other
Assets:
Investments in trusts	57
Fair Value, Measurements, Recurring | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	50
Fair Value, Measurements, Recurring | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	7
Fair Value, Measurements, Recurring | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO
Assets:
Cash equivalents	412
Other investments	33
Total	1,667
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	401
Other investments	0
Total	1,026
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	11
Other investments	33
Total	558
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	83
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives
Assets:
Derivatives	12
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	12
Liabilities:
Derivatives	4
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity
Assets:
Investments in trusts	653
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	448
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	205
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity
Assets:
Investments in trusts	160
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	145
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	15
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities
Assets:
Investments in trusts	20
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	20
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds
Assets:
Investments in trusts	240
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	235
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities
Assets:
Investments in trusts	26
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	26
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity
Assets:
Investments in trusts	83
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	83
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other
Assets:
Investments in trusts	27
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	27
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO
Assets:
Total	1,166
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	357
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Total	809
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Total	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives
Assets:
Derivatives	17
Liabilities:
Derivatives	8
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	17
Liabilities:
Derivatives	8
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity
Assets:
Investments in trusts	335
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	334
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity
Assets:
Investments in trusts	179
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	179
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities
Assets:
Investments in trusts	305
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	305
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds
Assets:
Investments in trusts	44
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	44
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds
Assets:
Investments in trusts	201
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	201
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities
Assets:
Investments in trusts	55
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	55
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other
Assets:
Investments in trusts	30
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	23
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	7
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives
Assets:
Derivatives	11
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	11
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO
Assets:
Cash equivalents	115
Total	157
Liabilities:
Contingent consideration	16
Total	40
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	115
Total	115
Liabilities:
Contingent consideration	0
Total	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	42
Liabilities:
Contingent consideration	0
Total	24
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	0
Liabilities:
Contingent consideration	16
Total	16
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives
Assets:
Derivatives	1
Liabilities:
Derivatives	1
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	1
Liabilities:
Derivatives	1
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives
Assets:
Derivatives	41
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	41
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS
Assets:
Cash equivalents	284
Total	857
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	284
Total	656
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	167
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	34
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives
Assets:
Derivatives	544
Liabilities:
Derivatives	504
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	372
Liabilities:
Derivatives	359
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	138
Liabilities:
Derivatives	139
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	34
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity
Assets:
Non-qualified deferred compensation trusts	8
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	8
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity
Assets:
Non-qualified deferred compensation trusts	3
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	3
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income
Assets:
Non-qualified deferred compensation trusts	18
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	18
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Increase (Decrease) In Fair Value Of Funds (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 39	$ (247)
ALABAMA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	41	(167)
GEORGIA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ (2)	$ (80)

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Millions	Mar. 31, 2021USD ($)$ / MMBTU
ALABAMA POWER CO | Private equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value	$ 83
Unfunded commitments	68
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value of derivatives	$ 28
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives | Forward Price | Valuation, Market Approach | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Measurement input (usd per mmbtu) | $ / MMBTU	(0.07)
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives | Forward Price | Valuation, Market Approach | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Measurement input (usd per mmbtu) | $ / MMBTU	0.30

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Mar. 31, 2021USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 50,035
Fair value	54,113
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	8,866
Fair value	9,821
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	13,220
Fair value	14,291
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying amount	1,398
Fair value	1,507
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying amount	4,030
Fair value	4,347
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	6,588
Fair value	$ 7,264

Fair Value Measurements - Sch_4

Fair Value Measurements - Schedule of Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component (Details) - SOUTHERN Co GAS $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 28
Instruments realized or otherwise settled during period	(2)
Changes in fair value	2
Ending balance	$ 28

Derivatives - Schedule of Energ

Derivatives - Schedule of Energy-Related Derivatives (Details) - Energy-related, Natural Gas MMBTU in Millions	Mar. 31, 2021MMBTU
Energy-related derivative contracts
Net Purchased mmBtu	907
ALABAMA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	73
GEORGIA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	125
MISSISSIPPI POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	85
SOUTHERN POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	9
SOUTHERN Co GAS
Energy-related derivative contracts
Net Purchased mmBtu	615
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Long
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	4,400
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Short
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	3,800

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2021USD ($)MMBTU	Dec. 31, 2020USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	39
Cash flow hedge gain (loss) to be reclassified within twelve months | $	$ (25,000,000)
Collateral already posted, assets, aggregate fair value | $	$ 27,000,000
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	10
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	12
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	12
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ 2,000,000
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value | $	0
SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value | $	$ 27,000,000	$ 28,000,000

Derivatives - Schedule of Inter

Derivatives - Schedule of Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Derivative [Line Items]
Notional Amount	$ 1,560
Fair Value Gain (Loss) at March 31, 2021	10
MISSISSIPPI POWER CO | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 60
Weighted Average Interest Rate Paid	0.58%
Fair Value Gain (Loss) at March 31, 2021	$ 0
Southern Company parent | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Fair Value Gain (Loss) at March 31, 2021	$ 10
London Interbank Offered Rate (LIBOR) | Southern Company parent | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Weighted Average Interest Rate Paid	0.87%

Derivatives - Schedule of Forei

Derivatives - Schedule of Foreign Currency Derivatives (Details) - 3 months ended Mar. 31, 2021 - Cash Flow Hedges of Existing Debt - Foreign currency derivatives € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) at March 31, 2021	18
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, 2021	$ 9
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, 2021	$ 9

Derivatives - Schedule of Deriv

Derivatives - Schedule of Derivative Category and Balance Sheet Location (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	$ 636	$ 810
Derivative asset, Gross amounts offset	(450)	(529)
Derivative asset, net amounts recognized in the balance sheets	186	281
Derivative liability, gross amount recognized	545	621
Derivative liability, Gross amounts offset	(477)	(557)
Derivative liability, net amounts recognized in the balance sheets	68	64
Collateral already posted, assets, aggregate fair value	27
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	537	658
Derivative liability, gross amount recognized	502	563
Derivatives not designated as hedging instruments | Energy-related derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	265	388
Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	265	331
Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	272	270
Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	237	232
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	46	42
Derivative liability, gross amount recognized	19	30
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]
Derivative asset, gross amount recognized	30	24
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]
Derivative liability, gross amount recognized	4	11
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]
Derivative asset, gross amount recognized	16	18
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]
Derivative liability, gross amount recognized	15	19
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]
Derivative asset, gross amount recognized	53	110
Derivative liability, gross amount recognized	24	28
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]
Derivative asset, gross amount recognized	2	3
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]
Derivative liability, gross amount recognized	1	5
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	10	20
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]
Derivative liability, gross amount recognized	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	0	0
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]
Derivative liability, gross amount recognized	23	23
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]
Derivative asset, gross amount recognized	41	87
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]
Derivative liability, gross amount recognized	0	0
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	12	12
Derivative asset, Gross amounts offset	(4)	(7)
Derivative asset, net amounts recognized in the balance sheets	8	5
Derivative liability, gross amount recognized	4	7
Derivative liability, Gross amounts offset	(4)	(7)
Derivative liability, net amounts recognized in the balance sheets	0	0
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	12	12
Derivative liability, gross amount recognized	4	7
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]
Derivative asset, gross amount recognized	7	7
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]
Derivative liability, gross amount recognized	0	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]
Derivative asset, gross amount recognized	5	5
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]
Derivative liability, gross amount recognized	4	5
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	17	15
Derivative asset, Gross amounts offset	(7)	(12)
Derivative asset, net amounts recognized in the balance sheets	10	3
Derivative liability, gross amount recognized	8	13
Derivative liability, Gross amounts offset	(7)	(12)
Derivative liability, net amounts recognized in the balance sheets	1	1
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	17	15
Derivative liability, gross amount recognized	8	13
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]
Derivative asset, gross amount recognized	11	7
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]
Derivative liability, gross amount recognized	2	5
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]
Derivative asset, gross amount recognized	6	8
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]
Derivative liability, gross amount recognized	6	8
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	11	9
Derivative asset, Gross amounts offset	(5)	(7)
Derivative asset, net amounts recognized in the balance sheets	6	2
Derivative liability, gross amount recognized	6	9
Derivative liability, Gross amounts offset	(5)	(7)
Derivative liability, net amounts recognized in the balance sheets	1	2
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	11	9
Derivative liability, gross amount recognized	6	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]
Derivative asset, gross amount recognized	6	4
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]
Derivative liability, gross amount recognized	1	3
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]
Derivative asset, gross amount recognized	5	5
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]
Derivative liability, gross amount recognized	5	6
SOUTHERN POWER CO
Derivatives, Fair Value [Line Items]
Derivative asset, net amounts recognized in the balance sheets	42	89
Derivative liability, net amounts recognized in the balance sheets	23	26
SOUTHERN POWER CO | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	0	0
Derivative liability, gross amount recognized	0	1
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	0	0
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	0	1
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]
Derivative asset, gross amount recognized	42	89
Derivative liability, gross amount recognized	23	25
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]
Derivative asset, gross amount recognized	1	2
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]
Derivative liability, gross amount recognized	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 | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	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]
Derivative liability, gross amount recognized	23	23
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	41	87
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]
Derivative liability, gross amount recognized	0	0
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	544	665
Derivative asset, Gross amounts offset	(434)	(503)
Derivative asset, net amounts recognized in the balance sheets	110	162
Derivative liability, gross amount recognized	504	566
Derivative liability, Gross amounts offset	(461)	(531)
Derivative liability, net amounts recognized in the balance sheets	43	35
Collateral already posted, assets, aggregate fair value	27	28
SOUTHERN Co GAS | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	537	658
Derivative liability, gross amount recognized	502	562
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	265	388
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	265	330
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	272	270
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	237	232
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivative asset, gross amount recognized	6	6
Derivative liability, gross amount recognized	1	1
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]
Derivative asset, gross amount recognized	6	6
SOUTHERN Co GAS | 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]
Derivative liability, gross amount recognized	1	1
SOUTHERN Co GAS | 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]
Derivative asset, gross amount recognized	1	1
Derivative liability, gross amount recognized	1	3
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]
Derivative asset, gross amount recognized	1	1
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 | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross amount recognized	$ 1	$ 3

Derivatives - Schedule of Pre-t

Derivatives - Schedule of Pre-tax Effects of Unrealized Derivative Gains (Losses) (Details) - Energy-related derivatives - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	$ 25	$ 12
Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(2)	(2)
Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	24	12
Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	3	2
ALABAMA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	8	6
ALABAMA POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	0	0
ALABAMA POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	7	5
ALABAMA POWER CO | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1	1
GEORGIA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	9	2
GEORGIA POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)	(1)
GEORGIA POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	9	2
GEORGIA POWER CO | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1	1
MISSISSIPPI POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	5	0
MISSISSIPPI POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)	(1)
MISSISSIPPI POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	5	1
MISSISSIPPI POWER CO | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1	0
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	3	4
SOUTHERN Co GAS | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	0	0
SOUTHERN Co GAS | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	3	4
SOUTHERN Co GAS | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	$ 0	$ 0

Derivatives - Schedule of Pre_2

Derivatives - Schedule of Pre-Tax Effects of Cash Flow Hedging on AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (39)	$ (113)
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	5	(4)
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	3	(26)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(47)	(83)
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(43)	(83)
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	4	0
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(47)	(83)
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	1	(27)
SOUTHERN Co GAS | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	1	(4)
SOUTHERN Co GAS | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 0	$ (23)

Derivatives - Schedule of Pre_3

Derivatives - Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Total cost of sales	$ 583	$ 439
Depreciation and amortization	871	857
Total interest expense, net of amounts capitalized	(450)	(456)
Total other income (expense), net	58	103
Cash Flow Hedging | Energy-related derivatives | Cost of Sales
Derivative [Line Items]
Gain (loss) on hedges	(3)	(7)
Cash Flow Hedging | Energy-related derivatives | Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)
Cash Flow Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(7)	(6)
Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)
Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	(60)	(31)
Fair Value Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(10)	29
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	119	117
Total interest expense, net of amounts capitalized	(38)	(39)
Total other income (expense), net	7	2
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives | Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	$ (60)	$ (31)

Derivatives - Schedule of Cumul

Derivatives - Schedule of Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - Securities due within one year - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (1,505)	$ (1,509)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ (5)	$ (10)

Derivatives - Schedule of Pre_4

Derivatives - Schedule of Pre-tax Effect of Interest Rate and Energy Related Derivatives on Income (Details) - Derivatives not designated as hedging instruments - Energy-related derivatives - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ (10)	$ 77
Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	(17)	70
Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 7	$ 7

Acquisitions and Dispositions -

Acquisitions and Dispositions - Schedule of Assets Held for Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets Held for Sale:
Total property, plant, and equipment	$ 7	$ 8
Leveraged leases	52	52
Total Assets Held for Sale	$ 59	$ 60

Acquisitions and Dispositions_2

Acquisitions and Dispositions - Schedule of Asset Acquisition (Details) - SOUTHERN POWER CO - Deuel Harvest $ in Millions	Mar. 30, 2021USD ($)	Feb. 28, 2021MW
Business Acquisition [Line Items]
Approximate nameplate capacity (in MWs) | MW		300
Proceeds from tax equity transaction | $	$ 220
Maximum
Business Acquisition [Line Items]
PPA Contract Period		25 years
Minimum
Business Acquisition [Line Items]
PPA Contract Period		15 years
Deuel Harvest
Business Acquisition [Line Items]
Ownership percentage by parent		100.00%

Acquisitions and Dispositions_3

Acquisitions and Dispositions - Southern Power Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Construction work in progress	$ 9,525		$ 8,697
Gain on equipment contribution	44	$ 39
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress	219		$ 127
Gain on equipment contribution	39	$ 39
SOUTHERN POWER CO | Series of Construction Projects
Business Acquisition [Line Items]
Construction work in progress	158
SOUTHERN POWER CO | Series of Construction Projects | Minimum
Business Acquisition [Line Items]
Estimated future construction payments	392
SOUTHERN POWER CO | Series of Construction Projects | Maximum
Business Acquisition [Line Items]
Estimated future construction payments	$ 460

Acquisitions and Dispositions_4

Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2021
Garland Solar Storage | Garland Solar Storage | Class B Membership Interest
Business Acquisition [Line Items]
Noncontrolling interest, ownership by parent, percentage sold	100.00%
Tranquillity Solar Storage | Tranquillity Solar Storage | Class B Membership Interest
Business Acquisition [Line Items]
Noncontrolling interest, ownership by parent, percentage sold	100.00%
Glass Sands | Glass Sands
Business Acquisition [Line Items]
Ownership percentage by parent	100.00%
Scenario, Forecast | Garland Solar Storage
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		88
PPA Contract Period		20 years
Scenario, Forecast | Tranquillity Solar Storage
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		72
PPA Contract Period		20 years
Scenario, Forecast | Glass Sands
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		118
PPA Contract Period		12 years

Acquisitions and Dispositions_5

Acquisitions and Dispositions - Southern Company Gas Narrative (Details) - SOUTHERN Co GAS - Disposal Group, Disposed of by Sale $ in Millions	Aug. 31, 2021USD ($)	Apr. 28, 2021USD ($)	Apr. 22, 2021USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020payment
Pivotal LNG
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of contingent milestone payments | payment					2
Sequent
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net book value excluding working capital				$ 46
Guarantor obligations, current carrying value				279
Guarantor obligations				$ 1,000
Sequent | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price		$ 50
Scenario, Forecast | Pivotal LNG
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contingent milestone payment, amount	$ 5		$ 5

Segment and Related Informati_3

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)segmentstate	Mar. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	3
Operating revenues	$ 6,900	$ 5,291
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	296	252
SOUTHERN POWER CO | Traditional Electric Operating Companies | Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Operating revenues	$ 81	86
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4
Operating revenues	$ 2,976	1,565
Number of reportable segments | segment	4
SOUTHERN Co GAS | SOUTHERN POWER CO | Natural gas
Segment Reporting Information [Line Items]
Operating revenues	$ 12	$ 10
Southern Natural Gas Company, LLC | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
PennEast Pipelines | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	20.00%
Dalton Pipeline | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
Atlantic Coast Pipeline | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	5.00%

Segment and Related Informati_4

Segment and Related Information - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 5,910	$ 5,018
Segment net income (loss)	1,135	868
Goodwill	5,280		$ 5,280
Total assets	125,393		122,935
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Gain on sale	41	38
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	440	375
Segment net income (loss)	97	75
Total assets	13,995		13,235
Gain on sale	39	39
SOUTHERN POWER CO | Wind Generating Facility
Segment Reporting Information [Line Items]
Gain on sale	37
Gain on sale, net of tax	28
SOUTHERN POWER CO | Disposal Group, Disposed of by Sale | Plant Mankato
Segment Reporting Information [Line Items]
Gain on sale		39
Gain on sale, net of tax		23
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,694	1,249
Segment net income (loss)	398	275
Goodwill	5,015		5,015
Total assets	23,377		22,630
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues	1,970	1,825
Total assets	47,349		47,080
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	36
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,117	3,695
Segment net income (loss)	853	717
Goodwill	2		2
Total assets	99,411		98,041
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,694	1,249
Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	4,034		4,034
Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	298	51
Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	981		981
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,701	1,256
Segment net income (loss)	394	274
Total assets	24,249		23,040
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	3,764	3,407
Segment net income (loss)	756	642
Goodwill	0		0
Total assets	86,053		85,486
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	440	375
Segment net income (loss)	97	75
Goodwill	2		2
Total assets	13,995		13,235
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,694	1,249
Segment net income (loss)	398	275
Goodwill	5,015		5,015
Total assets	23,377		22,630
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	134	114
Segment net income (loss)	(108)	(121)
Goodwill	263		263
Total assets	3,392		3,168
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	7	8
Segment net income (loss)	4	1
Total assets	11,477		11,336
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,200	1,020
Segment net income (loss)	183	164
Total assets	20,161		19,090
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	8	8
Segment net income (loss)	29	30
Total assets	1,596		1,597
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	298	51
Segment net income (loss)	126	23
Total assets	939		850
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	195	177
Segment net income (loss)	56	57
Total assets	1,553		1,503
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(35)	(40)
Segment net income (loss)	(8)	(3)
Goodwill	0		0
Total assets	(787)		(904)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(14)	(15)
Segment net income (loss)	0	0
Total assets	(12,349)		(11,746)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(87)	(87)
Segment net income (loss)	0	$ 0
Goodwill	0		0
Total assets	$ (637)		$ (680)

Segment and Related Informati_5

Segment and Related Information - Schedule of Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Concentration Risk [Line Items]
Operating revenues	$ 5,910	$ 5,018
Less Gross Gas Costs	583	439
Retail
Concentration Risk [Line Items]
Operating revenues	3,342	3,078
Wholesale
Concentration Risk [Line Items]
Operating revenues	545	418
Other
Concentration Risk [Line Items]
Operating revenues	170	151
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues	4,117	3,695
Electric Utilities' Revenues | Retail
Concentration Risk [Line Items]
Operating revenues	3,342	3,078
Electric Utilities' Revenues | Wholesale
Concentration Risk [Line Items]
Operating revenues	545	418
Electric Utilities' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	230	199
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	1,694	1,249
Southern Company Gas' Revenues | Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	1,192	1,013
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	298	51
Southern Company Gas' Revenues | Gas marketing services
Concentration Risk [Line Items]
Operating revenues	195	177
Southern Company Gas' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	9	8
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	1,694	1,249
Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	298	51
Less Gross Gas Costs	2,353	1,163
Third Party Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	2,588	1,185
Intercompany Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	63	29
Total Gross Revenues | Southern Company Gas' Revenues | Wholesale Gas Services
Concentration Risk [Line Items]
Operating revenues	$ 2,651	$ 1,214