Mississippi Power (MSPWP) 10-K 18 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 54.8
Entity Common Stock, Shares Outstanding (in shares)		1,056,609,660
Documents Incorporated by Reference	Documents incorporated by reference: specified portions of The Southern Company's Definitive Proxy Statement on Schedule 14A relating to the 2021 Annual Meeting of Stockholders are incorporated by reference into PART III. In addition, specified portions of Alabama Power Company's Definitive Proxy Statement on Schedule 14A relating to its 2021 Annual Meeting of Shareholders are incorporated by reference into PART III. Each of Georgia Power Company, Mississippi Power Company, Southern Power Company, and Southern Company Gas meets the conditions set forth in General Instructions I(1)(a) and (b) of Form 10-K and is therefore filing this Form 10-K with the reduced disclosure format specified in General Instructions I(2)(b), (c), and (d) of Form 10-K. This combined Form 10-K is separately filed by The Southern Company, Alabama Power Company, Georgia Power Company, Mississippi Power Company, Southern Power Company, and Southern Company Gas. Information contained herein relating to any individual registrant is filed by such registrant on its own behalf. Each registrant makes no representation as to information relating to the other registrants.
Entity Central Index Key	0000092122
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
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
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		30,537,500
Entity Central Index Key	0000003153
Alabama Power | 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
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.20% Series
Document Information [Line Items]
Title of 12(g) Security	4.20% Series
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.52% Series
Document Information [Line Items]
Title of 12(g) Security	4.52% Series
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.60% Series
Document Information [Line Items]
Title of 12(g) Security	4.60% Series
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.64% Series
Document Information [Line Items]
Title of 12(g) Security	4.64% Series
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.72% Series
Document Information [Line Items]
Title of 12(g) Security	4.72% Series
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.92% Series
Document Information [Line Items]
Title of 12(g) Security	4.92% Series
Georgia Power
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		9,261,500
Entity Central Index Key	0000041091
Georgia Power | 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
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,121,000
Entity Central Index Key	0000066904
Southern Power
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,000
Entity Central Index Key	0001160661
Southern Power | 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 | 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 Company 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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		100
Entity Central Index Key	0001004155

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues:
Total operating revenues	$ 20,375	$ 21,419	$ 23,495
Operating Expenses:
Other operations and maintenance	5,413	5,624	5,926
Depreciation and amortization	3,518	3,038	3,131
Taxes other than income taxes	1,234	1,230	1,315
Estimated loss on Plant Vogtle Units 3 and 4	325	0	1,060
Impairment charges	0	168	210
(Gain) loss on dispositions, net	(65)	(2,569)	(291)
Total operating expenses	15,490	13,683	19,304
Operating Income	4,885	7,736	4,191
Other Income and (Expense):
Allowance for equity funds used during construction	149	128	138
Earnings from equity method investments	153	162	148
Interest expense, net of amounts capitalized	(1,821)	(1,736)	(1,842)
Impairment of leveraged leases	(206)	0	0
Other income (expense), net	336	252	114
Total other income and (expense)	(1,389)	(1,194)	(1,442)
Earnings Before Income Taxes	3,496	6,542	2,749
Income taxes (benefit)	393	1,798	449
Net Income	3,103	4,744	2,300
Dividends on preferred stock of subsidiaries	15	15	16
Net income (loss) attributable to noncontrolling interests	(31)	(10)	58
Consolidated Net Income	$ 3,119	$ 4,739	$ 2,226
Earnings per share —
Basic (in dollars per share)	$ 2.95	$ 4.53	$ 2.18
Diluted (in dollars per share)	$ 2.93	$ 4.50	$ 2.17
Average number of shares of common stock outstanding — (in millions)
Basic (in shares)	1,058	1,046	1,020
Diluted (in shares)	1,065	1,054	1,025
Retail electric revenues
Operating Revenues:
Total operating revenues	$ 13,643	$ 14,084	$ 15,222
Wholesale revenues
Operating Revenues:
Total operating revenues	1,945	2,152	2,516
Other electric revenues
Operating Revenues:
Total operating revenues	672	636	664
Natural gas
Operating Revenues:
Total operating revenues	3,434	3,792	3,854
Operating Expenses:
Cost of sales	972	1,319	1,539
Other revenues
Operating Revenues:
Total operating revenues	681	755	1,239
Operating Expenses:
Cost of sales	327	435	806
Fuel
Operating Expenses:
Cost of sales	2,967	3,622	4,637
Purchased power
Operating Expenses:
Cost of sales	799	816	971
Alabama Power
Operating Revenues:
Total operating revenues	5,830	6,125	6,032
Operating Expenses:
Other operations and maintenance	1,619	1,821	1,669
Depreciation and amortization	812	793	764
Taxes other than income taxes	416	403	389
Total operating expenses	4,136	4,532	4,555
Operating Income	1,694	1,593	1,477
Other Income and (Expense):
Allowance for equity funds used during construction	46	52	62
Interest expense, net of amounts capitalized	(338)	(336)	(323)
Other income (expense), net	100	46	20
Total other income and (expense)	(192)	(238)	(241)
Earnings Before Income Taxes	1,502	1,355	1,236
Income taxes (benefit)	337	270	291
Net Income	1,165	1,085	945
Dividends on preferred stock of subsidiaries	15	15	15
Consolidated Net Income	1,150	1,070	930
Alabama Power | Retail electric revenues
Operating Revenues:
Total operating revenues	5,213	5,501	5,367
Alabama Power | Wholesale revenues
Operating Revenues:
Total operating revenues	269	258	279
Alabama Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	46	81	119
Alabama Power | Other revenues
Operating Revenues:
Total operating revenues	302	285	267
Alabama Power | Fuel
Operating Expenses:
Cost of sales	970	1,112	1,301
Alabama Power | Purchased power
Operating Expenses:
Cost of sales	191	203	216
Alabama Power | Purchased power, affiliates
Operating Expenses:
Cost of sales	128	200	216
Georgia Power
Operating Revenues:
Total operating revenues	8,309	8,408	8,420
Operating Expenses:
Other operations and maintenance	1,953	1,972	1,860
Depreciation and amortization	1,425	981	923
Taxes other than income taxes	444	454	437
Estimated loss on Plant Vogtle Units 3 and 4	325	0	1,060
Total operating expenses	6,337	5,947	7,131
Operating Income	1,972	2,461	1,289
Other Income and (Expense):
Allowance for equity funds used during construction	91	68	69
Interest expense, net of amounts capitalized	(425)	(409)	(397)
Other income (expense), net	180	140	115
Total other income and (expense)	(245)	(269)	(282)
Earnings Before Income Taxes	1,727	2,192	1,007
Income taxes (benefit)	152	472	214
Net Income	1,575	1,720	793
Georgia Power | Retail electric revenues
Operating Revenues:
Total operating revenues	7,609	7,707	7,752
Georgia Power | Wholesale revenues
Operating Revenues:
Total operating revenues	115	140	187
Georgia Power | Other revenues
Operating Revenues:
Total operating revenues	585	561	481
Georgia Power | Fuel
Operating Expenses:
Cost of sales	1,141	1,444	1,698
Georgia Power | Purchased power
Operating Expenses:
Cost of sales	540	521	430
Georgia Power | Purchased power, affiliates
Operating Expenses:
Cost of sales	509	575	723
Mississippi Power
Operating Revenues:
Total operating revenues	1,172	1,264	1,265
Operating Expenses:
Other operations and maintenance	284	307	350
Depreciation and amortization	183	192	169
Taxes other than income taxes	124	113	107
Total operating expenses	963	1,039	1,072
Operating Income	209	225	193
Other Income and (Expense):
Interest expense, net of amounts capitalized	(60)	(69)	(76)
Other income (expense), net	17	13	17
Total other income and (expense)	(43)	(56)	(59)
Earnings Before Income Taxes	166	169	134
Income taxes (benefit)	14	30	(102)
Net Income	152	139	236
Dividends on preferred stock of subsidiaries	0	0	1
Consolidated Net Income	152	139	235
Mississippi Power | Retail electric revenues
Operating Revenues:
Total operating revenues	821	877	889
Mississippi Power | Wholesale revenues
Operating Revenues:
Total operating revenues	215	237	263
Mississippi Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	111	132	91
Mississippi Power | Other revenues
Operating Revenues:
Total operating revenues	25	18	22
Mississippi Power | Fuel
Operating Expenses:
Cost of sales	350	407	405
Mississippi Power | Purchased power
Operating Expenses:
Cost of sales	22	20	41
Southern Power
Operating Revenues:
Total operating revenues	1,733	1,938	2,205
Operating Expenses:
Other operations and maintenance	353	359	395
Depreciation and amortization	494	479	493
Taxes other than income taxes	39	40	46
Impairment charges	0	3	156
(Gain) loss on dispositions, net	(39)	(23)	(2)
Total operating expenses	1,391	1,543	1,963
Operating Income	342	395	242
Other Income and (Expense):
Interest expense, net of amounts capitalized	(151)	(169)	(183)
Other income (expense), net	19	47	23
Total other income and (expense)	(132)	(122)	(160)
Earnings Before Income Taxes	210	273	82
Income taxes (benefit)	3	(56)	(164)
Net Income	207	329	246
Net income (loss) attributable to noncontrolling interests	(31)	(10)	59
Consolidated Net Income	238	339	187
Southern Power | Wholesale revenues
Operating Revenues:
Total operating revenues	1,355	1,528	1,757
Southern Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	364	398	435
Southern Power | Other revenues
Operating Revenues:
Total operating revenues	14	12	13
Southern Power | Fuel
Operating Expenses:
Cost of sales	470	577	699
Southern Power | Purchased power
Operating Expenses:
Cost of sales	74	108	176
Southern Company Gas
Operating Revenues:
Total operating revenues	3,434	3,792	3,909
Operating Expenses:
Other operations and maintenance	966	888	981
Depreciation and amortization	500	487	500
Taxes other than income taxes	206	213	211
Impairment charges	0	115	42
(Gain) loss on dispositions, net	(22)	0	(291)
Total operating expenses	2,622	3,022	2,994
Operating Income	812	770	915
Other Income and (Expense):
Earnings from equity method investments	141	157	148
Interest expense, net of amounts capitalized	(231)	(232)	(228)
Other income (expense), net	41	20	1
Total other income and (expense)	(49)	(55)	(79)
Earnings Before Income Taxes	763	715	836
Income taxes (benefit)	173	130	464
Net Income	590	585	372
Consolidated Net Income	590	585	372
Southern Company Gas | Natural gas
Operating Revenues:
Total operating revenues	3,431	3,793	3,874
Operating Expenses:
Cost of sales	972	1,319	1,539
Southern Company Gas | Other revenues
Operating Revenues:
Total operating revenues	0	0	55
Operating Expenses:
Cost of sales	0	0	12
Southern Company Gas | Alternative revenue programs
Operating Revenues:
Total operating revenues	$ 3	$ (1)	$ (20)

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Southern Company Gas
Excise taxes collected	$ 107	$ 117	$ 114

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Income	$ 3,103	$ 4,744	$ 2,300
Qualifying hedges:
Changes in fair value, net of tax	10	(115)	(47)
Reclassification adjustment for amounts included in net income, net of tax	(40)	57	72
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(55)	(64)	(5)
Reclassification adjustment for amounts included in net income, net of tax	10	4	6
Total other comprehensive income (loss)	(75)	(118)	26
Dividends on preferred stock of subsidiaries	15	15	16
Comprehensive income (loss) attributable to noncontrolling interests	(31)	(10)	58
Comprehensive Income (Loss) Attributable to Parent	3,044	4,621	2,252
Alabama Power
Net Income	1,165	1,085	945
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	4	4	4
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	4	4	4
Dividends on preferred stock of subsidiaries	15	15	15
Comprehensive Income (Loss) Attributable to Parent	1,169	1,089	949
Georgia Power
Net Income	1,575	1,720	793
Qualifying hedges:
Changes in fair value, net of tax	(2)	(44)	0
Reclassification adjustment for amounts included in net income, net of tax	6	2	3
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	4	(42)	3
Comprehensive Income (Loss) Attributable to Parent	1,579	1,678	796
Mississippi Power
Net Income	152	139	236
Qualifying hedges:
Changes in fair value, net of tax	0	0	(1)
Reclassification adjustment for amounts included in net income, net of tax	1	1	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1	0
Dividends on preferred stock of subsidiaries	0	0	1
Comprehensive Income (Loss) Attributable to Parent	153	140	236
Southern Power
Net Income	207	329	246
Qualifying hedges:
Changes in fair value, net of tax	33	(66)	(51)
Reclassification adjustment for amounts included in net income, net of tax	(65)	41	58
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(12)	(17)	5
Reclassification adjustment for amounts included in net income, net of tax	2	0	2
Total other comprehensive income (loss)	(42)	(42)	14
Comprehensive income (loss) attributable to noncontrolling interests	(31)	(10)	59
Comprehensive Income (Loss) Attributable to Parent	196	297	201
Southern Company Gas
Net Income	590	585	372
Qualifying hedges:
Changes in fair value, net of tax	(21)	(5)	5
Reclassification adjustment for amounts included in net income, net of tax	7	2	(1)
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(15)	(16)	0
Reclassification adjustment for amounts included in net income, net of tax	0	0	(2)
Total other comprehensive income (loss)	(29)	(19)	2
Comprehensive Income (Loss) Attributable to Parent	$ 561	$ 566	$ 374

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Qualifying hedges, change in fair value, tax	$ 3	$ (39)	$ (16)
Qualifying hedges, reclassification adjustment, tax	(13)	19	(24)
Pension and other postretirement benefit plans, gain (loss), tax	(17)	(31)	(2)
Reclassification adjustment for amounts included in net income, tax	3	1	5
Alabama Power
Qualifying hedges, reclassification adjustment, tax	2	2	2
Georgia Power
Qualifying hedges, change in fair value, tax	(1)	(15)	0
Qualifying hedges, reclassification adjustment, tax	2	1	1
Mississippi Power
Qualifying hedges, change in fair value, tax	0	0	(1)
Qualifying hedges, reclassification adjustment, tax	0	0	0
Southern Power
Qualifying hedges, change in fair value, tax	12	(22)	(17)
Qualifying hedges, reclassification adjustment, tax	(22)	14	19
Pension and other postretirement benefit plans, gain (loss), tax	(4)	(6)	2
Reclassification adjustment for amounts included in net income, tax	1	0	0
Southern Company Gas
Qualifying hedges, change in fair value, tax	(8)	(2)	2
Qualifying hedges, reclassification adjustment, tax	3	0	(1)
Pension and other postretirement benefit plans, gain (loss), tax	(3)	(14)	0
Reclassification adjustment for amounts included in net income, tax	$ 0	$ 0	$ 3

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Consolidated net income	$ 3,103,000	$ 4,744,000	$ 2,300,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	3,905,000	3,331,000	3,549,000
Deferred income taxes	(241,000)	611,000	89,000
Utilization of federal investment tax credits	341,000	757,000	5,000
Amortization of investment tax credits	(84,000)	(181,000)	(87,000)
Allowance for equity funds used during construction	(149,000)	(128,000)	(138,000)
Pension, postretirement, and other employee benefits	(259,000)	(204,000)	(103,000)
Pension and postretirement funding	(2,000)	(1,136,000)	(4,000)
Settlement of asset retirement obligations	(442,000)	(328,000)	(244,000)
Storm damage accruals	325,000	168,000	74,000
Stock based compensation expense	113,000	107,000	125,000
Estimated loss on Plant Vogtle Units 3 and 4	325,000	0	1,060,000
Impairment charges	206,000	168,000	210,000
Impairment charges	0	168,000	210,000
(Gain) loss on dispositions, net	(66,000)	(2,588,000)	(301,000)
Other, net	(74,000)	115,000	47,000
Changes in certain current assets and liabilities —
-Receivables	(222,000)	630,000	(426,000)
-Fossil fuel for generation	(29,000)	(120,000)	123,000
-Materials and supplies	(157,000)	(17,000)	(176,000)
-Other current assets	(132,000)	132,000	98,000
-Accounts payable	(27,000)	(693,000)	291,000
-Accrued taxes	242,000	117,000	267,000
-Retail fuel cost over recovery	96,000	62,000	36,000
-Customer refunds	(236,000)	126,000	67,000
-Other current liabilities	76,000	(73,000)	(4,000)
Net cash provided from operating activities	6,696,000	5,781,000	6,945,000
Investing Activities:
Business acquisitions, net of cash acquired	(81,000)	(50,000)	(65,000)
Property additions	(7,441,000)	(7,555,000)	(8,001,000)
Nuclear decommissioning trust fund purchases	(877,000)	(888,000)	(1,117,000)
Nuclear decommissioning trust fund sales	871,000	882,000	1,111,000
Proceeds from dispositions and asset sales	1,049,000	5,122,000	2,956,000
Cost of removal, net of salvage	(361,000)	(393,000)	(388,000)
Change in construction payables, net	37,000	(169,000)	50,000
Investments in unconsolidated subsidiaries	(80,000)	(148,000)	(114,000)
Payments pursuant to LTSAs	(211,000)	(234,000)	(186,000)
Other investing activities	64,000	41,000	(6,000)
Net cash used for investing activities	(7,030,000)	(3,392,000)	(5,760,000)
Financing Activities:
Increase (decrease) in notes payable, net		640,000
Increase (decrease) in notes payable, net	(1,096,000)		(774,000)
Proceeds —
Long-term debt	8,047,000	5,220,000	2,478,000
Common stock	74,000	844,000	1,090,000
Short-term borrowings	615,000	350,000	3,150,000
Redemptions and repurchases —
Long-term debt	(4,458,000)	(4,347,000)	(5,533,000)
Preferred and preference stock	0	0	(33,000)
Short-term borrowings	(840,000)	(1,850,000)	(1,900,000)
Distributions to noncontrolling interests	(271,000)	(256,000)	(153,000)
Capital contributions from noncontrolling interests	363,000	196,000	2,551,000
Payment of common stock dividends	(2,685,000)	(2,570,000)	(2,425,000)
Other financing activities	(325,000)	(157,000)	(264,000)
Net cash used for financing activities	(576,000)	(1,930,000)	(1,813,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(910,000)	459,000	(628,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	1,978,000	1,519,000	2,147,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	1,068,000	1,978,000	1,519,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	1,683,000	1,651,000	1,794,000
Income taxes (net of refunds)	64,000	276,000	172,000
Noncash transactions —
Accrued property additions at year-end	989,000	932,000	1,103,000
Alabama Power
Operating Activities:
Consolidated net income	1,165,000	1,085,000	945,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	963,000	951,000	917,000
Deferred income taxes	78,000	197,000	174,000
Allowance for equity funds used during construction	(46,000)	(52,000)	(62,000)
Pension and postretirement funding	(2,000)	(362,000)	(4,000)
Settlement of asset retirement obligations	(219,000)	(127,000)	(55,000)
Natural disaster reserve accruals	112,000	138,000	16,000
Other deferred charges – affiliated	0	(42,000)	0
Other, net	(38,000)	(91,000)	(17,000)
Changes in certain current assets and liabilities —
-Receivables	(49,000)	9,000	(149,000)
-Materials and supplies	(47,000)	23,000	(82,000)
-Other current assets	(66,000)	(89,000)	28,000
-Accounts payable	(90,000)	(41,000)	24,000
-Accrued taxes	84,000	49,000	10,000
-Retail fuel cost over recovery	(31,000)	47,000	0
-Customer refunds	(12,000)	30,000	114,000
-Other current liabilities	(28,000)	68,000	14,000
-Accrued compensation	(32,000)	(14,000)	8,000
Net cash provided from operating activities	1,742,000	1,779,000	1,881,000
Investing Activities:
Property additions	(1,970,000)	(1,757,000)	(2,158,000)
Nuclear decommissioning trust fund purchases	(268,000)	(261,000)	(279,000)
Nuclear decommissioning trust fund sales	267,000	260,000	278,000
Cost of removal, net of salvage	(98,000)	(103,000)	(130,000)
Change in construction payables, net	(34,000)	(71,000)	26,000
Other investing activities	(19,000)	(31,000)	(26,000)
Net cash used for investing activities	(2,122,000)	(1,963,000)	(2,289,000)
Proceeds —
Senior notes	600,000	600,000	500,000
Pollution control revenue bonds	87,000	0	120,000
Capital contributions from parent company	653,000	1,240,000	511,000
Redemptions and repurchases —
Senior notes	(250,000)	(200,000)	0
Pollution control revenue bonds	(87,000)	0	(120,000)
Payment of common stock dividends	(957,000)	(844,000)	(801,000)
Other financing activities	(30,000)	(31,000)	(33,000)
Net cash used for financing activities	16,000	765,000	177,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(364,000)	581,000	(231,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	894,000	313,000	544,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	530,000	894,000	313,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	321,000	311,000	284,000
Income taxes (net of refunds)	187,000	26,000	106,000
Noncash transactions —
Accrued property additions at year-end	166,000	200,000	272,000
Georgia Power
Operating Activities:
Consolidated net income	1,575,000	1,720,000	793,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	1,607,000	1,193,000	1,142,000
Deferred income taxes	(273,000)	179,000	(260,000)
Allowance for equity funds used during construction	(91,000)	(68,000)	(69,000)
Pension, postretirement, and other employee benefits	(137,000)	(146,000)	(75,000)
Pension and postretirement funding	0	(200,000)	0
Settlement of asset retirement obligations	(185,000)	(151,000)	(116,000)
Retail fuel cost over recovery – long-term	(73,000)	73,000	0
Storm damage accruals	213,000	30,000	30,000
Other deferred charges – affiliated	0	(108,000)	0
Estimated loss on Plant Vogtle Units 3 and 4	325,000	0	1,060,000
Other, net	14,000	50,000	18,000
Changes in certain current assets and liabilities —
-Receivables	(114,000)	177,000	8,000
-Fossil fuel for generation	(6,000)	(41,000)	83,000
-Materials and supplies	(91,000)	(4,000)	(19,000)
-Other current assets	(48,000)	(15,000)	(24,000)
-Accounts payable	59,000	(92,000)	95,000
-Accrued taxes	55,000	58,000	58,000
-Retail fuel cost over recovery	113,000	0	0
-Customer refunds	(223,000)	116,000	(69,000)
-Other current liabilities	64,000	34,000	(38,000)
-Prepaid income taxes	0	102,000	152,000
Net cash provided from operating activities	2,784,000	2,907,000	2,769,000
Investing Activities:
Property additions	(3,445,000)	(3,510,000)	(3,116,000)
Nuclear decommissioning trust fund purchases	(609,000)	(628,000)	(839,000)
Nuclear decommissioning trust fund sales	604,000	622,000	833,000
Cost of removal, net of salvage	(143,000)	(186,000)	(107,000)
Payments pursuant to LTSAs	(86,000)	(81,000)	(54,000)
Change in construction payables, net of joint owner portion	16,000	(122,000)	68,000
Proceeds from dispositions and asset sales	153,000	14,000	138,000
Other investing activities	7,000	6,000	(32,000)
Net cash used for investing activities	(3,503,000)	(3,885,000)	(3,109,000)
Financing Activities:
Increase (decrease) in notes payable, net			294,000
Increase (decrease) in notes payable, net	(55,000)	(179,000)
Proceeds —
FFB loan	848,000	1,218,000	0
Short-term borrowings	250,000	250,000	0
Senior notes	1,500,000	750,000	0
Pollution control revenue bonds	53,000	584,000	108,000
Capital contributions from parent company	1,392,000	634,000	2,985,000
Redemptions and repurchases —
FFB loan	(73,000)	0	0
Short-term borrowings	(375,000)	0	(150,000)
Senior notes	(950,000)	(500,000)	(1,500,000)
Pollution control revenue bonds	(336,000)	(223,000)	(469,000)
Other long-term debt	0	0	(100,000)
Payment of common stock dividends	(1,542,000)	(1,576,000)	(1,396,000)
Premiums on redemption and repurchases of senior notes	0	0	(152,000)
Other financing activities	(36,000)	(40,000)	(20,000)
Net cash used for financing activities	676,000	918,000	(400,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(43,000)	(60,000)	(740,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	52,000	112,000	852,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	9,000	52,000	112,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	380,000	373,000	408,000
Income taxes (net of refunds)	373,000	110,000	300,000
Noncash transactions —
Accrued property additions at year-end	553,000	560,000	683,000
Mississippi Power
Operating Activities:
Consolidated net income	152,000	139,000	236,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	191,000	197,000	177,000
Deferred income taxes	(4,000)	37,000	475,000
Pension and postretirement funding	0	(54,000)	0
Settlement of asset retirement obligations	(22,000)	(35,000)	(35,000)
Other, net	(1,000)	35,000	51,000
Changes in certain current assets and liabilities —
-Receivables	(7,000)	6,000	(19,000)
-Other current assets	(28,000)	(8,000)	(10,000)
-Accounts payable	20,000	3,000	15,000
-Accrued taxes	10,000	11,000	(46,000)
-Other current liabilities	(15,000)	(20,000)	(42,000)
-Prepaid income taxes	(3,000)	12,000	(12,000)
-Over recovered regulatory clause revenues	5,000	16,000	14,000
Net cash provided from operating activities	298,000	339,000	804,000
Investing Activities:
Property additions	(274,000)	(202,000)	(188,000)
Payments pursuant to LTSAs	(28,000)	(23,000)	(29,000)
Other investing activities	(21,000)	(38,000)	(15,000)
Net cash used for investing activities	(323,000)	(263,000)	(232,000)
Financing Activities:
Increase (decrease) in notes payable, net	25,000
Increase (decrease) in notes payable, net		0	(4,000)
Proceeds —
Short-term borrowings	40,000	0	300,000
Senior notes	0	0	600,000
Pollution control revenue bonds	34,000	43,000	0
Other long-term debt	100,000	0	0
Capital contributions from parent company	85,000	51,000	15,000
Redemptions and repurchases —
Preferred and preference stock	0	0	(33,000)
Short-term borrowings	(40,000)	0	(300,000)
Senior notes	(275,000)	(25,000)	(155,000)
Pollution control revenue bonds	(41,000)	0	(43,000)
Other long-term debt	0	0	(900,000)
Return of capital to parent company	(74,000)	(150,000)	0
Payment of common stock dividends	(74,000)	0	0
Other financing activities	(2,000)	(2,000)	(7,000)
Net cash used for financing activities	(222,000)	(83,000)	(527,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(247,000)	(7,000)	45,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	286,000	293,000	248,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	39,000	286,000	293,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	63,000	71,000	80,000
Income taxes (net of refunds)	28,000	(27,000)	(525,000)
Noncash transactions —
Accrued property additions at year-end	34,000	35,000	35,000
Southern Power
Operating Activities:
Consolidated net income	207,000	329,000	246,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	519,000	505,000	524,000
Deferred income taxes	(25,000)	(74,000)	(244,000)
Utilization of federal investment tax credits	340,000	734,000	5,000
Amortization of investment tax credits	(59,000)	(151,000)	(58,000)
Pension and postretirement funding	0	(24,000)	0
Income taxes receivable, non-current	(20,000)	25,000	42,000
Impairment charges	0	3,000	156,000
(Gain) loss on dispositions, net	(39,000)	(24,000)	(3,000)
Other, net	(5,000)	(9,000)	(4,000)
Changes in certain current assets and liabilities —
-Receivables	(4,000)	72,000	(20,000)
-Other current assets	(30,000)	(8,000)	(26,000)
-Accrued taxes	11,000	6,000	7,000
-Other current liabilities	(14,000)	(38,000)	(19,000)
-Prepaid income taxes	20,000	39,000	25,000
Net cash provided from operating activities	901,000	1,385,000	631,000
Investing Activities:
Business acquisitions, net of cash acquired	(81,000)	(50,000)	(65,000)
Property additions	(223,000)	(489,000)	(315,000)
Proceeds from dispositions and asset sales	666,000	572,000	203,000
Investments in unconsolidated subsidiaries	0	(116,000)	0
Payments pursuant to LTSAs	(76,000)	(104,000)	(75,000)
Other investing activities	88,000	20,000	25,000
Net cash used for investing activities	374,000	(167,000)	(227,000)
Financing Activities:
Increase (decrease) in notes payable, net		449,000
Increase (decrease) in notes payable, net	(274,000)		(105,000)
Proceeds —
Short-term borrowings	0	100,000	200,000
Capital contributions from parent company	6,000	64,000	2,000
Redemptions and repurchases —
Short-term borrowings	(100,000)	(100,000)	(100,000)
Senior notes	(825,000)	(600,000)	(350,000)
Other long-term debt	0	0	(420,000)
Return of capital to parent company	0	(755,000)	(1,650,000)
Distributions to noncontrolling interests	(271,000)	(256,000)	(153,000)
Capital contributions from noncontrolling interests	363,000	196,000	2,551,000
Purchase of membership interests from noncontrolling interests	(60,000)	0	0
Payment of common stock dividends	(201,000)	(206,000)	(312,000)
Other financing activities	(10,000)	(12,000)	(26,000)
Net cash used for financing activities	(1,372,000)	(1,120,000)	(363,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(97,000)	98,000	41,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	279,000	181,000	140,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	182,000	279,000	181,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	147,000	167,000	173,000
Income taxes (net of refunds)	(283,000)	(664,000)	79,000
Noncash transactions —
Accrued property additions at year-end	89,000	57,000	31,000
Southern Company Gas
Operating Activities:
Consolidated net income	590,000	585,000	372,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	500,000	487,000	500,000
Deferred income taxes	56,000	213,000	(1,000)
Pension and postretirement funding	0	(145,000)	0
Impairment charges	0	115,000	42,000
(Gain) loss on dispositions, net	(22,000)	0	(291,000)
Mark-to-market adjustments	61,000	(56,000)	(19,000)
Other, net	(29,000)	(55,000)	(24,000)
Changes in certain current assets and liabilities —
-Receivables	(93,000)	467,000	(218,000)
-Natural gas for sale	18,000	44,000	49,000
-Other current assets	(10,000)	31,000	4,000
-Accounts payable	103,000	(520,000)	372,000
-Accrued taxes	13,000	(69,000)	10,000
-Other current liabilities	(6,000)	(71,000)	(22,000)
-Prepaid income taxes	19,000	40,000	(42,000)
-Accrued compensation	7,000	1,000	32,000
Net cash provided from operating activities	1,207,000	1,067,000	764,000
Investing Activities:
Property additions	(1,471,000)	(1,408,000)	(1,388,000)
Proceeds from dispositions and asset sales	211,000	32,000	2,609,000
Cost of removal, net of salvage	(100,000)	(82,000)	(96,000)
Change in construction payables, net	20,000	24,000	(37,000)
Investments in unconsolidated subsidiaries	(79,000)	(31,000)	(110,000)
Returned investment in unconsolidated subsidiaries	13,000	67,000	20,000
Other investing activities	(11,000)	12,000	0
Net cash used for investing activities	(1,417,000)	(1,386,000)	998,000
Financing Activities:
Increase (decrease) in notes payable, net	(326,000)	0	(868,000)
Proceeds —
First mortgage bonds	325,000	300,000	300,000
Senior notes	500,000	0	0
Capital contributions from parent company	216,000	821,000	24,000
Redemptions and repurchases —
Gas facility revenue bonds	0	0	(200,000)
Senior notes	0	(300,000)	(155,000)
First mortgage bonds	0	(50,000)	0
Return of capital to parent company	0	0	(400,000)
Payment of common stock dividends	(533,000)	(471,000)	(468,000)
Other financing activities	(2,000)	(2,000)	(3,000)
Net cash used for financing activities	180,000	298,000	(1,770,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(30,000)	(21,000)	(8,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	49,000	70,000	78,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	19,000	49,000	70,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	232,000	251,000	249,000
Income taxes (net of refunds)	25,000	(41,000)	524,000
Noncash transactions —
Accrued property additions at year-end	$ 142,000	$ 122,000	$ 97,000

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net cash paid for capitalized interest	$ 81	$ 74	$ 72
Alabama Power
Net cash paid for capitalized interest	15	19	22
Georgia Power
Net cash paid for capitalized interest	47	35	26
Mississippi Power
Net cash paid for capitalized interest	0	1	0
Southern Power
Net cash paid for capitalized interest	11	15	17
Southern Company Gas
Net cash paid for capitalized interest	$ 7	$ 6	$ 7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 1,065	$ 1,975
Receivables —
Customer accounts	1,753	1,614
Energy marketing	516	428
Unbilled revenues	672	599
Other accounts and notes	512	817
Accumulated provision for uncollectible accounts	(118)	(49)
Materials and supplies	1,478	1,388
Fossil fuel for generation	550	521
Natural gas for sale	460	479
Prepaid expenses	276	314
Regulatory assets – asset retirement obligations	214	287
Assets from risk management activities, net of collateral	147	183
Other regulatory assets	810	885
Assets held for sale	60	188
Other current assets	222	188
Total current assets	8,617	9,817
Property, Plant, and Equipment:
In service	110,516	105,114
Less: Accumulated depreciation	32,397	30,765
Plant in service, net of depreciation	78,119	74,349
Nuclear fuel, at amortized cost	818	851
Construction work in progress	8,697	7,880
Total property, plant, and equipment	87,634	83,080
Other Property and Investments:
Goodwill	5,280	5,280
Nuclear decommissioning trusts, at fair value	2,303	2,036
Equity investments in unconsolidated subsidiaries	1,362	1,303
Other intangible assets, net of amortization	487	536
Leveraged leases	556	788
Miscellaneous property and investments	398	391
Total other property and investments	10,386	10,334
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,802	1,800
Deferred charges related to income taxes	796	798
Unamortized loss on reacquired debt	280	300
Regulatory assets – asset retirement obligations, deferred	4,934	4,094
Other regulatory assets, deferred	7,198	6,805
Assets held for sale, deferred	0	601
Other deferred charges and assets	1,288	1,071
Total deferred charges and other assets	16,298	15,469
Total Assets	122,935	118,700
Current Liabilities:
Securities due within one year	3,507	2,989
Notes payable	609	2,055
Energy marketing trade payables	494	442
Accounts payable —
Accounts payable	2,312	2,115
Customer deposits	487	496
Accrued taxes —
Accrued income taxes	130	0
Other accrued taxes	699	659
Accrued interest	513	474
Accrued compensation	1,025	992
Asset retirement obligations	585	504
Other regulatory liabilities	509	756
Liabilities held for sale	0	5
Operating lease obligations	241	229
Other current liabilities	968	830
Total current liabilities	12,079	12,546
Long-Term Debt	45,073	41,798
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	8,175	7,888
Deferred credits related to income taxes	5,767	6,078
Accumulated deferred ITCs	2,235	2,291
Employee benefit obligations	2,213	1,814
Operating lease obligations, deferred	1,611	1,615
Asset retirement obligations, deferred	10,099	9,282
Accrued environmental remediation	216	234
Other cost of removal obligations	2,211	2,239
Other regulatory liabilities, deferred	251	256
Other deferred credits and liabilities	480	609
Total deferred credits and other liabilities	33,258	32,306
Total Liabilities	90,410	86,650
Cumulative preferred stock
Redeemable preferred stock	291	291
Common Stockholders' Equity:
Common stock	5,268	5,257
Paid-in capital	11,834	11,734
Treasury, at cost	(46)	(42)
Retained earnings (accumulated deficit)	11,311	10,877
Accumulated other comprehensive income (loss)	(395)	(321)
Total common stockholders' equity	27,972	27,505
Noncontrolling Interests	4,262	4,254
Total Stockholders' Equity (See accompanying statements)	32,234	31,759
Total Liabilities and Stockholders' Equity	122,935	118,700
Commitments and Contingent Matters (See notes)
Redeemable Preferred Stock, $100 par or stated value
Cumulative preferred stock
Redeemable preferred stock	48	48
Redeemable Preferred Stock, $1 par value
Cumulative preferred stock
Redeemable preferred stock	243	243
Alabama Power
Current Assets:
Cash and cash equivalents	530	894
Receivables —
Customer accounts	429	425
Unbilled revenues	152	134
Other accounts and notes	66	72
Affiliated	31	37
Accumulated provision for uncollectible accounts	(43)	(22)
Materials and supplies	546	512
Fossil fuel for generation	235	212
Prepaid expenses	42	50
Other regulatory assets	226	242
Other current assets	33	30
Total current assets	2,247	2,586
Property, Plant, and Equipment:
In service	31,816	30,023
Less: Accumulated depreciation	10,009	9,540
Plant in service, net of depreciation	21,807	20,483
Nuclear fuel, at amortized cost	270	296
Construction work in progress	866	890
Total property, plant, and equipment	22,943	21,669
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,157	1,023
Equity investments in unconsolidated subsidiaries	63	66
Miscellaneous property and investments	131	128
Total other property and investments	1,351	1,217
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	151	132
Deferred charges related to income taxes	235	244
Regulatory assets – asset retirement obligations, deferred	1,441	1,019
Other regulatory assets, deferred	2,162	2,016
Other deferred charges and assets	273	269
Total deferred charges and other assets	4,262	3,680
Total Assets	30,803	29,152
Current Liabilities:
Securities due within one year	311	251
Accounts payable —
Affiliated	316	316
Other	545	514
Customer deposits	104	100
Accrued taxes —
Accrued taxes	152	78
Accrued interest	90	92
Accrued compensation	212	216
Asset retirement obligations	254	195
Other regulatory liabilities	108	193
Operating lease obligations	51	49
Other current liabilities	107	105
Total current liabilities	2,199	2,060
Long-Term Debt	8,558	8,270
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,273	3,260
Deferred credits related to income taxes	2,016	1,960
Accumulated deferred ITCs	94	100
Employee benefit obligations	214	206
Operating lease obligations, deferred	119	107
Asset retirement obligations, deferred	3,720	3,345
Other cost of removal obligations	335	412
Other regulatory liabilities, deferred	124	146
Other deferred credits and liabilities	50	40
Total deferred credits and other liabilities	9,945	9,576
Total Liabilities	20,702	19,906
Cumulative preferred stock
Redeemable preferred stock	291	291
Common Stockholders' Equity:
Common stock	1,222	1,222
Paid-in capital	5,413	4,755
Retained earnings (accumulated deficit)	3,194	3,001
Accumulated other comprehensive income (loss)	(19)	(23)
Total common stockholders' equity	9,810	8,955
Total Stockholders' Equity (See accompanying statements)	9,810	8,955
Total Liabilities and Stockholders' Equity	30,803	29,152
Commitments and Contingent Matters (See notes)
Alabama Power | Redeemable Preferred Stock, $100 par or stated value
Cumulative preferred stock
Redeemable preferred stock	48	48
Alabama Power | Redeemable Preferred Stock, $1 par value
Cumulative preferred stock
Redeemable preferred stock	243	243
Georgia Power
Current Assets:
Cash and cash equivalents	9	52
Receivables —
Customer accounts	621	533
Unbilled revenues	233	203
Joint owner accounts	123	136
Other accounts and notes	67	209
Affiliated	21	21
Accumulated provision for uncollectible accounts	(26)	(2)
Materials and supplies	592	501
Fossil fuel for generation	278	272
Prepaid expenses	54	63
Regulatory assets – storm damage	213	213
Regulatory assets – asset retirement obligations	166	254
Other regulatory assets	248	263
Other current assets	89	77
Total current assets	2,688	2,795
Property, Plant, and Equipment:
In service	39,682	38,137
Less: Accumulated depreciation	12,251	11,753
Plant in service, net of depreciation	27,431	26,384
Nuclear fuel, at amortized cost	548	555
Construction work in progress	6,857	5,650
Total property, plant, and equipment	34,836	32,589
Other Property and Investments:
Nuclear decommissioning trusts, at fair value	1,145	1,013
Equity investments in unconsolidated subsidiaries	51	52
Miscellaneous property and investments	63	64
Total other property and investments	1,259	1,129
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,308	1,428
Deferred charges related to income taxes	527	519
Regulatory assets – asset retirement obligations, deferred	3,291	2,865
Other regulatory assets, deferred	2,692	2,716
Other deferred charges and assets	479	500
Total deferred charges and other assets	8,297	8,028
Total Assets	47,080	44,541
Current Liabilities:
Securities due within one year	542	1,025
Notes payable	60	365
Accounts payable —
Affiliated	597	512
Other	753	711
Customer deposits	276	283
Accrued taxes —
Accrued taxes	407	407
Accrued interest	130	118
Accrued compensation	233	233
Asset retirement obligations	287	265
Other regulatory liabilities	228	447
Over recovered regulatory clause liabilities	113	0
Operating lease obligations	151	144
Other current liabilities	254	187
Total current liabilities	4,031	4,697
Long-Term Debt	12,428	10,791
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,272	3,257
Deferred credits related to income taxes	2,588	2,862
Accumulated deferred ITCs	273	255
Employee benefit obligations	586	540
Operating lease obligations, deferred	1,156	1,282
Asset retirement obligations, deferred	5,978	5,519
Accrued environmental remediation	0	0
Other deferred credits and liabilities	267	273
Total deferred credits and other liabilities	14,120	13,988
Total Liabilities	30,579	29,476
Common Stockholders' Equity:
Common stock	398	398
Paid-in capital	12,361	10,962
Retained earnings (accumulated deficit)	3,789	3,756
Accumulated other comprehensive income (loss)	(47)	(51)
Total common stockholders' equity	16,501	15,065
Total Stockholders' Equity (See accompanying statements)	16,501	15,065
Total Liabilities and Stockholders' Equity	47,080	44,541
Commitments and Contingent Matters (See notes)
Mississippi Power
Current Assets:
Cash and cash equivalents	39	286
Receivables —
Customer accounts	34	35
Unbilled revenues	38	39
Other accounts and notes	32	26
Affiliated	32	27
Materials and supplies	65	61
Fossil fuel for generation	24	26
Other regulatory assets	60	99
Other current assets	20	10
Total current assets	344	609
Property, Plant, and Equipment:
In service	5,011	4,857
Less: Accumulated depreciation	1,545	1,463
Plant in service, net of depreciation	3,466	3,394
Construction work in progress	146	126
Total property, plant, and equipment	3,612	3,520
Other Property and Investments:
Total other property and investments	151	131
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	9	6
Deferred charges related to income taxes	32	32
Regulatory assets – asset retirement obligations, deferred	201	210
Other regulatory assets, deferred	388	360
Accumulated deferred income taxes	129	139
Other deferred charges and assets	55	34
Total deferred charges and other assets	805	775
Total Assets	4,912	5,035
Current Liabilities:
Securities due within one year	406	281
Notes payable	25	0
Accounts payable —
Affiliated	63	76
Other	109	75
Accrued taxes —
Accrued taxes	114	105
Accrued interest	15	15
Accrued compensation	34	35
Asset retirement obligations	27	33
Other regulatory liabilities	49	21
Over recovered regulatory clause liabilities	34	29
Operating lease obligations	2	2
Other current liabilities	40	64
Total current liabilities	916	734
Long-Term Debt	1,013	1,308
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	447	424
Deferred credits related to income taxes	287	352
Employee benefit obligations	113	99
Operating lease obligations, deferred	7	4
Asset retirement obligations, deferred	150	157
Other cost of removal obligations	194	189
Other regulatory liabilities, deferred	15	76
Other deferred credits and liabilities	35	44
Total deferred credits and other liabilities	1,241	1,341
Total Liabilities	3,170	3,383
Common Stockholders' Equity:
Common stock	38	38
Paid-in capital	4,460	4,449
Retained earnings (accumulated deficit)	(2,754)	(2,832)
Accumulated other comprehensive income (loss)	(2)	(3)
Total common stockholders' equity	1,742	1,652
Total Stockholders' Equity (See accompanying statements)	1,742	1,652
Total Liabilities and Stockholders' Equity	4,912	5,035
Commitments and Contingent Matters (See notes)
Southern Power
Current Assets:
Cash and cash equivalents	182	279
Receivables —
Customer accounts	125	107
Other accounts and notes	27	73
Affiliated	37	30
Materials and supplies	157	191
Prepaid income taxes	11	36
Other current assets	36	43
Total current assets	575	759
Property, Plant, and Equipment:
In service	13,904	13,270
Less: Accumulated depreciation	2,842	2,464
Plant in service, net of depreciation	11,062	10,806
Construction work in progress	127	515
Total property, plant, and equipment	11,189	11,321
Other Property and Investments:
Intangible assets, net of amortization	302	322
Equity investments in unconsolidated subsidiaries	19	28
Total other property and investments	321	350
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	415	369
Prepaid LTSAs	155	128
Income taxes receivable, non-current	25	5
Assets held for sale, deferred	0	601
Accumulated deferred income taxes	262	551
Other deferred charges and assets	293	216
Total deferred charges and other assets	1,150	1,870
Total Assets	13,235	14,300
Current Liabilities:
Securities due within one year	299	824
Notes payable	175	549
Accounts payable —
Affiliated	65	56
Other	92	85
Accrued taxes —
Accrued taxes	30	26
Accrued interest	32	32
Operating lease obligations	25	22
Other current liabilities	132	132
Total current liabilities	825	1,704
Long-Term Debt	3,393	3,574
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	123	115
Accumulated deferred ITCs	1,672	1,731
Operating lease obligations, deferred	426	376
Other deferred credits and liabilities	165	178
Total deferred credits and other liabilities	2,386	2,400
Total Liabilities	6,604	7,678
Common Stockholders' Equity:
Common stock	0	0
Paid-in capital	914	909
Retained earnings (accumulated deficit)	1,522	1,485
Accumulated other comprehensive income (loss)	(67)	(26)
Total common stockholders' equity	2,369	2,368
Noncontrolling Interests	4,262	4,254
Total Stockholders' Equity (See accompanying statements)	6,631	6,622
Total Liabilities and Stockholders' Equity	13,235	14,300
Commitments and Contingent Matters (See notes)
Southern Company Gas
Current Assets:
Cash and cash equivalents	17	46
Receivables —
Customer accounts	353	323
Energy marketing	516	428
Unbilled revenues	219	183
Other accounts and notes	51	114
Affiliated	4	5
Accumulated provision for uncollectible accounts	(40)	(18)
Natural gas for sale	460	479
Prepaid expenses	48	65
Assets from risk management activities, net of collateral	118	177
Other regulatory assets	102	92
Assets held for sale	0	171
Other current assets	38	41
Total current assets	1,886	2,106
Property, Plant, and Equipment:
In service	17,611	16,344
Less: Accumulated depreciation	4,821	4,650
Plant in service, net of depreciation	12,790	11,694
Construction work in progress	648	613
Total property, plant, and equipment	13,438	12,307
Other Property and Investments:
Goodwill	5,015	5,015
Equity investments in unconsolidated subsidiaries	1,290	1,251
Other intangible assets, net of amortization	51	70
Miscellaneous property and investments	19	20
Total other property and investments	6,375	6,356
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	81	93
Other regulatory assets, deferred	615	618
Other deferred charges and assets	235	207
Total deferred charges and other assets	931	918
Total Assets	22,630	21,687
Current Liabilities:
Securities due within one year	333	0
Notes payable	324	650
Energy marketing trade payables	494	442
Accounts payable —
Affiliated	56	41
Other	373	315
Customer deposits	90	96
Accrued taxes —
Accrued taxes	83	71
Accrued interest	58	52
Accrued compensation	106	100
Other regulatory liabilities	122	94
Operating lease obligations	15	14
Other current liabilities	150	149
Total current liabilities	2,189	2,010
Long-Term Debt	6,293	5,845
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,265	1,219
Deferred credits related to income taxes	847	874
Employee benefit obligations	283	265
Operating lease obligations, deferred	67	78
Accrued environmental remediation	216	233
Other cost of removal obligations	1,649	1,606
Other deferred credits and liabilities	54	51
Total deferred credits and other liabilities	4,381	4,326
Total Liabilities	12,863	12,181
Common Stockholders' Equity:
Common stock	9,930	9,697
Retained earnings (accumulated deficit)	(141)	(198)
Accumulated other comprehensive income (loss)	(22)	7
Total common stockholders' equity	9,767	9,506
Total Stockholders' Equity (See accompanying statements)	9,767	9,506
Total Liabilities and Stockholders' Equity	22,630	21,687
Commitments and Contingent Matters (See notes)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Other intangible assets, amortization	$ 328,000,000	$ 280,000,000
Common Stockholders' Equity:
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, shares issued (in shares)	1,100,000,000	1,100,000,000
Treasury shares (in shares)	1,000,000	1,000,000
Redeemable Preferred Stock
Cumulative preferred stock
Annual dividend requirement	$ 15,000,000	$ 15,000,000
Redeemable Preferred Stock, $100 par or stated value
Cumulative preferred stock
Par value (in dollars per share)	$ 100	$ 100
Shares authorized (in shares)	10,000,000	10,000,000
Shares outstanding (in shares)	500,000	500,000
Redeemable Preferred Stock, $100 par or stated value | Minimum
Cumulative preferred stock
Dividend rate	4.20%	4.20%
Redeemable Preferred Stock, $100 par or stated value | Maximum
Cumulative preferred stock
Dividend rate	4.92%	4.92%
Redeemable Preferred Stock, $1 par value
Cumulative preferred stock
Par value (in dollars per share)	$ 1	$ 1
Dividend rate	5.00%	5.00%
Shares authorized (in shares)	28,000,000	28,000,000
Shares outstanding (in shares)	10,000,000	10,000,000
Alabama Power
Common Stockholders' Equity:
Common stock, par value (in dollars per share)	$ 40	$ 40
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares outstanding (in shares)	31,000,000	31,000,000
Alabama Power | Redeemable Preferred Stock
Cumulative preferred stock
Annual dividend requirement	$ 15,000,000	$ 15,000,000
Alabama Power | Redeemable Preferred Stock, $100 par or stated value
Cumulative preferred stock
Par value (in dollars per share)	$ 100	$ 100
Shares authorized (in shares)	3,900,000	3,900,000
Shares outstanding (in shares)	500,000	500,000
Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Minimum
Cumulative preferred stock
Dividend rate	4.20%	4.20%
Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Maximum
Cumulative preferred stock
Dividend rate	4.92%	4.92%
Alabama Power | Redeemable Preferred Stock, $1 par value
Cumulative preferred stock
Par value (in dollars per share)	$ 1	$ 1
Dividend rate	5.00%	5.00%
Shares authorized (in shares)	27,500,000	27,500,000
Shares outstanding (in shares)	10,000,000	10,000,000
Alabama Power | Redeemable Preferred Stock, $25 stated value
Cumulative preferred stock
Par value (in dollars per share)	$ 25	$ 25
Georgia Power
Common Stockholders' Equity:
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	9,000,000	9,000,000
Mississippi Power
Common Stockholders' Equity:
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares outstanding (in shares)	1,000,000	1,000,000
Southern Power
Other intangible assets, amortization	$ 89,000,000	$ 69,000,000
Cumulative preferred stock
Par value (in dollars per share)	$ 0.01	$ 0.01
Common Stockholders' Equity:
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares outstanding (in shares)	1,000	1,000
Southern Company Gas
Other intangible assets, amortization	$ 195,000,000	$ 176,000,000
Common Stockholders' Equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares outstanding (in shares)	100	100

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions		Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Alabama Power	Alabama PowerCommon Stock	Alabama PowerPaid-In Capital	Alabama PowerRetained Earnings	Alabama PowerAccumulated Other Comprehensive Income (Loss)	Georgia Power	Georgia PowerCommon Stock	Georgia PowerPaid-In Capital	Georgia PowerRetained Earnings	Georgia PowerAccumulated Other Comprehensive Income (Loss)	Mississippi Power	Mississippi PowerCommon Stock	Mississippi PowerPaid-In Capital	Mississippi PowerRetained Earnings	Mississippi PowerAccumulated Other Comprehensive Income (Loss)	Southern Power	Southern PowerPaid-In Capital	Southern PowerRetained Earnings	Southern PowerAccumulated Other Comprehensive Income (Loss)	Southern PowerTotal Common Stockholder's Equity	Southern PowerNoncontrolling Interests	Southern Company Gas	Southern Company GasPaid-In Capital	Southern Company GasRetained Earnings	Southern Company GasAccumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017			1,009	1						31					9					1
Beginning balance at Dec. 31, 2017		$ 25,528	$ 5,038	$ (36)	$ 10,469	$ 8,885	$ (189)	$ 1,361	$ 6,829	$ 1,222	$ 2,986	$ 2,647	$ (26)	$ 11,931	$ 398	$ 7,328	$ 4,215	$ (10)	$ 1,358	$ 38	$ 4,529	$ (3,205)	$ (4)	$ 6,498	$ 3,662	$ 1,478	$ (2)	$ 5,138	$ 1,360	$ 9,022	$ 9,214	$ (212)	$ 20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		2,284				2,226		58
Net income after dividends on preferred stock		2,226							930			930							235			235		187						372		372
Net Income		2,300							945					793			793		236					246		187		187	59	372
Return of capital to parent company																								(1,650)	(1,650)			(1,650)		(400)	(400)
Capital contributions from parent company									522		522			2,994		2,994			17		17			2	2			2		42	42
Other comprehensive income (loss)		26					26		4				4	3				3						14			14	14		2			2
Stock issued (in shares)			26
Stock issued		1,090	$ 126		964
Stock-based compensation		84			84
Cash dividends on common stock		(2,425)				(2,425)			(801)			(801)		(1,396)			(1,396)							(312)		(312)		(312)		(468)		(468)
Contributions from noncontrolling interests		1,372						1,372																1,372					1,372
Distributions to noncontrolling interests		(164)						(164)																(164)					(164)
Sale of noncontrolling interests		1,273			(417)			1,690																1,273	(417)			(417)	1,690
Other		(29)		$ (2)	(6)	20	(40)	(1)	(7)			(1)	(6)	(2)				(2)	(1)			(1)		5	3	(1)	4	6	(1)	0	0	(4)	4
Ending balance (in shares) at Dec. 31, 2018			1,035	1						31					9					1
Ending balance at Dec. 31, 2018		29,039	$ 5,164	$ (38)	11,094	8,706	(203)	4,316	7,477	$ 1,222	3,508	2,775	(28)	14,323	$ 398	10,322	3,612	(9)	1,609	$ 38	4,546	(2,971)	(4)	7,284	1,600	1,352	16	2,968	4,316	8,570	8,856	(312)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		4,729				4,739		(10)
Net income after dividends on preferred stock		4,739							1,070			1,070							139			139		339						585		585
Net Income		4,744							1,085					1,720			1,720		139					329		339		339	(10)	585
Return of capital to parent company																			(150)		(150)			(755)	(755)			(755)
Capital contributions from parent company									1,247		1,247			640		640			53		53			64	64			64		841	841
Other comprehensive income (loss)		(118)					(118)		4				4	(42)				(42)	1				1	(42)			(42)	(42)		(19)			(19)
Issuance of equity units	[1]	(198)			(198)
Stock issued (in shares)			19
Stock issued		844	$ 93		751
Stock-based compensation		66			66
Cash dividends on common stock		(2,570)				(2,570)			(844)			(844)		(1,576)			(1,576)							(206)		(206)		(206)		(471)		(471)
Contributions from noncontrolling interests		276						276																276					276
Distributions to noncontrolling interests		(327)						(327)																(327)					(327)
Other		18		$ (4)	21	2		(1)	1				1											(1)					(1)
Ending balance (in shares) at Dec. 31, 2019			1,054	1						31					9					1
Ending 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	909	1,485	(26)	2,368	4,254	9,506	9,697	(198)	7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)		3,088				3,119		(31)
Net income after dividends on preferred stock		3,119							1,150			1,150							152			152		238						590		590
Net Income		3,103							1,165					1,575			1,575		152					207		238		238	(31)	590
Return of capital to parent company																			(74)		(74)
Capital contributions from parent company									658		658			1,399		1,399			86		86			2	2			2		233	233
Other comprehensive income (loss)		(75)					(75)		4				4	4				4	1				1	(42)			(42)	(42)		(29)			(29)
Stock issued (in shares)			4
Stock issued		74	$ 11		63
Stock-based compensation		44			44
Cash dividends on common stock		(2,685)				(2,685)			(957)			(957)		(1,542)			(1,542)		(74)			(74)		(201)		(201)		(201)		(533)		(533)
Contributions from noncontrolling interests		307						307																307					307
Distributions to noncontrolling interests		(271)						(271)																(271)					(271)
Sale of noncontrolling interests		65			(2)			67																65	(2)			(2)	67
Purchase of membership interests from noncontrolling interests		(60)			5			(65)																(60)	5			5	(65)
Other		(12)		$ (4)	(10)		1	1											(1)		(1)			2			1	1	1
Ending balance (in shares) at Dec. 31, 2020			1,058	1						31					9					1
Ending 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	$ 914	$ 1,522	$ (67)	$ 2,369	$ 4,262	$ 9,767	$ 9,930	$ (141)	$ (22)
[1]	See Note 8 under "Equity Units" for additional information.

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 2.5400	$ 2.4600	$ 2.3800

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General Southern Company is the parent company of three traditional electric operating companies, as well as Southern Power, Southern Company Gas, SCS, Southern Linc, Southern Holdings, Southern Nuclear, PowerSecure, and other direct and indirect subsidiaries. The traditional electric operating companies – Alabama Power, Georgia Power, and Mississippi Power – are vertically integrated utilities providing electric service in three Southeastern states. In January 2019, Southern Company completed the sale of Gulf Power (another traditional electric operating company through December 31, 2018) to NextEra Energy. 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 natural gas distribution utilities, including Nicor Gas (Illinois), Atlanta Gas Light (Georgia), Virginia Natural Gas, and Chattanooga Gas (Tennessee). In 2018, Southern Company Gas sold its other natural gas utilities – Elizabethtown Gas (New Jersey), Florida City Gas, and Elkton Gas (Maryland). Southern Company Gas is also involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. SCS, the system service company, provides, at cost, specialized services to Southern Company and its subsidiary companies. Southern Linc provides digital wireless communications for use by Southern Company and its subsidiary companies and also markets these services to the public and provides fiber optics services within the Southeast. Southern Holdings is an intermediate holding company subsidiary, primarily for Southern Company's leveraged lease and other investments. Southern Nuclear operates and provides services to the Southern Company system's nuclear power plants, including Alabama Power's Plant Farley and Georgia Power's Plant Hatch and Plant Vogtle Units 1 and 2, and is currently managing construction and start-up of Plant Vogtle Units 3 and 4, which are co-owned by Georgia Power. PowerSecure provides energy solutions to electric utilities and their customers in the areas of distributed generation, energy storage and renewables, and energy efficiency. See Note 15 for information regarding disposition activities, including Southern Company's sale of Gulf Power. The Registrants' financial statements reflect investments in subsidiaries on a consolidated basis. Intercompany transactions have been eliminated in consolidation. The equity method is used for investments in entities in which a Registrant has significant influence but does not have control and for VIEs where a Registrant has an equity investment but is not the primary beneficiary. Southern Power has controlling ownership in certain legal entities for which the contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. For these arrangements, the noncontrolling interest is accounted for under a balance sheet approach utilizing the HLBV method. The HLBV method calculates each partner's share of income based on the change in net equity the partner can legally claim in a HLBV at the end of the period compared to the beginning of the period. See "Variable Interest Entities" herein and Note 7 for additional information. The traditional electric operating companies, Southern Power, certain subsidiaries of Southern Company Gas, and certain other subsidiaries are subject to regulation by the FERC, and the traditional electric operating companies and the natural gas distribution utilities are also subject to regulation by their respective state PSCs or other applicable state regulatory agencies. As such, the respective financial statements of the applicable Registrants reflect the effects of rate regulation in accordance with GAAP and comply with the accounting policies and practices prescribed by relevant state PSCs or other applicable state regulatory agencies. The preparation of financial statements in conformity with GAAP requires the use of estimates, and the actual results may differ from those estimates. Certain prior years' data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the Registrants' results of operations, financial position, or cash flows. At December 31, 2020 and/or 2019, Southern Company, Southern Power, and Southern Company Gas each had assets and liabilities held for sale on their balance sheets. Unless otherwise noted, the disclosures herein related to specific asset and liability balances at December 31, 2020 and 2019 exclude assets and liabilities held for sale. See Note 15 under "Assets Held for Sale" for additional information including major classes of assets and liabilities classified as held for sale by Southern Company, Southern Power, and Southern Company Gas. Recently Adopted Accounting Standards Effective January 1, 2019, the Registrants adopted ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 required lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changed the recognition, measurement, and presentation of expense associated with leases and provided clarification regarding the identification of certain components of contracts that would represent a lease. Lessor accounting was relatively unchanged and there was no change to the accounting for existing leveraged leases. See Note 9 for additional information and related disclosures. Affiliate Transactions The traditional electric operating companies, Southern Power, and Southern Company Gas have agreements with SCS under which certain of the following services are rendered to them at direct or allocated cost: general executive and advisory, general and design engineering, operations, purchasing, accounting, finance, treasury, legal, tax, information technology, marketing, auditing, insurance and pension administration, human resources, systems and procedures, digital wireless communications, cellular tower space, and other services with respect to business and operations, construction management, and Southern Company power pool transactions. These costs are primarily included in other operations and maintenance expenses or capitalized to property, plant, and equipment. Costs for these services from SCS in 2020, 2019, and 2018 were as follows: Alabama Georgia Mississippi Southern Southern Company Gas (in millions) 2020 $ 478 $ 639 $ 149 $ 87 $ 237 2019 527 704 118 90 183 2018 508 653 104 98 194 Alabama Power and Georgia Power also have agreements with Southern Nuclear under which Southern Nuclear renders the following nuclear-related services at cost: general executive and advisory services; general operations, management, and technical services; administrative services including procurement, accounting, employee relations, systems, and procedures services; strategic planning and budgeting services; other services with respect to business and operations; and, for Georgia Power, construction management. These costs are primarily included in other operations and maintenance expenses or capitalized to property, plant, and equipment. Costs for these services in 2020, 2019, and 2018 amounted to $262 million, $256 million, and $247 million, respectively, for Alabama Power and $883 million, $760 million, and $780 million, respectively, for Georgia Power. See Note 2 under "Georgia Power – Nuclear Construction" for additional information regarding Southern Nuclear's construction management of Plant Vogtle Units 3 and 4 for Georgia Power. Cost allocation methodologies used by SCS and Southern Nuclear prior to the repeal of the Public Utility Holding Company Act of 1935, as amended, were approved by the SEC. Subsequently, additional cost allocation methodologies have been reported to the FERC and management believes they are reasonable. The FERC permits services to be rendered at cost by system service companies. Alabama Power's and Georgia Power's power purchases from affiliates through the Southern Company power pool are included in purchased power, affiliates on their respective statements of income. Mississippi Power's and Southern Power's power purchases from affiliates through the Southern Company power pool are included in purchased power on their respective statements of income and were as follows: Mississippi Southern (in millions) 2020 $ 4 $ 8 2019 3 14 2018 15 41 Georgia Power has entered into several PPAs with Southern Power for capacity and energy. Georgia Power's total expenses associated with these PPAs were $141 million, $177 million, and $216 million in 2020, 2019, and 2018, respectively. Southern Power's total revenues from all PPAs with Georgia Power, included in wholesale revenue affiliates on Southern Power's consolidated statements of income, were $139 million, $174 million, and $215 million for 2020, 2019, and 2018, respectively. Included within these revenues were affiliate PPAs accounted for as operating leases, which totaled $115 million, $116 million, and $65 million for 2020, 2019, and 2018, respectively. See Note 9 for additional information. SCS (as agent for Alabama Power, Georgia Power, and Southern Power) and Southern Company Gas have long-term interstate natural gas transportation agreements with SNG that are governed by the terms and conditions of SNG's natural gas tariff and are subject to FERC regulation. See Note 7 under "Southern Company Gas – Equity Method Investments" for additional information. Transportation costs under these agreements in 2020, 2019, and 2018 were as follows: Alabama Georgia Southern Southern Company Gas (in millions) 2020 $ 15 $ 108 $ 29 $ 29 2019 17 99 28 31 2018 8 101 25 32 In 2018, SNG purchased the natural gas lateral pipeline serving Plant McDonough Units 4 through 6 from Georgia Power at net book value, as approved by the Georgia PSC. In January 2020, SNG paid Georgia Power $142 million, which included $71 million contributed to SNG by Southern Company Gas for its proportionate share. During the interim period, Georgia Power received a discounted shipping rate to reflect the deferred consideration and SNG constructed an extension to the pipeline. SCS, as agent for the traditional electric operating companies and Southern Power, has agreements with certain subsidiaries of Southern Company Gas to purchase natural gas. Natural gas purchases made under these agreements were immaterial for Alabama Power and Mississippi Power and as follows for Georgia Power and Southern Power in 2020, 2019, and 2018: Georgia Southern (in millions) 2020 $ — $ 26 2019 4 64 2018 21 119 Alabama Power and Mississippi Power jointly own Plant Greene County. The companies have an agreement under which Alabama Power operates Plant Greene County and Mississippi Power reimburses Alabama Power for its proportionate share of non-fuel operations and maintenance expenses, which totaled $9 million, $9 million, and $8 million in 2020, 2019, and 2018, respectively. See Note 5 under "Joint Ownership Agreements" for additional information. The traditional electric operating companies each have agreements with Gulf Power. Alabama Power previously made transmission system upgrades to ensure firm delivery of energy under a non-affiliate PPA from the Central Alabama Generating Station, and, under a related tariff, received $11 million from Gulf Power in 2018. Gulf Power owns a 25% portion of Plant Scherer Unit 3. Georgia Power operates Plant Scherer Unit 3 and Gulf Power reimburses Georgia Power for its 25% proportionate share of the related non-fuel expenses, which totaled $8 million in 2018. Gulf Power also owns a 50% portion of Plant Daniel Units 1 and 2. Mississippi Power operates Plant Daniel and Gulf Power reimburses Mississippi Power for its proportionate share of all associated non-fuel operations and maintenance expenses, which totaled $31 million in 2018. See Note 5 under "Joint Ownership Agreements" and Note 15 under "Southern Company" and "Alabama Power" for additional information. Alabama Power and Georgia Power each have agreements with PowerSecure for equipment purchases and/or services related to utility infrastructure construction, distributed energy, and energy efficiency projects. Alabama Power's costs for these services were immaterial for 2020 and totaled $7 million and $24 million in 2019 and 2018, respectively. Georgia Power's costs for these equipment purchases and services totaled approximately $11 million in 2020 and were immaterial for the other periods presented. See Note 7 under "SEGCO" for information regarding Alabama Power's and Georgia Power's equity method investment in SEGCO and related affiliate purchased power costs, as well as Alabama Power's gas pipeline ownership agreement with SEGCO. Southern Power has several agreements with SCS for transmission services, which are billed to Southern Power based on the Southern Company Open Access Transmission Tariff as filed with the FERC. Transmission services purchased by Southern Power from SCS totaled $15 million, $15 million, and $12 million for 2020, 2019, and 2018, respectively, and were charged to other operations and maintenance expenses in Southern Power's consolidated statements of income. The traditional electric operating companies and Southern Power may jointly enter into various types of wholesale energy, natural gas, and certain other contracts, either directly or through SCS as agent. Each participating company may be jointly and severally liable for the obligations incurred under these agreements. See Note 14 under "Contingent Features" for additional information. Southern Power and the traditional electric operating companies generally settle amounts related to the above transactions on a monthly basis in the month following the performance of such services or the purchase or sale of electricity. See "Revenues – Southern Power" herein for additional information. The traditional electric operating companies, Southern Power, and Southern Company Gas provide incidental services to and receive such services from other Southern Company subsidiaries which are generally minor in duration and amount. Except as described herein, the traditional electric operating companies, Southern Power, and Southern Company Gas neither provided nor received any material services to or from affiliates in any year presented. Regulatory Assets and Liabilities The traditional electric operating companies and the natural gas distribution utilities are subject to accounting requirements for the effects of rate regulation. Regulatory assets represent probable future revenues associated with certain costs that are expected to be recovered from customers through the ratemaking process. Regulatory liabilities represent costs recovered that are expected to be incurred in the future or probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. In the event that a portion of a traditional electric operating company's or a natural gas distribution utility's operations is no longer subject to applicable accounting rules for rate regulation, such company would be required to write off to income or reclassify to AOCI related regulatory assets and liabilities that are not specifically recoverable through regulated rates. In addition, the traditional electric operating company or the natural gas distribution utility would be required to determine if any impairment to other assets, including plant, exists and write down the assets, if impaired, to their fair values. All regulatory assets and liabilities are to be reflected in rates. See Note 2 for additional information including details of regulatory assets and liabilities reflected in the balance sheets for Southern Company, the traditional electric operating companies, and Southern Company Gas. Revenues The Registrants generate revenues from a variety of sources which are accounted for under various revenue accounting guidance, including revenue from contracts with customers, lease, derivative, and regulatory accounting. See Notes 4, 9, and 14 for additional information. Traditional Electric Operating Companies The majority of the revenues of the traditional electric operating companies are generated from contracts with retail electric customers. These revenues, generated from the integrated service to deliver electricity when and if called upon by the customer, are recognized as a single performance obligation satisfied over time, at a tariff rate, and as electricity is delivered to the customer during the month. Unbilled revenues related to retail sales are accrued at the end of each fiscal period. Retail rates may include provisions to adjust revenues for fluctuations in fuel costs, fuel hedging, the energy component of purchased power costs, and certain other costs. Revenues are adjusted for differences between these actual costs and amounts billed in current regulated rates. Under or over recovered regulatory clause revenues are recorded in the balance sheets and are recovered from or returned to customers, respectively, through adjustments to the billing factors. See Note 2 for additional information regarding regulatory matters of the traditional electric operating companies. Wholesale capacity revenues from PPAs are recognized in amounts billable under the contract terms. Energy and other revenues are generally recognized as services are provided. The contracts for capacity and energy in a wholesale PPA have multiple performance obligations where the contract's total transaction price is allocated to each performance obligation based on the standalone selling price. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, the traditional electric operating companies recognize revenue as the performance obligations are satisfied over time as electricity is delivered to the customer or as generation capacity is available to the customer. For both retail and wholesale revenues, the traditional electric operating companies have elected to recognize revenue for their sales of electricity and capacity using the invoice practical expedient as they generally have a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and that may be invoiced. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of the Registrants' performance obligation. Southern Power Southern Power sells capacity and energy at rates specified under contractual terms in long-term PPAs. These PPAs are accounted for as operating leases, non-derivatives, or normal sale derivatives. Capacity revenues from PPAs classified as operating leases are recognized on a straight-line basis over the term of the agreement. Energy revenues are recognized in the period the energy is delivered. Southern Power's non-lease contracts commonly include capacity and energy which are considered separate performance obligations. In these contracts, the total transaction price is allocated to each performance obligation based on the standalone selling price. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, Southern Power recognizes revenue as the performance obligations are satisfied over time, as electricity is delivered to the customer or as generation capacity is made available to the customer. Southern Power generally has a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of Southern Power's performance obligation. When multiple contracts exist with the same counterparty, the revenues from each contract are accounted for as separate arrangements. Southern Power may also enter into contracts to sell short-term capacity in the wholesale electricity markets. These sales are generally classified as mark-to-market derivatives and net unrealized gains and losses on such contracts are recorded in wholesale revenues. See Note 14 and "Financial Instruments" herein for additional information. Southern Company Gas Gas Distribution Operations Southern Company Gas records revenues when goods or services are provided to customers. Those revenues are based on rates approved by the state regulatory agencies of the natural gas distribution utilities. Atlanta Gas Light operates in a deregulated natural gas market wher eby M arketers, rather than a traditional utility, sell natural gas to end-use customers in Georgia and handle customer billing functions. As required by the Georgia PSC, Atlanta Gas Light bills Marketers in equal monthly installments for each residential, commercial, and industrial end-use customer's distribution costs as well as for capacity costs utilizing a seasonal rate design for the calculation of each residential end-use customer's annual straight-fixed-variable charge, which reflects the historic volumetric usage pattern for the entire residential class. The majority of the revenues of Southern Company Gas are generated from contracts with natural gas distribution customers. Revenues from this integrated service to deliver gas when and if called upon by the customer are recognized as a single performance obligation satisfied over time and are recognized at a tariff rate as gas is delivered to the customer during the month. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, Southern Company Gas recognizes revenue as the performance obligations are satisfied over time as natural gas is delivered to the customer. The performance obligations related to wholesale gas services are satisfied, and revenue is recognized, at a point in time when natural gas is delivered to the customer. Southern Company Gas has elected to recognize revenue for sales of gas using the invoice practical expedient as it generally has a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and that may be invoiced. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of Southern Company Gas' performance obligation. With the exception of Atlanta Gas Light, the natural gas distribution utilities have rate structures that include volumetric rate designs that allow the opportunity to recover certain costs based on gas usage. Revenues from sales and transportation services are recognized in the same period in which the related volumes are delivered to customers. Revenues from residential and certain commercial and industrial customers are recognized on the basis of scheduled meter readings. Additionally, unbilled revenues are recognized for estimated deliveries of gas not yet billed to these customers, from the last bill date to the end of the accounting period. For other commercial and industrial customers and for all wholesale customers, revenues are based on actual deliveries through the end of the period. The tariffs for several of the natural gas distribution utilities include provisions which allow for the recognition of certain revenues prior to the time such revenues are billed to customers. These provisions are referred to as alternative revenue programs and provide for the recognition of certain revenues prior to billing, as long as the amounts recognized will be collected from customers within 24 months of recognition. These programs are as follows: • Weather normalization adjustments – reduce customer bills when winter weather is colder than normal and increase customer bills when weather is warmer than normal and are included in the tariffs for Virginia Natural Gas, Chattanooga Gas, and, prior to its sale, Elizabethtown Gas; • Revenue normalization mechanisms – mitigate the impact of conservation and declining customer usage and are contained in the tariffs for Virginia Natural Gas, Chattanooga Gas, Nicor Gas (effective November 1, 2019), and, prior to its sale, Elkton Gas; and • Revenue true-up adjustment – included within the provisions of the GRAM program in which Atlanta Gas Light participates as a short-term alternative to formal rate case filings, the revenue true-up feature provides for a positive (or negative) adjustment to record revenue in the amount of any variance to budgeted revenues, which are submitted and approved annually as a requirement of GRAM. Such adjustments are reflected in customer billings in a subsequent program year. Wholesale Gas Services Southern Company Gas nets revenues from energy and risk management activities with the associated costs. Profits from sales between segments are eliminated and are recognized as goods or services sold to end-use customers. Southern Company Gas records transactions that qualify as derivatives at fair value with changes in fair value recognized in earnings in the period of change and characterized as unrealized gains or losses. Gains and losses on derivatives held for energy trading purposes are presented on a net basis in revenue. Gas Marketing Services Southern Company Gas recognizes revenues from natural gas sales and transportation services in the same period in which the related volumes are delivered to customers and recognizes sales revenues from residential and certain commercial and industrial customers on the basis of scheduled meter readings. Southern Company Gas also recognizes unbilled revenues for estimated deliveries of gas not yet billed to these customers from the most recent meter reading date to the end of the accounting period. For other commercial and industrial customers and for all wholesale customers, revenues are based on actual deliveries during the period. Southern Company Gas recognizes revenues on 12-month utility-bill management contracts as the lesser of cumulative earned or cumulative billed amounts. Concentration of Credit Risk Southern Company Gas' wholesale gas services business has a concentration of credit risk for services it provides to its counterparties. This credit risk is generally concentrated in 20 of its counterparties and is measured by 30-day receivable exposure plus forward exposure. Counterparty credit risk is evaluated using a S&P equivalent credit rating, which is determined by a process of converting the lower of the S&P or Moody's rating to an internal rating ranging from 9 to 1, with 9 being equivalent to AAA/Aaa by S&P and Moody's, respectively, and 1 being equivalent to D/Default by S&P and Moody's, respectively. A counterparty that does not have an external rating is assigned an internal rating based on the strength of its financial ratios. As of December 31, 2020, the top 20 counterparties represented 58%, or $234 million , of the total counterparty exposure and had a weighted average S&P equivalent rating of A-. Concentration of credit risk occurs at Atlanta Gas Light for amounts billed for services and other costs to its customers, which consist of 16 Marketers in Georgia (including SouthStar). The credit risk exposure to the Marketers varies seasonally, with the lowest exposure in the non-peak summer months and the highest exposure in the peak winter months. Marketers are responsible for the retail sale of natural gas to end-use customers in Georgia. The functions of the retail sale of gas include the purchase and sale of natural gas, customer service, billings, and collections. The provisions of Atlanta Gas Light's tariff allow Atlanta Gas Light to obtain credit security support in an amount equal to a minimum of two times a Marketer's highest month's estimated bill from Atlanta Gas Light. Concentration of Revenue Southern Company, Alabama Power, Georgia Power, Mississippi Power (with the exception of its full requirements cost-based MRA electric tariffs described below), and Southern Company Gas each have a diversified base of customers and no single customer or industry comprises 10% or more of each company's revenues. Mississippi Power provides service under long-term contracts with rural electric cooperative associations and a municipality located in southeastern Mississippi under full requirements cost-based MRA electric tariffs, which are subject to regulation by the FERC. The contracts with these wholesale customers represent ed 15.3% of Mississippi Power 's total operating revenues in 2020 and are generally subject to 10 -year rolling c ancellation notices. Historically, these wholesale customers have acted as a group and any changes in contractual relationships for one customer are likely to be followed by the other wholesale customers. Significant portions of Southern Power's revenues have been derived from certain customers pursuant to PPAs. The following table shows the percentage of total revenues for Southern Power's top three customers for each of the years presented: 2020 2019 2018 Southern California Edison 9.4 % 6.8 % 6.2 % Georgia Power 8.0 % 9.0 % 9.8 % Duke Energy Corporation 6.7 % N/A 6.8 % Morgan Stanley Capital Group N/A 4.9 % N/A Fuel Costs Fuel costs for the traditional electric operating companies and Southern Power are expensed as the fuel is used. Fuel expense generally includes fuel transportation costs and the cost of purchased emissions allowances as they are used. For Alabama Power and Georgia Power, fuel expense also includes the amortization of the cost of nuclear fuel. For the traditional electric operating companies, fuel costs also include gains and/or losses from fuel-hedging programs as approved by their respective state PSCs. Cost of Natural Gas Excluding Atlanta Gas Light, which does not sell natural gas to end-use customers, Southern Company Gas charges its utility customers for natural gas consumed using natural gas cost recovery mechanisms set by the applicable state regulatory agencies. Under these mechanisms, all prudently-incurred natural gas costs are passed through to customers without markup, subject to regulatory review. Southern Company Gas defers or accrues the difference between the actual cost of natural gas and the amount of commodity revenue earned in a given period such that no operating income is recognized related to these costs. The deferred or accrued amount is either billed or refunded to customers prospectively through adjustments to the commodity rate. Deferred and accrued natural gas costs are included in the balance sheets as regulatory assets and regulatory liabilities, respectively. Southern Company Gas' gas marketing services' customers are charged for actual or estimated natural gas consumed. Within cost of natural gas, Southern Company Gas also includes costs of lost and unaccounted for gas, adjustments to reduce the value of inventories to market value, and gains and losses associated with certain derivatives. Income Taxes The Registrants use the liability method of accounting for deferred income taxes and provide deferred income taxes for all significant income tax temporary differences. In accordance with regulatory requirements, deferred federal ITCs for the traditional electric operating companies are deferred and amortized over the average life of the related property, with such amortization normally applied as a credit to reduce depreciation and amortization in the statements of income. Southern Power's and the natural gas distribution utilities' deferred federal ITCs, as well as certain state ITCs for Nicor Gas, are deferred and amortized to income tax expense over the life of the respective asset. Under current tax law, certain projects at Southern Power related to the construction of renewable facilities are eligible for federal ITCs. Southern Power estimates eligible costs which, as they relate to acquisitions, may not be finalized until the allocation of the purchase price to assets has been finalized. Southern Power applies the deferred method to ITCs, whereby the ITCs are recorded as a deferred credit and amortized t

REGULATORY MATTERS

REGULATORY MATTERS	12 Months Ended
	Dec. 31, 2020
Regulated Operations [Abstract]
REGULATORY MATTERS	REGULATORY MATTERS Regulatory Assets and Liabilities Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2020 and 2019 are provided in the following tables: Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2020 AROs (a)(s) $ 5,147 $ 1,470 $ 3,457 $ 212 $ — Retiree benefit plans (b)(s) 4,958 1,265 1,647 238 187 Remaining net book value of retired assets (c) 1,183 632 527 24 — Deferred income tax charges (d) 801 235 531 32 — Environmental remediation (e)(s) 310 — 41 — 269 Loss on reacquired debt (f) 304 47 248 6 3 Storm damage (g) 262 — 262 — — Vacation pay (h)(s) 207 80 104 10 13 Under recovered regulatory clause revenues (i) 185 58 — 52 75 Regulatory clauses (j) 142 142 — — — Nuclear outage (k) 101 61 40 — — Long-term debt fair value adjustment (l) 92 — — — 92 Kemper County energy facility assets, net (m) 50 — — 50 — Plant Daniel Units 3 and 4 (n) 32 — — 32 — Other regulatory assets (o) 205 52 68 4 81 Deferred income tax credits (d) (6,016) (2,016) (2,805) (320) (847) Other cost of removal obligations (a) (1,999) (335) 212 (194) (1,649) Over recovered regulatory clause revenues (i) (185) (46) (44) — (95) Storm/property damage reserves (p) (81) (77) — (4) — Customer refunds (q) (56) (50) (6) — — Other regulatory liabilities (r) (149) (37) (30) (6) (54) Total regulatory assets (liabilities), net $ 5,493 $ 1,481 $ 4,252 $ 136 $ (1,925) Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2019 Retiree benefit plans (b)(s) $ 4,423 $ 1,131 $ 1,516 $ 213 $ 167 AROs (a)(s) 4,381 1,043 3,119 210 — Remaining net book value of retired assets (c) 1,275 649 596 30 — Deferred income tax charges (d) 803 245 523 33 — Storm damage (g) 410 — 410 — — Environmental remediation (e)(s) 349 — 52 — 296 Loss on reacquired debt (f) 323 52 262 6 4 Vacation pay (h)(s) 186 72 93 9 11 Under recovered regulatory clause revenues (i) 159 40 — 47 72 Regulatory clauses (j) 142 142 — — — Long-term debt fair value adjustment (l) 107 — — — 107 Nuclear outage (k) 105 78 27 — — Fuel-hedging (realized and unrealized) losses (t) 102 22 53 27 — Kemper County energy facility assets, net (m) 61 — — 61 — Plant Daniel Units 3 and 4 (n) 34 — — 34 — Other regulatory assets (o) 127 45 23 6 53 Deferred income tax credits (d) (6,301) (1,960) (3,078) (358) (874) Other cost of removal obligations (a) (2,084) (412) 156 (189) (1,606) Customer refunds (q) (285) (56) (229) — — Over recovered regulatory clause revenues (i) (205) (112) (10) — (82) Storm/property damage reserves (p) (204) (150) — (55) — Other regulatory liabilities (r) (70) (19) (6) (10) (22) Total regulatory assets (liabilities), net $ 3,838 $ 810 $ 3,507 $ 64 $ (1,874) Unless otherwise noted, the following recovery and amortization periods for these regulatory assets and (liabilities) have been approved by the respective state PSC or regulatory agency: (a) AROs and other cost of removal obligations generally are recorded over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. AROs and cost of removal obligations will be settled and trued up following completion of the related activities. Effective January 1, 2020, Georgia Power is recovering CCR AROs, including past under recovered costs and estimated annual compliance costs, over three-year periods ending December 31, 2022, 2023, and 2024 through its Environmental Compliance Cost Recovery (ECCR) tariff, as discussed further under "Georgia Power – Rate Plans" herein. See Note 6 for additional information on AROs. (b) Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power, 13 years for Georgia Power, 14 years for Mississippi Power, and 13 years for Southern Company Gas. Southern Company's balances also include amounts at SCS and Southern Nuclear that are allocated to the applicable regulated utilities. See Note 11 for additional information. (c) Alabama Power : Primarily represents the net book value of Plant Gorgas Units 8, 9, and 10 ($585 million at December 31, 2020). Being amortized over remaining periods not exceeding 17 years (through 2037). Georgia Power : Net book values of Plant Hammond Units 1 through 4 and Plant Branch Units 2 through 4 (totaling $503 million at December 31, 2020) are being amortized over remaining periods of between two Mississippi Power : Represents net book value associated with Plant Watson and Plant Greene County. The retail and wholesale portions totaling approximately $11 million and $13 million at December 31, 2020, respectively, are being amortized over a four-year period through 2024 and a 10-year period through 2030, respectively. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d) Deferred income tax charges are recovered and deferred income tax credits are amortized over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. See Note 10 for additional information. Included in the deferred income tax charges are amounts ($8 million, $9 million, and $1 million for Alabama Power, Georgia Power, and Mississippi Power, respectively, at December 31, 2020) for the retiree Medicare drug subsidy, which are being recovered and amortized through 2027, 2022, and 2024 for Alabama Power, Georgia Power, and Mississippi Power, respectively. As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, as described further below: Alabama Power: Related amounts are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts at December 31, 2020 include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $440 million of deferred income tax liabilities. The recovery of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 is expected to be determined in a future regulatory proceeding. Effective January 1, 2020, the deferred income tax liabilities are being amortized through 2022. Mississippi Power: Related amounts at December 31, 2020 include $74 million of deferred income tax liabilities, consisting of the retail portion of $66 million being amortized over three years (through 2023) and the wholesale portion of $9 million being amortized over two years (through 2021). See "Mississippi Power – 2019 Base Rate Case" and " – Municipal and Rural Associations Tariff" herein for additional information. Southern Company Gas : Related amounts at December 31, 2020 include $8 million of deferred income tax liabilities, which are being amortized through 2024. See "Southern Company Gas – Rate Proceedings" herein for additional information. (e) Georgia Power is recovering $12 million annually for environmental remediation. Southern Company Gas' costs are recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 under "Environmental Remediation" for additional information. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2020, the remaining amortization periods do not exceed 28 years for Alabama Power, 32 years for Georgia Power, eight years for Mississippi Power, and seven years for Southern Company Gas. (g) Georgia Power is recovering approximately $213 million annually for storm damage. See "Georgia Power – Storm Damage Recovery" herein and Note 1 under "Storm Damage Reserves" for additional information. (h) Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (i) Alabama Power : Balances are recorded monthly and expected to be recovered or returned within nine years. Recovery periods could change based on several factors including changes in cost estimates, load forecasts, and timing of rate adjustments. See "Alabama Power – Rate CNP PPA," " – Rate CNP Compliance," and " – Rate ECR" herein for additional information. Georgia Power : Balances are recorded monthly and expected to be recovered or returned within two years. See "Georgia Power – Rate Plans" herein for additional information. Mississippi Power : At December 31, 2020, $37 million is being amortized over a four-yea Southern Company Gas : Balances are recorded and recovered or amortized over periods generally not exceeding five years. In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities have various other cost recovery mechanisms for the recovery of costs, including those related to infrastructure replacement programs. (j) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2023. (k) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent period of 18 months for Alabama Power and up to 24 months for Georgia Power. See Note 5 for additional information. (l) Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 18 years at December 31, 2020. (m) Includes $62 million of regulatory assets and $12 million of regulatory liabilities at December 31, 2020. The retail portion includes $50 million of regulatory assets and $12 million of regulatory liabilities that are expected to be fully amortized by 2024 and 2023, respectively. The wholesale portion includes $12 million of regulatory assets that are expected to be fully amortized by 2029. See Note 3 under "Mississippi Power – Other Matters – Kemper County Energy Facility" for additional information. (n) Represents the difference between Mississippi Power's revenue requirement for Plant Daniel Units 3 and 4 under purchase accounting and operating lease accounting, which is expected to be amortized over a period to be determined in future retail and wholesale rate filings. (o) Except as otherwise noted, comprised of numerous immaterial components with remaining amortization periods generally not exceeding 23 years for Alabama Power, three years for Georgia Power, four years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. Balances at December 31, 2020 include deferred COVID-19 costs (except for Alabama Power), as discussed further under "Deferral of Incremental COVID-19 Costs" for each applicable Registrant herein. Balances for Georgia Power also include certain operations and maintenance costs associated with software and cloud computing projects for which the recovery period will be determined in its next base rate case. (p) Amortized as related expenses are incurred. See "Alabama Power – Rate NDR" and "Mississippi Power – System Restoration Rider" herein for additional information. (q) Primarily includes approximately $50 million and $53 million at December 31, 2020 and 2019, respectively, for Alabama Power and $110 million at December 31, 2019 for Georgia Power as a result of each company exceeding its allowed retail return range. Georgia Power's December 31, 2019 balance also includes approximately $105 million pursuant to the Georgia Power Tax Reform Settlement Agreement. Georgia Power's balances also include immaterial amounts related to refunds for transmission service customers. See "Alabama Power" and "Georgia Power – Rate Plans" herein for additional information. (r) Comprised of numerous immaterial components with remaining amortization periods generally not exceeding 17 years for Alabama Power, 12 years for Georgia Power, three years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. (s) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. (t) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts. Upon final settlement, actual costs incurred are recovered through the applicable traditional electric operating company's fuel cost recovery mechanism. Purchase contracts generally do not exceed three and a half years for Alabama Power, three years for Georgia Power, and five years for Mississippi Power. Immaterial amounts at December 31, 2020 are included in other regulatory assets and liabilities. Alabama Power Alabama Power's revenues from regulated retail operations are collected through various rate mechanisms subject to the oversight of the Alabama PSC. Alabama Power currently recovers its costs from the regulated retail business primarily through Rate RSE, Rate CNP, Rate ECR, and Rate NDR. In addition, the Alabama PSC issues accounting orders to address current events impacting Alabama Power. Petition for Certificate of Convenience and Necessity On August 14, 2020, the Alabama PSC issued its order regarding Alabama Power's September 2019 petition for a CCN, which authorized Alabama Power to (i) construct an approximately 720-MW combined cycle facility at Alabama Power's Plant Barry (Plant Barry Unit 8) that is expected to be placed in service by the end of 2023, (ii) complete the acquisition of the Central Alabama Generating Station, which occurred on August 31, 2020, (iii) purchase approximately 240 MWs of combined cycle generation under a long-term PPA, which began on September 1, 2020, and (iv) pursue up to approximately 200 MWs of cost-effective demand-side management and distributed energy resource programs. Alabama Power's petition for a CCN was predicated on the results of Alabama Power's 2019 IRP provided to the Alabama PSC, which identified an approximately 2,400-MW resource need for Alabama Power, driven by the need for additional winter reserve capacity. See Note 15 under "Alabama Power" for additional information on the acquisition of the Central Alabama Generating Station. The Alabama PSC authorized the recovery of actual costs for the construction of Plant Barry Unit 8 up to 5% above the estimated in-service cost of $652 million. In so doing, it recognized the potential for developments that could cause the project costs to exceed the capped amount, in which case Alabama Power would provide documentation to the Alabama PSC to explain and justify potential recovery of the additional costs. At December 31, 2020, project expenditures associated with Plant Barry Unit 8 included in CWIP totaled approximately $66 million. The Alabama PSC further directed that the proposed solar generation of approximately 400 MWs, coupled with battery energy storage systems (solar/battery systems), be evaluated under an existing Renewable Generation Certificate (RGC) issued by the Alabama PSC in September 2015. The contracts proposed in the CCN petition expired on July 31, 2020. Any future requests for solar/battery systems will be evaluated under the RGC process. Energy Alabama, Gasp, Inc., and the Sierra Club filed requests for reconsideration and rehearing with the Alabama PSC, and, on December 10, 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 14, 2020 CCN order and the December 10, 2020 order denying reconsideration and rehearing. Alabama Power expects to recover costs associated with Plant Barry Unit 8 pursuant to its Rate CNP New Plant. Alabama Power is recovering all costs associated with the Central Alabama Generating Station through the inclusion in Rate RSE of revenues from the existing power sales agreement and, on expiration of that agreement, expects to recover costs pursuant to Rate CNP New Plant. The recovery of costs associated with laws, regulations, and other such mandates directed at the utility industry are expected to be recovered through Rate CNP Compliance. Alabama Power expects to recover the capacity-related costs associated with the PPAs through its Rate CNP PPA. In addition, fuel and energy-related costs are expected to be recovered through Rate ECR. Any remaining costs associated with Plant Barry Unit 8 and the acquisition of the Central Alabama Generating Station are expected to be recovered through Rate RSE. The ultimate outcome of these matters cannot be determined at this time. Rate RSE The Alabama PSC has adopted Rate RSE that provides for periodic annual adjustments based upon Alabama Power's projected weighted common equity return (WCER) compared to an allowable range. Rate RSE adjustments are based on forward-looking information for the applicable upcoming calendar year. Rate RSE adjustments for any two-year period, when averaged together, cannot exceed 4.0% and any annual adjustment is limited to 5.0%. When the projected WCER is under the allowed range, there is an adjusting point of 5.98% and eligibility for a performance-based adder of seven basis points, or 0.07%, to the WCER adjusting point if Alabama Power (i) has an "A" credit rating equivalent with at least one of the recognized rating agencies or (ii) is in the top one-third of a designated customer value benchmark survey. As initially designed, if Alabama Power's actual retail return was above the allowed WCER range, the excess would be refunded to customers unless otherwise directed by the Alabama PSC; however, there was no provision for additional customer billings should the actual retail return fall below the WCER range. In 2018, the Alabama PSC approved modifications to Rate RSE and other commitments designed to position Alabama Power to address the growing pressure on its credit quality resulting from the Tax Reform Legislation, without increasing retail rates under Rate RSE in the near term. Alabama Power continues to reduce growth in total debt by increasing equity, with corresponding reductions in debt issuances, thereby de-leveraging its capital structure. Alabama Power's goal is to achieve an equity ratio of approximately 55% by the end of 2025. At December 31, 2020 and 2019, Alabama Power's equity ratio was approximately 51.6% and 50.3%, respectively. The approved modifications to Rate RSE began for billings in January 2019. The modifications include reducing the top of the allowed WCER range from 6.21% to 6.15% and modifications to the refund mechanism applicable to prior year actual results that allow Alabama Power to retain a portion of the revenue that causes the actual WCER for a given year to exceed the allowed range. Generally, during a year without a Rate RSE upward adjustment, if Alabama Power's actual WCER is between 6.15% and 7.65%, customers will receive 25% of the amount between 6.15% and 6.65%, 40% of the amount between 6.65% and 7.15%, and 75% of the amount between 7.15% and 7.65%. Customers will receive all amounts in excess of an actual WCER of 7.65%. During a year with a Rate RSE upward adjustment, if Alabama Power's actual WCER exceeds 6.15%, customers receive 50% of the amount between 6.15% and 6.90% and all amounts in excess of an actual WCER of 6.90%. There is no provision for additional customer billings should the actual retail return fall below the WCER range. In conjunction with these modifications to Rate RSE, in 2018, Alabama Power consented to a moratorium on any upward adjustments under Rate RSE for 2019 and 2020 and to return $50 million to customers through bill credits in 2019. Retail rates under Rate RSE remained unchanged for 2019 and 2020. Together with Rate RSE, Alabama Power has an established retail tariff that provides for an adjustment to customer billings to recognize the impact of a change in the statutory income tax rate. In accordance with this tariff, Alabama Power returned $267 million to retail customers through bill credits during 2018 as a result of the change in the federal income tax rate under the Tax Reform Legislation. At December 31, 2018, Alabama Power's retail return exceeded the allowed WCER range, which resulted in Alabama Power establishing a regulatory liability of $109 million for Rate RSE refunds. In accordance with an Alabama PSC order issued in February 2019, Alabama Power applied $78 million to reduce the Rate ECR under recovered balance and the remaining $31 million was refunded to customers through bill credits starting in July 2019. At December 31, 2019 and 2020, Alabama Power's WCER exceeded 6.15%, resulting in Alabama Power establishing a current regulatory liability of $53 million and $50 million, respectively, for Rate RSE refunds. In April 2020, the regulatory liability at December 31, 2019 was refunded to customers through bill credits. The $50 million regulatory liability at December 31, 2020 will be refunded to customers through bill credits in April 2021. During 2019, Alabama Power provided to the Alabama PSC and the Alabama Office of the Attorney General information related to the operation and utilization of Rate RSE, in accordance with the rules governing the operation of Rate RSE. During 2020, the Alabama PSC concluded that Rate RSE continues to fulfill its intended purposes and that no significant revisions are needed or warranted. On December 1, 2020, Alabama Power made its required annual Rate RSE submission to the Alabama PSC of projected data for calendar year 2021, resulting in an increase of 4.09%, or approximately $228 million annually, that became effective for the billing month of January 2021. Rate CNP New Plant Rate CNP New Plant allows for recovery of Alabama Power's retail costs associated with newly developed or acquired certificated generating facilities placed into retail service. No adjustments to Rate CNP New Plant occurred during the period 2018 through 2020. See "Petition for Certificate of Convenience and Necessity" herein for additional information. Rate CNP PPA Rate CNP PPA allows for the recovery of Alabama Power's retail costs associated with certificated PPAs. Revenues for Rate CNP PPA, as recorded on the financial statements, are adjusted for differences in actual recoverable costs and amounts billed in current regulated rates. Accordingly, changes in the billing factor will have no significant effect on Southern Company's or Alabama Power's revenues or net income but will affect annual cash flow. No adjustments to Rate CNP PPA occurred during the period 2018 through 2020 and no adjustment is expected for 2021. At December 31, 2020 and 2019, Alabama Power had an under recovered Rate CNP PPA balance of $58 million and $40 million, respectively, which is included in other regulatory assets, deferred on the balance sheet. Rate CNP Compliance Rate CNP Compliance allows for the recovery of Alabama Power's retail costs associated with laws, regulations, and other such mandates directed at the utility industry involving the environment, security, reliability, safety, sustainability, or similar considerations impacting Alabama Power's facilities or operations. Rate CNP Compliance is based on forward-looking information and provides for the recovery of these costs pursuant to factors that are calculated and submitted to the Alabama PSC by December 1 with rates effective for the following calendar year. Compliance costs to be recovered include operations and maintenance expenses, depreciation, and a return on certain invested capital. Revenues for Rate CNP Compliance, as recorded on the financial statements, are adjusted for differences in actual recoverable costs and amounts billed in current regulated rates. Accordingly, changes in the billing factor will have no significant effect on Southern Company's or Alabama Power's revenues or net income, but will affect annual cash flow. Changes in Rate CNP Compliance-related operations and maintenance expenses and depreciation generally will have no effect on net income. In November 2018, 2019, and 2020, Alabama Power submitted calculations associated with its cost of complying with governmental mandates for the following calendar year, as provided under Rate CNP Compliance. The 2018 filing reflected a projected under recovered retail revenue requirement of approximately $205 million, which was recovered in the billing months of January 2019 through December 2019. The 2019 filing reflected a projected over recovered retail revenue requirement, which resulted in a rate decrease of approximately $68 million that became effective for the billing month of January 2020. The 2020 filing reflected a projected under recovered retail revenue requirement of approximately $59 million. On December 1, 2020, the Alabama PSC issued a consent order that Alabama Power leave the 2020 Rate CNP Compliance factor in effect for 2021, with any prior year under collected amount deemed recovered before any current year amounts are recovered. Any remaining under recovered amount will be reflected in the 2021 filing. At December 31, 2020, Alabama Power had an over recovered Rate CNP Compliance balance of $28 million included in other regulatory liabilities, current on the balance sheet. At December 31, 2019, Alabama Power had an over recovered Rate CNP Compliance balance of $62 million, of which $55 million is included in other regulatory liabilities, current and $7 million is included in other regulatory liabilities, deferred on the balance sheet. Rate ECR Rate ECR recovers Alabama Power's retail energy costs based on an estimate of future energy costs and the current over or under recovered balance. Revenues recognized under Rate ECR and recorded on the financial statements are adjusted for the difference in actual recoverable fuel costs and amounts billed in current regulated rates. The difference in the recoverable fuel costs and amounts billed gives rise to the over or under recovered amounts recorded as regulatory assets or liabilities. Alabama Power, along with the Alabama PSC, continually monitors the over or under recovered cost balance to determine whether an adjustment to billing rates is required. Changes in the Rate ECR factor have no significant effect on Southern Company's or Alabama Power's net income but will impact operating cash flows. The Alabama PSC may approve billing rates under Rate ECR of up to 5.910 cents per KWH. In May 2018, the Alabama PSC approved an increase to Rate ECR from 2.015 cents per KWH to 2.353 cents per KWH effective July 2018 through December 2018. In December 2018, the Alabama PSC issued a consent order to leave this rate in effect through December 31, 2019. As discussed herein under "Rate RSE," in accordance with an Alabama PSC order issued in February 2019, Alabama Power utilized $78 million of the 2018 Rate RSE refund liability to reduce the Rate ECR under recovered balance. In December 2019, the Alabama PSC approved a decrease to Rate ECR from 2.353 cents per KWH to 2.160 cents per KWH, equal to 1.82%, or approximately $102 million annually, that became effective for the billing month of January 2020. In October 2020, Alabama Power reduced its over-collected fuel balance by $94.3 million in accordance with an August 7, 2020 Alabama PSC order authorizing Alabama Power to reduce its over-collected fuel balance by $100 million and return that amount to customers in the form of bill credits, with any undistributed amount remaining in the regulatory liability for the benefit of customers. On December 1, 2020, the Alabama PSC approved a decrease to Rate ECR from 2.160 cents per KWH to 1.960 cents per KWH, equal to 1.84%, or approximately $103 million annually, that became effective for the billing month of January 2021. The rate will adjust to 5.910 cents per KWH in January 2022 absent a further order from the Alabama PSC. At December 31, 2020, Alabama Power's over recovered fuel costs totaled $18 million and is included in other regulatory liabilities, current on the balance sheet. At December 31, 2019, Alabama Power's over recovered fuel costs totaled $49 million, of which $32 million is included in other regulatory liabilities, current and $17 million is included in other regulatory liabilities, deferred on the balance sheet. These classifications are based on estimates, which include such factors as weather, generation availability, energy demand, and the price of energy. A change in any of these factors could have a significant impact on the timing of any recovery or return of fuel costs. Tax Reform Accounting Order In 2018, the Alabama PSC approved an accounting order that authorized Alabama Power to defer the benefits of federal excess deferred income taxes associated with the Tax Reform Legislation for the year ended December 31, 2018 as a regulatory liability and to use up to $30 million of such deferrals to offset under recovered amounts under Rate ECR. The final excess deferred tax liability for the year ended December 31, 2018 totaled approximately $69 million, of which $30 million was used to offset the Rate ECR under recovered balance. In December 2019, the Alabama PSC issued an order authorizing Alabama Power to apply the remaining deferred balance of approximately $39 million to increase the balance in the NDR. See "Rate NDR" herein and Note 10 under "Current and Deferred Income Taxes" for additional information. Software Accounting Order In February 2019, the Alabama PSC approved an accounting order that authorizes Alabama Power to establish a regulatory asset for operations and maintenance costs associated with software implementation projects. The regulatory asset will be amortized ratably over the life of the related software. At December 31, 2020 and 2019, the regulatory asset balance totaled $17 million and $6 million, respectively, and is included in other deferred charges and assets on the balance sheet. Plant Greene County Alabama Power jointly owns Plant Greene County with an affiliate, Mississippi Power. See Note 5 under "Joint Ownership Agreements" for additional information. In December 2019, Mississippi Power updated its proposed RMP, originally filed in 2018 with the Mississippi PSC. The RMP proposed a four-year acceleration of the retirement of Plant Greene County Units 1 and 2 to the third quarter 2021 and the third quarter 2022, respectively. On December 17, 2020, the Mississippi PSC issued an order concluding the RMP docket and requiring Mississippi Power to incorporate into its 2021 IRP a schedule of early or anticipated retirement of 950 MWs of fossil-steam generation, which could include Plant Greene County, by year-end 2027 to reduce Mississippi Power's excess reserve margin. Mississippi Power's IRP is scheduled to be filed in April 2021. Any proposed Plant Greene County unit retirements by Mississippi Power would 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. Alabama Power will review all the facts and circumstances and will evaluate all of its alternatives prior to reaching a final determination on the ongoing operations of Plant Greene County. The ultimate outcome of this matter cannot be determined at this time. Rate NDR Based on an order from the Alabama PSC, Alabama Power maintains a reserve for operations and maintenance expenses to cover the cost of damages from major storms to its transmission and distribution facilities. The order approves a separate monthly Rate NDR charge to customers consisting of two components. The first component is intended to establish and maintain a reserve balance for future storms and is an on-going part of customer billing. When the reserve balance falls below $50 million, a reserve establishment charge will be activated (and the on-going reserve maintenance charge concurrently suspended) until the reserve balance reaches $75 million. The second component of the Rate NDR charge is intended to allow recovery of any existing deferred storm-related operations and maintenance costs and any future reserve deficits over a 24-month period. The Alabama PSC order gives Alabama Power authority to record a deficit balance in the NDR when costs of storm damage exceed any established reserve balance. Absent further Alabama PSC approval, the maximum total Rate NDR charge consisting of both components is $10 per month per non-residential customer account and $5 per month per residential customer account. Alabama Power has the authority, based on an order from the Alabama PSC, to accrue certain additional am

CONTINGENCIES, COMMITMENTS, AND

CONTINGENCIES, COMMITMENTS, AND GUARANTEES	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
CONTINGENCIES, COMMITMENTS, AND GUARANTEES	CONTINGENCIES, COMMITMENTS, AND GUARANTEES 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 January 2017, a securities class action complaint was filed in the U.S. District Court for the Northern District of Georgia by Monroe County Employees' Retirement System on behalf of all persons who purchased shares of Southern Company's common stock between April 25, 2012 and October 30, 2013, as subsequently amended. The amended complaint named as defendants Southern Company, certain of its current and former officers, and certain former Mississippi Power officers and alleged that the defendants made materially false and misleading statements regarding the Kemper County energy facility in violation of certain provisions under the Securities Exchange Act of 1934, as amended. The complaint sought, among other things, compensatory damages and litigation costs and attorneys' fees. In 2018, the court issued an order dismissing certain claims against certain officers of Southern Company and Mississippi Power and dismissing the allegations related to a number of the statements that plaintiffs challenged as being false or misleading. In 2018, the court denied the defendants' motion for reconsideration and also denied a motion to certify the issue for interlocutory appeal. In 2019, the court certified the plaintiffs' proposed class and entered an order staying all deadlines in the case pending mediation. In the third quarter 2020, the parties reached a settlement and the plaintiffs filed a stipulation of settlement and motion for preliminary approval to resolve the case on a class-wide basis, which the court granted on October 1, 2020. On January 14, 2021, the court granted final approval of the settlement. The settlement amount was paid entirely through existing insurance policies and did not have a material impact on Southern Company's financial statements. This matter is now concluded. 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, as well as 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 resolution of any dispositive motions or any settlement, whichever is earlier, in the securities class action. 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 on November 12, 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. On March 11, 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. The amount of any possible losses cannot be estimated at this time because, among other factors, it is unknown whether a class will be certified, the ultimate composition of any class, and whether any losses would be subject to recovery from any municipalities. On July 29, 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 on May 26, 2020 and March 27, 2020, respectively. Also on March 27, 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. On July 28, 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. On November 10, 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. An adverse outcome in this proceeding could have a material impact on Mississippi Power's financial statements. See "Other Matters – Mississippi Power – Kemper County Energy Facility" herein 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 conduct studies to determine the extent of any required cleanup and have recognized the estimated costs to clean up known impacted sites in the financial statements. A liability for environmental remediation costs is recognized only when a loss is determined to be probable and reasonably estimable and is reduced as expenditures are incurred. 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. Any difference between the liabilities accrued and costs recovered through rates is deferred as a regulatory asset or liability. These regulatory mechanisms are adjusted annually or as necessary within limits approved by the state PSCs or other applicable state regulatory agencies. At December 31, 2020 and 2019, Alabama Power did not have environmental remediation liabilities and Mississippi Power's balance was immaterial. 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. For 2020, 2019, and 2018, Georgia Power recovered approximately $12 million, $2 million, and $2 million, respectively, through the ECCR tariff for environmental remediation. In December 2019, Mississippi Power entered into an agreement with the Mississippi Commission on Environmental Quality related to groundwater conditions arising from the closed ash pond at Plant Watson. Mississippi Power will complete an assessment and remediation consistent with the requirements of the agreement and the CCR Rule. It is anticipated that corrective action will be needed; however, an estimate of remedial costs will not be available until further site assessment is completed. Mississippi Power expects to recover the retail portion of remedial costs through the ECO Plan and the wholesale portion through MRA rates. Southern Company Gas is subject to environmental remediation liabilities associated with 40 former MGP sites in four different states. Southern Company Gas' accrued environmental remediation liability at December 31, 2020 and 2019 was based on the estimated cost of environmental investigation and remediation associated with these sites. At December 31, 2020 and 2019, the environmental remediation liability and the balance of under recovered environmental remediation costs were reflected in the balance sheets as follows: Southern Company Georgia Southern Company Gas (in millions) December 31, 2020: Environmental remediation liability: Other current liabilities $ 44 $ 15 $ 29 Accrued environmental remediation 216 — 216 Under recovered environmental remediation costs: Other regulatory assets, current $ 46 $ 12 $ 34 Other regulatory assets, deferred 265 29 236 December 31, 2019: Environmental remediation liability: Other current liabilities $ 51 $ 15 $ 36 Accrued environmental remediation 234 — 233 Under recovered environmental remediation costs: Other regulatory assets, current $ 49 $ 12 $ 37 Other regulatory assets, deferred 300 40 260 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. Nuclear Fuel Disposal Costs Acting through the DOE and pursuant to the Nuclear Waste Policy Act of 1982, the U.S. government entered into contracts with Alabama Power and Georgia Power that required the DOE to dispose of spent nuclear fuel generated at Plants Farley, Hatch, and Vogtle Units 1 and 2 beginning no later than January 31, 1998. The DOE has yet to commence the performance of its contractual and statutory obligation to dispose of spent nuclear fuel. Consequently, Alabama Power and Georgia Power pursued and continue to pursue legal remedies against the U.S. government for its partial breach of contract. In 2014, Alabama Power and Georgia Power filed lawsuits against the U.S. government for the costs of continuing to store spent nuclear fuel at Plants Farley, Hatch, and Vogtle Units 1 and 2 for the period from January 1, 2011 through December 31, 2013. The damage period was subsequently extended to December 31, 2014. On June 12, 2019, the Court of Federal Claims granted Alabama Power's and Georgia Power's motion for summary judgment on damages not disputed by the U.S. government, awarding those undisputed damages to Alabama Power and Georgia Power. However, those undisputed damages are not collectible and no amounts will be recognized in the financial statements until the court enters final judgment on the remaining damages. In 2017, Alabama Power and Georgia Power filed additional lawsuits against the U.S. government in the Court of Federal Claims for the costs of continuing to store spent nuclear fuel at Plants Farley, Hatch, and Vogtle Units 1 and 2 for the period from January 1, 2015 through December 31, 2017. On August 13, 2020, Alabama Power and Georgia Power filed amended complaints in each of the lawsuits adding damages from January 1, 2018 to December 31, 2019 to the claim period. The outstanding claims for the period January 1, 2011 through December 31, 2019 total $110 million and $132 million for Alabama Power and Georgia Power (based on its ownership interests), respectively. Damages will continue to accumulate until the issue is resolved, the U.S. government disposes of Alabama Power's and Georgia Power's spent nuclear fuel pursuant to its contractual obligations, or alternative storage is otherwise provided. No amounts have been recognized in the financial statements as of December 31, 2020 for any potential recoveries from the pending lawsuits. The final outcome of these matters cannot be determined at this time. However, Alabama Power and Georgia Power expect to credit any recoveries for the benefit of customers in accordance with direction from their respective PSC; therefore, no material impact on Southern Company's, Alabama Power's, or Georgia Power's net income is expected. Nuclear Insurance Under the Price-Anderson Amendments Act (Act), Alabama Power and Georgia Power maintain agreements of indemnity with the NRC that, together with private insurance, cover third-party liability arising from any nuclear incident occurring at the companies' nuclear power plants. The Act provides funds up to $13.8 billion for public liability claims that could arise from a single nuclear incident. Each nuclear plant is insured against this liability to a maximum of $450 million by American Nuclear Insurers (ANI), with the remaining coverage provided by a mandatory program of deferred premiums that could be assessed, after a nuclear incident, against all owners of commercial nuclear reactors. A company could be assessed up to $138 million per incident for each licensed reactor it operates but not more than an aggregate of $20 million per incident to be paid in a calendar year for each reactor. Such maximum assessment, excluding any applicable state premium taxes, for Alabama Power and Georgia Power, based on its ownership and buyback interests in all licensed reactors, is $275 million and $267 million, respectively, per incident, but not more than an aggregate of $41 million and $40 million, respectively, to be paid for each incident in any one year. Both the maximum assessment per reactor and the maximum yearly assessment are adjusted for inflation at least every five years. The next scheduled adjustment is due no later than November 1, 2023. See Note 5 under "Joint Ownership Agreements" for additional information on joint ownership agreements. Alabama Power and Georgia Power are members of Nuclear Electric Insurance Limited (NEIL), a mutual insurer established to provide property damage insurance in an amount up to $1.5 billion for members' operating nuclear generating facilities. Additionally, both companies have NEIL policies that currently provide decontamination, excess property insurance, and premature decommissioning coverage up to $1.25 billion for nuclear losses and policies providing coverage up to $750 million for non-nuclear losses in excess of the $1.5 billion primary coverage. NEIL also covers the additional costs that would be incurred in obtaining replacement power during a prolonged accidental outage at a member's nuclear plant. Members can purchase this coverage, subject to a deductible waiting period of up to 26 weeks, with a maximum per occurrence per unit limit of $490 million. After the deductible period, weekly indemnity payments would be received until either the unit is operational or until the limit is exhausted. Alabama Power and Georgia Power each purchase limits based on the projected full cost of replacement power, subject to ownership limitations, and have each elected a 12-week deductible waiting period for each nuclear plant. A builders' risk property insurance policy has been purchased from NEIL for the construction of Plant Vogtle Units 3 and 4. This policy provides the Vogtle Owners up to $2.75 billion for accidental property damage occurring during construction. Under each of the NEIL policies, members are subject to assessments each year if losses exceed the accumulated funds available to the insurer. The maximum annual assessments for Alabama Power and Georgia Power as of December 31, 2020 under the NEIL policies would be $56 million and $84 million, respectively. Claims resulting from terrorist acts and cyber events are covered under both the ANI and NEIL policies (subject to normal policy limits). The maximum aggregate that NEIL will pay for all claims resulting from terrorist acts and cyber events in any 12-month period is $3.2 billion each, plus such additional amounts NEIL can recover through reinsurance, indemnity, or other sources. For all on-site property damage insurance policies for commercial nuclear power plants, the NRC requires that the proceeds of such policies shall be dedicated first for the sole purpose of placing the reactor in a safe and stable condition after an accident. Any remaining proceeds are to be applied next toward the costs of decontamination and debris removal operations ordered by the NRC, and any further remaining proceeds are to be paid either to the applicable company or to its debt trustees as may be appropriate under the policies and applicable trust indentures. In the event of a loss, the amount of insurance available might not be adequate to cover property damage and other expenses incurred. Uninsured losses and other expenses, to the extent not recovered from customers, would be borne by Alabama Power or Georgia Power, as applicable, and could have a material effect on Southern Company's, Alabama Power's, and Georgia Power's financial condition and results of operations. All retrospective assessments, whether generated for liability, property, or replacement power, may be subject to applicable state premium taxes. Southern Company As discussed in Note 1 under "Leveraged Leases," a subsidiary of Southern Holdings has four leveraged lease agreements, two domestic and two international. The ability of the lessees to make required payments to the Southern Holdings subsidiary is dependent on the operational performance of the assets. Since 2017, the financial and operational performance of one of the domestic lessees and the associated generation assets raised significant concerns about the short-term ability of the generation assets to produce cash flows sufficient to support ongoing operations and the lessee's contractual obligations and its ability to make the remaining semi-annual lease payments through the end of the lease term in 2047. In addition, following the expiration of the existing power offtake agreement in 2032, the lessee also is exposed to remarketing risk, which encompasses the price and availability of alternative sources of generation. In connection with the 2019 annual impairment analysis, Southern Company revised the estimated cash flows to be received under the leveraged lease, which resulted in an impairment charge of $17 million ($13 million after tax) recorded in the fourth quarter 2019. During the second quarter 2020, Southern Company received the latest annual forecasts of natural gas prices and considered the significant decline in forecasted prices to be an indicator of potential impairment that required an interim impairment assessment. Accordingly, consistent with prior impairment analyses, Southern Company evaluated the recoverability of the lease receivable and the expected residual value of the generation assets under various natural gas price scenarios to estimate the cash flows expected to be received from remarketing the generation assets following the expiration of the existing PPA and the residual value of the generation assets at the end of the lease. Based on the current forecasts of energy prices in the years following the expiration of the existing PPA, Southern Company concluded that it is no longer probable that any of the associated rental payments will be received, because it is no longer probable the generation assets will be successfully remarketed and continue to operate after that date. During the second quarter 2020, Southern Company revised the estimated cash flows to be received under the leveraged lease to reflect this conclusion, which resulted in a full impairment of the lease investment and a pre-tax charge to earnings of $154 million ($74 million after tax). All required lease payments through December 31, 2020 have been paid in full. If any future lease payments due prior to the expiration of the associated PPA are not paid in full, the Southern Holdings subsidiary may be unable to make its corresponding payment to the holders of the underlying non-recourse debt related to the generation assets. Failure to make the required payment to the debtholders could represent an event of default that would give the debtholders the right to foreclose on, and take ownership of, the generation assets, in effect terminating the lease. As the remaining amount of the lease investment was charged against earnings in the second quarter 2020, termination would not be expected to result in additional charges. Southern Company will continue to monitor the operational performance of the underlying assets and evaluate the ability of the lessee to continue to make the required lease payments and meet its obligations associated with a future closure or retirement of the generation assets and associated properties, including the dry ash landfill. During the fourth quarter 2020, Southern Company management initiated steps to sell the investment in its other domestic leveraged lease and reclassified the investment as held for sale. In connection with the annual impairment analysis of this investment, Southern Company management concluded that the estimated residual value of the generation assets should be reduced due to significant uncertainty as to whether the related natural gas generation assets will continue to operate at the end of the lease term in 2040 and recorded the resulting impairment charge. An additional charge was recorded to further reduce the related investment in the leveraged lease to its estimated fair value, less costs to sell. The pre-tax charges to earnings in the fourth quarter 2020 totaled $52 million ($31 million after tax). See Note 15 under "Assets Held for Sale" for additional information. The leveraged lease agreements for the two international projects include lessee purchase options related to the leased assets, which consist of nine gas distribution networks and two district heating systems in the Netherlands. The lessee has communicated its intent to exercise the first purchase option in 2022. The purchase options for the remaining ten assets are exercisable on various dates through 2028 with at least one year's notice. The exercise of these purchase options is not expected to result in any gain or loss. Mississippi Power Kemper County Energy Facility The Kemper County energy facility was designed to utilize IGCC technology with an expected output capacity of 582 MWs and to be fueled by locally mined lignite from a mine owned by Mississippi Power and situated adjacent to the Kemper County energy facility. In 2012, the Mississippi PSC issued an order confirming the CPCN originally approved by the Mississippi PSC in 2010 authorizing the acquisition, construction, and operation of the Kemper County energy facility. Mississippi Power placed the combined cycle and the associated common facilities portion of the Kemper County energy facility in service in 2014 and dedicated them as Plant Ratcliffe in 2018. In 2017, the Mississippi PSC issued an order directing Mississippi Power to pursue a settlement under which the Kemper County energy facility would be operated as a natural gas plant, rather than an IGCC plant, and address all issues associated with the Kemper County energy facility. Following this order, cost recovery of the gasifier portions was no longer probable and Mississippi Power recorded significant charges to income in 2017. In 2018, the Mississippi PSC approved a settlement agreement for the Kemper County energy facility, which resolved all cost recovery issues, modified the CPCN to limit the Kemper County energy facility to natural gas combined cycle operation, and reduced retail customer rates by approximately $26.8 million annually based on a revenue requirement that included no recovery for costs associated with the gasifier portion of the Kemper County energy facility. In 2018, 2019, and 2020, Mississippi Power recorded charges to income associated with abandonment and related closure costs and ongoing period costs, net of salvage proceeds, for the mine and gasifier-related assets at the Kemper County energy facility. These charges, including related tax impacts, totaled $37 million pre-tax ($68 million benefit after tax) in 2018, $24 million pre-tax and after tax in 2019, and $4 million pre-tax ($3 million after tax) in 2020. The pre-tax charges are included in other operations and maintenance expenses on the statements of income. Dismantlement of the abandoned gasifier-related assets and site restoration activities are expected to be completed by 2026. Additional pre-tax period costs associated with dismantlement and site restoration activities, including related costs for compliance and safety, ARO accretion, and property taxes, net of salvage, are estimated to total $10 million to $20 million annually through 2025. The Mississippi Power Rate Case Settlement Agreement eliminated separate rates associated with the Kemper County energy facility and included these costs in rates for PEP, ECO Plan, and ad valorem taxes, as applicable, effective with the revised rates in 2020. See Note 2 under "Mississippi Power – 2019 Base Rate Case" for additional information. Lignite Mine and CO 2 Pipeline Facilities Mississippi Power owns the lignite mine and equipment and mineral reserves located around the Kemper County energy facility site. The mine started commercial operation in 2013. In connection with the Kemper County energy facility construction, Mississippi Power also constructed a pipeline for the transport of captured CO 2 . In 2010, Mississippi Power executed a management fee contract with Liberty Fuels Company, LLC (Liberty Fuels), a wholly-owned subsidiary of The North American Coal Corporation, which developed, constructed, and is responsible for the mining operations through the end of the mine reclamation. As the mining permit holder, Liberty Fuels has a legal obligation to perform mine reclamation and Mississippi Power has a contractual obligation to fund all reclamation activities. As a result of the abandonment of the Kemper IGCC, final mine reclamation began in 2018 and was substantially completed in 2020, with monitoring expected to continue through 2027. See Note 6 for additional information. In December 2019, Mississippi Power transferred ownership of the CO 2 pipeline to an unrelated gas pipeline company, with no resulting impact on income. In conjunction with the transfer of the CO 2 pipeline, the parties agreed to enter into a 15-year firm transportation agreement, which became effective in December 2020, upon the conversion by the pipeline company of the CO 2 pipeline to a natural gas pipeline to be used for the delivery of natural gas to Plant Ratcliffe. The agreement is treated as a finance lease for accounting purposes. See Note 9 for additional information. Government Grants In 2010, the DOE, through a cooperative agreement with SCS, agreed to fund $270 million of the Kemper County energy facility through the grants awarded to the project by the DOE under the Clean Coal Power Initiative Round 2. In 2016, additional DOE grants in the amount of $137 million were awarded to the Kemper County energy facility. In 2018, Mississippi Power filed with the DOE its request for property closeout certification under the contract related to the $387 million of total grants received. On September 3, 2020, Mississippi Power and Southern Company executed an agreement with the DOE completing Mississippi Power's request, which enabled Mississippi Power to proceed with full dismantlement of the abandoned gasifier-related assets and site restoration activities. The expected impact of the closeout agreement was accrued in 2019. In connection with the DOE closeout discussions, in A

REVENUE FROM CONTRACTS WITH CUS

REVENUE FROM CONTRACTS WITH CUSTOMERS	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
REVENUE FROM CONTRACTS WITH CUSTOMERS	REVENUE FROM CONTRACTS WITH CUSTOMERS The Registrants generate revenues from a variety of sources, some of which are not accounted for as revenue from contracts with customers, such as leases, derivatives, and certain cost recovery mechanisms. See Note 1 under "Revenues" for additional information on the revenue policies of the Registrants. See Notes 9 and 14 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 periods presented: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Operating revenues Retail electric revenues Residential $ 6,113 $ 2,377 $ 3,476 $ 260 $ — $ — Commercial 4,699 1,512 2,933 254 — — Industrial 2,775 1,293 1,197 285 — — Other 90 21 60 9 — — Total retail electric revenues 13,677 5,203 7,666 808 — — Natural gas distribution revenues Residential 1,338 — — — — 1,338 Commercial 340 — — — — 340 Transportation 971 — — — — 971 Industrial 30 — — — — 30 Other 209 — — — — 209 Total natural gas distribution revenues 2,888 — — — — 2,888 Wholesale electric revenues PPA energy revenues 735 133 42 9 570 — PPA capacity revenues 454 108 50 3 296 — Non-PPA revenues 210 43 10 311 239 — Total wholesale electric revenues 1,399 284 102 323 1,105 — Other natural gas revenues Wholesale gas services 1,727 — — — — 1,727 Gas marketing services 391 — — — — 391 Other natural gas revenues 33 — — — — 33 Total natural gas revenues 2,151 — — — — 2,151 Other revenues 982 159 447 26 14 — Total revenue from contracts with customers 21,097 5,646 8,215 1,157 1,119 5,039 Other revenue sources (a) 3,764 184 94 15 614 2,881 Other adjustments (b) (4,486) — — — — (4,486) Total operating revenues $ 20,375 $ 5,830 $ 8,309 $ 1,172 $ 1,733 $ 3,434 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2019 Operating revenues Retail electric revenues Residential $ 6,164 $ 2,509 $ 3,377 $ 278 $ — $ — Commercial 5,065 1,677 3,097 291 — — Industrial 3,126 1,460 1,360 306 — — Other 90 25 54 11 — — Total retail electric revenues 14,445 5,671 7,888 886 — — Natural gas distribution revenues Residential 1,413 — — — — 1,413 Commercial 389 — — — — 389 Transportation 907 — — — — 907 Industrial 35 — — — — 35 Other 245 — — — — 245 Total natural gas distribution revenues 2,989 — — — — 2,989 Wholesale electric revenues PPA energy revenues 833 145 60 11 648 — PPA capacity revenues 453 102 54 3 322 — Non-PPA revenues 232 81 9 352 238 — Total wholesale electric revenues 1,518 328 123 366 1,208 — Other natural gas revenues Gas pipeline investments 32 — — — — 32 Wholesale gas services 2,095 — — — — 2,095 Gas marketing services 440 — — — — 440 Other natural gas revenues 42 — — — — 42 Total other natural gas revenues 2,609 — — — — 2,609 Other revenues 1,035 153 407 19 12 — Total revenue from contracts with customers 22,596 6,152 8,418 1,271 1,220 5,598 Other revenue sources (a) 4,266 (27) (10) (7) 718 3,637 Other adjustments (b) (5,443) — — — — (5,443) Total operating revenues $ 21,419 $ 6,125 $ 8,408 $ 1,264 $ 1,938 $ 3,792 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2018 Operating revenues Retail electric revenues Residential $ 6,586 $ 2,285 $ 3,295 $ 277 $ — $ — Commercial 5,255 1,541 3,025 290 — — Industrial 3,152 1,364 1,321 326 — — Other 94 25 56 9 — — Total retail electric revenues 15,087 5,215 7,697 902 — — Natural gas distribution revenues Residential 1,525 — — — — 1,525 Commercial 436 — — — — 436 Transportation 944 — — — — 944 Industrial 40 — — — — 40 Other 230 — — — — 230 Total natural gas distribution revenues 3,175 — — — — 3,175 Wholesale electric revenues PPA energy revenues 950 158 81 15 727 — PPA capacity revenues 498 101 53 6 394 — Non-PPA revenues 263 119 24 329 230 — Total wholesale electric revenues 1,711 378 158 350 1,351 — Other natural gas revenues Gas pipeline investments 32 — — — — 32 Wholesale gas services 3,083 — — — — 3,083 Gas marketing services 571 — — — — 571 Other natural gas revenues 53 — — — — 53 Total other natural gas revenues 3,739 — — — — 3,739 Other revenues 1,529 210 236 22 13 — Total revenue from contracts with customers 25,241 5,803 8,091 1,274 1,364 6,914 Other revenue sources (a) 5,108 229 329 (9) 841 3,849 Other adjustments (b) (6,854) — — — — (6,854) Total operating revenues $ 23,495 $ 6,032 $ 8,420 $ 1,265 $ 2,205 $ 3,909 (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 16 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 December 31, 2020 and 2019: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivables As of December 31, 2020 $ 2,614 $ 632 $ 806 $ 77 $ 112 $ 788 As of December 31, 2019 2,413 586 688 79 97 749 Contract Assets As of December 31, 2020 $ 158 $ 2 $ 71 $ — $ — $ — As of December 31, 2019 117 — 69 — — — Contract Liabilities As of December 31, 2020 $ 61 $ 6 $ 27 $ 1 $ 1 $ 1 As of December 31, 2019 52 10 13 — 1 1 As of December 31, 2020 and 2019, 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 contract assets of $81 million and $40 million at December 31, 2020 and 2019, respectively, and contract liabilities of $27 million and $28 million at December 31, 2020 and 2019, respectively, for outstanding performance obligations. The following table reflects revenue from contracts with customers recognized in 2020 and 2019 included in the contract liability at December 31, 2019 and December 31, 2018, respectively, for the applicable Registrants: Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) Revenue Recognized 2020 $ 33 $ 10 $ 8 $ 1 $ 1 2019 30 11 6 11 2 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 December 31, 2020 are expected to be recognized as follows: 2021 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 547 $ 395 $ 338 $ 326 $ 306 $ 2,634 Alabama Power 33 31 24 7 5 — Georgia Power 75 46 35 24 21 42 Southern Power 285 287 280 296 280 2,610 Revenue expected to be recognized for performance obligations remaining at December 31, 2020 was immaterial for Mississippi Power.

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT (Notes)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT, AND EQUIPMENT	PROPERTY, PLANT, AND EQUIPMENT Property, plant, and equipment is stated at original cost or fair value at acquisition, as appropriate, less any regulatory disallowances and impairments. Original cost may include: materials; labor; minor items of property; appropriate administrative and general costs; payroll-related costs such as taxes, pensions, and other benefits; and the interest capitalized and/or cost of equity funds used during construction. The Registrants' property, plant, and equipment in service consisted of the following at December 31, 2020 and 2019: At December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 52,179 $ 16,201 $ 18,675 $ 2,819 $ 13,872 $ — Transmission 12,879 5,033 6,951 856 — — Distribution 20,958 8,248 11,622 1,088 — — General/other 5,072 2,334 2,434 248 32 — Electric utilities' plant in service 91,088 31,816 39,682 5,011 13,904 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 14,610 — — — — 14,610 Storage facilities 1,752 — — — — 1,752 Other 1,249 — — — — 1,249 Southern Company Gas plant in service 17,611 — — — — 17,611 Other plant in service 1,817 — — — — — Total plant in service $ 110,516 $ 31,816 $ 39,682 $ 5,011 $ 13,904 $ 17,611 At December 31, 2019: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 50,329 $ 15,329 $ 18,341 $ 2,786 $ 13,241 $ — Transmission 12,157 4,719 6,590 808 — — Distribution 19,846 7,798 11,024 1,024 — — General/other 4,650 2,177 2,182 239 29 — Electric utilities' plant in service 86,982 30,023 38,137 4,857 13,270 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 13,518 — — — — 13,518 Storage facilities 1,634 — — — — 1,634 Other 1,192 — — — — 1,192 Southern Company Gas plant in service 16,344 — — — — 16,344 Other plant in service 1,788 — — — — — Total plant in service $ 105,114 $ 30,023 $ 38,137 $ 4,857 $ 13,270 $ 16,344 The cost of replacements of property, exclusive of minor items of property, is capitalized. The cost of maintenance, repairs, and replacement of minor items of property is charged to other operations and maintenance expenses as incurred or performed with the exception of nuclear refueling costs and certain maintenance costs including those described below. In accordance with orders from their respective state PSCs, Alabama Power and Georgia Power defer nuclear refueling outage operations and maintenance expenses to a regulatory asset when the charges are incurred. Alabama Power amortizes the costs over a subsequent 18-month period with Plant Farley's fall outage cost amortization beginning in January of the following year and spring outage cost amortization beginning in July of the same year. Georgia Power amortizes its costs over each unit's operating cycle, or 18 months for Plant Vogtle Units 1 and 2 and 24 months for Plant Hatch Units 1 and 2. Georgia Power's amortization period begins the month the refueling outage starts. A portion of Mississippi Power's railway track maintenance costs is charged to fuel stock and recovered through Mississippi Power's fuel clause. The portion of Southern Company Gas' non-working gas used to maintain the structural integrity of natural gas storage facilities that is considered to be non-recoverable is depreciated, while the recoverable or retained portion is not depreciated. See Note 9 for information on finance lease right-of-use (ROU) assets, net, which are included in property, plant, and equipment. The Registrants have deferred certain implementation costs related to cloud hosting arrangements. Once a hosted software is placed into service, the related deferred costs are amortized on a straight-line basis over the remaining expected hosting arrangement term, including any renewal options that are reasonably certain of exercise. The amortization is reflected with the associated cloud hosting fees, which are generally reflected in other operations and maintenance expenses on the Registrants' statements of income. At December 31, 2020, deferred cloud implementation costs, which are generally included in other deferred charges and assets on the Registrants' balance sheets, are as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) At December 31, 2020: Deferred cloud implementation costs $ 162 $ 38 $ 58 $ 7 $ 9 $ 17 Depreciation and Amortization The traditional electric operating companies' and Southern Company Gas' depreciation of the original cost of utility plant in service is provided primarily by using composite straight-line rates. The approximate rates for 2020, 2019, and 2018 are as follows: 2020 2019 2018 Alabama Power 2.6 % 3.1 % 3.0 % Georgia Power 3.0 % 2.6 % 2.6 % Mississippi Power 3.7 % 3.7 % 4.2 % Southern Company Gas 2.8 % 2.9 % 2.9 % Depreciation studies are conducted periodically to update the composite rates. These studies are filed with the respective state PSC and/or other applicable state and federal regulatory agencies for the traditional electric operating companies and the natural gas distribution utilities. During 2020, Georgia Power, Mississippi Power, and Atlanta Gas Light revised their depreciation rates in accordance with base rate case approvals by their respective PSCs. The revised rates were effective January 1, 2020 for Georgia Power and Atlanta Gas Light and April 1, 2020 for Mississippi Power. See Note 2 for additional information. When property, plant, and equipment subject to composite depreciation is retired or otherwise disposed of in the normal course of business, its original cost, together with the cost of removal, less salvage, is charged to accumulated depreciation. For other property dispositions, the applicable cost and accumulated depreciation are removed from the balance sheet accounts, and a gain or loss is recognized. Minor items of property included in the original cost of the asset are retired when the related property unit is retired. At December 31, 2020 and 2019, accumulated depreciation for Southern Company and Southern Company Gas consisted of utility plant in service totaling $31.6 billion and $30.0 billion, respectively, for Southern Company and $4.6 billion and $4.5 billion, respectively, for Southern Company Gas, as well as other plant in service totaling $817 million and $732 million, respectively, for Southern Company and $195 million and $155 million, respectively, for Southern Company Gas. Other plant in service includes the non-utility assets of Southern Company Gas, as well as, for Southern Company, certain other non-utility subsidiaries. Depreciation of the original cost of other plant in service is provided primarily on a straight-line basis over estimated useful lives. Useful lives for Southern Company Gas's non-utility assets range from five Southern Power Southern Power applies component depreciation, where depreciation is computed principally by the straight-line method over the estimated useful life of the asset. Certain of Southern Power's generation assets related to natural gas-fired facilities are depreciated on a units-of-production basis, using hours or starts, to better match outage and maintenance costs to the usage of, and revenues from, these assets. The primary assets in Southern Power's property, plant, and equipment are generating facilities, which generally have estimated useful lives as follows: Southern Power Generating Facility Useful life Natural gas Up to 50 years (*) Solar Up to 35 years Wind Up to 30 years (*) Effective January 1, 2020, Southern Power revised the depreciable lives of its natural gas generating facilities from up to 45 years to up to 50 years. This revision resulted in an immaterial decrease in depreciation for 2020. When Southern Power's depreciable property, plant, and equipment is retired, or otherwise disposed of in the normal course of business, the applicable cost and accumulated depreciation is removed and a gain or loss is recognized in the statements of income. Southern Power reviews its estimated useful lives and salvage values on an ongoing basis. The results of these reviews could result in changes which could have a material impact on Southern Power's net income. Joint Ownership Agreements At December 31, 2020, the Registrants' percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation were as follows: Facility (Type) Percent Plant in Service Accumulated CWIP (in millions) Alabama Power Greene County (natural gas) Units 1 and 2 60.0 % (a) $ 189 $ 76 $ 2 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,107 650 24 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,352 $ 624 $ 37 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,592 2,221 55 Plant Scherer (coal) Units 1 and 2 8.4 (c) 279 98 1 Plant Scherer (coal) Unit 3 75.0 (c) 1,320 520 4 Plant Wansley (coal) 53.5 (c) 1,068 418 10 Rocky Mountain (pumped storage) 25.4 (d) 183 144 1 Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 122 $ 54 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 775 238 15 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 271 $ 15 $ — (a) Jointly owned by Alabama Power and Mississippi Power and operated and maintained by Alabama Power. (b) Jointly owned with PowerSouth and operated and maintained by Alabama Power. (c) Georgia Power owns undivided interests in Plants Hatch, Vogtle Units 1 and 2, Scherer, and Wansley in varying amounts jointly with one or more of the following entities: OPC, MEAG Power, Dalton, Florida Power & Light Company, JEA, and Gulf Power. Georgia Power has been contracted to operate and maintain the plants as agent for the co-owners and is jointly and severally liable for third party claims related to these plants. (d) Jointly owned with OPC, which is the operator of the plant. (e) Jointly owned by Gulf Power and Mississippi Power. In accordance with the operating agreement, Mississippi Power acts as Gulf Power's agent with respect to the operation and maintenance of these units. See Note 3 under "Other Matters – Mississippi Power – Plant Daniel" for information regarding a commitment between Mississippi Power and Gulf Power to seek a restructuring of their 50% undivided ownership interests in Plant Daniel. (f) Jointly owned with The Williams Companies, Inc., the Dalton Pipeline is a 115-mile natural gas pipeline that serves as an extension of the Transcontinental Gas Pipe Line Company, LLC pipeline system into northwest Georgia. Southern Company Gas leases its 50% undivided ownership for approximately $26 million annually through 2042. The lessee is responsible for maintaining the pipeline during the lease term and for providing service to transportation customers under its FERC-regulated tariff. Georgia Power also owns 45.7% of Plant Vogtle Units 3 and 4, which are currently under construction and had a CWIP balance of $7.3 billion at December 31, 2020, excluding estimated probable losses recorded in 2018 and 2020. See Note 2 under "Georgia Power – Nuclear Construction" for additional information. The Registrants' proportionate share of their jointly-owned facility operating expenses is included in the corresponding operating expenses in the statements of income and each Registrant is responsible for providing its own financing. Assets Subject to Lien In 2018, the Mississippi PSC approved executed agreements between Mississippi Power and its largest retail customer, Chevron Products Company (Chevron), for Mississippi Power to continue providing retail service to the Chevron refinery in Pascagoula, Mississippi through 2038. The agreements grant Chevron a security interest in the co-generation assets owned by Mississippi Power, with a lease receivable balance of $138 million at December 31, 2020, located at the refinery that is exercisable upon the occurrence of (i) certain bankruptcy events or (ii) other events of default coupled with specific reductions in steam output at the facility and a downgrade of Mississippi Power's credit rating to below investment grade by two of the three rating agencies.

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
ASSET RETIREMENT OBLIGATIONS	ASSET RETIREMENT OBLIGATIONS AROs are computed as the present value of the estimated costs for an asset's future retirement and are recorded in the period in which the liability is incurred. The estimated costs are capitalized as part of the related long-lived asset and depreciated over the asset's useful life. In the absence of quoted market prices, AROs are estimated using present value techniques in which estimates of future cash outlays associated with the asset retirements are discounted using a credit-adjusted risk-free rate. Estimates of the timing and amounts of future cash outlays are based on projections of when and how the assets will be retired and the cost of future removal activities. Each traditional electric operating company and natural gas distribution utility has received accounting guidance from its state PSC or applicable state regulatory agency allowing the continued accrual or recovery of other retirement costs for long-lived assets that it does not have a legal obligation to retire. Accordingly, the accumulated removal costs for these obligations are reflected in the balance sheets as regulatory liabilities and amounts to be recovered are reflected in the balance sheets as regulatory assets. The ARO liabilities for the traditional electric operating companies primarily relate to facilities that are subject to the CCR Rule and the related state rules, principally ash ponds. In addition, Alabama Power and Georgia Power have retirement obligations related to the decommissioning of nuclear facilities (Alabama Power's Plant Farley and Georgia Power's ownership interests in Plant Hatch and Plant Vogtle Units 1 and 2). See "Nuclear Decommissioning" herein for additional information. Other significant AROs include various landfill sites and asbestos removal for Alabama Power, Georgia Power, and Mississippi Power and gypsum cells and mine reclamation for Mississippi Power. The ARO liability for Southern Power primarily relates to its solar and wind facilities, which are located on long-term land leases requiring the restoration of land at the end of the lease. The traditional electric operating companies and Southern Company Gas also have identified other retirement obligations, such as obligations related to certain electric transmission and distribution facilities, certain asbestos-containing material within long-term assets not subject to ongoing repair and maintenance activities, certain wireless communication towers, the disposal of polychlorinated biphenyls in certain transformers, leasehold improvements, equipment on customer property, and property associated with the Southern Company system's rail lines and natural gas pipelines. However, liabilities for the removal of these assets have not been recorded because the settlement timing for certain retirement obligations related to these assets is indeterminable and, therefore, the fair value of the retirement obligations cannot be reasonably estimated. A liability for these retirement obligations will be recognized when sufficient information becomes available to support a reasonable estimation of the ARO. Southern Company and the traditional electric operating companies will continue to recognize in their respective statements of income allowed removal costs in accordance with regulatory treatment. Any differences between costs recognized in accordance with accounting standards related to asset retirement and environmental obligations and those reflected in rates are recognized as either a regulatory asset or liability in the balance sheets as ordered by the various state PSCs. Details of the AROs included in the balance sheets are as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (*) (in millions) Balance at December 31, 2018 $ 9,394 $ 3,210 $ 5,829 $ 160 $ 84 Liabilities incurred 37 — 35 1 1 Liabilities settled (328) (127) (151) (35) — Accretion 402 145 243 7 4 Cash flow revisions 281 312 (172) 57 — Balance at December 31, 2019 $ 9,786 $ 3,540 $ 5,784 $ 190 $ 89 Liabilities incurred 19 — 10 — 9 Liabilities settled (442) (219) (185) (22) — Accretion 409 152 238 8 4 Cash flow revisions 912 501 418 — (7) Balance at December 31, 2020 $ 10,684 $ 3,974 $ 6,265 $ 176 $ 95 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. During 2019, Alabama Power recorded increases totaling approximately $312 million to its AROs primarily related to the CCR Rule and the related state rule based on management's completion of closure designs during the second and third quarters 2019 under the planned closure-in-place methodology for all but one of its ash pond facilities. During 2019, Mississippi Power recorded an increase of approximately $57 million to its AROs related to the CCR Rule, primarily associated with the ash pond facility at Plant Greene County, which is jointly owned with Alabama Power. During 2020, Alabama Power recorded increases totaling approximately $501 million to its AROs related to the CCR Rule and the related state rule primarily as a result of management's completion of the closure design for the remaining ash pond and the addition of a water treatment system to the design of another ash pond. The additional estimated costs to close these ash ponds under the planned closure-in-place methodology primarily relate to inputs from contractor bids, design revisions, and changes in the expected volume of ash handling. During the second half of 2019, Georgia Power completed an assessment of its plans to close the ash ponds at all of its generating plants in compliance with the CCR Rule and the related state rule. Cost estimates were revised to reflect further refined costs for closure plans and updates to the timing of future cash outlays. As a result, in December 2019, Georgia Power recorded a decrease of approximately $174 million to its AROs related to the CCR Rule and the related state rule. During the third quarter 2020, Georgia Power further refined the related cost estimates, including updates to long-term post-closure care requirements, market pricing, and timing of future cash outlays. As a result, in September 2020, Georgia Power recorded an increase of approximately $411 million to its AROs related to the CCR Rule and the related state rule. The cost estimates for AROs related to the disposal of CCR are based on information at December 31, 2020 using various assumptions related to closure and post-closure costs, timing of future cash outlays, inflation and discount rates, and the potential methods for complying with the CCR Rule and the related state rules. The traditional electric operating companies have periodically updated, and expect to continue periodically updating, their related cost estimates and ARO liabilities for each CCR unit as additional information related to these assumptions becomes available. Some of these updates have been, and future updates may be, material. Additionally, the closure designs and plans in the States of Alabama and Georgia are subject to approval by environmental regulatory agencies. Absent continued recovery of ARO costs through regulated rates, results of operations, cash flows, and financial condition for Southern Company and the traditional electric operating companies could be materially impacted. See Note 2 under "Georgia Power – Rate Plans" for additional information. The ultimate outcome of these matters cannot be determined at this time. Nuclear Decommissioning The NRC requires licensees of commercial nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. Alabama Power and Georgia Power have external trust funds (Funds) to comply with the NRC's regulations. Use of the Funds is restricted to nuclear decommissioning activities. The Funds are managed and invested in accordance with applicable requirements of various regulatory bodies, including the NRC, the FERC, and state PSCs, as well as the IRS. While Alabama Power and Georgia Power are allowed to prescribe an overall investment policy to the Funds' managers, neither Southern Company nor its subsidiaries or affiliates are allowed to engage in the day-to-day management of the Funds or to mandate individual investment decisions. Day-to-day management of the investments in the Funds is delegated to unrelated third-party managers with oversight by the management of Alabama Power and Georgia Power. The Funds' managers are authorized, within certain investment guidelines, to actively buy and sell securities at their own discretion in order to maximize the return on the Funds' investments. The Funds are invested in a tax-efficient manner in a diversified mix of equity and fixed income securities and are reported as trading securities. Alabama Power and Georgia Power record the investment securities held in the Funds at fair value, as disclosed in Note 13, as management believes that fair value best represents the nature of the Funds. Gains and losses, whether realized or unrealized, are recorded in the regulatory liability for AROs in the balance sheets and are not included in net income or OCI. Fair value adjustments and realized gains and losses are determined on a specific identification basis. The Funds at Georgia Power participate in a securities lending program through the managers of the Funds. Under this program, Georgia Power's Funds' investment securities are loaned to institutional investors for a fee. Securities loaned are fully collateralized by cash, letters of credit, and/or securities issued or guaranteed by the U.S. government or its agencies or instrumentalities. At December 31, 2020 and 2019, approximately $44 million and $28 million, respectively, of the fair market value of Georgia Power's Funds' securities were on loan and pledged to creditors under the Funds' managers' securities lending program. The fair value of the collateral received was approximately $45 million and $29 million at December 31, 2020 and 2019, respectively, and can only be sold by the borrower upon the return of the loaned securities. The collateral received is treated as a non-cash item in the statements of cash flows. Investment securities in the Funds for December 31, 2020 and 2019 were as follows: Southern Company Alabama Georgia (in millions) At December 31, 2020: Equity securities $ 1,339 $ 842 $ 497 Debt securities 851 231 620 Other securities 111 83 28 Total investment securities in the Funds $ 2,301 $ 1,156 $ 1,145 At December 31, 2019: Equity securities $ 1,159 $ 743 $ 416 Debt securities 798 218 580 Other securities 77 60 17 Total investment securities in the Funds $ 2,034 $ 1,021 $ 1,013 These amounts exclude receivables related to investment income and pending investment sales and payables related to pending investment purchases. For Southern Company and Georgia Power, these amounts include Georgia Power's investment securities pledged to creditors and collateral received and excludes payables related to Georgia Power's securities lending program. The fair value increases (decreases) of the Funds, including unrealized gains (losses) and reinvested interest and dividends and excluding the Funds' expenses, for 2020, 2019, and 2018 are shown in the table below. Southern Company Alabama Georgia (in millions) Fair value increases (decreases) 2020 $ 280 $ 142 $ 138 2019 344 194 150 2018 (67) (38) (29) Unrealized gains (losses) At December 31, 2020 $ 220 $ 121 $ 99 At December 31, 2019 259 149 110 At December 31, 2018 (183) (96) (87) The investment securities held in the Funds continue to be managed with a long-term focus. Accordingly, all purchases and sales within the Funds are presented separately in the statements of cash flows as investing cash flows, consistent with the nature of the securities and purpose for which the securities were acquired. For Alabama Power, approximately $15 million and $16 million at December 31, 2020 and 2019, respectively, previously recorded in internal reserves is being transferred into the Funds through 2040 as approved by the Alabama PSC. The NRC's minimum external funding requirements are based on a generic estimate of the cost to decommission only the radioactive portions of a nuclear unit based on the size and type of reactor. Alabama Power and Georgia Power have filed plans with the NRC designed to ensure that, over time, the deposits and earnings of the Funds will provide the minimum funding amounts prescribed by the NRC. At December 31, 2020 and 2019, the accumulated provisions for the external decommissioning trust funds were as follows: 2020 2019 (in millions) Alabama Power Plant Farley $ 1,156 $ 1,021 Georgia Power Plant Hatch $ 716 $ 634 Plant Vogtle Units 1 and 2 429 379 Total $ 1,145 $ 1,013 Site study cost is the estimate to decommission a specific facility as of the site study year. The decommissioning cost estimates are based on prompt dismantlement and removal of the plant from service. The actual decommissioning costs may vary from these estimates because of changes in the assumed date of decommissioning, changes in NRC requirements, or changes in the assumptions used in making these estimates. The estimated costs of decommissioning at December 31, 2020 based on the most current studies, which were each performed in 2018, were as follows: Plant Plant Hatch (*) Plant Vogtle Units 1 and 2 (*) Decommissioning periods: Beginning year 2037 2034 2047 Completion year 2076 2075 2079 (in millions) Site study costs: Radiated structures $ 1,234 $ 734 $ 601 Spent fuel management 387 172 162 Non-radiated structures 99 56 79 Total site study costs $ 1,720 $ 962 $ 842 (*) Based on Georgia Power's ownership interests. For ratemaking purposes, Alabama Power's decommissioning costs are based on the site study and Georgia Power's decommissioning costs are based on the NRC generic estimate to decommission the radioactive portion of the facilities and the site study estimate for spent fuel management as of 2018. Significant assumptions used to determine these costs for ratemaking were an estimated inflation rate of 4.5% and 2.75% for Alabama Power and Georgia Power, respectively, and an estimated trust earnings rate of 7.0% and 4.75% for Alabama Power and Georgia Power, respectively. Amounts previously contributed to the Funds for Plant Farley are currently projected to be adequate to meet the decommissioning obligations. Alabama Power will continue to provide site-specific estimates of the decommissioning costs and related projections of funds in the external trust to the Alabama PSC and, if necessary, would seek the Alabama PSC's approval to address any changes in a manner consistent with NRC and other applicable requirements. Effective January 1, 2020, in connection with the 2019 ARP, Georgia Power's annual decommissioning cost for ratemaking is a total of $4 million for Plant Hatch and Plant Vogtle Units 1 and 2. Georgia Power's annual decommissioning cost for ratemaking in 2019 totaled $5 million.

CONSOLIDATED ENTITIES AND EQUIT

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS	CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS The Registrants may hold ownership interests in a number of business ventures with varying ownership structures. Partnership interests and other variable interests are evaluated to determine if each entity is a VIE. If a venture is a VIE for which a Registrant is the primary beneficiary, the assets, liabilities, and results of operations of the entity are consolidated. The Registrants reassess the conclusion as to whether an entity is a VIE upon certain occurrences, which are deemed reconsideration events. For entities that are not determined to be VIEs, the Registrants evaluate whether they have control or significant influence over the investee to determine the appropriate consolidation and presentation. Generally, entities under the control of a Registrant are consolidated, and entities over which a Registrant can exert significant influence, but which a Registrant does not control, are accounted for under the equity method of accounting. Investments accounted for under the equity method are recorded within equity investments in unconsolidated subsidiaries in the balance sheets and, for Southern Company and Southern Company Gas, the equity income is recorded within earnings from equity method investments in the statements of income. See "SEGCO" and "Southern Company Gas" herein for additional information. SEGCO Alabama Power and Georgia Power own equally all of the outstanding capital stock of SEGCO, which owns electric generating units with a total rated capacity of 1,020 MWs, as well as associated transmission facilities. Alabama Power and Georgia Power account for SEGCO using the equity method; Southern Company consolidates SEGCO. The capacity of these units is sold equally to Alabama Power and Georgia Power. Alabama Power and Georgia Power make payments sufficient to provide for the operating expenses, taxes, interest expense, and a ROE. The share of purchased power included in purchased power, affiliates in the statements of income totaled $67 million in 2020, $93 million in 2019, and $102 million in 2018 for Alabama Power and $69 million in 2020, $95 million in 2019, and $105 million in 2018 for Georgia Power. SEGCO paid dividends of $12 million in 2020, $14 million in 2019, and $18 million in 2018, one half of which were paid to each of Alabama Power and Georgia Power. In addition, Alabama Power and Georgia Power each recognize 50% of SEGCO's net income. Alabama Power, which owns and operates a generating unit adjacent to the SEGCO generating units, has a joint ownership agreement with SEGCO for the ownership of an associated gas pipeline. Alabama Power owns 14% of the pipeline with the remaining 86% owned by SEGCO. See Note 3 under "Guarantees" for additional information regarding guarantees of Alabama Power and Georgia Power related to SEGCO. 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 In 2018, Southern Power sold a noncontrolling 33% limited partnership interest in SP Solar to Global Atlantic Financial Group Limited (Global Atlantic). See Note 15 under "Southern Power" for additional information. A wholly-owned subsidiary of Southern Power is the general partner and holds a 1% ownership interest in SP Solar and another wholly-owned subsidiary of Southern Power owns the remaining 66% ownership in SP Solar. SP Solar qualifies as a VIE since the arrangement is structured as a limited partnership and the 33% limited partner does not have substantive kick-out rights against the general partner. At December 31, 2020 and 2019, SP Solar had total assets of $6.1 billion and $6.4 billion, respectively, total liabilities of $387 million and $381 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. In 2018, Southern Power sold a noncontrolling tax-equity interest in SP Wind to three financial investors. SP Wind owns eight operating wind farms. See Note 15 under "Southern Power" for additional information. Southern Power owns 100% of the Class B membership interests and the three financial investors own 100% of the Class A membership interests. SP Wind qualifies as a VIE since the structure of the arrangement is similar to a limited partnership and the Class A members do not have substantive kick-out rights against Southern Power. At December 31, 2020 and 2019, SP Wind had total assets of $2.4 billion and $2.5 billion, respectively, total liabilities of $138 million and $128 million, respectively, and noncontrolling interests of $43 million and $45 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 December 31, 2020 and 2019, the other VIEs had total assets of $1.1 billion, total liabilities of $110 million and $104 million, respectively, and noncontrolling interests of $454 million and $409 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 December 31, 2020 and 2019, Southern Power had equity method investments in wind and battery storage projects totaling $19 million and $28 million, respectively. Southern Company Gas Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments at December 31, 2020 and 2019 and related income from those investments for the years ended December 31, 2020, 2019, and 2018 were as follows: Investment Balance 2020 2019 (a) (in millions) SNG (b) $ 1,167 $ 1,137 PennEast Pipeline (c) 91 82 Other 32 32 Total $ 1,290 $ 1,251 (a) Excludes investments in Atlantic Coast Pipeline and Pivotal JAX LNG classified as held for sale at December 31, 2019. See Note 15 under "Assets Held for Sale" for additional information. (b) Increase primarily relates to a capital contribution, partially offset by the continued amortization of deferred tax assets established upon acquisition. (c) See Note 3 under "Other Matters – Southern Company Gas" for additional information. Earnings from Equity Method Investments 2020 2019 2018 (in millions) SNG $ 129 $ 141 $ 131 Atlantic Coast Pipeline (a)(b) 3 13 7 PennEast Pipeline (a) 7 6 5 Other (c) 2 (3) 5 Total $ 141 $ 157 $ 148 (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 interest in Atlantic Coast Pipeline. See Note 15 under "Southern Company Gas" for additional information. (c) In May 2019, Southern Company Gas sold its investment in Triton, a cargo container leasing company that was aggregated into Southern Company Gas' all other segment. On March 24, 2020, Southern Company Gas completed the sale of its interest in Pivotal LNG. See Note 15 under "Southern Company Gas" for additional information.

FINANCING

FINANCING	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
FINANCING	FINANCING Long-term Debt Details of long-term debt at December 31, 2020 and 2019 are provided in the following table: At December 31, 2020 Balance Outstanding at Maturity Weighted Average 2020 2019 (in millions) Southern Company Senior notes (a) 2021-2050 3.78% $ 30,850 $ 30,023 Junior subordinated notes 2024-2080 4.30% 7,295 5,295 FFB loans (b) 2021-2044 2.92% 4,618 3,843 Pollution control revenue bonds (c) 2021-2053 1.11% 2,675 2,963 First mortgage bonds (d) 2023-2060 3.71% 1,900 1,575 Other revenue bonds (e) 2021-2040 6.45% 320 320 Debt payable to affiliated trusts (f) 2042 3.33% 206 206 Medium-term notes 2021-2027 7.88% 160 160 Other long-term debt 2021-2023 0.83% 370 145 Finance lease obligations (g) 231 226 Unamortized fair value adjustment 393 430 Unamortized debt premium (discount), net (201) (152) Unamortized debt issuance expenses (237) (247) Total long-term debt 48,580 44,787 Less: Amount due within one year 3,507 2,989 Total long-term debt excluding amount due within one year $ 45,073 $ 41,798 Alabama Power Senior notes 2021-2049 4.03% $ 7,625 $ 7,275 Pollution control revenue bonds (c) 2021-2038 0.53% 1,060 1,060 Debt payable to affiliated trusts (f) 2042 3.33% 206 206 Other long-term debt 2021 1.20% 45 45 Finance lease obligations (g) 5 4 Unamortized debt premium (discount), net (16) (14) Unamortized debt issuance expenses (56) (55) Total long-term debt 8,869 8,521 Less: Amount due within one year 311 251 Total long-term debt excluding amount due within one year $ 8,558 $ 8,270 Georgia Power Senior notes 2021-2050 3.59% $ 6,400 $ 5,850 Junior subordinated notes 2077 5.00% 270 270 FFB loans (b) 2021-2044 2.92% 4,618 3,843 Pollution control revenue bonds (c) 2025-2053 1.47% 1,538 1,821 Other long-term debt 2021 0.65% 125 — Finance lease obligations (g) 145 156 Unamortized debt premium (discount), net (12) (7) Unamortized debt issuance expenses (114) (117) Total long-term debt 12,970 11,816 Less: Amount due within one year 542 1,025 Total long-term debt excluding amount due within one year $ 12,428 $ 10,791 At December 31, 2020 Balance Outstanding at Maturity Weighted Average 2020 2019 (in millions) Mississippi Power Senior notes 2028-2042 4.23% $ 900 $ 1,175 Pollution control revenue bonds (c) 2025-2028 1.86% 76 83 Other revenue bonds (e) 2021-2040 6.45% 320 320 Other long-term debt 2021-2023 1.00% 100 — Finance lease obligations (g) 19 — Unamortized debt premium (discount), net 11 19 Unamortized debt issuance expenses (7) (8) Total long-term debt 1,419 1,589 Less: Amount due within one year 406 281 Total long-term debt excluding amount due within one year $ 1,013 $ 1,308 Southern Power Senior notes (a) 2021-2046 3.96% $ 3,714 $ 4,425 Unamortized debt premium (discount), net (6) (8) Unamortized debt issuance expenses (16) (19) Total long-term debt 3,692 4,398 Less: Amount due within one year 299 824 Total long-term debt excluding amount due within one year $ 3,393 $ 3,574 Southern Company Gas Senior notes 2021-2047 4.01% $ 4,200 $ 3,700 First mortgage bonds (d) 2023-2060 3.71% 1,900 1,575 Medium-term notes 2021-2027 7.88% 160 160 Unamortized fair value adjustment 393 430 Unamortized debt premium (discount), net (27) (20) Total long-term debt 6,626 5,845 Less: Amount due within one year 333 — Total long-term debt excluding amount due within one year $ 6,293 $ 5,845 (a) Includes a fair value gain (loss) of $109 million and $(5) million at December 31, 2020 and 2019, respectively, related to Southern Power's foreign currency hedge on its €1.1 billion senior notes. (b) Secured by a first priority lien on (i) Georgia Power's 45.7% undivided ownership interest in Plant Vogtle Units 3 and 4 (primarily the units under construction, the related real property, and any nuclear fuel loaded in the reactor core) and (ii) Georgia Power's rights and obligations under the principal contracts relating to Plant Vogtle Units 3 and 4. See "DOE Loan Guarantee Borrowings" for additional information. (c) Pollution control revenue bond obligations represent loans to the traditional electric operating companies from public authorities of funds derived from sales by such authorities of revenue bonds issued to finance pollution control and solid waste disposal facilities. In some cases, the pollution control revenue bond obligations represent obligations under installment sales agreements with respect to facilities constructed with the proceeds of revenue bonds issued by public authorities. The traditional electric operating companies are required to make payments sufficient for the authorities to meet principal and interest requirements of such bonds. Proceeds from certain issuances are restricted until qualifying expenditures are incurred. (d) Secured by substantially all of Nicor Gas' properties. (e) At December 31, 2020 and 2019, Mississippi Power had $270 million aggregate principal amount outstanding of Mississippi Business Finance Corporation Taxable Revenue Bonds, 7.13% Series 1999A due October 20, 2021, which are secured by Plant Daniel Units 3 and 4 and certain related personal property. Mississippi Power assumed the obligations in 2011 in connection with its election under its operating lease of Plant Daniel Units 3 and 4 to purchase the assets and recorded the bonds at fair value. At December 31, 2020 and 2019, Mississippi Power also had $50 million of tax-exempt revenue bond obligations outstanding representing loans to Mississippi Power through the Mississippi Business Finance Corporation issued to finance a portion of the costs of constructing the Kemper County energy facility. (f) Alabama Power has formed a wholly-owned trust subsidiary for the purpose of issuing preferred securities. The proceeds of the related equity investments and preferred security sales were loaned back to Alabama Power through the issuance of junior subordinated notes, which constitute substantially all of the assets of this trust. Alabama Power considers that the mechanisms and obligations relating to the preferred securities issued for its benefit, taken together, constitute a full and unconditional guarantee by it of the trust's payment obligations with respect to these securities. See Note 1 under "Variable Interest Entities" for additional information on the accounting treatment for this trust and the related securities. (g) Secured by the underlying lease ROU asset. See Note 9 for additional information. Maturities of long-term debt for the next five years are as follows: Southern Company (a) Alabama Power Georgia Power (b) Mississippi Power (c) Southern Power (d) Southern Company (in millions) 2021 $ 3,506 $ 311 $ 542 $ 406 $ 300 $ 330 2022 3,707 751 488 16 677 46 2023 3,131 301 889 1 290 400 2024 509 22 491 1 — — 2025 1,191 250 138 12 500 300 (a) Amount for 2022 includes junior subordinated notes totaling $1.725 billion at the parent entity with final maturity dates in 2024 and 2027 (one half in each year); however, in connection with related stock purchase contracts, Southern Company has agreed to remarket the notes in 2022. See "Equity Units" herein for additional information. Also see notes (b), (c), and (d) below. (b) Amounts include principal amortization related to the FFB borrowings; however, the final maturity date is February 20, 2044. See "DOE Loan Guarantee Borrowings" herein for additional information. (c) Amount for 2021 includes $50 million and $25 million of long-term debt with final maturity dates in 2040 and 2023, respectively, that Mississippi Power intends to repay in 2021. (d) Southern Power's 2022 maturity represents euro-denominated debt at the U.S. dollar denominated hedge settlement amount. DOE Loan Guarantee Borrowings Pursuant to the loan guarantee program established under Title XVII of the Energy Policy Act of 2005 (Title XVII Loan Guarantee Program), Georgia Power and the DOE entered into a loan guarantee agreement in 2014 and the Amended and Restated Loan Guarantee Agreement in March 2019. Under the Amended and Restated Loan Guarantee Agreement, the DOE agreed to guarantee the obligations of Georgia Power under the FFB Credit Facilities. Under the FFB Credit Facilities, Georgia Power may make term loan borrowings through the FFB in an amount up to approximately $5.130 billion, provided that total aggregate borrowings under the FFB Credit Facilities may not exceed 70% of (i) Eligible Project Costs minus (ii) approximately $1.492 billion (reflecting the amounts received by Georgia Power under the Guarantee Settlement Agreement less the related customer refunds). In June and December 2020, Georgia Power made borrowings under the FFB Credit Facilities in an aggregate principal amount of $519 million and $329 million, respectively, at an interest rate of 1.652% and 1.737%, respectively, through the final maturity date of February 20, 2044. During 2020, Georgia Power made principal amortization payments of $73 million under the FFB Credit Facilities. At December 31, 2020 and 2019, Georgia Power had $4.6 billion and $3.8 billion of borrowings outstanding under the FFB Credit Facilities, respectively. All borrowings under the FFB Credit Facilities are full recourse to Georgia Power, and Georgia Power is obligated to reimburse the DOE for any payments the DOE is required to make to the FFB under its guarantee. Georgia Power's reimbursement obligations to the DOE are full recourse and secured by a first priority lien on (i) Georgia Power's 45.7% undivided ownership interest in Plant Vogtle Units 3 and 4 (primarily the units under construction, the related real property, and any nuclear fuel loaded in the reactor core) and (ii) Georgia Power's rights and obligations under the principal contracts relating to Plant Vogtle Units 3 and 4. There are no restrictions on Georgia Power's ability to grant liens on other property. In addition to the conditions described above, future advances are subject to satisfaction of customary conditions, as well as certification of compliance with the requirements of the Title XVII Loan Guarantee Program, including accuracy of project-related representations and warranties, delivery of updated project-related information, and evidence of compliance with the prevailing wage requirements of the Davis-Bacon Act of 1931, as amended, and certification from the DOE's consulting engineer that proceeds of the advances are used to reimburse Eligible Project Costs. Upon satisfaction of all conditions described above, advances may be requested on a quarterly basis through 2023. The final maturity date for each advance under the FFB Credit Facilities is February 20, 2044. Interest is payable quarterly and principal payments began on February 20, 2020. Borrowings under the FFB Credit Facilities will bear interest at the applicable U.S. Treasury rate plus a spread equal to 0.375%. Under the Amended and Restated Loan Guarantee Agreement, Georgia Power is subject to customary borrower affirmative and negative covenants and events of default. In addition, Georgia Power is subject to project-related reporting requirements and other project-specific covenants and events of default. In the event certain mandatory prepayment events occur, the FFB's commitment to make further advances under the FFB Credit Facilities will terminate and Georgia Power will be required to prepay the outstanding principal amount of all borrowings under the FFB Credit Facilities over a period of five years (with level principal amortization). Among other things, these mandatory prepayment events include (i) the termination of the Vogtle Services Agreement or rejection of the Vogtle Services Agreement in any Westinghouse bankruptcy if Georgia Power does not maintain access to intellectual property rights under the related intellectual property licenses; (ii) termination of the Bechtel Agreement, unless the Vogtle Owners enter into a replacement agreement; (iii) cancellation of Plant Vogtle Units 3 and 4 by the Georgia PSC or by Georgia Power; (iv) failure of the holders of 90% of the ownership interests in Plant Vogtle Units 3 and 4 to vote to continue construction following certain schedule extensions; (v) cost disallowances by the Georgia PSC that could have a material adverse effect on completion of Plant Vogtle Units 3 and 4 or Georgia Power's ability to repay the outstanding borrowings under the FFB Credit Facilities; or (vi) loss of or failure to receive necessary regulatory approvals. Under certain circumstances, insurance proceeds and any proceeds from an event of taking must be applied to immediately prepay outstanding borrowings under the FFB Credit Facilities. Georgia Power also may voluntarily prepay outstanding borrowings under the FFB Credit Facilities. Under the FFB Credit Facilities, any prepayment (whether mandatory or optional) will be made with a make-whole premium or discount, as applicable. In connection with any cancellation of Plant Vogtle Units 3 and 4, the DOE may elect to continue construction of Plant Vogtle Units 3 and 4. In such an event, the DOE will have the right to assume Georgia Power's rights and obligations under the principal agreements relating to Plant Vogtle Units 3 and 4 and to acquire all or a portion of Georgia Power's ownership interest in Plant Vogtle Units 3 and 4. Secured Debt Each of Southern Company's subsidiaries is organized as a legal entity, separate and apart from Southern Company and its other subsidiaries. There are no agreements or other arrangements among the Southern Company system companies under which the assets of one company have been pledged or otherwise made available to satisfy obligations of Southern Company or any of its other subsidiaries. As discussed under "Long-term Debt" herein, the Registrants had secured debt outstanding at December 31, 2020 and 2019. Each Registrant's senior notes, junior subordinated notes, pollution control and other revenue bond obligations, bank term loans, credit facility borrowings, and notes payable are effectively subordinated to all secured debt of each respective Registrant. Equity Units In August 2019, Southern Company issued 34.5 million 2019 Series A Equity Units (Equity Units), initially in the form of corporate units (Corporate Units), at a stated amount of $50 per Corporate Unit, for a total stated amount of $1.725 billion. Net proceeds from the issuance were approximately $1.682 billion. The proceeds were used to repay short-term indebtedness and for other general corporate purposes, including investments in Southern Company's subsidiaries. Each Corporate Unit is comprised of (i) a 1/40 undivided beneficial ownership interest in $1,000 principal amount of Southern Company's Series 2019A Remarketable Junior Subordinated Notes (Series 2019A RSNs) due 2024, (ii) a 1/40 undivided beneficial ownership interest in $1,000 principal amount of Southern Company's Series 2019B Remarketable Junior Subordinated Notes (together with the Series 2019A RSNs, the RSNs) due 2027, and (iii) a stock purchase contract, which obligates the holder to purchase from Southern Company, no later than August 1, 2022, a certain number of shares of Southern Company's common stock for $50 in cash (Stock Purchase Contract). Southern Company has agreed to remarket the RSNs in 2022, at which time each interest rate on the RSNs will reset at the applicable market rate. Holders may choose to either remarket their RSNs, receive the proceeds, and use those funds to settle the related Stock Purchase Contract or retain the RSNs and use other funds to settle the related Stock Purchase Contract. If the remarketing is unsuccessful, holders will have the right to put their RSNs to Southern Company at a price equal to the principal amount. The Corporate Units carry an annual distribution rate of 6.75% of the stated amount, which is comprised of a quarterly interest payment on the RSNs of 2.70% per year and a quarterly purchase contract adjustment payment of 4.05% per year. Each Stock Purchase Contract obligates the holder to purchase, and Southern Company to sell, for $50 a number of shares of Southern Company common stock determined based on the applicable market value (as determined under the related Stock Purchase Contract) in accordance with the conversion ratios set forth below (subject to anti-dilution adjustments): • If the applicable market value is equal to or greater than $68.64, 0.7284 shares. • If the applicable market value is less than $68.64 but greater than $57.20, a number of shares equal to $50 divided by the applicable market value. • If the applicable market value is less than or equal to $57.20, 0.8741 shares. Bank Credit Arrangements At December 31, 2020, committed credit arrangements with banks were as follows: Expires Company 2021 2022 2023 2024 Total Unused Due within (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) — — — 600 600 591 — Southern Company Gas (b) — — — 1,750 1,750 1,745 — SEGCO 30 — — — 30 30 30 Southern Company $ 33 $ 675 $ 125 $ 6,900 $ 7,733 $ 7,671 $ 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 $5 million and $11 million, respectively, was unused at December 31, 2020. In December 2020, Southern Power amended its $120 million letter of credit facility, which, among other things, extended the expiration date from 2021 to 2023 and reduced the amount to $75 million. 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 $1.25 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 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. See "Structural Considerations" herein for additional information. The bank credit arrangements require payment of commitment fees based on the unused portion of the commitments. Commitment fees average less than 1 / 4 of 1% for the Registrants and Nicor Gas. Subject to applicable market conditions, Southern Company and its subsidiaries expect to renew or replace their bank credit arrangements as needed, prior to expiration. In connection therewith, Southern Company and its subsidiaries may extend the maturity dates and/or increase or decrease the lending commitments thereunder. These bank credit arrangements, as well as the term loan arrangements of the Registrants 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. Southern Company's, Southern Company Gas', and Nicor Gas' credit arrangements contain covenants that limit debt levels to 70% of total capitalization, as defined in the agreements, and the other subsidiaries' bank credit arrangements contain covenants that limit debt levels to 65% of total capitalization, as defined in the agreements. For purposes of these definitions, debt excludes the long-term debt payable to affiliated trusts and, in certain arrangements, other hybrid securities. Additionally, for Southern Company and Southern Power, for purposes of these definitions, debt excludes any project debt incurred by certain subsidiaries of Southern Power to the extent such debt is non-recourse to Southern Power and capitalization excludes the capital stock or other equity attributable to such subsidiaries. At December 31, 2020, 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 December 31, 2020 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 December 31, 2020, 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. At December 31, 2020 and 2019, Southern Power had $105 million and $104 million, respectively, of cash collateral posted related to PPA requirements, which is included in other deferred charges and assets on Southern Power's consolidated balance sheets. Notes Payable The Registrants, Nicor Gas, and SEGCO make short-term borrowings primarily through commercial paper programs that have the liquidity support of the committed bank credit arrangements described above under "Bank Credit Arrangements." Southern Power's subsidiaries are not parties or obligors to its commercial paper program. Southern Company Gas maintains commercial paper programs at Southern Company Gas Capital and at Nicor Gas. Nicor Gas' commercial paper program supports working capital needs at Nicor Gas as Nicor Gas is not permitted to make money pool loans to affiliates. All of Southern Company Gas' other subsidiaries benefit from Southern Company Gas Capital's commercial paper program. See "Structural Considerations" herein for additional information. In addition, Southern Company and certain of its subsidiaries have entered into various bank term loan agreements. Unless otherwise stated, the proceeds of these loans were used to repay existing indebtedness and for general corporate purposes, including working capital and, for the subsidiaries, their continuous construction programs. Commercial paper and short-term bank term loans are included in notes payable in the balance sheets. Details of short-term borrowings for the applicable Registrants were as follows: Notes Payable at December 31, 2020 Notes Payable at December 31, 2019 Amount Weighted Average Amount Weighted Average (in millions) (in millions) Southern Company Commercial paper $ 609 0.3 % $ 1,705 2.1 % Short-term bank debt — — % 350 2.3 % Total $ 609 0.3 % $ 2,055 2.1 % Georgia Power Commercial paper $ 60 0.3 % $ 115 2.1 % Short-term bank debt — — % 250 2.2 % Total $ 60 0.3 % $ 365 2.2 % Mississippi Power Commercial paper $ 25 0.4 % $ — — % Southern Power Commercial paper $ 175 0.3 % $ 449 2.1 % Short-term bank debt — — % 100 2.6 % Total $ 175 0.3 % $ 549 2.2 % Southern Company Gas Commercial paper: Southern Company Gas Capital $ 220 0.3 % $ 372 2.1 % Nicor Gas 104 0.2 % 278 1.8 % Total $ 324 0.2 % $ 650 2.0 % See "Bank Credit Arrangements" herein for information on bank term loan covenants that limit debt levels and cross-acceleration or cross-default provisions. Southern Company Common Stock Stock Issued During 2020, Southern Company issued approximately 3.3 million shares of common stock through employee equity compensation plans and received proceeds of approximately $74 million. See "Equity Units" herein for additional information. Shares Reserved At December 31, 2020, a total of 88 million shares were reserved for issuance pursuant to the Southern Investment Plan, employee savings plans, the Outside Directors Stock Plan, the Omnibus Incentive Compensation Plan (which includes stock options and performance share units as discussed in Note 12), and an at-the-market program. Of the total 88 million shares reserved, 6.8 million shares are available for awards under the Omnibus Incentive Compensation Plan at December 31, 2020. Diluted Earnings Per Share For Southern Company, the only differences in computing basic and diluted earnings per share (EPS) are attributable to awards outstanding under stock-based compensation plans and the Equity Units. Earnings per share dilution resulting from stock-based compensation plans and the Equity Units issuance is determined using the treasury stock method. Shares used to compute diluted EPS were as follows: Average Common Stock Shares 2020 2019 2018 (in millions) As reported shares 1,058 1,046 1,020 Effect of stock-based compensation 7 8 5 Diluted shares 1,065 1,054 1,025 In all years presented, an immaterial number of stock-based compensation awards was not included in the diluted EPS calculation because the awards were anti-dilutive. The Equity Units were excluded from the calculation of diluted EPS for 2020 and 2019 as the dilutive stock price threshold was not met. Redeemable Preferred Stock of Subsidiaries As discussed further under "Alabama Power" herein, the preferred stock of Alabama Power is presented as "Redeemable Preferred Stock of Subsidiaries" on Southern Company's balance sheets in a manner consistent with temporary equity under applicable accounting standards. In 2018, Mississippi Power completed the redemption of all outstanding shares and depository shares of its redeemable preferred stock totaling $33 million, as described further under "Mississippi Power" herein. Alabama Power Alabama Power has preferred stock, Class A preferred stock, and common stock outstanding. Alabama Power also has authorized preference stock, none of which is outstanding. Alabama Power's preferred stock and Class A preferred stock, without preference between classes, rank senior to Alabama Power's common stock with respect to payment of dividends and voluntary and involuntary dissolution. The preferred stock and Class A preferred stock of Alabama Power contain a feature that allows the holders to elect a majority of Alabama Power's board of directors if preferred dividends are not paid for four consecutive quarters. Because such a potential redemption-triggering event is not solely within the control of Alabama Power, the preferred stock and Class A preferred stock is presented as "Redeemable Preferred Stock" on Alabama Power's balance sheets in a manner consistent with temporary equity under applicable accounting standards. Alabama Power's preferred stock is subject to redemption at a price equal to the par value plus a premium. Alabama Power's Class A preferred stock is subject to redemption at a price equal to the stated capital. All series of Alabama Power's preferred stock currently are subject to redemption at the option of Alabama Power. The Class A preferred stock is subject to redemption on or after October 1, 2022, or following the occurrence of a rating agency event. Information for each outstanding series is in the table below: Preferred Stock Par Value/Stated Capital Per Share Shares Outstanding Redemption 4.92% Preferred Stock $100 80,000 $103.23 4.72% Preferred Stock $100 50,000 $102.18 4.64% Preferred Stock $100 60,000 $103.14 4.60% Preferred Stock $100 100,000 $104.20 4.52% Preferred Stock $100 50,000 $102.93 4.20% Preferred Stock $100 135,115 $105.00 5.00% Class A Preferred Stock $25 10,000,000 $25.00 (*) Georgia Power Georgia Power has preferred stock, Class A preferred stock, preference stock, and common stock authorized, but only common stock outstanding as of December 31, 2020 and 2019. Mississippi Power Mississippi Power has preferred stock and common stock authorized, but only common stock outstanding as of December 31, 2020 and 2019. In 2018, Mississippi Power completed the redemption of all outstanding shares and depository shares of its Preferred Stock. Dividend Restrictions The income of Southern Company is derived primarily from equity in earnings of its subsidiaries. At December 31, 2020, consolidated retained earnings included $5.6 billion of undistributed retained earnings of the subsidiaries. The traditional electric operating companies and Southern Power can only pay dividends to Southern Company out of retained earnings or paid-in-capital. See Note 7 under "Southern Power" for information regarding the distribution requirements for certain Southern Power subsidiaries. By regulation, Nicor Gas is restricted, to the extent of its retained earnings balance, in the amount it can dividend or loan to affiliates and is not permitted to make money pool loans to affiliates. At December 31, 2020, the amount of Southern Company Gas' subsidiary retained earnings restricted for dividend payment totaled $1.1 billion. Structural Considerations Since Southern Company and Southern Company Gas are holding companies, the right of Southern Company and Southern Company Gas and, hence, the right of creditors of Southern Company or Southern Company Gas to participate in any distribution of the assets of any respective subsidiary of Southern Company or Southern Company Gas, whether upon liquidation, reorganization or otherwise, is subject to prior claims of creditors and preferred stockholders of such subsidiary. Southern Company Gas' 100%-owned subsidiary, Southern Company Gas Capital, was established to provide for certain of Southern Company Gas' ongoing financing needs through a commercial paper program, the issuance of various debt, hybrid securities, and other financing arrangements. Southern Company Gas fully and unconditionally guarantees all debt issued by Southern Company Gas Capital. Nicor Gas is not permitted by regulation to make loans to affiliates or utilize Southern Company Gas Capital for its financing needs. Southern Power Company's senior notes, bank term loan, commercial paper, and bank credit arrangement are unsecured senior indebtedness, which rank equally with all other unsecured and unsubordinated debt of Southern Power Compan y. Southern Power's subsidiaries are not issuers, borrowers, or obligors, as applicable, under any of these unsecured senior debt arrangements, which are effectively subordinated to any future secured debt of Southern Power Company and any potential claims of creditors of Southern Power's subsidiaries.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
LEASES	LEASES On January 1, 2019, the Registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with ROU assets that will be amortized over the term of each lease. The Registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements were applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The Registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the Registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the Registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Electric generating units $ 941 $ 146 $ 1,368 $ — $ — $ — Real estate/land 815 4 53 2 451 61 Communication towers 158 2 3 — — 20 Railcars 42 16 23 3 — — Other 127 7 5 23 — 1 Total $ 2,083 $ 175 $ 1,452 $ 28 $ 451 $ 82 As of December 31, 2019 Electric generating units $ 990 $ 125 $ 1,487 $ — $ — $ — Real estate/land 782 4 54 2 398 74 Communication towers 154 2 3 — — 18 Railcars 51 21 26 3 — — Other 93 8 12 1 — — Total $ 2,070 $ 160 $ 1,582 $ 6 $ 398 $ 92 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 24 years while the land leases have remaining terms of up to 46 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies and Nicor Gas. Communication tower leases have original terms of up to 10 years with options to renew for periods up to 20 years. Renewal options exist in many of the leases. Except as otherwise noted, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. Land leases associated with renewable energy facilities at Southern Power and communication tower leases for automated meter infrastructure at Southern Company Gas include renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities and the automated meter infrastructure, respectively. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the PPA, which varies between three Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of December 31, 2020 and 2019. Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the Registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: Southern Company Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Operating Leases Operating lease ROU assets, net $ 1,802 $ 151 $ 1,308 $ 9 $ 415 $ 81 Operating lease obligations - current $ 241 $ 51 $ 151 $ 2 $ 25 $ 15 Operating lease obligations - non-current 1,611 119 1,156 7 426 67 Total operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance Leases Finance lease ROU assets, net $ 218 $ 5 $ 115 $ 19 $ — $ — Finance lease obligations - current $ 17 $ 1 $ 9 $ 1 $ — $ — Finance lease obligations - non-current 214 4 136 18 — — Total finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — As of December 31, 2019 Operating Leases Operating lease ROU assets, net $ 1,800 $ 132 $ 1,428 $ 6 $ 369 $ 93 Operating lease obligations - current $ 229 $ 49 $ 144 $ 2 $ 22 $ 14 Operating lease obligations - non-current 1,615 107 1,282 4 376 78 Total operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance Leases Finance lease ROU assets, net $ 216 $ 4 $ 130 $ — $ — $ — Finance lease obligations - current $ 21 $ 1 $ 11 $ — $ — $ — Finance lease obligations - non-current 205 3 145 — — — Total finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — If not presented separately on the Registrants' balance sheets, amounts related to leases are presented as follows: operating lease ROU assets, net are included in "other deferred charges and assets"; operating lease obligations are included in "other current liabilities" and "other deferred credits and liabilities," as applicable; finance lease ROU assets, net are included in "plant in service"; and finance lease obligations are included in "securities due within one year" and "long-term debt," as applicable. Lease costs for 2020 and 2019, which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease cost Operating lease cost $ 309 $ 55 $ 212 $ 3 $ 29 $ 19 Finance lease cost: Amortization of ROU assets 26 1 15 — — — Interest on lease obligations 11 — 16 — — — Total finance lease cost 37 1 31 — — — Short-term lease costs 39 11 26 — — — Variable lease cost 91 4 76 — 7 — Sublease income — (1) — — — — Total lease cost $ 476 $ 70 $ 345 $ 3 $ 36 $ 19 2019 Lease cost Operating lease cost $ 310 $ 54 $ 206 $ 3 $ 28 $ 18 Finance lease cost: Amortization of ROU assets 28 1 15 — — — Interest on lease obligations 12 — 18 — — — Total finance lease cost 40 1 33 — — — Short-term lease costs 48 19 22 — — — Variable lease cost 105 6 85 — 7 — Sublease income — (1) — — — — Total lease cost $ 503 $ 79 $ 346 $ 3 $ 35 $ 18 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs, including $39 million and $42 million in 2020 and 2019, respectively, from finance leases which are included in purchased power on Georgia Power's statements of income, $20 million of which was included in purchased power, affiliates in both 2020 and 2019. Rent expense and PPA capacity expense related to leases for 2018, prior to the adoption of ASC 842, were as follows: Southern Company (a)(b)(c) Alabama Georgia (a) Mississippi (b) Southern Power (c) Southern Company Gas (in millions) 2018: Rent expense $ 192 $ 23 $ 34 $ 4 $ 31 $ 15 PPA capacity expense 231 44 206 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million, of which $29 million related to solar PPAs with Southern Power. (b) Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million. (c) Rent expense includes contingent rent expense related to Southern Power's land leases based on wind production and escalation in the Consumer Price Index for All Urban Consumers. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 310 $ 55 $ 215 $ 3 $ 28 $ 18 Operating cash flows from finance leases 9 — 18 — — — Financing cash flows from finance leases 22 1 11 — — — ROU assets obtained in exchange for new operating lease obligations 227 63 32 — 51 4 ROU assets obtained in exchange for new finance lease obligations 10 2 — — — — 2019 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 323 $ 54 $ 210 $ 3 $ 27 $ 18 Operating cash flows from finance leases 10 — 19 — — — Financing cash flows from finance leases 32 1 13 — — — ROU assets obtained in exchange for new operating lease obligations 118 7 21 — 2 19 ROU assets obtained in exchange for new finance lease obligations 35 2 24 — — — Southern Alabama Georgia Mississippi Southern Power Southern Company Gas As of December 31, 2020 Weighted-average remaining lease term in years: Operating leases 14.5 7.8 9.4 6.5 32.1 9.8 Finance leases 18.2 9.7 9.5 14.9 N/A N/A Weighted-average discount rate: Operating leases 4.44 % 4.14 % 4.37 % 3.26 % 5.45 % 3.67 % Finance leases 4.79 % 3.20 % 10.81 % 2.74 % N/A N/A As of December 31, 2019 Weighted-average remaining lease term in years: Operating leases 14.2 3.1 10.2 7.0 32.8 9.9 Finance leases 18.8 12.1 10.5 N/A N/A N/A Weighted-average discount rate: Operating leases 4.53 % 3.33 % 4.46 % 4.02 % 5.66 % 3.7 % Finance leases 5.04 % 3.60 % 10.76 % N/A N/A N/A Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of December 31, 2020, Southern Power has additional leases that have not yet commenced, as detailed in the following table: Southern Lease category Land Expected commencement date 2021 Longest lease term expiration 30 years Estimated total obligations (in millions) $12 Lessor The Registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable Registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to seven years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include a tolling arrangement related to an electric generating unit accounted for as a sales-type lease with a remaining term of 18 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with remaining terms of up to 26 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 22 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with remaining terms of up to 14 years. Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35 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. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. No profit or loss was recognized by Mississippi Power upon commencement of a tolling arrangement accounted for as a sales-type lease during the first quarter 2019. Mississippi Power completed construction of additional leased assets under the lease during 2020 and, upon completion, the book value of $26 million was transferred from CWIP to lease receivables, of which $24 million and $2 million is included in other property and investments and other accounts and notes receivable, respectively, at December 31, 2020. The transfer represented a non-cash investing transaction for purposes of the statements of cash flows. Construction of additional leased assets is ongoing and will be transferred to a lease receivable as completed. The undiscounted cash flows to be received by Mississippi Power for in-service leased assets under the lease are as follows: At December 31, 2020 (in millions) 2021 $ 20 2022 19 2023 19 2024 18 2025 17 Thereafter 162 Total undiscounted cash flows $ 255 Lease receivable (*) 138 Difference between undiscounted cash flows and discounted cash flows $ 117 (*) Included in other current assets and other property and investments on the balance sheets. The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: At December 31, 2020 Southern Alabama Georgia Power Southern Southern Company Gas (in millions) 2021 $ 207 $ 83 $ 19 $ 86 $ 35 2022 187 76 8 87 35 2023 138 32 2 88 34 2024 106 4 — 90 33 2025 99 3 — 74 28 Thereafter 978 23 — 313 435 Total $ 1,715 $ 221 $ 29 $ 738 $ 600 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Alabama Power and Southern Power allocate revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the Registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with ROU assets that will be amortized over the term of each lease. The Registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements were applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The Registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the Registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the Registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Electric generating units $ 941 $ 146 $ 1,368 $ — $ — $ — Real estate/land 815 4 53 2 451 61 Communication towers 158 2 3 — — 20 Railcars 42 16 23 3 — — Other 127 7 5 23 — 1 Total $ 2,083 $ 175 $ 1,452 $ 28 $ 451 $ 82 As of December 31, 2019 Electric generating units $ 990 $ 125 $ 1,487 $ — $ — $ — Real estate/land 782 4 54 2 398 74 Communication towers 154 2 3 — — 18 Railcars 51 21 26 3 — — Other 93 8 12 1 — — Total $ 2,070 $ 160 $ 1,582 $ 6 $ 398 $ 92 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 24 years while the land leases have remaining terms of up to 46 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies and Nicor Gas. Communication tower leases have original terms of up to 10 years with options to renew for periods up to 20 years. Renewal options exist in many of the leases. Except as otherwise noted, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. Land leases associated with renewable energy facilities at Southern Power and communication tower leases for automated meter infrastructure at Southern Company Gas include renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities and the automated meter infrastructure, respectively. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the PPA, which varies between three Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of December 31, 2020 and 2019. Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the Registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: Southern Company Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Operating Leases Operating lease ROU assets, net $ 1,802 $ 151 $ 1,308 $ 9 $ 415 $ 81 Operating lease obligations - current $ 241 $ 51 $ 151 $ 2 $ 25 $ 15 Operating lease obligations - non-current 1,611 119 1,156 7 426 67 Total operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance Leases Finance lease ROU assets, net $ 218 $ 5 $ 115 $ 19 $ — $ — Finance lease obligations - current $ 17 $ 1 $ 9 $ 1 $ — $ — Finance lease obligations - non-current 214 4 136 18 — — Total finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — As of December 31, 2019 Operating Leases Operating lease ROU assets, net $ 1,800 $ 132 $ 1,428 $ 6 $ 369 $ 93 Operating lease obligations - current $ 229 $ 49 $ 144 $ 2 $ 22 $ 14 Operating lease obligations - non-current 1,615 107 1,282 4 376 78 Total operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance Leases Finance lease ROU assets, net $ 216 $ 4 $ 130 $ — $ — $ — Finance lease obligations - current $ 21 $ 1 $ 11 $ — $ — $ — Finance lease obligations - non-current 205 3 145 — — — Total finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — If not presented separately on the Registrants' balance sheets, amounts related to leases are presented as follows: operating lease ROU assets, net are included in "other deferred charges and assets"; operating lease obligations are included in "other current liabilities" and "other deferred credits and liabilities," as applicable; finance lease ROU assets, net are included in "plant in service"; and finance lease obligations are included in "securities due within one year" and "long-term debt," as applicable. Lease costs for 2020 and 2019, which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease cost Operating lease cost $ 309 $ 55 $ 212 $ 3 $ 29 $ 19 Finance lease cost: Amortization of ROU assets 26 1 15 — — — Interest on lease obligations 11 — 16 — — — Total finance lease cost 37 1 31 — — — Short-term lease costs 39 11 26 — — — Variable lease cost 91 4 76 — 7 — Sublease income — (1) — — — — Total lease cost $ 476 $ 70 $ 345 $ 3 $ 36 $ 19 2019 Lease cost Operating lease cost $ 310 $ 54 $ 206 $ 3 $ 28 $ 18 Finance lease cost: Amortization of ROU assets 28 1 15 — — — Interest on lease obligations 12 — 18 — — — Total finance lease cost 40 1 33 — — — Short-term lease costs 48 19 22 — — — Variable lease cost 105 6 85 — 7 — Sublease income — (1) — — — — Total lease cost $ 503 $ 79 $ 346 $ 3 $ 35 $ 18 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs, including $39 million and $42 million in 2020 and 2019, respectively, from finance leases which are included in purchased power on Georgia Power's statements of income, $20 million of which was included in purchased power, affiliates in both 2020 and 2019. Rent expense and PPA capacity expense related to leases for 2018, prior to the adoption of ASC 842, were as follows: Southern Company (a)(b)(c) Alabama Georgia (a) Mississippi (b) Southern Power (c) Southern Company Gas (in millions) 2018: Rent expense $ 192 $ 23 $ 34 $ 4 $ 31 $ 15 PPA capacity expense 231 44 206 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million, of which $29 million related to solar PPAs with Southern Power. (b) Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million. (c) Rent expense includes contingent rent expense related to Southern Power's land leases based on wind production and escalation in the Consumer Price Index for All Urban Consumers. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 310 $ 55 $ 215 $ 3 $ 28 $ 18 Operating cash flows from finance leases 9 — 18 — — — Financing cash flows from finance leases 22 1 11 — — — ROU assets obtained in exchange for new operating lease obligations 227 63 32 — 51 4 ROU assets obtained in exchange for new finance lease obligations 10 2 — — — — 2019 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 323 $ 54 $ 210 $ 3 $ 27 $ 18 Operating cash flows from finance leases 10 — 19 — — — Financing cash flows from finance leases 32 1 13 — — — ROU assets obtained in exchange for new operating lease obligations 118 7 21 — 2 19 ROU assets obtained in exchange for new finance lease obligations 35 2 24 — — — Southern Alabama Georgia Mississippi Southern Power Southern Company Gas As of December 31, 2020 Weighted-average remaining lease term in years: Operating leases 14.5 7.8 9.4 6.5 32.1 9.8 Finance leases 18.2 9.7 9.5 14.9 N/A N/A Weighted-average discount rate: Operating leases 4.44 % 4.14 % 4.37 % 3.26 % 5.45 % 3.67 % Finance leases 4.79 % 3.20 % 10.81 % 2.74 % N/A N/A As of December 31, 2019 Weighted-average remaining lease term in years: Operating leases 14.2 3.1 10.2 7.0 32.8 9.9 Finance leases 18.8 12.1 10.5 N/A N/A N/A Weighted-average discount rate: Operating leases 4.53 % 3.33 % 4.46 % 4.02 % 5.66 % 3.7 % Finance leases 5.04 % 3.60 % 10.76 % N/A N/A N/A Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of December 31, 2020, Southern Power has additional leases that have not yet commenced, as detailed in the following table: Southern Lease category Land Expected commencement date 2021 Longest lease term expiration 30 years Estimated total obligations (in millions) $12 Lessor The Registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable Registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to seven years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include a tolling arrangement related to an electric generating unit accounted for as a sales-type lease with a remaining term of 18 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with remaining terms of up to 26 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 22 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with remaining terms of up to 14 years. Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35 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. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. No profit or loss was recognized by Mississippi Power upon commencement of a tolling arrangement accounted for as a sales-type lease during the first quarter 2019. Mississippi Power completed construction of additional leased assets under the lease during 2020 and, upon completion, the book value of $26 million was transferred from CWIP to lease receivables, of which $24 million and $2 million is included in other property and investments and other accounts and notes receivable, respectively, at December 31, 2020. The transfer represented a non-cash investing transaction for purposes of the statements of cash flows. Construction of additional leased assets is ongoing and will be transferred to a lease receivable as completed. The undiscounted cash flows to be received by Mississippi Power for in-service leased assets under the lease are as follows: At December 31, 2020 (in millions) 2021 $ 20 2022 19 2023 19 2024 18 2025 17 Thereafter 162 Total undiscounted cash flows $ 255 Lease receivable (*) 138 Difference between undiscounted cash flows and discounted cash flows $ 117 (*) Included in other current assets and other property and investments on the balance sheets. The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: At December 31, 2020 Southern Alabama Georgia Power Southern Southern Company Gas (in millions) 2021 $ 207 $ 83 $ 19 $ 86 $ 35 2022 187 76 8 87 35 2023 138 32 2 88 34 2024 106 4 — 90 33 2025 99 3 — 74 28 Thereafter 978 23 — 313 435 Total $ 1,715 $ 221 $ 29 $ 738 $ 600 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Alabama Power and Southern Power allocate revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the Registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with ROU assets that will be amortized over the term of each lease. The Registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements were applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The Registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the Registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the Registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Electric generating units $ 941 $ 146 $ 1,368 $ — $ — $ — Real estate/land 815 4 53 2 451 61 Communication towers 158 2 3 — — 20 Railcars 42 16 23 3 — — Other 127 7 5 23 — 1 Total $ 2,083 $ 175 $ 1,452 $ 28 $ 451 $ 82 As of December 31, 2019 Electric generating units $ 990 $ 125 $ 1,487 $ — $ — $ — Real estate/land 782 4 54 2 398 74 Communication towers 154 2 3 — — 18 Railcars 51 21 26 3 — — Other 93 8 12 1 — — Total $ 2,070 $ 160 $ 1,582 $ 6 $ 398 $ 92 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 24 years while the land leases have remaining terms of up to 46 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies and Nicor Gas. Communication tower leases have original terms of up to 10 years with options to renew for periods up to 20 years. Renewal options exist in many of the leases. Except as otherwise noted, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. Land leases associated with renewable energy facilities at Southern Power and communication tower leases for automated meter infrastructure at Southern Company Gas include renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities and the automated meter infrastructure, respectively. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the PPA, which varies between three Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of December 31, 2020 and 2019. Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the Registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: Southern Company Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Operating Leases Operating lease ROU assets, net $ 1,802 $ 151 $ 1,308 $ 9 $ 415 $ 81 Operating lease obligations - current $ 241 $ 51 $ 151 $ 2 $ 25 $ 15 Operating lease obligations - non-current 1,611 119 1,156 7 426 67 Total operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance Leases Finance lease ROU assets, net $ 218 $ 5 $ 115 $ 19 $ — $ — Finance lease obligations - current $ 17 $ 1 $ 9 $ 1 $ — $ — Finance lease obligations - non-current 214 4 136 18 — — Total finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — As of December 31, 2019 Operating Leases Operating lease ROU assets, net $ 1,800 $ 132 $ 1,428 $ 6 $ 369 $ 93 Operating lease obligations - current $ 229 $ 49 $ 144 $ 2 $ 22 $ 14 Operating lease obligations - non-current 1,615 107 1,282 4 376 78 Total operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance Leases Finance lease ROU assets, net $ 216 $ 4 $ 130 $ — $ — $ — Finance lease obligations - current $ 21 $ 1 $ 11 $ — $ — $ — Finance lease obligations - non-current 205 3 145 — — — Total finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — If not presented separately on the Registrants' balance sheets, amounts related to leases are presented as follows: operating lease ROU assets, net are included in "other deferred charges and assets"; operating lease obligations are included in "other current liabilities" and "other deferred credits and liabilities," as applicable; finance lease ROU assets, net are included in "plant in service"; and finance lease obligations are included in "securities due within one year" and "long-term debt," as applicable. Lease costs for 2020 and 2019, which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease cost Operating lease cost $ 309 $ 55 $ 212 $ 3 $ 29 $ 19 Finance lease cost: Amortization of ROU assets 26 1 15 — — — Interest on lease obligations 11 — 16 — — — Total finance lease cost 37 1 31 — — — Short-term lease costs 39 11 26 — — — Variable lease cost 91 4 76 — 7 — Sublease income — (1) — — — — Total lease cost $ 476 $ 70 $ 345 $ 3 $ 36 $ 19 2019 Lease cost Operating lease cost $ 310 $ 54 $ 206 $ 3 $ 28 $ 18 Finance lease cost: Amortization of ROU assets 28 1 15 — — — Interest on lease obligations 12 — 18 — — — Total finance lease cost 40 1 33 — — — Short-term lease costs 48 19 22 — — — Variable lease cost 105 6 85 — 7 — Sublease income — (1) — — — — Total lease cost $ 503 $ 79 $ 346 $ 3 $ 35 $ 18 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs, including $39 million and $42 million in 2020 and 2019, respectively, from finance leases which are included in purchased power on Georgia Power's statements of income, $20 million of which was included in purchased power, affiliates in both 2020 and 2019. Rent expense and PPA capacity expense related to leases for 2018, prior to the adoption of ASC 842, were as follows: Southern Company (a)(b)(c) Alabama Georgia (a) Mississippi (b) Southern Power (c) Southern Company Gas (in millions) 2018: Rent expense $ 192 $ 23 $ 34 $ 4 $ 31 $ 15 PPA capacity expense 231 44 206 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million, of which $29 million related to solar PPAs with Southern Power. (b) Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million. (c) Rent expense includes contingent rent expense related to Southern Power's land leases based on wind production and escalation in the Consumer Price Index for All Urban Consumers. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 310 $ 55 $ 215 $ 3 $ 28 $ 18 Operating cash flows from finance leases 9 — 18 — — — Financing cash flows from finance leases 22 1 11 — — — ROU assets obtained in exchange for new operating lease obligations 227 63 32 — 51 4 ROU assets obtained in exchange for new finance lease obligations 10 2 — — — — 2019 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 323 $ 54 $ 210 $ 3 $ 27 $ 18 Operating cash flows from finance leases 10 — 19 — — — Financing cash flows from finance leases 32 1 13 — — — ROU assets obtained in exchange for new operating lease obligations 118 7 21 — 2 19 ROU assets obtained in exchange for new finance lease obligations 35 2 24 — — — Southern Alabama Georgia Mississippi Southern Power Southern Company Gas As of December 31, 2020 Weighted-average remaining lease term in years: Operating leases 14.5 7.8 9.4 6.5 32.1 9.8 Finance leases 18.2 9.7 9.5 14.9 N/A N/A Weighted-average discount rate: Operating leases 4.44 % 4.14 % 4.37 % 3.26 % 5.45 % 3.67 % Finance leases 4.79 % 3.20 % 10.81 % 2.74 % N/A N/A As of December 31, 2019 Weighted-average remaining lease term in years: Operating leases 14.2 3.1 10.2 7.0 32.8 9.9 Finance leases 18.8 12.1 10.5 N/A N/A N/A Weighted-average discount rate: Operating leases 4.53 % 3.33 % 4.46 % 4.02 % 5.66 % 3.7 % Finance leases 5.04 % 3.60 % 10.76 % N/A N/A N/A Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of December 31, 2020, Southern Power has additional leases that have not yet commenced, as detailed in the following table: Southern Lease category Land Expected commencement date 2021 Longest lease term expiration 30 years Estimated total obligations (in millions) $12 Lessor The Registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable Registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to seven years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include a tolling arrangement related to an electric generating unit accounted for as a sales-type lease with a remaining term of 18 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with remaining terms of up to 26 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 22 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with remaining terms of up to 14 years. Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35 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. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. No profit or loss was recognized by Mississippi Power upon commencement of a tolling arrangement accounted for as a sales-type lease during the first quarter 2019. Mississippi Power completed construction of additional leased assets under the lease during 2020 and, upon completion, the book value of $26 million was transferred from CWIP to lease receivables, of which $24 million and $2 million is included in other property and investments and other accounts and notes receivable, respectively, at December 31, 2020. The transfer represented a non-cash investing transaction for purposes of the statements of cash flows. Construction of additional leased assets is ongoing and will be transferred to a lease receivable as completed. The undiscounted cash flows to be received by Mississippi Power for in-service leased assets under the lease are as follows: At December 31, 2020 (in millions) 2021 $ 20 2022 19 2023 19 2024 18 2025 17 Thereafter 162 Total undiscounted cash flows $ 255 Lease receivable (*) 138 Difference between undiscounted cash flows and discounted cash flows $ 117 (*) Included in other current assets and other property and investments on the balance sheets. The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: At December 31, 2020 Southern Alabama Georgia Power Southern Southern Company Gas (in millions) 2021 $ 207 $ 83 $ 19 $ 86 $ 35 2022 187 76 8 87 35 2023 138 32 2 88 34 2024 106 4 — 90 33 2025 99 3 — 74 28 Thereafter 978 23 — 313 435 Total $ 1,715 $ 221 $ 29 $ 738 $ 600 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Alabama Power and Southern Power allocate revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the Registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with ROU assets that will be amortized over the term of each lease. The Registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements were applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The Registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the Registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the Registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Electric generating units $ 941 $ 146 $ 1,368 $ — $ — $ — Real estate/land 815 4 53 2 451 61 Communication towers 158 2 3 — — 20 Railcars 42 16 23 3 — — Other 127 7 5 23 — 1 Total $ 2,083 $ 175 $ 1,452 $ 28 $ 451 $ 82 As of December 31, 2019 Electric generating units $ 990 $ 125 $ 1,487 $ — $ — $ — Real estate/land 782 4 54 2 398 74 Communication towers 154 2 3 — — 18 Railcars 51 21 26 3 — — Other 93 8 12 1 — — Total $ 2,070 $ 160 $ 1,582 $ 6 $ 398 $ 92 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 24 years while the land leases have remaining terms of up to 46 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies and Nicor Gas. Communication tower leases have original terms of up to 10 years with options to renew for periods up to 20 years. Renewal options exist in many of the leases. Except as otherwise noted, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. Land leases associated with renewable energy facilities at Southern Power and communication tower leases for automated meter infrastructure at Southern Company Gas include renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities and the automated meter infrastructure, respectively. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the PPA, which varies between three Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of December 31, 2020 and 2019. Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the Registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: Southern Company Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Operating Leases Operating lease ROU assets, net $ 1,802 $ 151 $ 1,308 $ 9 $ 415 $ 81 Operating lease obligations - current $ 241 $ 51 $ 151 $ 2 $ 25 $ 15 Operating lease obligations - non-current 1,611 119 1,156 7 426 67 Total operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance Leases Finance lease ROU assets, net $ 218 $ 5 $ 115 $ 19 $ — $ — Finance lease obligations - current $ 17 $ 1 $ 9 $ 1 $ — $ — Finance lease obligations - non-current 214 4 136 18 — — Total finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — As of December 31, 2019 Operating Leases Operating lease ROU assets, net $ 1,800 $ 132 $ 1,428 $ 6 $ 369 $ 93 Operating lease obligations - current $ 229 $ 49 $ 144 $ 2 $ 22 $ 14 Operating lease obligations - non-current 1,615 107 1,282 4 376 78 Total operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance Leases Finance lease ROU assets, net $ 216 $ 4 $ 130 $ — $ — $ — Finance lease obligations - current $ 21 $ 1 $ 11 $ — $ — $ — Finance lease obligations - non-current 205 3 145 — — — Total finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — If not presented separately on the Registrants' balance sheets, amounts related to leases are presented as follows: operating lease ROU assets, net are included in "other deferred charges and assets"; operating lease obligations are included in "other current liabilities" and "other deferred credits and liabilities," as applicable; finance lease ROU assets, net are included in "plant in service"; and finance lease obligations are included in "securities due within one year" and "long-term debt," as applicable. Lease costs for 2020 and 2019, which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease cost Operating lease cost $ 309 $ 55 $ 212 $ 3 $ 29 $ 19 Finance lease cost: Amortization of ROU assets 26 1 15 — — — Interest on lease obligations 11 — 16 — — — Total finance lease cost 37 1 31 — — — Short-term lease costs 39 11 26 — — — Variable lease cost 91 4 76 — 7 — Sublease income — (1) — — — — Total lease cost $ 476 $ 70 $ 345 $ 3 $ 36 $ 19 2019 Lease cost Operating lease cost $ 310 $ 54 $ 206 $ 3 $ 28 $ 18 Finance lease cost: Amortization of ROU assets 28 1 15 — — — Interest on lease obligations 12 — 18 — — — Total finance lease cost 40 1 33 — — — Short-term lease costs 48 19 22 — — — Variable lease cost 105 6 85 — 7 — Sublease income — (1) — — — — Total lease cost $ 503 $ 79 $ 346 $ 3 $ 35 $ 18 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs, including $39 million and $42 million in 2020 and 2019, respectively, from finance leases which are included in purchased power on Georgia Power's statements of income, $20 million of which was included in purchased power, affiliates in both 2020 and 2019. Rent expense and PPA capacity expense related to leases for 2018, prior to the adoption of ASC 842, were as follows: Southern Company (a)(b)(c) Alabama Georgia (a) Mississippi (b) Southern Power (c) Southern Company Gas (in millions) 2018: Rent expense $ 192 $ 23 $ 34 $ 4 $ 31 $ 15 PPA capacity expense 231 44 206 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million, of which $29 million related to solar PPAs with Southern Power. (b) Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million. (c) Rent expense includes contingent rent expense related to Southern Power's land leases based on wind production and escalation in the Consumer Price Index for All Urban Consumers. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 310 $ 55 $ 215 $ 3 $ 28 $ 18 Operating cash flows from finance leases 9 — 18 — — — Financing cash flows from finance leases 22 1 11 — — — ROU assets obtained in exchange for new operating lease obligations 227 63 32 — 51 4 ROU assets obtained in exchange for new finance lease obligations 10 2 — — — — 2019 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 323 $ 54 $ 210 $ 3 $ 27 $ 18 Operating cash flows from finance leases 10 — 19 — — — Financing cash flows from finance leases 32 1 13 — — — ROU assets obtained in exchange for new operating lease obligations 118 7 21 — 2 19 ROU assets obtained in exchange for new finance lease obligations 35 2 24 — — — Southern Alabama Georgia Mississippi Southern Power Southern Company Gas As of December 31, 2020 Weighted-average remaining lease term in years: Operating leases 14.5 7.8 9.4 6.5 32.1 9.8 Finance leases 18.2 9.7 9.5 14.9 N/A N/A Weighted-average discount rate: Operating leases 4.44 % 4.14 % 4.37 % 3.26 % 5.45 % 3.67 % Finance leases 4.79 % 3.20 % 10.81 % 2.74 % N/A N/A As of December 31, 2019 Weighted-average remaining lease term in years: Operating leases 14.2 3.1 10.2 7.0 32.8 9.9 Finance leases 18.8 12.1 10.5 N/A N/A N/A Weighted-average discount rate: Operating leases 4.53 % 3.33 % 4.46 % 4.02 % 5.66 % 3.7 % Finance leases 5.04 % 3.60 % 10.76 % N/A N/A N/A Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of December 31, 2020, Southern Power has additional leases that have not yet commenced, as detailed in the following table: Southern Lease category Land Expected commencement date 2021 Longest lease term expiration 30 years Estimated total obligations (in millions) $12 Lessor The Registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable Registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to seven years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include a tolling arrangement related to an electric generating unit accounted for as a sales-type lease with a remaining term of 18 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with remaining terms of up to 26 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 22 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with remaining terms of up to 14 years. Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35 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. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. No profit or loss was recognized by Mississippi Power upon commencement of a tolling arrangement accounted for as a sales-type lease during the first quarter 2019. Mississippi Power completed construction of additional leased assets under the lease during 2020 and, upon completion, the book value of $26 million was transferred from CWIP to lease receivables, of which $24 million and $2 million is included in other property and investments and other accounts and notes receivable, respectively, at December 31, 2020. The transfer represented a non-cash investing transaction for purposes of the statements of cash flows. Construction of additional leased assets is ongoing and will be transferred to a lease receivable as completed. The undiscounted cash flows to be received by Mississippi Power for in-service leased assets under the lease are as follows: At December 31, 2020 (in millions) 2021 $ 20 2022 19 2023 19 2024 18 2025 17 Thereafter 162 Total undiscounted cash flows $ 255 Lease receivable (*) 138 Difference between undiscounted cash flows and discounted cash flows $ 117 (*) Included in other current assets and other property and investments on the balance sheets. The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: At December 31, 2020 Southern Alabama Georgia Power Southern Southern Company Gas (in millions) 2021 $ 207 $ 83 $ 19 $ 86 $ 35 2022 187 76 8 87 35 2023 138 32 2 88 34 2024 106 4 — 90 33 2025 99 3 — 74 28 Thereafter 978 23 — 313 435 Total $ 1,715 $ 221 $ 29 $ 738 $ 600 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Alabama Power and Southern Power allocate revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Mississippi Power are immaterial.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Southern Company files a consolidated federal income tax return and the Registrants file various state income tax returns, some of which are combined or unitary. Under a joint consolidated income tax allocation agreement, each Southern Company subsidiary's current and deferred tax expense is computed on a stand-alone basis and each subsidiary is allocated an amount of tax similar to that which would be paid if it filed a separate income tax return. In accordance with IRS regulations, each company is jointly and severally liable for the federal tax liability. Federal Tax Reform Legislation Following the enactment of the Tax Reform Legislation, the SEC staff issued Staff Accounting Bulletin 118 – "Income Tax Accounting Implications of the Tax Cuts and Jobs Act" (SAB 118), which provided for a measurement period of up to one year from the enactment date to complete accounting under GAAP for the tax effects of the legislation. Following the 2017 tax return filing in the fourth quarter 2018, each of the Registrants considered the measurement of impacts from the Tax Reform Legislation on deferred income tax assets and liabilities, primarily due to the impact of the reduction of the corporate income tax rate, to be complete as of December 31, 2018. Current and Deferred Income Taxes Details of income tax provisions are as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ 199 $ 198 $ 365 $ 18 $ (303) $ 82 Deferred 70 44 (224) (14) 299 53 269 242 141 4 (4) 135 State — Current 100 61 60 — (4) 35 Deferred 24 34 (49) 10 11 3 124 95 11 10 7 38 Total $ 393 $ 337 $ 152 $ 14 $ 3 $ 173 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ 156 $ 61 $ 264 $ (6) $ (717) $ (120) Deferred 1,237 125 180 26 647 195 1,393 186 444 20 (70) 75 State — Current 275 12 6 (1) 1 37 Deferred 130 72 22 11 13 18 405 84 28 10 14 55 Total $ 1,798 $ 270 $ 472 $ 30 $ (56) $ 130 2018 Southern Company Alabama Power Georgia Mississippi Southern Power Southern Company Gas (in millions) Federal — Current $ 167 $ 91 $ 393 $ (567) $ 85 $ 334 Deferred 231 123 (249) 575 (154) 33 398 214 144 8 (69) 367 State — Current 188 26 81 (10) (9) 131 Deferred (137) 51 (11) (100) (86) (34) 51 77 70 (110) (95) 97 Total $ 449 $ 291 $ 214 $ (102) $ (164) $ 464 Southern Company's and Southern Power's ITCs and PTCs generated in the current tax year and carried forward from prior tax years that cannot be utilized in the current tax year are reclassified from current to deferred taxes in federal income tax expense in the tables above. Southern Power's ITCs and PTCs reclassified in this manner include $5 million for 2020, $51 million for 2019, and $128 million for 2018. Southern Power received $340 million, $734 million, and $5 million of cash related to federal ITCs under renewable energy initiatives in 2020, 2019, and 2018, respectively. See "Deferred Tax Assets and Liabilities" and "Tax Credit Carryforwards" herein for additional information. In accordance with regulatory requirements, deferred federal ITCs for the traditional electric operating companies are deferred and amortized over the average life of the related property, with such amortization normally applied as a credit to reduce depreciation and amortization in the statements of income. Southern Power's and the natural gas distribution utilities' deferred federal ITCs, as well as certain state ITCs for Nicor Gas, are deferred and amortized to income tax expense over the life of the respective asset. ITCs amortized in 2020, 2019, and 2018 were immaterial for the traditional electric operating companies and Southern Company Gas and were as follows for Southern Company and Southern Power: Southern Company Southern Power (in millions) 2020 $ 84 $ 59 2019 181 151 2018 87 58 When Southern Power recognizes tax credits, the tax basis of the asset is reduced by 50% of the ITCs received, resulting in a net deferred tax asset. Southern Power has elected to recognize the tax benefit of this basis difference as a reduction to income tax expense in the year in which the plant reaches commercial operation. The tax benefit of the related basis differences reduced income tax expense by $5 million and $1 million in 2019 and 2018, respectively. State ITCs and other state credits, which are recognized in the period in which the credits are generated, reduced Georgia Power's income tax expense by $67 million in 2020, $51 million in 2019, and $21 million in 2018. Southern Power's federal and state PTCs, which are recognized in the period in which the credits are generated, reduced Southern Power's income tax expense by $15 million in 2020, $12 million in 2019, and $141 million in 2018. Legal Entity Reorganizations In 2018, Southern Power completed the final stage of a legal entity reorganization of various direct and indirect subsidiaries that own and operate substantially all of its solar facilities, including certain subsidiaries owned in partnership with various third parties, and also completed a legal entity reorganization of eight operating wind facilities under a new holding company, SP Wind. The reorganizations resulted in net state tax benefits related to certain changes in apportionment rates totaling approximately $65 million, which were recorded in 2018. 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. A reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 2.8 5.0 0.5 4.8 2.7 4.0 Employee stock plans' dividend deduction (0.7) — — — — — Non-deductible book depreciation 0.7 0.6 0.8 0.5 — — Flowback of excess deferred income taxes (8.8) (3.1) (12.0) (18.5) — (2.7) AFUDC-Equity (0.8) (0.6) (1.1) (0.1) — — Federal PTCs — — — — (2.5) — Amortization of ITC (1.6) (0.1) (0.1) (0.1) (22.1) (0.1) Noncontrolling interests — — — — 3.1 — Leveraged lease impairments (1.6) — — — — — Other 0.2 (0.3) (0.3) 0.9 (0.9) 0.5 Effective income tax (benefit) rate 11.2 % 22.5 % 8.8 % 8.5 % 1.3 % 22.7 % 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 4.9 4.9 1.0 4.3 4.0 6.1 Employee stock plans' dividend deduction (0.4) — — — — — Non-deductible book depreciation 0.3 0.6 0.5 0.4 — — Flowback of excess deferred income taxes (2.1) (5.3) — (12.6) — (6.0) AFUDC-Equity (0.4) (0.8) (0.6) (0.1) — — ITC basis difference (0.1) — — — (1.9) — Amortization of ITC (0.8) (0.1) (0.1) (0.1) (16.1) (0.1) Tax impact from sale of subsidiaries 5.1 — — — (27.6) (1.4) Noncontrolling interests — — — — 0.8 — Other — (0.4) (0.3) 4.9 (0.6) (1.4) Effective income tax (benefit) rate 27.5 % 19.9 % 21.5 % 17.8 % (20.4) % 18.2 % 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 1.8 5.0 5.5 (65.1) (90.8) 9.2 Employee stock plans' dividend deduction (1.0) — — — — — Non-deductible book depreciation 0.8 0.6 1.2 0.7 — — Flowback of excess deferred income taxes (4.0) (1.8) — (4.1) — (3.0) AFUDC-Equity (1.0) (1.0) (1.4) — — — ITC basis difference (0.6) — — — (0.2) — Federal PTCs (4.7) — — — (156.6) — Amortization of ITC (2.0) (0.1) (0.2) (0.2) (55.4) (0.1) Tax impact from sale of subsidiaries 8.6 — — — — 28.5 Tax Reform Legislation (1.4) — (4.9) (26.3) 96.1 (0.4) Noncontrolling interests (0.4) — — — (14.9) — Other (0.8) (0.1) 0.1 (1.4) 2.0 0.3 Effective income tax (benefit) rate 16.3 % 23.6 % 21.3 % (75.4) % (198.8) % 55.5 % Deferred Tax Assets and Liabilities The tax effects of temporary differences between the carrying amounts of assets and liabilities in the financial statements of the Registrants and their respective tax bases, which give rise to deferred tax assets and liabilities, are as follows: December 31, 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,950 $ 2,453 $ 3,228 $ 319 $ 1,389 $ 1,349 Property basis differences 1,999 1,010 689 148 — 135 Federal effect of net state deferred tax assets — — — 25 — — Leveraged lease basis differences 142 — — — — — Employee benefit obligations 739 250 362 39 12 26 Premium on reacquired debt 78 12 66 — — — Regulatory assets – Storm damage reserves 80 — 80 — — — Employee benefit obligations 1,313 348 438 62 — 45 Remaining book value of retired assets 270 123 141 6 — — AROs 1,969 764 1,165 40 — — AROs 804 328 429 — — — Other 437 128 82 66 12 138 Total deferred income tax liabilities 16,781 5,416 6,680 705 1,413 1,693 Deferred tax assets — Federal effect of net state deferred tax liabilities 284 151 59 — 26 70 State effect of federal deferred taxes 126 126 — — — — Employee benefit obligations 1,511 369 522 80 6 100 Other property basis differences 223 — 72 — 134 — ITC and PTC carryforward 1,853 12 539 — 1,110 — Long-term debt fair value adjustment 86 — — — — 86 Other partnership basis difference 166 — — — 166 — Other comprehensive losses 128 7 17 — 25 — AROs 2,773 1,092 1,594 40 — — Estimated loss on plants under construction 369 — 369 — — — Other deferred state tax attributes 357 — 9 250 68 10 Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 338 243 76 19 — — Other 660 143 186 39 52 166 Total deferred income tax assets 8,874 2,143 3,443 428 1,587 432 Valuation allowance (136) — (35) (41) (35) (4) Net deferred income tax assets 8,738 2,143 3,408 387 1,552 428 Net deferred income taxes (assets)/liabilities $ 8,043 $ 3,273 $ 3,272 $ 318 $ (139) $ 1,265 Recognized in the balance sheets: Accumulated deferred income taxes – assets $ (132) $ — $ — $ (129) $ (262) $ — Accumulated deferred income taxes – liabilities $ 8,175 $ 3,273 $ 3,272 $ 447 $ 123 $ 1,265 December 31, 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,711 $ 2,402 $ 3,058 $ 315 $ 1,422 $ 1,288 Property basis differences 1,843 912 643 143 — 133 Federal effect of net state deferred tax assets — — — 24 — — Leveraged lease basis differences 236 — — — — — Employee benefit obligations 704 242 351 38 12 12 Premium on reacquired debt 83 13 70 — — — Regulatory assets – Storm damage reserves 109 — 109 — — — Employee benefit obligations 1,174 311 403 55 — 45 Remaining book value of retired assets 341 174 159 8 — — AROs 1,723 613 1,066 44 — — AROs 814 360 405 — — — Other 523 134 81 68 11 198 Total deferred income tax liabilities 16,261 5,161 6,345 695 1,445 1,676 Deferred tax assets — Federal effect of net state deferred tax liabilities 277 162 63 — 24 56 Employee benefit obligations 1,385 334 488 72 5 111 Other property basis differences 230 — 65 — 146 — ITC and PTC carryforward 2,098 11 435 — 1,445 — Long-term debt fair value adjustment 97 — — — — 97 Other partnership basis difference 169 — — — 169 — Other comprehensive losses 112 8 18 — 10 — AROs 2,537 973 1,471 44 — — Estimated loss on plants under construction 283 — 283 — — — Other deferred state tax attributes 402 — 13 251 72 8 Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 401 240 133 28 — — Other 689 173 154 56 46 190 Total deferred income tax assets 8,680 1,901 3,123 451 1,917 462 Valuation allowance (137) — (35) (41) (36) (5) Net deferred income tax assets 8,543 1,901 3,088 410 1,881 457 Net deferred income taxes (assets)/liabilities $ 7,718 $ 3,260 $ 3,257 $ 285 $ (436) $ 1,219 Recognized in the balance sheets: Accumulated deferred income taxes – assets $ (170) $ — $ — $ (139) $ (551) $ — Accumulated deferred income taxes – liabilities $ 7,888 $ 3,260 $ 3,257 $ 424 $ 115 $ 1,219 The traditional electric operating companies and the natural gas distribution utilities have tax-related regulatory assets (deferred income tax charges) and regulatory liabilities (deferred income tax credits). The regulatory assets are primarily attributable to tax benefits flowed through to customers in prior years, deferred taxes previously recognized at rates lower than the current enacted tax law, and taxes applicable to capitalized interest. The regulatory liabilities are primarily attributable to deferred taxes previously recognized at rates higher than the current enacted tax law and to unamortized ITCs. See Note 2 for each Registrant's related balances at December 31, 2020 and 2019. Tax Credit Carryforwards Federal ITC/PTC carryforwards at December 31, 2020 were as follows: Southern Company Alabama Georgia Southern (in millions) Federal ITC/PTC carryforwards $ 1,428 $ 12 $ 114 $ 1,110 Tax Year in which federal ITC/PTC carryforwards begin expiring 2031 2032 2031 2035 Year by which federal ITC/PTC carryforwards are expected to be utilized 2024 2023 2023 2024 The estimated tax credit utilization reflects the various sale transactions described in Note 15 and could be further delayed 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, and changes in taxable income projections. See Note 2 under "Georgia Power – Nuclear Construction" for additional information on Plant Vogtle Units 3 and 4. At December 31, 2020, Georgia Power also had approximately $343 million in net state investment and other net state tax credit carryforwards for the State of Georgia that will expire between tax years 2021 and 2030 and are not expected to be fully utilized. Georgia Power has a net state valuation allowance of $28 million associated with these carryforwards. The ultimate outcome of these matters cannot be determined at this time. Net Operating Loss Carryforwards At December 31, 2020, the net state income tax benefit of state and local NOL carryforwards for Southern Company's subsidiaries were as follows: Company/Jurisdiction Approximate Net State Income Tax Benefit of NOL Carryforwards Tax Year NOL Mississippi Power Mississippi $ 200 2031 Southern Power Oklahoma 39 2035 Florida 11 2034 South Carolina 2 2036 Other states 1 Various Southern Power Total $ 53 Other (*) New York 11 2035 New York City 14 2035 Other states 21 Various Southern Company Total $ 299 (*) Represents other Southern Company subsidiaries. Alabama Power, Georgia Power, and Southern Company Gas did not have material state or local NOL carryforwards at December 31, 2020. State NOLs for Mississippi, Oklahoma, and Florida are not expected to be fully utilized prior to expiration. At December 31, 2020, Mississippi Power had a net state valuation allowance of $32 million for the Mississippi NOL and Southern Power had net state valuation allowances of $16 million for the Oklahoma NOL and $11 million for the Florida NOL. The ultimate outcome of these matters cannot be determined at this time. Unrecognized Tax Benefits Changes in unrecognized tax benefits for the periods presented were as follows: Southern Company (in millions) Unrecognized tax benefits at December 31, 2017 $ 18 Tax position changes – decrease from prior periods (18) Unrecognized tax benefits at December 31, 2018 and 2019 $ — Tax positions changes – increase from prior periods 44 Unrecognized tax benefits at December 31, 2020 $ 44 The unrecognized tax positions increase from prior periods for 2020 and the balance of unrecognized tax benefits at December 31, 2020 relate to a 2019 state tax filing position to exclude certain gains from 2019 dispositions from taxation in a certain unitary state. If accepted by the state, this position would decrease Southern Company's annual effective tax rate. The ultimate outcome of this unrecognized tax benefit is dependent on completion of the related state audit, which is not expected to be resolved within the next 12 months. All of the Registrants classify interest on tax uncertainties as interest expense. Accrued interest for all tax positions was immaterial for all years presented. None of the Registrants accrued any penalties on uncertain tax positions. The IRS has finalized its audits of Southern Company's consolidated federal income tax returns through 2019. Southern Company is a participant in the Compliance Assurance Process of the IRS. The audits for the Registrants' state income tax returns have either been concluded, or the statute of limitations has expired, for years prior to 2015.

RETIREMENT BENEFITS

RETIREMENT BENEFITS	12 Months Ended
	Dec. 31, 2020
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 PowerSecure employees. The qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No contributions to the qualified pension plan were made for the year ended December 31, 2020 and 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. For the year ending December 31, 2021, no contributions to any other postretirement trusts are expected. On January 1, 2019, Southern Company completed the sale of Gulf Power to NextEra Energy. See Note 15 under "Southern Company" for additional information. All amounts presented in this note reflect the benefit plan obligations and related plan assets for the Southern Company system's pension and other postretirement benefit plans, including the amounts attributable to Gulf Power prior to January 1, 2019. Actuarial Assumptions The weighted average rates assumed in the actuarial calculations used to determine both the net periodic costs for the pension and other postretirement benefit plans for the following year and the benefit obligations as of the measurement date are presented below. 2020 Assumptions used to determine net Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 3.41 % 3.44 % 3.40 % 3.41 % 3.52 % 3.39 % Discount rate – interest costs 2.99 3.01 2.96 2.99 3.18 2.99 Discount rate – service costs 3.66 3.69 3.67 3.67 3.70 3.53 Expected long-term return on plan assets 8.25 8.25 8.25 8.25 8.25 8.25 Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 Other postretirement benefit plans Discount rate – benefit obligations 3.24 % 3.28 % 3.22 % 3.22 % 3.39 % 3.19 % Discount rate – interest costs 2.80 2.84 2.79 2.76 2.97 2.71 Discount rate – service costs 3.57 3.61 3.57 3.57 3.57 3.52 Expected long-term return on plan assets 7.25 7.36 7.05 7.07 — 6.69 Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 2019 Assumptions used to determine net Southern Company Alabama Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 4.49 % 4.51 % 4.48 % 4.49 % 4.65 % 4.47 % Discount rate – interest costs 4.12 4.14 4.10 4.12 4.35 4.11 Discount rate – service costs 4.70 4.73 4.72 4.73 4.75 4.57 Expected long-term return on plan assets 7.75 7.75 7.75 7.75 7.75 7.75 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate – benefit obligations 4.37 % 4.40 % 4.36 % 4.35 % 4.50 % 4.32 % Discount rate – interest costs 3.98 4.01 3.97 3.95 4.14 3.91 Discount rate – service costs 4.63 4.67 4.64 4.64 4.65 4.56 Expected long-term return on plan assets 6.86 6.76 6.85 6.79 — 6.49 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 2018 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % 3.74 % Discount rate – interest costs 3.45 3.45 3.42 3.46 3.69 3.41 Discount rate – service costs 3.98 4.00 3.99 3.99 4.01 3.84 Expected long-term return on plan assets 7.95 7.95 7.95 7.95 7.95 7.95 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate – benefit obligations 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % 3.62 % Discount rate – interest costs 3.29 3.31 3.29 3.29 3.47 3.21 Discount rate – service costs 3.91 3.93 3.91 3.91 3.93 3.82 Expected long-term return on plan assets 6.83 6.83 6.80 6.99 — 5.89 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 2020 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 2.81 % 2.85 % 2.79 % 2.80 % 2.99 % 2.75 % Annual salary increase 4.80 4.80 4.80 4.80 4.80 4.80 Other postretirement benefit plans Discount rate 2.56 % 2.63 % 2.52 % 2.53 % 2.78 % 2.46 % Annual salary increase 4.80 4.80 4.80 4.80 4.80 4.80 2019 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 3.41 % 3.44 % 3.40 % 3.41 % 3.52 % 3.39 % Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 Other postretirement benefit plans Discount rate 3.24 % 3.28 % 3.22 % 3.22 % 3.39 % 3.19 % Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 The Registrants estimate the expected rate of return on pension plan and other postretirement benefit plan assets using a financial model to project the expected return on each current investment portfolio. The analysis projects an expected rate of return on each of the different asset classes in order to arrive at the expected return on the entire portfolio relying on each trust's target asset allocation and reasonable capital market assumptions. The financial model is based on four key inputs: anticipated returns by asset class (based in part on historical returns), each trust's target asset allocation, an anticipated inflation rate, and the projected impact of a periodic rebalancing of each trust's portfolio. Prior to 2020, the Registrants set the expected rate of return assumption using asset return modeling based on geometric returns that reflect the compound average returns for dependent annual periods. Beginning in 2020, the Registrants set the expected rate of return assumption using an arithmetic mean which represents the expected simple average return to be earned by the pension plan assets over any one year. The Registrants believe the use of the arithmetic mean is more compatible with the expected rate of return's function of estimating a single year's investment return. An additional assumption used in measuring the accumulated other postretirement benefit obligations (APBO) was a weighted average medical care cost trend rate. The weighted average medical care cost trend rates used in measuring the APBO for the Registrants at December 31, 2020 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Pre-65 6.00 % 4.50 % 2027 Post-65 medical 5.00 4.50 2027 Post-65 prescription 6.25 4.50 2028 Pension Plans The total accumulated benefit obligation for the pension plans at December 31, 2020 and 2019 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2020 $ 14,922 $ 3,414 $ 4,657 $ 683 $ 175 $ 1,072 December 31, 2019 13,391 3,053 4,222 615 151 963 Actuarial losses of $1.7 billion and $2.3 billion were recorded in the remeasurement of the Southern Company system pension plans at December 31, 2020 and 2019, respectively, primarily due to decreases of 60 and 108 basis points, respectively, in the overall discount rate used to calculate the benefit obligation as a result of lower market interest rates. Changes in the projected benefit obligations and the fair value of plan assets during the plan years ended December 31, 2020 and 2019 were as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 14,788 $ 3,404 $ 4,610 $ 671 $ 185 $ 1,067 Service cost 376 89 96 15 8 33 Interest cost 432 100 133 20 6 31 Benefits paid (629) (132) (202) (27) (6) (69) Actuarial (gain) loss 1,679 393 490 75 24 127 Balance at end of year 16,646 3,854 5,127 754 217 1,189 Change in plan assets Fair value of plan assets at beginning of year 14,057 3,357 4,442 641 169 1,050 Actual return (loss) on plan assets 1,881 450 594 85 22 139 Employer contributions 58 9 10 2 1 3 Benefits paid (629) (132) (202) (27) (6) (69) Fair value of plan assets at end of year 15,367 3,684 4,844 701 186 1,123 Accrued liability $ (1,279) $ (170) $ (283) $ (53) $ (31) $ (66) 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 12,763 $ 2,816 $ 3,905 $ 557 $ 123 $ 907 Dispositions (509) — — — — — Service cost 292 69 74 12 7 25 Interest cost 492 114 156 22 5 36 Benefits paid (596) (125) (194) (26) (4) (64) Actuarial (gain) loss 2,346 530 669 106 54 163 Balance at end of year 14,788 3,404 4,610 671 185 1,067 Change in plan assets Fair value of plan assets at beginning of year 11,611 2,575 3,663 505 123 798 Dispositions (509) — — — — — Actual return (loss) on plan assets 2,343 524 730 103 43 172 Employer contributions 1,208 383 243 59 7 144 Benefits paid (596) (125) (194) (26) (4) (64) Fair value of plan assets at end of year 14,057 3,357 4,442 641 169 1,050 Accrued liability $ (731) $ (47) $ (168) $ (30) $ (16) $ (17) The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2020 are shown in the following table. All pension plan assets are related to the qualified pension plan. Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Projected benefit obligations: Qualified pension plan $ 15,818 $ 3,719 $ 4,977 $ 718 $ 187 $ 1,114 Non-qualified pension plan 828 135 150 36 30 75 Amounts recognized in the balance sheets at December 31, 2020 and 2019 related to the Registrants' pension plans consist of the following: Southern Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2020: Other regulatory assets, deferred (*) $ 4,655 $ 1,286 $ 1,598 $ 235 $ — $ 205 Other deferred charges and assets — — — — — 70 Other current liabilities (52) (9) (10) (2) (2) (2) Employee benefit obligations (1,227) (161) (273) (51) (29) (134) Other regulatory liabilities, deferred (34) — — — — — AOCI 245 — — — 60 1 December 31, 2019: Prepaid pension costs $ 2 $ 71 $ — $ 2 $ 10 $ — Other regulatory assets, deferred (*) 4,072 1,130 1,416 204 — 172 Other deferred charges and assets — — — — — 82 Other current liabilities (54) (8) (11) (2) (2) (2) Employee benefit obligations (679) (110) (157) (30) (24) (97) Other regulatory liabilities, deferred (79) — — — — — AOCI 185 — — — 46 (14) (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. Presented below are the amounts included in regulatory assets at December 31, 2020 and 2019 related to the portion of the defined benefit pension plan attributable to Southern Company, the traditional electric operating companies, and Southern Company Gas that had not yet been recognized in net periodic pension cost. Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2020 Regulatory assets: Prior service cost $ 11 $ 5 $ 9 $ 2 $ (13) Net (gain) loss 4,610 1,281 1,589 233 135 Regulatory amortization — — — — 83 Total regulatory assets (*) $ 4,621 $ 1,286 $ 1,598 $ 235 $ 205 Balance at December 31, 2019 Regulatory assets: Prior service cost $ 13 $ 6 $ 10 $ 2 $ (15) Net (gain) loss 3,980 1,124 1,406 201 113 Regulatory amortization — — — — 74 Total regulatory assets (*) $ 3,993 $ 1,130 $ 1,416 $ 203 $ 172 (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. The changes in the balance of regulatory assets related to the portion of the defined benefit pension plan attributable to Southern Company, the traditional electric operating companies, and Southern Company Gas for the years ended December 31, 2020 and 2019 are presented in the following table: Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): (*) Balance at December 31, 2018 $ 3,458 $ 955 $ 1,230 $ 167 $ 160 Net (gain) loss 801 213 231 42 30 Dispositions (144) — — — — Reclassification adjustments: Amortization of prior service costs (3) (1) (1) — 2 Amortization of net gain (loss) (119) (37) (44) (6) — Amortization of regulatory assets (*) — — — — (20) Total reclassification adjustments (122) (38) (45) (6) (18) Total change 535 175 186 36 12 Balance at December 31, 2019 $ 3,993 $ 1,130 $ 1,416 $ 203 $ 172 Net (gain) loss 884 228 269 45 45 Reclassification adjustments: Amortization of prior service costs (1) (1) (1) — 2 Amortization of net gain (loss) (255) (71) (86) (13) (8) Amortization of regulatory assets (*) — — — — (6) Total reclassification adjustments (256) (72) (87) (13) (12) Total change 628 156 182 32 33 Balance at December 31, 2020 $ 4,621 $ 1,286 $ 1,598 $ 235 $ 205 (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. Presented below are the amounts included in AOCI at December 31, 2020 and 2019 related to the portion of the defined benefit pension plan attributable to Southern Company, Southern Power, and Southern Company Gas that had not yet been recognized in net periodic pension cost. Southern Southern Southern Company (in millions) Balance at December 31, 2020 AOCI: Prior service cost $ (3) $ — $ (4) Net (gain) loss 248 60 5 Total AOCI $ 245 $ 60 $ 1 Balance at December 31, 2019 AOCI: Prior service cost $ (3) $ — $ (6) Net (gain) loss 188 46 (8) Total AOCI $ 185 $ 46 $ (14) The components of OCI related to the portion of the defined benefit pension plan attributable to Southern Company, Southern Power, and Southern Company Gas for the years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Southern Southern Company (in millions) AOCI: Balance at December 31, 2018 $ 97 $ 26 $ (44) Net (gain) loss 88 20 30 Balance at December 31, 2019 $ 185 $ 46 $ (14) Net (gain) loss 74 16 15 Reclassification adjustments: Amortization of prior service costs — — 1 Amortization of net gain (loss) (14) (2) (1) Total reclassification adjustments (14) (2) — Total change 60 14 15 Balance at December 31, 2020 $ 245 $ 60 $ 1 Components of net periodic pension cost for the Registrants were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Service cost $ 376 $ 89 $ 96 $ 15 $ 8 $ 33 Interest cost 432 100 133 20 6 31 Expected return on plan assets (1,100) (264) (347) (51) (13) (75) Recognized net (gain) loss 269 71 86 13 2 6 Net amortization 1 1 1 — — 15 Prior service cost — — — — — (3) Net periodic pension cost $ (22) $ (3) $ (31) $ (3) $ 3 $ 7 2019 Service cost $ 292 $ 69 $ 74 $ 12 $ 7 $ 25 Interest cost 492 114 156 22 5 36 Expected return on plan assets (885) (206) (292) (40) (10) (60) Recognized net (gain) loss 120 37 44 6 1 2 Net amortization 2 — 1 — — 14 Prior service cost — — — — — (3) Net periodic pension cost $ 21 $ 14 $ (17) $ — $ 3 $ 14 2018 Service cost $ 359 $ 78 $ 87 $ 17 $ 9 $ 34 Interest cost 464 101 139 20 5 39 Expected return on plan assets (943) (207) (296) (41) (10) (75) Recognized net (gain) loss 213 54 69 10 1 12 Net amortization 4 1 2 — — 15 Prior service cost — — — — — (2) Net periodic pension cost $ 97 $ 27 $ 1 $ 6 $ 5 $ 23 The service cost component of net periodic pension cost is included in operations and maintenance expenses and all other components of net periodic pension cost are included in other income (expense), net in the Registrants' statements of income. Net periodic pension cost is the sum of service cost, interest cost, and other costs netted against the expected return on plan assets. The expected return on plan assets is determined by multiplying the expected rate of return on plan assets and the market-related value of plan assets. In determining the market-related value of plan assets, the Registrants have elected to amortize changes in the market value of return-seeking plan assets over five years and to recognize the changes in the market value of liability-hedging plan assets immediately. Given the significant concentration in return-seeking plan assets, the accounting value of plan assets that is used to calculate the expected return on plan assets differs from the current fair value of the plan assets. Effective January 1, 2020, Southern Company changed its method of calculating the market-related value of the liability-hedging securities included in its pension plan assets. The market-related value is used to determine the expected return on plan assets component of net periodic pension cost. Southern Company previously used the calculated value approach for all plan assets, which smoothed asset returns and deferred gains and losses by amortizing them into the calculation of the market-related value over five years. Southern Company changed to the fair value approach for liability-hedging securities, which includes measuring the market-related value of that portion of the plan assets at fair value for purposes of determining the expected return on plan assets. The remaining asset classes of plan assets will continue to be valued using the calculated value approach. Southern Company considers the fair value approach to be preferable for liability-hedging securities because it results in a current reflection of changes in the value of plan assets in the measurement of net periodic pension cost more consistent with the change in the related obligations. Southern Company determined the effect of this change in accounting method was immaterial to the historical and current financial statements of all Registrants; therefore, the effect of the change was recorded through earnings as a prior period adjustment for the amounts related to the unregulated businesses of Southern Company and Southern Power. Amounts related to the traditional electric operating companies and the natural gas distribution utilities were reflected as adjustments to regulatory assets, consistent with the expected regulatory treatment. Future benefit payments reflect expected future service and are estimated based on assumptions used to measure the projected benefit obligation for the pension plans. At December 31, 2020, estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2021 $ 651 $ 141 $ 208 $ 29 $ 6 $ 66 2022 678 147 215 30 6 66 2023 702 154 222 31 6 66 2024 725 158 229 32 6 65 2025 748 165 235 33 7 65 2026 to 2030 4,024 895 1,244 181 38 330 Other Postretirement Benefits Changes in the APBO and the fair value of the Registrants' plan assets during the plan years ended December 31, 2020 and 2019 were as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 1,985 $ 462 $ 742 $ 87 $ 11 $ 250 Service cost 22 6 6 1 1 2 Interest cost 54 13 20 2 — 7 Benefits paid (126) (29) (46) (6) — (17) Actuarial (gain) loss 7 9 (26) (3) — 6 Retiree drug subsidy 6 2 3 — — — Balance at end of year 1,948 463 699 81 12 248 Change in plan assets Fair value of plan assets at beginning of year 1,061 413 403 26 — 115 Actual return (loss) on plan assets 145 60 50 3 — 18 Employer contributions 72 12 17 4 — 12 Benefits paid (120) (27) (43) (6) — (17) Fair value of plan assets at end of year 1,158 458 427 27 — 128 Accrued liability $ (790) $ (5) $ (272) $ (54) $ (12) $ (120) 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 1,865 $ 403 $ 675 $ 81 $ 9 $ 244 Dispositions (69) — — — — — Service cost 18 5 5 1 1 1 Interest cost 69 16 26 3 — 9 Benefits paid (126) (27) (47) (6) (1) (17) Actuarial (gain) loss 223 63 80 8 2 13 Retiree drug subsidy 5 2 3 — — — Balance at end of year 1,985 462 742 87 11 250 Change in plan assets Fair value of plan assets at beginning of year 928 360 344 23 — 98 Dispositions (18) — — — — — Actual return (loss) on plan assets 189 76 68 4 — 21 Employer contributions 83 2 35 5 1 13 Benefits paid (121) (25) (44) (6) (1) (17) Fair value of plan assets at end of year 1,061 413 403 26 — 115 Accrued liability $ (924) $ (49) $ (339) $ (61) $ (11) $ (135) Amounts recognized in the balance sheets at December 31, 2020 and 2019 related to the Registrants' other postretirement benefit plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Southern Company Gas (in millions) December 31, 2020: Other regulatory assets, deferred (a) $ 137 $ — $ 47 $ 5 $ — $ (23) Other current liabilities (5) — — — — — Employee benefit obligations (b) (785) (5) (272) (54) (12) (120) Other regulatory liabilities, deferred (86) (21) — — — — AOCI 8 — — — 3 — December 31, 2019: Other regulatory assets, deferred (a) $ 183 $ 3 $ 96 $ 10 $ — $ (11) Other current liabilities (5) — — — — — Employee benefit obligations (b) (919) (49) (339) (61) (11) (135) Other regulatory liabilities, deferred (62) (2) — — — — AOCI 2 — — — 2 (4) (a) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company. (b) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. Presented below are the amounts included in net regulatory assets (liabilities) at December 31, 2020 and 2019 related to the other postretirement benefit plans of Southern Company, the traditional electric operating companies, and Southern Company Gas that had not yet been recognized in net periodic other postretirement benefit cost. Southern Company Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2020: Regulatory assets (liabilities): Prior service cost $ 12 $ 3 $ 5 $ — $ 1 Net (gain) loss 39 (24) 42 5 (49) Regulatory amortization — — — — 25 Total regulatory assets (liabilities) (*) $ 51 $ (21) $ 47 $ 5 $ (23) Balance at December 31, 2019: Regulatory assets (liabilities): Prior service cost $ 11 $ 3 $ 4 $ — $ 1 Net (gain) loss 110 (2) 92 10 (43) Regulatory amortization — — — — 31 Total regulatory assets (liabilities) (*) $ 121 $ 1 $ 96 $ 10 $ (11) (*) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company. The changes in the balance of net regulatory assets (liabilities) related to the other postretirement benefit plans for the plan years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Net regulatory assets (liabilities): (*) Balance at December 31, 2018 $ 22 $ (9) $ 60 $ 4 $ (4) Net (gain) loss 90 14 37 6 (1) Dispositions 5 — — — — Change in prior service costs 5 — — — — Reclassification adjustments: Amortization of prior service costs (3) (4) — — — Amortization of net gain (loss) 2 — (1) — — Amortization of regulatory assets (*) — — — — (6) Total reclassification adjustments (1) (4) (1) — (6) Total change 99 10 36 6 (7) Balance at December 31, 2019 $ 121 $ 1 $ 96 $ 10 $ (11) Net (gain) loss (65) (22) (47) (5) (5) Reclassification adjustments: Amortization of prior service costs 1 — 1 — — Amortization of net gain (loss) (6) — (3) — — Amortization of regulatory assets (*) — — — — (7) Total reclassification adjustments (5) — (2) — (7) Total change (70) (22) (49) (5) (12) Balance at December 31, 2020 $ 51 $ (21) $ 47 $ 5 $ (23) (*) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company. Presented below are the amounts included in AOCI at December 31, 2020 and 2019 related to the other postretirement benefit plans of Southern Company, Southern Power, and Southern Company Gas that had not yet been recognized in net periodic other postretirement benefit cost. Southern Southern Southern Company (in millions) Balance at December 31, 2020 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 7 3 (1) Total AOCI $ 8 $ 3 $ — Balance at December 31, 2019 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 1 2 (5) Total AOCI $ 2 $ 2 $ (4) The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Southern Southern Company Gas (in millions) AOCI: Balance at December 31, 2018 $ (4) $ 1 $ (4) Net (gain) loss 5 1 — Reclassification adjustments: Amortization of net gain (loss) 1 — — Total change 6 1 — Balance at December 31, 2019 $ 2 $ 2 $ (4) Net (gain) loss 2 1 — Reclassification adjustments: Amortization of net gain (loss) 4 — 4 Total change 6 1 4 Balance at December 31, 2020 $ 8 $ 3 $ — Components of the other postretirement benefit plans' net periodic cost for the Registrants were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Service cost $ 22 $ 6 $ 6 $ 1 $ 1 $ 2 Interest cost 54 13 20 2 — 7 Expected return on plan assets (72) (29) (26) (1) — (10) Net amortization 1 — 2 — — 6 Net periodic postretirement benefit cost $ 5 $ (10) $ 2 $ 2 $ 1 $ 5 2019 Service cost $ 18 $ 5 $ 5 $ 1 $ 1 $ 1 Interest cost 69 16 26 3 — 9 Expected return on plan assets (65) (26) (25) (2) — (7) Net amortization — 4 1 — — 6 Net periodic postretirement benefit cost $ 22 $ (1) $ 7 $ 2 $ 1 $ 9 2018 Service cost $ 24 $ 6 $ 6 $ 1 $ 1 $ 2 Interest cost 75 17 28 3 — 10 Expected return on plan assets (69) (26) (25) (2) — (7) Net amortization 21 5 10 1 — 6 Net periodic postretirement benefit cost $ 51 $ 2 $ 19 $ 3 $ 1 $ 11 The service cost component of net periodic postretirement benefit cost is included in operations and maintenance expenses and all other components of net periodic postretirement benefit cost are included in other income (expense), net in the Registrants' statements of income. The Registrants' future benefit payments, including prescription drug benefits, are provided in the table below. These amounts reflect expected future service and are estimated based on assumptions used to measure the APBO for the other postretirement benefit plans. Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit payments: 2021 $ 115 $ 25 $ 42 $ 6 $ — $ 18 2022 113 25 41 5 — 18 2023 111 25 40 5 — 18 2024 110 24 38 4 1 17 2025 113 25 40 5 1 17 2026 to 2030 550 127 199 23 3 76 Benefit Plan Assets Pension plan and other postretirement benefit plan assets are managed and invested in accordance with all applicable requirements, including ERISA and the Internal Revenue Code. The Registrants' investment policies for both the pension plans and the other postretirement benefit plans cover a diversified mix of assets as described below. Derivative instruments may be used to gain efficient exposure to the various asset classes and as hedging tools. Additionally, the Registrants minimize the risk of large losses primarily through diversification but also monitor and manage other aspects of risk. The investment strategy for plan assets related to the Southern Company system's qualified pension plan is to be broadly diversified across major asset classes. The asset allocation is established after consideration of various factors that affect the assets and liabilities of the pension plan including, but not limited to, historical and expected returns and interest rates, volatility, correlations of asset classes, the current level of assets and liabilities, and the assumed growth in assets and liabilities. Because a significant portion of the liability of the pension plan is long-term in nature, the assets are invested consistent with long-term investment expectations for return and risk. To manage the actual asset class exposures relative to the target asset allocation, the Southern Company system employs a formal rebalancing program. As additional risk management, external investment managers and service providers are subject to written guidelines to ensure appropriate and prudent investment practices. Management believes the portfolio is well-diversified with no significant concentrations of risk. Investment Strategies and Benefit Plan Asset Fair Values A description of the major asset classes that the pension and other postretirement benefit plans are comprised of, along with the valuation methods used for fair value measurement, is provided below: Description Valuation Methodology Domestic equity: A mix of large and small capitalization stocks with generally an equal distribution of value and growth attributes, managed both actively and through passive index approaches. International equity: A mix of large and small capitalization growth and value stocks with developed and emerging markets exposure, managed both actively and through fundamental indexing approaches. Domestic and international equities such as common stocks, American depositary receipts, and real estate investment trusts that trade on public exchanges are classified as Level 1 investments and are valued at the closing price in the active market. Equity funds with unpublished prices that are comprised of publicly traded securities (such as commingled/pooled funds) are also valued at the closing price in the active market, but are classified as Level 2. Fixed income: A mix of domestic and international bonds. Investments in fixed income securities, including fixed income pooled funds, are generally classified as Level 2 investments and are valued based on prices reported in the market place. Additionally, the value of fixed income securities takes into consideration certain items such as broker quotes, spreads, yield curves, interest rates, and discount rates that apply to the term of a specific instrument. Trust-owned life insurance (TOLI): Investments of taxable trusts aimed at minimizing the impact of taxes on the portfolio. Investments in TOLI policies are classified as Level 2 investments and are valued based on the underlying investments held in the policy's separate accounts. The underlying assets are equity and fixed income pooled funds that are comprised of Level 1 and Level 2 securities. Special situations: Investments in opportunistic strategies with the objective of diversifying and enhancing returns and exploiting short-term inefficiencies, as well as investments in promising new strategies of a longer-term nature. Real estate: Investments in traditional private market, equity-oriented investments in real properties (indirectly through pooled funds or partnerships) and in publicly traded real estate securities. Private equity: Investments in private partnerships that invest in private or public securities typically through privately-negotiated and/or structured transactions, including leveraged buyouts, venture capital, and distressed debt. Investments in real estate, private equity, and special situations are generally classified as Net Asset Value as a Practical Expedient, since the underlying assets typically do not have publicly available observable inputs. The fund manager values the assets using va

STOCK COMPENSATION

STOCK COMPENSATION	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
STOCK COMPENSATION	STOCK COMPENSATION Stock-Based Compensation Stock-based compensation primarily in the form of Southern Company performance share units (PSU) and restricted stock units (RSU) may be granted through the Omnibus Incentive Compensation Plan to Southern Company system employees ranging from line management to executives. At December 31, 2020, the number of current and former employees participating in stock-based compensation programs for the Registrants was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Number of employees 1,958 263 295 86 46 204 The majority of PSUs and RSUs awarded contain terms where employees become immediately vested in PSUs and RSUs upon retirement. As a result, compensation expense for employees that are retirement eligible at the grant date is recognized immediately, while compensation expense for employees that become retirement eligible during the vesting period is recognized over the period from grant date to the date of retirement eligibility. In addition, the Registrants recognize forfeitures as they occur. All unvested PSUs and RSUs vest immediately upon a change in control where Southern Company is not the surviving corporation. Performance Share Units PSUs granted to employees vest at the end of a three-year performance period. Shares of Southern Company common stock are delivered to employees at the end of the performance period with the number of shares issued ranging from 0% to 200% of the target number of PSUs granted, based on achievement of the performance goals established by the Compensation Committee of the Southern Company Board of Directors. Southern Company has issued three types of PSUs, each with a unique performance goal. These types of PSUs include total shareholder return (TSR) awards based on the TSR for Southern Company common stock during the three The fair value of TSR awards is determined as of the grant date using a Monte Carlo simulation model. In determining the fair value of the TSR awards issued to employees, the expected volatility is based on the historical volatility of Southern Company's stock over a period equal to the performance period. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant that covers the performance period of the awards. The following table shows the assumptions used in the pricing model and the weighted average grant-date fair value of TSR awards granted: Year Ended December 31 2020 2019 2018 Expected volatility 15.4% 15.6% 14.9% Expected term (in years) 3 3 3 Interest rate 1.4% 2.4% 2.4% Weighted average grant-date fair value $77.65 $62.71 $43.75 The Registrants recognize TSR award compensation expense on a straight-line basis over the three-year performance period without remeasurement. The fair values of EPS awards and ROE awards are based on the closing stock price of Southern Company common stock on the date of the grant. The weighted average grant-date fair value of the ROE awards granted during 2020, 2019, and 2018 was $68.42, $49.38, and $43.49, respectively. Compensation expense for EPS and ROE awards is generally recognized ratably over the three-year performance period adjusted for expected changes in EPS and ROE performance. Total compensation cost recognized for vested EPS awards and ROE awards reflects final performance metrics. Southern Company had 2.5 million unvested PSUs outstanding at December 31, 2019. In February 2020, the PSUs that vested for the three-year performance period ended December 31, 2019 were converted into 1.8 million shares outstanding at a share price of $68.59. During 2020, Southern Company granted 1.2 million PSUs and 1.5 million PSUs were vested or forfeited, resulting in 2.2 million unvested PSUs outstanding at December 31, 2020. In February 2021, the PSUs that vested for the three-year performance period ended December 31, 2020 were converted into 2.5 million shares outstanding at a share price of $60.10. Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2020, 2019, and 2018 are as follows: 2020 2019 2018 (in millions) Southern Company Compensation cost recognized in income $ 84 $ 77 $ 91 Tax benefit of compensation cost recognized in income 22 20 24 Southern Company Gas Compensation cost recognized in income $ 13 $ 14 $ 11 Tax benefit of compensation cost recognized in income 4 4 3 Total PSU compensation cost and the related tax benefit recognized in income were immaterial for all periods presented for all other Registrants. The compensation cost related to the grant of Southern Company PSUs to the employees of each Subsidiary Registrant is recognized in each Subsidiary Registrant's financial statements with a corresponding credit to equity representing a capital contribution from Southern Company. At December 31, 2020, Southern Company's total unrecognized compensation cost related to PSUs was $32 million and is expected to be recognized over a weighted-average period of approximately 19 months. The total unrecognized compensation cost related to PSUs as of December 31, 2020 was immaterial for all other Registrants. Restricted Stock Units The fair value of RSUs is based on the closing stock price of Southern Company common stock on the date of the grant. The weighted average grant-date fair values of RSUs granted during 2020, 2019, and 2018 were $67.60, $50.44, and $43.81, respectively. For most RSU awards, one-third of the RSUs vest each year throughout a three-year service period and compensation cost for RSUs is generally recognized over the corresponding one two Southern Company had 1.3 million RSUs outstanding at December 31, 2019. During 2020, Southern Company granted 0.5 million RSUs and 0.6 million RSUs were vested or forfeited, resulting in 1.2 million unvested RSUs outstanding at December 31, 2020, including RSUs related to employee retention agreements. For the years ended December 31, 2020, 2019, and 2018, Southern Company's total compensation cost for RSUs recognized in income was $29 million, $28 million, and $27 million, respectively. The related tax benefit also recognized in income was $8 million, $7 million, and $7 million for the years ended December 31, 2020, 2019, and 2018, respectively. Total unrecognized compensation cost related to RSUs as of December 31, 2020 for Southern Company of $11 million will be recognized over a weighted-average period of approximately 18 months. Total RSUs outstanding and total compensation cost and related tax benefit for the RSUs recognized in income for the years ended December 31, 2020, 2019, and 2018, as well as the total unrecognized compensation cost as of December 31, 2020, were immaterial for all other Registrants. The compensation cost related to the grant of Southern Company RSUs to the employees of each Subsidiary Registrant is recognized in such Subsidiary Registrant's financial statements with a corresponding credit to equity representing a capital contribution from Southern Company. Stock Options In 2015, Southern Company discontinued granting stock options. As of December 31, 2017, all stock option awards were vested and compensation cost fully recognized. Stock options expire no later than 10 years after the grant date and the latest possible exercise will occur by November 2024. As of December 31, 2020, the weighted average remaining contractual term for the options outstanding and exercisable was approximately two years. Southern Company's activity in the stock option program for 2020 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2019 5.9 $ 42.52 Exercised 1.6 41.13 Outstanding and Exercisable at December 31, 2020 4.3 $ 43.04 Southern Company's cash receipts from issuances related to stock options exercised under the share-based payment arrangements for the years ended December 31, 2020, 2019, and 2018 were $66 million, $482 million, and $41 million, respectively. At December 31, 2020, the aggregate intrinsic value for the options outstanding and exercisable was as follows: Southern Company Alabama Power Georgia Power Southern Company Gas (in millions) Total intrinsic value for outstanding and exercisable options $ 78 $ 8 $ 25 $ 6 The aggregate intrinsic value for the options outstanding and exercisable was immaterial for Mississippi Power and Southern Power at December 31, 2020. Total intrinsic value of options exercised, and the related tax benefit, for the years ended December 31, 2020, 2019, and 2018 are presented below: Year Ended December 31 2020 2019 2018 (in millions) Southern Company Intrinsic value of options exercised $ 38 $ 167 $ 9 Tax benefit of options exercised 9 35 2 Alabama Power Intrinsic value of options exercised $ 5 $ 21 $ 2 Tax benefit of options exercised 1 4 — Georgia Power Intrinsic value of options exercised $ 9 $ 30 $ 2 Tax benefit of options exercised 2 6 — Total intrinsic value of options exercised, and the related tax benefit recognized in income, for the years ended December 31, 2020, 2019, and 2018 were immaterial for Mississippi Power, Southern Power, and Southern Company Gas.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Fair value measurements are based on inputs of observable and unobservable market data that a market participant would use in pricing the asset or liability. The use of observable inputs is maximized where available and the use of unobservable inputs is minimized for fair value measurement and reflects a three-tier fair value hierarchy that prioritizes inputs to valuation techniques used for fair value measurement. • Level 1 consists of observable market data in an active market for identical assets or liabilities. • Level 2 consists of observable market data, other than that included in Level 1, that is either directly or indirectly observable. • Level 3 consists of unobservable market data. The input may reflect the assumptions of each Registrant of what a market participant would use in pricing an asset or liability. If there is little available market data, then each Registrant's own assumptions are the best available information. In the case of multiple inputs being used in a fair value measurement, the lowest level input that is significant to the fair value measurement represents the level in the fair value hierarchy in which the fair value measurement is reported. Net asset value as a practical expedient is the classification used for assets that do not have readily determined fair values. Fund managers value the assets using various inputs and techniques depending on the nature of the underlying investments. At December 31, 2020, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 401 $ 271 $ 32 $ — $ 704 Interest rate derivatives — 20 — — 20 Foreign currency derivatives — 87 — — 87 Investments in trusts: (b)(c) Domestic equity 862 151 — — 1,013 Foreign equity 85 253 — — 338 U.S. Treasury and government agency securities — 284 — — 284 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 13 386 — — 399 Mortgage and asset backed securities — 83 — — 83 Private equity — — — 76 76 Cash and cash equivalents 1 — — — 1 Other 28 7 — — 35 Cash equivalents 575 9 — — 584 Other investments 9 24 — — 33 Total $ 1,974 $ 1,677 $ 32 $ 76 $ 3,759 Liabilities: Energy-related derivatives (a) $ 389 $ 204 $ 4 $ — $ 597 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ 389 $ 227 $ 21 $ — $ 637 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Nuclear decommissioning trusts: (b) Domestic equity 543 141 — — 684 Foreign equity 85 73 — — 158 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 13 167 — — 180 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 76 76 Other 7 — — — 7 Cash equivalents 311 9 — — 320 Other investments — 24 — — 24 Total $ 959 $ 477 $ — $ 76 $ 1,512 Liabilities: Energy-related derivatives $ — $ 7 $ — $ — $ 7 Georgia Power Assets: Energy-related derivatives $ — $ 15 $ — $ — $ 15 Nuclear decommissioning trusts: (b)(c) Domestic equity 319 1 — — 320 Foreign equity — 177 — — 177 U.S. Treasury and government agency securities — 263 — — 263 Municipal bonds — 84 — — 84 Corporate bonds — 219 — — 219 Mortgage and asset backed securities — 54 — — 54 Other 21 7 — — 28 Total $ 340 $ 820 $ — $ — $ 1,160 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Cash equivalents 21 — — — 21 Total $ 21 $ 9 $ — $ — $ 30 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Foreign currency derivatives — 87 — — 87 Total $ — $ 89 $ — $ — $ 89 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ — $ 26 $ 17 $ — $ 43 Southern Company Gas Assets: Energy-related derivatives (a) $ 401 $ 233 $ 32 $ — $ 666 Non-qualified deferred compensation trusts: Domestic equity — 9 — — 9 Foreign equity — 3 — — 3 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Total $ 402 $ 262 $ 32 $ — $ 696 Liabilities: Energy-related derivatives (a)(b) $ 389 $ 172 $ 4 $ — $ 565 (a) Excludes $6 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $28 million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information. At December 31, 2019, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (b)(c) Domestic equity 751 135 — — 886 Foreign equity 68 220 — — 288 U.S. Treasury and government agency securities — 307 — — 307 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 23 297 — — 320 Mortgage and asset backed securities — 87 — — 87 Private equity — — — 56 56 Cash and cash equivalents 1 — — — 1 Other 17 5 — — 22 Cash equivalents 1,393 2 — — 1,395 Other investments 9 21 — — 30 Total $ 2,650 $ 1,461 $ 22 $ 56 $ 4,189 Liabilities: Energy-related derivatives (a) $ 442 $ 254 $ 7 $ — $ 703 Interest rate derivatives — 24 — — 24 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ 442 $ 302 $ 26 $ — $ 770 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b) Domestic equity 488 123 — — 611 Foreign equity 68 64 — — 132 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 23 144 — — 167 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 56 56 Other 3 1 — — 4 Cash equivalents 691 2 — — 693 Other investments — 21 — — 21 Total $ 1,273 $ 410 $ — $ 56 $ 1,739 Liabilities: Energy-related derivatives $ — $ 24 $ — $ — $ 24 Georgia Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b)(c) Domestic equity 263 1 — — 264 Foreign equity — 152 — — 152 U.S. Treasury and government agency securities — 286 — — 286 Municipal bonds — 84 — — 84 Corporate bonds — 153 — — 153 Mortgage and asset backed securities — 57 — — 57 Other 13 4 — — 17 Total $ 276 $ 741 $ — $ — $ 1,017 Liabilities: Energy-related derivatives $ — $ 53 $ — $ — $ 53 Interest rate derivatives — 17 — — 17 Total $ — $ 70 $ — $ — $ 70 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Cash equivalents 281 — — — 281 Total $ 281 $ 1 $ — $ — $ 282 Liabilities: Energy-related derivatives $ — $ 27 $ — $ — $ 27 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 16 — — 16 Cash equivalents 113 — — — 113 Total $ 113 $ 19 $ — $ — $ 132 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ — $ 27 $ 19 $ — $ 46 Southern Company Gas Assets: Energy-related derivatives (a) $ 388 $ 255 $ 22 $ — $ 665 Interest rate derivatives — 2 — — 2 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Cash equivalents 8 — — — 8 Total $ 397 $ 289 $ 22 $ — $ 708 Liabilities: Energy-related derivatives (a)(b) $ 442 $ 147 $ 7 $ — $ 596 (a) Excludes $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $99 million. (c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information. 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 14 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 under "Nuclear Decommissioning" 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. 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 $76 million and $56 million at December 31, 2020 and 2019, respectively. Unfunded commitments related to the private equity investments totaled $73 million and $70 million at December 31, 2020 and 2019, respectively. 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 December 31, 2020 and 2019, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) At December 31, 2020: Long-term debt, including securities due within one year: Carrying amount $ 48,349 $ 8,864 $ 12,825 $ 1,400 $ 3,692 $ 6,626 Fair value 56,264 10,702 15,198 1,590 4,165 7,973 At December 31, 2019: Long-term debt, including securities due within one year: Carrying amount $ 44,561 $ 8,517 $ 11,660 $ 1,589 $ 4,398 $ 5,845 Fair value 48,339 9,525 12,680 1,671 4,708 6,509 (*) 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 December 31, 2020, 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. 2020 (in millions) Beginning balance $ 14 Transfers to Level 3 70 Transfers from Level 3 (34) Instruments realized or otherwise settled during period (16) Changes in fair value (6) 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 methodologies are used to develop inputs that maximize the use of relevant observable inputs and minimize the use of unobservable inputs. Observable inputs, including some forward prices used for determining fair value, reflect the best available market information. Unobservable inputs are updated using industry standard techniques such as extrapolation, combining observable forward inputs supplemented by historical market and other relevant data. Level 3 physical natural gas forward contracts include unobservable forward price inputs (ranging from $(0.08) to $0.24 per mmBtu). Forward price increases (decreases) as of December 31, 2020 would have resulted in higher (lower) values on a net basis.

DERIVATIVES

DERIVATIVES	12 Months Ended
	Dec. 31, 2020
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 13 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 under "Financial Instruments" 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 AOCI 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 December 31, 2020, 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 (*) 835 2024 2031 Alabama Power 78 2024 — Georgia Power 135 2023 — Mississippi Power 89 2024 — Southern Power 10 2022 2021 Southern Company Gas (*) 523 2022 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 4,421 million mmBtu and short natural gas positions of 3,898 million mmBtu at December 31, 2020, which is also included in Southern Company's total volume. At December 31, 2020, the net volume of Southern Power's energy-related derivative contracts for power to be sold was 1 million MWHs, all of which expire in 2021. 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 29 million mmBtu for Southern Company, which includes 7 million mmBtu for Alabama Power, 9 million mmBtu for Georgia Power, 4 million mmBtu for Mississippi Power, and 9 million mmBtu for Southern Power. For cash flow hedges of energy-related derivatives, the estimated pre-tax gains (losses) expected to be reclassified from AOCI to earnings for the year ending December 31, 2021 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 December 31, 2020, the following interest rate derivatives were outstanding: Notional Interest Weighted Average Interest Hedge Fair Value (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 20 Southern Company $ 1,560 $ 20 For cash flow hedge interest rate derivatives, the estimated pre-tax gains (losses) expected to be reclassified from AOCI to interest expense for the year ending December 31, 2021 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 December 31, 2020, the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 40 Southern Power 564 3.78% 500 1.85% June 2026 25 Total $ 1,241 € 1,100 $ 65 The estimated pre-tax gains (losses) related to Southern Power's foreign currency derivatives expected to be reclassified from AOCI to earnings for the year ending December 31, 2021 are $10 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 sheets are presented net to the extent that there are netting arrangements or similar agreements with the counterparties. At December 31, 2020 and 2019, the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 24 $ 11 $ 3 $ 70 Other deferred charges and assets/Other deferred credits and liabilities 18 19 6 44 Total derivatives designated as hedging instruments for regulatory purposes $ 42 $ 30 $ 9 $ 114 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 3 $ 5 $ 1 $ 6 Interest rate derivatives: Assets from risk management activities/Other current liabilities 20 — 2 23 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Foreign currency derivatives: Assets from risk management activities/Other current liabilities — 23 — 24 Other deferred charges and assets/Other deferred credits and liabilities 87 — 16 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 110 $ 28 $ 19 $ 54 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 388 $ 331 $ 461 $ 358 Other deferred charges and assets/Other deferred credits and liabilities 270 232 207 225 Total derivatives not designated as hedging instruments $ 658 $ 563 $ 668 $ 583 Gross amounts recognized $ 810 $ 621 $ 696 $ 751 Gross amounts offset (a) $ (529) $ (557) $ (463) $ (562) Net amounts recognized in the Balance Sheets (b) $ 281 $ 64 $ 233 $ 189 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 7 $ 2 $ 2 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 5 5 2 10 Total derivatives designated as hedging instruments for regulatory purposes $ 12 $ 7 $ 4 $ 24 Gross amounts recognized $ 12 $ 7 $ 4 $ 24 Gross amounts offset $ (7) $ (7) $ (2) $ (2) Net amounts recognized in the Balance Sheets $ 5 $ — $ 2 $ 22 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 7 $ 5 $ 1 $ 32 Other deferred charges and assets/Other deferred credits and liabilities 8 8 3 21 Total derivatives designated as hedging instruments for regulatory purposes $ 15 $ 13 $ 4 $ 53 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 17 Gross amounts recognized $ 15 $ 13 $ 4 $ 70 Gross amounts offset $ (12) $ (12) $ (3) $ (3) Net amounts recognized in the Balance Sheets $ 3 $ 1 $ 1 $ 67 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 4 $ 3 $ — $ 15 Other deferred charges and assets/Other deferred credits and liabilities 5 6 1 12 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 9 $ 1 $ 27 Gross amounts recognized $ 9 $ 9 $ 1 $ 27 Gross amounts offset $ (7) $ (7) $ (1) $ (1) Net amounts recognized in the Balance Sheets $ 2 $ 2 $ — $ 26 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 1 $ 2 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 24 Other deferred charges and assets/Other deferred credits and liabilities 87 — 16 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 89 $ 25 $ 17 $ 26 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ 1 $ 2 $ 1 Net amounts recognized in the Balance Sheets $ 89 $ 26 $ 19 $ 27 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 6 $ 1 $ — $ 9 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 1 $ — $ 10 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 1 $ 3 $ — $ 4 Interest rate derivatives: Assets from risk management activities/Other current liabilities — — 2 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 1 $ 3 $ 2 $ 4 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 388 $ 330 $ 459 $ 357 Other deferred charges and assets/Other deferred credits and liabilities 270 232 207 225 Total derivatives not designated as hedging instruments $ 658 $ 562 $ 666 $ 582 Gross amounts recognized $ 665 $ 566 $ 668 $ 596 Gross amounts offset (a) $ (503) $ (531) $ (456) $ (555) Net amounts recognized in the Balance Sheets (b) $ 162 $ 35 $ 212 $ 41 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $28 million and $99 million at December 31, 2020 and 2019, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for all periods presented. Energy-related derivatives not designated as hedging instruments were immaterial for the traditional electric operating companies at December 31, 2019. There were no such instruments for the traditional electric operating companies at December 31, 2020. At December 31, 2020 and 2019, the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2020 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) 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 Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2019 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (63) $ (14) $ (31) $ (15) $ (3) Other regulatory assets, deferred (37) (8) (18) (11) — Other regulatory liabilities, current 6 2 — — 4 Total energy-related derivative gains (losses) $ (94) $ (20) $ (49) $ (26) $ 1 For the years ended December 31, 2020, 2019, and 2018, the pre-tax effects of cash flow hedge accounting on AOCI for the applicable Registrants were as follows: Gain (Loss) Recognized in OCI on Derivative 2020 2019 2018 (in millions) Southern Company Energy-related derivatives $ (8) $ (13) $ 17 Interest rate derivatives (26) (57) (1) Foreign currency derivatives 48 (84) (78) Total $ 14 $ (154) $ (62) Georgia Power Interest rate derivatives $ (3) $ (59) $ — Southern Power Energy-related derivatives $ (2) $ (4) $ 10 Foreign currency derivatives 48 (84) (78) Total $ 46 $ (88) $ (68) Southern Company Gas Energy-related derivatives $ (6) $ (9) $ 7 Interest rate derivatives (23) 2 — Total $ (29) $ (7) $ 7 For all years presented, the pre-tax effects of interest rate derivatives designated as cash flow hedging instruments on AOCI were immaterial for the other Registrants. The pre-tax effects of cash flow and fair value hedge accounting on income for the years ended December 31, 2020, 2019, and 2018 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2020 2019 2018 (in millions) Southern Company Total cost of natural gas $ 972 $ 1,319 $ 1,539 Gain (loss) on energy-related cash flow hedges (a) (8) (2) 2 Total depreciation and amortization 3,518 3,038 3,131 Gain (loss) on energy-related cash flow hedges (a) (3) (6) 7 Total interest expense, net of amounts capitalized (1,821) (1,736) (1,842) Gain (loss) on interest rate cash flow hedges (a) (26) (20) (21) Gain (loss) on foreign currency cash flow hedges (a) (23) (24) (24) Gain (loss) on interest rate fair value hedges (b) 27 42 (12) Total other income (expense), net 336 252 114 Gain (loss) on foreign currency cash flow hedges (a)(c) 114 (24) (60) Southern Power Total depreciation and amortization $ 494 $ 479 $ 493 Gain (loss) on energy-related cash flow hedges (a) (3) (6) 7 Total interest expense, net of amounts capitalized (151) (169) (183) Gain (loss) on foreign currency cash flow hedges (a) (23) (24) (24) Total other income (expense), net 19 47 23 Gain (loss) on foreign currency cash flow hedges (a)(c) 114 (24) (60) (a) Reclassified from AOCI 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 AOCI 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. The pre-tax effects of cash flow hedge accounting on income for interest rate derivatives and energy-related derivatives were immaterial for the other Registrants for all years presented. At December 31, 2020 and 2019, 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 At December 31, 2020 At December 31, 2019 At December 31, 2020 At December 31, 2019 (in millions) (in millions) Southern Company Securities due within one year $ (1,509) $ (599) $ (10) $ — Long-term debt — (1,494) — 3 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 for the years ended December 31, 2020, 2019, and 2018 were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2020 2019 2018 (in millions) Energy-related derivatives Natural gas revenues (*) $ 134 $ 223 $ (122) Cost of natural gas 15 10 (6) Total derivatives in non-designated hedging relationships $ 149 $ 233 $ (128) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $9 million, $3 million, and $5 million for the years ended December 31, 2020, 2019, and 2018, respectively, as they are accounted for based on intrinsic value rather than fair value. The pre-tax effects of energy-related derivatives not designated as hedging instruments were immaterial for all other Registrants for all years presented. Contingent Features Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not have any credit arrangements that would require material changes in payment schedules or terminations as a result of a credit rating downgrade. There are certain derivatives that could require collateral, but not accelerated payment, in the event of various credit rating changes of certain Southern Company subsidiaries. At December 31, 2020, the Registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the Registrants with interest rate derivatives at December 31, 2020, there were no interest rate derivative liabilities with contingent features. At December 31, 2020, 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, 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 December 31, 2020, 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 December 31, 2020, cash collateral held on deposit in broker margin accounts was $28 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	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS Southern Company In January 2019, Southern Company completed the sale of all of the capital stock of Gulf Power to a wholly-owned subsidiary of NextEra Energy, for an aggregate cash purchase price of approximately $5.8 billion (less $1.3 billion of indebtedness assumed), including the final working capital adjustments. The gain associated with the sale of Gulf Power totaled $2.6 billion pre-tax ($1.4 billion after tax). In July 2019, PowerSecure completed the sale of its utility infrastructure services business for approximately $65 million, including the final working capital adjustments. In contemplation of this sale, a goodwill impairment charge of $32 million was recorded in the second quarter 2019. In December 2019, PowerSecure completed the sale of its lighting business for approximately $9 million, which included cash of $4 million and a note receivable from the buyer of $5 million. In contemplation of this sale, an impairment charge of $18 million was recorded in the third quarter 2019 related to goodwill, identifiable intangibles, and other assets. In December 2019, Southern Company completed the sale of one of its leveraged lease investments for an aggregate cash purchase price of approximately $20 million. The sale resulted in an immaterial gain. During the fourth quarter 2020, management of Southern Company initiated steps to sell one of its leveraged leases and classified the investment in the leveraged lease as held for sale on Southern Company's balance sheet as of December 31, 2020. The ultimate outcome of this matter cannot be determined at this time. See Note 3 under "Other Matters – Southern Company" and "Assets Held for Sale" herein for additional information. Southern Power Southern Power's acquisition-related costs for the projects discussed under "Asset Acquisitions" and "Construction Projects" below were expensed as incurred and were not material for any of the years presented. Asset Acquisitions Project Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern COD PPA Contract Period Asset Acquisitions During 2020 Beech Ridge II Wind Invenergy Renewables LLC 56 Greenbrier County, WV 100% of Class A (a) May 12 years Asset Acquisitions During 2019 DSGP (b) Fuel Cell Bloom Energy 28 Delaware 100% of Class B N/A (c) 15 years (d) Asset Acquisitions During 2018 Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC 20 Kern County, CA 100% of Class B (e) March 2018 20 years (a) In May 2020, Southern Power purchased a controlling interest and now consolidates the project's operating results in its financial statements. The Class B member owns the noncontrolling interest. (b) During 2019, Southern Power purchased a controlling interest and now consolidates the project's operating results in its financial statements. The Class A and Class C members each own a noncontrolling interest. Southern Power records net income attributable to noncontrolling interests for approximately 10 MWs of the facility. (c) Southern Power's 18-MW share of the facility was repowered between June and August 2019. In December 2019, a Class C member joined the existing partnership between the Class A member and Southern Power and made an investment to repower the remaining 10 MWs. (d) Remaining PPA contract period at the time of acquisition. (e) Southern Power owns a controlling interest under a tax equity partnership. In March 2020, Southern Power entered into an agreement to acquire a controlling membership interest in an approximately 300-MW wind facility located in South Dakota. The acquisition is subject to certain customary conditions to closing, including commercial operation of the facility, which is expected to occur in the first quarter 2021. Subsequent to the acquisition, Southern Power expects to complete a tax equity transaction. The facility's output is contracted under two long-term PPAs. The ultimate outcome of this matter cannot be determined at this time. Construction Projects During 2020, Southern Power completed construction of and placed in service the Reading and Skookumchuck wind facilities, commenced construction of the Garland and Tranquillity battery energy storage facilities, and acquired and commenced construction of 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 December 31, 2020, the total costs of construction incurred and included in CWIP for these projects were $34 million. The ultimate outcome of these matters cannot be determined at this time. Project Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected PPA Contract Period Projects Under Construction at December 31, 2020 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 Projects Completed During 2020 Skookumchuck (c) Wind 136 Lewis and Thurston Counties, WA November 2020 20 years Reading (d) Wind 200 Osage and Lyon Counties, KS May 2020 12 years Projects Completed During 2019 (e) Wildhorse Mountain (f) Wind 100 Pushmataha County, OK December 2019 20 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. (c) In October 2019, Southern Power purchased 100% of the membership interests of the Skookumchuck facility pursuant to a joint development arrangement. In November 2020, Southern Power completed a tax equity transaction whereby it received $121 million, resulting in 100% ownership of the Class B membership interests. Southern Power subsequently sold a noncontrolling interest in the Class B membership interests and now retains the controlling ownership interest in the facility. (d) In 2018, Southern Power purchased 100% of the membership interests of the Reading facility pursuant to a joint development arrangement. In June 2020, Southern Power completed a tax equity transaction whereby it received $156 million and owns 100% of the Class B membership interests. (e) During 2019, Southern Power also completed the expansion of Plant Mankato, which was sold to a subsidiary of Xcel on January 17, 2020. See "Sales of Natural Gas and Biomass Plants" below for additional information. (f) In 2018, Southern Power purchased 100% of the membership interests of the Wildhorse Mountain facility. In December 2019, Southern Power entered into a tax equity partnership and owns 100% of the Class B membership interests. 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. Wind projects utilizing equipment purchased in 2016 and 2017, and reaching commercial operation by the end of 2021 and 2022, are expected to qualify for 100% and 80% PTCs, respectively. The significant majority of this equipment either has been deployed to projects that have been completed, are under construction, or are probable of completion, or has been sold to third parties. In 2018, as a result of a review of various options for probable dispositions of wind turbine equipment not deployed to development or construction projects, Southern Power recorded a $36 million asset impairment charge on the equipment. Gains on equipment sales were immaterial in 2020 and totaled approximately $17 million in 2019. Sales of Renewable Facility Interests In May 2018, Southern Power completed the sale of a noncontrolling 33% equity interest in SP Solar, a limited partnership indirectly owning substantially all of Southern Power's solar facilities, to Global Atlantic for approximately $1.2 billion. Since Southern Power retained control of the limited partnership, the sale was recorded as an equity transaction. On the date of the transaction, the noncontrolling interest was increased by $511 million to reflect 33% of the carrying value of the partnership. This difference, partially offset by the tax impact and other related transaction charges, also resulted in a $410 million decrease to Southern Power's common stockholder's equity. In December 2018, Southern Power completed the sale of a noncontrolling tax equity interest in SP Wind, which owns a portfolio of eight operating wind facilities, to three financial investors for approximately $1.2 billion. The tax equity investors together will generally receive 40% of the cash distributions from available cash and will receive 99% of the tax attributes, including future PTCs. Southern Power consolidates each entity, as the primary beneficiary of the VIE, since it controls the most significant activities, including operating and maintaining the assets. Sales of Natural Gas and Biomass Plants In December 2018, Southern Power completed the sale of all of its equity interests in Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) to NextEra Energy for $203 million, including final working capital adjustments. In contemplation of this sale transaction, Southern Power recorded an asset impairment charge of approximately $119 million ($89 million after tax) in the second quarter 2018. In June 2019, Southern Power completed the sale of its equity interests in Plant Nacogdoches, a 115-MW biomass facility located in Nacogdoches County, Texas, to Austin Energy, for a purchase price of approximately $461 million, including final working capital adjustments. Southern Power recorded a gain of $23 million ($88 million after tax) on the sale. On January 17, 2020, Southern Power completed the sale of its equity interests in Plant Mankato (including the 385-MW expansion unit completed in May 2019) to a subsidiary of Xcel for a purchase price of approximately $663 million, including final working capital adjustments. The sale resulted in a gain of approximately $39 million ($23 million after tax). The assets and liabilities of Plant Mankato were classified as held for sale on Southern Company's and Southern Power's balance sheets at December 31, 2019. See "Assets Held for Sale" herein for additional information. Southern Company Gas Sale of Pivotal Home Solutions In June 2018, Southern Company Gas completed the stock sale of Pivotal Home Solutions to American Water Enterprises LLC for a total cash purchase price of $365 million, which includes the final working capital adjustment. This disposition resulted in a net loss of $67 million, which includes $34 million of income tax expense. In contemplation of the transaction, a goodwill impairment charge of $42 million was recorded during 2018. The income tax expense included tax on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Southern Company Gas and American Water Enterprises LLC entered into a transition services agreement whereby Southern Company Gas provided certain administrative and operational services, which ended during 2018. Sales of Elizabethtown Gas and Elkton Gas In July 2018, a Southern Company Gas subsidiary, Pivotal Utility Holdings, completed the sales of the assets of two of its natural gas distribution utilities, Elizabethtown Gas and Elkton Gas, to South Jersey Industries, Inc. for a total cash purchase price of $1.7 billion, which includes the final working capital and other adjustments. This disposition resulted in a pre-tax gain that was entirely offset by $205 million of income tax expense, resulting in no material net income impact. The income tax expense included tax on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Southern Company Gas and South Jersey Industries, Inc. entered into transition services agreements whereby Southern Company Gas provided certain administrative and operational services through July 2, 2020. Sale of Florida City Gas In July 2018, Southern Company Gas and its wholly-owned direct subsidiary, NUI Corporation, completed the stock sale of Pivotal Utility Holdings, which primarily consisted of Florida City Gas, to NextEra Energy for a total cash purchase price of $587 million, which includes the final working capital adjustment. This disposition resulted in a net gain of $16 million, which includes $103 million of income tax expense. The income tax expense included tax on goodwill not deductible for tax purposes and for which a deferred tax liability had not been recorded previously. Southern Company Gas and NextEra Energy entered into a transition services agreement whereby Southern Company Gas provided certain administrative and operational services through July 28, 2020. Sale of Triton In May 2019, Southern Company Gas sold its investment in Triton, a cargo container leasing company that was aggregated into Southern Company Gas' all other segment. This disposition resulted in a pre-tax loss of $6 million and a net after-tax gain of $7 million as a result of reversing a $13 million federal income tax valuation allowance. Sale of Pivotal LNG and Atlantic Coast Pipeline On March 24, 2020, Southern Company Gas completed the sale of its interests in Pivotal LNG and Atlantic Coast Pipeline to Dominion Modular LNG Holdings, Inc. and Dominion Atlantic Coast Pipeline, LLC, respectively, with aggregate proceeds of $178 million, including final working capital adjustments. The loss associated with the transactions was immaterial. Southern Company Gas also expects to receive payments in April 2021 and August 2021 of $5 million each contingent upon Dominion Modular LNG Holdings, Inc. meeting certain milestones related to Pivotal LNG. During 2019, based on the terms of these transactions, Southern Company Gas recorded an asset impairment charge, exclusive of the contingent payments, for Pivotal LNG of approximately $24 million ($17 million after tax) as of December 31, 2019. The assets and liabilities of Pivotal LNG and the interest in Atlantic Coast Pipeline were classified as held for sale as of December 31, 2019. See Note 7 under "Southern Company Gas" and "Assets Held for Sale" herein for additional information. Sale of Natural Gas Storage Facility On December 1, 2020, Southern Company Gas completed the sale of Jefferson Island to EnLink Midstream, LLC for a total purchase price of $33 million, including estimated working capital adjustments. The gain associated with the sale totaled $22 million pre-tax ($16 million after tax). Assets Held for Sale Assets and liabilities held for sale have been classified separately on each company's balance sheet at the lower of carrying value or fair value less costs to sell at the time the criteria for held-for-sale classification were met. For assets and liabilities held for sale recorded at fair value on a nonrecurring basis, the fair value of assets held for sale is based primarily on unobservable inputs (Level 3), which includes the agreed upon sales prices in executed sales agreements. Since the depreciation of the assets sold in the Gulf Power transaction and Southern Company Gas' Elizabethtown Gas, Elkton Gas, and Florida City Gas transactions continued to be reflected in customer rates through the closing date of each sale and was reflected in the carryover basis of the assets when sold, Southern Company and Southern Company Gas continued to record depreciation on those assets through the respective closing date of each transaction. Upon classification as held for sale in May 2018 for the Florida Plants, November 2018 for Plant Mankato, and April 2019 for Plant Nacogdoches, Southern Power ceased recognizing depreciation and amortization on the long-lived assets being sold. The following table provides the major classes of assets and liabilities classified as held for sale for Southern Company, Southern Power, and Southern Company Gas at December 31, 2020 and/or 2019: Southern Southern Southern Company Gas At December 31, At December 31, At December 31, 2020 2019 2019 2019 (in millions) Assets Held for Sale: Current assets $ — $ 19 $ 17 $ 2 Total property, plant, and equipment 8 565 547 18 Goodwill and other intangible assets — 40 40 — Equity investments in unconsolidated subsidiaries — 151 — 151 Leveraged leases 52 — — — Other non-current assets — 14 14 — Total Assets Held for Sale $ 60 $ 789 $ 618 $ 171 Liabilities Held for Sale (all current): $ — $ 5 $ 3 $ 2 Southern Company, Southern Power, and Southern Company Gas each concluded that the asset sales, both individually and combined, did not represent a strategic shift in operations that has, or is expected to have, a major effect on its operations and financial results; therefore, none of the assets related to the sales have been classified as discontinued operations for any of the periods presented. Gulf Power and Southern Power's Florida Plants, Plant Nacogdoches, and Plant Mankato represented individually significant components of Southern Company and Southern Power, respectively. Pre-tax income for these components for the years ended December 31, 2020, 2019, and 2018 are presented below: 2020 2019 2018 (in millions) Earnings before income taxes: Gulf Power N/A N/A $ 140 Southern Power's Florida Plants (a)(b) N/A N/A $ 49 Southern Power's Plant Nacogdoches (a)(c) N/A $ 13 $ 27 Southern Power's Plant Mankato (a)(d) $ 2 $ 29 N/M N/M - Not material (a) Earnings before income taxes reflect the cessation of depreciation and amortization on the long-lived assets being sold upon classification as held for sale. (b) 2018 amount represents the period from January 1, 2018 to December 4, 2018 (the divestiture date). (c) 2019 amount represents the period from January 1, 2019 to June 13, 2019 (the divestiture date). (d) 2020 amount represents the period from January 1, 2020 to January 17, 2020 (the divestiture date).

SEGMENT AND RELATED INFORMATION

SEGMENT AND RELATED INFORMATION (Notes)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
SEGMENT AND RELATED INFORMATION	SEGMENT AND RELATED INFORMATION Southern Company 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 $364 million, $398 million, and $435 million in 2020, 2019, and 2018, respectively. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies and Southern Power were immaterial and $26 million, respectively, in 2020, $14 million and $64 million, respectively, in 2019, and $32 million and $119 million, respectively, in 2018. 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 years ended December 31, 2020, 2019, and 2018 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) 2020 Operating revenues $ 15,135 $ 1,733 $ (371) $ 16,497 $ 3,434 $ 596 $ (152) $ 20,375 Depreciation and amortization 2,447 494 — 2,941 500 77 — 3,518 Interest income 26 4 — 30 5 6 (4) 37 Earnings from equity method investments — — — — 141 12 — 153 Interest expense 825 151 — 976 231 614 — 1,821 Income taxes (benefit) 514 3 — 517 173 (297) — 393 Segment net income (loss) (a)(b)(c)(d)(e) 2,877 238 — 3,115 590 (592) 6 3,119 Goodwill — 2 — 2 5,015 263 — 5,280 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 2019 Operating revenues $ 15,569 $ 1,938 $ (412) $ 17,095 $ 3,792 $ 690 $ (158) $ 21,419 Depreciation and amortization 1,993 479 — 2,472 487 79 — 3,038 Interest income 38 9 — 47 3 16 (6) 60 Earnings from equity method investments 2 3 — 5 157 — — 162 Interest expense 818 169 — 987 232 517 — 1,736 Income taxes (benefit) 764 (56) — 708 130 960 — 1,798 Segment net income (loss) (a)(f)(g)(h) 2,929 339 — 3,268 585 908 (22) 4,739 Goodwill — 2 — 2 5,015 263 — 5,280 Total assets 81,063 14,300 (713) 94,650 21,687 3,511 (1,148) 118,700 2018 Operating revenues $ 16,843 $ 2,205 $ (477) $ 18,571 $ 3,909 $ 1,213 $ (198) $ 23,495 Depreciation and amortization 2,072 493 — 2,565 500 66 — 3,131 Interest income 23 8 — 31 4 8 (5) 38 Earnings from equity method investments (1) — — (1) 148 2 (1) 148 Interest expense 852 183 — 1,035 228 580 (1) 1,842 Income taxes (benefit) 371 (164) — 207 464 (222) — 449 Segment net income (loss) (a)(b)(i)(j) 2,117 187 — 2,304 372 (453) 3 2,226 Goodwill — 2 — 2 5,015 298 — 5,315 Total assets 79,382 14,883 (306) 93,959 21,448 3,285 (1,778) 116,914 (a) Attributable to Southern Company. (b) For the traditional electric operating companies, includes pre-tax charges at Georgia Power for estimated loss on Plant Vogtle Units 3 and 4 of $325 million ($242 million after tax) in 2020 and $1.1 billion ($0.8 billion after tax) in 2018. See Note 2 under "Georgia Power – Nuclear Construction" for additional information. (c) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 under "Southern Power" for additional information. (d) For Southern Company Gas, includes a $22 million pre-tax gain ($16 million gain after tax) on the sale of Jefferson Island. See Note 15 under "Southern Company Gas" for additional information. (e) For the "All Other" column, includes pre-tax impairment charges totaling $206 million ($105 million after tax) related to leveraged lease investments. See Note 3 under "Other Matters – Southern Company" for additional information. (f) For Southern Power, includes a $23 million pre-tax gain ($88 million gain after tax) on the sale of Plant Nacogdoches. See Note 15 under "Southern Power" for additional information. (g) For Southern Company Gas, includes pre-tax impairment charges totaling $115 million ($86 million after tax). See Notes 3 and 15 under "Other Matters – Southern Company Gas" and "Southern Company Gas – Sale of Pivotal LNG and Atlantic Coast Pipeline," respectively, for additional information. (h) For the "All Other" column, includes the pre-tax gain associated with the sale of Gulf Power of $2.6 billion ($1.4 billion after tax), the pre-tax loss, including related impairment charges, on the sales of certain PowerSecure business units totaling $58 million ($52 million after tax), and a pre-tax impairment charge of $17 million ($13 million after tax) related to a leveraged lease investment. See Notes 3 and 15 under "Other Matters – Southern Company" and "Southern Company," respectively, for additional information. (i) For Southern Power, includes pre-tax impairment charges of $156 million ($117 million after tax). See Note 15 under "Southern Power" for additional information. (j) For Southern Company Gas, includes a net gain on dispositions of $291 million ($51 million loss after tax), as well as a goodwill impairment charge of $42 million related to the sale of Pivotal Home Solutions. See Note 15 under "Southern Company Gas" for additional information. Products and Services Electric Utilities' Revenues Year Retail Wholesale Other Total (in millions) 2020 $ 13,643 $ 1,945 $ 909 $ 16,497 2019 14,084 2,152 859 17,095 2018 15,222 2,516 833 18,571 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2020 $ 2,902 $ 408 $ 124 $ 3,434 2019 3,001 456 335 3,792 2018 3,155 568 186 3,909 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 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. In July 2018, Southern Company Gas sold three of its natural gas distribution utilities, Elizabethtown Gas, Elkton Gas, and Florida City Gas. 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. See Notes 3, 5, and 7 for additional information. Wholesale gas services provides natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. Additionally, wholesale gas services engages in natural gas storage and gas pipeline arbitrage and related activities. Gas marketing services provides natural gas marketing to end-use customers primarily in Georgia and Illinois through SouthStar. In June 2018, Southern Company Gas sold Pivotal Home Solutions, which provided home equipment protection products and services. 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 though its sale on December 1, 2020, Pivotal LNG through its sale on March 24, 2020, and the investment in Triton through its sale on May 29, 2019. Financial data for business segments for the years ended December 31, 2020, 2019, and 2018 was as follows: Gas Distribution Operations (a) Gas Pipeline Investments Wholesale Gas Services (b) Gas Marketing Services (c) Total All Other (d) Eliminations Consolidated (in millions) 2020 Operating revenues $ 2,952 $ 32 $ 74 $ 408 $ 3,466 $ 36 $ (68) $ 3,434 Depreciation and amortization 442 5 1 22 470 30 — 500 Operating income (loss) 655 20 20 119 814 (7) 5 812 Earnings from equity method investments — 141 — — 141 — — 141 Interest expense 192 29 4 3 228 3 — 231 Income taxes (benefit) 114 33 3 28 178 (5) — 173 Segment net income (loss) 390 99 14 89 592 (2) — 590 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 2019 Operating revenues $ 3,028 $ 32 $ 294 $ 456 $ 3,810 $ 44 $ (62) $ 3,792 Depreciation and amortization 422 5 1 26 454 33 — 487 Operating income (loss) 573 20 219 112 924 (154) — 770 Earnings from equity method investments — 162 — — 162 (5) — 157 Interest expense 187 30 5 3 225 7 — 232 Income taxes (benefit) 63 58 52 27 200 (70) — 130 Segment net income (loss) 337 94 163 83 677 (92) — 585 Total assets at December 31, 2019 18,204 1,678 850 1,496 22,228 10,759 (11,300) 21,687 2018 Operating revenues $ 3,186 $ 32 $ 144 $ 568 $ 3,930 $ 55 $ (76) $ 3,909 Depreciation and amortization 409 5 2 37 453 47 — 500 Operating income (loss) 904 20 70 19 1,013 (98) — 915 Earnings from equity method investments — 145 — — 145 3 — 148 Interest expense 178 34 9 6 227 1 — 228 Income taxes (benefit) 409 28 4 54 495 (31) — 464 Segment net income (loss) 334 103 38 (40) 435 (63) — 372 Total assets at December 31, 2018 17,266 1,763 1,302 1,587 21,918 11,112 (11,582) 21,448 (a) Operating revenues for the three gas distribution operations dispositions were $244 million for 2018. Segment net income for gas distribution operations includes a gain on dispositions of $324 million ($16 million after tax) in 2018. (b) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) 2020 $ 4,544 $ 115 $ 4,659 $ 4,585 $ 74 2019 5,703 275 5,978 5,684 294 2018 6,955 451 7,406 7,262 144 (c) Operating revenues for the gas marketing services disposition were $55 million in 2018. Segment net income for gas marketing services includes a loss on disposition of $33 million ($67 million loss after tax) and a goodwill impairment charge of $42 million in 2018 recorded in contemplation of the sale of Pivotal Home Solutions. (d) Segment net income (loss) for the "All Other" column include s a $22 million pre-tax gain ($16 million g ain after tax) on the sale of Jefferson Island in 2020 and pre-tax impairment charges totaling $115 million ($86 million after tax) in 2019. See Note 3 under "Other Matters – Southern Company Gas" for additional information.

VALUATION AND QUALIFYING ACCOUN

VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
VALUATION AND QUALIFYING ACCOUNTS	THE SOUTHERN COMPANY AND SUBSIDIARY COMPANIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts (a) Deductions Reclassified to Held for Sale (b) Balance at End of Period Provision for uncollectible accounts (c) 2020 $ 49 $ 78 $ 27 $ 36 $ — $ 118 2019 50 68 — 69 — 49 2018 44 69 (1) 61 1 50 Tax valuation allowance (net state) (d) 2020 $ 113 $ — $ — $ 1 $ — $ 112 2019 100 13 — — — 113 2018 148 (38) — 10 — 100 (a) During 2020, Georgia Power recorded $23 million of expected bad debt related to the COVID-19 pandemic to a regulatory asset in accordance with orders from the Georgia PSC. See Note 2 to the financial statements under "Georgia Power – Deferral of Incremental COVID-19 Costs" in Item 8 herein for additional information. (b) Represents provision for uncollectible accounts at Gulf Power reclassified as held for sale during 2018. See Note 15 to the financial statements under "Southern Company" in Item 8 herein for additional information. (c) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (d) In 2018, as a result of higher projected state taxable income, Mississippi Power reduced a valuation allowance associated with a State of Mississippi net operating loss carryforward expected to expire prior to being fully utilized. In 2018, Georgia Power established a valuation allowance for certain Georgia state tax credits expected to expire prior to being fully utilized, as a result of lower projected state taxable income. See Note 10 to the financial statements in Item 8 herein for additional information. ALABAMA POWER COMPANY SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning Charged to Charged to Other Accounts Deductions (*) Balance at Provision for uncollectible accounts 2020 $ 22 $ 25 $ — $ 4 $ 43 2019 10 24 — 12 22 2018 9 13 — 12 10 (*) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. GEORGIA POWER COMPANY SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning Charged to Charged to Other Accounts (a) Deductions Balance at End of Period Provision for uncollectible accounts (b) 2020 $ 2 $ 14 $ 23 $ 13 $ 26 2019 2 13 — 13 2 2018 3 11 — 12 2 Tax valuation allowance (net state) (c) 2020 $ 28 $ — $ — $ — $ 28 2019 33 (5) — — 28 2018 — 39 — 6 33 (a) During 2020, Georgia Power recorded $23 million of expected bad debt related to the COVID-19 pandemic to a regulatory asset in accordance with orders from the Georgia PSC. See Note 2 to the financial statements under "Georgia Power – Deferral of Incremental COVID-19 Costs" in Item 8 herein for additional information. (b) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (c) In 2018, Georgia Power established a valuation allowance for certain Georgia state tax credits expected to expire prior to being fully utilized, which was reduced in 2019 as a result of higher projected state taxable income. See Note 10 to the financial statements in Item 8 herein for additional information. MISSISSIPPI POWER COMPANY SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning Charged to Charged to Other Deductions Balance at End of Period Provision for uncollectible accounts (a) 2020 $ 1 $ 1 $ — $ 1 $ 1 2019 1 2 — 2 1 2018 1 1 — 1 1 Tax valuation allowance (net state) (b) 2020 $ 32 $ — $ — $ — $ 32 2019 32 — — — 32 2018 124 (92) — — 32 (a) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (b) In 2018, as a result of higher projected state taxable income, Mississippi Power reduced a valuation allowance associated with a State of Mississippi net operating loss carryforward expected to expire prior to being fully utilized. See Note 10 to the financial statements in Item 8 herein for additional information. SOUTHERN POWER COMPANY AND SUBSIDIARY COMPANIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning Charged to Charged to Other Deductions Balance at End of Period Tax valuation allowance (net state) 2020 $ 29 $ (1) $ — $ 1 $ 27 2019 22 7 — — 29 2018 10 12 — — 22 SOUTHERN COMPANY GAS AND SUBSIDIARY COMPANIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019, AND 2018 (Stated in Millions of Dollars) Additions Description Balance at Beginning Charged to Charged to Other Accounts Deductions Balance at Provision for uncollectible accounts (a) 2020 $ 18 $ 35 $ 4 $ 17 $ 40 2019 30 29 — 41 18 2018 28 33 (1) 30 30 Tax valuation allowance (net state) (b) 2020 $ 4 $ — $ — $ — $ 4 2019 12 (8) — — 4 2018 11 1 — — 12 (a) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (b) In 2019, Southern Company Gas reversed a $13 million valuation allowance for a federal deferred tax asset in connection with the sale of Triton. Additionally, in 2019, a $5 million valuation allowance was established for a state net operating loss carryforward expected to expire prior to being fully utilized. See Note 10 to the financial statements and Note 15 to the financial statements under "Southern Company Gas" in Item 8 herein for additional information.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
General	General Southern Company is the parent company of three traditional electric operating companies, as well as Southern Power, Southern Company Gas, SCS, Southern Linc, Southern Holdings, Southern Nuclear, PowerSecure, and other direct and indirect subsidiaries. The traditional electric operating companies – Alabama Power, Georgia Power, and Mississippi Power – are vertically integrated utilities providing electric service in three Southeastern states. In January 2019, Southern Company completed the sale of Gulf Power (another traditional electric operating company through December 31, 2018) to NextEra Energy. 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 natural gas distribution utilities, including Nicor Gas (Illinois), Atlanta Gas Light (Georgia), Virginia Natural Gas, and Chattanooga Gas (Tennessee). In 2018, Southern Company Gas sold its other natural gas utilities – Elizabethtown Gas (New Jersey), Florida City Gas, and Elkton Gas (Maryland). Southern Company Gas is also involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. SCS, the system service company, provides, at cost, specialized services to Southern Company and its subsidiary companies. Southern Linc provides digital wireless communications for use by Southern Company and its subsidiary companies and also markets these services to the public and provides fiber optics services within the Southeast. Southern Holdings is an intermediate holding company subsidiary, primarily for Southern Company's leveraged lease and other investments. Southern Nuclear operates and provides services to the Southern Company system's nuclear power plants, including Alabama Power's Plant Farley and Georgia Power's Plant Hatch and Plant Vogtle Units 1 and 2, and is currently managing construction and start-up of Plant Vogtle Units 3 and 4, which are co-owned by Georgia Power. PowerSecure provides energy solutions to electric utilities and their customers in the areas of distributed generation, energy storage and renewables, and energy efficiency. See Note 15 for information regarding disposition activities, including Southern Company's sale of Gulf Power. The Registrants' financial statements reflect investments in subsidiaries on a consolidated basis. Intercompany transactions have been eliminated in consolidation. The equity method is used for investments in entities in which a Registrant has significant influence but does not have control and for VIEs where a Registrant has an equity investment but is not the primary beneficiary. Southern Power has controlling ownership in certain legal entities for which the contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. For these arrangements, the noncontrolling interest is accounted for under a balance sheet approach utilizing the HLBV method. The HLBV method calculates each partner's share of income based on the change in net equity the partner can legally claim in a HLBV at the end of the period compared to the beginning of the period. See "Variable Interest Entities" herein and Note 7 for additional information. The traditional electric operating companies, Southern Power, certain subsidiaries of Southern Company Gas, and certain other subsidiaries are subject to regulation by the FERC, and the traditional electric operating companies and the natural gas distribution utilities are also subject to regulation by their respective state PSCs or other applicable state regulatory agencies. As such, the respective financial statements of the applicable Registrants reflect the effects of rate regulation in accordance with GAAP and comply with the accounting policies and practices prescribed by relevant state PSCs or other applicable state regulatory agencies. The preparation of financial statements in conformity with GAAP requires the use of estimates, and the actual results may differ from those estimates. Certain prior years' data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the Registrants' results of operations, financial position, or cash flows.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards Effective January 1, 2019, the Registrants adopted ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 required lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changed the recognition, measurement, and presentation of expense associated with leases and provided clarification regarding the identification of certain components of contracts that would represent a lease. Lessor accounting was relatively unchanged and there was no change to the accounting for existing leveraged leases. See Note 9 for additional information and related disclosures.
Affiliate Transactions	Affiliate TransactionsThe traditional electric operating companies, Southern Power, and Southern Company Gas have agreements with SCS under which certain of the following services are rendered to them at direct or allocated cost: general executive and advisory, general and design engineering, operations, purchasing, accounting, finance, treasury, legal, tax, information technology, marketing, auditing, insurance and pension administration, human resources, systems and procedures, digital wireless communications, cellular tower space, and other services with respect to business and operations, construction management, and Southern Company power pool transactions. These costs are primarily included in other operations and maintenance expenses or capitalized to property, plant, and equipment.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities The traditional electric operating companies and the natural gas distribution utilities are subject to accounting requirements for the effects of rate regulation. Regulatory assets represent probable future revenues associated with certain costs that are expected to be recovered from customers through the ratemaking process. Regulatory liabilities represent costs recovered that are expected to be incurred in the future or probable future reductions in revenues associated with amounts that are expected to be credited to customers through the ratemaking process. In the event that a portion of a traditional electric operating company's or a natural gas distribution utility's operations is no longer subject to applicable accounting rules for rate regulation, such company would be required to write off to income or reclassify to AOCI related regulatory assets and liabilities that are not specifically recoverable through regulated rates. In addition, the traditional electric operating company or the natural gas distribution utility would be required to determine if any impairment to other assets, including plant, exists and write down the assets, if impaired, to their fair values. All regulatory assets and liabilities are to be reflected in rates. See Note 2 for additional information including details of regulatory assets and liabilities reflected in the balance sheets for Southern Company, the traditional electric operating companies, and Southern Company Gas.
Revenues	Revenues The Registrants generate revenues from a variety of sources which are accounted for under various revenue accounting guidance, including revenue from contracts with customers, lease, derivative, and regulatory accounting. See Notes 4, 9, and 14 for additional information. Traditional Electric Operating Companies The majority of the revenues of the traditional electric operating companies are generated from contracts with retail electric customers. These revenues, generated from the integrated service to deliver electricity when and if called upon by the customer, are recognized as a single performance obligation satisfied over time, at a tariff rate, and as electricity is delivered to the customer during the month. Unbilled revenues related to retail sales are accrued at the end of each fiscal period. Retail rates may include provisions to adjust revenues for fluctuations in fuel costs, fuel hedging, the energy component of purchased power costs, and certain other costs. Revenues are adjusted for differences between these actual costs and amounts billed in current regulated rates. Under or over recovered regulatory clause revenues are recorded in the balance sheets and are recovered from or returned to customers, respectively, through adjustments to the billing factors. See Note 2 for additional information regarding regulatory matters of the traditional electric operating companies. Wholesale capacity revenues from PPAs are recognized in amounts billable under the contract terms. Energy and other revenues are generally recognized as services are provided. The contracts for capacity and energy in a wholesale PPA have multiple performance obligations where the contract's total transaction price is allocated to each performance obligation based on the standalone selling price. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, the traditional electric operating companies recognize revenue as the performance obligations are satisfied over time as electricity is delivered to the customer or as generation capacity is available to the customer. For both retail and wholesale revenues, the traditional electric operating companies have elected to recognize revenue for their sales of electricity and capacity using the invoice practical expedient as they generally have a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and that may be invoiced. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of the Registrants' performance obligation. Southern Power Southern Power sells capacity and energy at rates specified under contractual terms in long-term PPAs. These PPAs are accounted for as operating leases, non-derivatives, or normal sale derivatives. Capacity revenues from PPAs classified as operating leases are recognized on a straight-line basis over the term of the agreement. Energy revenues are recognized in the period the energy is delivered. Southern Power's non-lease contracts commonly include capacity and energy which are considered separate performance obligations. In these contracts, the total transaction price is allocated to each performance obligation based on the standalone selling price. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, Southern Power recognizes revenue as the performance obligations are satisfied over time, as electricity is delivered to the customer or as generation capacity is made available to the customer. Southern Power generally has a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of Southern Power's performance obligation. When multiple contracts exist with the same counterparty, the revenues from each contract are accounted for as separate arrangements. Southern Power may also enter into contracts to sell short-term capacity in the wholesale electricity markets. These sales are generally classified as mark-to-market derivatives and net unrealized gains and losses on such contracts are recorded in wholesale revenues. See Note 14 and "Financial Instruments" herein for additional information. Southern Company Gas Gas Distribution Operations Southern Company Gas records revenues when goods or services are provided to customers. Those revenues are based on rates approved by the state regulatory agencies of the natural gas distribution utilities. Atlanta Gas Light operates in a deregulated natural gas market wher eby M arketers, rather than a traditional utility, sell natural gas to end-use customers in Georgia and handle customer billing functions. As required by the Georgia PSC, Atlanta Gas Light bills Marketers in equal monthly installments for each residential, commercial, and industrial end-use customer's distribution costs as well as for capacity costs utilizing a seasonal rate design for the calculation of each residential end-use customer's annual straight-fixed-variable charge, which reflects the historic volumetric usage pattern for the entire residential class. The majority of the revenues of Southern Company Gas are generated from contracts with natural gas distribution customers. Revenues from this integrated service to deliver gas when and if called upon by the customer are recognized as a single performance obligation satisfied over time and are recognized at a tariff rate as gas is delivered to the customer during the month. The standalone selling price is primarily determined by the price charged to customers for the specific goods or services transferred with the performance obligations. Generally, Southern Company Gas recognizes revenue as the performance obligations are satisfied over time as natural gas is delivered to the customer. The performance obligations related to wholesale gas services are satisfied, and revenue is recognized, at a point in time when natural gas is delivered to the customer. Southern Company Gas has elected to recognize revenue for sales of gas using the invoice practical expedient as it generally has a right to consideration in an amount that corresponds directly with the value to the customer of the performance completed to date and that may be invoiced. Payment for goods and services rendered is typically due in the subsequent month following satisfaction of Southern Company Gas' performance obligation. With the exception of Atlanta Gas Light, the natural gas distribution utilities have rate structures that include volumetric rate designs that allow the opportunity to recover certain costs based on gas usage. Revenues from sales and transportation services are recognized in the same period in which the related volumes are delivered to customers. Revenues from residential and certain commercial and industrial customers are recognized on the basis of scheduled meter readings. Additionally, unbilled revenues are recognized for estimated deliveries of gas not yet billed to these customers, from the last bill date to the end of the accounting period. For other commercial and industrial customers and for all wholesale customers, revenues are based on actual deliveries through the end of the period. The tariffs for several of the natural gas distribution utilities include provisions which allow for the recognition of certain revenues prior to the time such revenues are billed to customers. These provisions are referred to as alternative revenue programs and provide for the recognition of certain revenues prior to billing, as long as the amounts recognized will be collected from customers within 24 months of recognition. These programs are as follows: • Weather normalization adjustments – reduce customer bills when winter weather is colder than normal and increase customer bills when weather is warmer than normal and are included in the tariffs for Virginia Natural Gas, Chattanooga Gas, and, prior to its sale, Elizabethtown Gas; • Revenue normalization mechanisms – mitigate the impact of conservation and declining customer usage and are contained in the tariffs for Virginia Natural Gas, Chattanooga Gas, Nicor Gas (effective November 1, 2019), and, prior to its sale, Elkton Gas; and • Revenue true-up adjustment – included within the provisions of the GRAM program in which Atlanta Gas Light participates as a short-term alternative to formal rate case filings, the revenue true-up feature provides for a positive (or negative) adjustment to record revenue in the amount of any variance to budgeted revenues, which are submitted and approved annually as a requirement of GRAM. Such adjustments are reflected in customer billings in a subsequent program year. Wholesale Gas Services Southern Company Gas nets revenues from energy and risk management activities with the associated costs. Profits from sales between segments are eliminated and are recognized as goods or services sold to end-use customers. Southern Company Gas records transactions that qualify as derivatives at fair value with changes in fair value recognized in earnings in the period of change and characterized as unrealized gains or losses. Gains and losses on derivatives held for energy trading purposes are presented on a net basis in revenue. Gas Marketing Services Southern Company Gas recognizes revenues from natural gas sales and transportation services in the same period in which the related volumes are delivered to customers and recognizes sales revenues from residential and certain commercial and industrial customers on the basis of scheduled meter readings. Southern Company Gas also recognizes unbilled revenues for estimated deliveries of gas not yet billed to these customers from the most recent meter reading date to the end of the accounting period. For other commercial and industrial customers and for all wholesale customers, revenues are based on actual deliveries during the period. Southern Company Gas recognizes revenues on 12-month utility-bill management contracts as the lesser of cumulative earned or cumulative billed amounts. Concentration of Revenue Southern Company, Alabama Power, Georgia Power, Mississippi Power (with the exception of its full requirements cost-based MRA electric tariffs described below), and Southern Company Gas each have a diversified base of customers and no single customer or industry comprises 10% or more of each company's revenues. Mississippi Power provides service under long-term contracts with rural electric cooperative associations and a municipality located in southeastern Mississippi under full requirements cost-based MRA electric tariffs, which are subject to regulation by the FERC. The contracts with these wholesale customers represent ed 15.3% of Mississippi Power 's total operating revenues in 2020 and are generally subject to 10 -year rolling c ancellation notices. Historically, these wholesale customers have acted as a group and any changes in contractual relationships for one customer are likely to be followed by the other wholesale customers.
Concentration of Credit Risk	Concentration of Credit Risk Southern Company Gas' wholesale gas services business has a concentration of credit risk for services it provides to its counterparties. This credit risk is generally concentrated in 20 of its counterparties and is measured by 30-day receivable exposure plus forward exposure. Counterparty credit risk is evaluated using a S&P equivalent credit rating, which is determined by a process of converting the lower of the S&P or Moody's rating to an internal rating ranging from 9 to 1, with 9 being equivalent to AAA/Aaa by S&P and Moody's, respectively, and 1 being equivalent to D/Default by S&P and Moody's, respectively. A counterparty that does not have an external rating is assigned an internal rating based on the strength of its financial ratios. As of December 31, 2020, the top 20 counterparties represented 58%, or $234 million , of the total counterparty exposure and had a weighted average S&P equivalent rating of A-. Concentration of credit risk occurs at Atlanta Gas Light for amounts billed for services and other costs to its customers, which consist of 16 Marketers in Georgia (including SouthStar). The credit risk exposure to the Marketers varies seasonally, with the lowest exposure in the non-peak summer months and the highest exposure in the peak winter months. Marketers are responsible for the retail sale of natural gas to end-use customers in Georgia. The functions of the retail sale of gas include the purchase and sale of natural gas, customer service, billings, and collections. The provisions of Atlanta Gas Light's tariff allow Atlanta Gas Light to obtain credit security support in an amount equal to a minimum of two times a Marketer's highest month's estimated bill from Atlanta Gas Light.
Fuel Costs	Fuel Costs Fuel costs for the traditional electric operating companies and Southern Power are expensed as the fuel is used. Fuel expense generally includes fuel transportation costs and the cost of purchased emissions allowances as they are used. For Alabama Power and Georgia Power, fuel expense also includes the amortization of the cost of nuclear fuel. For the traditional electric operating companies, fuel costs also include gains and/or losses from fuel-hedging programs as approved by their respective state PSCs.
Cost of Natural Gas	Cost of Natural Gas Excluding Atlanta Gas Light, which does not sell natural gas to end-use customers, Southern Company Gas charges its utility customers for natural gas consumed using natural gas cost recovery mechanisms set by the applicable state regulatory agencies. Under these mechanisms, all prudently-incurred natural gas costs are passed through to customers without markup, subject to regulatory review. Southern Company Gas defers or accrues the difference between the actual cost of natural gas and the amount of commodity revenue earned in a given period such that no operating income is recognized related to these costs. The deferred or accrued amount is either billed or refunded to customers prospectively through adjustments to the commodity rate. Deferred and accrued natural gas costs are included in the balance sheets as regulatory assets and regulatory liabilities, respectively. Southern Company Gas' gas marketing services' customers are charged for actual or estimated natural gas consumed. Within cost of natural gas, Southern Company Gas also includes costs of lost and unaccounted for gas, adjustments to reduce the value of inventories to market value, and gains and losses associated with certain derivatives.
Income Taxes and Other Taxes	Income Taxes The Registrants use the liability method of accounting for deferred income taxes and provide deferred income taxes for all significant income tax temporary differences. In accordance with regulatory requirements, deferred federal ITCs for the traditional electric operating companies are deferred and amortized over the average life of the related property, with such amortization normally applied as a credit to reduce depreciation and amortization in the statements of income. Southern Power's and the natural gas distribution utilities' deferred federal ITCs, as well as certain state ITCs for Nicor Gas, are deferred and amortized to income tax expense over the life of the respective asset. Under current tax law, certain projects at Southern Power related to the construction of renewable facilities are eligible for federal ITCs. Southern Power estimates eligible costs which, as they relate to acquisitions, may not be finalized until the allocation of the purchase price to assets has been finalized. Southern Power applies the deferred method to ITCs, whereby the ITCs are recorded as a deferred credit and amortized to income tax expense over the life of the respective asset. Furthermore, the tax basis of the asset is reduced by 50% of the ITCs received, resulting in a net deferred tax asset. Southern Power has elected to recognize the tax benefit of this basis difference as a reduction to income tax expense in the year in which the plant reaches commercial operation. State ITCs are recognized as an income tax benefit in the period in which the credits are generated. In addition, certain projects are eligible for federal and state PTCs, which are recognized as an income tax benefit based on KWH production. Federal ITCs and PTCs, as well as state ITCs and other state tax credits available to reduce income taxes payable, were not fully utilized in 2020 and will be carried forward and utilized in future years. In addition, Southern Company is expected to have various state net operating loss (NOL) carryforwards for certain of its subsidiaries, including Mississippi Power and Southern Power, which would result in income tax benefits in the future, if utilized. See Note 10 under "Current and Deferred Income Taxes – Tax Credit Carryforwards" and " – Net Operating Loss Carryforwards" for additional information. The Registrants recognize tax positions that are "more likely than not" of being sustained upon examination by the appropriate taxing authorities. See Note 10 under "Unrecognized Tax Benefits" for additional information. Other Taxes Taxes imposed on and collected from customers on behalf of governmental agencies are presented net on the Registrants' statements of income and are excluded from the transaction price in determining the revenue related to contracts with a customer.
Allowance for Funds Used During Construction and Interest Capitalized	Allowance for Funds Used During Construction and Interest Capitalized The traditional electric operating companies and the natural gas distribution utilities record AFUDC, which represents the estimated debt and equity costs of capital funds that are necessary to finance the construction of new regulated facilities. While cash is not realized currently, AFUDC increases the revenue requirement and is recovered over the service life of the asset through a higher rate base and higher depreciation. The equity component of AFUDC is not taxable. Interest related to financing the construction of new facilities at Southern Power and new facilities not included in the traditional electric operating companies' and Southern Company Gas' regulated rates is capitalized in accordance with standard interest capitalization requirements.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Registrants evaluate long-lived assets and finite-lived intangible assets for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. The determination of whether an impairment has occurred is based on either a specific regulatory disallowance, a sales transaction price that is less than the asset group's carrying value, or an estimate of undiscounted future cash flows attributable to the asset group, as compared with the carrying value of the assets. If an impairment has occurred, the amount of the impairment recognized is determined by either the amount of regulatory disallowance or by estimating the fair value of the assets and recording a loss if the carrying value is greater than the
Goodwill and Other Intangible Assets and Liabilities	Goodwill and Other Intangible Assets and Liabilities Southern Power's intangible assets consist primarily of certain PPAs acquired, which are amortized over the term of the respective PPA. Southern Company Gas' goodwill and other intangible assets and liabilities primarily relate to its 2016 acquisition by Southern Company. In addition to these items, Southern Company's goodwill and other intangible assets also relate to its 2016 acquisition of PowerSecure.
Acquisition Accounting	Acquisition Accounting At the time of an acquisition, management will assess whether acquired assets and activities meet the definition of a business. For acquisitions that meet the definition of a business, operating results from the date of acquisition are included in the acquiring entity's financial statements. The purchase price, including any contingent consideration, is allocated based on the fair value of the identifiable assets acquired and liabilities assumed (including any intangible assets). Assets acquired that do not meet the definition of a business are accounted for as an asset acquisition. The purchase price of each asset acquisition is allocated based on the relative fair value of assets acquired. Determining the fair value of assets acquired and liabilities assumed requires management judgment and management may engage independent valuation experts to assist in this process. Fair values are determined by using market participant assumptions and typically include the timing and amounts of future cash flows, incurred construction costs, the nature of acquired contracts, discount rates, power market prices, and expected asset lives. Any due diligence or transition costs incurred for potential or successful acquisitions are expensed as incurred.
Development Costs	Development Costs For Southern Power, development costs are capitalized once a project is probable of completion, primarily based on a review of its economics and operational feasibility, as well as the status of power off-take agreements and regulatory approvals, if applicable. Southern Power's capitalized development costs are included in CWIP on the balance sheets. All of Southern Power's development costs incurred prior to the determination that a project is probable of completion are expensed as incurred and included in other operations and maintenance expense in the statements of income. If it is determined that a project is no longer probable of completion, any of Southern Power's capitalized development costs are expensed and included in other operations and maintenance expense in the statements of income.
Long-Term Service Agreements	Long-Term Service Agreements The traditional electric operating companies and Southern Power have entered into LTSAs for the purpose of securing maintenance support for certain of their generating facilities. The LTSAs cover all planned inspections on the covered equipment, which generally includes the cost of all labor and materials. The LTSAs also obligate the counterparties to cover the costs of unplanned maintenance on the covered equipment subject to limits and scope specified in each contract. Payments made under the LTSAs for the performance of any planned inspections or unplanned capital maintenance are recorded in the statements of cash flows as investing activities. Receipts of major parts into materials and supplies inventory prior to planned inspections are treated as noncash transactions in the statements of cash flows. Any payments made prior to the work being performed are recorded as prepayments in other current assets and noncurrent assets on the balance sheets. At the time work is performed, an appropriate amount is accrued for future payments or transferred from the prepayment and recorded as property, plant, and equipment or expensed.
Transmission Receivables/Prepayments	Transmission Receivables/Prepayments As a result of Southern Power's acquisition and construction of generating facilities, Southern Power has transmission receivables and/or prepayments representing the portion of interconnection network and transmission upgrades that will be reimbursed to Southern Power. Upon completion of the related project, transmission costs are generally reimbursed by the interconnection provider within a five-year period and the receivable/prepayments are reduced as payments or services are received.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of the financial statements, temporary cash investments are considered cash equivalents. Temporary cash investments are securities with original maturities of 90 days or less.
Restricted Cash	Restricted Cash At December 31, 2020 and 2019, Southern Company Gas had $2 million and $3 million, respectively, of restricted cash held as collateral for workers' compensation, life insurance, and long-term disability insurance, which is included in cash, cash equivalents, and restricted cash on the statements of cash flows.
Storm Damage Reserves	Storm Damage ReservesEach traditional electric operating company maintains a reserve to cover or is allowed to defer and recover the cost of damages from major storms to its transmission and distribution lines and, for Mississippi Power, the cost of uninsured damages to its generation facilities and other property.
Leveraged Leases	Leveraged Leases At December 31, 2020 and 2019, a subsidiary of Southern Holdings had four leveraged lease agreements, with original terms ranging up to 45 years, which relate to energy generation, distribution, and transportation assets, including two international projects. Southern Company receives federal income tax deductions for depreciation and amortization, as well as interest on long-term debt related to these investments. Southern Company reviews all important lease assumptions at least annually, or more frequently if events or changes in circumstances indicate that a change in assumptions has occurred or may occur. These assumptions include the effective tax rate, the residual value, the credit quality of the lessees, and the timing of expected tax cash flows. See Notes 3 and 15 under "Other Matters – Southern Company" and "Southern Company," respectively, for additional information on the leveraged lease investments, including impairment charges and completed and planned sales.
Materials and Supplies	Materials and Supplies Materials and supplies for the traditional electric operating companies generally includes the average cost of transmission, distribution, and generating plant materials. Materials and supplies for Southern Company Gas generally includes propane gas inventory, fleet fuel, and other materials and supplies. Materials and supplies for Southern Power generally includes the average cost of generating plant materials. Materials are recorded to inventory when purchased and then expensed or capitalized to property, plant, and equipment, as appropriate, at weighted average cost when installed. In addition, certain major parts are recorded as inventory when acquired and then capitalized at cost when installed to property, plant, and equipment.
Fuel Inventory	Fuel Inventory Fuel inventory for the traditional electric operating companies includes the average cost of coal, natural gas, oil, transportation, and emissions allowances. Fuel inventory for Southern Power, which is included in other current assets, includes the average cost of oil, natural gas, and emissions allowances. Fuel is recorded to inventory when purchased and then expensed, at weighted average cost, as used. Emissions allowances granted by the EPA are included in inventory at zero cost. The traditional electric operating companies recover fuel expense through fuel cost recovery rates approved by each state PSC or, for wholesale rates, the FERC.
Natural Gas for Sale	Natural Gas for Sale With the exception of Nicor Gas, the natural gas distribution utilities record natural gas inventories on a WACOG basis. In Georgia's deregulated, competitive environment, Marketers sell natural gas to firm end-use customers at market-based prices. On a monthly basis, Atlanta Gas Light assigns to Marketers the majority of the pipeline storage services that it has under contract, along with a corresponding amount of inventory. Atlanta Gas Light retains and manages a portion of its pipeline storage assets and related natural gas inventories for system balancing and to serve system demand. 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. The cost of natural gas, including inventory costs, is recovered from customers under a purchased gas recovery mechanism adjusted for differences between actual costs and amounts billed; therefore, LIFO liquidations have no impact on Southern Company's or Southern Company Gas' net income. At December 31, 2020, the Nicor Gas LIFO inventory balance was $178 million. Based on the average cost of gas purchased in December 2020, the estimated replacement cost of Nicor Gas' inventory at December 31, 2020 was $259 million.
Energy Marketing Receivables and Payables	Energy Marketing Receivables and Payables Southern Company Gas' wholesale gas services provides services to retail gas marketers, wholesale gas marketers, utility companies, and industrial customers. These counterparties utilize netting agreements that enable wholesale gas services to net receivables and payables by counterparty upon settlement. Southern Company Gas' wholesale gas services also nets 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, wholesale gas services' counterparties are settled net, they are recorded on a gross basis in the balance sheets as energy marketing receivables and energy marketing payables. Southern Company Gas' wholesale gas services has trade and credit contracts that contain minimum credit rating requirements. These credit rating requirements typically give counterparties the right to suspend or terminate credit if Southern Company Gas' credit ratings are downgraded to non-investment grade status. Under such circumstances, Southern Company Gas' wholesale gas services would need to post collateral to continue transacting business with some of its counterparties. As of December 31, 2020 and 2019, the required collateral in the event of a credit rating downgrade was $5 million and $11 million, respectively. Southern Company Gas' wholesale gas services 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. When more than one derivative transaction with the same counterparty is outstanding and a legally enforceable netting agreement exists with that counterparty, the "net" mark-to-market exposure represents a reasonable measure of Southern Company Gas' credit risk with that counterparty. Southern Company Gas' wholesale gas services also uses other netting agreements with certain counterparties with whom it conducts significant transactions.
Provision for Uncollectible Accounts	Provision for Uncollectible Accounts The customers of the traditional electric operating companies and the natural gas distribution utilities are billed monthly. For the majority of receivables, a provision for uncollectible accounts is established based on historical collection experience and other factors. For the remaining receivables, if the company is aware of a specific customer's inability to pay, a provision for uncollectible accounts is recorded to reduce the receivable balance to the amount reasonably expected to be collected. If circumstances change, the estimate of the recoverability of accounts receivable could change as well. Circumstances that could affect this estimate include, but are not limited to, customer credit issues, customer deposits, and general economic conditions. Customers' accounts are written off once they are deemed to be uncollectible. For all periods presented, uncollectible accounts averaged less than 1% of revenues for each Registrant. Credit risk exposure at Nicor Gas is mitigated by a bad debt rider approved by the Illinois Commission. The bad debt rider provides for the recovery from (or refund to) customers of the difference between Nicor Gas' actual bad debt experience on an annual basis and the benchmark bad debt expense used to establish its base rates for the respective year.
Financial Instruments	Financial Instruments The traditional electric operating companies and Southern Power use derivative financial instruments to limit exposure to fluctuations in interest rates, the prices of certain fuel purchases, electricity purchases and sales, and occasionally foreign currency exchange rates. Southern Company Gas uses derivative financial instruments to limit exposure to fluctuations in natural gas prices, weather, interest rates, and commodity prices. All derivative financial instruments are recognized as either assets or liabilities on the balance sheets (included in "Other" or shown separately as "Risk Management Activities") and are measured at fair value. See Note 13 for additional information regarding fair value. Substantially all of the traditional electric operating companies' and Southern Power's bulk energy purchases and sales contracts that meet the definition of a derivative are excluded from fair value accounting requirements because they qualify for the "normal" scope exception, and are accounted for under the accrual method. Derivative contracts that qualify as cash flow hedges of anticipated transactions or are recoverable through the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs result in the deferral of related gains and losses in AOCI or regulatory assets and liabilities, respectively, until the hedged transactions occur. Other derivative contracts that qualify as fair value hedges are marked to market through current period income and are recorded on a net basis in the statements of income. Cash flows from derivatives are classified on the statements of cash flows in the same category as the hedged item. See Note 14 for additional information regarding derivatives. The Registrants offset fair value amounts recognized for multiple derivative instruments executed with the same counterparty under netting arrangements. The Registrants had no outstanding collateral repayment obligations or rights to reclaim collateral arising from derivative instruments recognized at December 31, 2020. The Registrants are exposed to potential losses related to financial instruments in the event of counterparties' nonperformance. The Registrants have 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 Southern Company Gas enters into weather derivative contracts as economic hedges of natural gas revenues in the event of warmer-than-normal weather in the Heating Season. Exchange-traded options are carried at fair value, with changes reflected in natural gas revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are also reflected in natural gas revenues in the statements of income. Wholesale gas services purchases natural gas for storage when the current market price paid to buy and transport natural gas plus the cost to store and finance the natural gas is less than the market price that can be received in the future, resulting in positive net natural gas revenues. NYMEX futures and OTC contracts are used to sell natural gas at that future price to substantially protect the natural gas revenues that will ultimately be realized when the stored natural gas is sold. Southern Company Gas enters into transactions to secure transportation capacity between delivery points in order to serve its customers and various markets. NYMEX futures and OTC contracts are used to capture the price differential or spread between the locations served by the capacity in order to substantially protect the natural gas revenues that will ultimately be realized when the physical flow of natural gas between delivery points occurs. These contracts generally meet the definition of derivatives and are carried at fair value on the balance sheets, with changes in fair value recorded in natural gas revenues on the statements of income in the period of change. These contracts are not designated as hedges for accounting purposes. The purchase, transportation, storage, and sale of natural gas are accounted for on a weighted average cost or accrual basis, as appropriate, rather than on the fair value basis utilized for the derivatives used to mitigate the natural gas price risk associated with the storage and transportation portfolio. Monthly demand charges are incurred for the contracted storage and transportation capacity and payments associated with asset management agreements, and these demand charges and payments are recognized on the statements of income in the period they are incurred. This difference in accounting methods can result in volatility in reported earnings, even though the economic margin is substantially unchanged from the dates the transactions were consummated. 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 13 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 under "Financial Instruments" 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 AOCI 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 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. 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.
Comprehensive Income	Comprehensive Income The objective of comprehensive income is to report a measure of all changes in common stock equity of an enterprise that result from transactions and other economic events of the period other than transactions with owners. Comprehensive income consists of net income attributable to the Registrant, changes in the fair value of qualifying cash flow hedges, and reclassifications for amounts included in net income. Comprehensive income also consists of certain changes in pension and other postretirement benefit plans for Southern Company, Southern Power, and Southern Company Gas.
Variable Interest Entities	Variable Interest Entities The Registrants may hold ownership interests in a number of business ventures with varying ownership structures. Partnership interests and other variable interests are evaluated to determine if each entity is a VIE. The primary beneficiary of a VIE is required to consolidate the VIE when it has both the power to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. See Note 7 for additional information regarding VIEs. Alabama Power has established a wholly-owned trust to issue preferred securities. See Note 8 under "Long-term Debt" for additional information. However, Alabama Power is not considered the primary beneficiary of the trust. Therefore, the investment in the trust is reflected as other investments, and the related loan from the trust is reflected as long-term debt in Alabama Power's balance sheets.
Asset Retirement Obligations	AROs are computed as the present value of the estimated costs for an asset's future retirement and are recorded in the period in which the liability is incurred. The estimated costs are capitalized as part of the related long-lived asset and depreciated over the asset's useful life. In the absence of quoted market prices, AROs are estimated using present value techniques in which estimates of future cash outlays associated with the asset retirements are discounted using a credit-adjusted risk-free rate. Estimates of the timing and amounts of future cash outlays are based on projections of when and how the assets will be retired and the cost of future removal activities. Each traditional electric operating company and natural gas distribution utility has received accounting guidance from its state PSC or applicable state regulatory agency allowing the continued accrual or recovery of other retirement costs for long-lived assets that it does not have a legal obligation to retire. Accordingly, the accumulated removal costs for these obligations are reflected in the balance sheets as regulatory liabilities and amounts to be recovered are reflected in the balance sheets as regulatory assets. The ARO liabilities for the traditional electric operating companies primarily relate to facilities that are subject to the CCR Rule and the related state rules, principally ash ponds. In addition, Alabama Power and Georgia Power have retirement obligations related to the decommissioning of nuclear facilities (Alabama Power's Plant Farley and Georgia Power's ownership interests in Plant Hatch and Plant Vogtle Units 1 and 2). See "Nuclear Decommissioning" herein for additional information. Other significant AROs include various landfill sites and asbestos removal for Alabama Power, Georgia Power, and Mississippi Power and gypsum cells and mine reclamation for Mississippi Power. The ARO liability for Southern Power primarily relates to its solar and wind facilities, which are located on long-term land leases requiring the restoration of land at the end of the lease. The traditional electric operating companies and Southern Company Gas also have identified other retirement obligations, such as obligations related to certain electric transmission and distribution facilities, certain asbestos-containing material within long-term assets not subject to ongoing repair and maintenance activities, certain wireless communication towers, the disposal of polychlorinated biphenyls in certain transformers, leasehold improvements, equipment on customer property, and property associated with the Southern Company system's rail lines and natural gas pipelines. However, liabilities for the removal of these assets have not been recorded because the settlement timing for certain retirement obligations related to these assets is indeterminable and, therefore, the fair value of the retirement obligations cannot be reasonably estimated. A liability for these retirement obligations will be recognized when sufficient information becomes available to support a reasonable estimation of the ARO. Southern Company and the traditional electric operating companies will continue to recognize in their respective statements of income allowed removal costs in accordance with regulatory treatment. Any differences between costs recognized in accordance with accounting standards related to asset retirement and environmental obligations and those reflected in rates are recognized as either a regulatory asset or liability in the balance sheets as ordered by the various state PSCs. Details of the AROs included in the balance sheets are as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (*) (in millions) Balance at December 31, 2018 $ 9,394 $ 3,210 $ 5,829 $ 160 $ 84 Liabilities incurred 37 — 35 1 1 Liabilities settled (328) (127) (151) (35) — Accretion 402 145 243 7 4 Cash flow revisions 281 312 (172) 57 — Balance at December 31, 2019 $ 9,786 $ 3,540 $ 5,784 $ 190 $ 89 Liabilities incurred 19 — 10 — 9 Liabilities settled (442) (219) (185) (22) — Accretion 409 152 238 8 4 Cash flow revisions 912 501 418 — (7) Balance at December 31, 2020 $ 10,684 $ 3,974 $ 6,265 $ 176 $ 95 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. During 2019, Alabama Power recorded increases totaling approximately $312 million to its AROs primarily related to the CCR Rule and the related state rule based on management's completion of closure designs during the second and third quarters 2019 under the planned closure-in-place methodology for all but one of its ash pond facilities. During 2019, Mississippi Power recorded an increase of approximately $57 million to its AROs related to the CCR Rule, primarily associated with the ash pond facility at Plant Greene County, which is jointly owned with Alabama Power. During 2020, Alabama Power recorded increases totaling approximately $501 million to its AROs related to the CCR Rule and the related state rule primarily as a result of management's completion of the closure design for the remaining ash pond and the addition of a water treatment system to the design of another ash pond. The additional estimated costs to close these ash ponds under the planned closure-in-place methodology primarily relate to inputs from contractor bids, design revisions, and changes in the expected volume of ash handling. During the second half of 2019, Georgia Power completed an assessment of its plans to close the ash ponds at all of its generating plants in compliance with the CCR Rule and the related state rule. Cost estimates were revised to reflect further refined costs for closure plans and updates to the timing of future cash outlays. As a result, in December 2019, Georgia Power recorded a decrease of approximately $174 million to its AROs related to the CCR Rule and the related state rule. During the third quarter 2020, Georgia Power further refined the related cost estimates, including updates to long-term post-closure care requirements, market pricing, and timing of future cash outlays. As a result, in September 2020, Georgia Power recorded an increase of approximately $411 million to its AROs related to the CCR Rule and the related state rule. The cost estimates for AROs related to the disposal of CCR are based on information at December 31, 2020 using various assumptions related to closure and post-closure costs, timing of future cash outlays, inflation and discount rates, and the potential methods for complying with the CCR Rule and the related state rules. The traditional electric operating companies have periodically updated, and expect to continue periodically updating, their related cost estimates and ARO liabilities for each CCR unit as additional information related to these assumptions becomes available. Some of these updates have been, and future updates may be, material. Additionally, the closure designs and plans in the States of Alabama and Georgia are subject to approval by environmental regulatory agencies. Absent continued recovery of ARO costs through regulated rates, results of operations, cash flows, and financial condition for Southern Company and the traditional electric operating companies could be materially impacted. See Note 2 under "Georgia Power – Rate Plans" for additional information. The ultimate outcome of these matters cannot be determined at this time.
Nuclear Decommissioning	Nuclear Decommissioning The NRC requires licensees of commercial nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. Alabama Power and Georgia Power have external trust funds (Funds) to comply with the NRC's regulations. Use of the Funds is restricted to nuclear decommissioning activities. The Funds are managed and invested in accordance with applicable requirements of various regulatory bodies, including the NRC, the FERC, and state PSCs, as well as the IRS. While Alabama Power and Georgia Power are allowed to prescribe an overall investment policy to the Funds' managers, neither Southern Company nor its subsidiaries or affiliates are allowed to engage in the day-to-day management of the Funds or to mandate individual investment decisions. Day-to-day management of the investments in the Funds is delegated to unrelated third-party managers with oversight by the management of Alabama Power and Georgia Power. The Funds' managers are authorized, within certain investment guidelines, to actively buy and sell securities at their own discretion in order to maximize the return on the Funds' investments. The Funds are invested in a tax-efficient manner in a diversified mix of equity and fixed income securities and are reported as trading securities. Alabama Power and Georgia Power record the investment securities held in the Funds at fair value, as disclosed in Note 13, as management believes that fair value best represents the nature of the Funds. Gains and losses, whether realized or unrealized, are recorded in the regulatory liability for AROs in the balance sheets and are not included in net income or OCI. Fair value adjustments and realized gains and losses are determined on a specific identification basis. The Funds at Georgia Power participate in a securities lending program through the managers of the Funds. Under this program, Georgia Power's Funds' investment securities are loaned to institutional investors for a fee. Securities loaned are fully collateralized by cash, letters of credit, and/or securities issued or guaranteed by the U.S. government or its agencies or instrumentalities. At December 31, 2020 and 2019, approximately $44 million and $28 million, respectively, of the fair market value of Georgia Power's Funds' securities were on loan and pledged to creditors under the Funds' managers' securities lending program. The fair value of the collateral received was approximately $45 million and $29 million at December 31, 2020 and 2019, respectively, and can only be sold by the borrower upon the return of the loaned securities. The collateral received is treated as a non-cash item in the statements of cash flows. Investment securities in the Funds for December 31, 2020 and 2019 were as follows: Southern Company Alabama Georgia (in millions) At December 31, 2020: Equity securities $ 1,339 $ 842 $ 497 Debt securities 851 231 620 Other securities 111 83 28 Total investment securities in the Funds $ 2,301 $ 1,156 $ 1,145 At December 31, 2019: Equity securities $ 1,159 $ 743 $ 416 Debt securities 798 218 580 Other securities 77 60 17 Total investment securities in the Funds $ 2,034 $ 1,021 $ 1,013 These amounts exclude receivables related to investment income and pending investment sales and payables related to pending investment purchases. For Southern Company and Georgia Power, these amounts include Georgia Power's investment securities pledged to creditors and collateral received and excludes payables related to Georgia Power's securities lending program. The fair value increases (decreases) of the Funds, including unrealized gains (losses) and reinvested interest and dividends and excluding the Funds' expenses, for 2020, 2019, and 2018 are shown in the table below. Southern Company Alabama Georgia (in millions) Fair value increases (decreases) 2020 $ 280 $ 142 $ 138 2019 344 194 150 2018 (67) (38) (29) Unrealized gains (losses) At December 31, 2020 $ 220 $ 121 $ 99 At December 31, 2019 259 149 110 At December 31, 2018 (183) (96) (87) The investment securities held in the Funds continue to be managed with a long-term focus. Accordingly, all purchases and sales within the Funds are presented separately in the statements of cash flows as investing cash flows, consistent with the nature of the securities and purpose for which the securities were acquired. For Alabama Power, approximately $15 million and $16 million at December 31, 2020 and 2019, respectively, previously recorded in internal reserves is being transferred into the Funds through 2040 as approved by the Alabama PSC. The NRC's minimum external funding requirements are based on a generic estimate of the cost to decommission only the radioactive portions of a nuclear unit based on the size and type of reactor. Alabama Power and Georgia Power have filed plans with the NRC designed to ensure that, over time, the deposits and earnings of the Funds will provide the minimum funding amounts prescribed by the NRC. At December 31, 2020 and 2019, the accumulated provisions for the external decommissioning trust funds were as follows: 2020 2019 (in millions) Alabama Power Plant Farley $ 1,156 $ 1,021 Georgia Power Plant Hatch $ 716 $ 634 Plant Vogtle Units 1 and 2 429 379 Total $ 1,145 $ 1,013 Site study cost is the estimate to decommission a specific facility as of the site study year. The decommissioning cost estimates are based on prompt dismantlement and removal of the plant from service. The actual decommissioning costs may vary from these estimates because of changes in the assumed date of decommissioning, changes in NRC requirements, or changes in the assumptions used in making these estimates. The estimated costs of decommissioning at December 31, 2020 based on the most current studies, which were each performed in 2018, were as follows: Plant Plant Hatch (*) Plant Vogtle Units 1 and 2 (*) Decommissioning periods: Beginning year 2037 2034 2047 Completion year 2076 2075 2079 (in millions) Site study costs: Radiated structures $ 1,234 $ 734 $ 601 Spent fuel management 387 172 162 Non-radiated structures 99 56 79 Total site study costs $ 1,720 $ 962 $ 842 (*) Based on Georgia Power's ownership interests. For ratemaking purposes, Alabama Power's decommissioning costs are based on the site study and Georgia Power's decommissioning costs are based on the NRC generic estimate to decommission the radioactive portion of the facilities and the site study estimate for spent fuel management as of 2018. Significant assumptions used to determine these costs for ratemaking were an estimated inflation rate of 4.5% and 2.75% for Alabama Power and Georgia Power, respectively, and an estimated trust earnings rate of 7.0% and 4.75% for Alabama Power and Georgia Power, respectively. Amounts previously contributed to the Funds for Plant Farley are currently projected to be adequate to meet the decommissioning obligations. Alabama Power will continue to provide site-specific estimates of the decommissioning costs and related projections of funds in the external trust to the Alabama PSC and, if necessary, would seek the Alabama PSC's approval to address any changes in a manner consistent with NRC and other applicable requirements. Effective January 1, 2020, in connection with the 2019 ARP, Georgia Power's annual decommissioning cost for ratemaking is a total of $4 million for Plant Hatch and Plant Vogtle Units 1 and 2. Georgia Power's annual decommissioning cost for ratemaking in 2019 totaled $5 million.
Fair Value Measurement	Fair value measurements are based on inputs of observable and unobservable market data that a market participant would use in pricing the asset or liability. The use of observable inputs is maximized where available and the use of unobservable inputs is minimized for fair value measurement and reflects a three-tier fair value hierarchy that prioritizes inputs to valuation techniques used for fair value measurement. • Level 1 consists of observable market data in an active market for identical assets or liabilities. • Level 2 consists of observable market data, other than that included in Level 1, that is either directly or indirectly observable. • Level 3 consists of unobservable market data. The input may reflect the assumptions of each Registrant of what a market participant would use in pricing an asset or liability. If there is little available market data, then each Registrant's own assumptions are the best available information. In the case of multiple inputs being used in a fair value measurement, the lowest level input that is significant to the fair value measurement represents the level in the fair value hierarchy in which the fair value measurement is reported. 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 14 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 under "Nuclear Decommissioning" 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.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of costs for affiliate transactions	Costs for these services from SCS in 2020, 2019, and 2018 were as follows: Alabama Georgia Mississippi Southern Southern Company Gas (in millions) 2020 $ 478 $ 639 $ 149 $ 87 $ 237 2019 527 704 118 90 183 2018 508 653 104 98 194 Mississippi Southern (in millions) 2020 $ 4 $ 8 2019 3 14 2018 15 41 Alabama Georgia Southern Southern Company Gas (in millions) 2020 $ 15 $ 108 $ 29 $ 29 2019 17 99 28 31 2018 8 101 25 32 Georgia Southern (in millions) 2020 $ — $ 26 2019 4 64 2018 21 119 2020 2019 2018 Alabama Power 2.6 % 3.1 % 3.0 % Georgia Power 3.0 % 2.6 % 2.6 % Mississippi Power 3.7 % 3.7 % 4.2 % Southern Company Gas 2.8 % 2.9 % 2.9 %
Schedule of concentration of revenue	The following table shows the percentage of total revenues for Southern Power's top three customers for each of the years presented: 2020 2019 2018 Southern California Edison 9.4 % 6.8 % 6.2 % Georgia Power 8.0 % 9.0 % 9.8 % Duke Energy Corporation 6.7 % N/A 6.8 % Morgan Stanley Capital Group N/A 4.9 % N/A
Schedule of total AFUDC and interest capitalized	Total AFUDC and interest capitalized for the Registrants in 2020, 2019, and 2018 was as follows: Southern Company Alabama Georgia (*) Mississippi Southern Southern Company Gas (in millions) 2020 $ 230 $ 61 $ 138 $ 1 $ 11 $ 18 2019 202 71 103 — 15 13 2018 210 84 94 — 17 14 (*) See Note 2 under "Georgia Power – Nuclear Construction" for information on the inclusion of a portion of construction costs related to Plant Vogtle Units 3 and 4 in Georgia Power's rate base.
Schedule of average AFUDC composite rates	The average AFUDC composite rates for 2020, 2019, and 2018 for the traditional electric operating companies and the natural gas distribution utilities were as follows: 2020 2019 2018 Alabama Power 8.1 % 8.4 % 8.3 % Georgia Power (*) 6.9 % 6.9 % 7.3 % Mississippi Power 5.4 % 7.3 % 3.3 % Southern Company Gas: Atlanta Gas Light 7.7 % 7.8 % 7.9 % Chattanooga Gas 7.1 % 7.1 % 7.4 % Nicor Gas 0.7 % 2.3 % 2.1 % (*) Excludes AFUDC related to the construction of Plant Vogtle Units 3 and 4. See Note 2 under "Georgia Power – Nuclear Construction" for additional information.
Schedule of goodwill balances	At December 31, 2020 and 2019, goodwill 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 intangible assets subject to amortization	At December 31, 2020 and 2019, other intangible assets were as follows: At December 31, 2020 At December 31, 2019 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 $ (135) $ 77 $ 212 $ (116) $ 96 Trade names 64 (31) 33 64 (25) 39 Storage and transportation contracts 64 (64) — 64 (62) 2 PPA fair value adjustments 390 (89) 301 390 (69) 321 Other 10 (9) 1 11 (8) 3 Total other intangible assets subject to amortization $ 740 $ (328) $ 412 $ 741 $ (280) $ 461 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 815 $ (328) $ 487 $ 816 $ (280) $ 536 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (89) $ 301 $ 390 $ (69) $ 321 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (119) $ 37 $ 156 $ (104) $ 52 Trade names 26 (12) 14 26 (10) 16 Wholesale gas services Storage and transportation contracts 64 (64) — 64 (62) 2 Total other intangible assets subject to amortization $ 246 $ (195) $ 51 $ 246 $ (176) $ 70
Schedule of intangible assets not subject to amortization	At December 31, 2020 and 2019, other intangible assets were as follows: At December 31, 2020 At December 31, 2019 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 $ (135) $ 77 $ 212 $ (116) $ 96 Trade names 64 (31) 33 64 (25) 39 Storage and transportation contracts 64 (64) — 64 (62) 2 PPA fair value adjustments 390 (89) 301 390 (69) 321 Other 10 (9) 1 11 (8) 3 Total other intangible assets subject to amortization $ 740 $ (328) $ 412 $ 741 $ (280) $ 461 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 815 $ (328) $ 487 $ 816 $ (280) $ 536 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 390 $ (89) $ 301 $ 390 $ (69) $ 321 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (119) $ 37 $ 156 $ (104) $ 52 Trade names 26 (12) 14 26 (10) 16 Wholesale gas services Storage and transportation contracts 64 (64) — 64 (62) 2 Total other intangible assets subject to amortization $ 246 $ (195) $ 51 $ 246 $ (176) $ 70
Schedule of amortization associated with other intangible assets	Amortization associated with other intangible assets in 2020, 2019, and 2018 was as follows: 2020 2019 2018 (in millions) Southern Company (a) $ 49 $ 61 $ 89 Southern Power (b) 20 19 25 Southern Company Gas: Gas marketing services $ 17 $ 23 $ 32 Wholesale gas services (b) 2 8 20 Southern Company Gas total $ 19 $ 31 $ 52 (a) Includes $22 million, $27 million, and $45 million in 2020, 2019, and 2018, respectively, recorded as a reduction to operating revenues. (b) Recorded as a reduction to operating revenues.
Schedule of amortization of other intangible assets	At December 31, 2020, the estimated amortization associated with other intangible assets for the next five years is as follows: 2021 2022 2023 2024 2025 (in millions) Southern Company $ 43 $ 39 $ 37 $ 35 $ 32 Southern Power 20 20 20 20 20 Southern Company Gas 14 11 9 7 6
Schedule of storm damage reserves	In accordance with their respective state PSC orders, the traditional electric operating companies accrued the following amounts related to storm damage recovery in 2020, 2019, and 2018: Southern Company (a)(b) Alabama (b) Georgia Mississippi (in millions) 2020 $ 326 $ 112 $ 213 $ 1 2019 170 139 30 1 2018 74 16 30 1 (a) Includes accruals at Gulf Power of $26.9 million in 2018. See Note 15 under "Southern Company" for information regarding the sale of Gulf Power. (b) Includes $39 million applied in 2019 to Alabama Power's NDR from its remaining excess deferred income tax regulatory liability balance in accordance with an Alabama PSC order.
Schedule of net investment in domestic and international leveraged leases	Southern Company's net investment in leveraged leases consists of the following at December 31: 2020 (*) 2019 (in millions) Net rentals receivable $ 734 $ 1,410 Unearned income (178) (622) Investment in leveraged leases 556 788 Deferred taxes from leveraged leases (7) (238) Net investment in leveraged leases $ 549 $ 550 (*) Excludes the investment classified as held for sale at December 31, 2020. See Note 15 under "Assets Held for Sale" for additional information.
Summary of the components of income from leveraged leases	The following table provides a summary of the components of income related to leveraged lease investments. Income was impacted in 2020 and 2019 by the impairment charges discussed in Note 3 under "Other Matters – Southern Company." 2020 2019 2018 (in millions) Pretax leveraged lease income (loss) $ (180) $ 11 $ 25 Income tax benefit (expense) 98 — (6) Net leveraged lease income (loss) $ (82) $ 11 $ 19
Schedule of AOCI (loss) balances, net of tax effects	AOCI (loss) balances, net of tax effects, for Southern Company, Southern Power, and Southern Company Gas were as follows: Qualifying Pension and Other Accumulated Other (in millions) Southern Company Balance at December 31, 2019 $ (179) $ (142) $ (321) Current period change (30) (45) (75) Balance at December 31, 2020 (*) $ (209) $ (187) $ (395) Southern Power Balance at December 31, 2019 $ 11 $ (37) $ (26) Current period change (32) (10) (42) Balance at December 31, 2020 (*) $ (21) $ (47) $ (67) Southern Company Gas Balance at December 31, 2019 $ (6) $ 13 $ 7 Current period change (14) (15) (29) Balance at December 31, 2020 $ (20) $ (2) $ (22) (*) May not add due to rounding.

REGULATORY MATTERS (Tables)

REGULATORY MATTERS (Tables)	12 Months Ended
	Dec. 31, 2020
Regulated Operations [Abstract]
Schedule of regulatory assets	Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2020 and 2019 are provided in the following tables: Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2020 AROs (a)(s) $ 5,147 $ 1,470 $ 3,457 $ 212 $ — Retiree benefit plans (b)(s) 4,958 1,265 1,647 238 187 Remaining net book value of retired assets (c) 1,183 632 527 24 — Deferred income tax charges (d) 801 235 531 32 — Environmental remediation (e)(s) 310 — 41 — 269 Loss on reacquired debt (f) 304 47 248 6 3 Storm damage (g) 262 — 262 — — Vacation pay (h)(s) 207 80 104 10 13 Under recovered regulatory clause revenues (i) 185 58 — 52 75 Regulatory clauses (j) 142 142 — — — Nuclear outage (k) 101 61 40 — — Long-term debt fair value adjustment (l) 92 — — — 92 Kemper County energy facility assets, net (m) 50 — — 50 — Plant Daniel Units 3 and 4 (n) 32 — — 32 — Other regulatory assets (o) 205 52 68 4 81 Deferred income tax credits (d) (6,016) (2,016) (2,805) (320) (847) Other cost of removal obligations (a) (1,999) (335) 212 (194) (1,649) Over recovered regulatory clause revenues (i) (185) (46) (44) — (95) Storm/property damage reserves (p) (81) (77) — (4) — Customer refunds (q) (56) (50) (6) — — Other regulatory liabilities (r) (149) (37) (30) (6) (54) Total regulatory assets (liabilities), net $ 5,493 $ 1,481 $ 4,252 $ 136 $ (1,925) Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2019 Retiree benefit plans (b)(s) $ 4,423 $ 1,131 $ 1,516 $ 213 $ 167 AROs (a)(s) 4,381 1,043 3,119 210 — Remaining net book value of retired assets (c) 1,275 649 596 30 — Deferred income tax charges (d) 803 245 523 33 — Storm damage (g) 410 — 410 — — Environmental remediation (e)(s) 349 — 52 — 296 Loss on reacquired debt (f) 323 52 262 6 4 Vacation pay (h)(s) 186 72 93 9 11 Under recovered regulatory clause revenues (i) 159 40 — 47 72 Regulatory clauses (j) 142 142 — — — Long-term debt fair value adjustment (l) 107 — — — 107 Nuclear outage (k) 105 78 27 — — Fuel-hedging (realized and unrealized) losses (t) 102 22 53 27 — Kemper County energy facility assets, net (m) 61 — — 61 — Plant Daniel Units 3 and 4 (n) 34 — — 34 — Other regulatory assets (o) 127 45 23 6 53 Deferred income tax credits (d) (6,301) (1,960) (3,078) (358) (874) Other cost of removal obligations (a) (2,084) (412) 156 (189) (1,606) Customer refunds (q) (285) (56) (229) — — Over recovered regulatory clause revenues (i) (205) (112) (10) — (82) Storm/property damage reserves (p) (204) (150) — (55) — Other regulatory liabilities (r) (70) (19) (6) (10) (22) Total regulatory assets (liabilities), net $ 3,838 $ 810 $ 3,507 $ 64 $ (1,874) Unless otherwise noted, the following recovery and amortization periods for these regulatory assets and (liabilities) have been approved by the respective state PSC or regulatory agency: (a) AROs and other cost of removal obligations generally are recorded over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. AROs and cost of removal obligations will be settled and trued up following completion of the related activities. Effective January 1, 2020, Georgia Power is recovering CCR AROs, including past under recovered costs and estimated annual compliance costs, over three-year periods ending December 31, 2022, 2023, and 2024 through its Environmental Compliance Cost Recovery (ECCR) tariff, as discussed further under "Georgia Power – Rate Plans" herein. See Note 6 for additional information on AROs. (b) Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power, 13 years for Georgia Power, 14 years for Mississippi Power, and 13 years for Southern Company Gas. Southern Company's balances also include amounts at SCS and Southern Nuclear that are allocated to the applicable regulated utilities. See Note 11 for additional information. (c) Alabama Power : Primarily represents the net book value of Plant Gorgas Units 8, 9, and 10 ($585 million at December 31, 2020). Being amortized over remaining periods not exceeding 17 years (through 2037). Georgia Power : Net book values of Plant Hammond Units 1 through 4 and Plant Branch Units 2 through 4 (totaling $503 million at December 31, 2020) are being amortized over remaining periods of between two Mississippi Power : Represents net book value associated with Plant Watson and Plant Greene County. The retail and wholesale portions totaling approximately $11 million and $13 million at December 31, 2020, respectively, are being amortized over a four-year period through 2024 and a 10-year period through 2030, respectively. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d) Deferred income tax charges are recovered and deferred income tax credits are amortized over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. See Note 10 for additional information. Included in the deferred income tax charges are amounts ($8 million, $9 million, and $1 million for Alabama Power, Georgia Power, and Mississippi Power, respectively, at December 31, 2020) for the retiree Medicare drug subsidy, which are being recovered and amortized through 2027, 2022, and 2024 for Alabama Power, Georgia Power, and Mississippi Power, respectively. As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, as described further below: Alabama Power: Related amounts are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts at December 31, 2020 include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $440 million of deferred income tax liabilities. The recovery of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 is expected to be determined in a future regulatory proceeding. Effective January 1, 2020, the deferred income tax liabilities are being amortized through 2022. Mississippi Power: Related amounts at December 31, 2020 include $74 million of deferred income tax liabilities, consisting of the retail portion of $66 million being amortized over three years (through 2023) and the wholesale portion of $9 million being amortized over two years (through 2021). See "Mississippi Power – 2019 Base Rate Case" and " – Municipal and Rural Associations Tariff" herein for additional information. Southern Company Gas : Related amounts at December 31, 2020 include $8 million of deferred income tax liabilities, which are being amortized through 2024. See "Southern Company Gas – Rate Proceedings" herein for additional information. (e) Georgia Power is recovering $12 million annually for environmental remediation. Southern Company Gas' costs are recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 under "Environmental Remediation" for additional information. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2020, the remaining amortization periods do not exceed 28 years for Alabama Power, 32 years for Georgia Power, eight years for Mississippi Power, and seven years for Southern Company Gas. (g) Georgia Power is recovering approximately $213 million annually for storm damage. See "Georgia Power – Storm Damage Recovery" herein and Note 1 under "Storm Damage Reserves" for additional information. (h) Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (i) Alabama Power : Balances are recorded monthly and expected to be recovered or returned within nine years. Recovery periods could change based on several factors including changes in cost estimates, load forecasts, and timing of rate adjustments. See "Alabama Power – Rate CNP PPA," " – Rate CNP Compliance," and " – Rate ECR" herein for additional information. Georgia Power : Balances are recorded monthly and expected to be recovered or returned within two years. See "Georgia Power – Rate Plans" herein for additional information. Mississippi Power : At December 31, 2020, $37 million is being amortized over a four-yea Southern Company Gas : Balances are recorded and recovered or amortized over periods generally not exceeding five years. In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities have various other cost recovery mechanisms for the recovery of costs, including those related to infrastructure replacement programs. (j) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2023. (k) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent period of 18 months for Alabama Power and up to 24 months for Georgia Power. See Note 5 for additional information. (l) Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 18 years at December 31, 2020. (m) Includes $62 million of regulatory assets and $12 million of regulatory liabilities at December 31, 2020. The retail portion includes $50 million of regulatory assets and $12 million of regulatory liabilities that are expected to be fully amortized by 2024 and 2023, respectively. The wholesale portion includes $12 million of regulatory assets that are expected to be fully amortized by 2029. See Note 3 under "Mississippi Power – Other Matters – Kemper County Energy Facility" for additional information. (n) Represents the difference between Mississippi Power's revenue requirement for Plant Daniel Units 3 and 4 under purchase accounting and operating lease accounting, which is expected to be amortized over a period to be determined in future retail and wholesale rate filings. (o) Except as otherwise noted, comprised of numerous immaterial components with remaining amortization periods generally not exceeding 23 years for Alabama Power, three years for Georgia Power, four years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. Balances at December 31, 2020 include deferred COVID-19 costs (except for Alabama Power), as discussed further under "Deferral of Incremental COVID-19 Costs" for each applicable Registrant herein. Balances for Georgia Power also include certain operations and maintenance costs associated with software and cloud computing projects for which the recovery period will be determined in its next base rate case. (p) Amortized as related expenses are incurred. See "Alabama Power – Rate NDR" and "Mississippi Power – System Restoration Rider" herein for additional information. (q) Primarily includes approximately $50 million and $53 million at December 31, 2020 and 2019, respectively, for Alabama Power and $110 million at December 31, 2019 for Georgia Power as a result of each company exceeding its allowed retail return range. Georgia Power's December 31, 2019 balance also includes approximately $105 million pursuant to the Georgia Power Tax Reform Settlement Agreement. Georgia Power's balances also include immaterial amounts related to refunds for transmission service customers. See "Alabama Power" and "Georgia Power – Rate Plans" herein for additional information. (r) Comprised of numerous immaterial components with remaining amortization periods generally not exceeding 17 years for Alabama Power, 12 years for Georgia Power, three years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. (s) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. (t) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts. Upon final settlement, actual costs incurred are recovered through the applicable traditional electric operating company's fuel cost recovery mechanism. Purchase contracts generally do not exceed three and a half years for Alabama Power, three years for Georgia Power, and five years for Mississippi Power. Immaterial amounts at December 31, 2020 are included in other regulatory assets and liabilities. The following table illustrates Southern Company Gas' authorized ratemaking amounts that are not recognized on its balance sheets. These amounts are primarily composed of an allowed equity rate of return on assets associated with certain regulatory infrastructure programs. These amounts will be recognized as revenues in Southern Company Gas' financial statements in the periods they are billable to customers, the majority of which will be recovered by 2025. December 31, 2020 December 31, 2019 (in millions) Atlanta Gas Light $ 59 $ 70 Virginia Natural Gas 10 10 Nicor Gas 3 2 Total $ 72 $ 82
Schedule of regulatory liabilities	Details of regulatory assets and (liabilities) reflected in the balance sheets at December 31, 2020 and 2019 are provided in the following tables: Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2020 AROs (a)(s) $ 5,147 $ 1,470 $ 3,457 $ 212 $ — Retiree benefit plans (b)(s) 4,958 1,265 1,647 238 187 Remaining net book value of retired assets (c) 1,183 632 527 24 — Deferred income tax charges (d) 801 235 531 32 — Environmental remediation (e)(s) 310 — 41 — 269 Loss on reacquired debt (f) 304 47 248 6 3 Storm damage (g) 262 — 262 — — Vacation pay (h)(s) 207 80 104 10 13 Under recovered regulatory clause revenues (i) 185 58 — 52 75 Regulatory clauses (j) 142 142 — — — Nuclear outage (k) 101 61 40 — — Long-term debt fair value adjustment (l) 92 — — — 92 Kemper County energy facility assets, net (m) 50 — — 50 — Plant Daniel Units 3 and 4 (n) 32 — — 32 — Other regulatory assets (o) 205 52 68 4 81 Deferred income tax credits (d) (6,016) (2,016) (2,805) (320) (847) Other cost of removal obligations (a) (1,999) (335) 212 (194) (1,649) Over recovered regulatory clause revenues (i) (185) (46) (44) — (95) Storm/property damage reserves (p) (81) (77) — (4) — Customer refunds (q) (56) (50) (6) — — Other regulatory liabilities (r) (149) (37) (30) (6) (54) Total regulatory assets (liabilities), net $ 5,493 $ 1,481 $ 4,252 $ 136 $ (1,925) Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) At December 31, 2019 Retiree benefit plans (b)(s) $ 4,423 $ 1,131 $ 1,516 $ 213 $ 167 AROs (a)(s) 4,381 1,043 3,119 210 — Remaining net book value of retired assets (c) 1,275 649 596 30 — Deferred income tax charges (d) 803 245 523 33 — Storm damage (g) 410 — 410 — — Environmental remediation (e)(s) 349 — 52 — 296 Loss on reacquired debt (f) 323 52 262 6 4 Vacation pay (h)(s) 186 72 93 9 11 Under recovered regulatory clause revenues (i) 159 40 — 47 72 Regulatory clauses (j) 142 142 — — — Long-term debt fair value adjustment (l) 107 — — — 107 Nuclear outage (k) 105 78 27 — — Fuel-hedging (realized and unrealized) losses (t) 102 22 53 27 — Kemper County energy facility assets, net (m) 61 — — 61 — Plant Daniel Units 3 and 4 (n) 34 — — 34 — Other regulatory assets (o) 127 45 23 6 53 Deferred income tax credits (d) (6,301) (1,960) (3,078) (358) (874) Other cost of removal obligations (a) (2,084) (412) 156 (189) (1,606) Customer refunds (q) (285) (56) (229) — — Over recovered regulatory clause revenues (i) (205) (112) (10) — (82) Storm/property damage reserves (p) (204) (150) — (55) — Other regulatory liabilities (r) (70) (19) (6) (10) (22) Total regulatory assets (liabilities), net $ 3,838 $ 810 $ 3,507 $ 64 $ (1,874) Unless otherwise noted, the following recovery and amortization periods for these regulatory assets and (liabilities) have been approved by the respective state PSC or regulatory agency: (a) AROs and other cost of removal obligations generally are recorded over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. AROs and cost of removal obligations will be settled and trued up following completion of the related activities. Effective January 1, 2020, Georgia Power is recovering CCR AROs, including past under recovered costs and estimated annual compliance costs, over three-year periods ending December 31, 2022, 2023, and 2024 through its Environmental Compliance Cost Recovery (ECCR) tariff, as discussed further under "Georgia Power – Rate Plans" herein. See Note 6 for additional information on AROs. (b) Recovered and amortized over the average remaining service period, which may range up to 13 years for Alabama Power, 13 years for Georgia Power, 14 years for Mississippi Power, and 13 years for Southern Company Gas. Southern Company's balances also include amounts at SCS and Southern Nuclear that are allocated to the applicable regulated utilities. See Note 11 for additional information. (c) Alabama Power : Primarily represents the net book value of Plant Gorgas Units 8, 9, and 10 ($585 million at December 31, 2020). Being amortized over remaining periods not exceeding 17 years (through 2037). Georgia Power : Net book values of Plant Hammond Units 1 through 4 and Plant Branch Units 2 through 4 (totaling $503 million at December 31, 2020) are being amortized over remaining periods of between two Mississippi Power : Represents net book value associated with Plant Watson and Plant Greene County. The retail and wholesale portions totaling approximately $11 million and $13 million at December 31, 2020, respectively, are being amortized over a four-year period through 2024 and a 10-year period through 2030, respectively. See "Mississippi Power – Environmental Compliance Overview Plan" herein for additional information. (d) Deferred income tax charges are recovered and deferred income tax credits are amortized over the related property lives, which may range up to 53 years for Alabama Power, 60 years for Georgia Power, 55 years for Mississippi Power, and 80 years for Southern Company Gas. See Note 10 for additional information. Included in the deferred income tax charges are amounts ($8 million, $9 million, and $1 million for Alabama Power, Georgia Power, and Mississippi Power, respectively, at December 31, 2020) for the retiree Medicare drug subsidy, which are being recovered and amortized through 2027, 2022, and 2024 for Alabama Power, Georgia Power, and Mississippi Power, respectively. As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, as described further below: Alabama Power: Related amounts are being recovered and amortized ratably over the related property lives. Georgia Power: Related amounts at December 31, 2020 include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $440 million of deferred income tax liabilities. The recovery of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 is expected to be determined in a future regulatory proceeding. Effective January 1, 2020, the deferred income tax liabilities are being amortized through 2022. Mississippi Power: Related amounts at December 31, 2020 include $74 million of deferred income tax liabilities, consisting of the retail portion of $66 million being amortized over three years (through 2023) and the wholesale portion of $9 million being amortized over two years (through 2021). See "Mississippi Power – 2019 Base Rate Case" and " – Municipal and Rural Associations Tariff" herein for additional information. Southern Company Gas : Related amounts at December 31, 2020 include $8 million of deferred income tax liabilities, which are being amortized through 2024. See "Southern Company Gas – Rate Proceedings" herein for additional information. (e) Georgia Power is recovering $12 million annually for environmental remediation. Southern Company Gas' costs are recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 under "Environmental Remediation" for additional information. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2020, the remaining amortization periods do not exceed 28 years for Alabama Power, 32 years for Georgia Power, eight years for Mississippi Power, and seven years for Southern Company Gas. (g) Georgia Power is recovering approximately $213 million annually for storm damage. See "Georgia Power – Storm Damage Recovery" herein and Note 1 under "Storm Damage Reserves" for additional information. (h) Recorded as earned by employees and recovered as paid, generally within one year. Includes both vacation and banked holiday pay, if applicable. (i) Alabama Power : Balances are recorded monthly and expected to be recovered or returned within nine years. Recovery periods could change based on several factors including changes in cost estimates, load forecasts, and timing of rate adjustments. See "Alabama Power – Rate CNP PPA," " – Rate CNP Compliance," and " – Rate ECR" herein for additional information. Georgia Power : Balances are recorded monthly and expected to be recovered or returned within two years. See "Georgia Power – Rate Plans" herein for additional information. Mississippi Power : At December 31, 2020, $37 million is being amortized over a four-yea Southern Company Gas : Balances are recorded and recovered or amortized over periods generally not exceeding five years. In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities have various other cost recovery mechanisms for the recovery of costs, including those related to infrastructure replacement programs. (j) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2023. (k) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent period of 18 months for Alabama Power and up to 24 months for Georgia Power. See Note 5 for additional information. (l) Recovered over the remaining lives of the original debt issuances at acquisition, which range up to 18 years at December 31, 2020. (m) Includes $62 million of regulatory assets and $12 million of regulatory liabilities at December 31, 2020. The retail portion includes $50 million of regulatory assets and $12 million of regulatory liabilities that are expected to be fully amortized by 2024 and 2023, respectively. The wholesale portion includes $12 million of regulatory assets that are expected to be fully amortized by 2029. See Note 3 under "Mississippi Power – Other Matters – Kemper County Energy Facility" for additional information. (n) Represents the difference between Mississippi Power's revenue requirement for Plant Daniel Units 3 and 4 under purchase accounting and operating lease accounting, which is expected to be amortized over a period to be determined in future retail and wholesale rate filings. (o) Except as otherwise noted, comprised of numerous immaterial components with remaining amortization periods generally not exceeding 23 years for Alabama Power, three years for Georgia Power, four years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. Balances at December 31, 2020 include deferred COVID-19 costs (except for Alabama Power), as discussed further under "Deferral of Incremental COVID-19 Costs" for each applicable Registrant herein. Balances for Georgia Power also include certain operations and maintenance costs associated with software and cloud computing projects for which the recovery period will be determined in its next base rate case. (p) Amortized as related expenses are incurred. See "Alabama Power – Rate NDR" and "Mississippi Power – System Restoration Rider" herein for additional information. (q) Primarily includes approximately $50 million and $53 million at December 31, 2020 and 2019, respectively, for Alabama Power and $110 million at December 31, 2019 for Georgia Power as a result of each company exceeding its allowed retail return range. Georgia Power's December 31, 2019 balance also includes approximately $105 million pursuant to the Georgia Power Tax Reform Settlement Agreement. Georgia Power's balances also include immaterial amounts related to refunds for transmission service customers. See "Alabama Power" and "Georgia Power – Rate Plans" herein for additional information. (r) Comprised of numerous immaterial components with remaining amortization periods generally not exceeding 17 years for Alabama Power, 12 years for Georgia Power, three years for Mississippi Power, and 20 years for Southern Company Gas at December 31, 2020. (s) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. (t) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts. Upon final settlement, actual costs incurred are recovered through the applicable traditional electric operating company's fuel cost recovery mechanism. Purchase contracts generally do not exceed three and a half years for Alabama Power, three years for Georgia Power, and five years for Mississippi Power. Immaterial amounts at December 31, 2020 are included in other regulatory assets and liabilities.
Schedule of revised cost and schedule	Georgia Power's approximate proportionate share of the remaining estimated capital cost to complete Plant Vogtle Units 3 and 4 by the expected in-service dates of November 2021 and November 2022, respectively, is as follows: (in billions) Base project capital cost forecast (a)(b) $ 8.5 Construction contingency estimate 0.2 Total project capital cost forecast (a)(b) 8.7 Net investment as of December 31, 2020 (b) (7.2) Remaining estimate to complete (a) $ 1.5 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $246 million, of which $93 million had been accrued through December 31, 2020. (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related customer refunds.
Public utilities general disclosures	In December 2019, the Georgia PSC voted to approve the 2019 ARP, under which Georgia Power increased its rates on January 1, 2020. On December 15, 2020, the Georgia PSC approved tariff adjustments effective January 1, 2021. Details of tariff adjustments are provided in the table below: Tariff 2020 2021 (in millions) Traditional base $ — $ 120 ECCR (*) 318 2 DSM 12 (15) MFF 12 4 Total $ 342 $ 111 (*) Effective January 1, 2020, CCR AROs are being recovered through the ECCR tariff. The following table provides regulatory information for Southern Company Gas' natural gas distribution utilities: Nicor Gas Atlanta Gas Light Virginia Natural Gas Chattanooga Gas Authorized ROE (a) 9.73% 10.25% 9.50% 9.80% Weather normalization mechanisms (b) ü ü Decoupled, including straight-fixed-variable rates (c) ü ü ü Regulatory infrastructure program rates (d) ü ü Bad debt rider (e) ü ü ü Energy efficiency plan (f) ü ü Annual base rate adjustment mechanism (g) ü ü Year of last base rate case decision 2019 2019 2017 2018 (a) Represents the authorized ROE, or the mid-point of the authorized ROE range, at December 31, 2020. (b) Designed to help stabilize operating results by allowing recovery of costs in the event of unseasonal weather, but are not direct offsets to the potential impacts on earnings of weather and customer consumption. (c) Allows for recovery of fixed customer service costs separately from assumed natural gas volumes used by customers and provides a benchmark level of revenue for recovery. (d) Programs that update or expand distribution systems and LNG facilities. (e) The recovery (refund) of bad debt expense over (under) an established benchmark expense. The gas portion of bad debt expense is recovered through purchased gas adjustment mechanisms. Nicor Gas also has a rider to recover the non-gas portion of bad debt expense. (f) Recovery of costs associated with plans to achieve specified energy savings goals. (g) Regulatory mechanism allowing annual adjustments to base rates up or down based on authorized ROE and/or ROE range. The following table and discussions provide updates on the infrastructure replacement programs and capital projects at the natural gas distribution utilities at December 31, 2020. These programs are risk-based and designed to update and replace cast iron, bare steel, and mid-vintage plastic materials or expand Southern Company Gas' distribution systems to improve reliability and meet operational flexibility and growth. Utility Program Recovery Expenditures in 2020 Expenditures Since Project Inception Pipe Scope of Program Duration Last (in millions) (miles) (miles) (years) Nicor Gas Investing in Illinois (*) Rider $ 389 $ 2,101 996 1,450 9 2023 Virginia Natural Gas Steps to Advance Virginia's Energy (SAVE) Rider 49 293 413 770 13 2024 Total $ 438 $ 2,394 1,409 2,220

CONTINGENCIES, COMMITMENTS, A_2

CONTINGENCIES, COMMITMENTS, AND GUARANTEES (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of regulatory assets and liabilities	At December 31, 2020 and 2019, the environmental remediation liability and the balance of under recovered environmental remediation costs were reflected in the balance sheets as follows: Southern Company Georgia Southern Company Gas (in millions) December 31, 2020: Environmental remediation liability: Other current liabilities $ 44 $ 15 $ 29 Accrued environmental remediation 216 — 216 Under recovered environmental remediation costs: Other regulatory assets, current $ 46 $ 12 $ 34 Other regulatory assets, deferred 265 29 236 December 31, 2019: Environmental remediation liability: Other current liabilities $ 51 $ 15 $ 36 Accrued environmental remediation 234 — 233 Under recovered environmental remediation costs: Other regulatory assets, current $ 49 $ 12 $ 37 Other regulatory assets, deferred 300 40 260
Expected future contractual obligations	Southern Company Gas' expected future contractual obligations for pipeline charges, storage capacity, and gas supply that are not recognized on the balance sheets at December 31, 2020 were as follows: Pipeline Charges, Storage Capacity, and Gas Supply (in millions) 2021 $ 719 2022 529 2023 441 2024 311 2025 285 Thereafter 1,035 Total $ 3,320

REVENUE FROM CONTRACTS WITH C_2

REVENUE FROM CONTRACTS WITH CUSTOMERS (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	The following table disaggregates revenue from contracts with customers for the periods presented: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Operating revenues Retail electric revenues Residential $ 6,113 $ 2,377 $ 3,476 $ 260 $ — $ — Commercial 4,699 1,512 2,933 254 — — Industrial 2,775 1,293 1,197 285 — — Other 90 21 60 9 — — Total retail electric revenues 13,677 5,203 7,666 808 — — Natural gas distribution revenues Residential 1,338 — — — — 1,338 Commercial 340 — — — — 340 Transportation 971 — — — — 971 Industrial 30 — — — — 30 Other 209 — — — — 209 Total natural gas distribution revenues 2,888 — — — — 2,888 Wholesale electric revenues PPA energy revenues 735 133 42 9 570 — PPA capacity revenues 454 108 50 3 296 — Non-PPA revenues 210 43 10 311 239 — Total wholesale electric revenues 1,399 284 102 323 1,105 — Other natural gas revenues Wholesale gas services 1,727 — — — — 1,727 Gas marketing services 391 — — — — 391 Other natural gas revenues 33 — — — — 33 Total natural gas revenues 2,151 — — — — 2,151 Other revenues 982 159 447 26 14 — Total revenue from contracts with customers 21,097 5,646 8,215 1,157 1,119 5,039 Other revenue sources (a) 3,764 184 94 15 614 2,881 Other adjustments (b) (4,486) — — — — (4,486) Total operating revenues $ 20,375 $ 5,830 $ 8,309 $ 1,172 $ 1,733 $ 3,434 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2019 Operating revenues Retail electric revenues Residential $ 6,164 $ 2,509 $ 3,377 $ 278 $ — $ — Commercial 5,065 1,677 3,097 291 — — Industrial 3,126 1,460 1,360 306 — — Other 90 25 54 11 — — Total retail electric revenues 14,445 5,671 7,888 886 — — Natural gas distribution revenues Residential 1,413 — — — — 1,413 Commercial 389 — — — — 389 Transportation 907 — — — — 907 Industrial 35 — — — — 35 Other 245 — — — — 245 Total natural gas distribution revenues 2,989 — — — — 2,989 Wholesale electric revenues PPA energy revenues 833 145 60 11 648 — PPA capacity revenues 453 102 54 3 322 — Non-PPA revenues 232 81 9 352 238 — Total wholesale electric revenues 1,518 328 123 366 1,208 — Other natural gas revenues Gas pipeline investments 32 — — — — 32 Wholesale gas services 2,095 — — — — 2,095 Gas marketing services 440 — — — — 440 Other natural gas revenues 42 — — — — 42 Total other natural gas revenues 2,609 — — — — 2,609 Other revenues 1,035 153 407 19 12 — Total revenue from contracts with customers 22,596 6,152 8,418 1,271 1,220 5,598 Other revenue sources (a) 4,266 (27) (10) (7) 718 3,637 Other adjustments (b) (5,443) — — — — (5,443) Total operating revenues $ 21,419 $ 6,125 $ 8,408 $ 1,264 $ 1,938 $ 3,792 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2018 Operating revenues Retail electric revenues Residential $ 6,586 $ 2,285 $ 3,295 $ 277 $ — $ — Commercial 5,255 1,541 3,025 290 — — Industrial 3,152 1,364 1,321 326 — — Other 94 25 56 9 — — Total retail electric revenues 15,087 5,215 7,697 902 — — Natural gas distribution revenues Residential 1,525 — — — — 1,525 Commercial 436 — — — — 436 Transportation 944 — — — — 944 Industrial 40 — — — — 40 Other 230 — — — — 230 Total natural gas distribution revenues 3,175 — — — — 3,175 Wholesale electric revenues PPA energy revenues 950 158 81 15 727 — PPA capacity revenues 498 101 53 6 394 — Non-PPA revenues 263 119 24 329 230 — Total wholesale electric revenues 1,711 378 158 350 1,351 — Other natural gas revenues Gas pipeline investments 32 — — — — 32 Wholesale gas services 3,083 — — — — 3,083 Gas marketing services 571 — — — — 571 Other natural gas revenues 53 — — — — 53 Total other natural gas revenues 3,739 — — — — 3,739 Other revenues 1,529 210 236 22 13 — Total revenue from contracts with customers 25,241 5,803 8,091 1,274 1,364 6,914 Other revenue sources (a) 5,108 229 329 (9) 841 3,849 Other adjustments (b) (6,854) — — — — (6,854) Total operating revenues $ 23,495 $ 6,032 $ 8,420 $ 1,265 $ 2,205 $ 3,909 (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 16 under "Southern Company Gas" for additional information on the components of wholesale gas services' operating revenues.
Contract with customer, asset and liability	The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at December 31, 2020 and 2019: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivables As of December 31, 2020 $ 2,614 $ 632 $ 806 $ 77 $ 112 $ 788 As of December 31, 2019 2,413 586 688 79 97 749 Contract Assets As of December 31, 2020 $ 158 $ 2 $ 71 $ — $ — $ — As of December 31, 2019 117 — 69 — — — Contract Liabilities As of December 31, 2020 $ 61 $ 6 $ 27 $ 1 $ 1 $ 1 As of December 31, 2019 52 10 13 — 1 1 The following table reflects revenue from contracts with customers recognized in 2020 and 2019 included in the contract liability at December 31, 2019 and December 31, 2018, respectively, for the applicable Registrants: Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) Revenue Recognized 2020 $ 33 $ 10 $ 8 $ 1 $ 1 2019 30 11 6 11 2
Revenue, remaining performance obligation, expected timing of satisfaction	Revenues from contracts with customers related to these performance obligations remaining at December 31, 2020 are expected to be recognized as follows: 2021 2022 2023 2024 2025 Thereafter (in millions) Southern Company $ 547 $ 395 $ 338 $ 326 $ 306 $ 2,634 Alabama Power 33 31 24 7 5 — Georgia Power 75 46 35 24 21 42 Southern Power 285 287 280 296 280 2,610

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property, plant and equipment	The Registrants' property, plant, and equipment in service consisted of the following at December 31, 2020 and 2019: At December 31, 2020: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 52,179 $ 16,201 $ 18,675 $ 2,819 $ 13,872 $ — Transmission 12,879 5,033 6,951 856 — — Distribution 20,958 8,248 11,622 1,088 — — General/other 5,072 2,334 2,434 248 32 — Electric utilities' plant in service 91,088 31,816 39,682 5,011 13,904 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 14,610 — — — — 14,610 Storage facilities 1,752 — — — — 1,752 Other 1,249 — — — — 1,249 Southern Company Gas plant in service 17,611 — — — — 17,611 Other plant in service 1,817 — — — — — Total plant in service $ 110,516 $ 31,816 $ 39,682 $ 5,011 $ 13,904 $ 17,611 At December 31, 2019: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 50,329 $ 15,329 $ 18,341 $ 2,786 $ 13,241 $ — Transmission 12,157 4,719 6,590 808 — — Distribution 19,846 7,798 11,024 1,024 — — General/other 4,650 2,177 2,182 239 29 — Electric utilities' plant in service 86,982 30,023 38,137 4,857 13,270 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 13,518 — — — — 13,518 Storage facilities 1,634 — — — — 1,634 Other 1,192 — — — — 1,192 Southern Company Gas plant in service 16,344 — — — — 16,344 Other plant in service 1,788 — — — — — Total plant in service $ 105,114 $ 30,023 $ 38,137 $ 4,857 $ 13,270 $ 16,344 Southern Power Generating Facility Useful life Natural gas Up to 50 years (*) Solar Up to 35 years Wind Up to 30 years (*) Effective January 1, 2020, Southern Power revised the depreciable lives of its natural gas generating facilities from up to 45 years to up to 50 years. This revision resulted in an immaterial decrease in depreciation for 2020.
Deferred cloud implementation costs	At December 31, 2020, deferred cloud implementation costs, which are generally included in other deferred charges and assets on the Registrants' balance sheets, are as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) At December 31, 2020: Deferred cloud implementation costs $ 162 $ 38 $ 58 $ 7 $ 9 $ 17
Composite straight-line rates	Costs for these services from SCS in 2020, 2019, and 2018 were as follows: Alabama Georgia Mississippi Southern Southern Company Gas (in millions) 2020 $ 478 $ 639 $ 149 $ 87 $ 237 2019 527 704 118 90 183 2018 508 653 104 98 194 Mississippi Southern (in millions) 2020 $ 4 $ 8 2019 3 14 2018 15 41 Alabama Georgia Southern Southern Company Gas (in millions) 2020 $ 15 $ 108 $ 29 $ 29 2019 17 99 28 31 2018 8 101 25 32 Georgia Southern (in millions) 2020 $ — $ 26 2019 4 64 2018 21 119 2020 2019 2018 Alabama Power 2.6 % 3.1 % 3.0 % Georgia Power 3.0 % 2.6 % 2.6 % Mississippi Power 3.7 % 3.7 % 4.2 % Southern Company Gas 2.8 % 2.9 % 2.9 %
Ownership and investment in jointly-owned facilities	At December 31, 2020, the Registrants' percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation were as follows: Facility (Type) Percent Plant in Service Accumulated CWIP (in millions) Alabama Power Greene County (natural gas) Units 1 and 2 60.0 % (a) $ 189 $ 76 $ 2 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,107 650 24 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,352 $ 624 $ 37 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,592 2,221 55 Plant Scherer (coal) Units 1 and 2 8.4 (c) 279 98 1 Plant Scherer (coal) Unit 3 75.0 (c) 1,320 520 4 Plant Wansley (coal) 53.5 (c) 1,068 418 10 Rocky Mountain (pumped storage) 25.4 (d) 183 144 1 Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 122 $ 54 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 775 238 15 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 271 $ 15 $ — (a) Jointly owned by Alabama Power and Mississippi Power and operated and maintained by Alabama Power. (b) Jointly owned with PowerSouth and operated and maintained by Alabama Power. (c) Georgia Power owns undivided interests in Plants Hatch, Vogtle Units 1 and 2, Scherer, and Wansley in varying amounts jointly with one or more of the following entities: OPC, MEAG Power, Dalton, Florida Power & Light Company, JEA, and Gulf Power. Georgia Power has been contracted to operate and maintain the plants as agent for the co-owners and is jointly and severally liable for third party claims related to these plants. (d) Jointly owned with OPC, which is the operator of the plant. (e) Jointly owned by Gulf Power and Mississippi Power. In accordance with the operating agreement, Mississippi Power acts as Gulf Power's agent with respect to the operation and maintenance of these units. See Note 3 under "Other Matters – Mississippi Power – Plant Daniel" for information regarding a commitment between Mississippi Power and Gulf Power to seek a restructuring of their 50% undivided ownership interests in Plant Daniel. (f) Jointly owned with The Williams Companies, Inc., the Dalton Pipeline is a 115-mile natural gas pipeline that serves as an extension of the Transcontinental Gas Pipe Line Company, LLC pipeline system into northwest Georgia. Southern Company Gas leases its 50% undivided ownership for approximately $26 million annually through 2042. The lessee is responsible for maintaining the pipeline during the lease term and for providing service to transportation customers under its FERC-regulated tariff.

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
Details of AROs included in the balance sheets	Details of the AROs included in the balance sheets are as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (*) (in millions) Balance at December 31, 2018 $ 9,394 $ 3,210 $ 5,829 $ 160 $ 84 Liabilities incurred 37 — 35 1 1 Liabilities settled (328) (127) (151) (35) — Accretion 402 145 243 7 4 Cash flow revisions 281 312 (172) 57 — Balance at December 31, 2019 $ 9,786 $ 3,540 $ 5,784 $ 190 $ 89 Liabilities incurred 19 — 10 — 9 Liabilities settled (442) (219) (185) (22) — Accretion 409 152 238 8 4 Cash flow revisions 912 501 418 — (7) Balance at December 31, 2020 $ 10,684 $ 3,974 $ 6,265 $ 176 $ 95 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets.
Investment securities in the Funds	Investment securities in the Funds for December 31, 2020 and 2019 were as follows: Southern Company Alabama Georgia (in millions) At December 31, 2020: Equity securities $ 1,339 $ 842 $ 497 Debt securities 851 231 620 Other securities 111 83 28 Total investment securities in the Funds $ 2,301 $ 1,156 $ 1,145 At December 31, 2019: Equity securities $ 1,159 $ 743 $ 416 Debt securities 798 218 580 Other securities 77 60 17 Total investment securities in the Funds $ 2,034 $ 1,021 $ 1,013
Fair value increases (decreases) of the Funds	The fair value increases (decreases) of the Funds, including unrealized gains (losses) and reinvested interest and dividends and excluding the Funds' expenses, for 2020, 2019, and 2018 are shown in the table below. Southern Company Alabama Georgia (in millions) Fair value increases (decreases) 2020 $ 280 $ 142 $ 138 2019 344 194 150 2018 (67) (38) (29) Unrealized gains (losses) At December 31, 2020 $ 220 $ 121 $ 99 At December 31, 2019 259 149 110 At December 31, 2018 (183) (96) (87) At December 31, 2020, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 401 $ 271 $ 32 $ — $ 704 Interest rate derivatives — 20 — — 20 Foreign currency derivatives — 87 — — 87 Investments in trusts: (b)(c) Domestic equity 862 151 — — 1,013 Foreign equity 85 253 — — 338 U.S. Treasury and government agency securities — 284 — — 284 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 13 386 — — 399 Mortgage and asset backed securities — 83 — — 83 Private equity — — — 76 76 Cash and cash equivalents 1 — — — 1 Other 28 7 — — 35 Cash equivalents 575 9 — — 584 Other investments 9 24 — — 33 Total $ 1,974 $ 1,677 $ 32 $ 76 $ 3,759 Liabilities: Energy-related derivatives (a) $ 389 $ 204 $ 4 $ — $ 597 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ 389 $ 227 $ 21 $ — $ 637 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Nuclear decommissioning trusts: (b) Domestic equity 543 141 — — 684 Foreign equity 85 73 — — 158 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 13 167 — — 180 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 76 76 Other 7 — — — 7 Cash equivalents 311 9 — — 320 Other investments — 24 — — 24 Total $ 959 $ 477 $ — $ 76 $ 1,512 Liabilities: Energy-related derivatives $ — $ 7 $ — $ — $ 7 Georgia Power Assets: Energy-related derivatives $ — $ 15 $ — $ — $ 15 Nuclear decommissioning trusts: (b)(c) Domestic equity 319 1 — — 320 Foreign equity — 177 — — 177 U.S. Treasury and government agency securities — 263 — — 263 Municipal bonds — 84 — — 84 Corporate bonds — 219 — — 219 Mortgage and asset backed securities — 54 — — 54 Other 21 7 — — 28 Total $ 340 $ 820 $ — $ — $ 1,160 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Cash equivalents 21 — — — 21 Total $ 21 $ 9 $ — $ — $ 30 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Foreign currency derivatives — 87 — — 87 Total $ — $ 89 $ — $ — $ 89 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ — $ 26 $ 17 $ — $ 43 Southern Company Gas Assets: Energy-related derivatives (a) $ 401 $ 233 $ 32 $ — $ 666 Non-qualified deferred compensation trusts: Domestic equity — 9 — — 9 Foreign equity — 3 — — 3 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Total $ 402 $ 262 $ 32 $ — $ 696 Liabilities: Energy-related derivatives (a)(b) $ 389 $ 172 $ 4 $ — $ 565 (a) Excludes $6 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $28 million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information. At December 31, 2019, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (b)(c) Domestic equity 751 135 — — 886 Foreign equity 68 220 — — 288 U.S. Treasury and government agency securities — 307 — — 307 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 23 297 — — 320 Mortgage and asset backed securities — 87 — — 87 Private equity — — — 56 56 Cash and cash equivalents 1 — — — 1 Other 17 5 — — 22 Cash equivalents 1,393 2 — — 1,395 Other investments 9 21 — — 30 Total $ 2,650 $ 1,461 $ 22 $ 56 $ 4,189 Liabilities: Energy-related derivatives (a) $ 442 $ 254 $ 7 $ — $ 703 Interest rate derivatives — 24 — — 24 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ 442 $ 302 $ 26 $ — $ 770 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b) Domestic equity 488 123 — — 611 Foreign equity 68 64 — — 132 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 23 144 — — 167 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 56 56 Other 3 1 — — 4 Cash equivalents 691 2 — — 693 Other investments — 21 — — 21 Total $ 1,273 $ 410 $ — $ 56 $ 1,739 Liabilities: Energy-related derivatives $ — $ 24 $ — $ — $ 24 Georgia Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b)(c) Domestic equity 263 1 — — 264 Foreign equity — 152 — — 152 U.S. Treasury and government agency securities — 286 — — 286 Municipal bonds — 84 — — 84 Corporate bonds — 153 — — 153 Mortgage and asset backed securities — 57 — — 57 Other 13 4 — — 17 Total $ 276 $ 741 $ — $ — $ 1,017 Liabilities: Energy-related derivatives $ — $ 53 $ — $ — $ 53 Interest rate derivatives — 17 — — 17 Total $ — $ 70 $ — $ — $ 70 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Cash equivalents 281 — — — 281 Total $ 281 $ 1 $ — $ — $ 282 Liabilities: Energy-related derivatives $ — $ 27 $ — $ — $ 27 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 16 — — 16 Cash equivalents 113 — — — 113 Total $ 113 $ 19 $ — $ — $ 132 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ — $ 27 $ 19 $ — $ 46 Southern Company Gas Assets: Energy-related derivatives (a) $ 388 $ 255 $ 22 $ — $ 665 Interest rate derivatives — 2 — — 2 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Cash equivalents 8 — — — 8 Total $ 397 $ 289 $ 22 $ — $ 708 Liabilities: Energy-related derivatives (a)(b) $ 442 $ 147 $ 7 $ — $ 596 (a) Excludes $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $99 million. (c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information.
Accumulated provisions for the external decommissioning trust funds	At December 31, 2020 and 2019, the accumulated provisions for the external decommissioning trust funds were as follows: 2020 2019 (in millions) Alabama Power Plant Farley $ 1,156 $ 1,021 Georgia Power Plant Hatch $ 716 $ 634 Plant Vogtle Units 1 and 2 429 379 Total $ 1,145 $ 1,013
Estimated costs of decommissioning	The estimated costs of decommissioning at December 31, 2020 based on the most current studies, which were each performed in 2018, were as follows: Plant Plant Hatch (*) Plant Vogtle Units 1 and 2 (*) Decommissioning periods: Beginning year 2037 2034 2047 Completion year 2076 2075 2079 (in millions) Site study costs: Radiated structures $ 1,234 $ 734 $ 601 Spent fuel management 387 172 162 Non-radiated structures 99 56 79 Total site study costs $ 1,720 $ 962 $ 842 (*) Based on Georgia Power's ownership interests.

CONSOLIDATED ENTITIES AND EQU_2

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Equity method investments	The carrying amounts of Southern Company Gas' equity method investments at December 31, 2020 and 2019 and related income from those investments for the years ended December 31, 2020, 2019, and 2018 were as follows: Investment Balance 2020 2019 (a) (in millions) SNG (b) $ 1,167 $ 1,137 PennEast Pipeline (c) 91 82 Other 32 32 Total $ 1,290 $ 1,251 (a) Excludes investments in Atlantic Coast Pipeline and Pivotal JAX LNG classified as held for sale at December 31, 2019. See Note 15 under "Assets Held for Sale" for additional information. (b) Increase primarily relates to a capital contribution, partially offset by the continued amortization of deferred tax assets established upon acquisition. (c) See Note 3 under "Other Matters – Southern Company Gas" for additional information.
Equity method investments related income	Earnings from Equity Method Investments 2020 2019 2018 (in millions) SNG $ 129 $ 141 $ 131 Atlantic Coast Pipeline (a)(b) 3 13 7 PennEast Pipeline (a) 7 6 5 Other (c) 2 (3) 5 Total $ 141 $ 157 $ 148 (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 interest in Atlantic Coast Pipeline. See Note 15 under "Southern Company Gas" for additional information. (c) In May 2019, Southern Company Gas sold its investment in Triton, a cargo container leasing company that was aggregated into Southern Company Gas' all other segment. On March 24, 2020, Southern Company Gas completed the sale of its interest in Pivotal LNG. See Note 15 under "Southern Company Gas" for additional information.

FINANCING (Tables)

FINANCING (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Summary of long-term debt	Details of long-term debt at December 31, 2020 and 2019 are provided in the following table: At December 31, 2020 Balance Outstanding at Maturity Weighted Average 2020 2019 (in millions) Southern Company Senior notes (a) 2021-2050 3.78% $ 30,850 $ 30,023 Junior subordinated notes 2024-2080 4.30% 7,295 5,295 FFB loans (b) 2021-2044 2.92% 4,618 3,843 Pollution control revenue bonds (c) 2021-2053 1.11% 2,675 2,963 First mortgage bonds (d) 2023-2060 3.71% 1,900 1,575 Other revenue bonds (e) 2021-2040 6.45% 320 320 Debt payable to affiliated trusts (f) 2042 3.33% 206 206 Medium-term notes 2021-2027 7.88% 160 160 Other long-term debt 2021-2023 0.83% 370 145 Finance lease obligations (g) 231 226 Unamortized fair value adjustment 393 430 Unamortized debt premium (discount), net (201) (152) Unamortized debt issuance expenses (237) (247) Total long-term debt 48,580 44,787 Less: Amount due within one year 3,507 2,989 Total long-term debt excluding amount due within one year $ 45,073 $ 41,798 Alabama Power Senior notes 2021-2049 4.03% $ 7,625 $ 7,275 Pollution control revenue bonds (c) 2021-2038 0.53% 1,060 1,060 Debt payable to affiliated trusts (f) 2042 3.33% 206 206 Other long-term debt 2021 1.20% 45 45 Finance lease obligations (g) 5 4 Unamortized debt premium (discount), net (16) (14) Unamortized debt issuance expenses (56) (55) Total long-term debt 8,869 8,521 Less: Amount due within one year 311 251 Total long-term debt excluding amount due within one year $ 8,558 $ 8,270 Georgia Power Senior notes 2021-2050 3.59% $ 6,400 $ 5,850 Junior subordinated notes 2077 5.00% 270 270 FFB loans (b) 2021-2044 2.92% 4,618 3,843 Pollution control revenue bonds (c) 2025-2053 1.47% 1,538 1,821 Other long-term debt 2021 0.65% 125 — Finance lease obligations (g) 145 156 Unamortized debt premium (discount), net (12) (7) Unamortized debt issuance expenses (114) (117) Total long-term debt 12,970 11,816 Less: Amount due within one year 542 1,025 Total long-term debt excluding amount due within one year $ 12,428 $ 10,791 At December 31, 2020 Balance Outstanding at Maturity Weighted Average 2020 2019 (in millions) Mississippi Power Senior notes 2028-2042 4.23% $ 900 $ 1,175 Pollution control revenue bonds (c) 2025-2028 1.86% 76 83 Other revenue bonds (e) 2021-2040 6.45% 320 320 Other long-term debt 2021-2023 1.00% 100 — Finance lease obligations (g) 19 — Unamortized debt premium (discount), net 11 19 Unamortized debt issuance expenses (7) (8) Total long-term debt 1,419 1,589 Less: Amount due within one year 406 281 Total long-term debt excluding amount due within one year $ 1,013 $ 1,308 Southern Power Senior notes (a) 2021-2046 3.96% $ 3,714 $ 4,425 Unamortized debt premium (discount), net (6) (8) Unamortized debt issuance expenses (16) (19) Total long-term debt 3,692 4,398 Less: Amount due within one year 299 824 Total long-term debt excluding amount due within one year $ 3,393 $ 3,574 Southern Company Gas Senior notes 2021-2047 4.01% $ 4,200 $ 3,700 First mortgage bonds (d) 2023-2060 3.71% 1,900 1,575 Medium-term notes 2021-2027 7.88% 160 160 Unamortized fair value adjustment 393 430 Unamortized debt premium (discount), net (27) (20) Total long-term debt 6,626 5,845 Less: Amount due within one year 333 — Total long-term debt excluding amount due within one year $ 6,293 $ 5,845 (a) Includes a fair value gain (loss) of $109 million and $(5) million at December 31, 2020 and 2019, respectively, related to Southern Power's foreign currency hedge on its €1.1 billion senior notes. (b) Secured by a first priority lien on (i) Georgia Power's 45.7% undivided ownership interest in Plant Vogtle Units 3 and 4 (primarily the units under construction, the related real property, and any nuclear fuel loaded in the reactor core) and (ii) Georgia Power's rights and obligations under the principal contracts relating to Plant Vogtle Units 3 and 4. See "DOE Loan Guarantee Borrowings" for additional information. (c) Pollution control revenue bond obligations represent loans to the traditional electric operating companies from public authorities of funds derived from sales by such authorities of revenue bonds issued to finance pollution control and solid waste disposal facilities. In some cases, the pollution control revenue bond obligations represent obligations under installment sales agreements with respect to facilities constructed with the proceeds of revenue bonds issued by public authorities. The traditional electric operating companies are required to make payments sufficient for the authorities to meet principal and interest requirements of such bonds. Proceeds from certain issuances are restricted until qualifying expenditures are incurred. (d) Secured by substantially all of Nicor Gas' properties. (e) At December 31, 2020 and 2019, Mississippi Power had $270 million aggregate principal amount outstanding of Mississippi Business Finance Corporation Taxable Revenue Bonds, 7.13% Series 1999A due October 20, 2021, which are secured by Plant Daniel Units 3 and 4 and certain related personal property. Mississippi Power assumed the obligations in 2011 in connection with its election under its operating lease of Plant Daniel Units 3 and 4 to purchase the assets and recorded the bonds at fair value. At December 31, 2020 and 2019, Mississippi Power also had $50 million of tax-exempt revenue bond obligations outstanding representing loans to Mississippi Power through the Mississippi Business Finance Corporation issued to finance a portion of the costs of constructing the Kemper County energy facility. (f) Alabama Power has formed a wholly-owned trust subsidiary for the purpose of issuing preferred securities. The proceeds of the related equity investments and preferred security sales were loaned back to Alabama Power through the issuance of junior subordinated notes, which constitute substantially all of the assets of this trust. Alabama Power considers that the mechanisms and obligations relating to the preferred securities issued for its benefit, taken together, constitute a full and unconditional guarantee by it of the trust's payment obligations with respect to these securities. See Note 1 under "Variable Interest Entities" for additional information on the accounting treatment for this trust and the related securities. (g) Secured by the underlying lease ROU asset. See Note 9 for additional information.
Schedule of maturities of long-term debt for the next five years	Maturities of long-term debt for the next five years are as follows: Southern Company (a) Alabama Power Georgia Power (b) Mississippi Power (c) Southern Power (d) Southern Company (in millions) 2021 $ 3,506 $ 311 $ 542 $ 406 $ 300 $ 330 2022 3,707 751 488 16 677 46 2023 3,131 301 889 1 290 400 2024 509 22 491 1 — — 2025 1,191 250 138 12 500 300 (a) Amount for 2022 includes junior subordinated notes totaling $1.725 billion at the parent entity with final maturity dates in 2024 and 2027 (one half in each year); however, in connection with related stock purchase contracts, Southern Company has agreed to remarket the notes in 2022. See "Equity Units" herein for additional information. Also see notes (b), (c), and (d) below. (b) Amounts include principal amortization related to the FFB borrowings; however, the final maturity date is February 20, 2044. See "DOE Loan Guarantee Borrowings" herein for additional information. (c) Amount for 2021 includes $50 million and $25 million of long-term debt with final maturity dates in 2040 and 2023, respectively, that Mississippi Power intends to repay in 2021. (d) Southern Power's 2022 maturity represents euro-denominated debt at the U.S. dollar denominated hedge settlement amount.
Summary of committed credit arrangements	At December 31, 2020, committed credit arrangements with banks were as follows: Expires Company 2021 2022 2023 2024 Total Unused Due within (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) — — — 600 600 591 — Southern Company Gas (b) — — — 1,750 1,750 1,745 — SEGCO 30 — — — 30 30 30 Southern Company $ 33 $ 675 $ 125 $ 6,900 $ 7,733 $ 7,671 $ 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 $5 million and $11 million, respectively, was unused at December 31, 2020. In December 2020, Southern Power amended its $120 million letter of credit facility, which, among other things, extended the expiration date from 2021 to 2023 and reduced the amount to $75 million. 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 $1.25 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 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. See "Structural Considerations" herein for additional information.
Details of short-term borrowings	Details of short-term borrowings for the applicable Registrants were as follows: Notes Payable at December 31, 2020 Notes Payable at December 31, 2019 Amount Weighted Average Amount Weighted Average (in millions) (in millions) Southern Company Commercial paper $ 609 0.3 % $ 1,705 2.1 % Short-term bank debt — — % 350 2.3 % Total $ 609 0.3 % $ 2,055 2.1 % Georgia Power Commercial paper $ 60 0.3 % $ 115 2.1 % Short-term bank debt — — % 250 2.2 % Total $ 60 0.3 % $ 365 2.2 % Mississippi Power Commercial paper $ 25 0.4 % $ — — % Southern Power Commercial paper $ 175 0.3 % $ 449 2.1 % Short-term bank debt — — % 100 2.6 % Total $ 175 0.3 % $ 549 2.2 % Southern Company Gas Commercial paper: Southern Company Gas Capital $ 220 0.3 % $ 372 2.1 % Nicor Gas 104 0.2 % 278 1.8 % Total $ 324 0.2 % $ 650 2.0 %
Shares used to compute diluted EPS	Shares used to compute diluted EPS were as follows: Average Common Stock Shares 2020 2019 2018 (in millions) As reported shares 1,058 1,046 1,020 Effect of stock-based compensation 7 8 5 Diluted shares 1,065 1,054 1,025
Schedule of preferred stock	Information for each outstanding series is in the table below: Preferred Stock Par Value/Stated Capital Per Share Shares Outstanding Redemption 4.92% Preferred Stock $100 80,000 $103.23 4.72% Preferred Stock $100 50,000 $102.18 4.64% Preferred Stock $100 60,000 $103.14 4.60% Preferred Stock $100 100,000 $104.20 4.52% Preferred Stock $100 50,000 $102.93 4.20% Preferred Stock $100 135,115 $105.00 5.00% Class A Preferred Stock $25 10,000,000 $25.00 (*)

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Major categories of lease obligations	The major categories of lease obligations are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Electric generating units $ 941 $ 146 $ 1,368 $ — $ — $ — Real estate/land 815 4 53 2 451 61 Communication towers 158 2 3 — — 20 Railcars 42 16 23 3 — — Other 127 7 5 23 — 1 Total $ 2,083 $ 175 $ 1,452 $ 28 $ 451 $ 82 As of December 31, 2019 Electric generating units $ 990 $ 125 $ 1,487 $ — $ — $ — Real estate/land 782 4 54 2 398 74 Communication towers 154 2 3 — — 18 Railcars 51 21 26 3 — — Other 93 8 12 1 — — Total $ 2,070 $ 160 $ 1,582 $ 6 $ 398 $ 92
Balance sheet amounts recorded for operating and financing leases	Balance sheet amounts recorded for operating and finance leases are as follows: Southern Company Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) As of December 31, 2020 Operating Leases Operating lease ROU assets, net $ 1,802 $ 151 $ 1,308 $ 9 $ 415 $ 81 Operating lease obligations - current $ 241 $ 51 $ 151 $ 2 $ 25 $ 15 Operating lease obligations - non-current 1,611 119 1,156 7 426 67 Total operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance Leases Finance lease ROU assets, net $ 218 $ 5 $ 115 $ 19 $ — $ — Finance lease obligations - current $ 17 $ 1 $ 9 $ 1 $ — $ — Finance lease obligations - non-current 214 4 136 18 — — Total finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ — As of December 31, 2019 Operating Leases Operating lease ROU assets, net $ 1,800 $ 132 $ 1,428 $ 6 $ 369 $ 93 Operating lease obligations - current $ 229 $ 49 $ 144 $ 2 $ 22 $ 14 Operating lease obligations - non-current 1,615 107 1,282 4 376 78 Total operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance Leases Finance lease ROU assets, net $ 216 $ 4 $ 130 $ — $ — $ — Finance lease obligations - current $ 21 $ 1 $ 11 $ — $ — $ — Finance lease obligations - non-current 205 3 145 — — — Total finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ —
Lease costs and other information	Lease costs for 2020 and 2019, which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease cost Operating lease cost $ 309 $ 55 $ 212 $ 3 $ 29 $ 19 Finance lease cost: Amortization of ROU assets 26 1 15 — — — Interest on lease obligations 11 — 16 — — — Total finance lease cost 37 1 31 — — — Short-term lease costs 39 11 26 — — — Variable lease cost 91 4 76 — 7 — Sublease income — (1) — — — — Total lease cost $ 476 $ 70 $ 345 $ 3 $ 36 $ 19 2019 Lease cost Operating lease cost $ 310 $ 54 $ 206 $ 3 $ 28 $ 18 Finance lease cost: Amortization of ROU assets 28 1 15 — — — Interest on lease obligations 12 — 18 — — — Total finance lease cost 40 1 33 — — — Short-term lease costs 48 19 22 — — — Variable lease cost 105 6 85 — 7 — Sublease income — (1) — — — — Total lease cost $ 503 $ 79 $ 346 $ 3 $ 35 $ 18 Rent expense and PPA capacity expense related to leases for 2018, prior to the adoption of ASC 842, were as follows: Southern Company (a)(b)(c) Alabama Georgia (a) Mississippi (b) Southern Power (c) Southern Company Gas (in millions) 2018: Rent expense $ 192 $ 23 $ 34 $ 4 $ 31 $ 15 PPA capacity expense 231 44 206 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million, of which $29 million related to solar PPAs with Southern Power. (b) Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million. (c) Rent expense includes contingent rent expense related to Southern Power's land leases based on wind production and escalation in the Consumer Price Index for All Urban Consumers. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) 2020 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 310 $ 55 $ 215 $ 3 $ 28 $ 18 Operating cash flows from finance leases 9 — 18 — — — Financing cash flows from finance leases 22 1 11 — — — ROU assets obtained in exchange for new operating lease obligations 227 63 32 — 51 4 ROU assets obtained in exchange for new finance lease obligations 10 2 — — — — 2019 Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 323 $ 54 $ 210 $ 3 $ 27 $ 18 Operating cash flows from finance leases 10 — 19 — — — Financing cash flows from finance leases 32 1 13 — — — ROU assets obtained in exchange for new operating lease obligations 118 7 21 — 2 19 ROU assets obtained in exchange for new finance lease obligations 35 2 24 — — — Southern Alabama Georgia Mississippi Southern Power Southern Company Gas As of December 31, 2020 Weighted-average remaining lease term in years: Operating leases 14.5 7.8 9.4 6.5 32.1 9.8 Finance leases 18.2 9.7 9.5 14.9 N/A N/A Weighted-average discount rate: Operating leases 4.44 % 4.14 % 4.37 % 3.26 % 5.45 % 3.67 % Finance leases 4.79 % 3.20 % 10.81 % 2.74 % N/A N/A As of December 31, 2019 Weighted-average remaining lease term in years: Operating leases 14.2 3.1 10.2 7.0 32.8 9.9 Finance leases 18.8 12.1 10.5 N/A N/A N/A Weighted-average discount rate: Operating leases 4.53 % 3.33 % 4.46 % 4.02 % 5.66 % 3.7 % Finance leases 5.04 % 3.60 % 10.76 % N/A N/A N/A
Maturities of operating lease liabilities	Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ —
Maturities of finance lease liabilities	Maturities of lease liabilities are as follows: As of December 31, 2020 Southern Alabama Georgia Mississippi Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2021 $ 300 $ 57 $ 205 $ 2 $ 30 $ 18 2022 287 58 202 4 25 14 2023 230 9 200 1 27 12 2024 187 6 164 1 27 11 2025 165 6 137 — 27 10 Thereafter 1,546 74 701 2 873 35 Total 2,715 210 1,609 10 1,009 100 Less: Present value discount 863 40 302 1 558 18 Operating lease obligations $ 1,852 $ 170 $ 1,307 $ 9 $ 451 $ 82 Finance leases: 2021 $ 28 $ 1 $ 24 $ 2 $ — $ — 2022 25 1 25 1 — — 2023 22 1 25 2 — — 2024 19 1 25 1 — — 2025 16 — 25 2 — — Thereafter 246 1 109 15 — — Total 356 5 233 23 — — Less: Present value discount 125 — 88 4 — — Finance lease obligations $ 231 $ 5 $ 145 $ 19 $ — $ —
Leases not yet commenced	As of December 31, 2020, Southern Power has additional leases that have not yet commenced, as detailed in the following table: Southern Lease category Land Expected commencement date 2021 Longest lease term expiration 30 years Estimated total obligations (in millions) $12
Lease income, operating leases	Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35
Lease income, sales-type leases	Lease income for 2020 and 2019 is as follows: Southern Alabama Power Georgia Power Mississippi Southern Power Southern Company Gas (in millions) 2020 Lease income - interest income on sales-type leases $ 16 $ — $ — $ 12 $ — $ — Lease income - operating leases 208 45 58 2 87 35 Variable lease income 419 — — — 449 — Total lease income $ 643 $ 45 $ 58 $ 14 $ 536 $ 35 2019 Lease income - interest income on sales-type leases $ 9 $ — $ — $ 9 $ — $ — Lease income - operating leases 273 24 71 — 160 35 Variable lease income 403 — — — 434 — Total lease income $ 685 $ 24 $ 71 $ 9 $ 594 $ 35
Undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases	The undiscounted cash flows to be received by Mississippi Power for in-service leased assets under the lease are as follows: At December 31, 2020 (in millions) 2021 $ 20 2022 19 2023 19 2024 18 2025 17 Thereafter 162 Total undiscounted cash flows $ 255 Lease receivable (*) 138 Difference between undiscounted cash flows and discounted cash flows $ 117 (*) Included in other current assets and other property and investments on the balance sheets.
Undiscounted cash flows to be received under PPAs accounted for as operating leases	The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: At December 31, 2020 Southern Alabama Georgia Power Southern Southern Company Gas (in millions) 2021 $ 207 $ 83 $ 19 $ 86 $ 35 2022 187 76 8 87 35 2023 138 32 2 88 34 2024 106 4 — 90 33 2025 99 3 — 74 28 Thereafter 978 23 — 313 435 Total $ 1,715 $ 221 $ 29 $ 738 $ 600

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Details of income tax provisions	Details of income tax provisions are as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ 199 $ 198 $ 365 $ 18 $ (303) $ 82 Deferred 70 44 (224) (14) 299 53 269 242 141 4 (4) 135 State — Current 100 61 60 — (4) 35 Deferred 24 34 (49) 10 11 3 124 95 11 10 7 38 Total $ 393 $ 337 $ 152 $ 14 $ 3 $ 173 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ 156 $ 61 $ 264 $ (6) $ (717) $ (120) Deferred 1,237 125 180 26 647 195 1,393 186 444 20 (70) 75 State — Current 275 12 6 (1) 1 37 Deferred 130 72 22 11 13 18 405 84 28 10 14 55 Total $ 1,798 $ 270 $ 472 $ 30 $ (56) $ 130 2018 Southern Company Alabama Power Georgia Mississippi Southern Power Southern Company Gas (in millions) Federal — Current $ 167 $ 91 $ 393 $ (567) $ 85 $ 334 Deferred 231 123 (249) 575 (154) 33 398 214 144 8 (69) 367 State — Current 188 26 81 (10) (9) 131 Deferred (137) 51 (11) (100) (86) (34) 51 77 70 (110) (95) 97 Total $ 449 $ 291 $ 214 $ (102) $ (164) $ 464
Summary of amortization of tax credits	ITCs amortized in 2020, 2019, and 2018 were immaterial for the traditional electric operating companies and Southern Company Gas and were as follows for Southern Company and Southern Power: Southern Company Southern Power (in millions) 2020 $ 84 $ 59 2019 181 151 2018 87 58
Schedule of effective income tax reconciliation	A reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 2.8 5.0 0.5 4.8 2.7 4.0 Employee stock plans' dividend deduction (0.7) — — — — — Non-deductible book depreciation 0.7 0.6 0.8 0.5 — — Flowback of excess deferred income taxes (8.8) (3.1) (12.0) (18.5) — (2.7) AFUDC-Equity (0.8) (0.6) (1.1) (0.1) — — Federal PTCs — — — — (2.5) — Amortization of ITC (1.6) (0.1) (0.1) (0.1) (22.1) (0.1) Noncontrolling interests — — — — 3.1 — Leveraged lease impairments (1.6) — — — — — Other 0.2 (0.3) (0.3) 0.9 (0.9) 0.5 Effective income tax (benefit) rate 11.2 % 22.5 % 8.8 % 8.5 % 1.3 % 22.7 % 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 4.9 4.9 1.0 4.3 4.0 6.1 Employee stock plans' dividend deduction (0.4) — — — — — Non-deductible book depreciation 0.3 0.6 0.5 0.4 — — Flowback of excess deferred income taxes (2.1) (5.3) — (12.6) — (6.0) AFUDC-Equity (0.4) (0.8) (0.6) (0.1) — — ITC basis difference (0.1) — — — (1.9) — Amortization of ITC (0.8) (0.1) (0.1) (0.1) (16.1) (0.1) Tax impact from sale of subsidiaries 5.1 — — — (27.6) (1.4) Noncontrolling interests — — — — 0.8 — Other — (0.4) (0.3) 4.9 (0.6) (1.4) Effective income tax (benefit) rate 27.5 % 19.9 % 21.5 % 17.8 % (20.4) % 18.2 % 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income tax, net of federal deduction 1.8 5.0 5.5 (65.1) (90.8) 9.2 Employee stock plans' dividend deduction (1.0) — — — — — Non-deductible book depreciation 0.8 0.6 1.2 0.7 — — Flowback of excess deferred income taxes (4.0) (1.8) — (4.1) — (3.0) AFUDC-Equity (1.0) (1.0) (1.4) — — — ITC basis difference (0.6) — — — (0.2) — Federal PTCs (4.7) — — — (156.6) — Amortization of ITC (2.0) (0.1) (0.2) (0.2) (55.4) (0.1) Tax impact from sale of subsidiaries 8.6 — — — — 28.5 Tax Reform Legislation (1.4) — (4.9) (26.3) 96.1 (0.4) Noncontrolling interests (0.4) — — — (14.9) — Other (0.8) (0.1) 0.1 (1.4) 2.0 0.3 Effective income tax (benefit) rate 16.3 % 23.6 % 21.3 % (75.4) % (198.8) % 55.5 %
Tax effects between the carrying amounts of assets and liabilities	The tax effects of temporary differences between the carrying amounts of assets and liabilities in the financial statements of the Registrants and their respective tax bases, which give rise to deferred tax assets and liabilities, are as follows: December 31, 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,950 $ 2,453 $ 3,228 $ 319 $ 1,389 $ 1,349 Property basis differences 1,999 1,010 689 148 — 135 Federal effect of net state deferred tax assets — — — 25 — — Leveraged lease basis differences 142 — — — — — Employee benefit obligations 739 250 362 39 12 26 Premium on reacquired debt 78 12 66 — — — Regulatory assets – Storm damage reserves 80 — 80 — — — Employee benefit obligations 1,313 348 438 62 — 45 Remaining book value of retired assets 270 123 141 6 — — AROs 1,969 764 1,165 40 — — AROs 804 328 429 — — — Other 437 128 82 66 12 138 Total deferred income tax liabilities 16,781 5,416 6,680 705 1,413 1,693 Deferred tax assets — Federal effect of net state deferred tax liabilities 284 151 59 — 26 70 State effect of federal deferred taxes 126 126 — — — — Employee benefit obligations 1,511 369 522 80 6 100 Other property basis differences 223 — 72 — 134 — ITC and PTC carryforward 1,853 12 539 — 1,110 — Long-term debt fair value adjustment 86 — — — — 86 Other partnership basis difference 166 — — — 166 — Other comprehensive losses 128 7 17 — 25 — AROs 2,773 1,092 1,594 40 — — Estimated loss on plants under construction 369 — 369 — — — Other deferred state tax attributes 357 — 9 250 68 10 Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 338 243 76 19 — — Other 660 143 186 39 52 166 Total deferred income tax assets 8,874 2,143 3,443 428 1,587 432 Valuation allowance (136) — (35) (41) (35) (4) Net deferred income tax assets 8,738 2,143 3,408 387 1,552 428 Net deferred income taxes (assets)/liabilities $ 8,043 $ 3,273 $ 3,272 $ 318 $ (139) $ 1,265 Recognized in the balance sheets: Accumulated deferred income taxes – assets $ (132) $ — $ — $ (129) $ (262) $ — Accumulated deferred income taxes – liabilities $ 8,175 $ 3,273 $ 3,272 $ 447 $ 123 $ 1,265 December 31, 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,711 $ 2,402 $ 3,058 $ 315 $ 1,422 $ 1,288 Property basis differences 1,843 912 643 143 — 133 Federal effect of net state deferred tax assets — — — 24 — — Leveraged lease basis differences 236 — — — — — Employee benefit obligations 704 242 351 38 12 12 Premium on reacquired debt 83 13 70 — — — Regulatory assets – Storm damage reserves 109 — 109 — — — Employee benefit obligations 1,174 311 403 55 — 45 Remaining book value of retired assets 341 174 159 8 — — AROs 1,723 613 1,066 44 — — AROs 814 360 405 — — — Other 523 134 81 68 11 198 Total deferred income tax liabilities 16,261 5,161 6,345 695 1,445 1,676 Deferred tax assets — Federal effect of net state deferred tax liabilities 277 162 63 — 24 56 Employee benefit obligations 1,385 334 488 72 5 111 Other property basis differences 230 — 65 — 146 — ITC and PTC carryforward 2,098 11 435 — 1,445 — Long-term debt fair value adjustment 97 — — — — 97 Other partnership basis difference 169 — — — 169 — Other comprehensive losses 112 8 18 — 10 — AROs 2,537 973 1,471 44 — — Estimated loss on plants under construction 283 — 283 — — — Other deferred state tax attributes 402 — 13 251 72 8 Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 401 240 133 28 — — Other 689 173 154 56 46 190 Total deferred income tax assets 8,680 1,901 3,123 451 1,917 462 Valuation allowance (137) — (35) (41) (36) (5) Net deferred income tax assets 8,543 1,901 3,088 410 1,881 457 Net deferred income taxes (assets)/liabilities $ 7,718 $ 3,260 $ 3,257 $ 285 $ (436) $ 1,219 Recognized in the balance sheets: Accumulated deferred income taxes – assets $ (170) $ — $ — $ (139) $ (551) $ — Accumulated deferred income taxes – liabilities $ 7,888 $ 3,260 $ 3,257 $ 424 $ 115 $ 1,219
Summary of tax credit carryforwards	Federal ITC/PTC carryforwards at December 31, 2020 were as follows: Southern Company Alabama Georgia Southern (in millions) Federal ITC/PTC carryforwards $ 1,428 $ 12 $ 114 $ 1,110 Tax Year in which federal ITC/PTC carryforwards begin expiring 2031 2032 2031 2035 Year by which federal ITC/PTC carryforwards are expected to be utilized 2024 2023 2023 2024
Summary of operating loss carryforward	At December 31, 2020, the net state income tax benefit of state and local NOL carryforwards for Southern Company's subsidiaries were as follows: Company/Jurisdiction Approximate Net State Income Tax Benefit of NOL Carryforwards Tax Year NOL Mississippi Power Mississippi $ 200 2031 Southern Power Oklahoma 39 2035 Florida 11 2034 South Carolina 2 2036 Other states 1 Various Southern Power Total $ 53 Other (*) New York 11 2035 New York City 14 2035 Other states 21 Various Southern Company Total $ 299 (*) Represents other Southern Company subsidiaries. Alabama Power, Georgia Power, and Southern Company Gas did not have material state or local NOL carryforwards at December 31, 2020.
Changes in unrecognized tax benefits	Southern Company (in millions) Unrecognized tax benefits at December 31, 2017 $ 18 Tax position changes – decrease from prior periods (18) Unrecognized tax benefits at December 31, 2018 and 2019 $ — Tax positions changes – increase from prior periods 44 Unrecognized tax benefits at December 31, 2020 $ 44

RETIREMENT BENEFITS (Tables)

RETIREMENT BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Summary of actuarial assumptions	The weighted average rates assumed in the actuarial calculations used to determine both the net periodic costs for the pension and other postretirement benefit plans for the following year and the benefit obligations as of the measurement date are presented below. 2020 Assumptions used to determine net Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 3.41 % 3.44 % 3.40 % 3.41 % 3.52 % 3.39 % Discount rate – interest costs 2.99 3.01 2.96 2.99 3.18 2.99 Discount rate – service costs 3.66 3.69 3.67 3.67 3.70 3.53 Expected long-term return on plan assets 8.25 8.25 8.25 8.25 8.25 8.25 Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 Other postretirement benefit plans Discount rate – benefit obligations 3.24 % 3.28 % 3.22 % 3.22 % 3.39 % 3.19 % Discount rate – interest costs 2.80 2.84 2.79 2.76 2.97 2.71 Discount rate – service costs 3.57 3.61 3.57 3.57 3.57 3.52 Expected long-term return on plan assets 7.25 7.36 7.05 7.07 — 6.69 Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 2019 Assumptions used to determine net Southern Company Alabama Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 4.49 % 4.51 % 4.48 % 4.49 % 4.65 % 4.47 % Discount rate – interest costs 4.12 4.14 4.10 4.12 4.35 4.11 Discount rate – service costs 4.70 4.73 4.72 4.73 4.75 4.57 Expected long-term return on plan assets 7.75 7.75 7.75 7.75 7.75 7.75 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate – benefit obligations 4.37 % 4.40 % 4.36 % 4.35 % 4.50 % 4.32 % Discount rate – interest costs 3.98 4.01 3.97 3.95 4.14 3.91 Discount rate – service costs 4.63 4.67 4.64 4.64 4.65 4.56 Expected long-term return on plan assets 6.86 6.76 6.85 6.79 — 6.49 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 2018 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate – benefit obligations 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % 3.74 % Discount rate – interest costs 3.45 3.45 3.42 3.46 3.69 3.41 Discount rate – service costs 3.98 4.00 3.99 3.99 4.01 3.84 Expected long-term return on plan assets 7.95 7.95 7.95 7.95 7.95 7.95 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate – benefit obligations 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % 3.62 % Discount rate – interest costs 3.29 3.31 3.29 3.29 3.47 3.21 Discount rate – service costs 3.91 3.93 3.91 3.91 3.93 3.82 Expected long-term return on plan assets 6.83 6.83 6.80 6.99 — 5.89 Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 2020 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 2.81 % 2.85 % 2.79 % 2.80 % 2.99 % 2.75 % Annual salary increase 4.80 4.80 4.80 4.80 4.80 4.80 Other postretirement benefit plans Discount rate 2.56 % 2.63 % 2.52 % 2.53 % 2.78 % 2.46 % Annual salary increase 4.80 4.80 4.80 4.80 4.80 4.80 2019 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 3.41 % 3.44 % 3.40 % 3.41 % 3.52 % 3.39 % Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73 Other postretirement benefit plans Discount rate 3.24 % 3.28 % 3.22 % 3.22 % 3.39 % 3.19 % Annual salary increase 4.73 4.73 4.73 4.73 4.73 4.73
Schedule of health care cost trend rates	The weighted average medical care cost trend rates used in measuring the APBO for the Registrants at December 31, 2020 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Pre-65 6.00 % 4.50 % 2027 Post-65 medical 5.00 4.50 2027 Post-65 prescription 6.25 4.50 2028
Schedule of accumulated and projected benefit obligations	The total accumulated benefit obligation for the pension plans at December 31, 2020 and 2019 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2020 $ 14,922 $ 3,414 $ 4,657 $ 683 $ 175 $ 1,072 December 31, 2019 13,391 3,053 4,222 615 151 963 The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2020 are shown in the following table. All pension plan assets are related to the qualified pension plan. Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Projected benefit obligations: Qualified pension plan $ 15,818 $ 3,719 $ 4,977 $ 718 $ 187 $ 1,114 Non-qualified pension plan 828 135 150 36 30 75
Changes in projected benefit obligations and fair value of plan assets	Changes in the projected benefit obligations and the fair value of plan assets during the plan years ended December 31, 2020 and 2019 were as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 14,788 $ 3,404 $ 4,610 $ 671 $ 185 $ 1,067 Service cost 376 89 96 15 8 33 Interest cost 432 100 133 20 6 31 Benefits paid (629) (132) (202) (27) (6) (69) Actuarial (gain) loss 1,679 393 490 75 24 127 Balance at end of year 16,646 3,854 5,127 754 217 1,189 Change in plan assets Fair value of plan assets at beginning of year 14,057 3,357 4,442 641 169 1,050 Actual return (loss) on plan assets 1,881 450 594 85 22 139 Employer contributions 58 9 10 2 1 3 Benefits paid (629) (132) (202) (27) (6) (69) Fair value of plan assets at end of year 15,367 3,684 4,844 701 186 1,123 Accrued liability $ (1,279) $ (170) $ (283) $ (53) $ (31) $ (66) 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 12,763 $ 2,816 $ 3,905 $ 557 $ 123 $ 907 Dispositions (509) — — — — — Service cost 292 69 74 12 7 25 Interest cost 492 114 156 22 5 36 Benefits paid (596) (125) (194) (26) (4) (64) Actuarial (gain) loss 2,346 530 669 106 54 163 Balance at end of year 14,788 3,404 4,610 671 185 1,067 Change in plan assets Fair value of plan assets at beginning of year 11,611 2,575 3,663 505 123 798 Dispositions (509) — — — — — Actual return (loss) on plan assets 2,343 524 730 103 43 172 Employer contributions 1,208 383 243 59 7 144 Benefits paid (596) (125) (194) (26) (4) (64) Fair value of plan assets at end of year 14,057 3,357 4,442 641 169 1,050 Accrued liability $ (731) $ (47) $ (168) $ (30) $ (16) $ (17)
Amounts recognized in balance sheets	Amounts recognized in the balance sheets at December 31, 2020 and 2019 related to the Registrants' pension plans consist of the following: Southern Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2020: Other regulatory assets, deferred (*) $ 4,655 $ 1,286 $ 1,598 $ 235 $ — $ 205 Other deferred charges and assets — — — — — 70 Other current liabilities (52) (9) (10) (2) (2) (2) Employee benefit obligations (1,227) (161) (273) (51) (29) (134) Other regulatory liabilities, deferred (34) — — — — — AOCI 245 — — — 60 1 December 31, 2019: Prepaid pension costs $ 2 $ 71 $ — $ 2 $ 10 $ — Other regulatory assets, deferred (*) 4,072 1,130 1,416 204 — 172 Other deferred charges and assets — — — — — 82 Other current liabilities (54) (8) (11) (2) (2) (2) Employee benefit obligations (679) (110) (157) (30) (24) (97) Other regulatory liabilities, deferred (79) — — — — — AOCI 185 — — — 46 (14) (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. Presented below are the amounts included in regulatory assets at December 31, 2020 and 2019 related to the portion of the defined benefit pension plan attributable to Southern Company, the traditional electric operating companies, and Southern Company Gas that had not yet been recognized in net periodic pension cost. Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2020 Regulatory assets: Prior service cost $ 11 $ 5 $ 9 $ 2 $ (13) Net (gain) loss 4,610 1,281 1,589 233 135 Regulatory amortization — — — — 83 Total regulatory assets (*) $ 4,621 $ 1,286 $ 1,598 $ 235 $ 205 Balance at December 31, 2019 Regulatory assets: Prior service cost $ 13 $ 6 $ 10 $ 2 $ (15) Net (gain) loss 3,980 1,124 1,406 201 113 Regulatory amortization — — — — 74 Total regulatory assets (*) $ 3,993 $ 1,130 $ 1,416 $ 203 $ 172 (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. Amounts recognized in the balance sheets at December 31, 2020 and 2019 related to the Registrants' other postretirement benefit plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Southern Company Gas (in millions) December 31, 2020: Other regulatory assets, deferred (a) $ 137 $ — $ 47 $ 5 $ — $ (23) Other current liabilities (5) — — — — — Employee benefit obligations (b) (785) (5) (272) (54) (12) (120) Other regulatory liabilities, deferred (86) (21) — — — — AOCI 8 — — — 3 — December 31, 2019: Other regulatory assets, deferred (a) $ 183 $ 3 $ 96 $ 10 $ — $ (11) Other current liabilities (5) — — — — — Employee benefit obligations (b) (919) (49) (339) (61) (11) (135) Other regulatory liabilities, deferred (62) (2) — — — — AOCI 2 — — — 2 (4) (a) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company. (b) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. Presented below are the amounts included in net regulatory assets (liabilities) at December 31, 2020 and 2019 related to the other postretirement benefit plans of Southern Company, the traditional electric operating companies, and Southern Company Gas that had not yet been recognized in net periodic other postretirement benefit cost. Southern Company Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2020: Regulatory assets (liabilities): Prior service cost $ 12 $ 3 $ 5 $ — $ 1 Net (gain) loss 39 (24) 42 5 (49) Regulatory amortization — — — — 25 Total regulatory assets (liabilities) (*) $ 51 $ (21) $ 47 $ 5 $ (23) Balance at December 31, 2019: Regulatory assets (liabilities): Prior service cost $ 11 $ 3 $ 4 $ — $ 1 Net (gain) loss 110 (2) 92 10 (43) Regulatory amortization — — — — 31 Total regulatory assets (liabilities) (*) $ 121 $ 1 $ 96 $ 10 $ (11) (*) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company.
Changes in balances of regulatory assets and regulatory liabilities related to defined benefit pension plans	The changes in the balance of regulatory assets related to the portion of the defined benefit pension plan attributable to Southern Company, the traditional electric operating companies, and Southern Company Gas for the years ended December 31, 2020 and 2019 are presented in the following table: Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): (*) Balance at December 31, 2018 $ 3,458 $ 955 $ 1,230 $ 167 $ 160 Net (gain) loss 801 213 231 42 30 Dispositions (144) — — — — Reclassification adjustments: Amortization of prior service costs (3) (1) (1) — 2 Amortization of net gain (loss) (119) (37) (44) (6) — Amortization of regulatory assets (*) — — — — (20) Total reclassification adjustments (122) (38) (45) (6) (18) Total change 535 175 186 36 12 Balance at December 31, 2019 $ 3,993 $ 1,130 $ 1,416 $ 203 $ 172 Net (gain) loss 884 228 269 45 45 Reclassification adjustments: Amortization of prior service costs (1) (1) (1) — 2 Amortization of net gain (loss) (255) (71) (86) (13) (8) Amortization of regulatory assets (*) — — — — (6) Total reclassification adjustments (256) (72) (87) (13) (12) Total change 628 156 182 32 33 Balance at December 31, 2020 $ 4,621 $ 1,286 $ 1,598 $ 235 $ 205 (*) Amounts for Southern Company exclude regulatory assets of $224 million and $252 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company. The changes in the balance of net regulatory assets (liabilities) related to the other postretirement benefit plans for the plan years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Net regulatory assets (liabilities): (*) Balance at December 31, 2018 $ 22 $ (9) $ 60 $ 4 $ (4) Net (gain) loss 90 14 37 6 (1) Dispositions 5 — — — — Change in prior service costs 5 — — — — Reclassification adjustments: Amortization of prior service costs (3) (4) — — — Amortization of net gain (loss) 2 — (1) — — Amortization of regulatory assets (*) — — — — (6) Total reclassification adjustments (1) (4) (1) — (6) Total change 99 10 36 6 (7) Balance at December 31, 2019 $ 121 $ 1 $ 96 $ 10 $ (11) Net (gain) loss (65) (22) (47) (5) (5) Reclassification adjustments: Amortization of prior service costs 1 — 1 — — Amortization of net gain (loss) (6) — (3) — — Amortization of regulatory assets (*) — — — — (7) Total reclassification adjustments (5) — (2) — (7) Total change (70) (22) (49) (5) (12) Balance at December 31, 2020 $ 51 $ (21) $ 47 $ 5 $ (23) (*) Amounts for Southern Company exclude regulatory assets of $47 million and $50 million at December 31, 2020 and 2019, respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company.
Amounts included in AOCI related to defined benefit pension plans	Presented below are the amounts included in AOCI at December 31, 2020 and 2019 related to the portion of the defined benefit pension plan attributable to Southern Company, Southern Power, and Southern Company Gas that had not yet been recognized in net periodic pension cost. Southern Southern Southern Company (in millions) Balance at December 31, 2020 AOCI: Prior service cost $ (3) $ — $ (4) Net (gain) loss 248 60 5 Total AOCI $ 245 $ 60 $ 1 Balance at December 31, 2019 AOCI: Prior service cost $ (3) $ — $ (6) Net (gain) loss 188 46 (8) Total AOCI $ 185 $ 46 $ (14) Presented below are the amounts included in AOCI at December 31, 2020 and 2019 related to the other postretirement benefit plans of Southern Company, Southern Power, and Southern Company Gas that had not yet been recognized in net periodic other postretirement benefit cost. Southern Southern Southern Company (in millions) Balance at December 31, 2020 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 7 3 (1) Total AOCI $ 8 $ 3 $ — Balance at December 31, 2019 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 1 2 (5) Total AOCI $ 2 $ 2 $ (4)
Components of OCI related to defined benefit pension plan	The components of OCI related to the portion of the defined benefit pension plan attributable to Southern Company, Southern Power, and Southern Company Gas for the years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Southern Southern Company (in millions) AOCI: Balance at December 31, 2018 $ 97 $ 26 $ (44) Net (gain) loss 88 20 30 Balance at December 31, 2019 $ 185 $ 46 $ (14) Net (gain) loss 74 16 15 Reclassification adjustments: Amortization of prior service costs — — 1 Amortization of net gain (loss) (14) (2) (1) Total reclassification adjustments (14) (2) — Total change 60 14 15 Balance at December 31, 2020 $ 245 $ 60 $ 1 The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2020 and 2019 are presented in the following table: Southern Company Southern Southern Company Gas (in millions) AOCI: Balance at December 31, 2018 $ (4) $ 1 $ (4) Net (gain) loss 5 1 — Reclassification adjustments: Amortization of net gain (loss) 1 — — Total change 6 1 — Balance at December 31, 2019 $ 2 $ 2 $ (4) Net (gain) loss 2 1 — Reclassification adjustments: Amortization of net gain (loss) 4 — 4 Total change 6 1 4 Balance at December 31, 2020 $ 8 $ 3 $ —
Components of net periodic benefit cost	Components of net periodic pension cost for the Registrants were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Service cost $ 376 $ 89 $ 96 $ 15 $ 8 $ 33 Interest cost 432 100 133 20 6 31 Expected return on plan assets (1,100) (264) (347) (51) (13) (75) Recognized net (gain) loss 269 71 86 13 2 6 Net amortization 1 1 1 — — 15 Prior service cost — — — — — (3) Net periodic pension cost $ (22) $ (3) $ (31) $ (3) $ 3 $ 7 2019 Service cost $ 292 $ 69 $ 74 $ 12 $ 7 $ 25 Interest cost 492 114 156 22 5 36 Expected return on plan assets (885) (206) (292) (40) (10) (60) Recognized net (gain) loss 120 37 44 6 1 2 Net amortization 2 — 1 — — 14 Prior service cost — — — — — (3) Net periodic pension cost $ 21 $ 14 $ (17) $ — $ 3 $ 14 2018 Service cost $ 359 $ 78 $ 87 $ 17 $ 9 $ 34 Interest cost 464 101 139 20 5 39 Expected return on plan assets (943) (207) (296) (41) (10) (75) Recognized net (gain) loss 213 54 69 10 1 12 Net amortization 4 1 2 — — 15 Prior service cost — — — — — (2) Net periodic pension cost $ 97 $ 27 $ 1 $ 6 $ 5 $ 23 Components of the other postretirement benefit plans' net periodic cost for the Registrants were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 2020 Service cost $ 22 $ 6 $ 6 $ 1 $ 1 $ 2 Interest cost 54 13 20 2 — 7 Expected return on plan assets (72) (29) (26) (1) — (10) Net amortization 1 — 2 — — 6 Net periodic postretirement benefit cost $ 5 $ (10) $ 2 $ 2 $ 1 $ 5 2019 Service cost $ 18 $ 5 $ 5 $ 1 $ 1 $ 1 Interest cost 69 16 26 3 — 9 Expected return on plan assets (65) (26) (25) (2) — (7) Net amortization — 4 1 — — 6 Net periodic postretirement benefit cost $ 22 $ (1) $ 7 $ 2 $ 1 $ 9 2018 Service cost $ 24 $ 6 $ 6 $ 1 $ 1 $ 2 Interest cost 75 17 28 3 — 10 Expected return on plan assets (69) (26) (25) (2) — (7) Net amortization 21 5 10 1 — 6 Net periodic postretirement benefit cost $ 51 $ 2 $ 19 $ 3 $ 1 $ 11
Estimated pension benefit payments	At December 31, 2020, estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2021 $ 651 $ 141 $ 208 $ 29 $ 6 $ 66 2022 678 147 215 30 6 66 2023 702 154 222 31 6 66 2024 725 158 229 32 6 65 2025 748 165 235 33 7 65 2026 to 2030 4,024 895 1,244 181 38 330 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit payments: 2021 $ 115 $ 25 $ 42 $ 6 $ — $ 18 2022 113 25 41 5 — 18 2023 111 25 40 5 — 18 2024 110 24 38 4 1 17 2025 113 25 40 5 1 17 2026 to 2030 550 127 199 23 3 76
Changes in the APBO and the fair value of plan assets	Changes in the APBO and the fair value of the Registrants' plan assets during the plan years ended December 31, 2020 and 2019 were as follows: 2020 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 1,985 $ 462 $ 742 $ 87 $ 11 $ 250 Service cost 22 6 6 1 1 2 Interest cost 54 13 20 2 — 7 Benefits paid (126) (29) (46) (6) — (17) Actuarial (gain) loss 7 9 (26) (3) — 6 Retiree drug subsidy 6 2 3 — — — Balance at end of year 1,948 463 699 81 12 248 Change in plan assets Fair value of plan assets at beginning of year 1,061 413 403 26 — 115 Actual return (loss) on plan assets 145 60 50 3 — 18 Employer contributions 72 12 17 4 — 12 Benefits paid (120) (27) (43) (6) — (17) Fair value of plan assets at end of year 1,158 458 427 27 — 128 Accrued liability $ (790) $ (5) $ (272) $ (54) $ (12) $ (120) 2019 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 1,865 $ 403 $ 675 $ 81 $ 9 $ 244 Dispositions (69) — — — — — Service cost 18 5 5 1 1 1 Interest cost 69 16 26 3 — 9 Benefits paid (126) (27) (47) (6) (1) (17) Actuarial (gain) loss 223 63 80 8 2 13 Retiree drug subsidy 5 2 3 — — — Balance at end of year 1,985 462 742 87 11 250 Change in plan assets Fair value of plan assets at beginning of year 928 360 344 23 — 98 Dispositions (18) — — — — — Actual return (loss) on plan assets 189 76 68 4 — 21 Employer contributions 83 2 35 5 1 13 Benefits paid (121) (25) (44) (6) (1) (17) Fair value of plan assets at end of year 1,061 413 403 26 — 115 Accrued liability $ (924) $ (49) $ (339) $ (61) $ (11) $ (135)
Summary of investment strategies and benefit plan asset fair values	A description of the major asset classes that the pension and other postretirement benefit plans are comprised of, along with the valuation methods used for fair value measurement, is provided below: Description Valuation Methodology Domestic equity: A mix of large and small capitalization stocks with generally an equal distribution of value and growth attributes, managed both actively and through passive index approaches. International equity: A mix of large and small capitalization growth and value stocks with developed and emerging markets exposure, managed both actively and through fundamental indexing approaches. Domestic and international equities such as common stocks, American depositary receipts, and real estate investment trusts that trade on public exchanges are classified as Level 1 investments and are valued at the closing price in the active market. Equity funds with unpublished prices that are comprised of publicly traded securities (such as commingled/pooled funds) are also valued at the closing price in the active market, but are classified as Level 2. Fixed income: A mix of domestic and international bonds. Investments in fixed income securities, including fixed income pooled funds, are generally classified as Level 2 investments and are valued based on prices reported in the market place. Additionally, the value of fixed income securities takes into consideration certain items such as broker quotes, spreads, yield curves, interest rates, and discount rates that apply to the term of a specific instrument. Trust-owned life insurance (TOLI): Investments of taxable trusts aimed at minimizing the impact of taxes on the portfolio. Investments in TOLI policies are classified as Level 2 investments and are valued based on the underlying investments held in the policy's separate accounts. The underlying assets are equity and fixed income pooled funds that are comprised of Level 1 and Level 2 securities. Special situations: Investments in opportunistic strategies with the objective of diversifying and enhancing returns and exploiting short-term inefficiencies, as well as investments in promising new strategies of a longer-term nature. Real estate: Investments in traditional private market, equity-oriented investments in real properties (indirectly through pooled funds or partnerships) and in publicly traded real estate securities. Private equity: Investments in private partnerships that invest in private or public securities typically through privately-negotiated and/or structured transactions, including leveraged buyouts, venture capital, and distressed debt. Investments in real estate, private equity, and special situations are generally classified as Net Asset Value as a Practical Expedient, since the underlying assets typically do not have publicly available observable inputs. The fund manager values the assets using various inputs and techniques depending on the nature of the underlying investments. Techniques may include purchase multiples for comparable transactions, comparable public company trading multiples, discounted cash flow analysis, prevailing market capitalization rates, recent sales of comparable investments, and independent third-party appraisals. The fair value of partnerships is determined by aggregating the value of the underlying assets less liabilities.
Fair values of plan assets	The fair values, and actual allocations relative to the target allocations, of the Southern Company system's pension plans at December 31, 2020 and 2019 are presented below. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Equity: 51 % 56 % Domestic equity $ 2,852 $ 1,247 $ — $ 4,099 International equity 2,660 1,497 — 4,157 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 951 — 951 Mortgage- and asset-backed securities — 9 — 9 Corporate bonds — 1,673 — 1,673 Pooled funds — 772 — 772 Cash equivalents and other 356 5 — 361 Real estate investments 542 — 1,596 2,138 14 13 Special situations — — 166 166 3 1 Private equity — — 1,104 1,104 9 7 Total $ 6,410 $ 6,154 $ 2,866 $ 15,430 100 % 100 % Alabama Power Assets: Equity: 51 % 56 % Domestic equity $ 685 $ 299 $ — $ 984 International equity 638 359 — 997 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 228 — 228 Mortgage- and asset-backed securities — 2 — 2 Corporate bonds — 401 — 401 Pooled funds — 185 — 185 Cash equivalents and other 85 1 — 86 Real estate investments 130 — 382 512 14 13 Special situations — — 40 40 3 1 Private equity — — 264 264 9 7 Total $ 1,538 $ 1,475 $ 686 $ 3,699 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Equity: 51 % 56 % Domestic equity $ 899 $ 393 $ — $ 1,292 International equity 839 472 — 1,311 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 300 — 300 Mortgage- and asset-backed securities — 3 — 3 Corporate bonds — 527 — 527 Pooled funds — 243 — 243 Cash equivalents and other 112 1 — 113 Real estate investments 171 — 503 674 14 13 Special situations — — 53 53 3 1 Private equity — — 348 348 9 7 Total $ 2,021 $ 1,939 $ 904 $ 4,864 100 % 100 % Mississippi Power Assets: Equity: 51 % 56 % Domestic equity $ 131 $ 57 $ — $ 188 International equity 122 68 — 190 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 43 — 43 Corporate bonds — 76 — 76 Pooled funds — 35 — 35 Cash equivalents and other 16 — — 16 Real estate investments 25 — 73 98 14 13 Special situations — — 8 8 3 1 Private equity — — 50 50 9 7 Total $ 294 $ 279 $ 131 $ 704 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) Total (in millions) Southern Power Assets: Equity: 51 % 56 % Domestic equity $ 35 $ 15 $ — $ 50 International equity 32 19 — 51 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 12 — 12 Corporate bonds — 20 — 20 Pooled funds — 9 — 9 Cash equivalents and other 4 — — 4 Real estate investments 7 — 19 26 14 13 Special situations — — 2 2 3 1 Private equity — — 13 13 9 7 Total $ 78 $ 75 $ 34 $ 187 100% 100 % Southern Company Gas Assets: Equity: 51 % 56 % Domestic equity $ 209 $ 91 $ — $ 300 International equity 195 109 — 304 Fixed income: 23 23 U.S. Treasury, government, and agency bonds — 69 — 69 Mortgage- and asset-backed securities — 1 — 1 Corporate bonds — 122 — 122 Pooled funds — 56 — 56 Cash equivalents and other 26 — — 26 Real estate investments 40 — 117 157 14 13 Special situations — — 12 12 3 1 Private equity — — 81 81 9 7 Total $ 470 $ 448 $ 210 $ 1,128 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Equity: 51 % 51 % Domestic equity $ 2,220 $ 898 $ — $ 3,118 International equity 2,360 1,286 — 3,646 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 965 — 965 Mortgage- and asset-backed securities — 9 — 9 Corporate bonds — 1,315 — 1,315 Pooled funds — 684 — 684 Cash equivalents and other 1,317 — — 1,317 Real estate investments 539 — 1,418 1,957 14 12 Special situations — — 155 155 3 1 Private equity — — 953 953 9 7 Total $ 6,436 $ 5,157 $ 2,526 $ 14,119 100 % 100 % Alabama Power Assets: Equity: 51 % 51 % Domestic equity $ 530 $ 214 $ — $ 744 International equity 564 307 — 871 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 230 — 230 Mortgage- and asset-backed securities — 2 — 2 Corporate bonds — 314 — 314 Pooled funds — 163 — 163 Cash equivalents and other 315 — — 315 Real estate investments 129 — 339 468 14 12 Special situations — — 37 37 3 1 Private equity — — 228 228 9 7 Total $ 1,538 $ 1,230 $ 604 $ 3,372 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Equity: 51 % 51 % Domestic equity $ 701 $ 284 $ — $ 985 International equity 746 407 — 1,153 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 305 — 305 Mortgage- and asset-backed securities — 3 — 3 Corporate bonds — 415 — 415 Pooled funds — 216 — 216 Cash equivalents and other 416 — — 416 Real estate investments 170 — 448 618 14 12 Special situations — — 49 49 3 1 Private equity — — 301 301 9 7 Total $ 2,033 $ 1,630 $ 798 $ 4,461 100 % 100 % Mississippi Power Assets: Equity: 51 % 51 % Domestic equity $ 101 $ 41 $ — $ 142 International equity 108 59 — 167 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 44 — 44 Corporate bonds — 60 — 60 Pooled funds — 31 — 31 Cash equivalents and other 60 — — 60 Real estate investments 25 — 65 90 14 12 Special situations — — 7 7 3 1 Private equity — — 43 43 9 7 Total $ 294 $ 235 $ 115 $ 644 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Southern Power Assets: Equity: 51 % 51 % Domestic equity $ 27 $ 11 $ — $ 38 International equity 28 16 — 44 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 12 — 12 Corporate bonds — 16 — 16 Pooled funds — 8 — 8 Cash equivalents and other 16 — — 16 Real estate investments 6 — 17 23 14 12 Special situations — — 2 2 3 1 Private equity — — 11 11 9 7 Total $ 77 $ 63 $ 30 $ 170 100 % 100 % Southern Company Gas Assets: Equity: 51 % 51 % Domestic equity $ 166 $ 67 $ — $ 233 International equity 176 96 — 272 Fixed income: 23 29 U.S. Treasury, government, and agency bonds — 72 — 72 Mortgage- and asset-backed securities — 1 — 1 Corporate bonds — 98 — 98 Pooled funds — 51 — 51 Cash equivalents and other 98 — — 98 Real estate investments 40 — 106 146 14 12 Special situations — — 12 12 3 1 Private equity — — 71 71 9 7 Total $ 480 $ 385 $ 189 $ 1,054 100 % 100 % The fair values, and actual allocations relative to the target allocations, of the applicable Registrants' other postretirement benefit plan assets at December 31, 2020 and 2019 are presented below. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) (in millions) Southern Company Assets: Equity: 63 % 66 % Domestic equity $ 113 $ 98 $ — $ 211 International equity 71 102 — 173 Fixed income: 28 27 U.S. Treasury, government, and agency bonds — 32 — 32 Corporate bonds — 44 — 44 Pooled funds — 86 — 86 Cash equivalents and other 15 — — 15 Trust-owned life insurance — 508 — 508 Real estate investments 15 — 42 57 5 5 Special situations — — 4 4 1 — Private equity — — 29 29 3 2 Total $ 214 $ 870 $ 75 $ 1,159 100 % 100 % Alabama Power Assets: Equity: 68 % 69 % Domestic equity $ 26 $ 11 $ — $ 37 International equity 23 13 — 36 Fixed income: 24 25 U.S. Treasury, government, and agency bonds — 11 — 11 Corporate bonds — 14 — 14 Pooled funds — 7 — 7 Cash equivalents and other 5 — — 5 Trust-owned life insurance — 321 — 321 Real estate investments 5 — 13 18 4 4 Special situations — — 1 1 1 — Private equity — — 9 9 3 2 Total $ 59 $ 377 $ 23 $ 459 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) (in millions) Georgia Power Assets: Equity: 60 % 64 % Domestic equity $ 58 $ 10 $ — $ 68 International equity 21 50 — 71 Fixed income: 33 30 U.S. Treasury, government, and agency bonds — 8 — 8 Corporate bonds — 13 — 13 Pooled funds — 46 — 46 Cash equivalents and other 5 — — 5 Trust-owned life insurance — 188 — 188 Real estate investments 5 — 13 18 4 4 Special situations — — 1 1 1 — Private equity — — 9 9 2 2 Total $ 89 $ 315 $ 23 $ 427 100 % 100 % Mississippi Power Assets: Equity: 43 % 46 % Domestic equity $ 4 $ 2 $ — $ 6 International equity 4 2 — 6 Fixed income: 37 36 U.S. Treasury, government, and agency bonds — 5 — 5 Corporate bonds — 2 — 2 Pooled funds — 1 — 1 Cash equivalents and other 1 — — 1 Real estate investments 1 — 2 3 11 11 Special situations — — — — 2 1 Private equity — — 2 2 7 6 Total $ 10 $ 12 $ 4 $ 26 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2020: (Level 1) (Level 2) (NAV) (in millions) Southern Company Gas Assets: Equity: 72 % 76 % Domestic equity $ 2 $ 66 $ — $ 68 International equity 2 25 — 27 Fixed income: 26 22 U.S. Treasury, government, and agency bonds — 1 — 1 Corporate bonds — 1 — 1 Pooled funds — 25 — 25 Cash equivalents and other 1 — — 1 Real estate investments — — 1 1 1 1 Private equity — — 1 1 1 1 Total $ 5 $ 118 $ 2 $ 125 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Equity: 63 % 64 % Domestic equity $ 95 $ 81 $ — $ 176 International equity 69 80 — 149 Fixed income: 28 30 U.S. Treasury, government, and agency bonds — 31 — 31 Corporate bonds — 35 — 35 Pooled funds — 82 — 82 Cash equivalents and other 42 — — 42 Trust-owned life insurance — 463 — 463 Real estate investments 15 — 38 53 5 4 Special situations — — 4 4 1 — Private equity — — 25 25 3 2 Total $ 221 $ 772 $ 67 $ 1,060 100 % 100 % Alabama Power Assets: Equity: 68 % 67 % Domestic equity $ 26 $ 8 $ — $ 34 International equity 21 11 — 32 Fixed income: 24 27 U.S. Treasury, government, and agency bonds — 10 — 10 Corporate bonds — 11 — 11 Pooled funds — 6 — 6 Cash equivalents and other 12 — — 12 Trust-owned life insurance — 281 — 281 Real estate investments 5 — 12 17 4 4 Special situations — — 1 1 1 — Private equity — — 8 8 3 2 Total $ 64 $ 327 $ 21 $ 412 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Equity: 60 % 61 % Domestic equity $ 48 $ 7 $ — $ 55 International equity 25 36 — 61 Fixed income: 33 34 U.S. Treasury, government, and agency bonds — 7 — 7 Corporate bonds — 11 — 11 Pooled funds — 45 — 45 Cash equivalents and other 16 — — 16 Trust-owned life insurance — 182 — 182 Real estate investments 5 — 11 16 4 3 Special situations — — 1 1 1 — Private equity — — 8 8 2 2 Total $ 94 $ 288 $ 20 $ 402 100 % 100 % Mississippi Power Assets: Equity: 43 % 41 % Domestic equity $ 3 $ 1 $ — $ 4 International equity 4 2 — 6 Fixed income: 37 42 U.S. Treasury, government, and agency bonds — 6 — 6 Corporate bonds — 2 — 2 Pooled funds — 1 — 1 Cash equivalents and other 2 — — 2 Real estate investments 1 — 2 3 11 10 Special situations — — — — 2 1 Private equity — — 1 1 7 6 Total $ 10 $ 12 $ 3 $ 25 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Gas Assets: Equity: 72 % 73 % Domestic equity $ 2 $ 58 $ — $ 60 International equity 2 21 — 23 Fixed income: 26 25 U.S. Treasury, government, and agency bonds — 1 — 1 Corporate bonds — 1 — 1 Pooled funds — 25 — 25 Cash equivalents and other 2 — — 2 Real estate investments — — 1 1 1 1 Private equity — — 1 1 1 1 Total $ 6 $ 106 $ 2 $ 114 100 % 100 %
Total matching contributions	Total matching contributions made to the plans for 2020, 2019, and 2018 were as follows: Southern Company Alabama Georgia Mississippi Southern Southern Company Gas (in millions) 2020 $ 120 $ 26 $ 29 $ 5 $ 2 $ 16 2019 113 25 27 4 2 15 2018 119 24 26 5 3 18

STOCK COMPENSATION (Tables)

STOCK COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Schedule of employees participating in stock-based compensation programs	At December 31, 2020, the number of current and former employees participating in stock-based compensation programs for the Registrants was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Number of employees 1,958 263 295 86 46 204
Assumptions used in the pricing model and the weighted average grant-date fair value of performance share award units granted	The following table shows the assumptions used in the pricing model and the weighted average grant-date fair value of TSR awards granted: Year Ended December 31 2020 2019 2018 Expected volatility 15.4% 15.6% 14.9% Expected term (in years) 3 3 3 Interest rate 1.4% 2.4% 2.4% Weighted average grant-date fair value $77.65 $62.71 $43.75
Schedule of compensation costs and related tax benefits	Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2020, 2019, and 2018 are as follows: 2020 2019 2018 (in millions) Southern Company Compensation cost recognized in income $ 84 $ 77 $ 91 Tax benefit of compensation cost recognized in income 22 20 24 Southern Company Gas Compensation cost recognized in income $ 13 $ 14 $ 11 Tax benefit of compensation cost recognized in income 4 4 3 Total intrinsic value of options exercised, and the related tax benefit, for the years ended December 31, 2020, 2019, and 2018 are presented below: Year Ended December 31 2020 2019 2018 (in millions) Southern Company Intrinsic value of options exercised $ 38 $ 167 $ 9 Tax benefit of options exercised 9 35 2 Alabama Power Intrinsic value of options exercised $ 5 $ 21 $ 2 Tax benefit of options exercised 1 4 — Georgia Power Intrinsic value of options exercised $ 9 $ 30 $ 2 Tax benefit of options exercised 2 6 —
Share-based compensation, stock options, activity	Southern Company's activity in the stock option program for 2020 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2019 5.9 $ 42.52 Exercised 1.6 41.13 Outstanding and Exercisable at December 31, 2020 4.3 $ 43.04
Schedule of aggregate and total intrinsic value of options exercised	At December 31, 2020, the aggregate intrinsic value for the options outstanding and exercisable was as follows: Southern Company Alabama Power Georgia Power Southern Company Gas (in millions) Total intrinsic value for outstanding and exercisable options $ 78 $ 8 $ 25 $ 6

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value on a recurring basis	The fair value increases (decreases) of the Funds, including unrealized gains (losses) and reinvested interest and dividends and excluding the Funds' expenses, for 2020, 2019, and 2018 are shown in the table below. Southern Company Alabama Georgia (in millions) Fair value increases (decreases) 2020 $ 280 $ 142 $ 138 2019 344 194 150 2018 (67) (38) (29) Unrealized gains (losses) At December 31, 2020 $ 220 $ 121 $ 99 At December 31, 2019 259 149 110 At December 31, 2018 (183) (96) (87) At December 31, 2020, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 401 $ 271 $ 32 $ — $ 704 Interest rate derivatives — 20 — — 20 Foreign currency derivatives — 87 — — 87 Investments in trusts: (b)(c) Domestic equity 862 151 — — 1,013 Foreign equity 85 253 — — 338 U.S. Treasury and government agency securities — 284 — — 284 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 13 386 — — 399 Mortgage and asset backed securities — 83 — — 83 Private equity — — — 76 76 Cash and cash equivalents 1 — — — 1 Other 28 7 — — 35 Cash equivalents 575 9 — — 584 Other investments 9 24 — — 33 Total $ 1,974 $ 1,677 $ 32 $ 76 $ 3,759 Liabilities: Energy-related derivatives (a) $ 389 $ 204 $ 4 $ — $ 597 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ 389 $ 227 $ 21 $ — $ 637 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 12 $ — $ — $ 12 Nuclear decommissioning trusts: (b) Domestic equity 543 141 — — 684 Foreign equity 85 73 — — 158 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 13 167 — — 180 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 76 76 Other 7 — — — 7 Cash equivalents 311 9 — — 320 Other investments — 24 — — 24 Total $ 959 $ 477 $ — $ 76 $ 1,512 Liabilities: Energy-related derivatives $ — $ 7 $ — $ — $ 7 Georgia Power Assets: Energy-related derivatives $ — $ 15 $ — $ — $ 15 Nuclear decommissioning trusts: (b)(c) Domestic equity 319 1 — — 320 Foreign equity — 177 — — 177 U.S. Treasury and government agency securities — 263 — — 263 Municipal bonds — 84 — — 84 Corporate bonds — 219 — — 219 Mortgage and asset backed securities — 54 — — 54 Other 21 7 — — 28 Total $ 340 $ 820 $ — $ — $ 1,160 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2020: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Cash equivalents 21 — — — 21 Total $ 21 $ 9 $ — $ — $ 30 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Foreign currency derivatives — 87 — — 87 Total $ — $ 89 $ — $ — $ 89 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 17 — 17 Total $ — $ 26 $ 17 $ — $ 43 Southern Company Gas Assets: Energy-related derivatives (a) $ 401 $ 233 $ 32 $ — $ 666 Non-qualified deferred compensation trusts: Domestic equity — 9 — — 9 Foreign equity — 3 — — 3 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Total $ 402 $ 262 $ 32 $ — $ 696 Liabilities: Energy-related derivatives (a)(b) $ 389 $ 172 $ 4 $ — $ 565 (a) Excludes $6 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $28 million. (b) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (c) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information. At December 31, 2019, 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 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (b)(c) Domestic equity 751 135 — — 886 Foreign equity 68 220 — — 288 U.S. Treasury and government agency securities — 307 — — 307 Municipal bonds — 85 — — 85 Pooled funds – fixed income — 17 — — 17 Corporate bonds 23 297 — — 320 Mortgage and asset backed securities — 87 — — 87 Private equity — — — 56 56 Cash and cash equivalents 1 — — — 1 Other 17 5 — — 22 Cash equivalents 1,393 2 — — 1,395 Other investments 9 21 — — 30 Total $ 2,650 $ 1,461 $ 22 $ 56 $ 4,189 Liabilities: Energy-related derivatives (a) $ 442 $ 254 $ 7 $ — $ 703 Interest rate derivatives — 24 — — 24 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ 442 $ 302 $ 26 $ — $ 770 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b) Domestic equity 488 123 — — 611 Foreign equity 68 64 — — 132 U.S. Treasury and government agency securities — 21 — — 21 Municipal bonds — 1 — — 1 Corporate bonds 23 144 — — 167 Mortgage and asset backed securities — 29 — — 29 Private equity — — — 56 56 Other 3 1 — — 4 Cash equivalents 691 2 — — 693 Other investments — 21 — — 21 Total $ 1,273 $ 410 $ — $ 56 $ 1,739 Liabilities: Energy-related derivatives $ — $ 24 $ — $ — $ 24 Georgia Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (b)(c) Domestic equity 263 1 — — 264 Foreign equity — 152 — — 152 U.S. Treasury and government agency securities — 286 — — 286 Municipal bonds — 84 — — 84 Corporate bonds — 153 — — 153 Mortgage and asset backed securities — 57 — — 57 Other 13 4 — — 17 Total $ 276 $ 741 $ — $ — $ 1,017 Liabilities: Energy-related derivatives $ — $ 53 $ — $ — $ 53 Interest rate derivatives — 17 — — 17 Total $ — $ 70 $ — $ — $ 70 Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient At December 31, 2019: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Cash equivalents 281 — — — 281 Total $ 281 $ 1 $ — $ — $ 282 Liabilities: Energy-related derivatives $ — $ 27 $ — $ — $ 27 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 16 — — 16 Cash equivalents 113 — — — 113 Total $ 113 $ 19 $ — $ — $ 132 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 19 — 19 Total $ — $ 27 $ 19 $ — $ 46 Southern Company Gas Assets: Energy-related derivatives (a) $ 388 $ 255 $ 22 $ — $ 665 Interest rate derivatives — 2 — — 2 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 17 — — 17 Cash equivalents 1 — — — 1 Cash equivalents 8 — — — 8 Total $ 397 $ 289 $ 22 $ — $ 708 Liabilities: Energy-related derivatives (a)(b) $ 442 $ 147 $ 7 $ — $ 596 (a) Excludes $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value and cash collateral of $99 million. (c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information. (d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information.
Financial instruments not having carrying amount equal to fair value	At December 31, 2020 and 2019, other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) At December 31, 2020: Long-term debt, including securities due within one year: Carrying amount $ 48,349 $ 8,864 $ 12,825 $ 1,400 $ 3,692 $ 6,626 Fair value 56,264 10,702 15,198 1,590 4,165 7,973 At December 31, 2019: Long-term debt, including securities due within one year: Carrying amount $ 44,561 $ 8,517 $ 11,660 $ 1,589 $ 4,398 $ 5,845 Fair value 48,339 9,525 12,680 1,671 4,708 6,509 (*) 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 transfers to Level 3	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. 2020 (in millions) Beginning balance $ 14 Transfers to Level 3 70 Transfers from Level 3 (34) Instruments realized or otherwise settled during period (16) Changes in fair value (6) Ending balance $ 28

DERIVATIVES (Tables)

DERIVATIVES (Tables)	12 Months Ended
	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of energy-related derivatives	At December 31, 2020, 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 (*) 835 2024 2031 Alabama Power 78 2024 — Georgia Power 135 2023 — Mississippi Power 89 2024 — Southern Power 10 2022 2021 Southern Company Gas (*) 523 2022 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 4,421 million mmBtu and short natural gas positions of 3,898 million mmBtu at December 31, 2020, which is also included in Southern Company's total volume.
Notional amount of interest rate derivatives	At December 31, 2020, the following interest rate derivatives were outstanding: Notional Interest Weighted Average Interest Hedge Fair Value (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 20 Southern Company $ 1,560 $ 20
Schedule of foreign exchange contracts	At December 31, 2020, the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 40 Southern Power 564 3.78% 500 1.85% June 2026 25 Total $ 1,241 € 1,100 $ 65
Fair value of energy-related derivatives and interest rate derivatives	At December 31, 2020 and 2019, the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 24 $ 11 $ 3 $ 70 Other deferred charges and assets/Other deferred credits and liabilities 18 19 6 44 Total derivatives designated as hedging instruments for regulatory purposes $ 42 $ 30 $ 9 $ 114 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 3 $ 5 $ 1 $ 6 Interest rate derivatives: Assets from risk management activities/Other current liabilities 20 — 2 23 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Foreign currency derivatives: Assets from risk management activities/Other current liabilities — 23 — 24 Other deferred charges and assets/Other deferred credits and liabilities 87 — 16 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 110 $ 28 $ 19 $ 54 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 388 $ 331 $ 461 $ 358 Other deferred charges and assets/Other deferred credits and liabilities 270 232 207 225 Total derivatives not designated as hedging instruments $ 658 $ 563 $ 668 $ 583 Gross amounts recognized $ 810 $ 621 $ 696 $ 751 Gross amounts offset (a) $ (529) $ (557) $ (463) $ (562) Net amounts recognized in the Balance Sheets (b) $ 281 $ 64 $ 233 $ 189 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 7 $ 2 $ 2 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 5 5 2 10 Total derivatives designated as hedging instruments for regulatory purposes $ 12 $ 7 $ 4 $ 24 Gross amounts recognized $ 12 $ 7 $ 4 $ 24 Gross amounts offset $ (7) $ (7) $ (2) $ (2) Net amounts recognized in the Balance Sheets $ 5 $ — $ 2 $ 22 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 7 $ 5 $ 1 $ 32 Other deferred charges and assets/Other deferred credits and liabilities 8 8 3 21 Total derivatives designated as hedging instruments for regulatory purposes $ 15 $ 13 $ 4 $ 53 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 17 Gross amounts recognized $ 15 $ 13 $ 4 $ 70 Gross amounts offset $ (12) $ (12) $ (3) $ (3) Net amounts recognized in the Balance Sheets $ 3 $ 1 $ 1 $ 67 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 4 $ 3 $ — $ 15 Other deferred charges and assets/Other deferred credits and liabilities 5 6 1 12 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 9 $ 1 $ 27 Gross amounts recognized $ 9 $ 9 $ 1 $ 27 Gross amounts offset $ (7) $ (7) $ (1) $ (1) Net amounts recognized in the Balance Sheets $ 2 $ 2 $ — $ 26 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 1 $ 2 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 24 Other deferred charges and assets/Other deferred credits and liabilities 87 — 16 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 89 $ 25 $ 17 $ 26 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ 1 $ 2 $ 1 Net amounts recognized in the Balance Sheets $ 89 $ 26 $ 19 $ 27 2020 2019 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) Southern Company Gas Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 6 $ 1 $ — $ 9 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 1 $ — $ 10 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 1 $ 3 $ — $ 4 Interest rate derivatives: Assets from risk management activities/Other current liabilities — — 2 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 1 $ 3 $ 2 $ 4 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Other current liabilities $ 388 $ 330 $ 459 $ 357 Other deferred charges and assets/Other deferred credits and liabilities 270 232 207 225 Total derivatives not designated as hedging instruments $ 658 $ 562 $ 666 $ 582 Gross amounts recognized $ 665 $ 566 $ 668 $ 596 Gross amounts offset (a) $ (503) $ (531) $ (456) $ (555) Net amounts recognized in the Balance Sheets (b) $ 162 $ 35 $ 212 $ 41 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $28 million and $99 million at December 31, 2020 and 2019, respectively. (b) Net amounts of derivative instruments outstanding exclude immaterial premium and intrinsic value associated with weather derivatives for all periods presented.
Pre-tax effects on the balance sheets	At December 31, 2020 and 2019, the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2020 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) 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 Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2019 Derivative Category and Balance Sheet Southern Alabama Georgia Mississippi Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (63) $ (14) $ (31) $ (15) $ (3) Other regulatory assets, deferred (37) (8) (18) (11) — Other regulatory liabilities, current 6 2 — — 4 Total energy-related derivative gains (losses) $ (94) $ (20) $ (49) $ (26) $ 1
Pre-tax effects of interest rate derivatives, designated as cash flow hedging instruments	For the years ended December 31, 2020, 2019, and 2018, the pre-tax effects of cash flow hedge accounting on AOCI for the applicable Registrants were as follows: Gain (Loss) Recognized in OCI on Derivative 2020 2019 2018 (in millions) Southern Company Energy-related derivatives $ (8) $ (13) $ 17 Interest rate derivatives (26) (57) (1) Foreign currency derivatives 48 (84) (78) Total $ 14 $ (154) $ (62) Georgia Power Interest rate derivatives $ (3) $ (59) $ — Southern Power Energy-related derivatives $ (2) $ (4) $ 10 Foreign currency derivatives 48 (84) (78) Total $ 46 $ (88) $ (68) Southern Company Gas Energy-related derivatives $ (6) $ (9) $ 7 Interest rate derivatives (23) 2 — Total $ (29) $ (7) $ 7
Pre-tax effect of interest rate and energy related derivatives	The pre-tax effects of cash flow and fair value hedge accounting on income for the years ended December 31, 2020, 2019, and 2018 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2020 2019 2018 (in millions) Southern Company Total cost of natural gas $ 972 $ 1,319 $ 1,539 Gain (loss) on energy-related cash flow hedges (a) (8) (2) 2 Total depreciation and amortization 3,518 3,038 3,131 Gain (loss) on energy-related cash flow hedges (a) (3) (6) 7 Total interest expense, net of amounts capitalized (1,821) (1,736) (1,842) Gain (loss) on interest rate cash flow hedges (a) (26) (20) (21) Gain (loss) on foreign currency cash flow hedges (a) (23) (24) (24) Gain (loss) on interest rate fair value hedges (b) 27 42 (12) Total other income (expense), net 336 252 114 Gain (loss) on foreign currency cash flow hedges (a)(c) 114 (24) (60) Southern Power Total depreciation and amortization $ 494 $ 479 $ 493 Gain (loss) on energy-related cash flow hedges (a) (3) (6) 7 Total interest expense, net of amounts capitalized (151) (169) (183) Gain (loss) on foreign currency cash flow hedges (a) (23) (24) (24) Total other income (expense), net 19 47 23 Gain (loss) on foreign currency cash flow hedges (a)(c) 114 (24) (60) (a) Reclassified from AOCI 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 AOCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes.
Schedule of fair value hedging instruments, statements of financial performance and financial position, location	At December 31, 2020 and 2019, 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 At December 31, 2020 At December 31, 2019 At December 31, 2020 At December 31, 2019 (in millions) (in millions) Southern Company Securities due within one year $ (1,509) $ (599) $ (10) $ — Long-term debt — (1,494) — 3
Pre-tax effect of interest rate and energy related derivatives	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 for the years ended December 31, 2020, 2019, and 2018 were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2020 2019 2018 (in millions) Energy-related derivatives Natural gas revenues (*) $ 134 $ 223 $ (122) Cost of natural gas 15 10 (6) Total derivatives in non-designated hedging relationships $ 149 $ 233 $ (128) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $9 million, $3 million, and $5 million for the years ended December 31, 2020, 2019, and 2018, respectively, as they are accounted for based on intrinsic value rather than fair value.

ACQUISITIONS AND DISPOSITIONS (

ACQUISITIONS AND DISPOSITIONS (Tables)	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Schedule of business acquisitions, by acquisition	Project Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern COD PPA Contract Period Asset Acquisitions During 2020 Beech Ridge II Wind Invenergy Renewables LLC 56 Greenbrier County, WV 100% of Class A (a) May 12 years Asset Acquisitions During 2019 DSGP (b) Fuel Cell Bloom Energy 28 Delaware 100% of Class B N/A (c) 15 years (d) Asset Acquisitions During 2018 Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC 20 Kern County, CA 100% of Class B (e) March 2018 20 years (a) In May 2020, Southern Power purchased a controlling interest and now consolidates the project's operating results in its financial statements. The Class B member owns the noncontrolling interest. (b) During 2019, Southern Power purchased a controlling interest and now consolidates the project's operating results in its financial statements. The Class A and Class C members each own a noncontrolling interest. Southern Power records net income attributable to noncontrolling interests for approximately 10 MWs of the facility. (c) Southern Power's 18-MW share of the facility was repowered between June and August 2019. In December 2019, a Class C member joined the existing partnership between the Class A member and Southern Power and made an investment to repower the remaining 10 MWs. (d) Remaining PPA contract period at the time of acquisition. (e) Southern Power owns a controlling interest under a tax equity partnership.
Schedule of construction projects	During 2020, Southern Power completed construction of and placed in service the Reading and Skookumchuck wind facilities, commenced construction of the Garland and Tranquillity battery energy storage facilities, and acquired and commenced construction of 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 December 31, 2020, the total costs of construction incurred and included in CWIP for these projects were $34 million. The ultimate outcome of these matters cannot be determined at this time. Project Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected PPA Contract Period Projects Under Construction at December 31, 2020 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 Projects Completed During 2020 Skookumchuck (c) Wind 136 Lewis and Thurston Counties, WA November 2020 20 years Reading (d) Wind 200 Osage and Lyon Counties, KS May 2020 12 years Projects Completed During 2019 (e) Wildhorse Mountain (f) Wind 100 Pushmataha County, OK December 2019 20 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. (c) In October 2019, Southern Power purchased 100% of the membership interests of the Skookumchuck facility pursuant to a joint development arrangement. In November 2020, Southern Power completed a tax equity transaction whereby it received $121 million, resulting in 100% ownership of the Class B membership interests. Southern Power subsequently sold a noncontrolling interest in the Class B membership interests and now retains the controlling ownership interest in the facility. (d) In 2018, Southern Power purchased 100% of the membership interests of the Reading facility pursuant to a joint development arrangement. In June 2020, Southern Power completed a tax equity transaction whereby it received $156 million and owns 100% of the Class B membership interests. (e) During 2019, Southern Power also completed the expansion of Plant Mankato, which was sold to a subsidiary of Xcel on January 17, 2020. See "Sales of Natural Gas and Biomass Plants" below for additional information. (f) In 2018, Southern Power purchased 100% of the membership interests of the Wildhorse Mountain facility. In December 2019, Southern Power entered into a tax equity partnership and owns 100% of the Class B membership interests.
Disposal groups, including discontinued operations	The following table provides the major classes of assets and liabilities classified as held for sale for Southern Company, Southern Power, and Southern Company Gas at December 31, 2020 and/or 2019: Southern Southern Southern Company Gas At December 31, At December 31, At December 31, 2020 2019 2019 2019 (in millions) Assets Held for Sale: Current assets $ — $ 19 $ 17 $ 2 Total property, plant, and equipment 8 565 547 18 Goodwill and other intangible assets — 40 40 — Equity investments in unconsolidated subsidiaries — 151 — 151 Leveraged leases 52 — — — Other non-current assets — 14 14 — Total Assets Held for Sale $ 60 $ 789 $ 618 $ 171 Liabilities Held for Sale (all current): $ — $ 5 $ 3 $ 2 2020 2019 2018 (in millions) Earnings before income taxes: Gulf Power N/A N/A $ 140 Southern Power's Florida Plants (a)(b) N/A N/A $ 49 Southern Power's Plant Nacogdoches (a)(c) N/A $ 13 $ 27 Southern Power's Plant Mankato (a)(d) $ 2 $ 29 N/M N/M - Not material (a) Earnings before income taxes reflect the cessation of depreciation and amortization on the long-lived assets being sold upon classification as held for sale. (b) 2018 amount represents the period from January 1, 2018 to December 4, 2018 (the divestiture date). (c) 2019 amount represents the period from January 1, 2019 to June 13, 2019 (the divestiture date). (d) 2020 amount represents the period from January 1, 2020 to January 17, 2020 (the divestiture date).

SEGMENT AND RELATED INFORMATI_2

SEGMENT AND RELATED INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Financial data for business segments	Financial data for business segments and products and services for the years ended December 31, 2020, 2019, and 2018 was as follows: Electric Utilities Traditional Southern Eliminations Total Southern Company Gas All Eliminations Consolidated (in millions) 2020 Operating revenues $ 15,135 $ 1,733 $ (371) $ 16,497 $ 3,434 $ 596 $ (152) $ 20,375 Depreciation and amortization 2,447 494 — 2,941 500 77 — 3,518 Interest income 26 4 — 30 5 6 (4) 37 Earnings from equity method investments — — — — 141 12 — 153 Interest expense 825 151 — 976 231 614 — 1,821 Income taxes (benefit) 514 3 — 517 173 (297) — 393 Segment net income (loss) (a)(b)(c)(d)(e) 2,877 238 — 3,115 590 (592) 6 3,119 Goodwill — 2 — 2 5,015 263 — 5,280 Total assets 85,486 13,235 (680) 98,041 22,630 3,168 (904) 122,935 2019 Operating revenues $ 15,569 $ 1,938 $ (412) $ 17,095 $ 3,792 $ 690 $ (158) $ 21,419 Depreciation and amortization 1,993 479 — 2,472 487 79 — 3,038 Interest income 38 9 — 47 3 16 (6) 60 Earnings from equity method investments 2 3 — 5 157 — — 162 Interest expense 818 169 — 987 232 517 — 1,736 Income taxes (benefit) 764 (56) — 708 130 960 — 1,798 Segment net income (loss) (a)(f)(g)(h) 2,929 339 — 3,268 585 908 (22) 4,739 Goodwill — 2 — 2 5,015 263 — 5,280 Total assets 81,063 14,300 (713) 94,650 21,687 3,511 (1,148) 118,700 2018 Operating revenues $ 16,843 $ 2,205 $ (477) $ 18,571 $ 3,909 $ 1,213 $ (198) $ 23,495 Depreciation and amortization 2,072 493 — 2,565 500 66 — 3,131 Interest income 23 8 — 31 4 8 (5) 38 Earnings from equity method investments (1) — — (1) 148 2 (1) 148 Interest expense 852 183 — 1,035 228 580 (1) 1,842 Income taxes (benefit) 371 (164) — 207 464 (222) — 449 Segment net income (loss) (a)(b)(i)(j) 2,117 187 — 2,304 372 (453) 3 2,226 Goodwill — 2 — 2 5,015 298 — 5,315 Total assets 79,382 14,883 (306) 93,959 21,448 3,285 (1,778) 116,914 (a) Attributable to Southern Company. (b) For the traditional electric operating companies, includes pre-tax charges at Georgia Power for estimated loss on Plant Vogtle Units 3 and 4 of $325 million ($242 million after tax) in 2020 and $1.1 billion ($0.8 billion after tax) in 2018. See Note 2 under "Georgia Power – Nuclear Construction" for additional information. (c) For Southern Power, includes a $39 million pre-tax gain ($23 million gain after tax) on the sale of Plant Mankato. See Note 15 under "Southern Power" for additional information. (d) For Southern Company Gas, includes a $22 million pre-tax gain ($16 million gain after tax) on the sale of Jefferson Island. See Note 15 under "Southern Company Gas" for additional information. (e) For the "All Other" column, includes pre-tax impairment charges totaling $206 million ($105 million after tax) related to leveraged lease investments. See Note 3 under "Other Matters – Southern Company" for additional information. (f) For Southern Power, includes a $23 million pre-tax gain ($88 million gain after tax) on the sale of Plant Nacogdoches. See Note 15 under "Southern Power" for additional information. (g) For Southern Company Gas, includes pre-tax impairment charges totaling $115 million ($86 million after tax). See Notes 3 and 15 under "Other Matters – Southern Company Gas" and "Southern Company Gas – Sale of Pivotal LNG and Atlantic Coast Pipeline," respectively, for additional information. (h) For the "All Other" column, includes the pre-tax gain associated with the sale of Gulf Power of $2.6 billion ($1.4 billion after tax), the pre-tax loss, including related impairment charges, on the sales of certain PowerSecure business units totaling $58 million ($52 million after tax), and a pre-tax impairment charge of $17 million ($13 million after tax) related to a leveraged lease investment. See Notes 3 and 15 under "Other Matters – Southern Company" and "Southern Company," respectively, for additional information. (i) For Southern Power, includes pre-tax impairment charges of $156 million ($117 million after tax). See Note 15 under "Southern Power" for additional information. (j) For Southern Company Gas, includes a net gain on dispositions of $291 million ($51 million loss after tax), as well as a goodwill impairment charge of $42 million related to the sale of Pivotal Home Solutions. See Note 15 under "Southern Company Gas" for additional information. Financial data for business segments for the years ended December 31, 2020, 2019, and 2018 was as follows: Gas Distribution Operations (a) Gas Pipeline Investments Wholesale Gas Services (b) Gas Marketing Services (c) Total All Other (d) Eliminations Consolidated (in millions) 2020 Operating revenues $ 2,952 $ 32 $ 74 $ 408 $ 3,466 $ 36 $ (68) $ 3,434 Depreciation and amortization 442 5 1 22 470 30 — 500 Operating income (loss) 655 20 20 119 814 (7) 5 812 Earnings from equity method investments — 141 — — 141 — — 141 Interest expense 192 29 4 3 228 3 — 231 Income taxes (benefit) 114 33 3 28 178 (5) — 173 Segment net income (loss) 390 99 14 89 592 (2) — 590 Total assets at December 31, 2020 19,090 1,597 850 1,503 23,040 11,336 (11,746) 22,630 2019 Operating revenues $ 3,028 $ 32 $ 294 $ 456 $ 3,810 $ 44 $ (62) $ 3,792 Depreciation and amortization 422 5 1 26 454 33 — 487 Operating income (loss) 573 20 219 112 924 (154) — 770 Earnings from equity method investments — 162 — — 162 (5) — 157 Interest expense 187 30 5 3 225 7 — 232 Income taxes (benefit) 63 58 52 27 200 (70) — 130 Segment net income (loss) 337 94 163 83 677 (92) — 585 Total assets at December 31, 2019 18,204 1,678 850 1,496 22,228 10,759 (11,300) 21,687 2018 Operating revenues $ 3,186 $ 32 $ 144 $ 568 $ 3,930 $ 55 $ (76) $ 3,909 Depreciation and amortization 409 5 2 37 453 47 — 500 Operating income (loss) 904 20 70 19 1,013 (98) — 915 Earnings from equity method investments — 145 — — 145 3 — 148 Interest expense 178 34 9 6 227 1 — 228 Income taxes (benefit) 409 28 4 54 495 (31) — 464 Segment net income (loss) 334 103 38 (40) 435 (63) — 372 Total assets at December 31, 2018 17,266 1,763 1,302 1,587 21,918 11,112 (11,582) 21,448 (a) Operating revenues for the three gas distribution operations dispositions were $244 million for 2018. Segment net income for gas distribution operations includes a gain on dispositions of $324 million ($16 million after tax) in 2018. (b) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) 2020 $ 4,544 $ 115 $ 4,659 $ 4,585 $ 74 2019 5,703 275 5,978 5,684 294 2018 6,955 451 7,406 7,262 144 (c) Operating revenues for the gas marketing services disposition were $55 million in 2018. Segment net income for gas marketing services includes a loss on disposition of $33 million ($67 million loss after tax) and a goodwill impairment charge of $42 million in 2018 recorded in contemplation of the sale of Pivotal Home Solutions. (d) Segment net income (loss) for the "All Other" column include s a $22 million pre-tax gain ($16 million g ain after tax) on the sale of Jefferson Island in 2020 and pre-tax impairment charges totaling $115 million ($86 million after tax) in 2019. See Note 3 under "Other Matters – Southern Company Gas" for additional information.
Financial data for products and services	Products and Services Electric Utilities' Revenues Year Retail Wholesale Other Total (in millions) 2020 $ 13,643 $ 1,945 $ 909 $ 16,497 2019 14,084 2,152 859 17,095 2018 15,222 2,516 833 18,571 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2020 $ 2,902 $ 408 $ 124 $ 3,434 2019 3,001 456 335 3,792 2018 3,155 568 186 3,909
Schedule of reconciliation of operating revenues and intercompany revenues	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) 2020 $ 4,544 $ 115 $ 4,659 $ 4,585 $ 74 2019 5,703 275 5,978 5,684 294 2018 6,955 451 7,406 7,262 144

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - General (Narrative) (Details)	Dec. 31, 2020electric_companystate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of traditional electric operating companies | electric_company	3
Traditional Operating Companies
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity provides utilities | state	3

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 478	$ 527	$ 508
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	15	17	8
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	639	704	653
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	108	99	101
Georgia Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	0	4	21
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	149	118	104
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	4	3	15
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	87	90	98
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	8	14	41
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	29	28	25
Southern Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	26	64	119
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	237	183	194
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 29	$ 31	$ 32

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Affiliate Transactions (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Southern Company Gas
Related Party Transaction [Line Items]
Proceeds from affiliate	$ 71,000,000
Southern Nuclear Operating Company, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		$ 262,000,000	$ 256,000,000	$ 247,000,000
Southern Nuclear Operating Company, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services		883,000,000	760,000,000	780,000,000
Southern Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services		141,000,000	177,000,000	216,000,000
Southern Natural Gas Company, LLC | Alabama Power
Related Party Transaction [Line Items]
Costs for services		15,000,000	17,000,000	8,000,000
Southern Natural Gas Company, LLC | Georgia Power
Related Party Transaction [Line Items]
Costs for services		108,000,000	99,000,000	101,000,000
Proceeds from affiliate	$ 142,000,000
Southern Natural Gas Company, LLC | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services		29,000,000	31,000,000	32,000,000
Southern Natural Gas Company, LLC | Southern Power
Related Party Transaction [Line Items]
Costs for services		29,000,000	28,000,000	25,000,000
Gulf Power | Alabama Power
Related Party Transaction [Line Items]
Amounts received related to tariff				11,000,000
Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services				8,000,000
Gulf Power | Mississippi Power
Related Party Transaction [Line Items]
Costs for services				31,000,000
PowerSecure International, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		0	7,000,000	24,000,000
PowerSecure International, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services		11,000,000	0	0
Southern Company Services, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		478,000,000	527,000,000	508,000,000
Southern Company Services, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services		639,000,000	704,000,000	653,000,000
Southern Company Services, Inc. | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services		237,000,000	183,000,000	194,000,000
Southern Company Services, Inc. | Mississippi Power
Related Party Transaction [Line Items]
Costs for services		149,000,000	118,000,000	104,000,000
Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services		87,000,000	90,000,000	98,000,000
Non-Fuel Expense | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services		9,000,000	9,000,000	8,000,000
Purchased Power from Affiliates | Southern Power
Related Party Transaction [Line Items]
Costs for services		139,000,000	174,000,000	215,000,000
Operating Lease PPA | Southern Power
Related Party Transaction [Line Items]
Costs for services		115,000,000	116,000,000	65,000,000
Electric Transmission | Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services		$ 15,000,000	$ 15,000,000	$ 12,000,000
Plant Scherer (coal) Unit 3 | Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Proportionate share of related non-fuel expenses (percent)		25.00%
Plant Daniel | Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Proportionate share of related non-fuel expenses (percent)		50.00%

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020
Southern Company Gas
Disaggregation of Revenue [Line Items]
Period for collection of revenue prior to billings	24 months

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Credit Risk (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)counterpartycustomer	Dec. 31, 2019USD ($)
Concentration Risk [Line Items]
Accounts Receivables	$ 2,614	$ 2,413
Southern Company Gas
Concentration Risk [Line Items]
Accounts Receivables	$ 788	$ 749
Atlanta Gas Light
Concentration Risk [Line Items]
Number of customers in Georgia | customer	16
Percent of highest month's estimated bill	200.00%
Credit Concentration Risk | Wholesale gas services | Accounts Receivable | Southern Company Gas
Concentration Risk [Line Items]
Number of top counterparties | counterparty	20
Credit risk exposure, measurement period	30 days
Concentration risk (as percent)	58.00%
Accounts Receivables	$ 234

SUMMARY OF SIGNIFICANT ACCOUN_9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Revenue (Narrative) (Details) - Mississippi Power	12 Months Ended
	Dec. 31, 2020
Concentration Risk [Line Items]
Wholesale customers representing total operating revenues (percent)	15.30%
Period of cancellation notices	10 years

SUMMARY OF SIGNIFICANT ACCOU_10

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Concentration of Revenue (Details) - Southern Power - Sales Revenue, Goods, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Southern California Edison
Concentration Risk [Line Items]
Percentage of total revenues	9.40%	6.80%	6.20%
Georgia Power
Concentration Risk [Line Items]
Percentage of total revenues	8.00%	9.00%	9.80%
Duke Energy Corporation
Concentration Risk [Line Items]
Percentage of total revenues	6.70%		6.80%
Morgan Stanley Capital Group
Concentration Risk [Line Items]
Percentage of total revenues		4.90%

SUMMARY OF SIGNIFICANT ACCOU_11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income and Other Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Southern Power
Tax Credit Carryforward [Line Items]
Percentage reduction in tax basis of assets	50.00%
Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected	$ 107	$ 117	$ 114
Included In Operating Expenses | Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected	$ 104	$ 114	$ 111

SUMMARY OF SIGNIFICANT ACCOU_12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Total AFUDC and Interest Capitalized (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 230	$ 202	$ 210
Alabama Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	61	71	84
Georgia Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	138	103	94
Mississippi Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	1	0	0
Southern Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	11	15	17
Southern Company Gas
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 18	$ 13	$ 14

SUMMARY OF SIGNIFICANT ACCOU_13

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Average AFUDC Composite Rates (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Alabama Power
Capitalized Contract Cost [Line Items]
Composite rate	8.10%	8.40%	8.30%
Georgia Power
Capitalized Contract Cost [Line Items]
Composite rate	6.90%	6.90%	7.30%
Mississippi Power
Capitalized Contract Cost [Line Items]
Composite rate	5.40%	7.30%	3.30%
Atlanta Gas Light
Capitalized Contract Cost [Line Items]
Composite rate	7.70%	7.80%	7.90%
Chattanooga Gas
Capitalized Contract Cost [Line Items]
Composite rate	7.10%	7.10%	7.40%
Nicor Gas
Capitalized Contract Cost [Line Items]
Composite rate	0.70%	2.30%	2.10%

SUMMARY OF SIGNIFICANT ACCOU_14

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill and Other Intangible Assets and Liabilities (Narrative) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0
Goodwill	5,280,000,000			$ 5,280,000,000	$ 5,315,000,000
Intangible liabilities included in other deferred credits and liabilities	480,000,000			609,000,000
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	0
Goodwill	5,015,000,000			5,015,000,000
Intangible liabilities included in other deferred credits and liabilities	54,000,000			$ 51,000,000
Intangible liabilities | Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Intangible liabilities included in other deferred credits and liabilities	91,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure Utility Infrastructure Services Unit
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment			$ 32,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure Utility Infrastructure Services Unit | COVID-19
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 263,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure International, Inc. Lighting Business
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment		$ 2,000,000
Impairment of intangible assets		$ 3,000,000

SUMMARY OF SIGNIFICANT ACCOU_15

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Goodwill Balances (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 5,280	$ 5,280	$ 5,315
Southern Company Gas
Goodwill [Line Items]
Goodwill	5,015	5,015
Gas distribution operations | Southern Company Gas
Goodwill [Line Items]
Goodwill	4,034	4,034
Gas marketing services | Southern Company Gas
Goodwill [Line Items]
Goodwill	$ 981	$ 981

SUMMARY OF SIGNIFICANT ACCOU_16

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 740	$ 741
Accumulated Amortization	(328)	(280)
Other Intangible Assets, Net	412	461
Intangible assets, gross	815	816
Intangible assets, net	487	536
Federal Communications Commission licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	75	75
Accumulated Amortization	0	0
Other Intangible Assets, Net	75	75
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	212	212
Accumulated Amortization	(135)	(116)
Other Intangible Assets, Net	77	96
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(31)	(25)
Other Intangible Assets, Net	33	39
Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(62)
Other Intangible Assets, Net	0	2
PPA fair value adjustments
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	390
Accumulated Amortization	(89)	(69)
Other Intangible Assets, Net	301	321
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10	11
Accumulated Amortization	(9)	(8)
Other Intangible Assets, Net	1	3
Southern Power
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(89)	(69)
Southern Power | PPA fair value adjustments
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	390
Accumulated Amortization	(89)	(69)
Other Intangible Assets, Net	301	321
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	246	246
Accumulated Amortization	(195)	(176)
Other Intangible Assets, Net	51	70
Intangible assets, net	51	70
Southern Company Gas | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	156	156
Accumulated Amortization	(119)	(104)
Other Intangible Assets, Net	37	52
Southern Company Gas | Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26	26
Accumulated Amortization	(12)	(10)
Other Intangible Assets, Net	14	16
Southern Company Gas | Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(64)	(62)
Other Intangible Assets, Net	$ 0	$ 2

SUMMARY OF SIGNIFICANT ACCOU_17

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 49	$ 61	$ 89
Estimated future amortization
2021	43
2022	39
2023	37
2024	35
2025	32
Southern Power
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	20	19	25
Estimated future amortization
2021	20
2022	20
2023	20
2024	20
2025	20
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	19	31	52
Estimated future amortization
2021	14
2022	11
2023	9
2024	7
2025	6
Southern Company Gas | Gas marketing services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	17	23	32
Southern Company Gas | Wholesale gas services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	2	8	20
Operating Revenues
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 22	$ 27	$ 45

SUMMARY OF SIGNIFICANT ACCOU_18

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Transmission Receivables/Prepayments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020
Southern Power
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Period of reimbursement for transmission costs	5 years

SUMMARY OF SIGNIFICANT ACCOU_19

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Other Accounts and Notes Receivable | Southern Company Gas
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 2	$ 3

SUMMARY OF SIGNIFICANT ACCOU_20

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Storm Damage Reserves (Details) - Major storms - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 326,000,000	$ 170,000,000	$ 74,000,000
Alabama Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs	100,000,000	84,000,000	0
Storm damage reserves	112,000,000	139,000,000	16,000,000
Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	213,000,000	30,000,000	30,000,000
Mississippi Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 1,000,000	1,000,000	1,000,000
Gulf Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			$ 26,900,000
Accumulated Deferred Income Taxes | Alabama Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves		$ 39,000,000

SUMMARY OF SIGNIFICANT ACCOU_21

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leveraged Leases (Narrative) (Details) - leveraged_lease	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leveraged Lease [Line Items]
Number of leveraged leases	4	4
Maximum
Leveraged Lease [Line Items]
Original term (up to)	45 years	45 years

SUMMARY OF SIGNIFICANT ACCOU_22

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Net Investment in Domestic and International Leveraged Leases (Details) - Domestic and international leveraged leases - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leveraged Lease [Line Items]
Net rentals receivable	$ 734	$ 1,410
Unearned income	(178)	(622)
Investment in leveraged leases	556	788
Deferred taxes from leveraged leases	(7)	(238)
Net investment in leveraged leases	$ 549	$ 550

SUMMARY OF SIGNIFICANT ACCOU_23

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of the Components of Income from Leveraged Leases (Details) - Domestic and international leveraged leases - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leveraged Lease [Line Items]
Pretax leveraged lease income (loss)	$ (180)	$ 11	$ 25
Income tax benefit (expense)	98	0	(6)
Net leveraged lease income (loss)	$ (82)	$ 11	$ 19

SUMMARY OF SIGNIFICANT ACCOU_24

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Natural Gas for Sale (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nicor Gas
Inventory [Line Items]
LIFO inventory balance	$ 178
Estimated replacement cost of inventory	259
Southern Company Gas
Inventory [Line Items]
LOCOM adjustments	$ 1	$ 21	$ 10

SUMMARY OF SIGNIFICANT ACCOU_25

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Energy Marketing Receivables and Payables (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Required collateral in the event of a credit rating downgrade	$ 5	$ 11

SUMMARY OF SIGNIFICANT ACCOU_26

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Uncollectible accounts, average percent of revenues (less than)	1.00%

SUMMARY OF SIGNIFICANT ACCOU_27

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Financial Instruments (Narrative) (Details)	Dec. 31, 2020USD ($)
Alabama Power
Derivative [Line Items]
Derivative collateral obligation to return cash	$ 0

SUMMARY OF SIGNIFICANT ACCOU_28

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AOCI (Loss) Balances, Net of Tax Effects (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 31,759	$ 29,039	$ 25,528
Current period change	(75)	(118)	26
Ending balance	32,234	31,759	29,039
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(179)
Current period change	(30)
Ending balance	(209)	(179)
Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(142)
Current period change	(45)
Ending balance	(187)	(142)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(321)	(203)	(189)
Current period change	(75)
Ending balance	(395)	(321)	(203)
Southern Power
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,622	7,284	6,498
Current period change	(42)	(42)	14
Ending balance	6,631	6,622	7,284
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	11
Current period change	(32)
Ending balance	(21)	11
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(37)
Current period change	(10)
Ending balance	(47)	(37)
Southern Power | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(26)	16	(2)
Current period change	(42)
Ending balance	(67)	(26)	16
Southern Company Gas
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	9,506	8,570	9,022
Current period change	(29)	(19)	2
Ending balance	9,767	9,506	8,570
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(6)
Current period change	(14)
Ending balance	(20)	(6)
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	13
Current period change	(15)
Ending balance	(2)	13
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	7	26	20
Current period change	(29)
Ending balance	$ (22)	$ 7	$ 26

REGULATORY MATTERS - Schedule o

REGULATORY MATTERS - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 17, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 5,493	$ 3,838
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,481	810
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		28 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,252	3,507
Costs recovered annually		12	2	$ 2
Recoveries for storm damage		$ 213
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		32 years
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 136	64
Regulatory asset amortization period	4 years
Regulatory liability amortization period	3 years
Mississippi Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		8 years
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (1,925)	(1,874)
Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		7 years
Deferred Income Tax Credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (6,016)	(6,301)
Deferred Income Tax Credits | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(2,016)	(1,960)
Deferred Income Tax Credits | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(2,805)	(3,078)
Deferred Income Tax Credits | Georgia Power | Plant Vogtle Units 3 And 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities		440
Deferred Income Tax Credits | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(320)	(358)
Regulatory liabilities		74
Deferred Income Tax Credits | Mississippi Power | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities		$ 66
Regulatory liability amortization period		3 years
Deferred Income Tax Credits | Mississippi Power | Wholesale electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities		$ 9
Regulatory liability amortization period		2 years
Deferred Income Tax Credits | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (847)	(874)
Other Cost of Removal Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(1,999)	(2,084)
Other Cost of Removal Obligations | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(335)	(412)
Other Cost of Removal Obligations | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		212	156
Other Cost of Removal Obligations | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(194)	(189)
Other Cost of Removal Obligations | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(1,649)	(1,606)
Over Recovered Regulatory Clause Revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(185)	(205)
Over Recovered Regulatory Clause Revenues | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (46)	(112)
Regulatory liability amortization period		9 years
Over Recovered Regulatory Clause Revenues | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (44)	(10)
Regulatory liability amortization period		2 years
Over Recovered Regulatory Clause Revenues | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
Over Recovered Regulatory Clause Revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (95)	(82)
Regulatory liability amortization period		5 years
Storm/Property Damage Reserves
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (81)	(204)
Storm/Property Damage Reserves | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(77)	(150)
Storm/Property Damage Reserves | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Storm/Property Damage Reserves | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(4)	(55)
Storm/Property Damage Reserves | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Customer Refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(56)	(285)
Customer Refunds | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(50)	(56)
Regulatory liabilities		50	53
Customer Refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(6)	(229)
Regulatory liabilities			110
Customer Refunds | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Customer Refunds | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Other Regulatory Liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(149)	(70)
Other Regulatory Liabilities | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (37)	(19)
Regulatory liability amortization period		17 years
Other Regulatory Liabilities | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (30)	(6)
Regulatory liability amortization period		12 years
Other Regulatory Liabilities | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (6)	(10)
Regulatory liability amortization period		3 years
Other Regulatory Liabilities | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (54)	(22)
Regulatory liability amortization period		20 years
Excess Deferred Income Tax Liabilities Not Subject To Normalization | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 8
Tax Reform Settlement Agreement | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities			105
AROs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		5,147	4,381
AROs | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,470	1,043
AROs | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		53 years
AROs | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,457	3,119
AROs | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		60 years
AROs | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 212	210
AROs | Mississippi Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		55 years
AROs | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
AROs | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		80 years
Retiree Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,958	4,423
Retiree Benefit Plans | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,265	1,131
Retiree Benefit Plans | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		13 years
Retiree Benefit Plans | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,647	1,516
Retiree Benefit Plans | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		13 years
Retiree Benefit Plans | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 238	213
Retiree Benefit Plans | Mississippi Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		14 years
Retiree Benefit Plans | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 187	167
Retiree Benefit Plans | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		13 years
Remaining Net Book Value of Retired Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,183	1,275
Remaining Net Book Value of Retired Assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		632	649
Remaining Net Book Value of Retired Assets | Alabama Power | Plant Gorgas Units 8, 9, And 10
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 585
Remaining Net Book Value of Retired Assets | Alabama Power | Maximum | Plant Gorgas Units 8, 9, And 10
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		17 years
Remaining Net Book Value of Retired Assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 527	$ 596
Remaining Net Book Value of Retired Assets | Georgia Power | Plant Hammond Units 1 - 4 and Plant Branch Units 2 - 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		503
Remaining Net Book Value of Retired Assets | Georgia Power | Plant McIntosh Unit 1 and Plant Mitchell Unit 3
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 24
Remaining Net Book Value of Retired Assets | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period			3 years
Remaining Net Book Value of Retired Assets | Georgia Power | Maximum | Plant Hammond Units 1 - 4 and Plant Branch Units 2 - 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		15 years
Remaining Net Book Value of Retired Assets | Georgia Power | Minimum | Plant Hammond Units 1 - 4 and Plant Branch Units 2 - 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		2 years
Remaining Net Book Value of Retired Assets | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 24	$ 30
Remaining Net Book Value of Retired Assets | Mississippi Power | Plant Watson and Plant Greene County | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 11
Regulatory asset amortization period		4 years
Remaining Net Book Value of Retired Assets | Mississippi Power | Plant Watson and Plant Greene County | Wholesale electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 13
Regulatory asset amortization period		10 years
Remaining Net Book Value of Retired Assets | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
Deferred Income Tax Charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		801	803
Deferred Income Tax Charges | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		235	245
Deferred Income Tax Charges | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		531	523
Deferred Income Tax Charges | Georgia Power | Plant Vogtle Units 3 And 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset		145
Deferred Income Tax Charges | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		32	33
Deferred Income Tax Charges | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Environmental Remediation
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		310	349
Environmental Remediation | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Environmental Remediation | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		41	52
Environmental Remediation | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Environmental Remediation | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		269	296
Loss on Reacquired Debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		304	323
Loss on Reacquired Debt | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		47	52
Loss on Reacquired Debt | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		248	262
Loss on Reacquired Debt | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		6	6
Loss on Reacquired Debt | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		3	4
Storm Damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		262	410
Storm Damage | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Storm Damage | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		262	410
Storm Damage | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Storm Damage | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Vacation Pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 207	186
Regulatory asset amortization period		1 year
Vacation Pay | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 80	72
Vacation Pay | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		104	93
Vacation Pay | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		10	9
Vacation Pay | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		13	11
Under Recovered Regulatory Clause Revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		185	159
Under Recovered Regulatory Clause Revenues | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 58	40
Regulatory asset amortization period		9 years
Under Recovered Regulatory Clause Revenues | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
Regulatory asset amortization period		2 years
Under Recovered Regulatory Clause Revenues | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 52	47
Under Recovered Regulatory Clause Revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 75	72
Regulatory asset amortization period		5 years
Regulatory Clauses
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 142	142
Regulatory Clauses | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		142	142
Regulatory Clauses | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Regulatory Clauses | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Regulatory Clauses | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Nuclear Outage
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		101	105
Nuclear Outage | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 61	78
Regulatory asset amortization period		18 months
Nuclear Outage | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 40	27
Nuclear Outage | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		24 months
Nuclear Outage | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
Nuclear Outage | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 0	0
Fuel Hedging (Realized And Unrealized) Losses
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			102
Fuel Hedging (Realized And Unrealized) Losses | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			22
Regulatory asset amortization period		3 years 6 months
Fuel Hedging (Realized And Unrealized) Losses | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			53
Regulatory asset amortization period		3 years
Fuel Hedging (Realized And Unrealized) Losses | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			27
Regulatory asset amortization period		5 years
Fuel Hedging (Realized And Unrealized) Losses | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			0
Long Term Debt Fair Value Adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 92	107
Long Term Debt Fair Value Adjustment | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Long Term Debt Fair Value Adjustment | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Long Term Debt Fair Value Adjustment | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Long Term Debt Fair Value Adjustment | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 92	107
Long Term Debt Fair Value Adjustment | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		18 years
Kemper County energy facility assets, net
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 50	61
Kemper County energy facility assets, net | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Kemper County energy facility assets, net | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Kemper County energy facility assets, net | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		50	61
Regulatory asset		62
Regulatory liabilities		12
Kemper County energy facility assets, net | Mississippi Power | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset		50
Regulatory liabilities		12
Kemper County energy facility assets, net | Mississippi Power | Wholesale electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset		12
Kemper County energy facility assets, net | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		32	34
Plant Daniel Units 3 and 4 | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Plant Daniel Units 3 and 4 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Plant Daniel Units 3 and 4 | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		32	34
Plant Daniel Units 3 and 4 | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		0	0
Other Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		205	127
Other Regulatory Assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 52	45
Regulatory asset amortization period		23 years
Other Regulatory Assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 68	23
Regulatory asset amortization period		3 years
Other Regulatory Assets | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4	6
Regulatory asset amortization period		4 years
Other Regulatory Assets | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 81	$ 53
Regulatory asset amortization period		20 years
CCR AROs | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset amortization period		3 years
Retiree Medicare Drug Subsidy | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 8
Retiree Medicare Drug Subsidy | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		9
Retiree Medicare Drug Subsidy | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		1
Regulatory Clauses, Amortized Through PEP | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 37
Regulatory asset amortization period		4 years
Ad Valorem Tax Adjustment Clause | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 15

REGULATORY MATTERS - APC Petiti

REGULATORY MATTERS - APC Petition for Certificate of Convenience and Necessity (Details) $ in Millions	Dec. 31, 2020USD ($)MW	Aug. 14, 2020USD ($)MW	Dec. 31, 2019USD ($)MW
Schedule of Regulatory Assets and Liabilities [Line Items]
Construction work in progress | $	$ 8,697		$ 7,880
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Approved additional generating capacity, demand-side management and distributed energy resource programs		200
Additional generating capacity, petitioned megawatts, total			2,400
Construction work in progress | $	$ 866		$ 890
Alabama Power | Year 2020
Schedule of Regulatory Assets and Liabilities [Line Items]
PPA, additional generating capacity (in MWs)		240
Alabama Power | Years 2022 Through 2024
Schedule of Regulatory Assets and Liabilities [Line Items]
PPA, additional generating capacity (in MWs)	400
Plant Barry Unit 8 | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Approximate nameplate capacity (in MW)		720
Costs incurred, percentage of estimated in-service cost		5.00%
Estimated in-service cost | $		$ 652
Construction work in progress | $	$ 66

REGULATORY MATTERS - APC Rate R

REGULATORY MATTERS - APC Rate RSE (Details) - Alabama Power - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2025	Dec. 31, 2020	Dec. 31, 2019	Dec. 01, 2020	Aug. 07, 2020	Feb. 28, 2019	Dec. 31, 2018
Public Utilities, General Disclosures [Line Items]
Rate adjustment period			2 years
Maximum percentage of rate RSE			4.00%
Maximum annual percentage of ratio rate			5.00%
Adjusting point of weighted cost of equity			5.98%
Percent of basis points			0.07%
Percent of designated customer value benchmark survey			33.33%
Authorized ROE			51.60%	50.30%
Weighted common equity return	6.15%			6.21%
Customer refundable fees, refund payments, tranche one, percentage			25.00%
Customer refundable fees, refund payments, tranche two, percentage			40.00%
Customer refundable fees, refund payments, tranche two, percentage			75.00%
Customer refundable fees, refund payments, tranche one, review year with rate RSE upward adjustment, percentage			50.00%
Contract with customer, liability, bill credits				$ 50		$ 100		$ 267
Rate RSE refund liability			$ 50	$ 53			$ 78
Rate RSE increase					4.09%
Rate RSE increase amount					$ 228
Revenue Subject to Refund
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities								$ 109
Rate ECR refunds
Public Utilities, General Disclosures [Line Items]
Contract with customer, liability, bill credits							$ 31
Minimum
Public Utilities, General Disclosures [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage			6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one			6.15%	6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two			6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three			7.15%
Public utilities, actual weighted common equity return, threshold, review year with rate RSE upward adjustment, percentage			6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, review year with rate RSE upward adjustment, percentage, tranche one			6.15%
Maximum
Public Utilities, General Disclosures [Line Items]
Public utilities, actual weighted common equity return, threshold, percentage			7.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one			6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two			7.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three			7.65%
Customer refundable fees, refund payments, percentage			7.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, review year with rate RSE upward adjustment, percentage, tranche one			6.90%
Customer refundable fees, refund payments, review year with rate RSE upward adjustment, percentage			6.90%
Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Authorized ROE		55.00%

REGULATORY MATTERS - APC Rate C

REGULATORY MATTERS - APC Rate CNP (Details) - Alabama Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements	$ 58	$ 40
Retail revenue requirement for environmental compliance	59	68	$ 205
Over (under) recovered environmental clause	$ 28	62
Regulatory Liabilities, Current
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered environmental clause		55
Regulatory Liabilities, Noncurrent
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered environmental clause		$ 7

REGULATORY MATTERS - APC Rate E

REGULATORY MATTERS - APC Rate ERC (Details) - Alabama Power $ in Millions	Dec. 01, 2020USD ($)$ / KWH_Kilowatt_hour	Apr. 30, 2018$ / KWH_Kilowatt_hour	Jan. 31, 2022$ / KWH_Kilowatt_hour	Oct. 31, 2020USD ($)	Dec. 31, 2019USD ($)$ / KWH_Kilowatt_hour	May 31, 2018$ / KWH_Kilowatt_hour	Dec. 31, 2020USD ($)$ / KWH_Kilowatt_hour	Aug. 07, 2020USD ($)	Feb. 28, 2019USD ($)	Dec. 31, 2018USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Current billing rates under rate ECR (usd per KWH) | $ / KWH_Kilowatt_hour	1.960	0.02015			0.02160	0.02353	0.05910
Rate RSE refund liability					$ 53		$ 50		$ 78
Current billing rates under rate ECR, percentage decrease	1.84%				1.82%
Current billing rates under rate ECR, decrease, amount	$ 103				$ 102
Reduction of over-collected fuel balance				$ 94.3
Contract with customer, liability, bill credits					50			$ 100		$ 267
Over (under) recovered fuel cost					49		$ 18
Other regulatory liabilities, current
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered fuel cost					32
Other regulatory liabilities, deferred
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered fuel cost					$ 17
Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Current billing rates under rate ECR (usd per KWH) | $ / KWH_Kilowatt_hour			0.05910

REGULATORY MATTERS - APC Accoun

REGULATORY MATTERS - APC Accounting Orders and Plant Greene County (Details)	1 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2018USD ($)	Dec. 17, 2020MW
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 15,469,000,000	$ 16,298,000,000
Alabama Power
Public Utilities, General Disclosures [Line Items]
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit, maximum amount used to offset under recovered amounts			$ 30,000,000
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit		69,000,000
Amount offset under recovered balance		30,000,000
Tax Cuts and Jobs Act of 2017, change in tax rate, deferred tax liability, income tax benefit, amount increasing NDR balance	39,000,000
Other deferred charges and assets	3,680,000,000	4,262,000,000
Alabama Power | Software Accounting Order
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	6,000,000	17,000,000
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Other deferred charges and assets	$ 775,000,000	$ 805,000,000
Required fossil-stream generation retirements (in MWs) | MW				950
Mississippi Power | Plant Greene County Units 1 And 2
Public Utilities, General Disclosures [Line Items]
Alternative accelerated retirement period	4 years		4 years

REGULATORY MATTERS - APC Rate N

REGULATORY MATTERS - APC Rate NDR (Details) - USD ($)	Jan. 01, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2020
Major storms
Public Utilities, General Disclosures [Line Items]
Storm damage reserves			$ 326,000,000	$ 170,000,000	$ 74,000,000
Alabama Power
Public Utilities, General Disclosures [Line Items]
Minimum natural disaster reserve balance, triggering establishment charge		$ 50,000,000	50,000,000
Natural disaster reserve authorized limit		75,000,000	$ 75,000,000			$ 75,000,000
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits			24 months
Maximum rate NDR charge per month, monthly nonresidential customer account		10	$ 10
Maximum rate NDR charge per month, monthly residential customer account		5	5
Annual recovery amount			5,000,000	16,000,000	16,000,000
Alabama Power | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Natural disaster reserve authorized limit	$ 50,000,000
Annual recovery amount	$ 3,000,000
Alabama Power | Major storms
Public Utilities, General Disclosures [Line Items]
Additional accruals authorized by state PSCs			100,000,000	84,000,000	0
Storm damage reserves			112,000,000	139,000,000	$ 16,000,000
Regulatory asset, amortization period		113,000,000	113,000,000	150,000,000
Alabama Power | Major storms | Other regulatory liabilities, current
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period		37,000,000	37,000,000
Alabama Power | Major storms | Accumulated Deferred Income Taxes
Public Utilities, General Disclosures [Line Items]
Storm damage reserves				$ 39,000,000
Alabama Power | Hurricane Sally And Zeta | Other regulatory liabilities, current
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period		77,000,000	$ 77,000,000
Alabama Power | Hurricane Sally
Public Utilities, General Disclosures [Line Items]
Storm damage reserves		51,000,000
Alabama Power | Hurricane Zeta
Public Utilities, General Disclosures [Line Items]
Storm damage reserves		$ 67,000,000

REGULATORY MATTERS - GPC Regula

REGULATORY MATTERS - GPC Regulatory Matters - Tariffs (Details) - Georgia Power $ in Millions	Dec. 31, 2019USD ($)
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	$ 342
Rate increase 2021	111
Traditional base
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	0
Rate increase 2021	120
ECCR
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	318
Rate increase 2021	2
DSM
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	12
Rate increase 2021	(15)
MFF
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	12
Rate increase 2021	$ 4

REGULATORY MATTERS - GPC Rate P

REGULATORY MATTERS - GPC Rate Plans and COVID-19 Costs (Details) - Georgia Power - USD ($) $ in Millions	Sep. 17, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2013	Oct. 31, 2020	Jun. 30, 2020
Public Utilities, General Disclosures [Line Items]
Retail rate of return on common equity	10.50%				10.95%
Portion of actual earnings above approved ROE band applied to reduce regulatory assets (percent)	40.00%
Portion of actual earnings above approved ROE band retained by subsidiary company	20.00%
Portion of actual earnings above approved ROE band refunded to customers	40.00%	50.00%	50.00%		66.67%
Portion of actual earnings above approved ROE band retained by Georgia Power					33.33%
Portion of actual earnings above approved ROE band refunded to customers, used to reduce regulatory assets		50.00%		50.00%
Portion of actual earning above approved ROE band refunded to customers, used to reduce regulatory assets, value		$ 60		$ 50
Portion of actual earnings above approved ROE band refunded to customers, value		50	$ 60			$ 60	$ 50
Customer refund liability in absence of base rate case			110
Incremental COVID-19 costs deferred		$ 38
Customer Refunds
Public Utilities, General Disclosures [Line Items]
Portion of actual earnings above approved ROE band refunded to customers, value			$ 110
Maximum
Public Utilities, General Disclosures [Line Items]
Regulatory asset amortization period		32 years
Retail rate of return on common equity	12.00%				12.00%
Maximum | Remaining Net Book Value of Retired Assets
Public Utilities, General Disclosures [Line Items]
Regulatory asset amortization period			3 years
Minimum
Public Utilities, General Disclosures [Line Items]
Retail rate of return on common equity	9.50%				10.00%

REGULATORY MATTERS - GPC Fuel C

REGULATORY MATTERS - GPC Fuel Cost and Storm Damage Recovery (Details) - USD ($) $ in Millions	May 28, 2020	Sep. 30, 2020	Dec. 31, 2020	Oct. 31, 2020	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Net regulatory assets			$ 5,493		$ 3,838
Other regulatory assets			810		885
Other regulatory assets, deferred			7,198		6,805
Georgia Power
Public Utilities, General Disclosures [Line Items]
Approved decrease in annual billing based on fuel cost recovery rate	$ 740
Approved decrease in annual billing based on fuel cost recovery rate, term	2 years
Requested rate decrease, amount		$ 44
Adjustment to fuel cost recovery rate if under recovered fuel balance exceeds budget thereafter			200
Over recovered fuel balance			$ 113		73
Required period for options and hedges			36 months
Recoveries for storm damage			$ 213
Net regulatory assets			4,252		3,507
Other regulatory assets			248		263
Other regulatory assets, deferred			2,692		2,716
Georgia Power | Storm damage reserves
Public Utilities, General Disclosures [Line Items]
Net regulatory assets			262		410
Incremental restoration costs				$ 50
Georgia Power | Storm/Property Damage Reserves
Public Utilities, General Disclosures [Line Items]
Other regulatory assets			213
Other regulatory assets, deferred			$ 49		$ 197

REGULATORY MATTERS - GPC Nuclea

REGULATORY MATTERS - GPC Nuclear Construction (Details) $ in Millions	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)	Apr. 30, 2020	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2012utilityMW	Jun. 30, 2018USD ($)
Public Utilities, General Disclosures [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4				$ 325	$ 0	$ 1,060
Georgia Power
Public Utilities, General Disclosures [Line Items]
Number of construction units approved | utility							2
Electric generating capacity (in MWs) | MW							1,100
Estimated loss on Plant Vogtle Units 3 and 4				$ 325	$ 0	$ 1,060
Plant Vogtle Units 3 And 4 | Georgia Power
Public Utilities, General Disclosures [Line Items]
Percent ownership	45.70%			45.70%
Estimated construction financing costs	$ 3,000			$ 3,000
Construction financing costs incurred to date	2,600			2,600
Construction contingency estimate, subject to rate recovery evaluation		$ 366
Estimated cost to complete, amount in excess of initial construction contingency estimate	171			171				$ 34
Estimated cost to complete, additional construction contingency estimate	5			$ 5				$ 115
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	131	111
Estimated loss on Plant Vogtle Units 3 and 4	176	$ 149
Expected number of positions reduced, percent			20.00%
Plant Vogtle Units 3 And 4 | Georgia Power | Minimum | COVID-19
Public Utilities, General Disclosures [Line Items]
Estimated months of productivity loss				3 months
Construction financing costs	150			$ 150
Plant Vogtle Units 3 And 4 | Georgia Power | Maximum | COVID-19
Public Utilities, General Disclosures [Line Items]
Estimated months of productivity loss				4 months
Construction financing costs	$ 190			$ 190
Plant Vogtle Units 3 And 4 | Georgia Power | Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Period of notice required in the event letters of credit are not renewed				30 days

REGULATORY MATTERS - GPC Schedu

REGULATORY MATTERS - GPC Schedule of Nuclear Construction Cost and Schedule (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commitments [Line Items]
Total AFUDC and interest capitalized		$ 230	$ 202	$ 210
Georgia Power
Commitments [Line Items]
Total AFUDC and interest capitalized		138	$ 103	$ 94
Georgia Power | Plant Vogtle Units 3 And 4
Commitments [Line Items]
Base project capital cost forecast		8,500
Construction contingency estimate		200
Total project capital cost forecast		8,700
Net investment		(7,200)
Remaining estimate to complete		1,500
Total AFUDC and interest capitalized		246
Total AFUDC and interest capitalized, accrual amount		93
Georgia Power | Plant Vogtle Unit
Commitments [Line Items]
Additional base capital costs per month		25
Georgia Power | Plant Watson Unit 4
Commitments [Line Items]
Additional base capital costs per month		$ 15
Twenty Third Vogtle Construction Monitoring Report | Georgia Power | Plant Vogtle Units 3 And 4
Commitments [Line Items]
Maximum guarantee	$ 1,700
Customer refund	$ 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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2015	Aug. 31, 2018
Public Utilities, General Disclosures [Line Items]
Production tax credits, aggregate purchase price (up to)	$ 300
Preliminary estimated cost to complete	$ 8,700
Additional construction capital costs		$ 3,300
Remaining share of construction costs, agreement to pay, percentage	100.00%
Ownership interest percentage 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 responsible to pay	55.70%
Additional construction capital costs	$ 80
Category II | Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs responsible 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 responsible to pay	65.70%
Additional construction capital costs	$ 100
Category III | Vogtle Owners
Public Utilities, General Disclosures [Line Items]
Percentage of construction costs responsible to pay	34.30%
Category III | Maximum
Public Utilities, General Disclosures [Line Items]
Additional construction capital costs, threshold	$ 2,100

REGULATORY MATTERS - GPC Nucl_2

REGULATORY MATTERS - GPC Nuclear Construction Regulatory Matters (Details) - Georgia Power $ in Millions

Feb. 18, 2021USD ($)

Jan. 01, 2021

Nov. 03, 2020USD ($)

Jan. 01, 2020

Jan. 11, 2018USD ($)

Jan. 01, 2018

Jan. 01, 2016

Jun. 30, 2020USD ($)report

Dec. 31, 2022USD ($)

Dec. 31, 2021USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2015USD ($)

Dec. 31, 2009USD ($)

Sep. 17, 2019

Dec. 31, 2013

Public Utilities, General Disclosures [Line Items]

Retail rate of return on common equity

10.50%

10.95%

Plant Vogtle Units 3 And 4

Public Utilities, General Disclosures [Line Items]

Estimated in-service capital cost

$ 4,418

Proceeds from recovery of financing costs

$ 2,500

Project capital cost forecast

$ 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%

Authorized ROE

8.30%

10.00%

10.00%

Potential decrease each month, percentage

0.10%

Return on equity reduction, negative impact on earnings

$ 150

$ 75

$ 100

Plant Vogtle Units 3 And 4 | Subsequent Event

Public Utilities, General Disclosures [Line Items]

Approval of construction capital costs

$ 670

Plant Vogtle Units 3 And 4 | Twenty Third Vogtle Construction Monitoring Report

Public Utilities, General Disclosures [Line Items]

Number of approved construction monitoring reports | report

23

Approval of construction capital costs

$ 8,100

Maximum guarantee

1,700

Customer refund

$ 188

Plant Vogtle Units 3 And 4 | Scenario, Forecast

Public Utilities, General Disclosures [Line Items]

Authorized ROE

5.30%

Return on equity reduction, negative impact on earnings

$ 200

$ 260

REGULATORY MATTERS - MPC 2019 B

REGULATORY MATTERS - MPC 2019 Base Rate Case and Performance Evaluation Plan (Details) $ in Millions	Jun. 25, 2020USD ($)	Mar. 17, 2020USD ($)	Dec. 31, 2020USD ($)filing	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
Public Utilities, General Disclosures [Line Items]
Net regulatory assets			$ 5,493		$ 3,838
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount		$ (16.7)		$ 21.6
Approved rate decrease, percent		1.85%
Base rate case filing, measurement input, average equity ratio		53.00%
Base rate case filing, measurement input, maximum equity ratio		55.00%
Base rate case filing, measurement input, return on investment		7.57%
Regulatory asset amortization period		4 years
Regulatory liability amortization period		3 years
Annual base rate adjustment, increase in depreciation		$ 10
Annual base rate adjustment, compensation costs excluded		$ 3.9
Performance evaluation plan, number of filings per calendar year | filing			2
Requested rate increase, amount	$ 2			$ 26
Authorized ROE				9.33%
Regulatory equity ratio				50.00%
Amount approved for recovery				$ 2
Net regulatory assets			$ 136		64
Retail rate of return on common equity				9.31%
Mississippi Power | Deferred Income Tax Charges
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities				$ 44
Mississippi Power | Contested Compensation Costs
Public Utilities, General Disclosures [Line Items]
Regulatory asset amortization period			4 years
Net regulatory assets				$ 4	$ 4
Mississippi Power | Weighted Average | Measurement Input, Average Customer Price
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input			0.40
Mississippi Power | Weighted Average | Measurement Input, Service Reliability
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input			0.40
Mississippi Power | Weighted Average | Measurement Input, Customer Satisfaction
Public Utilities, General Disclosures [Line Items]
Performance evaluation plan, measurement input			0.20
Mississippi Power | Maximum
Public Utilities, General Disclosures [Line Items]
Regulatory asset amortization period			8 years
Allowed equity ratio				51.00%

REGULATORY MATTERS - MPC Reserv

REGULATORY MATTERS - MPC Reserve Margin and Environmental Compliance Overview Plans (Details) $ in Millions	Feb. 12, 2021USD ($)	Jun. 25, 2020USD ($)	Mar. 17, 2020	Dec. 31, 2019	Dec. 31, 2018USD ($)	Dec. 17, 2020MW	Oct. 31, 2019USD ($)
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Required fossil-stream generation retirements (in MWs) | MW						950
Requested rate increase, amount		$ 2			$ 26
Approved rate increase, percent			(1.85%)
Mississippi Power | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase, amount	$ 28
Mississippi Power | Environmental Compliance Overview Plan
Public Utilities, General Disclosures [Line Items]
Requested rate increase, amount					$ 17
Percent ownership							50.00%
Public utilities, requested cost to complete environmental compliance projects							$ 66
Mississippi Power | Environmental Compliance Overview Plan | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase, amount	$ 9
Mississippi Power | Maximum | Environmental Compliance Overview Plan
Public Utilities, General Disclosures [Line Items]
Approved rate increase, percent					2.00%
Mississippi Power And Gulf Power | Environmental Compliance Overview Plan
Public Utilities, General Disclosures [Line Items]
Public utilities, requested cost to complete environmental compliance projects							125
Plant Watson Unit 4 | Mississippi Power
Public Utilities, General Disclosures [Line Items]
Alternative accelerated retirement period				2 years
Plant Watson Unit 5 | Mississippi Power
Public Utilities, General Disclosures [Line Items]
Alternative accelerated retirement period				7 years
Plant Greene County Units 1 And 2 | Mississippi Power
Public Utilities, General Disclosures [Line Items]
Alternative accelerated retirement period				4 years	4 years
Ash Pond | Mississippi Power | Environmental Compliance Overview Plan
Public Utilities, General Disclosures [Line Items]
Public utilities, requested cost to complete environmental compliance projects							$ 17

REGULATORY MATTERS - MPC Fuel C

REGULATORY MATTERS - MPC Fuel Cost Recovery and Ad Valorem Tax Adjustment (Details) - Mississippi Power - USD ($) $ in Millions

Feb. 12, 2021

Jun. 25, 2020

Mar. 17, 2020

Feb. 28, 2021

Jan. 31, 2021

Feb. 29, 2020

Jan. 31, 2020

Feb. 28, 2019

Jan. 31, 2019

Feb. 28, 2018

Dec. 31, 2018

Dec. 31, 2020

Dec. 31, 2019

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (16.7)

$ 21.6

PSC retail increase

7

$ 10

$ 2

Requested rate increase, amount

$ 2

$ 26

Subsequent Event

Public Utilities, General Disclosures [Line Items]

Requested rate increase, amount

$ 28

Retail electric revenues

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (24)

$ (35)

$ 39

Over recovered fuel cost

24

23

Retail electric revenues | Scenario, Forecast

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 2

MRA Revenue

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 1

$ 16

Over recovered fuel cost

$ 10

$ 6

MRA Revenue | Subsequent Event

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 5

REGULATORY MATTERS - MPC System

REGULATORY MATTERS - MPC System Restoration Rider (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 28, 2020
Major storms
Public Utilities, General Disclosures [Line Items]
Storm damage reserves	$ 326,000,000	$ 170,000,000	$ 74,000,000
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Threshold above which actual damages are charged to the reserve (individually exceed)	$ 50,000
SRR rate	0.00%	0.00%	0.00%
Mississippi Power | Retail electric revenues
Public Utilities, General Disclosures [Line Items]
Property damage reserve	$ 4,000,000
Mississippi Power | Major storms
Public Utilities, General Disclosures [Line Items]
Storm damage reserves	$ 1,000,000	$ 1,000,000	$ 1,000,000
Mississippi Power | Hurricane Zeta
Public Utilities, General Disclosures [Line Items]
Property damage reserve				$ 43,000,000
Mississippi Power | Mississippi Public Service Commission
Public Utilities, General Disclosures [Line Items]
Period to agree on system restoration rider	3 years

REGULATORY MATTERS - MPC Deferr

REGULATORY MATTERS - MPC Deferral of Incremental COVID-19 Costs and Municipal and Rural Associations Tariff (Details) $ in Millions	Apr. 01, 2021	Feb. 12, 2021USD ($)	Jun. 25, 2020USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2018USD ($)	Apr. 01, 2018MW	Mar. 31, 2018MW
Mississippi Power
Public Utilities, General Disclosures [Line Items]
Incremental COVID-19 costs deferred					$ 1
Requested rate increase, amount			$ 2			$ 26
Mississippi Power | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase, amount		$ 28
Mississippi Power | MRA Revenue
Public Utilities, General Disclosures [Line Items]
Decrease in base rate under cost based electric tariff due to settlement				$ 3.7
Mississippi Power | Cooperative Energy
Public Utilities, General Disclosures [Line Items]
Period of notice to cancel counterparty					10 years
Counterparty's option to decrease services, percentage					2.50%
Counterparty's option to reduce services, maximum percentage					11.00%
Counterparty's option to reduce services, maximum					$ 9
Approximate nameplate capacity (in MW) | MW							286	86
Cooperative Energy | Southern Company Services, Inc.
Public Utilities, General Disclosures [Line Items]
Network integration transmission service agreement, term of agreement					10 years
Cooperative Energy | Southern Company Services, Inc. | Subsequent Event | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Network integration transmission service agreement, renewal term	10 years

REGULATORY MATTERS - GAS Schedu

REGULATORY MATTERS - GAS Schedule of Utility Regulation and Rate Design (Details)	1 Months Ended			12 Months Ended
	Dec. 31, 2019	Oct. 31, 2019	Jan. 31, 2018	Dec. 31, 2020	Dec. 31, 2017
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Authorized ROE		9.73%	9.80%	9.73%
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Authorized ROE	10.25%			10.25%
Virginia Natural Gas
Public Utilities, General Disclosures [Line Items]
Authorized ROE				9.50%	9.50%
Chattanooga Gas
Public Utilities, General Disclosures [Line Items]
Authorized ROE				9.80%

REGULATORY MATTERS - GAS Infras

REGULATORY MATTERS - GAS Infrastructure Replacement Programs and Capital Projects (Details) $ in Millions	12 Months Ended					21 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)mi	Dec. 31, 2018USD ($)	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2019USD ($)	Dec. 15, 2020mi
Public Utilities, General Disclosures [Line Items]
Capital expenditures related to qualifying projects	$ 7,441	$ 7,555	$ 8,001
Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Capital expenditures related to qualifying projects	1,471	1,408	1,388
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase, recovery of investment amount						$ 65
Capital expenditures related to qualifying projects		$ 396	$ 409
Nicor Gas | Regulatory Infrastructure Program
Public Utilities, General Disclosures [Line Items]
Program duration period				9 years
Nicor Gas | Maximum
Public Utilities, General Disclosures [Line Items]
Infrastructure investment, annual customer rate increase				4.00%
Infrastructure investment, annual customer rate increase in any given year				5.50%
Virginia Natural Gas
Public Utilities, General Disclosures [Line Items]
Header improvement project, scope of project (in miles) | mi		24.1					9.5
Virginia Natural Gas | SAVE
Public Utilities, General Disclosures [Line Items]
Program duration period					6 years
Approved infrastructure replacement program, approved investment amount, current fiscal year	365
Infrastructure replacement program, approved investment variance amount	5
Virginia Natural Gas | SAVE | Year 2018
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	35
Virginia Natural Gas | SAVE | Year 2019
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	40
Virginia Natural Gas | SAVE | Year 2020
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	50
Virginia Natural Gas | SAVE | Year 2021
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	60
Virginia Natural Gas | SAVE | Year 2022
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70
Virginia Natural Gas | SAVE | Year 2023
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70
Virginia Natural Gas | SAVE | Year 2024
Public Utilities, General Disclosures [Line Items]
Approved infrastructure replacement program, approved investment amount, current fiscal year	70
Atlanta Gas Light
Public Utilities, General Disclosures [Line Items]
Annual proceeds from strategic economic development projects	15
Atlanta Gas Light | True Up Recovery
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount	113
Atlanta Gas Light | True-Up Recovery, Unrecognized Equity
Public Utilities, General Disclosures [Line Items]
Gain contingency, unrecorded amount	59
Operating Segments | Gas distribution operations | Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Gross property additions	$ 1,500

REGULATORY MATTERS - GAS Sche_2

REGULATORY MATTERS - GAS Schedule of Infrastructure Replacement Programs and Capital Projects (Details) - Southern Company Gas $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)mi
Public Utilities, General Disclosures [Line Items]
Expenditures in 2020 | $	$ 438
Expenditures Since Project Inception | $	$ 2,394
Pipe Installed Since Project Inception (in miles) | mi	1,409
Scope of Program (in miles) | mi	2,220
Investing In Illinois
Public Utilities, General Disclosures [Line Items]
Expenditures in 2020 | $	$ 389
Expenditures Since Project Inception | $	$ 2,101
Pipe Installed Since Project Inception (in miles) | mi	996
Scope of Program (in miles) | mi	1,450
Program Duration	9 years
SAVE
Public Utilities, General Disclosures [Line Items]
Expenditures in 2020 | $	$ 49
Expenditures Since Project Inception | $	$ 293
Pipe Installed Since Project Inception (in miles) | mi	413
Scope of Program (in miles) | mi	770
Program Duration	13 years

REGULATORY MATTERS - GAS Natura

REGULATORY MATTERS - GAS Natural Gas Cost Recovery (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Southern Company Gas
Public Utilities, General Disclosures [Line Items]
Over recovered fuel cost	$ 88	$ 74

REGULATORY MATTERS - GAS Rate P

REGULATORY MATTERS - GAS Rate Proceedings and Infrastructure Replacement Programs and Capital Projects (Details) - USD ($) $ in Millions

Feb. 16, 2021

Jan. 14, 2021

Jul. 01, 2020

Jun. 01, 2020

May 05, 2018

Dec. 31, 2019

Oct. 31, 2019

Jan. 31, 2018

Dec. 31, 2020

Dec. 31, 2018

Dec. 31, 2017

Oct. 31, 2018

Jul. 31, 2018

Public Utilities, General Disclosures [Line Items]

Net regulatory assets

$ 3,838

$ 5,493

Nicor Gas

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (44)

$ 168

$ 137

Authorized ROE

9.73%

9.80%

9.73%

Public utilities, approved equity capital structure, percentage

54.20%

Nicor Gas | COVID-19

Public Utilities, General Disclosures [Line Items]

Net regulatory assets

$ 9

Nicor Gas | Subsequent Event

Public Utilities, General Disclosures [Line Items]

Requested rate increase, amount

$ 293

Requested rate increase, amount, recovery of investments

$ 94

Requested ROE

10.35%

Requested equity ratio

54.50%

Nicor Gas | Investing In Illinois

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase amount recovery of investments

$ 65

$ 93

Atlanta Gas Light

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 65

$ (16)

Authorized ROE

10.25%

10.25%

Public utilities, approved equity capital structure, percentage

56.00%

Requested rate increase, amount

$ 37.6

Requested rate increase, projected test year, term

12 months

Contract with customer, liability, bill credits

$ 8

$ 8

Approved rate increase, percent

4.00%

Regulatory equity ratio

55.00%

Public utilities, maximum base rate percentage

5.00%

5.00%

Atlanta Gas Light | Subsequent Event

Public Utilities, General Disclosures [Line Items]

Integrated capacity delivery plan, interstate and intrastate capacity asset requirements, term

10 years

Integrated capacity delivery plan, interstate and intrastate capacity asset requirements, detailed plan term

3 years

Integrated capacity delivery plan, capital budgets and related operations and maintenance spending, term

10 years

Atlanta Gas Light | Minimum

Public Utilities, General Disclosures [Line Items]

Authorized ROE

10.05%

10.55%

Atlanta Gas Light | Maximum

Public Utilities, General Disclosures [Line Items]

Authorized ROE

10.45%

10.95%

Virginia Natural Gas

Public Utilities, General Disclosures [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (14)

Authorized ROE

9.50%

9.50%

Requested rate increase, amount

$ 49.6

Requested rate increase, projected test year, term

12 months

Requested ROE

10.35%

Requested equity ratio

54.00%

Contract with customer, liability, bill credits

$ 14

Virginia Natural Gas | Minimum

Public Utilities, General Disclosures [Line Items]

Authorized ROE

9.00%

Virginia Natural Gas | Maximum

Public Utilities, General Disclosures [Line Items]

Authorized ROE

10.00%

REGULATORY MATTERS - GAS Sche_3

REGULATORY MATTERS - GAS Schedule of Unrecognized Ratemaking Amounts (Details) - Regulatory Asset Off Balance Sheet - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 59	$ 70
Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	10	10
Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	3	2
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 72	$ 82

CONTINGENCIES, COMMITMENTS, A_3

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Litigation (Details) - Shareholder Derivative Lawsuits - Pending Litigation - lawsuit	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Number of claims		2
Stay period	30 days

CONTINGENCIES, COMMITMENTS, A_4

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - MPC Litigation (Details) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019plaintiff	Dec. 31, 2018USD ($)plaintiffdefendant
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of plaintiffs		10
Purported Violations Of Mississippi Consumer Protection Act | Pending Litigation | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of plaintiffs	4
Loss contingency, number of defendants | defendant		3
Public utilities, underpayment of refunds | $		$ 23.5

CONTINGENCIES, COMMITMENTS, A_5

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Environmental Remediation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)sitestate	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Accrued environmental remediation	$ 216	$ 234
Georgia Power
Environmental Exit Cost [Line Items]
Costs recovered annually	12	2	$ 2
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	15	15
Accrued environmental remediation	0	0
Under recovered environmental remediation costs, other regulatory assets, current	12	12
Under recovered environmental remediation costs, other regulatory assets, deferred	29	40
Southern Company
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	44	51
Accrued environmental remediation	216	234
Under recovered environmental remediation costs, other regulatory assets, current	46	49
Under recovered environmental remediation costs, other regulatory assets, deferred	265	300
Southern Company Gas
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	29	36
Accrued environmental remediation	216	233
Under recovered environmental remediation costs, other regulatory assets, current	34	37
Under recovered environmental remediation costs, other regulatory assets, deferred	$ 236	$ 260
Southern Company Gas | Manufactured Gas Plants
Environmental Exit Cost [Line Items]
Number of sites | site	40
Number of states in which subject to environmental remediation liabilities | state	4

CONTINGENCIES, COMMITMENTS, A_6

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Nuclear Fuel Disposal Costs and Nuclear Insurance (Details)	12 Months Ended	108 Months Ended
	Dec. 31, 2020USD ($)plant	Dec. 31, 2019USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Maximum fund for public liability claims arising from a single nuclear incident under price - anderson amendments act	$ 13,800,000,000
Maximum insurance coverage provided by American Nuclear Insurers to each nuclear plant	450,000,000
Maximum amount that a company could be assessed per incident for each licensed reactor	138,000,000
Maximum aggregate amount that a reactor can assess in a calendar period for each incident	$ 20,000,000
Block period considered for inflation adjustment against maximum assessment per reactor	5 years
Maximum deductible waiting period	182 days
Maximum coverage per occurrence per unit limit to obtain replacement power	$ 490,000,000
Aggregate payment for claims resulting from terrorist acts in one year period	3,200,000,000
Vogtle Units 3 and 4
Jointly Owned Utility Plant Interests [Line Items]
Maximum limits for accidental property damage occurring during construction	$ 2,750,000,000
Alabama Power and Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Number of nuclear fuel plants | plant	3
Maximum property damage insurance provided to nuclear generating facilities	$ 1,500,000,000
Maximum additional coverage provided for losses under excess insurance	1,250,000,000
Maximum additional coverage provided for losses under excess insurance, non-nuclear losses	$ 750,000,000
Elected deductible waiting period	84 days
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Maximum assessment, excluding any applicable state premium taxes	$ 275,000,000
Maximum aggregate amount to be paid in one year	41,000,000
Current maximum annual assessments under NEIL policies	56,000,000
Alabama Power | Positive Outcome of Litigation
Jointly Owned Utility Plant Interests [Line Items]
Outstanding claims		$ 110,000,000
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Maximum assessment, excluding any applicable state premium taxes	267,000,000
Maximum aggregate amount to be paid in one year	40,000,000
Current maximum annual assessments under NEIL policies	$ 84,000,000
Georgia Power | Positive Outcome of Litigation
Jointly Owned Utility Plant Interests [Line Items]
Outstanding claims		$ 132,000,000

CONTINGENCIES, COMMITMENTS, A_7

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Other Matters (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2020USD ($)leveraged_leaseassetnetworkheating_system	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)leveraged_lease	Dec. 31, 2020USD ($)leveraged_leaseassetnetworkheating_system	Dec. 31, 2019USD ($)leveraged_lease	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of leveraged leases	4		4	4	4
Number of domestic leveraged leases	2		2	2	2
Number of international leveraged leases	2		2	2	2
Lease, impairment loss | $	$ 52	$ 154	$ 17	$ 206	$ 0	$ 0
Lease, impairment loss, after tax | $	$ 31	$ 74	$ 13
Leveraged leases, number of gas distribution networks | network	9			9
Leveraged leases, number of district heating systems | heating_system	2			2
Leveraged leases, number of assets remaining | asset	10			10
Leveraged leases, purchase option, notice period				1 year

CONTINGENCIES, COMMITMENTS, A_8

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - MPC Other Matters (Details)	Dec. 31, 2019	Jan. 01, 2019USD ($)	Dec. 31, 2020USD ($)MW	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2025USD ($)	Jan. 15, 2024USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2010USD ($)
Loss Contingencies [Line Items]
Period costs			$ 19,000,000	$ 37,000,000
Mississippi Power
Loss Contingencies [Line Items]
Plant capacity under coal gasification combined cycle technology | MW			582
Period costs			$ 0	1,000,000
Kemper County energy facility assets, net | Mississippi Power
Loss Contingencies [Line Items]
Reduction in customer rates annually					$ 26,800,000
Pre-tax charge to income			4,000,000	$ 24,000,000	37,000,000
After tax charge to income			$ 3,000,000		68,000,000
Firm transportation agreement, term	15 years
Government grants expected								$ 137,000,000	$ 270,000,000
Government grants received					$ 387,000,000
Scenario, Forecast | Kemper County energy facility assets, net | Mississippi Power | Minimum
Loss Contingencies [Line Items]
Period costs						$ 10,000,000
Scenario, Forecast | Kemper County energy facility assets, net | Mississippi Power | Maximum
Loss Contingencies [Line Items]
Period costs						$ 20,000,000
Scenario, Forecast | Plant Daniel | Mississippi Power
Loss Contingencies [Line Items]
Payments to acquire businesses							$ 1
Business combination, option to purchase, period							120 days
Scenario, Forecast | Plant Daniel | Gulf Power
Loss Contingencies [Line Items]
Undivided ownership interest to be restructured							50.00%
Percent ownership in individual unit							100.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Loss Contingencies [Line Items]
Proceeds from divestiture of businesses, amount held back		$ 75,000,000

CONTINGENCIES, COMMITMENTS, A_9

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GAS Other Matters (Details)	Feb. 20, 2020	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 30, 2020phasemi	Dec. 31, 2015miBcf
Loss Contingencies [Line Items]
Equity investments in unconsolidated subsidiaries		$ 1,362,000,000	$ 1,303,000,000
Impairment charges		0	168,000,000	$ 210,000,000
Southern Company Gas
Loss Contingencies [Line Items]
Equity investments in unconsolidated subsidiaries		1,290,000,000	1,251,000,000
Impairment of long-lived assets		0
Impairment charges		0	115,000,000	$ 42,000,000
Southern Company Gas | PennEast Pipeline
Loss Contingencies [Line Items]
Ownership percentage, equity method investment						20.00%
Pipeline infrastructure | mi						118
Equity investments in unconsolidated subsidiaries		$ 91,000,000	82,000,000
Southern Company Gas | SNG
Loss Contingencies [Line Items]
Ownership percentage, equity method investment		50.00%
Equity investments in unconsolidated subsidiaries		$ 1,167,000,000	1,137,000,000
PennEast Pipeline
Loss Contingencies [Line Items]
Extension request, term	2 years
Construction amendment, number of phases | phase					2
Construction amendment, number of miles of pipe, phase one | mi					68
Minimum | Southern Company Gas | PennEast Pipeline
Loss Contingencies [Line Items]
Natural gas pipeline capacity (volume) | Bcf						1
Maximum | PennEast Pipeline | Southern Company Gas
Loss Contingencies [Line Items]
Construction contingency estimate		$ 300,000,000
Natural Gas Storage Facility | Southern Company Gas
Loss Contingencies [Line Items]
Impairment charges			91,000,000
Impairment charges, after tax			$ 69,000,000

CONTINGENCIES, COMMITMENTS, _10

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Commitments (Details) - Georgia Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
MEAG Power
Loss Contingencies [Line Items]
Percent ownership	5.00%
Plant Vogtle Units 1 and 2
Loss Contingencies [Line Items]
Capacity payments	$ 5	$ 6	$ 8
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
Recorded unconditional purchase obligation	49
2021	5
2022	4
2023	3
2024	3
2025	3
2026 and thereafter	$ 31

CONTINGENCIES, COMMITMENTS, _11

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GAS Commitments (Details) MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)MMBTU
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	$ 3,506
Southern Company Gas
Long-term Purchase Commitment [Line Items]
Natural gas pipeline capacity | MMBTU	31
Long-term purchase commitment amount	$ 72
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	$ 330
Southern Company Gas | SNG
Pipeline Charges, Storage Capacity, and Gas Supply
Ownership percentage, equity method investment	50.00%
Commitment to fund contingent capital contribution	$ 150
SNG
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	300
Pipeline Charges, Storage Capacity, and Gas Supply | Southern Company Gas
Pipeline Charges, Storage Capacity, and Gas Supply
2021	719
2022	529
2023	441
2024	311
2025	285
Thereafter	1,035
Total	$ 3,320

CONTINGENCIES, COMMITMENTS, _12

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	$ 609	$ 2,055
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Jointly owned affiliate equity	85
Jointly owned affiliate long term debt	100
SEGCO | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	25
SEGCO | Maturity December 1, 2018 | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Guarantee of unsecured senior notes	$ 100

REVENUE FROM CONTRACTS WITH C_3

REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 21,097	$ 22,596	$ 25,241
Total operating revenues	20,375	21,419	23,495
Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13,677	14,445	15,087
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,113	6,164	6,586
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,699	5,065	5,255
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,775	3,126	3,152
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90	90	94
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,888	2,989	3,175
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,338	1,413	1,525
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	340	389	436
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	971	907	944
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	35	40
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	209	245	230
Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,399	1,518	1,711
PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	735	833	950
PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	454	453	498
Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	210	232	263
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,151	2,609	3,739
Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		32	32
Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,727	2,095	3,083
Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	391	440	571
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	33	42	53
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	982	1,035	1,529
Other revenue sources
Disaggregation of Revenue [Line Items]
Other	3,764	4,266	5,108
Other adjustments
Disaggregation of Revenue [Line Items]
Other	(4,486)	(5,443)	(6,854)
Alabama Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,646	6,152	5,803
Total operating revenues	5,830	6,125	6,032
Alabama Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,203	5,671	5,215
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,377	2,509	2,285
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,512	1,677	1,541
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,293	1,460	1,364
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	25	25
Alabama Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	284	328	378
Alabama Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	133	145	158
Alabama Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	108	102	101
Alabama Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	43	81	119
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		0	0
Alabama Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	159	153	210
Alabama Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	184	(27)	229
Alabama Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Georgia Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8,215	8,418	8,091
Total operating revenues	8,309	8,408	8,420
Georgia Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,666	7,888	7,697
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,476	3,377	3,295
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,933	3,097	3,025
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,197	1,360	1,321
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60	54	56
Georgia Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	102	123	158
Georgia Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	42	60	81
Georgia Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	50	54	53
Georgia Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	9	24
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		0	0
Georgia Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	447	407	236
Georgia Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	94	(10)	329
Georgia Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Mississippi Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,157	1,271	1,274
Total operating revenues	1,172	1,264	1,265
Mississippi Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	808	886	902
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	260	278	277
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	254	291	290
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	285	306	326
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	9
Mississippi Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	323	366	350
Mississippi Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	15
Mississippi Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	3	6
Mississippi Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	311	352	329
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		0	0
Mississippi Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26	19	22
Mississippi Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	15	(7)	(9)
Mississippi Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Southern Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,119	1,220	1,364
Total operating revenues	1,733	1,938	2,205
Southern Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,105	1,208	1,351
Southern Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	570	648	727
Southern Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	296	322	394
Southern Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	239	238	230
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		0	0
Southern Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	12	13
Southern Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	614	718	841
Southern Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Southern Company Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,039	5,598	6,914
Total operating revenues	3,434	3,792	3,909
Southern Company Gas | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,888	2,989	3,175
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,338	1,413	1,525
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	340	389	436
Southern Company Gas | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	971	907	944
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	35	40
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	209	245	230
Southern Company Gas | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,151	2,609	3,739
Southern Company Gas | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers		32	32
Southern Company Gas | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,727	2,095	3,083
Southern Company Gas | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	391	440	571
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	33	42	53
Southern Company Gas | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	2,881	3,637	3,849
Southern Company Gas | Other adjustments
Disaggregation of Revenue [Line Items]
Other	$ (4,486)	$ (5,443)	$ (6,854)

REVENUE FROM CONTRACTS WITH C_4

REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	$ 2,614	$ 2,413
Contract Assets	158	117
Contract Liabilities	61	52
Revenue Recognized	33	30
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	81	40
Contract Liabilities	27	28
Alabama Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	632	586
Contract Assets	2	0
Contract Liabilities	6	10
Revenue Recognized	10	11
Georgia Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	806	688
Contract Assets	71	69
Contract Liabilities	$ 27	13
Performance obligation, expected timing of satisfaction	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.
Revenue Recognized	$ 8	6
Mississippi Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	77	79
Contract Assets	0	0
Contract Liabilities	1	0
Southern Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	112	97
Contract Assets	0	0
Contract Liabilities	1	1
Revenue Recognized	1	11
Southern Company Gas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivables	788	749
Contract Assets	0	0
Contract Liabilities	1	1
Revenue Recognized	$ 1	$ 2

REVENUE FROM CONTRACTS WITH C_5

REVENUE FROM CONTRACTS WITH CUSTOMERS - Performance Obligations (Details) $ in Millions	Dec. 31, 2020USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 547
Expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 395
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	$ 338
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	$ 326
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	$ 306
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	$ 2,634
Expected timing of satisfaction
Alabama Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 33
Expected timing of satisfaction	1 year
Alabama Power | 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
Expected timing of satisfaction	1 year
Alabama Power | 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
Expected timing of satisfaction	1 year
Alabama Power | 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
Expected timing of satisfaction	1 year
Alabama Power | 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
Expected timing of satisfaction	1 year
Alabama Power | 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
Expected timing of satisfaction
Georgia Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 75
Expected timing of satisfaction	1 year
Georgia Power | 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	$ 46
Expected timing of satisfaction	1 year
Georgia Power | 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	$ 35
Expected timing of satisfaction	1 year
Georgia Power | 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
Expected timing of satisfaction	1 year
Georgia Power | 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
Expected timing of satisfaction	1 year
Georgia Power | 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	$ 42
Expected timing of satisfaction
Southern Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 285
Expected timing of satisfaction	1 year
Southern Power | 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
Expected timing of satisfaction	1 year
Southern Power | 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
Expected timing of satisfaction	1 year
Southern Power | 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
Expected timing of satisfaction	1 year
Southern Power | 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
Expected timing of satisfaction	1 year
Southern Power | 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	$ 2,610
Expected timing of satisfaction

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT - Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Electric utilities:
Generation	$ 52,179	$ 50,329
Transmission	12,879	12,157
Distribution	20,958	19,846
General/other	5,072	4,650
Electric utilities' plant in service	91,088	86,982
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	14,610	13,518
Storage facilities	1,752	1,634
Other	1,249	1,192
Southern Company Gas plant in service	17,611	16,344
Other plant in service	1,817	1,788
Total plant in service	110,516	105,114
Alabama Power
Electric utilities:
Generation	16,201	15,329
Transmission	5,033	4,719
Distribution	8,248	7,798
General/other	2,334	2,177
Electric utilities' plant in service	31,816	30,023
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	31,816	30,023
Georgia Power
Electric utilities:
Generation	18,675	18,341
Transmission	6,951	6,590
Distribution	11,622	11,024
General/other	2,434	2,182
Electric utilities' plant in service	39,682	38,137
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	39,682	38,137
Mississippi Power
Electric utilities:
Generation	2,819	2,786
Transmission	856	808
Distribution	1,088	1,024
General/other	248	239
Electric utilities' plant in service	5,011	4,857
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	5,011	4,857
Southern Power
Electric utilities:
Generation	13,872	13,241
Transmission	0	0
Distribution	0	0
General/other	32	29
Electric utilities' plant in service	13,904	13,270
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	13,904	13,270
Southern Company Gas
Electric utilities:
Generation	0	0
Transmission	0	0
Distribution	0	0
General/other	0	0
Electric utilities' plant in service	0	0
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	14,610	13,518
Storage facilities	1,752	1,634
Other	1,249	1,192
Southern Company Gas plant in service	17,611	16,344
Other plant in service	0	0
Total plant in service	$ 17,611	$ 16,344

PROPERTY, PLANT, AND EQUIPMEN_4

PROPERTY, PLANT, AND EQUIPMENT - Additional Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020
Alabama Power | Maximum
Property, Plant and Equipment [Line Items]
Regulatory asset amortization period	28 years
Alabama Power | Nuclear Outage
Property, Plant and Equipment [Line Items]
Regulatory asset amortization period	18 months
Georgia Power | Maximum
Property, Plant and Equipment [Line Items]
Regulatory asset amortization period	32 years
Georgia Power | Nuclear Outage | Maximum
Property, Plant and Equipment [Line Items]
Regulatory asset amortization period	24 months
Plant Vogtle Units 1 and 2 | Georgia Power
Property, Plant and Equipment [Line Items]
Unit operating cycle	18 months

PROPERTY, PLANT, AND EQUIPMEN_5

PROPERTY, PLANT, AND EQUIPMENT - Composite Straight-Line Rates (Details) - Utility plant in service	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Alabama Power
Property, Plant and Equipment [Line Items]
Composite rate	2.60%	3.10%	3.00%
Georgia Power
Property, Plant and Equipment [Line Items]
Composite rate	3.00%	2.60%	2.60%
Mississippi Power
Property, Plant and Equipment [Line Items]
Composite rate	3.70%	3.70%	4.20%
Southern Company Gas
Property, Plant and Equipment [Line Items]
Composite rate	2.80%	2.90%	2.90%

PROPERTY, PLANT, AND EQUIPMEN_6

PROPERTY, PLANT, AND EQUIPMENT - Deferred Cloud Implementation Costs (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	$ 16,298	$ 15,469
Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	162
Alabama Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	4,262	3,680
Alabama Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	38
Georgia Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	8,297	8,028
Georgia Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	58
Mississippi Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	805	775
Mississippi Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	7
Southern Power
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	1,150	1,870
Southern Power | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	9
Southern Company Gas
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	931	$ 918
Southern Company Gas | Deferred Cloud Implementation Costs
Property, Plant and Equipment [Line Items]
Deferred cloud implementation costs	$ 17

PROPERTY, PLANT, AND EQUIPMEN_7

PROPERTY, PLANT, AND EQUIPMENT - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 32,397	$ 30,765
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	31,600	30,000
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 817	732
Other plant in service | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	37 years
Southern Company Gas
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 4,821	4,650
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	4,600	4,500
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 195	$ 155
Southern Company Gas | Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	12 years
Southern Company Gas | Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	5 years
Southern Company Gas | Storage facilities | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	75 years
Southern Company Gas | Storage facilities | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	30 years
Southern Company Gas | Other assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost	75 years

PROPERTY, PLANT, AND EQUIPMEN_8

PROPERTY, PLANT, AND EQUIPMENT - Southern Power Useful Lives (Details) - Southern Power - Maximum	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Natural Gas Generating Facility
Property, Plant and Equipment [Line Items]
Useful life	50 years	45 years
Solar Generating Facility
Property, Plant and Equipment [Line Items]
Useful life	35 years
Wind Generating Facility
Property, Plant and Equipment [Line Items]
Useful life	30 years

PROPERTY, PLANT, AND EQUIPMEN_9

PROPERTY, PLANT, AND EQUIPMENT - Ownership and Investment in Jointly-Owned Facilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)mi
Alabama Power
Other Ownership Interests [Line Items]
Percent Ownership	14.00%
Alabama Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	60.00%
Plant in Service	$ 189
Accumulated Depreciation	76
CWIP	$ 2
Alabama Power | Plant Miller (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	91.80%
Plant in Service	$ 2,107
Accumulated Depreciation	650
CWIP	$ 24
Georgia Power | Plant Hatch (nuclear)
Other Ownership Interests [Line Items]
Percent Ownership	50.10%
Plant in Service	$ 1,352
Accumulated Depreciation	624
CWIP	$ 37
Georgia Power | Plant Vogtle (nuclear) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	45.70%
Plant in Service	$ 3,592
Accumulated Depreciation	2,221
CWIP	$ 55
Georgia Power | Plant Scherer (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	8.40%
Plant in Service	$ 279
Accumulated Depreciation	98
CWIP	$ 1
Georgia Power | Plant Scherer (coal) Unit 3
Other Ownership Interests [Line Items]
Percent Ownership	75.00%
Plant in Service	$ 1,320
Accumulated Depreciation	520
CWIP	$ 4
Georgia Power | Plant Wansley (coal)
Other Ownership Interests [Line Items]
Percent Ownership	53.50%
Plant in Service	$ 1,068
Accumulated Depreciation	418
CWIP	$ 10
Georgia Power | Rocky Mountain (pumped storage)
Other Ownership Interests [Line Items]
Percent Ownership	25.40%
Plant in Service	$ 183
Accumulated Depreciation	144
CWIP	$ 1
Mississippi Power | Plant Daniel (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 775
Accumulated Depreciation	238
CWIP	$ 15
Southern Company Gas | Dalton Pipeline (natural gas pipeline)
Other Ownership Interests [Line Items]
Percent Ownership	50.00%
Plant in Service	$ 271
Accumulated Depreciation	15
CWIP	$ 0
Pipeline infrastructure (miles) | mi	115
Agreement to lease undivided ownership (percent)	50.00%
Future minimum payments receivable	$ 26
Alabama Power | Mississippi Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership	40.00%
Plant in Service	$ 122
Accumulated Depreciation	54
CWIP	$ 1

PROPERTY, PLANT, AND EQUIPME_10

PROPERTY, PLANT, AND EQUIPMENT - Joint Ownership Agreements (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 8,697	$ 7,880
Georgia Power
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 6,857	$ 5,650
Plant Vogtle Units 3 And 4 | Georgia Power
Property, Plant and Equipment [Line Items]
Percent ownership	45.70%
Construction work in progress	$ 7,300

PROPERTY, PLANT, AND EQUIPME_11

PROPERTY, PLANT, AND EQUIPMENT - Assets Subject to Lien (Narrative) (Details) $ in Millions	Dec. 31, 2020USD ($)
Mississippi Power | Chevron
Property, Plant and Equipment [Line Items]
Net book value of co-generation assets	$ 138

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Details of AROs Included in the Balance Sheets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 9,786	$ 9,394
Liabilities incurred	19	37
Liabilities settled	(442)	(328)
Accretion	409	402
Cash flow revisions	912	281
Balance at end of year	10,684	9,786
Alabama Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	3,540	3,210
Liabilities incurred	0	0
Liabilities settled	(219)	(127)
Accretion	152	145
Cash flow revisions	501	312
Balance at end of year	3,974	3,540
Georgia Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	5,784	5,829
Liabilities incurred	10	35
Liabilities settled	(185)	(151)
Accretion	238	243
Cash flow revisions	418	(172)
Balance at end of year	6,265	5,784
Mississippi Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	190	160
Liabilities incurred	0	1
Liabilities settled	(22)	(35)
Accretion	8	7
Cash flow revisions	0	57
Balance at end of year	176	190
Southern Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	89	84
Liabilities incurred	9	1
Liabilities settled	0	0
Accretion	4	4
Cash flow revisions	(7)	0
Balance at end of year	$ 95	$ 89

ASSET RETIREMENT OBLIGATIONS _2

ASSET RETIREMENT OBLIGATIONS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs			$ 501	$ 312
Estimated inflation rate			4.50%
Estimated trust earnings rate			7.00%
Alabama Power | Internal reserves
Jointly Owned Utility Plant Interests [Line Items]
Accumulated provisions for decommissioning		$ 16	$ 15	16
Mississippi Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs				57
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs	$ 411	(174)
Fair market value of securities on loan and pledged to creditors		28	44	28
Fair value of collateral received		$ 29	$ 45	29
Estimated inflation rate			2.75%
Estimated trust earnings rate			4.75%
Georgia Power | Plant Hatch and Plant Vogtle Units 1 And 2
Jointly Owned Utility Plant Interests [Line Items]
Annual decommissioning cost for ratemaking			$ 4	$ 5

ASSET RETIREMENT OBLIGATIONS _3

ASSET RETIREMENT OBLIGATIONS - Investment Securities in the Funds (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 2,301	$ 2,034
Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	1,339	1,159
Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	851	798
Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	111	77
Alabama Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,156	1,021
Alabama Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	842	743
Alabama Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	231	218
Alabama Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	83	60
Georgia Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,145	1,013
Georgia Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	497	416
Georgia Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	620	580
Georgia Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 28	$ 17

ASSET RETIREMENT OBLIGATIONS _4

ASSET RETIREMENT OBLIGATIONS - Fair Value Increases (Decreases) of the Funds (Details) - Securities held in the Funds - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair value increases (decreases)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ 280	$ 344	$ (67)
Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	220	259	(183)
Alabama Power | Fair value increases (decreases)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	142	194	(38)
Alabama Power | Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	121	149	(96)
Georgia Power | Fair value increases (decreases)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	138	150	(29)
Georgia Power | Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ 99	$ 110	$ (87)

ASSET RETIREMENT OBLIGATIONS _5

ASSET RETIREMENT OBLIGATIONS - Accumulated Provisions for the External Decommissioning Trust Funds (Details) - External decommissioning trust funds - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 1,145	$ 1,013
Plant Farley | Alabama Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	1,156	1,021
Plant Hatch | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	716	634
Plant Vogtle Units 1 and 2 | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 429	$ 379

ASSET RETIREMENT OBLIGATIONS _6

ASSET RETIREMENT OBLIGATIONS - Estimated Costs of Decommissioning (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Alabama Power | Plant Farley
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2037
Decommissioning periods: Completion year	2076
Site study costs	$ 1,720
Alabama Power | Radiated structures | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	1,234
Alabama Power | Spent fuel management | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	387
Alabama Power | Non-radiated structures | Plant Farley
Public Utilities, General Disclosures [Line Items]
Site study costs	$ 99
Georgia Power | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2034
Decommissioning periods: Completion year	2075
Site study costs	$ 962
Georgia Power | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2047
Decommissioning periods: Completion year	2079
Site study costs	$ 842
Georgia Power | Radiated structures | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	734
Georgia Power | Radiated structures | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	601
Georgia Power | Spent fuel management | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	172
Georgia Power | Spent fuel management | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	162
Georgia Power | Non-radiated structures | Plant Hatch
Public Utilities, General Disclosures [Line Items]
Site study costs	56
Georgia Power | Non-radiated structures | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Site study costs	$ 79

CONSOLIDATED ENTITIES AND EQU_3

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - SEGCO Equity Method Investments Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)MW	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%
Percent ownership	14.00%
Alabama Power | SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity (in MWs) | MW	1,020
Share of purchased power	$ 67	$ 93	$ 102
Dividends paid by equity method investment	$ 12	14	18
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%
Georgia Power | SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Share of purchased power	$ 69	$ 95	$ 105
SEGCO | Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	86.00%

CONSOLIDATED ENTITIES AND EQU_4

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - SPC Noncontrolling Interests and VIEs Narrative (Details) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2018USD ($)investorwind_farm	May 31, 2018	Dec. 31, 2020USD ($)	Dec. 31, 2018USD ($)investorwind_farmoperating_facility	Dec. 31, 2019USD ($)
Redeemable Noncontrolling Interest [Line Items]
Assets	$ 116,914		$ 122,935	$ 116,914	$ 118,700
Liabilities			90,410		86,650
Equity investments in unconsolidated subsidiaries			1,362		1,303
Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets			13,235		14,300
Liabilities			6,604		7,678
Number of wind facilities | operating_facility				8
Equity investments in unconsolidated subsidiaries			$ 19		28
Southern Power | SP Solar Holdings I, LP
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership				33.00%
Southern Power | SP Wind
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership				100.00%
Wholly Owned Subsidiary Of Southern Power | Southern Power | SP Solar Holdings I, LP
Redeemable Noncontrolling Interest [Line Items]
Ownership interest				66.00%
Wholly Owned Subsidiary Of Southern Power | Southern Power | SP Wind
Redeemable Noncontrolling Interest [Line Items]
Ownership interest				100.00%
SP Solar Holdings I, LP | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage			67.00%
SP Solar Holdings I, LP | Southern Power | SP Solar Holdings I, LP
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership		33.00%
SP Solar Holdings I, LP | Global Atlantic
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage			33.00%
SP Wind
Redeemable Noncontrolling Interest [Line Items]
Number of wind facilities | wind_farm	8			8
SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage			60.00%
Number of financial investors | investor				3
SP Wind | Southern Power | SP Wind
Redeemable Noncontrolling Interest [Line Items]
Number of financial investors | investor	3
SP Wind | Financial Investors
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	40.00%		40.00%
General Partner | Wholly Owned Subsidiary Of Southern Power | Southern Power | SP Solar Holdings I, LP
Redeemable Noncontrolling Interest [Line Items]
Ownership interest				1.00%
Variable Interest Entity, Primary Beneficiary | SP Solar Holdings I, LP | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets			$ 6,100		6,400
Liabilities			387		381
Noncontrolling interests related to other partners' interest			1,100
Variable Interest Entity, Primary Beneficiary | SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets			2,400		2,500
Liabilities			138		128
Noncontrolling interests related to other partners' interest			43		45
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets			1,100
Liabilities			110		104
Noncontrolling interests related to other partners' interest			$ 454		$ 409

CONSOLIDATED ENTITIES AND EQU_5

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,362	$ 1,303
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,290	1,251
SNG | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,167	1,137
PennEast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	91	82
Other | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 32	$ 32

CONSOLIDATED ENTITIES AND EQU_6

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Income Statement Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 153	$ 162	$ 148
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	141	157	148
Southern Company Gas | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	129	141	131
Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	3	13	7
Southern Company Gas | Penn East Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	7	6	5
Southern Company Gas | Other
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 2	$ (3)	$ 5

FINANCING - Long-Term Debt (Det

FINANCING - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt, gross	$ 48,349	$ 44,561
Finance lease obligations	231	226
Unamortized fair value adjustment	393	430
Unamortized debt premium (discount), net	(201)	(152)
Unamortized debt issuance expense	(237)	(247)
Total long-term debt	48,580	44,787
Less: Amount due within one year	3,507	2,989
Long-Term Debt	$ 45,073	41,798
Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	3.78%
Long-term debt, gross	$ 30,850	30,023
Junior subordinated notes
Debt Instrument [Line Items]
Weighted average interest rate	4.30%
Long-term debt, gross	$ 7,295	5,295
FFB loans
Debt Instrument [Line Items]
Weighted average interest rate	2.92%
Long-term debt, gross	$ 4,618	3,843
Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	1.11%
Long-term debt, gross	$ 2,675	2,963
First mortgage bonds
Debt Instrument [Line Items]
Weighted average interest rate	3.71%
Long-term debt, gross	$ 1,900	1,575
Other revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	6.45%
Long-term debt, gross	$ 320	320
Affiliated trusts
Debt Instrument [Line Items]
Weighted average interest rate	3.33%
Long-term debt, gross	$ 206	206
Medium-term notes
Debt Instrument [Line Items]
Weighted average interest rate	7.88%
Long-term debt, gross	$ 160	160
Other long-term debt
Debt Instrument [Line Items]
Weighted average interest rate	0.83%
Long-term debt, gross	$ 370	145
Alabama Power
Debt Instrument [Line Items]
Long-term debt, gross	8,864	8,517
Finance lease obligations	5	4
Unamortized debt premium (discount), net	(16)	(14)
Unamortized debt issuance expense	(56)	(55)
Total long-term debt	8,869	8,521
Less: Amount due within one year	311	251
Long-Term Debt	$ 8,558	8,270
Percent ownership	14.00%
Alabama Power | Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	4.03%
Long-term debt, gross	$ 7,625	7,275
Alabama Power | Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	0.53%
Long-term debt, gross	$ 1,060	1,060
Alabama Power | Affiliated trusts
Debt Instrument [Line Items]
Weighted average interest rate	3.33%
Long-term debt, gross	$ 206	206
Alabama Power | Other long-term debt
Debt Instrument [Line Items]
Weighted average interest rate	1.20%
Long-term debt, gross	$ 45	45
Georgia Power
Debt Instrument [Line Items]
Long-term debt, gross	12,825	11,660
Finance lease obligations	145	156
Unamortized debt premium (discount), net	(12)	(7)
Unamortized debt issuance expense	(114)	(117)
Total long-term debt	12,970	11,816
Less: Amount due within one year	542	1,025
Long-Term Debt	$ 12,428	10,791
Georgia Power | Plant Vogtle Units 3 And 4
Debt Instrument [Line Items]
Percent ownership	45.70%
Georgia Power | Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	3.59%
Long-term debt, gross	$ 6,400	5,850
Georgia Power | Junior subordinated notes
Debt Instrument [Line Items]
Weighted average interest rate	5.00%
Long-term debt, gross	$ 270	270
Georgia Power | FFB loans
Debt Instrument [Line Items]
Weighted average interest rate	2.92%
Long-term debt, gross	$ 4,618	3,843
Georgia Power | Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	1.47%
Long-term debt, gross	$ 1,538	1,821
Georgia Power | Other long-term debt
Debt Instrument [Line Items]
Weighted average interest rate	0.65%
Long-term debt, gross	$ 125	0
Mississippi Power
Debt Instrument [Line Items]
Long-term debt, gross	1,400	1,589
Finance lease obligations	19	0
Unamortized debt premium (discount), net	11	19
Unamortized debt issuance expense	(7)	(8)
Total long-term debt	1,419	1,589
Less: Amount due within one year	406	281
Long-Term Debt	$ 1,013	1,308
Mississippi Power | Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	4.23%
Long-term debt, gross	$ 900	1,175
Mississippi Power | Pollution control revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	1.86%
Long-term debt, gross	$ 76	83
Mississippi Power | Other revenue bonds
Debt Instrument [Line Items]
Weighted average interest rate	6.45%
Long-term debt, gross	$ 320	320
Mississippi Power | Other long-term debt
Debt Instrument [Line Items]
Weighted average interest rate	1.00%
Long-term debt, gross	$ 100	0
Southern Power
Debt Instrument [Line Items]
Long-term debt, gross	3,692	4,398
Finance lease obligations	0	0
Unamortized debt premium (discount), net	(6)	(8)
Unamortized debt issuance expense	(16)	(19)
Total long-term debt	3,692	4,398
Less: Amount due within one year	299	824
Long-Term Debt	3,393	3,574
Fair value gain (loss)	109	(5)
Derivative notional amount, receive	$ 1,100
Southern Power | Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	3.96%
Long-term debt, gross	$ 3,714	4,425
Southern Company Gas
Debt Instrument [Line Items]
Long-term debt, gross	6,626	5,845
Finance lease obligations	0	0
Unamortized fair value adjustment	393	430
Unamortized debt premium (discount), net	(27)	(20)
Total long-term debt	6,626	5,845
Less: Amount due within one year	333	0
Long-Term Debt	$ 6,293	5,845
Southern Company Gas | Senior notes
Debt Instrument [Line Items]
Weighted average interest rate	4.01%
Long-term debt, gross	$ 4,200	3,700
Southern Company Gas | First mortgage bonds
Debt Instrument [Line Items]
Weighted average interest rate	3.71%
Long-term debt, gross	$ 1,900	1,575
Southern Company Gas | Medium-term notes
Debt Instrument [Line Items]
Weighted average interest rate	7.88%
Long-term debt, gross	$ 160	160
Mississippi Business Finance Corporation Taxable Revenue Bonds | Mississippi Power | Corporate bonds
Debt Instrument [Line Items]
Long-term debt	$ 270	$ 270
Quarterly interest rate	7.13%	7.13%
Tax-exempt Revenue Bonds | Mississippi Power | Secured Debt
Debt Instrument [Line Items]
Long-term debt	$ 50	$ 50

FINANCING - Maturities of Long-

FINANCING - Maturities of Long-Term Debt (Details) $ in Millions	Dec. 31, 2020USD ($)
Debt Disclosure [Line Items]
2021	$ 3,506
2022	3,707
2023	3,131
2024	509
2025	1,191
Alabama Power
Debt Disclosure [Line Items]
2021	311
2022	751
2023	301
2024	22
2025	250
Georgia Power
Debt Disclosure [Line Items]
2021	542
2022	488
2023	889
2024	491
2025	138
Mississippi Power
Debt Disclosure [Line Items]
2021	406
2022	16
2023	1
2024	1
2025	12
Long-term debt maturing in 2040 intended to be repaid in 2021	50
Long-term debt maturing in 2023 intended to be repaid in 2021	25
Southern Power
Debt Disclosure [Line Items]
2021	300
2022	677
2023	290
2024	0
2025	500
Southern Company Gas
Debt Disclosure [Line Items]
2021	330
2022	46
2023	400
2024	0
2025	$ 300

FINANCING - DOE Loan Guarantee

FINANCING - DOE Loan Guarantee Borrowings (Details) - USD ($)	1 Months Ended			12 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019	Aug. 31, 2018
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 7,733,000,000			$ 7,733,000,000
Georgia Power
Debt Instrument [Line Items]
Percent of eligible project costs (may not exceed)			70.00%
Principal amortization payments				73,000,000	$ 0	$ 0
Line of credit facility, maximum borrowing capacity	$ 1,750,000,000			$ 1,750,000,000
Basis spread on variable rate			0.375%
Amortization period			5 years
Plant Vogtle Units 3 And 4 | Georgia Power
Debt Instrument [Line Items]
Percent ownership	45.70%			45.70%
FFB Loan | Georgia Power
Debt Instrument [Line Items]
Eligible project costs to be reimbursed			$ 5,130,000,000
Proceeds from lines of credit	$ 329,000,000	$ 519,000,000
Fixed stated interest rate of debt obligation	1.737%			1.737%			1.652%
Principal amortization payments				$ 73,000,000
Line of credit facility, maximum borrowing capacity	$ 4,600,000,000			$ 4,600,000,000	$ 3,800,000,000
Additional FFB Credit Facility | Georgia Power
Debt Instrument [Line Items]
Funds received under guarantee settlement agreement, less customer refunds			$ 1,492,000,000
Plant Vogtle Units 3 And 4 | Georgia Power
Debt Instrument [Line Items]
Percent ownership	45.70%			45.70%
Ownership interest percentage required for voting for continuing construction								90.00%

FINANCING - Equity Units (Detai

FINANCING - Equity Units (Details) - USD ($)	1 Months Ended
	Aug. 31, 2019	Dec. 31, 2020
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Number of shares indexed (in shares)	34,500,000
Equity units, per unit issuance price (in dollars per share)	$ 50
Proceeds from issuance of mandatory redeemable capital securities	$ 1,682,000,000
Maximum number of shares (in shares)	30,200,000
Junior subordinated notes
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, settlement terms, contract adjustment payments, accretion period	3 years
Series 2019A and Series 2019B Remarketable Junior Subordinated Notes | Junior subordinated notes
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, annual distribution rate	6.75%
Quarterly interest rate	2.70%
Interest rate	4.05%
Purchase contract adjustment liability	$ 198,000,000	$ 119,000,000
Purchase contract adjustment liability, current		$ 67,000,000
Series 2019A Remarketable Junior Subordinated Notes | Junior subordinated notes
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Debt face amount	$ 1,725,000,000
Equity units, percentage interest in attached debt instrument	0.0025%
Series 2019B Remarketable Junior Subordinated Notes | Junior subordinated notes
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, percentage interest in attached debt instrument	0.0025%
Anti-Dilution Scenario One
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, conversion ratio (in shares)	0.7284
Anti-Dilution Scenario One | Minimum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price upper threshold (in dollars per share)	$ 68.64
Anti-Dilution Scenario Two
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, per unit issuance price (in dollars per share)	50
Anti-Dilution Scenario Two | Minimum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price lower threshold (in dollars per share)	57.20
Anti-Dilution Scenario Two | Maximum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price upper threshold (in dollars per share)	$ 68.64
Anti-Dilution Scenario Three
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, conversion ratio (in shares)	0.8741
Anti-Dilution Scenario Three | Maximum
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, stock price lower threshold (in dollars per share)	$ 57.20

FINANCING - Bank Credit Arrange

FINANCING - Bank Credit Arrangements (Details) - USD ($)	Dec. 31, 2020	Nov. 30, 2020
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	7,671,000,000
Due within One Year	33,000,000
Southern Company
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
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
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
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
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	591,000,000
Due within One Year	0
Southern Power | Continuing Letter of Credit Facility A
Line of Credit Facility [Line Items]
Expires, 2023	75,000,000
Total		$ 120,000,000
Unused	5,000,000
Southern Power | Continuing Letter of Credit Facility B
Line of Credit Facility [Line Items]
Expires, 2023	60,000,000
Unused	11,000,000
Southern Company 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
Other Subsidiaries
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	1,250,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 500,000,000

FINANCING - Bank Credit Arran_2

FINANCING - Bank Credit Arrangements Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	70.00%
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	$ 1,400
Other Subsidiaries
Debt Disclosure [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	65.00%
Alabama Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	$ 854
Georgia Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	550
Remarketed pollution control bonds	174
Mississippi Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	34
Remarketed pollution control bonds	50
Southern Power | Power Purchase Agreement
Debt Disclosure [Line Items]
Debt instrument, collateral amount	$ 105	$ 104

FINANCING - Notes Payable (Deta

FINANCING - Notes Payable (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount Outstanding	$ 609	$ 2,055
Weighted Average Interest Rate	0.30%	2.10%
Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 609	$ 1,705
Weighted Average Interest Rate	0.30%	2.10%
Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 350
Weighted Average Interest Rate	0.00%	2.30%
Georgia Power
Short-term Debt [Line Items]
Amount Outstanding	$ 60	$ 365
Weighted Average Interest Rate	0.30%	2.20%
Georgia Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 60	$ 115
Weighted Average Interest Rate	0.30%	2.10%
Georgia Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 250
Weighted Average Interest Rate	0.00%	2.20%
Mississippi Power
Short-term Debt [Line Items]
Amount Outstanding	$ 25	$ 0
Mississippi Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 25	$ 0
Weighted Average Interest Rate	0.40%	0.00%
Southern Power
Short-term Debt [Line Items]
Amount Outstanding	$ 175	$ 549
Weighted Average Interest Rate	0.30%	2.20%
Southern Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 175	$ 449
Weighted Average Interest Rate	0.30%	2.10%
Southern Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 100
Weighted Average Interest Rate	0.00%	2.60%
Southern Company Gas
Short-term Debt [Line Items]
Amount Outstanding	$ 324	$ 650
Southern Company Gas | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 324	$ 650
Weighted Average Interest Rate	0.20%	2.00%
Southern Company Gas Capital | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 220	$ 372
Weighted Average Interest Rate	0.30%	2.10%
Nicor Gas | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 104	$ 278
Weighted Average Interest Rate	0.20%	1.80%

FINANCING - Outstanding Classes

FINANCING - Outstanding Classes of Capital Stock Narrative (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Stock issued employee and director stock plans (in shares)	3.3
Proceeds from issuance of shares under share-based compensation plans	$ 74
Number of shares reserved for issuance to stock-based compensation plan (in shares)	88
Payments for redemption of all outstanding shares of redeemable preferred stock	$ 0	$ 0	$ 33
Southern Company Common Stock
Debt Instrument [Line Items]
Remaining shares available for awards (in shares)	6.8
Mississippi Power
Debt Instrument [Line Items]
Payments for redemption of all outstanding shares of redeemable preferred stock	$ 0	$ 0	$ 33

FINANCING - Diluted Earnings Pe

FINANCING - Diluted Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
As reported shares	1,058	1,046	1,020
Effect of stock-based compensation	7	8	5
Diluted shares	1,065	1,054	1,025

FINANCING - Preferred Stock Red

FINANCING - Preferred Stock Redemption (Details) - Alabama Power	12 Months Ended
	Dec. 31, 2020$ / sharesshares	Sep. 30, 2022$ / shares
4.92% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0492
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	80,000
Redemption Price Per Share (in dollars per share)	$ 103.23
4.72% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0472
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	50,000
Redemption Price Per Share (in dollars per share)	$ 102.18
4.64% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0464
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	60,000
Redemption Price Per Share (in dollars per share)	$ 103.14
4.60% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0460
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	100,000
Redemption Price Per Share (in dollars per share)	$ 104.20
4.52% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0452
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	50,000
Redemption Price Per Share (in dollars per share)	$ 102.93
4.20% Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0420
Par Value/Stated Capital Per Share (in dollars per share)	$ 100
Shares outstanding (in shares) | shares	135,115
Redemption Price Per Share (in dollars per share)	$ 105
5.00% Class A Preferred Stock
Debt Instrument, Redemption [Line Items]
Dividend rate percentage	0.0500
Par Value/Stated Capital Per Share (in dollars per share)	$ 25
Shares outstanding (in shares) | shares	10,000,000
Redemption Price Per Share (in dollars per share)	$ 25
5.00% Class A Preferred Stock | Scenario, Forecast
Debt Instrument, Redemption [Line Items]
Redemption Price Per Share (in dollars per share)		$ 25.50

FINANCING - Dividend Restrictio

FINANCING - Dividend Restrictions and Structural Considerations Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Variable Interest Entity [Line Items]
Undistributed retained earnings of subsidiaries	$ 5,600
Southern Company Gas
Variable Interest Entity [Line Items]
Retained earnings, unappropriated	$ 1,100
Southern Company Gas | Southern Company Gas Capital
Variable Interest Entity [Line Items]
Noncontrolling ownership percentage held by parent	100.00%

LEASES - Major Categories of Le

LEASES - Major Categories of Lease Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Lease obligations	$ 2,083	$ 2,070
Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	175	160
Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,452	1,582
Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	28	6
Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	451	398
Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	82	92
Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	941	990
Electric generating units | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	146	125
Electric generating units | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,368	1,487
Electric generating units | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Electric generating units | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Electric generating units | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	815	782
Real estate/land | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	4	4
Real estate/land | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	53	54
Real estate/land | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	2	2
Real estate/land | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	451	398
Real estate/land | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	61	74
Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	158	154
Communication towers | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	2	2
Communication towers | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	3	3
Communication towers | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Communication towers | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Communication towers | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	20	18
Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	42	51
Railcars | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	16	21
Railcars | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	23	26
Railcars | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	3	3
Railcars | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Railcars | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Other
Lessee, Lease, Description [Line Items]
Lease obligations	127	93
Other | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	7	8
Other | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	5	12
Other | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	23	1
Other | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Other | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	$ 1	$ 0

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 1,852	$ 1,852	$ 1,844
Maximum | Real estate
Lessee, Lease, Description [Line Items]
Remaining terms		24 years
Maximum | Land
Lessee, Lease, Description [Line Items]
Lessee, lease term		46 years
Maximum | Communication towers
Lessee, Lease, Description [Line Items]
Lessee, lease term		10 years
Lessee, renewal period		20 years
Maximum | Fuel cells
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	14 years	14 years
Alabama Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 170	$ 170	156
Alabama Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term	17 years	17 years
Alabama Power | Minimum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term	3 years	3 years
Georgia Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 1,307	$ 1,307	1,426
Variable lease, payment		39	42
Georgia Power | Purchased power, affiliates
Lessee, Lease, Description [Line Items]
Variable lease, payment		20	20
Southern Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 451	$ 451	398
Southern Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	26 years	26 years
Mississippi Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 9	$ 9	6
Transfer of construction work in progress to lease receivables	26
Sales-type lease, lease receivable	26	26
Mississippi Power | Other Property and Investments
Lessee, Lease, Description [Line Items]
Sales-type lease, lease receivable	24	24
Mississippi Power | Other Accounts, Notes, and Loans Receivable
Lessee, Lease, Description [Line Items]
Sales-type lease, lease receivable	$ 2	$ 2
Mississippi Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, lease term, sales-type lease	18 years	18 years
Southern Company Gas
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 82	$ 82	92
Southern Company Gas | Maximum
Lessee, Lease, Description [Line Items]
Lessor, remaining term		22 years
Affiliate | Georgia Power | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 575	$ 575	$ 624
Traditional Electric Operating Companies | Maximum | Outdoor lighting
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	7 years	7 years

LEASES - Balance Sheet Amounts

LEASES - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
Operating lease ROU assets, net	$ 1,802	$ 1,800
Operating lease obligations - current	241	229
Operating lease obligations - non-current	1,611	1,615
Total operating lease obligations	$ 1,852	$ 1,844
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	so:PlantInServiceNetOfDepreciation	so:PlantInServiceNetOfDepreciation
Finance lease ROU assets, net	$ 218	$ 216
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance lease obligations - current	$ 17	$ 21
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations
Finance lease obligations - non-current	$ 214	$ 205
Total finance lease obligations	231	226
Alabama Power
Operating Leases
Operating lease ROU assets, net	$ 151	$ 132
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease obligations - current	$ 51	$ 49
Operating lease obligations - non-current	119	107
Total operating lease obligations	$ 170	$ 156
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	so:PlantInServiceNetOfDepreciation	so:PlantInServiceNetOfDepreciation
Finance lease ROU assets, net	$ 5	$ 4
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance lease obligations - current	$ 1	$ 1
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations
Finance lease obligations - non-current	$ 4	$ 3
Total finance lease obligations	5	4
Georgia Power
Operating Leases
Operating lease ROU assets, net	1,308	1,428
Operating lease obligations - current	151	144
Operating lease obligations - non-current	1,156	1,282
Total operating lease obligations	$ 1,307	$ 1,426
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	so:PlantInServiceNetOfDepreciation	so:PlantInServiceNetOfDepreciation
Finance lease ROU assets, net	$ 115	$ 130
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance lease obligations - current	$ 9	$ 11
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations
Finance lease obligations - non-current	$ 136	$ 145
Total finance lease obligations	$ 145	$ 156
Mississippi Power
Operating Leases
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Operating lease ROU assets, net	$ 9	$ 6
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease obligations - current	$ 2	$ 2
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Operating lease obligations - non-current	$ 7	$ 4
Total operating lease obligations	$ 9	6
Finance Leases
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	so:PlantInServiceNetOfDepreciation
Finance lease ROU assets, net	$ 19	0
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance lease obligations - current	$ 1	0
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations
Finance lease obligations - non-current	$ 18	0
Total finance lease obligations	19	0
Southern Power
Operating Leases
Operating lease ROU assets, net	$ 415	$ 369
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease obligations - current	$ 25	$ 22
Operating lease obligations - non-current	426	376
Total operating lease obligations	451	398
Finance Leases
Finance lease ROU assets, net	0	0
Finance lease obligations - current	0	0
Finance lease obligations - non-current	0	0
Total finance lease obligations	0	0
Southern Company Gas
Operating Leases
Operating lease ROU assets, net	$ 81	$ 93
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease obligations - current	$ 15	$ 14
Operating lease obligations - non-current	67	78
Total operating lease obligations	82	92
Finance Leases
Finance lease ROU assets, net	0	0
Finance lease obligations - current	0	0
Finance lease obligations - non-current	0	0
Total finance lease obligations	$ 0	$ 0

LEASES - Lease Costs (Details)

LEASES - Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease cost
Operating lease cost	$ 309	$ 310
Finance lease cost:
Amortization of ROU assets	26	28
Interest on lease obligations	11	12
Total finance lease cost	37	40
Short-term lease costs	39	48
Variable lease cost	91	105
Sublease income	0	0
Total lease cost	476	503
Alabama Power
Lease cost
Operating lease cost	55	54
Finance lease cost:
Amortization of ROU assets	1	1
Interest on lease obligations	0	0
Total finance lease cost	1	1
Short-term lease costs	11	19
Variable lease cost	4	6
Sublease income	(1)	(1)
Total lease cost	70	79
Georgia Power
Lease cost
Operating lease cost	212	206
Finance lease cost:
Amortization of ROU assets	15	15
Interest on lease obligations	16	18
Total finance lease cost	31	33
Short-term lease costs	26	22
Variable lease cost	76	85
Sublease income	0	0
Total lease cost	345	346
Mississippi Power
Lease cost
Operating lease cost	3	3
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	0	0
Sublease income	0	0
Total lease cost	3	3
Southern Power
Lease cost
Operating lease cost	29	28
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	7	7
Sublease income	0	0
Total lease cost	36	35
Southern Company Gas
Lease cost
Operating lease cost	19	18
Finance lease cost:
Amortization of ROU assets	0	0
Interest on lease obligations	0	0
Total finance lease cost	0	0
Short-term lease costs	0	0
Variable lease cost	0	0
Sublease income	0	0
Total lease cost	$ 19	$ 18

LEASES - Rent Expense and PPA C

LEASES - Rent Expense and PPA Capacity Expense Related to Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Lessee, Lease, Description [Line Items]
Rent expense	$ 192
PPA capacity expense	231
Alabama Power
Lessee, Lease, Description [Line Items]
Rent expense	23
PPA capacity expense	44
Georgia Power
Lessee, Lease, Description [Line Items]
Rent expense	34
PPA capacity expense	206
Operating leases, contingent rent expense	72
Mississippi Power
Lessee, Lease, Description [Line Items]
Rent expense	4
PPA capacity expense	0
Operating leases, contingent rent expense	10
Southern Power
Lessee, Lease, Description [Line Items]
Rent expense	31
PPA capacity expense	0
Southern Company Gas
Lessee, Lease, Description [Line Items]
Rent expense	15
PPA capacity expense	0
Affiliate Operating Lease PPA | Georgia Power
Lessee, Lease, Description [Line Items]
Operating leases, contingent rent expense	$ 29

LEASES - Other Information (Det

LEASES - Other Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 310	$ 323
Operating cash flows from finance leases	9	10
Financing cash flows from finance leases	22	32
ROU assets obtained in exchange for new operating lease obligations	227	118
ROU assets obtained in exchange for new finance lease obligations	$ 10	$ 35
Weighted-average remaining lease term in years:
Operating leases	14 years 6 months	14 years 2 months 12 days
Finance leases	18 years 2 months 12 days	18 years 9 months 18 days
Weighted-average discount rate:
Operating leases	4.44%	4.53%
Finance leases	4.79%	5.04%
Alabama Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 55	$ 54
Operating cash flows from finance leases	0	0
Financing cash flows from finance leases	1	1
ROU assets obtained in exchange for new operating lease obligations	63	7
ROU assets obtained in exchange for new finance lease obligations	$ 2	$ 2
Weighted-average remaining lease term in years:
Operating leases	7 years 9 months 18 days	3 years 1 month 6 days
Finance leases	9 years 8 months 12 days	12 years 1 month 6 days
Weighted-average discount rate:
Operating leases	4.14%	3.33%
Finance leases	3.20%	3.60%
Georgia Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 215	$ 210
Operating cash flows from finance leases	18	19
Financing cash flows from finance leases	11	13
ROU assets obtained in exchange for new operating lease obligations	32	21
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 24
Weighted-average remaining lease term in years:
Operating leases	9 years 4 months 24 days	10 years 2 months 12 days
Finance leases	9 years 6 months	10 years 6 months
Weighted-average discount rate:
Operating leases	4.37%	4.46%
Finance leases	10.81%	10.76%
Mississippi Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 3	$ 3
Operating cash flows from finance leases	0	0
Financing cash flows from finance leases	0	0
ROU assets obtained in exchange for new operating lease obligations	0	0
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0
Weighted-average remaining lease term in years:
Operating leases	6 years 6 months	7 years
Finance leases	14 years 10 months 24 days
Weighted-average discount rate:
Operating leases	3.26%	4.02%
Finance leases	2.74%
Southern Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 28	$ 27
Operating cash flows from finance leases	0	0
Financing cash flows from finance leases	0	0
ROU assets obtained in exchange for new operating lease obligations	51	2
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0
Weighted-average remaining lease term in years:
Operating leases	32 years 1 month 6 days	32 years 9 months 18 days
Weighted-average discount rate:
Operating leases	5.45%	5.66%
Southern Company Gas
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 18	$ 18
Operating cash flows from finance leases	0	0
Financing cash flows from finance leases	0	0
ROU assets obtained in exchange for new operating lease obligations	4	19
ROU assets obtained in exchange for new finance lease obligations	$ 0	$ 0
Weighted-average remaining lease term in years:
Operating leases	9 years 9 months 18 days	9 years 10 months 24 days
Weighted-average discount rate:
Operating leases	3.67%	3.70%

LEASES - Maturities of Lease Li

LEASES - Maturities of Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating leases:
2021	$ 300
2022	287
2023	230
2024	187
2025	165
Thereafter	1,546
Total	2,715
Less: Present value discount	863
Operating lease obligations, including held for sale	1,852
Operating lease obligations	1,852	$ 1,844
Finance leases:
2021	28
2022	25
2023	22
2024	19
2025	16
Thereafter	246
Total	356
Less: Present value discount	125
Finance lease obligations	231	226
Alabama Power
Operating leases:
2021	57
2022	58
2023	9
2024	6
2025	6
Thereafter	74
Total	210
Less: Present value discount	40
Operating lease obligations	170	156
Finance leases:
2021	1
2022	1
2023	1
2024	1
2025	0
Thereafter	1
Total	5
Less: Present value discount	0
Finance lease obligations	5	4
Georgia Power
Operating leases:
2021	205
2022	202
2023	200
2024	164
2025	137
Thereafter	701
Total	1,609
Less: Present value discount	302
Operating lease obligations	1,307	1,426
Finance leases:
2021	24
2022	25
2023	25
2024	25
2025	25
Thereafter	109
Total	233
Less: Present value discount	88
Finance lease obligations	145	156
Mississippi Power
Operating leases:
2021	2
2022	4
2023	1
2024	1
2025	0
Thereafter	2
Total	10
Less: Present value discount	1
Operating lease obligations	9	6
Finance leases:
2021	2
2022	1
2023	2
2024	1
2025	2
Thereafter	15
Total	23
Less: Present value discount	4
Finance lease obligations	19	0
Southern Power
Operating leases:
2021	30
2022	25
2023	27
2024	27
2025	27
Thereafter	873
Total	1,009
Less: Present value discount	558
Operating lease obligations	451	398
Finance leases:
2021	0
2022	0
2023	0
2024	0
2025	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0	0
Southern Company Gas
Operating leases:
2021	18
2022	14
2023	12
2024	11
2025	10
Thereafter	35
Total	100
Less: Present value discount	18
Operating lease obligations	82	92
Finance leases:
2021	0
2022	0
2023	0
2024	0
2025	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	$ 0	$ 0

LEASES - Leases Not Yet Commenc

LEASES - Leases Not Yet Commenced (Details) - Southern Power $ in Millions	Dec. 31, 2020USD ($)
Lessee, Lease, Description [Line Items]
Estimated total obligations	$ 12
Maximum
Lessee, Lease, Description [Line Items]
Longest lease term expiration	30 years

LEASES - Lease Income (Details)

LEASES - Lease Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 16	$ 9
Lease income - operating leases	208	273
Variable lease income	419	403
Total lease income	643	685
Alabama Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	45	24
Variable lease income	0	0
Total lease income	45	24
Georgia Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	58	71
Variable lease income	0	0
Total lease income	58	71
Mississippi Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	12	9
Lease income - operating leases	2	0
Variable lease income	0	0
Total lease income	14	9
Southern Power
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	87	160
Variable lease income	449	434
Total lease income	536	594
Southern Company Gas
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0	0
Lease income - operating leases	35	35
Variable lease income	0	0
Total lease income	$ 35	$ 35

LEASES - Undiscounted Cash Flow

LEASES - Undiscounted Cash Flows to be Received Under Tolling Arrangements Accounted for as Sales-type Leases (Details) - Mississippi Power $ in Millions	Dec. 31, 2020USD ($)
Sales-type and Direct Financing Leases, Lease Receivable, Fiscal Year Maturity [Abstract]
2021	$ 20
2022	19
2023	19
2024	18
2025	17
Thereafter	162
Total undiscounted cash flows	255
Lease receivable	138
Difference between undiscounted cash flows and discounted cash flows	$ 117

LEASES - Undiscounted Cash Fl_2

LEASES - Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases (Details) $ in Millions	Dec. 31, 2020USD ($)
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	$ 207
2022	187
2023	138
2024	106
2025	99
Thereafter	978
Total	1,715
Alabama Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	83
2022	76
2023	32
2024	4
2025	3
Thereafter	23
Total	221
Georgia Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	19
2022	8
2023	2
2024	0
2025	0
Thereafter	0
Total	29
Southern Power
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	86
2022	87
2023	88
2024	90
2025	74
Thereafter	313
Total	738
Southern Company Gas
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2021	35
2022	35
2023	34
2024	33
2025	28
Thereafter	435
Total	$ 600

INCOME TAXES - Current and Defe

INCOME TAXES - Current and Deferred Income Tax Provisions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Federal —
Current	$ 199	$ 156	$ 167
Deferred	70	1,237	231
Total federal taxes	269	1,393	398
State —
Current	100	275	188
Deferred	24	130	(137)
Total state taxes	124	405	51
Income taxes	393	1,798	449
Alabama Power
Federal —
Current	198	61	91
Deferred	44	125	123
Total federal taxes	242	186	214
State —
Current	61	12	26
Deferred	34	72	51
Total state taxes	95	84	77
Income taxes	337	270	291
Georgia Power
Federal —
Current	365	264	393
Deferred	(224)	180	(249)
Total federal taxes	141	444	144
State —
Current	60	6	81
Deferred	(49)	22	(11)
Total state taxes	11	28	70
Income taxes	152	472	214
Mississippi Power
Federal —
Current	18	(6)	(567)
Deferred	(14)	26	575
Total federal taxes	4	20	8
State —
Current	0	(1)	(10)
Deferred	10	11	(100)
Total state taxes	10	10	(110)
Income taxes	14	30	(102)
Southern Power
Federal —
Current	(303)	(717)	85
Deferred	299	647	(154)
Total federal taxes	(4)	(70)	(69)
State —
Current	(4)	1	(9)
Deferred	11	13	(86)
Total state taxes	7	14	(95)
Income taxes	3	(56)	(164)
Southern Company Gas
Federal —
Current	82	(120)	334
Deferred	53	195	33
Total federal taxes	135	75	367
State —
Current	35	37	131
Deferred	3	18	(34)
Total state taxes	38	55	97
Income taxes	$ 173	$ 130	$ 464

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)operating_facility
Income Tax Disclosure [Line Items]
Deferred income tax assets	$ 8,874	$ 8,680
Income tax benefit	(393)	(1,798)	$ (449)
ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	1,853	2,098
Southern Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	$ 1,587	1,917
Percentage reduction in tax basis of assets	50.00%
Number of wind facilities | operating_facility			8
Income tax benefit	$ (3)	56	$ 164
Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits	340	734	5
Southern Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	1,110	1,445
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits		5	1
Southern Power | Production Tax Credit Carryforward
Income Tax Disclosure [Line Items]
Effective income tax rate reconciliation, tax credit, production, amount	15	12	141
Georgia Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	3,443	3,123
Income tax benefit	(152)	(472)	(214)
State investment tax credit carryforward	343
Georgia Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	539	435
Mississippi Power
Income Tax Disclosure [Line Items]
Deferred income tax assets	428	451
Income tax benefit	(14)	(30)	102
Mississippi Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets	0	0
State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Income tax benefit			65
State and Local Jurisdiction | Georgia Power
Income Tax Disclosure [Line Items]
Valuation allowance	28
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits	67	51	21
Deferred Charges Related To Income Taxes, Current | Other Noncurrent Assets | Southern Power | Unrealized Tax Credits
Income Tax Disclosure [Line Items]
Deferred income tax assets	5	$ 51	$ 128
Mississippi | State and Local Jurisdiction | Mississippi Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	32
Oklahoma | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	16
Florida | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance	$ 11

INCOME TAXES - Amortization of

INCOME TAXES - Amortization of Deferred Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 84	$ 181	$ 87
Southern Power
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 59	$ 151	$ 58

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	2.80%	4.90%	1.80%
Employee stock plans' dividend deduction	(0.70%)	(0.40%)	(1.00%)
Non-deductible book depreciation	0.70%	0.30%	0.80%
Flowback of excess deferred income taxes	(8.80%)	(2.10%)	(4.00%)
AFUDC-Equity	(0.80%)	(0.40%)	(1.00%)
ITC basis difference		(0.10%)	(0.60%)
Federal PTCs	0.00%		(4.70%)
Amortization of ITC	(1.60%)	(0.80%)	(2.00%)
Tax impact from sale of subsidiaries		5.10%	8.60%
Tax Reform Legislation			(1.40%)
Noncontrolling interests	0.00%	0.00%	(0.40%)
Leveraged lease impairments	(1.60%)
Other	0.20%	0.00%	(0.80%)
Effective income tax (benefit) rate	11.20%	27.50%	16.30%
Alabama Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	5.00%	4.90%	5.00%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.60%	0.60%	0.60%
Flowback of excess deferred income taxes	(3.10%)	(5.30%)	(1.80%)
AFUDC-Equity	(0.60%)	(0.80%)	(1.00%)
ITC basis difference		0.00%	0.00%
Federal PTCs	0.00%		0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries		0.00%	0.00%
Tax Reform Legislation			0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments	0.00%
Other	(0.30%)	(0.40%)	(0.10%)
Effective income tax (benefit) rate	22.50%	19.90%	23.60%
Georgia Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	0.50%	1.00%	5.50%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.80%	0.50%	1.20%
Flowback of excess deferred income taxes	(12.00%)	0.00%	0.00%
AFUDC-Equity	(1.10%)	(0.60%)	(1.40%)
ITC basis difference		0.00%	0.00%
Federal PTCs	0.00%		0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.20%)
Tax impact from sale of subsidiaries		0.00%	0.00%
Tax Reform Legislation			(4.90%)
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments	0.00%
Other	(0.30%)	(0.30%)	0.10%
Effective income tax (benefit) rate	8.80%	21.50%	21.30%
Mississippi Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	4.80%	4.30%	(65.10%)
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.50%	0.40%	0.70%
Flowback of excess deferred income taxes	(18.50%)	(12.60%)	(4.10%)
AFUDC-Equity	(0.10%)	(0.10%)	0.00%
ITC basis difference		0.00%	0.00%
Federal PTCs	0.00%		0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.20%)
Tax impact from sale of subsidiaries		0.00%	0.00%
Tax Reform Legislation			(26.30%)
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments	0.00%
Other	0.90%	4.90%	(1.40%)
Effective income tax (benefit) rate	8.50%	17.80%	(75.40%)
Southern Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	2.70%	4.00%	(90.80%)
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.00%	0.00%	0.00%
Flowback of excess deferred income taxes	0.00%	0.00%	0.00%
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference		(1.90%)	(0.20%)
Federal PTCs	(2.50%)		(156.60%)
Amortization of ITC	(22.10%)	(16.10%)	(55.40%)
Tax impact from sale of subsidiaries		(27.60%)	0.00%
Tax Reform Legislation			96.10%
Noncontrolling interests	3.10%	0.80%	(14.90%)
Leveraged lease impairments	0.00%
Other	(0.90%)	(0.60%)	2.00%
Effective income tax (benefit) rate	1.30%	(20.40%)	(198.80%)
Southern Company Gas
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	21.00%
State income tax, net of federal deduction	4.00%	6.10%	9.20%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.00%	0.00%	0.00%
Flowback of excess deferred income taxes	(2.70%)	(6.00%)	(3.00%)
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference		0.00%	0.00%
Federal PTCs	0.00%		0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.10%)
Tax impact from sale of subsidiaries		(1.40%)	28.50%
Tax Reform Legislation			(0.40%)
Noncontrolling interests	0.00%	0.00%	0.00%
Leveraged lease impairments	0.00%
Other	0.50%	(1.40%)	0.30%
Effective income tax (benefit) rate	22.70%	18.20%	55.50%

INCOME TAXES - Deferred Tax Ass

INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities —
Deferred income tax liabilities	$ 16,781	$ 16,261
Deferred tax assets —
Deferred income tax assets	8,874	8,680
Valuation allowance	(136)	(137)
Net deferred income tax assets	8,738	8,543
Net deferred income taxes liabilities	8,043	7,718
Accumulated deferred income taxes – assets	(132)	(170)
Accumulated deferred income taxes – liabilities	8,175	7,888
Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	8,950	8,711
Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	1,999	1,843
Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	284	277
Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	142	236
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	739	704
Deferred tax assets —
Deferred income tax assets	1,511	1,385
Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	78	83
Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	80	109
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	1,313	1,174
Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	270	341
AROs
Deferred tax liabilities —
Deferred income tax liabilities	1,969	1,723
AROs
Deferred tax liabilities —
Deferred income tax liabilities	804	814
Other
Deferred tax liabilities —
Deferred income tax liabilities	437	523
Other property basis differences
Deferred tax assets —
Deferred income tax assets	223	230
ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	1,853	2,098
Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	86	97
Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	166	169
Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	128	112
AROs
Deferred tax assets —
Deferred income tax assets	2,773	2,537
Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	369	283
Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	357	402
Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	338	401
Other
Deferred tax assets —
Deferred income tax assets	660	689
Alabama Power
Deferred tax liabilities —
Deferred income tax liabilities	5,416	5,161
Deferred tax assets —
Deferred income tax assets	2,143	1,901
Valuation allowance	0	0
Net deferred income tax assets	2,143	1,901
Net deferred income taxes liabilities	3,273	3,260
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,273	3,260
Alabama Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	2,453	2,402
Alabama Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	1,010	912
Alabama Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	151	162
Alabama Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Alabama Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	250	242
Deferred tax assets —
Deferred income tax assets	369	334
Alabama Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	12	13
Alabama Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Alabama Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	348	311
Alabama Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	123	174
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	764	613
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	328	360
Alabama Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	128	134
Alabama Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	12	11
Alabama Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	7	8
Alabama Power | AROs
Deferred tax assets —
Deferred income tax assets	1,092	973
Alabama Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	243	240
Alabama Power | Other
Deferred tax assets —
Deferred income tax assets	143	173
Georgia Power
Deferred tax liabilities —
Deferred income tax liabilities	6,680	6,345
Deferred tax assets —
Deferred income tax assets	3,443	3,123
Valuation allowance	(35)	(35)
Net deferred income tax assets	3,408	3,088
Net deferred income taxes liabilities	3,272	3,257
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,272	3,257
Georgia Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	3,228	3,058
Georgia Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	689	643
Georgia Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	59	63
Georgia Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	362	351
Deferred tax assets —
Deferred income tax assets	522	488
Georgia Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	66	70
Georgia Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	80	109
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	438	403
Georgia Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	141	159
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	1,165	1,066
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	429	405
Georgia Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	82	81
Georgia Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	72	65
Georgia Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	539	435
Georgia Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Georgia Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Georgia Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	17	18
Georgia Power | AROs
Deferred tax assets —
Deferred income tax assets	1,594	1,471
Georgia Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	369	283
Georgia Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	9	13
Georgia Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	76	133
Georgia Power | Other
Deferred tax assets —
Deferred income tax assets	186	154
Mississippi Power
Deferred tax liabilities —
Deferred income tax liabilities	705	695
Deferred tax assets —
Deferred income tax assets	428	451
Valuation allowance	(41)	(41)
Net deferred income tax assets	387	410
Net deferred income taxes liabilities	318	285
Accumulated deferred income taxes – assets	(129)	(139)
Accumulated deferred income taxes – liabilities	447	424
Mississippi Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	319	315
Mississippi Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	148	143
Mississippi Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	25	24
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	39	38
Deferred tax assets —
Deferred income tax assets	80	72
Mississippi Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	62	55
Mississippi Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	6	8
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	40	44
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	66	68
Mississippi Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | AROs
Deferred tax assets —
Deferred income tax assets	40	44
Mississippi Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	250	251
Mississippi Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	19	28
Mississippi Power | Other
Deferred tax assets —
Deferred income tax assets	39	56
Southern Power
Deferred tax liabilities —
Deferred income tax liabilities	1,413	1,445
Deferred tax assets —
Deferred income tax assets	1,587	1,917
Valuation allowance	(35)	(36)
Net deferred income tax assets	1,552	1,881
Net deferred income taxes assets	(139)	(436)
Accumulated deferred income taxes – assets	(262)	(551)
Accumulated deferred income taxes – liabilities	123	115
Southern Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,389	1,422
Southern Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	26	24
Southern Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	12	12
Deferred tax assets —
Deferred income tax assets	6	5
Southern Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	12	11
Southern Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	134	146
Southern Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	1,110	1,445
Southern Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	166	169
Southern Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	25	10
Southern Power | AROs
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	68	72
Southern Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other
Deferred tax assets —
Deferred income tax assets	52	46
Southern Company Gas
Deferred tax liabilities —
Deferred income tax liabilities	1,693	1,676
Deferred tax assets —
Deferred income tax assets	432	462
Valuation allowance	(4)	(5)
Net deferred income tax assets	428	457
Net deferred income taxes liabilities	1,265	1,219
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	1,265	1,219
Southern Company Gas | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,349	1,288
Southern Company Gas | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	135	133
Southern Company Gas | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	70	56
Southern Company Gas | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	26	12
Deferred tax assets —
Deferred income tax assets	100	111
Southern Company Gas | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	45	45
Southern Company Gas | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Other
Deferred tax liabilities —
Deferred income tax liabilities	138	198
Southern Company Gas | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	86	97
Southern Company Gas | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | AROs
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	10	8
Southern Company Gas | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other
Deferred tax assets —
Deferred income tax assets	$ 166	$ 190

INCOME TAXES - Federal ITC_PTC

INCOME TAXES - Federal ITC/PTC Carryforwards (Details) - ITC and PTC carryforward $ in Millions	Dec. 31, 2020USD ($)
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 1,428
Alabama Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	12
Georgia Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	114
Southern Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 1,110

INCOME TAXES - NOL Carryforward

INCOME TAXES - NOL Carryforwards (Details) $ in Millions	Dec. 31, 2020USD ($)
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	$ 299
Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	200
Southern Power
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	53
Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	39
Southern Power | Florida
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	11
Southern Power | South Carolina
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	2
Southern Power | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	1
Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	21
Other Subsidiaries | New York
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	11
Other Subsidiaries | New York City
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit of NOL Carryforwards	$ 14

INCOME TAXES - Changes in Unrec

INCOME TAXES - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 0	$ 18
Tax position changes – decrease from prior periods		(18)
Tax positions changes – increase from prior periods	44
Balance at end of year	$ 44	$ 0

RETIREMENT BENEFITS - Narrative

RETIREMENT BENEFITS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Plan asset amortization period	5 years
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 58,000,000	$ 1,208,000,000
Expected future employer contributions, next fiscal year	0
Actuarial losses	$ (1,679,000,000)	$ (2,346,000,000)
Change in discount rate	6000.00%	1.08%
Pension plans | Qualified pension plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 0
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	72,000,000	$ 83,000,000
Expected future employer contributions, next fiscal year	0
Actuarial losses	$ (7,000,000)	$ (223,000,000)

RETIREMENT BENEFITS - Defined B

RETIREMENT BENEFITS - Defined Benefit Plan Related to Gulf Power (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 16,646	$ 14,788	$ 12,763
Defined Benefit Plan, Plan Assets, Amount	15,367	14,057	11,611
Accrued liability	(1,279)	(731)
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	1,948	1,985	1,865
Defined Benefit Plan, Plan Assets, Amount	1,158	1,061	$ 928
Accrued liability	$ (790)	$ (924)

RETIREMENT BENEFITS - Actuarial

RETIREMENT BENEFITS - Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.41%	4.49%	3.80%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	4.34%	4.34%
Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.99%	4.12%	3.45%
Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.66%	4.70%	3.98%
Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.81%	3.41%
Annual salary increase	4.80%	4.73%
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.24%	4.37%	3.68%
Expected long-term return on plan assets	7.25%	6.86%	6.83%
Annual salary increase, net periodic costs	4.73%	4.34%	4.34%
Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.80%	3.98%	3.29%
Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.57%	4.63%	3.91%
Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.56%	3.24%
Annual salary increase	4.80%	4.73%
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.44%	4.51%	3.81%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Alabama Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.01%	4.14%	3.45%
Alabama Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.69%	4.73%	4.00%
Alabama Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.85%	3.44%
Annual salary increase	4.80%	4.73%
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.28%	4.40%	3.71%
Expected long-term return on plan assets	7.36%	6.76%	6.83%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Alabama Power | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.84%	4.01%	3.31%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.61%	4.67%	3.93%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.63%	3.28%
Annual salary increase	4.80%	4.73%
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.40%	4.48%	3.79%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Georgia Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.96%	4.10%	3.42%
Georgia Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.67%	4.72%	3.99%
Georgia Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.79%	3.40%
Annual salary increase	4.80%	4.73%
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.22%	4.36%	3.68%
Expected long-term return on plan assets	7.05%	6.85%	6.80%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Georgia Power | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.79%	3.97%	3.29%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.57%	4.64%	3.91%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.52%	3.22%
Annual salary increase	4.80%	4.73%
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.41%	4.49%	3.80%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Mississippi Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.99%	4.12%	3.46%
Mississippi Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.67%	4.73%	3.99%
Mississippi Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.80%	3.41%
Annual salary increase	4.80%	4.73%
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.22%	4.35%	3.68%
Expected long-term return on plan assets	7.07%	6.79%	6.99%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Mississippi Power | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.76%	3.95%	3.29%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.57%	4.64%	3.91%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.53%	3.22%
Annual salary increase	4.80%	4.73%
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.52%	4.65%	3.94%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Southern Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.18%	4.35%	3.69%
Southern Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.70%	4.75%	4.01%
Southern Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.99%	3.52%
Annual salary increase	4.80%	4.73%
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.39%	4.50%	3.81%
Expected long-term return on plan assets	0.00%	0.00%	0.00%
Annual salary increase, net periodic costs	4.73%	4.46%	4.46%
Southern Power | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.97%	4.14%	3.47%
Southern Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.57%	4.65%	3.93%
Southern Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.78%	3.39%
Annual salary increase	4.80%	4.73%
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.39%	4.47%	3.74%
Expected long-term return on plan assets	8.25%	7.75%	7.95%
Annual salary increase, net periodic costs	4.73%	3.07%	3.07%
Southern Company Gas | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.99%	4.11%	3.41%
Southern Company Gas | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.53%	4.57%	3.84%
Southern Company Gas | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.75%	3.39%
Annual salary increase	4.80%	4.73%
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.19%	4.32%	3.62%
Expected long-term return on plan assets	6.69%	6.49%	5.89%
Annual salary increase, net periodic costs	4.73%	3.07%	3.07%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.71%	3.91%	3.21%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.52%	4.56%	3.82%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	2.46%	3.19%
Annual salary increase	4.80%	4.73%

RETIREMENT BENEFITS - Schedule

RETIREMENT BENEFITS - Schedule of Health Care Cost Trend Rates (Details) - Other postretirement benefit plans	Dec. 31, 2020
Pre-65
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate	6.00%
Ultimate Cost Trend Rate	4.50%
Post-65 medical
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate	5.00%
Ultimate Cost Trend Rate	4.50%
Post-65 prescription
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate	6.25%
Ultimate Cost Trend Rate	4.50%

RETIREMENT BENEFITS - Accumulat

RETIREMENT BENEFITS - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 14,922	$ 13,391
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	3,414	3,053
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	4,657	4,222
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	683	615
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	175	151
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 1,072	$ 963

RETIREMENT BENEFITS - Changes i

RETIREMENT BENEFITS - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	$ 14,788,000,000	$ 12,763,000,000
Dispositions		(509,000,000)
Service cost	376,000,000	292,000,000	$ 359,000,000
Interest cost	432,000,000	492,000,000	464,000,000
Benefits paid	(629,000,000)	(596,000,000)
Actuarial (gain) loss	1,679,000,000	2,346,000,000
Balance at end of year	16,646,000,000	14,788,000,000	12,763,000,000
Change in plan assets
Fair value of plan assets at beginning of year	14,057,000,000	11,611,000,000
Dispositions		(509,000,000)
Actual return (loss) on plan assets	1,881,000,000	2,343,000,000
Employer contributions	58,000,000	1,208,000,000
Benefits paid	(629,000,000)	(596,000,000)
Fair value of plan assets at end of year	15,367,000,000	14,057,000,000	11,611,000,000
Accrued liability	(1,279,000,000)	(731,000,000)
Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	1,985,000,000	1,865,000,000
Dispositions		(69,000,000)
Service cost	22,000,000	18,000,000	24,000,000
Interest cost	54,000,000	69,000,000	75,000,000
Benefits paid	(126,000,000)	(126,000,000)
Actuarial (gain) loss	7,000,000	223,000,000
Retiree drug subsidy	6,000,000	5,000,000
Balance at end of year	1,948,000,000	1,985,000,000	1,865,000,000
Change in plan assets
Fair value of plan assets at beginning of year	1,061,000,000	928,000,000
Dispositions		(18,000,000)
Actual return (loss) on plan assets	145,000,000	189,000,000
Employer contributions	72,000,000	83,000,000
Benefits paid	(120,000,000)	(121,000,000)
Fair value of plan assets at end of year	1,158,000,000	1,061,000,000	928,000,000
Accrued liability	(790,000,000)	(924,000,000)
Alabama Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	3,404,000,000	2,816,000,000
Dispositions		0
Service cost	89,000,000	69,000,000	78,000,000
Interest cost	100,000,000	114,000,000	101,000,000
Benefits paid	(132,000,000)	(125,000,000)
Actuarial (gain) loss	393,000,000	530,000,000
Balance at end of year	3,854,000,000	3,404,000,000	2,816,000,000
Change in plan assets
Fair value of plan assets at beginning of year	3,357,000,000	2,575,000,000
Dispositions		0
Actual return (loss) on plan assets	450,000,000	524,000,000
Employer contributions	9,000,000	383,000,000
Benefits paid	(132,000,000)	(125,000,000)
Fair value of plan assets at end of year	3,684,000,000	3,357,000,000	2,575,000,000
Accrued liability	(170,000,000)	(47,000,000)
Alabama Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	462,000,000	403,000,000
Dispositions		0
Service cost	6,000,000	5,000,000	6,000,000
Interest cost	13,000,000	16,000,000	17,000,000
Benefits paid	(29,000,000)	(27,000,000)
Actuarial (gain) loss	9,000,000	63,000,000
Retiree drug subsidy	2,000,000	2,000,000
Balance at end of year	463,000,000	462,000,000	403,000,000
Change in plan assets
Fair value of plan assets at beginning of year	413,000,000	360,000,000
Dispositions		0
Actual return (loss) on plan assets	60,000,000	76,000,000
Employer contributions	12,000,000	2,000,000
Benefits paid	(27,000,000)	(25,000,000)
Fair value of plan assets at end of year	458,000,000	413,000,000	360,000,000
Accrued liability	(5,000,000)	(49,000,000)
Georgia Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	4,610,000,000	3,905,000,000
Dispositions		0
Service cost	96,000,000	74,000,000	87,000,000
Interest cost	133,000,000	156,000,000	139,000,000
Benefits paid	(202,000,000)	(194,000,000)
Actuarial (gain) loss	490,000,000	669,000,000
Balance at end of year	5,127,000,000	4,610,000,000	3,905,000,000
Change in plan assets
Fair value of plan assets at beginning of year	4,442,000,000	3,663,000,000
Dispositions		0
Actual return (loss) on plan assets	594,000,000	730,000,000
Employer contributions	10,000,000	243,000,000
Benefits paid	(202,000,000)	(194,000,000)
Fair value of plan assets at end of year	4,844,000,000	4,442,000,000	3,663,000,000
Accrued liability	(283,000,000)	(168,000,000)
Georgia Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	742,000,000	675,000,000
Dispositions		0
Service cost	6,000,000	5,000,000	6,000,000
Interest cost	20,000,000	26,000,000	28,000,000
Benefits paid	(46,000,000)	(47,000,000)
Actuarial (gain) loss	(26,000,000)	80,000,000
Retiree drug subsidy	3,000,000	3,000,000
Balance at end of year	699,000,000	742,000,000	675,000,000
Change in plan assets
Fair value of plan assets at beginning of year	403,000,000	344,000,000
Dispositions		0
Actual return (loss) on plan assets	50,000,000	68,000,000
Employer contributions	17,000,000	35,000,000
Benefits paid	(43,000,000)	(44,000,000)
Fair value of plan assets at end of year	427,000,000	403,000,000	344,000,000
Accrued liability	(272,000,000)	(339,000,000)
Mississippi Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	671,000,000	557,000,000
Dispositions		0
Service cost	15,000,000	12,000,000	17,000,000
Interest cost	20,000,000	22,000,000	20,000,000
Benefits paid	(27,000,000)	(26,000,000)
Actuarial (gain) loss	75,000,000	106,000,000
Balance at end of year	754,000,000	671,000,000	557,000,000
Change in plan assets
Fair value of plan assets at beginning of year	641,000,000	505,000,000
Dispositions		0
Actual return (loss) on plan assets	85,000,000	103,000,000
Employer contributions	2,000,000	59,000,000
Benefits paid	(27,000,000)	(26,000,000)
Fair value of plan assets at end of year	701,000,000	641,000,000	505,000,000
Accrued liability	(53,000,000)	(30,000,000)
Mississippi Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	87,000,000	81,000,000
Dispositions		0
Service cost	1,000,000	1,000,000	1,000,000
Interest cost	2,000,000	3,000,000	3,000,000
Benefits paid	(6,000,000)	(6,000,000)
Actuarial (gain) loss	(3,000,000)	8,000,000
Retiree drug subsidy	0	0
Balance at end of year	81,000,000	87,000,000	81,000,000
Change in plan assets
Fair value of plan assets at beginning of year	26,000,000	23,000,000
Dispositions		0
Actual return (loss) on plan assets	3,000,000	4,000,000
Employer contributions	4,000,000	5,000,000
Benefits paid	(6,000,000)	(6,000,000)
Fair value of plan assets at end of year	27,000,000	26,000,000	23,000,000
Accrued liability	(54,000,000)	(61,000,000)
Southern Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	185,000,000	123,000,000
Dispositions		0
Service cost	8,000,000	7,000,000	9,000,000
Interest cost	6,000,000	5,000,000	5,000,000
Benefits paid	(6,000,000)	(4,000,000)
Actuarial (gain) loss	24,000,000	54,000,000
Balance at end of year	217,000,000	185,000,000	123,000,000
Change in plan assets
Fair value of plan assets at beginning of year	169,000,000	123,000,000
Dispositions		0
Actual return (loss) on plan assets	22,000,000	43,000,000
Employer contributions	1,000,000	7,000,000
Benefits paid	(6,000,000)	(4,000,000)
Fair value of plan assets at end of year	186,000,000	169,000,000	123,000,000
Accrued liability	(31,000,000)	(16,000,000)
Southern Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	11,000,000	9,000,000
Dispositions		0
Service cost	1,000,000	1,000,000	1,000,000
Interest cost	0	0	0
Benefits paid	0	(1,000,000)
Actuarial (gain) loss	0	2,000,000
Retiree drug subsidy	0	0
Balance at end of year	12,000,000	11,000,000	9,000,000
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Dispositions		0
Actual return (loss) on plan assets	0	0
Employer contributions	0	1,000,000
Benefits paid	0	(1,000,000)
Fair value of plan assets at end of year	0	0	0
Accrued liability	(12,000,000)	(11,000,000)
Southern Company Gas | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	1,067,000,000	907,000,000
Dispositions		0
Service cost	33,000,000	25,000,000	34,000,000
Interest cost	31,000,000	36,000,000	39,000,000
Benefits paid	(69,000,000)	(64,000,000)
Actuarial (gain) loss	127,000,000	163,000,000
Balance at end of year	1,189,000,000	1,067,000,000	907,000,000
Change in plan assets
Fair value of plan assets at beginning of year	1,050,000,000	798,000,000
Dispositions		0
Actual return (loss) on plan assets	139,000,000	172,000,000
Employer contributions	3,000,000	144,000,000
Benefits paid	(69,000,000)	(64,000,000)
Fair value of plan assets at end of year	1,123,000,000	1,050,000,000	798,000,000
Accrued liability	(66,000,000)	(17,000,000)
Southern Company Gas | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	250,000,000	244,000,000
Dispositions		0
Service cost	2,000,000	1,000,000	2,000,000
Interest cost	7,000,000	9,000,000	10,000,000
Benefits paid	(17,000,000)	(17,000,000)
Actuarial (gain) loss	6,000,000	13,000,000
Retiree drug subsidy	0	0
Balance at end of year	248,000,000	250,000,000	244,000,000
Change in plan assets
Fair value of plan assets at beginning of year	115,000,000	98,000,000
Dispositions		0
Actual return (loss) on plan assets	18,000,000	21,000,000
Employer contributions	12,000,000	13,000,000
Benefits paid	(17,000,000)	(17,000,000)
Fair value of plan assets at end of year	128,000,000	115,000,000	$ 98,000,000
Accrued liability	(120,000,000)	$ (135,000,000)
Qualified pension plan | Pension plans
Change in benefit obligation
Balance at end of year	15,818,000,000
Change in plan assets
Employer contributions	0
Qualified pension plan | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year	3,719,000,000
Qualified pension plan | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year	4,977,000,000
Qualified pension plan | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year	718,000,000
Qualified pension plan | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year	187,000,000
Qualified pension plan | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year	1,114,000,000
Non-qualified pension plan | Pension plans
Change in benefit obligation
Balance at end of year	828,000,000
Non-qualified pension plan | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year	135,000,000
Non-qualified pension plan | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year	150,000,000
Non-qualified pension plan | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year	36,000,000
Non-qualified pension plan | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year	30,000,000
Non-qualified pension plan | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year	$ 75,000,000

RETIREMENT BENEFITS - Amounts R

RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	$ 7,198	$ 6,805
Other deferred charges and assets	1,288	1,071
Other current liabilities	(968)	(830)
Employee benefit obligations	(2,213)	(1,814)
Other regulatory liabilities, deferred	(251)	(256)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		2
Other regulatory assets, deferred	4,655	4,072
Other deferred charges and assets	0	0
Other current liabilities	(52)	(54)
Employee benefit obligations	(1,227)	(679)
Other regulatory liabilities, deferred	(34)	(79)
AOCI	245	185
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	137	183
Other current liabilities	(5)	(5)
Employee benefit obligations	(785)	(919)
Other regulatory liabilities, deferred	(86)	(62)
AOCI	8	2
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	2,162	2,016
Other deferred charges and assets	273	269
Other current liabilities	(107)	(105)
Employee benefit obligations	(214)	(206)
Other regulatory liabilities, deferred	(124)	(146)
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		71
Other regulatory assets, deferred	1,286	1,130
Other deferred charges and assets	0	0
Other current liabilities	(9)	(8)
Employee benefit obligations	(161)	(110)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	0	3
Other current liabilities	0	0
Employee benefit obligations	(5)	(49)
Other regulatory liabilities, deferred	(21)	(2)
AOCI	0	0
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	2,692	2,716
Other deferred charges and assets	479	500
Other current liabilities	(254)	(187)
Employee benefit obligations	(586)	(540)
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		0
Other regulatory assets, deferred	1,598	1,416
Other deferred charges and assets	0	0
Other current liabilities	(10)	(11)
Employee benefit obligations	(273)	(157)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	47	96
Other current liabilities	0	0
Employee benefit obligations	(272)	(339)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	388	360
Other deferred charges and assets	55	34
Other current liabilities	(40)	(64)
Employee benefit obligations	(113)	(99)
Other regulatory liabilities, deferred	(15)	(76)
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		2
Other regulatory assets, deferred	235	204
Other deferred charges and assets	0	0
Other current liabilities	(2)	(2)
Employee benefit obligations	(51)	(30)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	5	10
Other current liabilities	0	0
Employee benefit obligations	(54)	(61)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Other deferred charges and assets	293	216
Other current liabilities	(132)	(132)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		10
Other regulatory assets, deferred	0	0
Other deferred charges and assets	0	0
Other current liabilities	(2)	(2)
Employee benefit obligations	(29)	(24)
Other regulatory liabilities, deferred	0	0
AOCI	60	46
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	0	0
Other current liabilities	0	0
Employee benefit obligations	(12)	(11)
Other regulatory liabilities, deferred	0	0
AOCI	3	2
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	615	618
Other deferred charges and assets	235	207
Other current liabilities	(150)	(149)
Employee benefit obligations	(283)	(265)
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs		0
Other regulatory assets, deferred	205	172
Other deferred charges and assets	70	82
Other current liabilities	(2)	(2)
Employee benefit obligations	(134)	(97)
Other regulatory liabilities, deferred	0	0
AOCI	1	(14)
Regulatory asset	224	252
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	(23)	(11)
Other current liabilities	0	0
Employee benefit obligations	(120)	(135)
Other regulatory liabilities, deferred	0	0
AOCI	0	(4)
Regulatory asset	$ 47	$ 50

RETIREMENT BENEFITS - Component

RETIREMENT BENEFITS - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 31,759	$ 29,039	$ 25,528
Total other comprehensive income (loss)	(75)	(118)	26
Ending balance	32,234	31,759	29,039
Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(142)
Total other comprehensive income (loss)	(45)
Ending balance	(187)	(142)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(3)	(3)
Net (gain) loss	248	188
Total AOCI	245	185
Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	11	13
Net (gain) loss	4,610	3,980
Regulatory amortization	0	0
Regulatory asset	4,621	3,993
Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	185	97
Reclassification adjustments	(14)
Total other comprehensive income (loss)	60
Ending balance	245	185	97
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3,993	3,458
Reclassification adjustments	(256)	(122)
Total other comprehensive income (loss)	628	535
Ending balance	4,621	3,993	3,458
Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(74)	(88)
Reclassification adjustments	(14)
Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(884)	(801)
Reclassification adjustments	(255)	(119)
Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		144
Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0
Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(3)
Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	7	1
Total AOCI	8	2
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	4	1
Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	12	11
Net (gain) loss	39	110
Regulatory amortization	0	0
Regulatory asset	51	121
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	2	(4)
Total other comprehensive income (loss)	6	6
Ending balance	8	2	(4)
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	121	22
Reclassification adjustments	(5)	(1)
Total other comprehensive income (loss)	(70)	99
Ending balance	51	121	22
Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	2	5
Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	65	(90)
Reclassification adjustments	(6)	2
Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(5)
Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(5)
Reclassification adjustments	1	(3)
Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	8,955	7,477	6,829
Total other comprehensive income (loss)	4	4	4
Ending balance	9,810	8,955	7,477
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	5	6
Net (gain) loss	1,281	1,124
Regulatory amortization	0	0
Regulatory asset	1,286	1,130
Alabama Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,130	955
Reclassification adjustments	(72)	(38)
Total other comprehensive income (loss)	156	175
Ending balance	1,286	1,130	955
Alabama Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(228)	(213)
Reclassification adjustments	(71)	(37)
Alabama Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Alabama Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(1)
Alabama Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	3	3
Net (gain) loss	(24)	(2)
Regulatory amortization	0	0
Regulatory asset		1
Regulatory liabilities	(21)
Alabama Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1	(9)
Reclassification adjustments	0	(4)
Total other comprehensive income (loss)	(22)	10
Ending balance	(21)	1	(9)
Alabama Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	22	(14)
Reclassification adjustments	0	0
Alabama Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Alabama Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	0	(4)
Alabama Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	15,065	14,323	11,931
Total other comprehensive income (loss)	4	(42)	3
Ending balance	16,501	15,065	14,323
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	9	10
Net (gain) loss	1,589	1,406
Regulatory amortization	0	0
Regulatory asset	1,598	1,416
Georgia Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,416	1,230
Reclassification adjustments	(87)	(45)
Total other comprehensive income (loss)	182	186
Ending balance	1,598	1,416	1,230
Georgia Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(269)	(231)
Reclassification adjustments	(86)	(44)
Georgia Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Georgia Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(1)
Georgia Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	5	4
Net (gain) loss	42	92
Regulatory amortization	0	0
Regulatory asset	47	96
Georgia Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	96	60
Reclassification adjustments	(2)	(1)
Total other comprehensive income (loss)	(49)	36
Ending balance	47	96	60
Georgia Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	47	(37)
Reclassification adjustments	(3)	(1)
Georgia Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Georgia Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	1	0
Georgia Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,652	1,609	1,358
Total other comprehensive income (loss)	1	1	0
Ending balance	1,742	1,652	1,609
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	2	2
Net (gain) loss	233	201
Regulatory amortization	0	0
Regulatory asset	235	203
Mississippi Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	203	167
Reclassification adjustments	(13)	(6)
Total other comprehensive income (loss)	32	36
Ending balance	235	203	167
Mississippi Power | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(45)	(42)
Reclassification adjustments	(13)	(6)
Mississippi Power | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Mississippi Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	5	10
Regulatory amortization	0	0
Regulatory asset	5	10
Mississippi Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	10	4
Reclassification adjustments	0	0
Total other comprehensive income (loss)	(5)	6
Ending balance	5	10	4
Mississippi Power | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	5	(6)
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Mississippi Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	6,622	7,284	6,498
Total other comprehensive income (loss)	(42)	(42)	14
Ending balance	6,631	6,622	7,284
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(37)
Total other comprehensive income (loss)	(10)
Ending balance	(47)	(37)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	60	46
Total AOCI	60	46
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	46	26
Reclassification adjustments	(2)
Total other comprehensive income (loss)	14
Ending balance	60	46	26
Southern Power | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(16)	(20)
Reclassification adjustments	(2)
Southern Power | Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	3	2
Total AOCI	3	2
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	2	1
Total other comprehensive income (loss)	1	1
Ending balance	3	2	1
Southern Power | Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	1	1
Southern Company Gas
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	9,506	8,570	9,022
Total other comprehensive income (loss)	(29)	(19)	2
Ending balance	9,767	9,506	8,570
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	13
Total other comprehensive income (loss)	(15)
Ending balance	(2)	13
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(4)	(6)
Net (gain) loss	5	(8)
Total AOCI	1	(14)
Regulatory asset	224	252
Southern Company Gas | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(13)	(15)
Net (gain) loss	135	113
Regulatory amortization	83	74
Regulatory asset	205	172
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(14)	(44)
Reclassification adjustments	0
Total other comprehensive income (loss)	15
Ending balance	1	(14)	(44)
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	172	160
Reclassification adjustments	(12)	(18)
Total other comprehensive income (loss)	33	12
Ending balance	205	172	160
Southern Company Gas | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(15)	(30)
Reclassification adjustments	(1)
Southern Company Gas | Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(45)	(30)
Reclassification adjustments	(8)	0
Southern Company Gas | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Company Gas | Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	1
Southern Company Gas | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	2	2
Southern Company Gas | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(6)	(20)
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	(1)	(5)
Total AOCI	0	(4)
Regulatory asset	47	50
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	4	0
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	(49)	(43)
Regulatory amortization	25	31
Regulatory liabilities	(23)	(11)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	(4)
Total other comprehensive income (loss)	4	0
Ending balance	0	(4)	(4)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(11)	(4)
Reclassification adjustments	(7)	(6)
Total other comprehensive income (loss)	(12)	(7)
Ending balance	(23)	(11)	$ (4)
Southern Company Gas | Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	0	0
Southern Company Gas | Other postretirement benefit plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	5	1
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Company Gas | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	$ (7)	$ (6)

RETIREMENT BENEFITS - Compone_2

RETIREMENT BENEFITS - Components of Net Periodic Benefit Cost and Estimated Future Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension plans
Components of net periodic
Service cost	$ 376	$ 292	$ 359
Interest cost	432	492	464
Expected return on plan assets	(1,100)	(885)	(943)
Recognized net (gain) loss	269	120	213
Net amortization	1	2	4
Prior service cost	0	0	0
Total change	(22)	21	97
Benefit payments:
2021	651
2022	678
2023	702
2024	725
2025	748
2026 to 2030	4,024
Other postretirement benefit plans
Components of net periodic
Service cost	22	18	24
Interest cost	54	69	75
Expected return on plan assets	(72)	(65)	(69)
Prior service cost	1	0	21
Total change	5	22	51
Benefit payments:
2021	115
2022	113
2023	111
2024	110
2025	113
2026 to 2030	550
Alabama Power | Pension plans
Components of net periodic
Service cost	89	69	78
Interest cost	100	114	101
Expected return on plan assets	(264)	(206)	(207)
Recognized net (gain) loss	71	37	54
Net amortization	1	0	1
Prior service cost	0	0	0
Total change	(3)	14	27
Benefit payments:
2021	141
2022	147
2023	154
2024	158
2025	165
2026 to 2030	895
Alabama Power | Other postretirement benefit plans
Components of net periodic
Service cost	6	5	6
Interest cost	13	16	17
Expected return on plan assets	(29)	(26)	(26)
Prior service cost	0	4	5
Total change	(10)	(1)	2
Benefit payments:
2021	25
2022	25
2023	25
2024	24
2025	25
2026 to 2030	127
Georgia Power | Pension plans
Components of net periodic
Service cost	96	74	87
Interest cost	133	156	139
Expected return on plan assets	(347)	(292)	(296)
Recognized net (gain) loss	86	44	69
Net amortization	1	1	2
Prior service cost	0	0	0
Total change	(31)	(17)	1
Benefit payments:
2021	208
2022	215
2023	222
2024	229
2025	235
2026 to 2030	1,244
Georgia Power | Other postretirement benefit plans
Components of net periodic
Service cost	6	5	6
Interest cost	20	26	28
Expected return on plan assets	(26)	(25)	(25)
Prior service cost	2	1	10
Total change	2	7	19
Benefit payments:
2021	42
2022	41
2023	40
2024	38
2025	40
2026 to 2030	199
Mississippi Power | Pension plans
Components of net periodic
Service cost	15	12	17
Interest cost	20	22	20
Expected return on plan assets	(51)	(40)	(41)
Recognized net (gain) loss	13	6	10
Net amortization	0	0	0
Prior service cost	0	0	0
Total change	(3)	0	6
Benefit payments:
2021	29
2022	30
2023	31
2024	32
2025	33
2026 to 2030	181
Mississippi Power | Other postretirement benefit plans
Components of net periodic
Service cost	1	1	1
Interest cost	2	3	3
Expected return on plan assets	(1)	(2)	(2)
Prior service cost	0	0	1
Total change	2	2	3
Benefit payments:
2021	6
2022	5
2023	5
2024	4
2025	5
2026 to 2030	23
Southern Power | Pension plans
Components of net periodic
Service cost	8	7	9
Interest cost	6	5	5
Expected return on plan assets	(13)	(10)	(10)
Recognized net (gain) loss	2	1	1
Net amortization	0	0	0
Prior service cost	0	0	0
Total change	3	3	5
Benefit payments:
2021	6
2022	6
2023	6
2024	6
2025	7
2026 to 2030	38
Southern Power | Other postretirement benefit plans
Components of net periodic
Service cost	1	1	1
Interest cost	0	0	0
Expected return on plan assets	0	0	0
Prior service cost	0	0	0
Total change	1	1	1
Benefit payments:
2021	0
2022	0
2023	0
2024	1
2025	1
2026 to 2030	3
Southern Company Gas | Pension plans
Components of net periodic
Service cost	33	25	34
Interest cost	31	36	39
Expected return on plan assets	(75)	(60)	(75)
Recognized net (gain) loss	6	2	12
Net amortization	15	14	15
Prior service cost	(3)	(3)	(2)
Total change	7	14	23
Benefit payments:
2021	66
2022	66
2023	66
2024	65
2025	65
2026 to 2030	330
Southern Company Gas | Other postretirement benefit plans
Components of net periodic
Service cost	2	1	2
Interest cost	7	9	10
Expected return on plan assets	(10)	(7)	(7)
Prior service cost	6	6	6
Total change	5	$ 9	$ 11
Benefit payments:
2021	18
2022	18
2023	18
2024	17
2025	17
2026 to 2030	$ 76

RETIREMENT BENEFITS - Fair Valu

RETIREMENT BENEFITS - Fair Values of Pension Plan and Other Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets Fair Value
Target plan asset allocations	100.00%
Actual plan asset allocations	100.00%
Pension plans
Assets Fair Value
Plan assets	$ 15,430	$ 14,119
Target plan asset allocations		100.00%
Actual plan asset allocations		100.00%
Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 4,099	$ 3,118
Pension plans | International equity
Assets Fair Value
Plan assets	$ 4,157	$ 3,646
Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 951	$ 965
Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	9	9
Pension plans | Corporate bonds
Assets Fair Value
Plan assets	1,673	1,315
Pension plans | Pooled funds
Assets Fair Value
Plan assets	772	684
Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	361	1,317
Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 2,138	$ 1,957
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Pension plans | Special situations
Assets Fair Value
Plan assets	$ 166	$ 155
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Pension plans | Private equity
Assets Fair Value
Plan assets	$ 1,104	$ 953
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Other postretirement benefit plans
Assets Fair Value
Plan assets	$ 1,159	$ 1,060
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Other postretirement benefit plans | Equity
Assets Fair Value
Target plan asset allocations	63.00%	63.00%
Actual plan asset allocations	66.00%	64.00%
Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	$ 211	$ 176
Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	$ 173	$ 149
Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations	28.00%	28.00%
Actual plan asset allocations	27.00%	30.00%
Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 32	$ 31
Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	44	35
Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	86	82
Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	15	42
Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	508	463
Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	$ 57	$ 53
Target plan asset allocations	5.00%	5.00%
Actual plan asset allocations	5.00%	4.00%
Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	$ 4	$ 4
Target plan asset allocations	1.00%	1.00%
Actual plan asset allocations	0.00%	0.00%
Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 29	$ 25
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	2.00%	2.00%
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 6,410	$ 6,436
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	2,852	2,220
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	2,660	2,360
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	356	1,317
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	542	539
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Plan assets	214	221
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	113	95
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	71	69
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	15	42
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	15	15
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	6,154	5,157
Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	1,247	898
Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	1,497	1,286
Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	951	965
Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	9	9
Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	1,673	1,315
Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	772	684
Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	5	0
Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Plan assets	870	772
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	98	81
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	102	80
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	32	31
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	44	35
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	86	82
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	508	463
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	2,866	2,526
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	1,596	1,418
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	166	155
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	1,104	953
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Plan assets	75	67
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	42	38
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	4	4
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	29	25
Alabama Power | Pension plans
Assets Fair Value
Plan assets	$ 3,699	$ 3,372
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Alabama Power | Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Alabama Power | Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 984	$ 744
Alabama Power | Pension plans | International equity
Assets Fair Value
Plan assets	$ 997	$ 871
Alabama Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Alabama Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 228	$ 230
Alabama Power | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	2	2
Alabama Power | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	401	314
Alabama Power | Pension plans | Pooled funds
Assets Fair Value
Plan assets	185	163
Alabama Power | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	86	315
Alabama Power | Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 512	$ 468
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Alabama Power | Pension plans | Special situations
Assets Fair Value
Plan assets	$ 40	$ 37
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Alabama Power | Pension plans | Private equity
Assets Fair Value
Plan assets	$ 264	$ 228
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Alabama Power | Other postretirement benefit plans
Assets Fair Value
Plan assets	$ 459	$ 412
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Alabama Power | Other postretirement benefit plans | Equity
Assets Fair Value
Target plan asset allocations	68.00%	68.00%
Actual plan asset allocations	69.00%	67.00%
Alabama Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	$ 37	$ 34
Alabama Power | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	$ 36	$ 32
Alabama Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations	24.00%	24.00%
Actual plan asset allocations	25.00%	27.00%
Alabama Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 11	$ 10
Alabama Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	14	11
Alabama Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	7	6
Alabama Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	5	12
Alabama Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	321	281
Alabama Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	$ 18	$ 17
Target plan asset allocations	4.00%	4.00%
Actual plan asset allocations	4.00%	4.00%
Alabama Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	$ 1	$ 1
Target plan asset allocations	1.00%	1.00%
Actual plan asset allocations	0.00%	0.00%
Alabama Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 9	$ 8
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	2.00%	2.00%
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 1,538	$ 1,538
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	685	530
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	638	564
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	85	315
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	130	129
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Plan assets	59	64
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	26	26
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	23	21
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	5	12
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	5	5
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	1,475	1,230
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	299	214
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	359	307
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	228	230
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	2	2
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	401	314
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	185	163
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Plan assets	377	327
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	11	8
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	13	11
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	11	10
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	14	11
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	7	6
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	321	281
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	686	604
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	382	339
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	40	37
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	264	228
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Plan assets	23	21
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	13	12
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	1	1
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	9	8
Georgia Power | Pension plans
Assets Fair Value
Plan assets	$ 4,864	$ 4,461
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Georgia Power | Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Georgia Power | Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 1,292	$ 985
Georgia Power | Pension plans | International equity
Assets Fair Value
Plan assets	$ 1,311	$ 1,153
Georgia Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Georgia Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 300	$ 305
Georgia Power | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	3	3
Georgia Power | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	527	415
Georgia Power | Pension plans | Pooled funds
Assets Fair Value
Plan assets	243	216
Georgia Power | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	113	416
Georgia Power | Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 674	$ 618
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Georgia Power | Pension plans | Special situations
Assets Fair Value
Plan assets	$ 53	$ 49
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Georgia Power | Pension plans | Private equity
Assets Fair Value
Plan assets	$ 348	$ 301
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Georgia Power | Other postretirement benefit plans
Assets Fair Value
Plan assets	$ 427	$ 402
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Georgia Power | Other postretirement benefit plans | Equity
Assets Fair Value
Target plan asset allocations	60.00%	60.00%
Actual plan asset allocations	64.00%	61.00%
Georgia Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	$ 68	$ 55
Georgia Power | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	$ 71	$ 61
Georgia Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations	33.00%	33.00%
Actual plan asset allocations	30.00%	34.00%
Georgia Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 8	$ 7
Georgia Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	13	11
Georgia Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	46	45
Georgia Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	5	16
Georgia Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	188	182
Georgia Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	$ 18	$ 16
Target plan asset allocations	4.00%	4.00%
Actual plan asset allocations	4.00%	3.00%
Georgia Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	$ 1	$ 1
Target plan asset allocations	1.00%	1.00%
Actual plan asset allocations	0.00%	0.00%
Georgia Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 9	$ 8
Target plan asset allocations	2.00%	2.00%
Actual plan asset allocations	2.00%	2.00%
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 2,021	$ 2,033
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	899	701
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	839	746
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	112	416
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	171	170
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Plan assets	89	94
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	58	48
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	21	25
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	5	16
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	5	5
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	1,939	1,630
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	393	284
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	472	407
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	300	305
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	3	3
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	527	415
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	243	216
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Plan assets	315	288
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	10	7
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	50	36
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	8	7
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	13	11
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	46	45
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	188	182
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	904	798
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	503	448
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	53	49
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	348	301
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Plan assets	23	20
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	13	11
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	1	1
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	9	8
Mississippi Power | Pension plans
Assets Fair Value
Plan assets	$ 704	$ 644
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Mississippi Power | Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Mississippi Power | Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 188	$ 142
Mississippi Power | Pension plans | International equity
Assets Fair Value
Plan assets	$ 190	$ 167
Mississippi Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Mississippi Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 43	$ 44
Mississippi Power | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	76	60
Mississippi Power | Pension plans | Pooled funds
Assets Fair Value
Plan assets	35	31
Mississippi Power | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	16	60
Mississippi Power | Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 98	$ 90
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Mississippi Power | Pension plans | Special situations
Assets Fair Value
Plan assets	$ 8	$ 7
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Mississippi Power | Pension plans | Private equity
Assets Fair Value
Plan assets	$ 50	$ 43
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Mississippi Power | Other postretirement benefit plans
Assets Fair Value
Plan assets	$ 26	$ 25
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Mississippi Power | Other postretirement benefit plans | Equity
Assets Fair Value
Target plan asset allocations	43.00%	43.00%
Actual plan asset allocations	46.00%	41.00%
Mississippi Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	$ 6	$ 4
Mississippi Power | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	$ 6	$ 6
Mississippi Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations	37.00%	37.00%
Actual plan asset allocations	36.00%	42.00%
Mississippi Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 5	$ 6
Mississippi Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	2	2
Mississippi Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	1	1
Mississippi Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	2
Mississippi Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	$ 3	$ 3
Target plan asset allocations	11.00%	11.00%
Actual plan asset allocations	11.00%	10.00%
Mississippi Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	$ 0	$ 0
Target plan asset allocations	2.00%	2.00%
Actual plan asset allocations	1.00%	1.00%
Mississippi Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 2	$ 1
Target plan asset allocations	7.00%	7.00%
Actual plan asset allocations	6.00%	6.00%
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 294	$ 294
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	131	101
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	122	108
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	16	60
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	25	25
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Plan assets	10	10
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	4	3
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	4	4
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	2
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	1	1
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	279	235
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	57	41
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	68	59
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	43	44
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	76	60
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	35	31
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Plan assets	12	12
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	2	1
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	2	2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	5	6
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	2	2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	1	1
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	131	115
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	73	65
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	8	7
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	50	43
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Plan assets	4	3
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	2	2
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	2	1
Southern Power | Pension plans
Assets Fair Value
Plan assets	$ 187	$ 170
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Power | Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Southern Power | Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 50	$ 38
Southern Power | Pension plans | International equity
Assets Fair Value
Plan assets	$ 51	$ 44
Southern Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Southern Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 12	$ 12
Southern Power | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	20	16
Southern Power | Pension plans | Pooled funds
Assets Fair Value
Plan assets	9	8
Southern Power | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	4	16
Southern Power | Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 26	$ 23
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Southern Power | Pension plans | Special situations
Assets Fair Value
Plan assets	$ 2	$ 2
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Southern Power | Pension plans | Private equity
Assets Fair Value
Plan assets	$ 13	$ 11
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 78	$ 77
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	35	27
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	32	28
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	4	16
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	7	6
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	75	63
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	15	11
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	19	16
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	12	12
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	20	16
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	9	8
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	34	30
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	19	17
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	2	2
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	13	11
Southern Company Gas | Pension plans
Assets Fair Value
Plan assets	$ 1,128	$ 1,054
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Company Gas | Pension plans | Equity
Assets Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	56.00%	51.00%
Southern Company Gas | Pension plans | Domestic equity
Assets Fair Value
Plan assets	$ 300	$ 233
Southern Company Gas | Pension plans | International equity
Assets Fair Value
Plan assets	$ 304	$ 272
Southern Company Gas | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	23.00%	29.00%
Southern Company Gas | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 69	$ 72
Southern Company Gas | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	122	98
Southern Company Gas | Pension plans | Pooled funds
Assets Fair Value
Plan assets	56	51
Southern Company Gas | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	26	98
Southern Company Gas | Pension plans | Real estate investments
Assets Fair Value
Plan assets	$ 157	$ 146
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	13.00%	12.00%
Southern Company Gas | Pension plans | Special situations
Assets Fair Value
Plan assets	$ 12	$ 12
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Southern Company Gas | Pension plans | Private equity
Assets Fair Value
Plan assets	$ 81	$ 71
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Southern Company Gas | Other postretirement benefit plans
Assets Fair Value
Plan assets	$ 125	$ 114
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Company Gas | Other postretirement benefit plans | Equity
Assets Fair Value
Target plan asset allocations	72.00%	72.00%
Actual plan asset allocations	76.00%	73.00%
Southern Company Gas | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	$ 68	$ 60
Southern Company Gas | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	$ 27	$ 23
Southern Company Gas | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations	26.00%	26.00%
Actual plan asset allocations	22.00%	25.00%
Southern Company Gas | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	$ 1	$ 1
Southern Company Gas | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	25	25
Southern Company Gas | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	2
Southern Company Gas | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	$ 1	$ 1
Target plan asset allocations	1.00%	1.00%
Actual plan asset allocations	1.00%	1.00%
Southern Company Gas | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 1	$ 1
Target plan asset allocations	1.00%	1.00%
Actual plan asset allocations	1.00%	1.00%
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Plan assets	$ 470	$ 480
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	209	166
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Plan assets	195	176
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	26	98
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	40	40
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Plan assets	5	6
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	2	2
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	2	2
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	1	2
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Plan assets	448	385
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	91	67
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Plan assets	109	96
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	69	72
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	122	98
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	56	51
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Plan assets	118	106
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	66	58
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	25	21
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	25	25
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Plan assets	210	189
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Plan assets	117	106
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Plan assets	12	12
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Plan assets	81	71
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Plan assets	2	2
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Plan assets	1	1
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Plan assets	$ 1	$ 1

RETIREMENT BENEFITS - 401K Plan

RETIREMENT BENEFITS - 401K Plan Matching Contributions (Details) - Employee Savings Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 120	$ 113	$ 119
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	26	25	24
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	29	27	26
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	5	4	5
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	2	2	3
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 16	$ 15	$ 18

STOCK COMPENSATION - Schedule o

STOCK COMPENSATION - Schedule of Employees Participating in Stock-Based Compensation Programs (Details)	Dec. 31, 2020employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	1,958
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	263
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	295
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	86
Southern Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	46
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	204

STOCK COMPENSATION - Performanc

STOCK COMPENSATION - Performance Shares Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Feb. 28, 2021$ / sharesshares	Feb. 29, 2020$ / sharesshares	Dec. 31, 2020USD ($)type$ / sharesshares	Dec. 31, 2019$ / sharesshares	Dec. 31, 2018$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares converted (in shares)		1,800,000
Shares converted (in dollars per share) | $ / shares		$ 68.59
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares converted (in shares)	2,500,000
Shares converted (in dollars per share) | $ / shares	$ 60.10
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of performance share units issued under performance share plan			3 years	3 years
Minimum percentage of transfer performance shares to common stock based on actual total shareholder return			0.00%
Maximum percentage of transfer performance shares to common stock based on actual total shareholder return			200.00%
Number of types of PSUs | type			3
Performance share units, unvested (in shares)			2,200,000	2,500,000
Equity instrument, granted (in shares)			1,200,000
Equity instruments, vested (in shares)			1,500,000
Unrecognized compensation cost | $			$ 32
Total unrecognized compensation cost related to award, weighted average period			19 months
EPS-based and ROE-based Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of performance share units issued under performance share plan			3 years
Equity instrument granted in period, weighted average grant date fair value (in dollars per share) | $ / shares			$ 68.42	$ 49.38	$ 43.49

STOCK COMPENSATION - Performa_2

STOCK COMPENSATION - Performance Shares, Assumptions Used (Details) - Performance Shares - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	15.40%	15.60%	14.90%
Expected term (in years)	3 years	3 years	3 years
Interest rate	1.40%	2.40%	2.40%
Weighted average grant-date fair value (in dollars per share)	$ 77.65	$ 62.71	$ 43.75

STOCK COMPENSATION - Performa_3

STOCK COMPENSATION - Performance Shares, Compensation Costs and Related Tax Benefit (Details) - Performance Shares - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	$ 84	$ 77	$ 91
Tax benefit of compensation cost recognized in income	22	20	24
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	13	14	11
Tax benefit of compensation cost recognized in income	$ 4	$ 4	$ 3

STOCK COMPENSATION - Restricted

STOCK COMPENSATION - Restricted Stock Units Narrative (Details) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 67.60	$ 50.44	$ 43.81
Award requisite service period	3 years
Total unrecognized compensation cost related to award, weighted average period	18 months
Restricted stock units, unvested (in shares)	1.2	1.3
Equity instrument, granted (in shares)	0.5
Vested or forfeited (in shares)	0.6
Total compensation cost for award recognized in income	$ 29	$ 28	$ 27
Total compensation cost for award recognized in income, tax benefit	8	$ 7	$ 7
Total unrecognized compensation cost related to award	$ 11
One-year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to award, weighted average period	1 year
Two-year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to award, weighted average period	2 years
Three-year vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to award, weighted average period	3 years

STOCK COMPENSATION - Stock Opti

STOCK COMPENSATION - Stock Options Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from issuance related to option exercise	$ 66	$ 482	$ 41
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term for options outstanding	2 years
Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years

STOCK COMPENSATION - Stock Op_2

STOCK COMPENSATION - Stock Option Activity (Details) shares in Millions	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares Subject to Option
Beginning balance (in shares) | shares	5.9
Exercised (in shares) | shares	1.6
Ending balance (in shares) | shares	4.3
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 42.52
Exercised (in dollars per share) | $ / shares	41.13
Ending balance (in dollars per share) | $ / shares	$ 43.04

STOCK COMPENSATION - Aggregate

STOCK COMPENSATION - Aggregate Intrinsic Value for Options Exercised (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 78
Aggregate intrinsic value for options exercisable	78
Intrinsic value of options exercised	38	$ 167	$ 9
Tax benefit of options exercised	9	35	2
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	8
Aggregate intrinsic value for options exercisable	8
Intrinsic value of options exercised	5	21	2
Tax benefit of options exercised	1	4	0
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	25
Aggregate intrinsic value for options exercisable	25
Intrinsic value of options exercised	9	30	2
Tax benefit of options exercised	2	$ 6	$ 0
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	6
Aggregate intrinsic value for options exercisable	$ 6

FAIR VALUE MEASUREMENTS - Asset

FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets:
Derivative asset	$ 281	$ 233
Liabilities:
Derivative liability	64	189
Weather derivative premium	6	4
Collateral already posted, aggregate fair value	28	99
Recurring
Assets:
Cash equivalents	584	1,395
Other investments	33	30
Total	3,759	4,189
Liabilities:
Contingent consideration	17	19
Total	637	770
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	575	1,393
Other investments	9	9
Total	1,974	2,650
Liabilities:
Contingent consideration	0	0
Total	389	442
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	9	2
Other investments	24	21
Total	1,677	1,461
Liabilities:
Contingent consideration	0	0
Total	227	302
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Other investments	0	0
Total	32	22
Liabilities:
Contingent consideration	17	19
Total	21	26
Recurring | Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Total	76	56
Alabama Power
Assets:
Derivative asset	5	2
Liabilities:
Derivative liability	0	22
Alabama Power | Recurring
Assets:
Cash equivalents	320	693
Other investments	24	21
Total	1,512	1,739
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	311	691
Other investments	0	0
Total	959	1,273
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	9	2
Other investments	24	21
Total	477	410
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Other investments	0	0
Total	0	0
Alabama Power | Recurring | Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Total	76	56
Georgia Power
Assets:
Derivative asset	3	1
Liabilities:
Derivative liability	1	67
Georgia Power | Recurring
Assets:
Total	1,160	1,017
Liabilities:
Total		70
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	340	276
Liabilities:
Total		0
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Total	820	741
Liabilities:
Total		70
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Liabilities:
Total		0
Mississippi Power
Assets:
Derivative asset	2	0
Liabilities:
Derivative liability	2	26
Mississippi Power | Recurring
Assets:
Cash equivalents	21	281
Total	30	282
Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	21	281
Total	21	281
Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total	9	1
Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total	0	0
Southern Power
Assets:
Derivative asset	89	19
Liabilities:
Derivative liability	26	27
Southern Power | Recurring
Assets:
Cash equivalents		113
Total	89	132
Liabilities:
Contingent consideration	17	19
Total	43	46
Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents		113
Total	0	113
Liabilities:
Contingent consideration	0	0
Total	0	0
Southern Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents		0
Total	89	19
Liabilities:
Contingent consideration	0	0
Total	26	27
Southern Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents		0
Total	0	0
Liabilities:
Contingent consideration	17	19
Total	17	19
Southern Company Gas
Assets:
Derivative asset	162	212
Liabilities:
Derivative liability	35	41
Collateral already posted, aggregate fair value	28	99
Southern Company Gas | Recurring
Assets:
Cash equivalents		8
Total	696	708
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents		8
Total	402	397
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents		0
Total	262	289
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents		0
Total	32	22
Energy-related derivatives | Recurring
Assets:
Derivative asset	704	677
Liabilities:
Derivative liability	597	703
Energy-related derivatives | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	401	388
Liabilities:
Derivative liability	389	442
Energy-related derivatives | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	271	267
Liabilities:
Derivative liability	204	254
Energy-related derivatives | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	32	22
Liabilities:
Derivative liability	4	7
Energy-related derivatives | Alabama Power | Recurring
Assets:
Derivative asset	12	4
Liabilities:
Derivative liability	7	24
Energy-related derivatives | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	12	4
Liabilities:
Derivative liability	7	24
Energy-related derivatives | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Georgia Power | Recurring
Assets:
Derivative asset	15	4
Liabilities:
Derivative liability	13	53
Energy-related derivatives | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	15	4
Liabilities:
Derivative liability	13	53
Energy-related derivatives | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Mississippi Power | Recurring
Assets:
Derivative asset	9	1
Liabilities:
Derivative liability	9	27
Energy-related derivatives | Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	9	1
Liabilities:
Derivative liability	9	27
Energy-related derivatives | Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Southern Power | Recurring
Assets:
Derivative asset	2	3
Liabilities:
Derivative liability	3	3
Energy-related derivatives | Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Southern Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	2	3
Liabilities:
Derivative liability	3	3
Energy-related derivatives | Southern Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives | Southern Company Gas | Recurring
Assets:
Derivative asset	666	665
Liabilities:
Derivative liability	565	596
Energy-related derivatives | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	401	388
Liabilities:
Derivative liability	389	442
Energy-related derivatives | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	233	255
Liabilities:
Derivative liability	172	147
Energy-related derivatives | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	32	22
Liabilities:
Derivative liability	4	7
Interest rate derivatives | Recurring
Assets:
Derivative asset	20	2
Liabilities:
Derivative liability		24
Interest rate derivatives | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability		0
Interest rate derivatives | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	20	2
Liabilities:
Derivative liability		24
Interest rate derivatives | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability		0
Interest rate derivatives | Georgia Power | Recurring
Liabilities:
Derivative liability		17
Interest rate derivatives | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Derivative liability		0
Interest rate derivatives | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivative liability		17
Interest rate derivatives | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liability		0
Interest rate derivatives | Southern Company Gas | Recurring
Assets:
Derivative asset		2
Interest rate derivatives | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset		0
Interest rate derivatives | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset		2
Interest rate derivatives | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset		0
Foreign currency derivatives | Recurring
Assets:
Derivative asset	87	16
Liabilities:
Derivative liability	23	24
Foreign currency derivatives | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	87	16
Liabilities:
Derivative liability	23	24
Foreign currency derivatives | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives | Southern Power | Recurring
Assets:
Derivative asset	87	16
Liabilities:
Derivative liability	23	24
Foreign currency derivatives | Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives | Southern Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	87	16
Liabilities:
Derivative liability	23	24
Foreign currency derivatives | Southern Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Domestic equity | Recurring
Assets:
Nuclear decommissioning trusts	1,013	886
Domestic equity | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	862	751
Domestic equity | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	151	135
Domestic equity | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	684	611
Domestic equity | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	543	488
Domestic equity | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	141	123
Domestic equity | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	320	264
Domestic equity | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	319	263
Domestic equity | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	1	1
Domestic equity | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity | Southern Company Gas | Recurring
Assets:
Non-qualified deferred compensation trusts	9	11
Domestic equity | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0	0
Domestic equity | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	9	11
Domestic equity | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
Foreign equity | Recurring
Assets:
Nuclear decommissioning trusts	338	288
Foreign equity | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	85	68
Foreign equity | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	253	220
Foreign equity | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	158	132
Foreign equity | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	85	68
Foreign equity | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	73	64
Foreign equity | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	177	152
Foreign equity | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	177	152
Foreign equity | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity | Southern Company Gas | Recurring
Assets:
Non-qualified deferred compensation trusts	3	4
Foreign equity | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0	0
Foreign equity | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	3	4
Foreign equity | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
U.S. Treasury and government agency securities | Recurring
Assets:
Nuclear decommissioning trusts	284	307
U.S. Treasury and government agency securities | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	284	307
U.S. Treasury and government agency securities | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	21	21
U.S. Treasury and government agency securities | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	21	21
U.S. Treasury and government agency securities | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	263	286
U.S. Treasury and government agency securities | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	263	286
U.S. Treasury and government agency securities | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Recurring
Assets:
Nuclear decommissioning trusts	85	85
Municipal bonds | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	85	85
Municipal bonds | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	1	1
Municipal bonds | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	1	1
Municipal bonds | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	84	84
Municipal bonds | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Municipal bonds | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	84	84
Municipal bonds | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Pooled funds – fixed income | Recurring
Assets:
Nuclear decommissioning trusts	17	17
Pooled funds – fixed income | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Pooled funds – fixed income | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	17	17
Pooled funds – fixed income | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Pooled funds – fixed income | Southern Company Gas | Recurring
Assets:
Non-qualified deferred compensation trusts	17	17
Pooled funds – fixed income | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0	0
Pooled funds – fixed income | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	17	17
Pooled funds – fixed income | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
Corporate bonds | Recurring
Assets:
Nuclear decommissioning trusts	399	320
Corporate bonds | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	13	23
Corporate bonds | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	386	297
Corporate bonds | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Corporate bonds | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	180	167
Corporate bonds | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	13	23
Corporate bonds | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	167	144
Corporate bonds | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Corporate bonds | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	219	153
Corporate bonds | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Corporate bonds | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	219	153
Corporate bonds | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Recurring
Assets:
Nuclear decommissioning trusts	83	87
Mortgage and asset backed securities | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	83	87
Mortgage and asset backed securities | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	29	29
Mortgage and asset backed securities | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	29	29
Mortgage and asset backed securities | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	54	57
Mortgage and asset backed securities | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Mortgage and asset backed securities | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	54	57
Mortgage and asset backed securities | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Recurring
Assets:
Nuclear decommissioning trusts	76	56
Private equity | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Recurring | Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Nuclear decommissioning trusts	76	56
Private equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	76	56
Private equity | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Private equity | Alabama Power | Recurring | Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Nuclear decommissioning trusts	76	56
Cash and cash equivalents | Recurring
Assets:
Nuclear decommissioning trusts	1	1
Cash and cash equivalents | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	1	1
Cash and cash equivalents | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	0	0
Cash and cash equivalents | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Cash equivalents | Southern Company Gas | Recurring
Assets:
Non-qualified deferred compensation trusts	1	1
Cash equivalents | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	1	1
Cash equivalents | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	0	0
Cash equivalents | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
Other | Recurring
Assets:
Nuclear decommissioning trusts	35	22
Other | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	28	17
Other | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	7	5
Other | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Other | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	7	4
Other | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	7	3
Other | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	0	1
Other | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Other | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	28	17
Other | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	21	13
Other | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	7	4
Other | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	Dec. 31, 2020USD ($)$ / MMBTU	Dec. 31, 2019USD ($)
Private equity | Alabama Power
Fair Value, Option, Quantitative Disclosures [Line Items]
Alternative investment	$ 76	$ 56
Unfunded commitments	73	$ 70
Energy-related derivatives | Significant Unobservable Inputs (Level 3) | Southern Company Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, at fair value, net	$ 28
Minimum | Measurement Input, Commodity Forward Price | Valuation, Market Approach | Energy-related derivatives | Significant Unobservable Inputs (Level 3) | Southern Company Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative asset net, measurement input | $ / MMBTU	(0.08)
Maximum | Measurement Input, Commodity Forward Price | Valuation, Market Approach | Energy-related derivatives | Significant Unobservable Inputs (Level 3) | Southern Company Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative asset net, measurement input | $ / MMBTU	0.24

FAIR VALUE MEASUREMENTS - Finan

FAIR VALUE MEASUREMENTS - Financial Instruments, Carrying Amount Not Equal to Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$ 48,349	$ 44,561
Fair Value	56,264	48,339
Alabama Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	8,864	8,517
Fair Value	10,702	9,525
Georgia Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	12,825	11,660
Fair Value	15,198	12,680
Mississippi Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	1,400	1,589
Fair Value	1,590	1,671
Southern Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	3,692	4,398
Fair Value	4,165	4,708
Southern Company Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	6,626	5,845
Fair Value	$ 7,973	$ 6,509

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component (Details) - Southern Company Gas $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 14
Transfers to Level 3	70
Transfers from Level 3	(34)
Instruments realized or otherwise settled during period	(16)
Changes in fair value	(6)
Ending balance	$ 28

DERIVATIVES - Energy-Related De

DERIVATIVES - Energy-Related Derivative Contracts (Details) - Energy-related, Natural Gas MMBTU in Millions	Dec. 31, 2020MMBTU
Derivative [Line Items]
Net Purchased mmBtu	835
Alabama Power
Derivative [Line Items]
Net Purchased mmBtu	78
Georgia Power
Derivative [Line Items]
Net Purchased mmBtu	135
Mississippi Power
Derivative [Line Items]
Net Purchased mmBtu	89
Southern Power
Derivative [Line Items]
Net Purchased mmBtu	10
Southern Company Gas
Derivative [Line Items]
Net Purchased mmBtu	523
Long | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	4,421
Short | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	3,898

DERIVATIVES - Narrative (Detail

DERIVATIVES - Narrative (Details) MWh in Millions, MMBTU in Millions	12 Months Ended
	Dec. 31, 2020USD ($)MWhMMBTU	Dec. 31, 2019USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	29
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period | $	$ (25,000,000)
Collateral already posted, aggregate fair value | $	$ 28,000,000	$ 99,000,000
Southern Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	9
Southern Power | Public Utilities, Inventory, Power Position
Derivative [Line Items]
Net Purchased mmBtu | MWh	1
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	7
Georgia Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	9
Mississippi Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	4
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ 10,000,000
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, aggregate fair value | $	$ 0

DERIVATIVES - Interest Rate Der

DERIVATIVES - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Derivative [Line Items]
Notional Amount	$ 1,560
Fair Value Gain (Loss) December 31, 2020	20
Mississippi Power | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 60
Weighted Average Interest Rate Paid	0.58%
Fair Value Gain (Loss) December 31, 2020	$ 0
Southern Company | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Weighted Average Interest Rate Paid	0.87%
Fair Value Gain (Loss) December 31, 2020	$ 20

DERIVATIVES - Foreign Currency

DERIVATIVES - Foreign Currency Derivatives (Details) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Dec. 31, 2019USD ($)
Foreign currency derivatives | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) December 31, 2020	65
Southern Power
Derivative [Line Items]
Receive Notional	1,100
Fair Value Gain (Loss) December 31, 2020	109		$ (5)
Southern Power | Foreign currency derivatives | June 2022 | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain (Loss) December 31, 2020	$ 40
Southern Power | Foreign currency derivatives | June 2026 | Cash Flow Hedges of Existing Debt
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) December 31, 2020	$ 25

DERIVATIVES - Derivative Financ

DERIVATIVES - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	$ 810	$ 696
Derivative asset, gross amount offset	(529)	(463)
Derivative asset, net amounts recognized in the balance sheets	281	233
Derivative liability, gross amounts recognized	621	751
Derivative liability, gross amounts offset	(557)	(562)
Derivative liability, gross amounts recognized in balance sheets	64	189
Collateral already posted, aggregate fair value	28	99
Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	658	668
Derivative liability, gross amounts recognized	563	583
Energy-related derivatives | Other deferred charges and assets | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	270	207
Energy-related derivatives | Other deferred credits and liabilities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	232	225
Energy-related derivatives | Assets from risk management activities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	388	461
Energy-related derivatives | Liabilities from risk management activities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	331	358
Alabama Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	12	4
Derivative asset, gross amount offset	(7)	(2)
Derivative asset, net amounts recognized in the balance sheets	5	2
Derivative liability, gross amounts recognized	7	24
Derivative liability, gross amounts offset	(7)	(2)
Derivative liability, gross amounts recognized in balance sheets	0	22
Georgia Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	15	4
Derivative asset, gross amount offset	(12)	(3)
Derivative asset, net amounts recognized in the balance sheets	3	1
Derivative liability, gross amounts recognized	13	70
Derivative liability, gross amounts offset	(12)	(3)
Derivative liability, gross amounts recognized in balance sheets	1	67
Mississippi Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	9	1
Derivative asset, gross amount offset	(7)	(1)
Derivative asset, net amounts recognized in the balance sheets	2	0
Derivative liability, gross amounts recognized	9	27
Derivative liability, gross amounts offset	(7)	(1)
Derivative liability, gross amounts recognized in balance sheets	2	26
Southern Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, net amounts recognized in the balance sheets	89	19
Derivative liability, gross amounts recognized in balance sheets	26	27
Southern Power | Energy-related derivatives | Other current assets | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	2
Southern Power | Energy-related derivatives | Other current liabilities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	1	1
Southern Company Gas
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	665	668
Derivative asset, gross amount offset	(503)	(456)
Derivative asset, net amounts recognized in the balance sheets	162	212
Derivative liability, gross amounts recognized	566	596
Derivative liability, gross amounts offset	(531)	(555)
Derivative liability, gross amounts recognized in balance sheets	35	41
Collateral already posted, aggregate fair value	28	99
Southern Company Gas | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	658	666
Derivative liability, gross amounts recognized	562	582
Southern Company Gas | Energy-related derivatives | Other current liabilities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	330	357
Southern Company Gas | Energy-related derivatives | Other deferred charges and assets | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	270	207
Southern Company Gas | Energy-related derivatives | Other deferred credits and liabilities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	232	225
Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	388	459
Hedging Instruments for Regulatory Purposes | Energy-related derivatives | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	42	9
Derivative liability, gross amounts recognized	30	114
Hedging Instruments for Regulatory Purposes | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	18	6
Hedging Instruments for Regulatory Purposes | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	19	44
Hedging Instruments for Regulatory Purposes | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	24	3
Hedging Instruments for Regulatory Purposes | Energy-related derivatives | Liabilities from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	11	70
Hedging Instruments for Regulatory Purposes | Alabama Power | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	12	4
Derivative liability, gross amounts recognized	7	24
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	7	2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	2	14
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	5	2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	5	10
Hedging Instruments for Regulatory Purposes | Georgia Power | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	15	4
Derivative liability, gross amounts recognized	13	53
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	7	1
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	5	32
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	8	3
Hedging Instruments for Regulatory Purposes | Georgia Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	8	21
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	9	1
Derivative liability, gross amounts recognized	9	27
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	4	0
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	3	15
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	5	1
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	6	12
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	6	0
Derivative liability, gross amounts recognized	1	10
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	1	9
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	1
Hedging Instruments for Regulatory Purposes | Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	6	0
Cash Flow and Fair Value Hedging | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	110	19
Derivative liability, gross amounts recognized	28	54
Cash Flow and Fair Value Hedging | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	3	1
Cash Flow and Fair Value Hedging | Energy-related derivatives | Liabilities from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	5	6
Cash Flow and Fair Value Hedging | Interest rate derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Interest rate derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	1
Cash Flow and Fair Value Hedging | Interest rate derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	20	2
Cash Flow and Fair Value Hedging | Interest rate derivatives | Liabilities from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	23
Cash Flow and Fair Value Hedging | Foreign currency derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	87	16
Cash Flow and Fair Value Hedging | Foreign currency derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Foreign currency derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Foreign currency derivatives | Liabilities from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	23	24
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Georgia Power | Interest rate derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	17
Cash Flow and Fair Value Hedging | Southern Power | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	89	17
Derivative liability, gross amounts recognized	25	26
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	2	1
Cash Flow and Fair Value Hedging | Southern Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	2	2
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	23	24
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other deferred charges and assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	87	16
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	1	2
Derivative liability, gross amounts recognized	3	4
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	3	4
Cash Flow and Fair Value Hedging | Southern Company Gas | Energy-related derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	1	0
Cash Flow and Fair Value Hedging | Southern Company Gas | Interest rate derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Southern Company Gas | Interest rate derivatives | Assets from risk management activities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	$ 0	$ 2

DERIVATIVES - Schedule of Unrea

DERIVATIVES - Schedule of Unrealized Gain (Loss) Recognized in the Balance Sheet (Details) - Energy-related derivatives - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	$ 12	$ (94)
Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(63)
Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(2)	(37)
Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	12	6
Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	2
Alabama Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	6	(20)
Alabama Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(14)
Alabama Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	(8)
Alabama Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	5	2
Alabama Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1
Georgia Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	2	(49)
Georgia Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(31)
Georgia Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(1)	(18)
Georgia Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	2	0
Georgia Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1
Mississippi Power
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	(26)
Mississippi Power | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(15)
Mississippi Power | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(1)	(11)
Mississippi Power | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1	0
Mississippi Power | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0
Southern Company Gas
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	4	1
Southern Company Gas | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(3)
Southern Company Gas | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	0
Southern Company Gas | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	4	$ 4
Southern Company Gas | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	$ 0

DERIVATIVES - Pre-Tax Effects o

DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Cash Flow Hedging on AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 14	$ (154)	$ (62)
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(8)	(13)	17
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(26)	(57)	(1)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	48	(84)	(78)
Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(3)	(59)	0
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	46	(88)	(68)
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(2)	(4)	10
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	48	(84)	(78)
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(29)	(7)	7
Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(6)	(9)	7
Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (23)	$ 2	$ 0

DERIVATIVES - Pre-Tax Effects_2

DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Cash Flow and Fair Value Hedging on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	$ 3,518	$ 3,038	$ 3,131
Interest expense, net of amounts capitalized	(1,821)	(1,736)	(1,842)
Other income (expense), net	336	252	114
Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(8)	(2)	2
Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(3)	(6)	7
Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(26)	(20)	(21)
Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	27	42	(12)
Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(23)	(24)	(24)
Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	114	(24)	(60)
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	494	479	493
Interest expense, net of amounts capitalized	(151)	(169)	(183)
Other income (expense), net	19	47	23
Southern Power | Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(3)	(6)	7
Southern Power | Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(23)	(24)	(24)
Southern Power | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 114	$ (24)	$ (60)

DERIVATIVES - Cumulative Basis

DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Securities due within one year
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	$ (1,509)	$ (599)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	(10)	0
Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	0	(1,494)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 0	$ 3

DERIVATIVES - Pre-Tax Effects_3

DERIVATIVES - Pre-Tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 149	$ 233	$ (128)
Energy-related derivatives | Natural Gas Revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	134	223	(122)
Energy-related derivatives | Cost of Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	15	10	(6)
Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	$ 9	$ 3	$ 5

ACQUISITIONS AND DISPOSITIONS -

ACQUISITIONS AND DISPOSITIONS - Southern Company Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended			12 Months Ended
	Dec. 31, 2019	Jan. 31, 2019	Dec. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2019	Jul. 31, 2019
Business Acquisition [Line Items]
Gain (loss) on dispositions						$ 66,000,000	$ 2,588,000,000	$ 301,000,000
Impairment charges			$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Business Acquisition [Line Items]
Cash proceeds from sale of business		$ 5,800,000,000
Indebtedness assumed		1,300,000,000
Gain (loss) on dispositions		2,600,000,000					2,600,000,000
Gain (loss) on dispositions, after tax		$ 1,400,000,000					1,400,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PowerSecure Utility Infrastructure Services Unit
Business Acquisition [Line Items]
Consideration for sale										$ 65,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PowerSecure International, Inc. Lighting Business
Business Acquisition [Line Items]
Cash proceeds from sale of business	$ 4,000,000
Indebtedness assumed	5,000,000						5,000,000
Gain (loss) on dispositions							(58,000,000)
Gain (loss) on dispositions, after tax							(52,000,000)
Consideration for sale	$ 9,000,000						$ 9,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure Utility Infrastructure Services Unit
Business Acquisition [Line Items]
Impairment charges					$ 32,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | PowerSecure International, Inc. Lighting Business
Business Acquisition [Line Items]
Impairment charges				$ 2,000,000
Goodwill and intangible asset impairment				$ 18,000,000
Disposal Group, Held-for-sale, Not Discontinued Operations | Leveraged Lease Investment
Business Acquisition [Line Items]
Consideration for sale									$ 20,000,000

ACQUISITIONS AND DISPOSITIONS_2

ACQUISITIONS AND DISPOSITIONS - Alabama Power Narrative (Details) - Alabama Power - Autauga Combined Cycle $ in Millions	Aug. 31, 2020USD ($)MW
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW	885
Purchase price	$ 461
Property, plant, and equipment	$ 452
Power sales agreement, remaining term	3 years

ACQUISITIONS AND DISPOSITIONS_3

ACQUISITIONS AND DISPOSITIONS - Schedule of Acquisitions (Details) - Southern Power - MW	1 Months Ended		12 Months Ended
	May 31, 2020	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					300
Beech Ridge II
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	56
PPA Contract Period	12 years
DSGP
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				28
PPA Contract Period				15 years
Noncontrolling interest, approximate nameplate capacity (in MW)				10
Approximate nameplate capacity, repowered amount (in MW)			18
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		20
PPA Contract Period		20 years
Beech Ridge II | Beech Ridge II
Business Acquisition [Line Items]
Ownership Percentage	100.00%
DSGP | DSGP
Business Acquisition [Line Items]
Ownership Percentage				100.00%
Gaskell West 1 | Gaskell West 1
Business Acquisition [Line Items]
Ownership Percentage		100.00%

ACQUISITIONS AND DISPOSITIONS_4

ACQUISITIONS AND DISPOSITIONS - Southern Power Narrative (Details) $ in Millions	Jan. 17, 2020USD ($)	Jun. 30, 2019USD ($)MW	Dec. 31, 2018USD ($)investorwind_farm	May 31, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2021	Dec. 31, 2020USD ($)agreement	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)investorwind_farmoperating_facility	Mar. 31, 2020MW	May 31, 2019MW
Business Acquisition [Line Items]
Construction work in progress							$ 8,697	$ 7,880
Impairment charges							0	168	$ 210
(Gain) loss on dispositions, net							65	2,569	291
Sale of noncontrolling interests							65		1,273
Purchase of membership interests from noncontrolling interests							60
Gain (loss) on dispositions							$ 66	2,588	301
Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW										300
Number of Power Purchase Agreements | agreement							2
Construction work in progress							$ 127	515
Impairment charges							0	3	156
(Gain) loss on dispositions, net							39	23	2
Sale of noncontrolling interests							65		$ 1,273
Purchase of membership interests from noncontrolling interests							60
Number of wind facilities | operating_facility									8
Gain (loss) on dispositions							39	24	$ 3
Southern Power | Series of Business Acquisitions
Business Acquisition [Line Items]
Construction work in progress							34
Southern Power | Minimum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs							392
Southern Power | Maximum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs							$ 460
SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership									33.00%
SP Wind | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership									100.00%
Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage							100.00%
Impairment charges									$ 36
(Gain) loss on dispositions, net							$ 0	$ 17
Scenario, Forecast | Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage						80.00%
SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Distribution made to limited partner, cash distributions paid, percentage							67.00%
SP Solar Holdings I, LP | SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership				33.00%
Proceeds from sale of equity method investments				$ 1,200
Sale of noncontrolling interests				511
SP Wind
Business Acquisition [Line Items]
Number of wind facilities | wind_farm			8						8
SP Wind | Southern Power
Business Acquisition [Line Items]
Number of financial investors | investor									3
Distribution made to limited partner, cash distributions paid, percentage							60.00%
SP Wind | Financial Investors
Business Acquisition [Line Items]
Distribution made to limited partner, cash distributions paid, percentage			40.00%				40.00%
Allocation of tax attributes to limited partner			99.00%
SP Wind | SP Wind | Southern Power
Business Acquisition [Line Items]
Proceeds from sale of equity method investments			$ 1,200
Number of financial investors | investor			3
Common stockholders' equity | Southern Power
Business Acquisition [Line Items]
Sale of noncontrolling interests							$ (2)		$ (417)
Purchase of membership interests from noncontrolling interests				$ 410			$ (5)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Florida Plants | Southern Power
Business Acquisition [Line Items]
Cash proceeds from sale of business			$ 203
Asset impairment charge					$ 119
Asset impairment charge, after tax					$ 89
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Nacogdoches Biomass-Fueled Facility | Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW		115
Consideration for sale		$ 461
Gain (loss) on dispositions		23
Gain (loss) on dispositions, after tax		$ 88
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mankato | Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW											385
Consideration for sale	$ 663
Gain (loss) on dispositions	39
Gain (loss) on dispositions, after tax	$ 23

ACQUISITIONS AND DISPOSITIONS_5

ACQUISITIONS AND DISPOSITIONS - Schedule of Construction Projects (Details) - Southern Power $ in Millions	1 Months Ended					3 Months Ended
	Dec. 31, 2020MW	Nov. 30, 2020USD ($)MW	Jun. 30, 2020USD ($)	May 31, 2020MW	Dec. 31, 2019	Dec. 31, 2021MW	Sep. 30, 2021MW	Mar. 31, 2020MW	Oct. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)								300
Garland Solar Storage | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)							88
PPA Contract Period							20 years
Glass Sands | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)						118
PPA Contract Period						12 years
Tranquility Solar Storage | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)						72
PPA Contract Period						20 years
Skookumchuck
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		136
PPA Contract Period		20 years
Reading
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				200
PPA Contract Period				12 years
Wild Horse Mountain
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	100
PPA Contract Period					20 years
Garland Solar Storage | Class B Membership Interest | Garland Solar Storage
Business Acquisition [Line Items]
Noncontrolling ownership percentage sold by parent	100.00%
Tranquility Solar Storage | Class B Membership Interest | Tranquility Solar Storage
Business Acquisition [Line Items]
Noncontrolling ownership percentage sold by parent	100.00%
Glass Sands | Glass Sands
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent	100.00%
Skookumchuck | Skookumchuck
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent									100.00%
Proceeds from tax equity transaction | $		$ 121
Skookumchuck | Class B Membership Interest | Skookumchuck
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent		100.00%
Reading | Reading
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent										100.00%
Proceeds from tax equity transaction | $			$ 156
Reading | Class B Membership Interest | Reading
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent	100.00%
Wild Horse Mountain | Wild Horse Mountain
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent										100.00%
Wild Horse Mountain | Class B Membership Interest | Wild Horse Mountain
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent	100.00%

ACQUISITIONS AND DISPOSITIONS_6

ACQUISITIONS AND DISPOSITIONS - GAS Acquisitions and Dispositions Narrative (Details)	Dec. 01, 2020USD ($)	Feb. 07, 2020USD ($)	May 29, 2019USD ($)	May 31, 2019USD ($)	Jul. 31, 2018USD ($)utility	Jun. 30, 2018USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Mar. 24, 2020USD ($)
Business Acquisition [Line Items]
Impairment charges							$ 0
Gain (loss) on dispositions								$ 66,000,000	$ 2,588,000,000	$ 301,000,000
Southern Company Gas
Business Acquisition [Line Items]
Impairment charges							$ 0
Number of natural gas distribution utilities sold | utility					3
Gain (loss) on dispositions								22,000,000	0	291,000,000
Southern Company Gas | Triton
Business Acquisition [Line Items]
Realized loss on disposal				$ 6,000,000
Realized gain on disposal, net of tax				7,000,000
Reversal of federal income tax valuation allowance			$ 13,000,000	$ 13,000,000
Southern Company Gas | Pivotal LNG And Atlantic Coast Pipeline
Business Acquisition [Line Items]
Contingent milestone payment, amount											$ 5,000,000
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business		$ 178,000,000				$ 365,000,000
Gain (loss) on dispositions, after tax						(67,000,000)			(17,000,000)
Tax on sale of business						34,000,000
Impairment charges						$ 42,000,000				$ 42,000,000
Gain (loss) on dispositions									$ (24,000,000)
Elizabethtown Gas and Elkton Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax					$ 0
Tax on sale of business					$ 205,000,000
Number of natural gas distribution utilities sold | utility					2
Proceeds from sale of oil and gas property and equipment					$ 1,700,000,000
Florida City Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business					587,000,000
Gain (loss) on dispositions, after tax					16,000,000
Tax on sale of business					$ 103,000,000
Jefferson Island | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business	$ 33,000,000
Gain (loss) on dispositions, after tax								16,000,000
Gain (loss) on dispositions								$ 22,000,000

ACQUISITIONS AND DISPOSITIONS_7

ACQUISITIONS AND DISPOSITIONS - Held For Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets Held for Sale:
Current assets	$ 0	$ 19
Total property, plant, and equipment	8	565
Goodwill and other intangible assets	0	40
Equity investments in unconsolidated subsidiaries	0	151
Leveraged leases	52	0
Other non-current assets	0	14
Total Assets Held for Sale	60	789
Liabilities Held for Sale (all current):	$ 0	5
Southern Power
Assets Held for Sale:
Current assets		17
Total property, plant, and equipment		547
Goodwill and other intangible assets		40
Equity investments in unconsolidated subsidiaries		0
Leveraged leases		0
Other non-current assets		14
Total Assets Held for Sale		618
Liabilities Held for Sale (all current):		3
Southern Company Gas
Assets Held for Sale:
Current assets		2
Total property, plant, and equipment		18
Goodwill and other intangible assets		0
Equity investments in unconsolidated subsidiaries		151
Leveraged leases		0
Other non-current assets		0
Total Assets Held for Sale		171
Liabilities Held for Sale (all current):		$ 2

ACQUISITIONS AND DISPOSITIONS_8

ACQUISITIONS AND DISPOSITIONS - Pre-tax Profit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gulf Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes			$ 140
Florida Plants | Southern Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes			49
Plant Nacogdoches | Southern Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes		$ 13	$ 27
Mankato | Southern Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 2	$ 29

SEGMENT AND RELATED INFORMATI_3

SEGMENT AND RELATED INFORMATION - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018utility	Dec. 31, 2020USD ($)statesegment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Total operating revenues		$ 21,097	$ 22,596	$ 25,241
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues		1,119	1,220	1,364
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues		$ 5,039	5,598	6,914
Number of reportable segments | segment		4
Number of states in which entity operates | state		4
Number of natural gas distribution utilities sold | utility	3
Southern Natural Gas Company, LLC | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		50.00%
PennEast Pipeline | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		20.00%
Dalton Pipeline | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		50.00%
Atlantic Coast Pipeline | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		5.00%
Natural gas | Southern Company Gas | Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Total operating revenues		$ 0	14	32
Natural gas | Southern Company Gas | Southern Power
Segment Reporting Information [Line Items]
Total operating revenues		$ 26	$ 64	$ 119

SEGMENT AND RELATED INFORMATI_4

SEGMENT AND RELATED INFORMATION - Financial Data for Business Segments (Details)	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)	Jan. 17, 2020USD ($)	Jan. 31, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)utility
Segment Reporting Information [Line Items]
Total operating revenues									$ 20,375,000,000	$ 21,419,000,000	$ 23,495,000,000
Depreciation and amortization									3,518,000,000	3,038,000,000	3,131,000,000
Interest income									37,000,000	60,000,000	38,000,000
Operating income (loss)									4,885,000,000	7,736,000,000	4,191,000,000
Earnings from equity method investments									153,000,000	162,000,000	148,000,000
Interest expense									1,821,000,000	1,736,000,000	1,842,000,000
Income taxes (benefit)									393,000,000	1,798,000,000	449,000,000
Segment net income (loss)									3,119,000,000	4,739,000,000	2,226,000,000
Goodwill	$ 5,280,000,000					$ 5,280,000,000		$ 5,280,000,000	5,280,000,000	5,280,000,000	5,315,000,000
Total Assets	122,935,000,000					122,935,000,000		118,700,000,000	122,935,000,000	118,700,000,000	116,914,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000	0	1,060,000,000
Gain (loss) on dispositions									66,000,000	2,588,000,000	301,000,000
Lease, impairment loss						52,000,000	$ 154,000,000	17,000,000	206,000,000	0	0
Lease, impairment loss, after tax						31,000,000	$ 74,000,000	13,000,000
Impairment charges									0	168,000,000	210,000,000
Net gain on dispositions									65,000,000	2,569,000,000	291,000,000
Goodwill impairment						0
Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									16,497,000,000	17,095,000,000	18,571,000,000
Depreciation and amortization									2,941,000,000	2,472,000,000	2,565,000,000
Interest income									30,000,000	47,000,000	31,000,000
Earnings from equity method investments									0	5,000,000	(1,000,000)
Interest expense									976,000,000	987,000,000	1,035,000,000
Income taxes (benefit)									517,000,000	708,000,000	207,000,000
Segment net income (loss)									3,115,000,000	3,268,000,000	2,304,000,000
Goodwill	2,000,000					2,000,000		2,000,000	2,000,000	2,000,000	2,000,000
Total Assets	98,041,000,000					98,041,000,000		94,650,000,000	98,041,000,000	94,650,000,000	93,959,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
All Other
Segment and Related Information (Textual) [Abstract]
Lease, impairment loss									206,000,000
Lease, impairment loss, after tax									105,000,000
Operating Segments | Traditional Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									15,135,000,000	15,569,000,000	16,843,000,000
Depreciation and amortization									2,447,000,000	1,993,000,000	2,072,000,000
Interest income									26,000,000	38,000,000	23,000,000
Earnings from equity method investments									0	2,000,000	(1,000,000)
Interest expense									825,000,000	818,000,000	852,000,000
Income taxes (benefit)									514,000,000	764,000,000	371,000,000
Segment net income (loss)									2,877,000,000	2,929,000,000	2,117,000,000
Goodwill	0					0		0	0	0	0
Total Assets	85,486,000,000					85,486,000,000		81,063,000,000	85,486,000,000	81,063,000,000	79,382,000,000
Operating Segments | Southern Power | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									1,733,000,000	1,938,000,000	2,205,000,000
Depreciation and amortization									494,000,000	479,000,000	493,000,000
Interest income									4,000,000	9,000,000	8,000,000
Earnings from equity method investments									0	3,000,000	0
Interest expense									151,000,000	169,000,000	183,000,000
Income taxes (benefit)									3,000,000	(56,000,000)	(164,000,000)
Segment net income (loss)									238,000,000	339,000,000	187,000,000
Goodwill	2,000,000					2,000,000		2,000,000	2,000,000	2,000,000	2,000,000
Total Assets	13,235,000,000					13,235,000,000		14,300,000,000	13,235,000,000	14,300,000,000	14,883,000,000
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
Depreciation and amortization									500,000,000	487,000,000	500,000,000
Interest income									5,000,000	3,000,000	4,000,000
Earnings from equity method investments									141,000,000	157,000,000	148,000,000
Interest expense									231,000,000	232,000,000	228,000,000
Income taxes (benefit)									173,000,000	130,000,000	464,000,000
Segment net income (loss)									590,000,000	585,000,000	372,000,000
Goodwill	5,015,000,000					5,015,000,000		5,015,000,000	5,015,000,000	5,015,000,000	5,015,000,000
Total Assets	22,630,000,000					22,630,000,000		21,687,000,000	22,630,000,000	21,687,000,000	21,448,000,000
Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues									596,000,000	690,000,000	1,213,000,000
Depreciation and amortization									77,000,000	79,000,000	66,000,000
Interest income									6,000,000	16,000,000	8,000,000
Earnings from equity method investments									12,000,000	0	2,000,000
Interest expense									614,000,000	517,000,000	580,000,000
Income taxes (benefit)									(297,000,000)	960,000,000	(222,000,000)
Segment net income (loss)									(592,000,000)	908,000,000	(453,000,000)
Goodwill	263,000,000					263,000,000		263,000,000	263,000,000	263,000,000	298,000,000
Total Assets	3,168,000,000					3,168,000,000		3,511,000,000	3,168,000,000	3,511,000,000	3,285,000,000
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues									(152,000,000)	(158,000,000)	(198,000,000)
Depreciation and amortization									0	0	0
Interest income									(4,000,000)	(6,000,000)	(5,000,000)
Earnings from equity method investments									0	0	(1,000,000)
Interest expense									0	0	(1,000,000)
Income taxes (benefit)									0	0	0
Segment net income (loss)									6,000,000	(22,000,000)	3,000,000
Goodwill	0					0		0	0	0	0
Total Assets	(904,000,000)					(904,000,000)		(1,148,000,000)	(904,000,000)	(1,148,000,000)	(1,778,000,000)
Intersegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									(371,000,000)	(412,000,000)	(477,000,000)
Depreciation and amortization									0	0	0
Interest income									0	0	0
Earnings from equity method investments									0	0	0
Interest expense									0	0	0
Income taxes (benefit)									0	0	0
Segment net income (loss)									0	0	0
Goodwill	0					0		0	0	0	0
Total Assets	(680,000,000)					(680,000,000)		(713,000,000)	(680,000,000)	(713,000,000)	(306,000,000)
Georgia Power
Segment Reporting Information [Line Items]
Total operating revenues									8,309,000,000	8,408,000,000	8,420,000,000
Depreciation and amortization									1,425,000,000	981,000,000	923,000,000
Operating income (loss)									1,972,000,000	2,461,000,000	1,289,000,000
Interest expense									425,000,000	409,000,000	397,000,000
Income taxes (benefit)									152,000,000	472,000,000	214,000,000
Total Assets	47,080,000,000					47,080,000,000		44,541,000,000	47,080,000,000	44,541,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000	0	1,060,000,000
Georgia Power | Plant Vogtle Units 3 And 4
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4	176,000,000	$ 149,000,000
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	131,000,000	$ 111,000,000
Georgia Power | Traditional Operating Companies | Plant Vogtle Units 3 And 4
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000		1,100,000,000
Estimated loss on Plant Vogtle Units 3 and 4, net of tax									242,000,000		800,000,000
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues									1,733,000,000	1,938,000,000	2,205,000,000
Depreciation and amortization									494,000,000	479,000,000	493,000,000
Operating income (loss)									342,000,000	395,000,000	242,000,000
Interest expense									151,000,000	169,000,000	183,000,000
Income taxes (benefit)									3,000,000	(56,000,000)	(164,000,000)
Segment net income (loss)									238,000,000	339,000,000	187,000,000
Total Assets	13,235,000,000					13,235,000,000		14,300,000,000	13,235,000,000	14,300,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									39,000,000	24,000,000	3,000,000
Impairment charges									0	3,000,000	156,000,000
Impairment charges, after tax											117,000,000
Net gain on dispositions									39,000,000	23,000,000	2,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
Depreciation and amortization									500,000,000	487,000,000	500,000,000
Operating income (loss)									812,000,000	770,000,000	915,000,000
Earnings from equity method investments									141,000,000	157,000,000	148,000,000
Interest expense									231,000,000	232,000,000	228,000,000
Income taxes (benefit)									173,000,000	130,000,000	464,000,000
Segment net income (loss)									590,000,000	585,000,000	372,000,000
Goodwill	5,015,000,000					5,015,000,000		5,015,000,000	5,015,000,000	5,015,000,000
Total Assets	22,630,000,000					22,630,000,000		21,687,000,000	22,630,000,000	21,687,000,000	21,448,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									22,000,000	0	291,000,000
Impairment charges									0	115,000,000	42,000,000
Net gain on dispositions									22,000,000	0	291,000,000
Goodwill impairment						0
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Goodwill	4,034,000,000					4,034,000,000		4,034,000,000	4,034,000,000	4,034,000,000
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Goodwill	981,000,000					981,000,000		981,000,000	981,000,000	981,000,000
Segment and Related Information (Textual) [Abstract]
Net gain on dispositions											(33,000,000)
Net gain on dispositions, after tax											(67,000,000)
Disposal group, including discontinued operation, revenue											55,000,000
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues									3,466,000,000	3,810,000,000	3,930,000,000
Depreciation and amortization									470,000,000	454,000,000	453,000,000
Operating income (loss)									814,000,000	924,000,000	1,013,000,000
Earnings from equity method investments									141,000,000	162,000,000	145,000,000
Interest expense									228,000,000	225,000,000	227,000,000
Income taxes (benefit)									178,000,000	200,000,000	495,000,000
Segment net income (loss)									592,000,000	677,000,000	435,000,000
Total Assets	23,040,000,000					23,040,000,000		22,228,000,000	23,040,000,000	22,228,000,000	21,918,000,000
Southern Company Gas | Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues									36,000,000	44,000,000	55,000,000
Depreciation and amortization									30,000,000	33,000,000	47,000,000
Operating income (loss)									(7,000,000)	(154,000,000)	(98,000,000)
Earnings from equity method investments									0	(5,000,000)	3,000,000
Interest expense									3,000,000	7,000,000	1,000,000
Income taxes (benefit)									(5,000,000)	(70,000,000)	(31,000,000)
Segment net income (loss)									(2,000,000)	(92,000,000)	(63,000,000)
Total Assets	11,336,000,000					11,336,000,000		10,759,000,000	11,336,000,000	10,759,000,000	11,112,000,000
Southern Company Gas | Operating Segments | Gas distribution operations
Segment Reporting Information [Line Items]
Total operating revenues									2,952,000,000	3,028,000,000	3,186,000,000
Depreciation and amortization									442,000,000	422,000,000	409,000,000
Operating income (loss)									655,000,000	573,000,000	904,000,000
Earnings from equity method investments									0	0	0
Interest expense									192,000,000	187,000,000	178,000,000
Income taxes (benefit)									114,000,000	63,000,000	409,000,000
Segment net income (loss)									390,000,000	337,000,000	334,000,000
Total Assets	19,090,000,000					19,090,000,000		18,204,000,000	19,090,000,000	18,204,000,000	17,266,000,000
Southern Company Gas | Operating Segments | Gas Pipeline Investments
Segment Reporting Information [Line Items]
Total operating revenues									32,000,000	32,000,000	32,000,000
Depreciation and amortization									5,000,000	5,000,000	5,000,000
Operating income (loss)									20,000,000	20,000,000	20,000,000
Earnings from equity method investments									141,000,000	162,000,000	145,000,000
Interest expense									29,000,000	30,000,000	34,000,000
Income taxes (benefit)									33,000,000	58,000,000	28,000,000
Segment net income (loss)									99,000,000	94,000,000	103,000,000
Total Assets	1,597,000,000					1,597,000,000		1,678,000,000	1,597,000,000	1,678,000,000	1,763,000,000
Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									74,000,000	294,000,000	144,000,000
Depreciation and amortization									1,000,000	1,000,000	2,000,000
Operating income (loss)									20,000,000	219,000,000	70,000,000
Earnings from equity method investments									0	0	0
Interest expense									4,000,000	5,000,000	9,000,000
Income taxes (benefit)									3,000,000	52,000,000	4,000,000
Segment net income (loss)									14,000,000	163,000,000	38,000,000
Total Assets	850,000,000					850,000,000		850,000,000	850,000,000	850,000,000	1,302,000,000
Southern Company Gas | Operating Segments | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues									408,000,000	456,000,000	568,000,000
Depreciation and amortization									22,000,000	26,000,000	37,000,000
Operating income (loss)									119,000,000	112,000,000	19,000,000
Earnings from equity method investments									0	0	0
Interest expense									3,000,000	3,000,000	6,000,000
Income taxes (benefit)									28,000,000	27,000,000	54,000,000
Segment net income (loss)									89,000,000	83,000,000	(40,000,000)
Total Assets	1,503,000,000					1,503,000,000		1,496,000,000	1,503,000,000	1,496,000,000	1,587,000,000
Southern Company Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues									(68,000,000)	(62,000,000)	(76,000,000)
Depreciation and amortization									0	0	0
Operating income (loss)									5,000,000	0	0
Earnings from equity method investments									0	0	0
Interest expense									0	0	0
Income taxes (benefit)									0	0	0
Segment net income (loss)									0	0	0
Total Assets	$ (11,746,000,000)					$ (11,746,000,000)		$ (11,300,000,000)	(11,746,000,000)	(11,300,000,000)	(11,582,000,000)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas | Gas distribution operations
Segment and Related Information (Textual) [Abstract]
Net gain on dispositions											324,000,000
Net gain on dispositions, after tax											$ 16,000,000
Number of distribution utilities | utility											3
Disposal group, including discontinued operation, revenue											$ 244,000,000
Mankato | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Power
Segment and Related Information (Textual) [Abstract]
Gain on sale									39,000,000
Gain on sale, after tax									23,000,000
Gain (loss) on dispositions			$ 39,000,000
Gain (loss) on dispositions, after tax			$ 23,000,000
Plant Nacogdoches | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Power
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										23,000,000
Gain (loss) on dispositions, after tax										88,000,000
Gulf Power | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions				$ 2,600,000,000						2,600,000,000
Gain (loss) on dispositions, after tax				$ 1,400,000,000						1,400,000,000
PowerSecure International, Inc. Lighting Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										(58,000,000)
Gain (loss) on dispositions, after tax										(52,000,000)
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										(24,000,000)
Gain (loss) on dispositions, after tax					$ (67,000,000)					(17,000,000)
Net gain on dispositions											291,000,000
Net gain on dispositions, after tax											(51,000,000)
Goodwill impairment					$ 42,000,000						$ 42,000,000
Jefferson Island | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									22,000,000
Gain (loss) on dispositions, after tax									$ 16,000,000
Natural Gas Storage Facility | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Impairment charges										115,000,000
Impairment charges, after tax										$ 86,000,000

SEGMENT AND RELATED INFORMATI_5

SEGMENT AND RELATED INFORMATION - Electric Utilities' Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Total operating revenues	$ 20,375	$ 21,419	$ 23,495
Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	672	636	664
Electric Utilities
Revenue from External Customer [Line Items]
Total operating revenues	16,497	17,095	18,571
Electric Utilities | Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	13,643	14,084	15,222
Electric Utilities | Wholesale electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	1,945	2,152	2,516
Electric Utilities | Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	$ 909	$ 859	$ 833

SEGMENT AND RELATED INFORMATI_6

SEGMENT AND RELATED INFORMATION - Gas Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total operating revenues	$ 20,375	$ 21,419	$ 23,495
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	3,434	3,792	3,909
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	3,466	3,810	3,930
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	3,434	3,792	3,909
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Total operating revenues	2,902	3,001	3,155
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues	408	456	568
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Total operating revenues	124	335	186
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	3,434	3,792	3,909
Wholesale gas services | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	74	294	144
Less Gross Gas Costs	4,585	5,684	7,262
Wholesale gas services | Operating Segments | Third Party Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	4,544	5,703	6,955
Wholesale gas services | Operating Segments | Intercompany Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	115	275	451
Wholesale gas services | Operating Segments | Total Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 4,659	$ 5,978	$ 7,406

VALUATION AND QUALIFYING ACCO_2

VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Millions	May 29, 2019	May 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			$ 49	$ 50	$ 44
Charged to Income			78	68	69
Charged to Other Accounts			27	0	(1)
Deductions			36	69	61
Reclassified to Held for Sale			0	0	1
Balance at End of Period			118	49	50
Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			113	100	148
Charged to Income			0	13	(38)
Charged to Other Accounts			0	0	0
Deductions			1	0	10
Reclassified to Held for Sale			0	0	0
Balance at End of Period			112	113	100
Alabama Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			22	10	9
Charged to Income			25	24	13
Charged to Other Accounts			0	0	0
Deductions			4	12	12
Balance at End of Period			43	22	10
Georgia Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			2	2	3
Charged to Income			14	13	11
Charged to Other Accounts			23	0	0
Deductions			13	13	12
Balance at End of Period			26	2	2
Georgia Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			28	33	0
Charged to Income			0	(5)	39
Charged to Other Accounts			0	0	0
Deductions			0	0	6
Balance at End of Period			28	28	33
Mississippi Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			1	1	1
Charged to Income			1	2	1
Charged to Other Accounts			0	0	0
Deductions			1	2	1
Balance at End of Period			1	1	1
Mississippi Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			32	32	124
Charged to Income			0	0	(92)
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period			32	32	32
Southern Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			29	22	10
Charged to Income			(1)	7	12
Charged to Other Accounts			0	0	0
Deductions			1	0	0
Balance at End of Period			27	29	22
Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			18	30	28
Charged to Income			35	29	33
Charged to Other Accounts			4	0	(1)
Deductions			17	41	30
Balance at End of Period			40	18	30
Southern Company Gas | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			4	12	11
Charged to Income			0	(8)	1
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period			4	$ 4	$ 12
Triton | Southern Company Gas
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Reversal of federal income tax valuation allowance	$ 13	$ 13
State and Local Jurisdiction | Georgia Power
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance			28
State and Local Jurisdiction | Southern Company Gas
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance			$ 5