Georgia Power (GPJA) 10-K 20 Feb 20 2019 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 28, 2019
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
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 Shell Company	false
Entity Public Float			$ 57.8
Entity Common Stock, Shares Outstanding (in shares)		1,054,228,409
Documents Incorporated by Reference	Documents incorporated by reference: specified portions of The Southern Company's Definitive Proxy Statement on Schedule 14A relating to the 2020 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 2020 Annual Meeting of Shareholders are incorporated by reference into PART III.
Entity Central Index Key	0000092122
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	false
Entity Small Business	false
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 2015A 6.25% Junior Subordinated Notes due 2075
Document Information [Line Items]
Title of 12(b) Security	Series 2015A 6.25% Junior Subordinated Notes due 2075
Trading Symbol	SOJA
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
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 Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		30,537,500
Entity Central Index Key	0000003153
Entity Emerging Growth Company	false
Entity Small Business	false
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 Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		9,261,500
Entity Central Index Key	0000041091
Entity Emerging Growth Company	false
Entity Small Business	false
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 Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,121,000
Entity Central Index Key	0000066904
Entity Emerging Growth Company	false
Entity Small Business	false
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 Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,000
Entity Central Index Key	0001160661
Entity Emerging Growth Company	false
Entity Small Business	false
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 Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		100
Entity Central Index Key	0001004155
Entity Emerging Growth Company	false
Entity Small Business	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Revenues:
Total operating revenues	$ 21,419,000,000	$ 23,495,000,000	$ 23,031,000,000
Operating Expenses:
Other operations and maintenance	5,600,000,000	5,889,000,000	5,739,000,000
Depreciation and amortization	3,038,000,000	3,131,000,000	3,010,000,000
Taxes other than income taxes	1,230,000,000	1,315,000,000	1,250,000,000
Estimated loss on plants	24,000,000	1,097,000,000	3,362,000,000
Impairment charges	168,000,000	210,000,000	0
(Gain) loss on dispositions, net	(2,569,000,000)	(291,000,000)	(40,000,000)
Gain on dispositions, net	2,588,000,000	301,000,000	42,000,000
Depreciation and amortization	3,331,000,000	3,549,000,000	3,457,000,000
Total operating expenses	13,683,000,000	19,304,000,000	20,698,000,000
Operating Income	7,736,000,000	4,191,000,000	2,333,000,000
Other Income and (Expense):
Allowance for equity funds used during construction	128,000,000	138,000,000	160,000,000
Earnings from equity method investments	162,000,000	148,000,000	106,000,000
Interest expense, net of amounts capitalized	(1,736,000,000)	(1,842,000,000)	(1,694,000,000)
Other income (expense), net	252,000,000	114,000,000	163,000,000
Total other income and (expense)	(1,194,000,000)	(1,442,000,000)	(1,265,000,000)
Earnings Before Income Taxes	6,542,000,000	2,749,000,000	1,068,000,000
Income taxes	1,798,000,000	449,000,000	142,000,000
Net Income	4,744,000,000	2,300,000,000	926,000,000
Dividends on preferred and preference stock of subsidiaries	15,000,000	16,000,000	38,000,000
Net income (loss) attributable to noncontrolling interests	(10,000,000)	58,000,000	46,000,000
Net Income (Loss)	$ 4,739,000,000	$ 2,226,000,000	$ 842,000,000
Earnings per share —
Basic (in dollars per share)	$ 4.53	$ 2.18	$ 0.84
Diluted (in dollars per share)	$ 4.50	$ 2.17	$ 0.84
Average number of shares of common stock outstanding — (in millions)
Basic (in shares)	1,046	1,020	1,000
Diluted (in shares)	1,054	1,025	1,008
Retail electric revenues
Operating Revenues:
Total operating revenues	$ 14,084,000,000	$ 15,222,000,000	$ 15,330,000,000
Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues	2,152,000,000	2,516,000,000	2,426,000,000
Other electric revenues
Operating Revenues:
Total operating revenues	636,000,000	664,000,000	681,000,000
Fuel
Operating Expenses:
Cost of revenue	3,622,000,000	4,637,000,000	4,400,000,000
Purchased power
Operating Expenses:
Cost of revenue	816,000,000	971,000,000	863,000,000
Natural gas revenues
Operating Revenues:
Total operating revenues	3,792,000,000	3,854,000,000	3,791,000,000
Operating Expenses:
Cost of revenue	1,319,000,000	1,539,000,000	1,601,000,000
Other revenues
Operating Revenues:
Total operating revenues	755,000,000	1,239,000,000	803,000,000
Operating Expenses:
Cost of revenue	435,000,000	806,000,000	513,000,000
Alabama Power
Operating Revenues:
Total operating revenues	6,125,000,000	6,032,000,000	6,039,000,000
Operating Expenses:
Other operations and maintenance	1,821,000,000	1,669,000,000	1,709,000,000
Depreciation and amortization	793,000,000	764,000,000	736,000,000
Taxes other than income taxes	403,000,000	389,000,000	384,000,000
Purchased power, non-affiliates	203,000,000	216,000,000	170,000,000
Purchased power, affiliates	200,000,000	216,000,000	158,000,000
Depreciation and amortization	951,000,000	917,000,000	888,000,000
Total operating expenses	4,532,000,000	4,555,000,000	4,382,000,000
Operating Income	1,593,000,000	1,477,000,000	1,657,000,000
Other Income and (Expense):
Allowance for equity funds used during construction	52,000,000	62,000,000	39,000,000
Interest expense, net of amounts capitalized	(336,000,000)	(323,000,000)	(305,000,000)
Other income (expense), net	46,000,000	20,000,000	43,000,000
Total other income and (expense)	(238,000,000)	(241,000,000)	(223,000,000)
Earnings Before Income Taxes	1,355,000,000	1,236,000,000	1,434,000,000
Income taxes	270,000,000	291,000,000	568,000,000
Net Income	1,085,000,000	945,000,000	866,000,000
Dividends on preferred and preference stock of subsidiaries	15,000,000	15,000,000	18,000,000
Net Income (Loss)	1,070,000,000	930,000,000	848,000,000
Alabama Power | Retail electric revenues
Operating Revenues:
Total operating revenues	5,501,000,000	5,367,000,000	5,458,000,000
Alabama Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues	258,000,000	279,000,000	276,000,000
Alabama Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	81,000,000	119,000,000	97,000,000
Alabama Power | Fuel
Operating Expenses:
Cost of revenue	1,112,000,000	1,301,000,000	1,225,000,000
Alabama Power | Other revenues
Operating Revenues:
Total operating revenues	285,000,000	267,000,000	208,000,000
Georgia Power
Operating Revenues:
Total operating revenues	8,408,000,000	8,420,000,000	8,310,000,000
Operating Expenses:
Other operations and maintenance	1,972,000,000	1,860,000,000	1,724,000,000
Depreciation and amortization	981,000,000	923,000,000	895,000,000
Taxes other than income taxes	454,000,000	437,000,000	409,000,000
Estimated loss on plants	0	1,060,000,000	0
Purchased power, non-affiliates	521,000,000	430,000,000	416,000,000
Purchased power, affiliates	575,000,000	723,000,000	622,000,000
Depreciation and amortization	1,193,000,000	1,142,000,000	1,100,000,000
Total operating expenses	5,947,000,000	7,131,000,000	5,737,000,000
Operating Income	2,461,000,000	1,289,000,000	2,573,000,000
Other Income and (Expense):
Interest expense, net of amounts capitalized	(409,000,000)	(397,000,000)	(419,000,000)
Other income (expense), net	140,000,000	115,000,000	104,000,000
Total other income and (expense)	(269,000,000)	(282,000,000)	(315,000,000)
Earnings Before Income Taxes	2,192,000,000	1,007,000,000	2,258,000,000
Income taxes	472,000,000	214,000,000	830,000,000
Net Income	1,720,000,000	793,000,000	1,428,000,000
Dividends on preferred and preference stock of subsidiaries	0	0	14,000,000
Net Income (Loss)	1,720,000,000	793,000,000	1,414,000,000
Georgia Power | Retail electric revenues
Operating Revenues:
Total operating revenues	7,707,000,000	7,752,000,000	7,738,000,000
Georgia Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues	129,000,000	163,000,000	163,000,000
Georgia Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	11,000,000	24,000,000	26,000,000
Georgia Power | Fuel
Operating Expenses:
Cost of revenue	1,444,000,000	1,698,000,000	1,671,000,000
Georgia Power | Other revenues
Operating Revenues:
Total operating revenues	561,000,000	481,000,000	383,000,000
Mississippi Power
Operating Revenues:
Total operating revenues	1,264,000,000	1,265,000,000	1,187,000,000
Operating Expenses:
Other operations and maintenance	283,000,000	313,000,000	291,000,000
Depreciation and amortization	192,000,000	169,000,000	161,000,000
Taxes other than income taxes	113,000,000	107,000,000	104,000,000
Estimated loss on plants	24,000,000	37,000,000	3,362,000,000
Purchased power, affiliates	20,000,000	41,000,000	25,000,000
Depreciation and amortization	197,000,000	177,000,000	198,000,000
Total operating expenses	1,039,000,000	1,072,000,000	4,338,000,000
Operating Income	225,000,000	193,000,000	(3,151,000,000)
Other Income and (Expense):
Allowance for equity funds used during construction	1,000,000	0	72,000,000
Interest expense, net of amounts capitalized	(69,000,000)	(76,000,000)	(42,000,000)
Other income (expense), net	12,000,000	17,000,000	1,000,000
Total other income and (expense)	(56,000,000)	(59,000,000)	31,000,000
Earnings Before Income Taxes	169,000,000	134,000,000	(3,120,000,000)
Income taxes	30,000,000	(102,000,000)	(532,000,000)
Net Income	139,000,000	236,000,000	(2,588,000,000)
Dividends on preferred and preference stock of subsidiaries	0	1,000,000	2,000,000
Net Income (Loss)	139,000,000	235,000,000	(2,590,000,000)
Mississippi Power | Retail electric revenues
Operating Revenues:
Total operating revenues	877,000,000	889,000,000	854,000,000
Mississippi Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues	237,000,000	263,000,000	259,000,000
Mississippi Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	132,000,000	91,000,000	56,000,000
Mississippi Power | Fuel
Operating Expenses:
Cost of revenue	407,000,000	405,000,000	395,000,000
Mississippi Power | Other revenues
Operating Revenues:
Total operating revenues	18,000,000	22,000,000	18,000,000
Southern Power
Operating Revenues:
Total operating revenues	1,938,000,000	2,205,000,000	2,075,000,000
Operating Expenses:
Other operations and maintenance	359,000,000	395,000,000	386,000,000
Depreciation and amortization	479,000,000	493,000,000	503,000,000
Taxes other than income taxes	40,000,000	46,000,000	48,000,000
Impairment charges	3,000,000	156,000,000	0
Gain on dispositions, net	(23,000,000)	(2,000,000)	0
Purchased power, non-affiliates	108,000,000	176,000,000	149,000,000
Depreciation and amortization	505,000,000	524,000,000	536,000,000
Total operating expenses	1,543,000,000	1,963,000,000	1,707,000,000
Operating Income	395,000,000	242,000,000	368,000,000
Other Income and (Expense):
Interest expense, net of amounts capitalized	(169,000,000)	(183,000,000)	(191,000,000)
Other income (expense), net	47,000,000	23,000,000	1,000,000
Total other income and (expense)	(122,000,000)	(160,000,000)	(190,000,000)
Earnings Before Income Taxes	273,000,000	82,000,000	178,000,000
Income taxes	(56,000,000)	(164,000,000)	(939,000,000)
Net Income	329,000,000	246,000,000	1,117,000,000
Net income (loss) attributable to noncontrolling interests	(10,000,000)	59,000,000	46,000,000
Net Income (Loss)	339,000,000	187,000,000	1,071,000,000
Southern Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues	1,528,000,000	1,757,000,000	1,671,000,000
Southern Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	398,000,000	435,000,000	392,000,000
Southern Power | Fuel
Operating Expenses:
Cost of revenue	577,000,000	699,000,000	621,000,000
Southern Power | Other revenues
Operating Revenues:
Total operating revenues	12,000,000	13,000,000	12,000,000
Southern Company Gas
Operating Revenues:
Total operating revenues	3,792,000,000	3,909,000,000	3,920,000,000
Operating Expenses:
Other operations and maintenance	888,000,000	981,000,000	945,000,000
Taxes other than income taxes	213,000,000	211,000,000	184,000,000
Impairment charges	115,000,000	42,000,000	0
(Gain) loss on dispositions, net	0	(291,000,000)	0
Gain on dispositions, net	0	291,000,000	0
Depreciation and amortization	487,000,000	500,000,000	501,000,000
Total operating expenses	3,022,000,000	2,994,000,000	3,260,000,000
Operating Income	770,000,000	915,000,000	660,000,000
Other Income and (Expense):
Earnings from equity method investments	157,000,000	148,000,000	106,000,000
Interest expense, net of amounts capitalized	(232,000,000)	(228,000,000)	(200,000,000)
Other income (expense), net	20,000,000	1,000,000	44,000,000
Total other income and (expense)	(55,000,000)	(79,000,000)	(50,000,000)
Earnings Before Income Taxes	715,000,000	836,000,000	610,000,000
Income taxes	130,000,000	464,000,000	367,000,000
Net Income	585,000,000	372,000,000	243,000,000
Net Income (Loss)	585,000,000	372,000,000	243,000,000
Southern Company Gas | Natural gas revenues
Operating Revenues:
Total operating revenues	3,793,000,000	3,874,000,000	3,787,000,000
Operating Expenses:
Cost of revenue	1,319,000,000	1,539,000,000	1,601,000,000
Southern Company Gas | Alternative revenue programs
Operating Revenues:
Total operating revenues	(1,000,000)	(20,000,000)	4,000,000
Southern Company Gas | Other revenues
Operating Revenues:
Total operating revenues	0	55,000,000	129,000,000
Operating Expenses:
Cost of revenue	$ 0	$ 12,000,000	$ 29,000,000

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Southern Company Gas
Excise taxes collected	$ 117	$ 114	$ 100

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Net Income	$ 4,744	$ 2,300	$ 926
Qualifying hedges:
Changes in fair value, net of tax	(115)
Changes in fair value, net of tax		(47)	57
Reclassification adjustment for amounts included in net income, net of tax	57
Reclassification adjustment for amounts included in net income, net of tax		72	(60)
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(64)	(5)	17
Reclassification adjustment for amounts included in net income, net of tax	4	6	(23)
Total other comprehensive income (loss)	(118)	26	(9)
Dividends on preferred and preference stock of subsidiaries	15	16	38
Comprehensive income (loss) attributable to noncontrolling interests	(10)	58	46
Current period change	4,621	2,252	833
Alabama Power
Consolidated Net Income	1,085	945	866
Qualifying hedges:
Changes in fair value, net of tax	0
Changes in fair value, net of tax		0	1
Reclassification adjustment for amounts included in net income, net of tax	4
Reclassification adjustment for amounts included in net income, net of tax		4	3
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	4	4	4
Dividends on preferred and preference stock of subsidiaries	15	15	18
Current period change	1,089	949	870
Georgia Power
Consolidated Net Income	1,720	793	1,428
Qualifying hedges:
Changes in fair value, net of tax	(44)
Changes in fair value, net of tax		0	0
Reclassification adjustment for amounts included in net income, net of tax	2
Reclassification adjustment for amounts included in net income, net of tax		3	3
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	(42)	3	3
Dividends on preferred and preference stock of subsidiaries	0	0	14
Current period change	1,678	796	1,431
Mississippi Power
Consolidated Net Income	139	236	(2,588)
Qualifying hedges:
Changes in fair value, net of tax	0
Changes in fair value, net of tax		(1)	(1)
Reclassification adjustment for amounts included in net income, net of tax	1
Reclassification adjustment for amounts included in net income, net of tax		1	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	0	0
Dividends on preferred and preference stock of subsidiaries	0	1	2
Current period change	140	236	(2,588)
Southern Power
Consolidated Net Income	329	246	1,117
Qualifying hedges:
Changes in fair value, net of tax	(66)
Changes in fair value, net of tax		(51)	63
Reclassification adjustment for amounts included in net income, net of tax	41
Reclassification adjustment for amounts included in net income, net of tax		58	(73)
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(17)	5	0
Reclassification adjustment for amounts included in net income, net of tax	0	2	0
Total other comprehensive income (loss)	(42)	14	(10)
Comprehensive income (loss) attributable to noncontrolling interests	(10)	59	46
Current period change	297	201	1,061
Southern Company Gas
Consolidated Net Income	585	372	243
Qualifying hedges:
Changes in fair value, net of tax	(5)
Changes in fair value, net of tax		5	(5)
Reclassification adjustment for amounts included in net income, net of tax	2
Reclassification adjustment for amounts included in net income, net of tax		(1)	1
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	(16)	0	(1)
Reclassification adjustment for amounts included in net income, net of tax	0	(2)	0
Total other comprehensive income (loss)	(19)	2	(5)
Current period change	$ 566	$ 374	$ 238

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Qualifying hedges, change in fair value, tax	$ (39)
Qualifying hedges, change in fair value, tax		$ (16)	$ 34
Qualifying hedges, reclassification adjustment, tax	19
Qualifying hedges, reclassification adjustment, tax		24	(37)
Pension and other postretirement benefit plans, gain (loss), tax	(31)	(2)	6
Reclassification adjustment for amounts included in net income, tax	1	5	(6)
Alabama Power
Qualifying hedges, change in fair value, tax	0
Qualifying hedges, change in fair value, tax		0	(1)
Qualifying hedges, reclassification adjustment, tax	2
Qualifying hedges, reclassification adjustment, tax		2	2
Georgia Power
Qualifying hedges, change in fair value, tax	(15)
Qualifying hedges, change in fair value, tax		0	0
Qualifying hedges, reclassification adjustment, tax	1
Qualifying hedges, reclassification adjustment, tax		1	1
Mississippi Power
Qualifying hedges, change in fair value, tax	0
Qualifying hedges, change in fair value, tax		(1)	(1)
Qualifying hedges, reclassification adjustment, tax	0
Qualifying hedges, reclassification adjustment, tax		0	1
Southern Power
Qualifying hedges, change in fair value, tax	(22)
Qualifying hedges, change in fair value, tax		(17)	39
Qualifying hedges, reclassification adjustment, tax	14
Qualifying hedges, reclassification adjustment, tax		19	(46)
Pension and other postretirement benefit plans, gain (loss), tax	(6)	2	0
Reclassification adjustment for amounts included in net income, tax	0	0	0
Southern Company Gas
Qualifying hedges, change in fair value, tax	(2)
Qualifying hedges, change in fair value, tax		2	(3)
Qualifying hedges, reclassification adjustment, tax	0
Qualifying hedges, reclassification adjustment, tax		(1)	0
Pension and other postretirement benefit plans, gain (loss), tax	(14)	0	0
Reclassification adjustment for amounts included in net income, tax	$ 0	$ 3	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Consolidated net income	$ 4,744,000,000	$ 2,300,000,000	$ 926,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	3,331,000,000	3,549,000,000	3,457,000,000
Deferred income taxes	611,000,000	89,000,000	166,000,000
Utilization of federal investment tax credits	757,000,000	5,000,000	0
Amortization of investment tax credits	(181,000,000)	(87,000,000)	(79,000,000)
Allowance for equity funds used during construction	(128,000,000)	(138,000,000)	(160,000,000)
Pension, postretirement, and other employee benefits	(204,000,000)	(103,000,000)	(84,000,000)
Pension and postretirement funding	(1,136,000,000)	(4,000,000)	(2,000,000)
Settlement of asset retirement obligations	(328,000,000)	(244,000,000)	(177,000,000)
Storm damage reserve accruals	168,000,000	74,000,000	38,000,000
Stock based compensation expense	107,000,000	125,000,000	109,000,000
Estimated loss on plants under construction	15,000,000	1,093,000,000	3,179,000,000
Impairment charges	168,000,000	210,000,000	0
(Gain) loss on dispositions, net	(2,588,000,000)	(301,000,000)	(42,000,000)
Other, net	102,000,000	14,000,000	(63,000,000)
Changes in certain current assets and liabilities —
-Receivables	630,000,000	(426,000,000)	(202,000,000)
-Fossil fuel for generation	(120,000,000)	123,000,000	36,000,000
-Natural gas for sale	44,000,000	49,000,000	36,000,000
-Other current assets	70,000,000	(127,000,000)	(143,000,000)
-Accounts payable	(693,000,000)	291,000,000	(280,000,000)
-Accrued taxes	117,000,000	267,000,000	(142,000,000)
-Retail fuel cost over recovery	62,000,000	36,000,000	(212,000,000)
-Other current liabilities	61,000,000	30,000,000	(38,000,000)
-Accrued compensation	(9,000,000)	33,000,000	(8,000,000)
Net cash provided from operating activities	5,781,000,000	6,945,000,000	6,394,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(50,000,000)	(65,000,000)	(1,054,000,000)
Property additions	(7,555,000,000)	(8,001,000,000)	(7,423,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	0	1,682,000,000
Nuclear decommissioning trust fund purchases	(888,000,000)	(1,117,000,000)	(811,000,000)
Nuclear decommissioning trust fund sales	882,000,000	1,111,000,000	805,000,000
Proceeds from dispositions and asset sales	5,122,000,000	2,956,000,000	97,000,000
Cost of removal, net of salvage	(393,000,000)	(388,000,000)	(313,000,000)
Change in construction payables, net	(169,000,000)	50,000,000	259,000,000
Investments in unconsolidated subsidiaries	(148,000,000)	(114,000,000)	(152,000,000)
Payments pursuant to LTSAs	(234,000,000)	(186,000,000)	(227,000,000)
Other investing activities	41,000,000	(6,000,000)	(53,000,000)
Net cash used for investing activities	(3,392,000,000)	(5,760,000,000)	(7,190,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	640,000,000
Increase (decrease) in notes payable, net		(774,000,000)	(401,000,000)
Proceeds —
Long-term debt	5,220,000,000	2,478,000,000	5,858,000,000
Common stock	844,000,000	1,090,000,000	793,000,000
Preferred stock	0	0	250,000,000
Short-term borrowings	350,000,000	3,150,000,000	1,259,000,000
Redemptions and repurchases —
Long-term debt	(4,347,000,000)	(5,533,000,000)	(2,930,000,000)
Preferred and preference stock	0	(33,000,000)	(658,000,000)
Short-term borrowings	(1,850,000,000)	(1,900,000,000)	(659,000,000)
Distributions to noncontrolling interests	(256,000,000)	(153,000,000)	(119,000,000)
Capital contributions from noncontrolling interests	196,000,000	2,551,000,000	80,000,000
Payment of common stock dividends	(2,570,000,000)	(2,425,000,000)	(2,300,000,000)
Other financing activities	(157,000,000)	(264,000,000)	(222,000,000)
Net cash provided from (used for) financing activities	(1,930,000,000)	(1,813,000,000)	951,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	459,000,000	(628,000,000)	155,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	1,519,000,000	2,147,000,000	1,992,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	1,978,000,000	1,519,000,000	2,147,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	1,651,000,000	1,794,000,000	1,676,000,000
Income taxes (net of refunds)	276,000,000	172,000,000	(410,000,000)
Noncash transactions —
Accrued property additions at year-end	932,000,000	1,103,000,000	985,000,000
Alabama Power
Operating Activities:
Consolidated net income	1,085,000,000	945,000,000	866,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	951,000,000	917,000,000	888,000,000
Deferred income taxes	197,000,000	174,000,000	409,000,000
Allowance for equity funds used during construction	(52,000,000)	(62,000,000)	(39,000,000)
Pension and postretirement funding	(362,000,000)	(4,000,000)	(2,000,000)
Settlement of asset retirement obligations	(127,000,000)	(55,000,000)	(26,000,000)
Natural disaster reserve accruals	138,000,000	16,000,000	4,000,000
Other deferred charges – affiliated	(42,000,000)	0	0
Other, net	(90,000,000)	(17,000,000)	9,000,000
Changes in certain current assets and liabilities —
-Receivables	9,000,000	(149,000,000)	(168,000,000)
-Prepayments	(4,000,000)	(2,000,000)	(2,000,000)
-Other current assets	(85,000,000)	30,000,000	20,000,000
-Accounts payable	(41,000,000)	24,000,000	71,000,000
-Accrued taxes	49,000,000	10,000,000	(84,000,000)
-Retail fuel cost over recovery	47,000,000	0	(76,000,000)
-Other current liabilities	97,000,000	128,000,000	3,000,000
-Materials and supplies	23,000,000	(82,000,000)	(34,000,000)
-Accrued compensation	(14,000,000)	8,000,000	(2,000,000)
Net cash provided from operating activities	1,779,000,000	1,881,000,000	1,837,000,000
Investing Activities:
Property additions	(1,757,000,000)	(2,158,000,000)	(1,882,000,000)
Nuclear decommissioning trust fund purchases	(261,000,000)	(279,000,000)	(237,000,000)
Nuclear decommissioning trust fund sales	260,000,000	278,000,000	237,000,000
Cost of removal, net of salvage	(103,000,000)	(130,000,000)	(112,000,000)
Change in construction payables, net	(71,000,000)	26,000,000	161,000,000
Other investing activities	(31,000,000)	(26,000,000)	(43,000,000)
Net cash used for investing activities	(1,963,000,000)	(2,289,000,000)	(1,876,000,000)
Proceeds —
Preferred stock	0	0	250,000,000
Senior notes	600,000,000	500,000,000	1,100,000,000
Pollution control revenue bonds	0	120,000,000	0
Capital contributions from parent company	1,240,000,000	511,000,000	361,000,000
Redemptions and repurchases —
Preferred and preference stock	0	0	(238,000,000)
Senior notes	(200,000,000)	0	(525,000,000)
Pollution control revenue bonds	0	(120,000,000)	(36,000,000)
Payment of common stock dividends	(844,000,000)	(801,000,000)	(714,000,000)
Other financing activities	(31,000,000)	(33,000,000)	(35,000,000)
Net cash provided from (used for) financing activities	765,000,000	177,000,000	163,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	581,000,000	(231,000,000)	124,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	313,000,000	544,000,000	420,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	894,000,000	313,000,000	544,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	311,000,000	284,000,000	285,000,000
Income taxes (net of refunds)	26,000,000	106,000,000	236,000,000
Noncash transactions —
Accrued property additions at year-end	200,000,000	272,000,000	245,000,000
Georgia Power
Operating Activities:
Consolidated net income	1,720,000,000	793,000,000	1,428,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	1,193,000,000	1,142,000,000	1,100,000,000
Deferred income taxes	179,000,000	(260,000,000)	458,000,000
Pension, postretirement, and other employee benefits	(146,000,000)	(75,000,000)	(68,000,000)
Pension and postretirement funding	(200,000,000)	0	0
Settlement of asset retirement obligations	(151,000,000)	(116,000,000)	(120,000,000)
Retail fuel cost over recovery – long-term	73,000,000	0	0
Other deferred charges – affiliated	(108,000,000)	0	0
Estimated loss on plants under construction	0	1,060,000,000	0
Other, net	12,000,000	(21,000,000)	(83,000,000)
Changes in certain current assets and liabilities —
-Receivables	177,000,000	8,000,000	(256,000,000)
-Fossil fuel for generation	(41,000,000)	83,000,000	(16,000,000)
-Other current assets	(19,000,000)	(43,000,000)	(28,000,000)
-Accounts payable	(92,000,000)	95,000,000	(219,000,000)
-Accrued taxes	58,000,000	58,000,000	1,000,000
-Retail fuel cost over recovery	0	0	(84,000,000)
-Other current liabilities	150,000,000	(107,000,000)	(33,000,000)
-Prepaid income taxes	102,000,000	152,000,000	(168,000,000)
Net cash provided from operating activities	2,907,000,000	2,769,000,000	1,912,000,000
Investing Activities:
Property additions	(3,510,000,000)	(3,116,000,000)	(2,704,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	0	1,682,000,000
Nuclear decommissioning trust fund purchases	(628,000,000)	(839,000,000)	(574,000,000)
Nuclear decommissioning trust fund sales	622,000,000	833,000,000	568,000,000
Cost of removal, net of salvage	(186,000,000)	(107,000,000)	(100,000,000)
Payments pursuant to LTSAs	(81,000,000)	(54,000,000)	(64,000,000)
Change in construction payables, net of joint owner portion	(122,000,000)	68,000,000	223,000,000
Proceeds from dispositions and asset sales	14,000,000	138,000,000	96,000,000
Other investing activities	6,000,000	(32,000,000)	(39,000,000)
Net cash used for investing activities	(3,885,000,000)	(3,109,000,000)	(912,000,000)
Financing Activities:
Increase (decrease) in notes payable, net		294,000,000
Increase (decrease) in notes payable, net	(179,000,000)		(391,000,000)
Proceeds —
Short-term borrowings	250,000,000	0	700,000,000
Senior notes	750,000,000	0	1,350,000,000
Pollution control revenue bonds	584,000,000	108,000,000	65,000,000
Other long-term debt	0	0	370,000,000
Capital contributions from parent company	634,000,000	2,985,000,000	431,000,000
FFB loan	1,218,000,000	0	0
Redemptions and repurchases —
Preferred and preference stock	0	0	(270,000,000)
Short-term borrowings	0	(150,000,000)	(550,000,000)
Senior notes	(500,000,000)	(1,500,000,000)	(450,000,000)
Pollution control revenue bonds	(223,000,000)	(469,000,000)	(65,000,000)
Other long-term debt	0	(100,000,000)	0
Payment of common stock dividends	(1,576,000,000)	(1,396,000,000)	(1,281,000,000)
Premiums on redemption and repurchases of senior notes	0	(152,000,000)	0
Other financing activities	(40,000,000)	(20,000,000)	(60,000,000)
Net cash provided from (used for) financing activities	918,000,000	(400,000,000)	(151,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(60,000,000)	(740,000,000)	849,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	112,000,000	852,000,000	3,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	52,000,000	112,000,000	852,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	373,000,000	408,000,000	386,000,000
Income taxes (net of refunds)	110,000,000	300,000,000	496,000,000
Noncash transactions —
Accrued property additions at year-end	560,000,000	683,000,000	550,000,000
Mississippi Power
Operating Activities:
Consolidated net income	139,000,000	236,000,000	(2,588,000,000)
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	197,000,000	177,000,000	198,000,000
Deferred income taxes	37,000,000	475,000,000	(727,000,000)
Allowance for equity funds used during construction	(1,000,000)	0	(72,000,000)
Pension and postretirement funding	(54,000,000)	0	0
Settlement of asset retirement obligations	(35,000,000)	(35,000,000)	(23,000,000)
Estimated loss on plants under construction	15,000,000	33,000,000	3,179,000,000
Other, net	21,000,000	18,000,000	(8,000,000)
Changes in certain current assets and liabilities —
-Receivables	6,000,000	(19,000,000)	540,000,000
-Fossil fuel for generation	(6,000,000)	(3,000,000)	24,000,000
-Other current assets	(2,000,000)	(7,000,000)	(13,000,000)
-Accounts payable	3,000,000	15,000,000	(3,000,000)
-Accrued taxes	11,000,000	(46,000,000)	80,000,000
-Other current liabilities	(20,000,000)	(41,000,000)	(4,000,000)
-Prepaid income taxes	12,000,000	(12,000,000)	0
-Accrued interest	0	(1,000,000)	(29,000,000)
-Over recovered regulatory clause revenues	16,000,000	14,000,000	(51,000,000)
Net cash provided from operating activities	339,000,000	804,000,000	503,000,000
Investing Activities:
Property additions	(202,000,000)	(188,000,000)	(429,000,000)
Change in construction payables, net	(1,000,000)	4,000,000	(47,000,000)
Payments pursuant to LTSAs	(23,000,000)	(29,000,000)	(10,000,000)
Other investing activities	(37,000,000)	(19,000,000)	(18,000,000)
Net cash used for investing activities	(263,000,000)	(232,000,000)	(504,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	0	(4,000,000)	(18,000,000)
Proceeds —
Short-term borrowings	0	300,000,000	109,000,000
Senior notes	0	600,000,000	0
Pollution control revenue bonds	43,000,000	0	0
Capital contributions from parent company	51,000,000	15,000,000	1,002,000,000
Long-term debt issuance to parent company	0	0	40,000,000
Redemptions and repurchases —
Preferred and preference stock	0	(33,000,000)	0
Short-term borrowings	0	(300,000,000)	(109,000,000)
Senior notes	(25,000,000)	(155,000,000)	(35,000,000)
Pollution control revenue bonds	0	(43,000,000)	0
Long-term debt to parent company	0	0	(591,000,000)
Capital leases	0	0	(71,000,000)
Other long-term debt	0	(900,000,000)	(300,000,000)
Return of capital to parent company	(150,000,000)	0	0
Other financing activities	(2,000,000)	(7,000,000)	(2,000,000)
Net cash provided from (used for) financing activities	(83,000,000)	(527,000,000)	25,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(7,000,000)	45,000,000	24,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	293,000,000	248,000,000	224,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	286,000,000	293,000,000	248,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	71,000,000	80,000,000	65,000,000
Income taxes (net of refunds)	(27,000,000)	(525,000,000)	(424,000,000)
Noncash transactions —
Accrued property additions at year-end	35,000,000	35,000,000	32,000,000
Southern Power
Operating Activities:
Consolidated net income	329,000,000	246,000,000	1,117,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	505,000,000	524,000,000	536,000,000
Deferred income taxes	(74,000,000)	(244,000,000)	(263,000,000)
Utilization of federal investment tax credits	734,000,000	5,000,000	0
Amortization of investment tax credits	(151,000,000)	(58,000,000)	(57,000,000)
Pension and postretirement funding	(24,000,000)	0	0
Income taxes receivable, non-current	25,000,000	42,000,000	(61,000,000)
Impairment charges	3,000,000	156,000,000	0
(Gain) loss on dispositions, net	23,000,000	2,000,000	0
Accrued income taxes, non-current	0	(14,000,000)	14,000,000
Other, net	(33,000,000)	7,000,000	(13,000,000)
Changes in certain current assets and liabilities —
-Receivables	72,000,000	(20,000,000)	(60,000,000)
-Other current assets	(8,000,000)	(26,000,000)	(28,000,000)
-Accrued taxes	6,000,000	7,000,000	(55,000,000)
-Other current liabilities	(38,000,000)	(19,000,000)	1,000,000
-Prepaid income taxes	39,000,000	25,000,000	24,000,000
Net cash provided from operating activities	1,385,000,000	631,000,000	1,155,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(50,000,000)	(65,000,000)	(1,016,000,000)
Property additions	(489,000,000)	(315,000,000)	(268,000,000)
Proceeds from dispositions and asset sales	572,000,000	203,000,000	0
Investments in unconsolidated subsidiaries	(116,000,000)	0	0
Change in construction payables, net of joint owner portion	7,000,000	(6,000,000)	(153,000,000)
Payments pursuant to LTSAs and for equipment not yet received	(104,000,000)	(75,000,000)	(203,000,000)
Other investing activities	13,000,000	31,000,000	15,000,000
Net cash used for investing activities	(167,000,000)	(227,000,000)	(1,625,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	449,000,000
Increase (decrease) in notes payable, net		(105,000,000)	(104,000,000)
Proceeds —
Short-term borrowings	100,000,000	200,000,000	0
Senior notes	0	0	525,000,000
Other long-term debt	0	0	43,000,000
Capital contributions from parent company	64,000,000	2,000,000	0
Redemptions and repurchases —
Short-term borrowings	(100,000,000)	(100,000,000)	0
Senior notes	(600,000,000)	(350,000,000)	(500,000,000)
Other long-term debt	0	(420,000,000)	(18,000,000)
Return of capital to parent company	(755,000,000)	(1,650,000,000)	0
Distributions to noncontrolling interests	(256,000,000)	(153,000,000)	(119,000,000)
Capital contributions from noncontrolling interests	196,000,000	2,551,000,000	80,000,000
Purchase of membership interests from noncontrolling interests	0	0	(59,000,000)
Payment of common stock dividends	(206,000,000)	(312,000,000)	(317,000,000)
Other financing activities	(12,000,000)	(26,000,000)	(33,000,000)
Net cash provided from (used for) financing activities	(1,120,000,000)	(363,000,000)	(502,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	98,000,000	41,000,000	(972,000,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	181,000,000	140,000,000	1,112,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	279,000,000	181,000,000	140,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	167,000,000	173,000,000	189,000,000
Income taxes (net of refunds)	(664,000,000)	79,000,000	(487,000,000)
Noncash transactions —
Accrued property additions at year-end	57,000,000	31,000,000	32,000,000
Southern Company Gas
Operating Activities:
Consolidated net income	585,000,000	372,000,000	243,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	487,000,000	500,000,000	501,000,000
Deferred income taxes	213,000,000	(1,000,000)	236,000,000
Pension and postretirement funding	(145,000,000)	0	0
Impairment charges	115,000,000	42,000,000	0
(Gain) loss on dispositions, net	0	(291,000,000)	0
Mark-to-market adjustments	(56,000,000)	(19,000,000)	(24,000,000)
Other, net	(55,000,000)	(24,000,000)	(51,000,000)
Changes in certain current assets and liabilities —
-Receivables	467,000,000	(218,000,000)	(94,000,000)
-Natural gas for sale	44,000,000	49,000,000	36,000,000
-Other current assets	31,000,000	4,000,000	(24,000,000)
-Accounts payable	(520,000,000)	372,000,000	(20,000,000)
-Accrued taxes	(69,000,000)	10,000,000	110,000,000
-Other current liabilities	(71,000,000)	(22,000,000)	(8,000,000)
-Prepaid income taxes	40,000,000	(42,000,000)	(39,000,000)
-Accrued compensation	1,000,000	32,000,000	15,000,000
Net cash provided from operating activities	1,067,000,000	764,000,000	881,000,000
Investing Activities:
Property additions	(1,408,000,000)	(1,388,000,000)	(1,514,000,000)
Proceeds from dispositions and asset sales	32,000,000	2,609,000,000	0
Cost of removal, net of salvage	(82,000,000)	(96,000,000)	(66,000,000)
Change in construction payables, net	24,000,000	(37,000,000)	72,000,000
Investments in unconsolidated subsidiaries	(31,000,000)	(110,000,000)	(145,000,000)
Returned investment in unconsolidated subsidiaries	67,000,000	20,000,000	80,000,000
Other investing activities	12,000,000	0	5,000,000
Net cash used for investing activities	(1,386,000,000)	998,000,000	(1,568,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	0		262,000,000
Increase (decrease) in notes payable, net		(868,000,000)
Proceeds —
First mortgage bonds	300,000,000	300,000,000	400,000,000
Senior notes	0	0	450,000,000
Capital contributions from parent company	821,000,000	24,000,000	103,000,000
Redemptions and repurchases —
Gas facility revenue bonds	0	(200,000,000)	0
Medium-term notes	0	0	(22,000,000)
Senior notes	(300,000,000)	(155,000,000)	0
First mortgage bonds	(50,000,000)	0	0
Return of capital to parent company	0	(400,000,000)	0
Payment of common stock dividends	(471,000,000)	(468,000,000)	(443,000,000)
Other financing activities	(2,000,000)	(3,000,000)	(9,000,000)
Net cash provided from (used for) financing activities	298,000,000	(1,770,000,000)	741,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(21,000,000)	(8,000,000)	54,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	70,000,000	78,000,000	24,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	49,000,000	70,000,000	78,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	251,000,000	249,000,000	223,000,000
Income taxes (net of refunds)	(41,000,000)	524,000,000	72,000,000
Noncash transactions —
Accrued property additions at year-end	$ 122,000,000	$ 97,000,000	$ 135,000,000

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net cash paid for capitalized interest	$ 74	$ 72	$ 89
Alabama Power
Net cash paid for capitalized interest	19	22	15
Georgia Power
Net cash paid for capitalized interest	35	26	23
Mississippi Power
Net cash paid for capitalized interest	(1)	0	29
Southern Power
Net cash paid for capitalized interest	15	17	11
Southern Company Gas
Net cash paid for capitalized interest	$ 6	$ 7	$ 11

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 1,975	$ 1,396
Receivables —
Customer accounts receivable	1,614	1,726
Energy marketing receivable	428	801
Unbilled revenues	599	654
Under recovered fuel clause revenues	0	115
Other accounts and notes receivable	817	813
Accumulated provision for uncollectible accounts	(49)	(50)
Materials and supplies	1,388	1,465
Fossil fuel for generation	521	405
Natural gas for sale	479	524
Prepaid expenses	314	432
Regulatory assets – asset retirement obligations	287	0
Assets from risk management activities, net of collateral	183	222
Other regulatory assets	885	525
Assets held for sale	188	393
Other current assets	188	162
Total current assets	9,817	9,583
Property, Plant, and Equipment:
In service	105,114	103,706
Less: Accumulated depreciation	30,765	31,038
Plant in service, net of depreciation	74,349	72,668
Nuclear fuel, at amortized cost	851	875
Construction work in progress	7,880	7,254
Total property, plant, and equipment	83,080	80,797
Other Property and Investments:
Goodwill	5,280	5,315
Equity investments in unconsolidated subsidiaries	1,303	1,580
Other intangible assets, net of amortization	536	613
Nuclear decommissioning trusts, at fair value	2,036	1,721
Leveraged leases	788	798
Miscellaneous property and investments	391	269
Total other property and investments	10,334	10,296
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,800
Deferred charges related to income taxes	798	794
Unamortized loss on reacquired debt	300	323
Regulatory assets – asset retirement obligations, deferred	4,094	2,933
Other regulatory assets, deferred	6,805	5,375
Assets held for sale, deferred	601	5,350
Other deferred charges and assets	1,071	1,463
Total deferred charges and other assets	15,469	16,238
Total Assets	118,700	116,914
Current Liabilities:
Securities due within one year	2,989	3,198
Notes payable	2,055	2,915
Accounts payable —
Energy marketing trade payables	442	856
Accounts payable	2,115	2,580
Customer deposits	496	522
Accrued income taxes	0	21
Other accrued taxes	659	635
Accrued interest	474	472
Accrued compensation	992	1,030
Asset retirement obligations	504	404
Other regulatory liabilities	756	376
Liabilities held for sale	5	425
Operating lease obligations	229
Other current liabilities	830	852
Total current liabilities	12,546	14,286
Long-Term Debt:
Unamortized debt premium (discount), net	152	158
Unamortized debt issuance expense	(247)	(208)
Total long-term debt	41,798	40,736
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	7,888	6,558
Deferred credits related to income taxes	6,078	6,460
Accumulated deferred ITCs	2,291	2,372
Employee benefit obligations	1,814	2,147
Operating lease obligations, deferred	1,615
Asset retirement obligations, deferred	9,282	8,990
Accrued environmental remediation	234	268
Other cost of removal obligations	2,239	2,297
Other regulatory liabilities, deferred	256	169
Liabilities held for sale, deferred	0	2,836
Other deferred credits and liabilities	609	465
Total deferred credits and other liabilities	32,306	32,562
Total Liabilities	86,650	87,584
Common Stockholder's Equity:
Common stock	5,257	5,164
Paid-in capital	11,734	11,094
Retained earnings	10,877	8,706
Accumulated other comprehensive income (loss)	(321)	(203)
Total common stockholders' equity	27,505	24,723
Redeemable Preferred Stock of Subsidiaries	291	291
Total Stockholders' Equity	31,759	29,039
Total Liabilities and Stockholder's Equity	118,700	116,914
Commitments and Contingent Matters
Alabama Power
Current Assets:
Cash and cash equivalents	894	313
Receivables —
Customer accounts receivable	425	403
Unbilled revenues	134	150
Other accounts and notes receivable	72	51
Affiliated	37	94
Accumulated provision for uncollectible accounts	(22)	(10)
Materials and supplies	512	546
Fossil fuel for generation	212	141
Prepaid expenses	50	66
Other regulatory assets	242	137
Other current assets	30	18
Total current assets	2,586	1,909
Property, Plant, and Equipment:
In service	30,023	30,402
Less: Accumulated depreciation	9,540	9,988
Plant in service, net of depreciation	20,483	20,414
Nuclear fuel, at amortized cost	296	324
Construction work in progress	890	1,113
Total property, plant, and equipment	21,669	21,851
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	66	65
Nuclear decommissioning trusts, at fair value	1,023	847
Miscellaneous property and investments	128	127
Total other property and investments	1,217	1,039
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	132
Deferred charges related to income taxes	244	240
Deferred under recovered regulatory clause revenues	40	116
Regulatory assets – asset retirement obligations, deferred	1,019	147
Other regulatory assets, deferred	1,976	1,240
Other deferred charges and assets	269	188
Total deferred charges and other assets	3,680	1,931
Total Assets	29,152	26,730
Current Liabilities:
Securities due within one year	251	201
Accounts payable —
Affiliated	316	364
Other	514	614
Customer deposits	100	96
Accrued income taxes	78	44
Accrued interest	92	89
Accrued compensation	216	227
Asset retirement obligations	195	163
Other regulatory liabilities	193	116
Operating lease obligations	49
Other current liabilities	105	45
Total current liabilities	2,060	1,959
Long-Term Debt:
Unamortized debt premium (discount), net	14	12
Unamortized debt issuance expense	(55)	(54)
Total long-term debt	8,270	7,923
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,260	2,962
Deferred credits related to income taxes	1,960	2,027
Accumulated deferred ITCs	100	106
Employee benefit obligations	206	314
Operating lease obligations, deferred	107
Asset retirement obligations, deferred	3,345	3,047
Other cost of removal obligations	412	497
Other regulatory liabilities, deferred	146	69
Other deferred credits and liabilities	40	58
Total deferred credits and other liabilities	9,576	9,080
Total Liabilities	19,906	18,962
Redeemable Preferred Stock	291	291
Common Stockholder's Equity:
Common stock	1,222	1,222
Paid-in capital	4,755	3,508
Retained earnings	3,001	2,775
Accumulated other comprehensive income (loss)	(23)	(28)
Total common stockholders' equity	8,955	7,477
Redeemable Preferred Stock of Subsidiaries	291	291
Total Stockholders' Equity	8,955	7,477
Total Liabilities and Stockholder's Equity	29,152	26,730
Commitments and Contingent Matters
Georgia Power
Current Assets:
Cash and cash equivalents	52	4
Restricted cash and cash equivalents	0	108
Receivables —
Customer accounts receivable	533	591
Unbilled revenues	203	208
Under recovered fuel clause revenues	0	115
Joint owner accounts receivable	136	170
Other accounts and notes receivable	209	80
Affiliated	21	39
Accumulated provision for uncollectible accounts	(2)	(2)
Materials and supplies	501	519
Fossil fuel for generation	272	231
Prepaid expenses	63	142
Regulatory assets – storm damage reserves	213	30
Regulatory assets – asset retirement obligations	254	0
Other regulatory assets	263	169
Other current assets	77	70
Total current assets	2,795	2,474
Property, Plant, and Equipment:
In service	38,137	37,675
Less: Accumulated depreciation	11,753	12,096
Plant in service, net of depreciation	26,384	25,579
Nuclear fuel, at amortized cost	555	550
Construction work in progress	5,650	4,833
Total property, plant, and equipment	32,589	30,962
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	52	51
Nuclear decommissioning trusts, at fair value	1,013	873
Miscellaneous property and investments	64	72
Total other property and investments	1,129	996
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,428
Deferred charges related to income taxes	519	517
Regulatory assets – asset retirement obligations, deferred	2,865	2,644
Other regulatory assets, deferred	2,716	2,258
Other deferred charges and assets	500	514
Total deferred charges and other assets	8,028	5,933
Total Assets	44,541	40,365
Current Liabilities:
Securities due within one year	1,025	617
Notes payable	365	294
Accounts payable —
Affiliated	512	575
Other	711	890
Customer deposits	283	276
Other accrued taxes	407	377
Accrued interest	118	105
Accrued compensation	233	221
Asset retirement obligations	265	202
Other regulatory liabilities	447	169
Operating lease obligations	144
Other current liabilities	187	183
Total current liabilities	4,697	3,909
Long-Term Debt:
Unamortized debt premium (discount), net	7	6
Unamortized debt issuance expense	(117)	(108)
Total long-term debt	10,791	9,364
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,257	3,062
Deferred credits related to income taxes	2,862	3,080
Accumulated deferred ITCs	255	262
Employee benefit obligations	540	599
Operating lease obligations, deferred	1,282
Asset retirement obligations, deferred	5,519	5,627
Accrued environmental remediation	0	0
Other deferred credits and liabilities	273	139
Total deferred credits and other liabilities	13,988	12,769
Total Liabilities	29,476	26,042
Common Stockholder's Equity:
Common stock	398	398
Paid-in capital	10,962	10,322
Retained earnings	3,756	3,612
Accumulated other comprehensive income (loss)	(51)	(9)
Total common stockholders' equity	15,065	14,323
Total Stockholders' Equity	15,065	14,323
Total Liabilities and Stockholder's Equity	44,541	40,365
Commitments and Contingent Matters
Mississippi Power
Current Assets:
Cash and cash equivalents	286	293
Receivables —
Customer accounts receivable	35	34
Unbilled revenues	39	41
Other accounts and notes receivable	26	31
Affiliated	27	21
Materials and supplies	61	53
Fossil fuel for generation	26	20
Other regulatory assets	99	116
Prepaid income taxes	0	12
Other current assets	10	7
Total current assets	609	628
Property, Plant, and Equipment:
In service	4,857	4,900
Less: Accumulated depreciation	1,463	1,429
Plant in service, net of depreciation	3,394	3,471
Construction work in progress	126	103
Total property, plant, and equipment	3,520	3,574
Other Property and Investments:
Total other property and investments	131	24
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	6
Deferred charges related to income taxes	32	33
Regulatory assets – asset retirement obligations, deferred	210	143
Other regulatory assets, deferred	360	331
Accumulated deferred income taxes	139	150
Other deferred charges and assets	34	3
Total deferred charges and other assets	775	660
Total Assets	5,035	4,886
Current Liabilities:
Securities due within one year	281	40
Accounts payable —
Affiliated	76	60
Other	75	90
Accrued income taxes	105	95
Accrued interest	15	15
Accrued compensation	35	38
Accrued plant closure costs	15	29
Asset retirement obligations	33	34
Other regulatory liabilities	21	12
Over recovered regulatory clause liabilities	29	14
Operating lease obligations	2
Other current liabilities	49	28
Total current liabilities	734	455
Long-Term Debt:
Unamortized debt premium (discount), net	(19)	(27)
Unamortized debt issuance expense	(8)	(8)
Total long-term debt	1,308	1,539
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	424	378
Deferred credits related to income taxes	352	382
Employee benefit obligations	99	115
Operating lease obligations, deferred	4
Asset retirement obligations, deferred	157	126
Other cost of removal obligations	189	185
Other regulatory liabilities, deferred	76	81
Other deferred credits and liabilities	44	16
Total deferred credits and other liabilities	1,341	1,283
Total Liabilities	3,383	3,277
Common Stockholder's Equity:
Common stock	38	38
Paid-in capital	4,449	4,546
Retained earnings	(2,832)	(2,971)
Accumulated other comprehensive income (loss)	(3)	(4)
Total common stockholders' equity	1,652	1,609
Total Stockholders' Equity	1,652	1,609
Total Liabilities and Stockholder's Equity	5,035	4,886
Commitments and Contingent Matters
Southern Power
Current Assets:
Cash and cash equivalents	279	181
Receivables —
Customer accounts receivable	107	111
Other accounts and notes receivable	73	116
Affiliated	30	55
Materials and supplies	191	220
Prepaid income taxes	36	25
Other current assets	43	37
Total current assets	759	745
Property, Plant, and Equipment:
In service	13,270	13,271
Less: Accumulated depreciation	2,464	2,171
Plant in service, net of depreciation	10,806	11,100
Construction work in progress	515	430
Total property, plant, and equipment	11,321	11,530
Other Property and Investments:
Intangible assets, net of amortization	322	345
Miscellaneous property and investments	28	0
Total other property and investments	350	345
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	369
Prepaid LTSAs	128	98
Income taxes receivable, non-current	5	30
Assets held for sale, deferred	601	576
Accumulated deferred income taxes	551	1,186
Other deferred charges and assets	216	373
Total deferred charges and other assets	1,870	2,263
Total Assets	14,300	14,883
Current Liabilities:
Securities due within one year	824	599
Notes payable	549	100
Accounts payable —
Affiliated	56	92
Other	85	77
Accrued income taxes	26	6
Accrued interest	32	36
Operating lease obligations	22
Other current liabilities	132	121
Total current liabilities	1,704	1,031
Long-Term Debt:
Unamortized debt premium (discount), net	(8)	(9)
Unamortized debt issuance expense	(19)	(23)
Total long-term debt	3,574	4,418
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	115	105
Accumulated deferred ITCs	1,731	1,832
Operating lease obligations, deferred	376
Other deferred credits and liabilities	178	213
Total deferred credits and other liabilities	2,400	2,150
Total Liabilities	7,678	7,599
Common Stockholder's Equity:
Common stock	0	0
Paid-in capital	909	1,600
Retained earnings	1,485	1,352
Accumulated other comprehensive income (loss)	(26)	16
Total common stockholders' equity	2,368	2,968
Noncontrolling Interests	4,254	4,316
Total Stockholders' Equity	6,622	7,284
Total Liabilities and Stockholder's Equity	14,300	14,883
Commitments and Contingent Matters
Southern Power | 2.375% due 2020
Long-Term Debt:
Senior notes	0	300
Southern Power | 2.50% due 2021
Long-Term Debt:
Senior notes	300	300
Southern Power | 1.00% due 2022
Long-Term Debt:
Senior notes	674	687
Southern Power | 2.75% due 2023
Long-Term Debt:
Senior notes	290	290
Southern Power | Weighted average interest rate 4.12% at 12/31/19 due 2025-2046
Long-Term Debt:
Senior notes	2,337	2,348
Southern Power | Variable rate (3.34% at 12/31/18) due 2020
Long-Term Debt:
Other long-term debt	0	525
Southern Company Gas
Current Assets:
Cash and cash equivalents	46	64
Receivables —
Customer accounts receivable	323	370
Energy marketing receivable	428	801
Unbilled revenues	183	213
Other accounts and notes receivable	114	142
Affiliated	5	11
Accumulated provision for uncollectible accounts	(18)	(30)
Natural gas for sale	479	524
Prepaid expenses	65	118
Assets from risk management activities, net of collateral	177	219
Other regulatory assets	92	73
Assets held for sale	171	0
Other current assets	41	50
Total current assets	2,106	2,555
Property, Plant, and Equipment:
In service	16,344	15,177
Less: Accumulated depreciation	4,650	4,400
Plant in service, net of depreciation	11,694	10,777
Construction work in progress	613	580
Total property, plant, and equipment	12,307	11,357
Other Property and Investments:
Goodwill	5,015	5,015
Equity investments in unconsolidated subsidiaries	1,251	1,538
Other intangible assets, net of amortization	70	101
Miscellaneous property and investments	20	20
Total other property and investments	6,356	6,674
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	93
Other regulatory assets, deferred	618	669
Other deferred charges and assets	207	193
Total deferred charges and other assets	918	862
Total Assets	21,687	21,448
Current Liabilities:
Securities due within one year	0	357
Notes payable	650	650
Accounts payable —
Affiliated	41	45
Other	315	402
Energy marketing trade payables	442	856
Customer deposits	96	133
Accrued income taxes	0	66
Other accrued taxes	71	75
Accrued interest	52	55
Accrued compensation	100	100
Other regulatory liabilities	94	79
Liabilities from risk management activities	21	76
Operating lease obligations	14
Other current liabilities	128	130
Total current liabilities	2,010	3,024
Long-Term Debt:
Total long-term debt	5,845	5,583
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,219	1,016
Deferred credits related to income taxes	874	940
Employee benefit obligations	265	357
Operating lease obligations, deferred	78
Accrued environmental remediation	233	268
Other cost of removal obligations	1,606	1,585
Other deferred credits and liabilities	51	105
Total deferred credits and other liabilities	4,326	4,271
Total Liabilities	12,181	12,878
Common Stockholder's Equity:
Paid-in capital	9,697	8,856
Retained earnings	(198)	(312)
Accumulated other comprehensive income (loss)	7	26
Total common stockholders' equity	9,506	8,570
Total Stockholders' Equity	9,506	8,570
Total Liabilities and Stockholder's Equity	21,687	21,448
Commitments and Contingent Matters

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accumulated Amortization	$ 280	$ 235
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Southern Power
Accumulated Amortization	$ 69	$ 61
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares outstanding (in shares)	1,000	1,000
Southern Power | 2.375% due 2020
Fixed stated interest rate of debt obligation	2.375%	2.375%
Southern Power | 2.50% due 2021
Fixed stated interest rate of debt obligation	2.50%	2.50%
Southern Power | 1.00% due 2022
Fixed stated interest rate of debt obligation	1.00%	1.00%
Southern Power | 2.75% due 2023
Fixed stated interest rate of debt obligation	2.75%	2.75%
Southern Power | Variable rate (3.34% at 12/31/18) due 2020
Fixed stated interest rate of debt obligation		3.34%
Southern Company Gas
Accumulated Amortization	$ 176	$ 145
Common stock, par value (in dollars per share)	$ 0.01	$ 10,000
Common stock, shares authorized (in shares)	100,000,000	100
Common stock, shares outstanding (in shares)	100	100
Weighted Average | Southern Power | Weighted average interest rate 4.12% at 12/31/19 due 2025-2046
Fixed stated interest rate of debt obligation	4.12%
Minimum | Southern Power | Weighted average interest rate 4.12% at 12/31/19 due 2025-2046
Fixed stated interest rate of debt obligation	1.85%	0.00%
Maximum | Southern Power | Weighted average interest rate 4.12% at 12/31/19 due 2025-2046
Fixed stated interest rate of debt obligation	5.25%	0.00%

Consolidated Statements of Capi

Consolidated Statements of Capitalization - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Maturity
2020	$ 2,991
2021	3,214
2022	2,003
2023	2,413
2024	492
Total long-term senior notes and debt	30,377	$ 34,025
Pollution control revenue bonds —
Total other long-term debt	13,947	10,684
Unamortized fair value adjustment of long-term debt	430	474
Finance lease obligations	226
Finance lease obligations		197
Unamortized debt premium (discount), net	(152)	(158)
Unamortized debt issuance expense	(247)	(208)
Total long-term debt	44,787	45,220
Amount due within one year	2,989	3,198
Amount held for sale	0	1,286
Long-term debt excluding amounts due within one year and held for sale	$ 41,798	$ 40,736
Percent capitalization	56.60%	58.10%
Cumulative preferred stock
Redeemable preferred stock	$ 291	$ 291
Total redeemable preferred stock - percent capitalization	0.40%	0.40%
Common Stockholders' Equity:
Common stock	$ 5,257	$ 5,164
Paid-in capital	11,734	11,094
Treasury, at cost	(42)	(38)
Retained earnings	10,877	8,706
Accumulated other comprehensive loss	(321)	(203)
Total common stockholders' equity	$ 27,505	$ 24,723
Total common stockholders' equity - percent capitalization	37.20%	35.30%
Total preferred and preference stock of subsidiaries - percent capitalization	5.80%	6.20%
Total Stockholders' Equity	$ 31,759	$ 29,039
Total Capitalization	$ 73,848	$ 70,066
Percent capitalization	100.00%	100.00%
Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Cumulative preferred stock
Redeemable preferred stock	$ 48	$ 48
Redeemable Preferred Stock, $1 par value | Cumulative preferred stock
Cumulative preferred stock
Redeemable preferred stock	243	243
Noncontrolling interests
Common Stockholders' Equity:
Total preferred and preference stock of subsidiaries and noncontrolling interests	$ 4,254	4,316
Long-term debt payable to affiliated trusts — variable rate due 2042
Weighted average interest rate	5.20%
Long-Term Debt:
Long-term debt payable to affiliated trusts, variable rate due 2042	$ 206	206
Long-term senior notes and debt matured in 2019 | Senior Notes
Maturity
2019	$ 0	2,948
Long-term senior notes and debt maturing 2020 | Senior Notes
Weighted average interest rate	2.43%
Maturity
2020	$ 2,100	2,271
Long-term senior notes and debt maturing 2021 | Senior Notes
Weighted average interest rate	2.70%
Maturity
2021	$ 2,672	2,638
Long-term senior notes and debt maturing 2021 | Adjustable Rate Loans
Weighted average interest rate	2.50%
Maturity
2020	$ 800	1,875
Long-term senior notes and debt maturing 2022 | Senior Notes
Weighted average interest rate	2.53%
Maturity
2022	$ 1,870	1,983
Long-term senior notes and debt maturing 2022 | Adjustable Rate Loans
Weighted average interest rate	2.42%
Maturity
2021	$ 125	125
Long-term senior notes and debt maturing 2023 | Senior Notes
Weighted average interest rate	3.05%
Maturity
2023	$ 2,290	2,290
Long-term senior notes and debt maturing 2024 | Senior Notes
Weighted average interest rate	2.20%
Maturity
2024	$ 400	0
Long-term senior notes and debt maturing 2025-2049 | Senior Notes
Weighted average interest rate	4.27%
Maturity
thereafter	$ 20,120	19,895
Pollution control revenue bonds due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	$ 0	25
Pollution control revenue bonds due 2022
Weighted average interest rate	2.35%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 53	90
Pollution control revenue bonds due 2023
Pollution control revenue bonds —
Pollution control revenue bonds	$ 0	33
Pollution control revenue bonds due 2025 through 2053
Weighted average interest rate	2.40%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 1,466	1,112
Pollution control revenue bonds - variable rates due 2020
Weighted average interest rate	1.80%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 7	148
Pollution control revenue bonds - variable rates due 2021
Weighted average interest rate	1.75%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 65	65
Pollution control revenue bonds - variable rates due 2022
Pollution control revenue bonds —
Pollution control revenue bonds	$ 0	4
Pollution control revenue bonds - variable rates due 2024
Weighted average interest rate	1.72%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 21	21
Pollution control revenue bonds - variable rates due 2025-2052
Weighted average interest rate	1.69%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 1,351	1,396
Plant Daniel revenue bonds due 2021
Weighted average interest rate	7.13%
Pollution control revenue bonds —
Plant Daniel revenue bonds due 2021	$ 270	270
FFB loans — due 2020
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
FFB loans — due 2021
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
FFB loans — due 2022
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
FFB loans — due 2023
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
FFB loans — due 2024
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
FFB loans — due 2025-2044
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 3,523	2,405
First mortgage bonds — due 2019
Pollution control revenue bonds —
First mortgage bonds	$ 0	50
First mortgage bonds — due 2023
Weighted average interest rate	5.80%
Pollution control revenue bonds —
First mortgage bonds	$ 50	50
First mortgage bonds — due 2026-2059
Weighted average interest rate	3.94%
Pollution control revenue bonds —
First mortgage bonds	$ 1,525	1,225
Junior subordinated notes due 2024 | Junior Subordinated Debt
Weighted average interest rate	2.70%
Pollution control revenue bonds —
Junior subordinated notes	$ 863	0
Junior subordinated notes due 2027 to 2077 | Junior Subordinated Debt
Weighted average interest rate	5.00%
Pollution control revenue bonds —
Junior subordinated notes	$ 4,433	3,570
Alabama Power
Maturity
2020	251
2021	311
2022	751
2023	301
2024	22
Total long-term notes payable	7,320	6,920
Pollution control revenue bonds —
Total other long-term debt	1,060	1,060
Finance lease obligations	4
Finance lease obligations		4
Unamortized debt premium (discount), net	(14)	(12)
Unamortized debt issuance expense	(55)	(54)
Total long-term debt	8,521	8,124
Amount due within one year	251	201
Long-term debt excluding amounts due within one year and held for sale	$ 8,270	$ 7,923
Percent capitalization	47.20%	50.40%
Cumulative preferred stock
Redeemable preferred stock	$ 291	$ 291
Total redeemable preferred stock - percent capitalization	1.70%	1.90%
Common Stockholders' Equity:
Common stock	$ 1,222	$ 1,222
Paid-in capital	4,755	3,508
Retained earnings	3,001	2,775
Accumulated other comprehensive loss	(23)	(28)
Total common stockholders' equity	$ 8,955	$ 7,477
Total common stockholders' equity - percent capitalization	51.10%	47.70%
Total Stockholders' Equity	$ 8,955	$ 7,477
Total Capitalization	$ 17,516	$ 15,691
Percent capitalization	100.00%	100.00%
Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Cumulative preferred stock
Redeemable preferred stock	$ 48	$ 48
Alabama Power | Redeemable Preferred Stock, $1 par value | Cumulative preferred stock
Cumulative preferred stock
Redeemable preferred stock	$ 243	243
Alabama Power | Long-term debt payable to affiliated trusts — variable rate due 2042
Weighted average interest rate	5.20%
Long-Term Debt:
Long-term debt payable to affiliated trusts, variable rate due 2042	$ 206	206
Alabama Power | Long-term senior notes and debt matured in 2019 | Senior Notes
Maturity
2019	$ 0	200
Alabama Power | Long-term senior notes and debt maturing 2020 | Senior Notes
Weighted average interest rate	3.38%
Maturity
2020	$ 250	250
Alabama Power | Long-term senior notes and debt maturing 2021 | Senior Notes
Weighted average interest rate	3.81%
Maturity
2021	$ 220	220
Alabama Power | Long-term senior notes and debt maturing 2022 | Senior Notes
Weighted average interest rate	3.36%
Maturity
2022	$ 750	750
Alabama Power | Long-term senior notes and debt maturing 2023 | Senior Notes
Weighted average interest rate	3.55%
Maturity
2023	$ 300	300
Alabama Power | Long-term senior notes and debt maturing 2025-2049 | Senior Notes
Weighted average interest rate	4.41%
Maturity
thereafter	$ 5,775	5,175
Alabama Power | Long-term senior notes and debt, variable rate due 2021 | Adjustable Rate Loans
Weighted average interest rate	2.90%
Maturity
2021	$ 25	25
Alabama Power | Pollution control revenue bonds due 2034
Weighted average interest rate	2.46%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 207	207
Alabama Power | Pollution control revenue bonds - variable rates due 2021
Weighted average interest rate	1.75%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 65	65
Alabama Power | Pollution control revenue bonds - variable rates due 2024
Weighted average interest rate	1.72%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 21	21
Alabama Power | Pollution control revenue bonds - variable rates due 2028-2038
Weighted average interest rate	1.65%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 767	767
Georgia Power
Maturity
2020	1,025
2021	397
2022	527
2023	175
2024	477
Total long-term notes payable	5,850	5,598
Pollution control revenue bonds —
Total other long-term debt	5,934	4,355
Finance lease obligations	156
Finance lease obligations		142
Unamortized debt premium (discount), net	(7)	(6)
Unamortized debt issuance expense	(117)	(108)
Total long-term debt	11,816	9,981
Amount due within one year	1,025	617
Long-term debt excluding amounts due within one year and held for sale	$ 10,791	$ 9,364
Percent capitalization	41.70%	39.50%
Common Stockholders' Equity:
Common stock	$ 398	$ 398
Paid-in capital	10,962	10,322
Retained earnings	3,756	3,612
Accumulated other comprehensive loss	(51)	(9)
Total common stockholders' equity	$ 15,065	$ 14,323
Total common stockholders' equity - percent capitalization	58.30%	60.50%
Total Stockholders' Equity	$ 15,065	$ 14,323
Total Capitalization	$ 25,856	$ 23,687
Percent capitalization	100.00%	100.00%
Georgia Power | Long-term senior notes and debt matured in 2019
Maturity
2019	$ 0	$ 498
Georgia Power | Long-term senior notes and debt maturing 2020 | Senior Notes
Weighted average interest rate	2.00%
Maturity
2020	$ 950	950
Georgia Power | Long-term senior notes and debt maturing 2021 | Senior Notes
Weighted average interest rate	2.40%
Maturity
2021	$ 325	325
Georgia Power | Long-term senior notes and debt maturing 2022 | Senior Notes
Weighted average interest rate	2.85%
Maturity
2022	$ 400	400
Georgia Power | Long-term senior notes and debt maturing 2023 | Senior Notes
Weighted average interest rate	5.75%
Maturity
2023	$ 100	100
Georgia Power | Long-term senior notes and debt maturing 2024 | Senior Notes
Weighted average interest rate	2.20%
Maturity
2024	$ 400	0
Georgia Power | Long-term senior notes and debt maturing 2026-2043 | Senior Notes
Weighted average interest rate	4.21%
Maturity
thereafter	$ 3,675	3,325
Georgia Power | Pollution control revenue bonds due 2022
Weighted average interest rate	2.35%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 53	53
Georgia Power | Pollution control revenue bonds due 2025 through 2053
Weighted average interest rate	2.37%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 1,217	748
Georgia Power | Pollution control revenue bonds - variable rates due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	$ 0	108
Georgia Power | Pollution control revenue bonds - variable rates due 2026-2052
Weighted average interest rate	1.74%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 551	551
Georgia Power | FFB loans — due 2020
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
Georgia Power | FFB loans — due 2021
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
Georgia Power | FFB loans — due 2022
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
Georgia Power | FFB loans — due 2023
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
Georgia Power | FFB loans — due 2024
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 64	44
Georgia Power | FFB loans — due 2025-2044
Weighted average interest rate	3.20%
Pollution control revenue bonds —
FFB loans	$ 3,523	2,405
Georgia Power | Junior subordinated notes due 2077 | Junior Subordinated Debt
Weighted average interest rate	5.00%
Pollution control revenue bonds —
Junior subordinated notes	$ 270	270
Mississippi Power
Maturity
2020	281
2021	270
2022	0
2023	0
2024	0
Total long-term notes payable	1,225	1,250
Pollution control revenue bonds —
Total other long-term debt	353	310
Finance lease obligations	0
Unamortized debt premium (discount), net	19	27
Unamortized debt issuance expense	(8)	(8)
Total long-term debt	1,589	1,579
Amount due within one year	281	40
Long-term debt excluding amounts due within one year and held for sale	$ 1,308	$ 1,539
Percent capitalization	44.20%	48.90%
Common Stockholders' Equity:
Common stock	$ 38	$ 38
Paid-in capital	4,449	4,546
Retained earnings	(2,832)	(2,971)
Accumulated other comprehensive loss	(3)	(4)
Total common stockholders' equity	$ 1,652	$ 1,609
Total common stockholders' equity - percent capitalization	55.80%	51.10%
Total Stockholders' Equity	$ 1,652	$ 1,609
Total Capitalization	$ 2,960	$ 3,148
Percent capitalization	100.00%	100.00%
Mississippi Power | Long-term debt payable to affiliated trusts — variable rate due 2028-2042 | Senior Notes
Weighted average interest rate	4.16%
Maturity
thereafter	$ 950	$ 950
Mississippi Power | Long-term senior notes and debt maturing 2020 | Adjustable Rate Loans
Weighted average interest rate	2.59%
Maturity
2020	$ 275	300
Mississippi Power | Pollution control revenue bonds due 2028
Weighted average interest rate	3.20%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 43	0
Mississippi Power | Pollution control revenue bonds - variable rates due 2020
Weighted average interest rate	1.80%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 7	40
Mississippi Power | Pollution control revenue bonds - variable rates due 2025-2028
Weighted average interest rate	1.80%
Pollution control revenue bonds —
Pollution control revenue bonds	$ 33	0
Mississippi Power | Plant Daniel revenue bonds due 2021
Weighted average interest rate	7.13%
Pollution control revenue bonds —
Plant Daniel revenue bonds due 2021	$ 270	270
Southern Company Gas
Maturity
2020	0
2021	330
2022	46
2023	400
2024	0
Total long-term notes payable	3,860	4,160
Pollution control revenue bonds —
Total other long-term debt	1,575	1,325
Unamortized fair value adjustment of long-term debt	430	474
Finance lease obligations	0
Unamortized debt discount	(20)	(19)
Total long-term debt	5,845	5,940
Amount due within one year	0	357
Long-term debt excluding amounts due within one year and held for sale	$ 5,845	$ 5,583
Percent capitalization	38.10%	39.40%
Common Stockholders' Equity:
Paid-in capital	$ 9,697	$ 8,856
Retained earnings	(198)	(312)
Accumulated other comprehensive loss	7	26
Total common stockholders' equity	$ 9,506	$ 8,570
Total common stockholders' equity - percent capitalization	61.90%	60.60%
Total Stockholders' Equity	$ 9,506	$ 8,570
Total Capitalization	$ 15,351	$ 14,153
Percent capitalization	100.00%	100.00%
Southern Company Gas | Long-term senior notes and debt matured in 2019 | Senior Notes
Maturity
2019	$ 0	$ 300
Southern Company Gas | Long-term senior notes and debt maturing 2021 | Senior Notes
Weighted average interest rate	4.01%
Maturity
2021	$ 330	330
Southern Company Gas | Long-term senior notes and debt maturing 2022 | Senior Notes
Weighted average interest rate	8.63%
Maturity
2022	$ 46	46
Southern Company Gas | Long-term senior notes and debt maturing 2023 | Senior Notes
Weighted average interest rate	2.45%
Maturity
2023	$ 350	350
Southern Company Gas | Long-term senior notes and debt maturing 2025-2047 | Senior Notes
Weighted average interest rate	4.68%
Maturity
thereafter	$ 3,134	3,134
Southern Company Gas | First mortgage bonds — due 2019
Pollution control revenue bonds —
First mortgage bonds	$ 0	50
Southern Company Gas | First mortgage bonds — due 2023
Weighted average interest rate	5.80%
Pollution control revenue bonds —
First mortgage bonds	$ 50	50
Southern Company Gas | First mortgage bonds — due 2026-2059
Weighted average interest rate	3.94%
Pollution control revenue bonds —
First mortgage bonds	$ 1,525	$ 1,225

Consolidated Statements of Ca_3

Consolidated Statements of Capitalization (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
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	1,000,000,000
Treasury shares (in shares)	1,000,000	1,000,000
Redeemable Preferred Stock, $100 par or stated value
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	475,115	475,115
Redeemable Preferred Stock, $1 par value
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, dividend rate	5.00%	5.00%
Redeemable cumulative preferred stock, shares authorized (in shares)	28,000,000	28,000,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	10,000,000	10,000,000
Redeemable Preferred Stock
Annual dividend requirement	$ 15,000,000	$ 15,000,000
Alabama Power
Common stock, par value (in dollars per share)	$ 40	$ 40
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares outstanding (in shares)	30,537,500	30,537,500
Alabama Power | 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
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	3,850,000	3,850,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	475,115	475,115
Alabama Power | Redeemable Preferred Stock, $1 par value | Cumulative preferred stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, dividend rate	5.00%	5.00%
Redeemable cumulative preferred stock, shares authorized (in shares)	27,500,000	27,500,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	10,000,000	10,000,000
Alabama Power | Redeemable Preferred Stock, $25 stated value | Cumulative preferred stock
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Georgia Power
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	9,261,500	9,261,500
Mississippi Power
Common stock, shares authorized (in shares)	1,130,000	1,130,000
Common stock, shares outstanding (in shares)	1,121,000	1,121,000
Southern Company Gas
Common stock, par value (in dollars per share)	$ 0.01	$ 10,000
Common stock, shares authorized (in shares)	100,000,000	100
Common stock, shares outstanding (in shares)	100	100
Minimum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%
Minimum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%	4.20%
Maximum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.92%
Maximum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.92%	4.92%

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)	Preferred and Preference Stock of Subsidiaries	Noncontrolling Interests	[1]	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 PowerCommon Stock	Southern PowerPaid-In Capital		Southern PowerRetained Earnings	Southern PowerAccumulated Other Comprehensive Income (Loss)	Southern PowerTotal Common Stockholder's Equity		Southern PowerNoncontrolling Interests	[2]	Southern Company Gas	Southern Company GasCommon Stock	Southern Company GasPaid-In Capital	Southern Company GasRetained Earnings	Southern Company GasAccumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2016			991	1								31					9					1						0										0
Beginning balance at Dec. 31, 2016		$ 26,612	$ 4,952	$ (31)	$ 9,661	$ 10,356	$ (180)	$ 609	$ 1,245		$ 6,323	$ 1,222	$ 2,613	$ 2,518	$ (30)	$ 11,356	$ 398	$ 6,885	$ 4,086	$ (13)	$ 2,943	$ 38	$ 3,525	$ (616)	$ (4)	$ 5,675		$ 0	$ 3,671		$ 724	$ 35	$ 4,430		$ 1,245		$ 9,109	$ 0	$ 9,095	$ (12)	$ 26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income attributable to Southern Company		842				842					848			848		1,414			1,414		(2,590)			(2,590)		1,071					1,071		1,071				243			243
Capital contributions from (to) parent company											373		373			443		443			1,004		1,004			(2)			(2)				(2)				117		117
Other comprehensive income (loss)		(9)					(9)				4				4	3				3						(10)						(10)	(10)				(5)				(5)
Stock issued (in shares)			18
Stock issued		793	$ 86		707
Stock-based compensation		105			105
Cash dividends on common stock		(2,300)				(2,300)					(714)			(714)		(1,281)			(1,281)							(317)					(317)		(317)				(443)			(443)
Other Comprehensive Income (Loss), Transfer from Service Company	[3]																									(27)						(27)	(27)
Preferred and preference stock redemptions		(609)						(609)
Contributions from noncontrolling interests		79							79																	79									79
Distributions to noncontrolling interests		122							122																	122									122
Net income attributable to noncontrolling interests		44							44																	(44)									(44)
Reclassification from redeemable noncontrolling interests		114							114																	114									114
Other		(21)		$ (5)	(4)	(13)			1		(5)			(5)		(4)			(4)		1			1		(7)			(7)				(7)				1		2		(1)
Ending balance (in shares) at Dec. 31, 2017			1,009	1								31					9					1						0										0
Ending balance at Dec. 31, 2017		25,528	$ 5,038	$ (36)	10,469	8,885	(189)	0	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		$ 0	3,662		1,478	(2)	5,138		1,360		9,022	$ 0	9,214	(212)	20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income attributable to Southern Company		2,226				2,226					930			930		793			793		235			235		187					187		187				372			372
Return of capital																										(1,650)			(1,650)				(1,650)				(400)		(400)
Capital contributions from (to) 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
Net income attributable to noncontrolling interests		58							58																	(59)									(59)
Sale of noncontrolling interests		1,273			(417)				1,690																	1,273	[4]		(417)	[4]			(417)	[4]	1,690	[4]
Other		(29)		$ (2)	(6)	20	40		(1)		(7)			(1)	(6)	(2)			0	2	(1)			(1)		5			3		1	(4)	6		1		0			(4)	4
Ending balance (in shares) at Dec. 31, 2018			1,035	1								31					9					1						0										0
Ending balance at Dec. 31, 2018		29,039	$ 5,164	$ (38)	11,094	8,706	(203)	0	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		$ 0	1,600		1,352	16	2,968		4,316		8,570	$ 0	8,856	(312)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income attributable to Southern Company		4,739				4,739					1,070			1,070		1,720			1,720		139			139		339					339		339				585			585
Return of capital																					(150)		(150)			(755)			(755)				(755)
Capital contributions from (to) 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	[5]	(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)
Net income attributable to noncontrolling interests		(10)							(10)																	10									10
Other		18		$ (4)	21				(1)		1			0	1											(1)									(1)
Ending balance (in shares) at Dec. 31, 2019			1,054	1								31					9					1						0										0
Ending balance at Dec. 31, 2019		$ 31,759	$ 5,257	$ (42)	$ 11,734	$ 10,877	$ (321)	$ 0	$ 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		$ 0	$ 909		$ 1,485	$ (26)	$ 2,368		$ 4,254		$ 9,506	$ 0	$ 9,697	$ (198)	$ 7
[1]	Excludes redeemable noncontrolling interests. See Note 7 to the financial statements under " Southern Power – Redeemable Noncontrolling Interests " for additional information.
[2]	Excludes redeemable noncontrolling interests. See Note 7 to the financial statements under "Noncontrolling Interests" for additional information.
[3]	In connection with Southern Power becoming a participant to the Southern Company qualified pension plan and other postretirement benefit plan, $27 million of other comprehensive income, net of tax of $9 million , was transferred from SCS.
[4]	See Note 15 under " Southern Power - Sales of Renewable Facility Interests " for additional information.
[5]	See Note 8 under " Equity Units " for additional information.

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash dividends (in dollars per share)	$ 2.4600	$ 2.3800	$ 2.3000
Other comprehensive income (loss), net of tax	$ (118)	$ 26	$ (9)
Pension and Other Postretirement Benefit Plans
Other comprehensive income (loss), net of tax	$ (60)
Pension and Other Postretirement Benefit Plans | SCS
Other comprehensive income (loss), net of tax			27
Other comprehensive income (loss), tax			$ 9

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2019
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. On January 1, 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 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 of and developing 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 at Southern Power and Southern Company Gas, as well as additional information regarding 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 partial 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 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 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. In addition, during 2018, Southern Company Gas recast its reportable segments. See Note 16 under " Southern Company Gas " for additional information. At December 31, 2019 and 2018, Southern Company and Southern Power each had assets and liabilities held for sale on their balance sheets. At December 31, 2019, Southern Company Gas had assets and liabilities held for sale on its balance sheet. Unless otherwise noted, the disclosures herein related to specific asset and liability balances at December 31, 2019 and 2018 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 See Note 4 for information on the Registrants' adoption of ASC 606, Revenue from Contracts with Customers (ASC 606) effective January 1, 2018. In 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged and there is no change to the accounting for existing leveraged leases. The Registrants adopted the new standard effective January 1, 2019. 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 2019 , 2018 , and 2017 were as follows: Alabama Georgia Mississippi Southern Power (*) Southern Company Gas (in millions) 2019 $ 527 $ 704 $ 118 $ 90 $ 183 2018 508 653 104 98 194 2017 479 625 140 218 63 (*) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. 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 2019 , 2018 , and 2017 amounted to $256 million , $247 million , and $248 million , respectively, for Alabama Power and $760 million , $780 million , and $675 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 Power Southern Power (in millions) 2019 $ 3 $ 14 2018 15 41 2017 16 27 Georgia Power has entered into several PPAs with Southern Power for capacity and energy. Georgia Power's total expenses associated with these PPAs were $177 million , $216 million , and $235 million in 2019 , 2018 , and 2017 , 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 $174 million , $215 million , and $233 million for 2019 , 2018 , and 2017 , respectively. Included within these revenues were affiliate PPAs accounted for as operating leases, which totaled $116 million , $65 million , and $81 million for 2019 , 2018 , and 2017 , 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. The interstate transportation service provided to Alabama Power, Georgia Power, Southern Power, and Southern Company Gas by SNG pursuant to these agreements is governed by the terms and conditions of SNG's natural gas tariff and is subject to FERC regulation. See Note 7 under " Southern Company Gas – Equity Method Investments – SNG " for additional information. Transportation costs under these agreements in 2019 , 2018 , and 2017 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2019 $ 17 $ 99 $ 28 $ 31 2018 8 101 25 32 2017 9 102 25 32 In November 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 2019 , 2018 , and 2017 : Georgia Southern Power (in millions) 2019 $ 4 $ 64 2018 21 119 2017 22 119 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 , $8 million , and $9 million in 2019 , 2018 , and 2017 , respectively. See Note 5 under " Joint Ownership Agreements " for additional information. Alabama Power has an agreement with Gulf Power under which Alabama Power made transmission system upgrades to ensure firm delivery of energy under a non-affiliate PPA from a combined cycle plant located in Autauga County, Alabama. Under a related tariff, Alabama Power received $11 million in each of 2018 and 2017 . See Note 15 under " Southern Company " for information regarding the sale of Gulf Power. Alabama Power has agreements with PowerSecure for services related to utility infrastructure construction, distributed energy, and energy efficiency projects. Costs for these services amounted to approximately $7 million , $24 million , and $11 million in 2019 , 2018 , and 2017 , respectively. 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. Georgia Power has a joint ownership agreement with Gulf Power under which Gulf Power owns a 25% portion of Plant Scherer Unit 3. Under this agreement, 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 were $8 million and $11 million in 2018 and 2017, respectively. See Note 5 under " Joint Ownership Agreements " and Note 15 under " Southern Company " for additional information. Mississippi Power has an agreement with Gulf Power under which Gulf Power owns a portion of Plant Daniel. 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 each of 2018 and 2017 . See Note 5 under " Joint Ownership Agreements " and Note 15 under " Southern Company " for additional information. Southern Power has several agreements with SCS for transmission services. Transmission services purchased by Southern Power from SCS totaled $15 million , $12 million , and $13 million for 2019 , 2018 , and 2017 , respectively, and were charged to other operations and maintenance expenses in Southern Power's consolidated statements of income. All charges were billed to Southern Power based on the Southern Company Open Access Transmission Tariff as filed with the FERC. 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 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 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 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 ASC 606, lease, derivative, and regulatory accounting. Other than the timing of recognition of guaranteed and fixed billing arrangements at Southern Company Gas, the adoption of ASC 606 in 2018 had no impact on the timing or amount of revenue recognized under previous guidance. See Note 4 for information regarding the Registrants' adoption of ASC 606 and related disclosures. Traditional Electric Operating Companies The majority of the revenues of the traditional electric operating companies are generated from contracts with retail electric customers. Retail revenues recognized under ASC 606 are consistent with prior revenue recognition policies. 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 billings 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 either on a levelized basis over the appropriate contract period or the amount billable under the contract terms. Energy and other revenues are generally recognized as services are provided. The accounting for these revenues under ASC 606 is consistent with prior revenue recognition policies. 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 generally have a right to consideration in an amount that corresponds directly with the value to the customer of the entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice and has elected to recognize revenue for its sales of electricity and capacity using the invoice practical expedient. In addition, payment for goods and services rendered is typically due in the subsequent month following satisfaction of the Registrants' performance obligation. 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 entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice. In addition, 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. The natural gas market for Atlanta Gas Light was deregulated in 1997. Accordingly, Marketers, 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 is recognized as a single performance obligation satisfied over time and is 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 generally has a right to consideration in an amount that corresponds directly with the value to the customer of the entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice and has elected to recognize revenue for its sales of natural gas using the invoice practical expedient. In addition, payment for goods and services rendered is typically due in the subsequent month following satisfaction of 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 monthly 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. Prior to the sale of Pivotal Home Solutions in 2018, revenues for warranty and repair contracts were recognized on a straight-line basis over the contract term while revenues for maintenance services were recognized at the time such services were performed. See Note 15 under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. Concentration of Revenue Southern Company, Alabama Power, Georgia Power, Mississippi Power (with the exception of its 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 serves long-term contracts with rural electric cooperative associations and municipalities located in southeastern Mississippi under cost-based MRA electric tariffs, which are subject to regulation by the FERC. The contracts with these wholesale customers represent ed 15.7% of Mississippi Power 's total operating revenues in 2019 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: 2019 2018 2017 Georgia Power 9.0 % 9.8 % 11.3 % Duke Energy Corporation N/A 6.8 % 6.7 % Southern California Edison 6.8 % 6.2 % N/A Morgan Stanley Capital Group 4.9 % N/A 4.5 % On January 29, 2019, Pacific Gas & Electric Company (PG&E) filed petitions to reorganize under Chapter 11 of the U.S. Bankruptcy Code. Southern Power, together with its noncontrolling partners, owns four solar facilities where PG&E is the energy off-taker for approximately 207 MWs of capacity under long-term PPAs. PG&E is also the transmission provider for these four facilities and two of Southern Power's other solar facilities. At December 31, 2019, Southern Power had outstanding accounts receivables due from PG&E of $2 million related to the PPAs and $33 million related to the transmission interconnections (of which $27 million is classified in receivables – other and $6 million is classified in other deferred charges and assets). Subsequent to December 31, 2019, Southern Power received $15 million in accordance with a November 2019 bankruptcy court order granting payment of transmission interconnections for amounts due and owing. Southern Power continues to evaluate the recoverability of its investments in these solar facilities under various scenarios, including selling the related energy into the competitive markets, and has concluded that these solar facilities are not impaired. PG&E has continued to perform under the terms of the PPAs. Southern Power does not expect a material impact to its financial statements if, as a result of the bankruptcy proceedings, PG&E does not perform in accordance with the PPAs or the terms of the PPAs are renegotiated; however, the ultimate outcome of this matter cannot be determined at this time. 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

REGULATORY MATTERS

REGULATORY MATTERS	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
REGULATORY MATTERS	REGULATORY MATTERS Southern Company Regulatory Assets and Liabilities Regulatory assets and (liabilities) reflected in the consolidated balance sheets of Southern Company at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 4,423 $ 3,658 (a,o) Asset retirement obligations-asset 4,381 2,933 (b,o) Remaining net book value of retired assets 1,275 211 (c) Deferred income tax charges 803 799 (b,n) Property damage reserves-asset 410 416 (d) Environmental remediation-asset 349 366 (e,o) Loss on reacquired debt 323 346 (f) Under recovered regulatory clause revenues 254 407 (g) Vacation pay 186 182 (h,o) Long-term debt fair value adjustment 107 121 (i) Other regulatory assets 492 581 (j) Deferred income tax credits (6,301 ) (6,455 ) (b,n) Other cost of removal obligations (2,084 ) (2,297 ) (b) Customer refunds (285 ) (293 ) (k) Over recovered regulatory clause revenues (205 ) (47 ) (g) Property damage reserves-liability (204 ) (76 ) (l) Other regulatory liabilities (86 ) (132 ) (m) Total regulatory assets (liabilities), net $ 3,838 $ 720 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the respective PSC or regulatory agency and are as follows: (a) Recovered and amortized over the average remaining service period, which may range up to 15 years . See Note 11 for additional information. (b) AROs and other cost of removal obligations are recorded, deferred income tax assets are recovered, and deferred income tax liabilities are amortized over the related property lives, which may range up to 80 years . Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. Included in the deferred income tax assets is $23 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Amortized over periods not exceeding 18 years . (d) Effective January 1, 2020, Georgia Power is recovering approximately $213 million annually for storm damage. See " Georgia Power – Rate Plans – 2019 ARP " and " – Storm Damage Recovery " herein for additional information. (e) Recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 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, 2019 , the remaining amortization periods do not exceed 34 years . (g) Recorded and recovered or amortized over periods generally not exceeding six years . (h) Recorded as earned by employees and recovered as paid, generally within one year . (i) Recovered over the remaining life of the original debt issuances at acquisition, which range up to 19 years as of December 31, 2019 . (j) Comprised of numerous immaterial components including nuclear outage costs, fuel-hedging losses, cancelled construction projects, property tax, and other miscellaneous assets. These costs are amortized over remaining periods generally not exceeding eight years as of December 31, 2019 . (k) At December 31, 2019 and 2018, primarily includes approximately $53 million and $109 million , respectively, at Alabama Power and $110 million and $100 million , respectively, at Georgia Power as a result of each company exceeding its allowed retail return range, as well as approximately $105 million and $55 million , respectively, pursuant to the Georgia Power Tax Reform Settlement Agreement. See " Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (l) Amortized as related expenses are incurred. See " Alabama Power – Rate NDR " and " Mississippi Power – System Restoration Rider " herein for additional information. (m) Comprised of numerous components including building leases, fuel-hedging gains, and other liabilities that are recovered over remaining periods not exceeding 20 years . (n) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, including $778 million of liabilities being amortized over periods not exceeding six years as of December 31, 2019 . See " Georgia Power ," " Mississippi Power ," and " Southern Company Gas " herein and Note 10 for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Gulf Power On January 1, 2019, Southern Company completed its sale of Gulf Power to NextEra Energy. See Note 15 under " Southern Company " for additional information. In accordance with a Florida PSC-approved settlement agreement, Gulf Power's rates effective for the first billing cycle in July 2017 increased by approximately $54 million annually (2017 Gulf Power Rate Case Settlement Agreement), including a $62 million increase in base revenues, less an $8 million purchased power capacity cost recovery clause credit. The 2017 Gulf Power Rate Case Settlement Agreement also resulted in a $32.5 million write-down of Gulf Power's ownership of Plant Scherer Unit 3, which was recorded in the first quarter 2017. As a continuation of the 2017 Gulf Power Rate Case Settlement Agreement, in March 2018, the Florida PSC approved a stipulation and settlement agreement addressing Gulf Power's retail revenue requirement effects of the Tax Reform Legislation (Gulf Power Tax Reform Settlement Agreement). Beginning on April 1, 2018, the Gulf Power Tax Reform Settlement Agreement resulted in annual reductions of approximately $18 million to Gulf Power's base rates and approximately $16 million to Gulf Power's environmental cost recovery rates and a one-time refund of approximately $69 million for the retail portion of unprotected (not subject to normalization) deferred tax liabilities, which was credited to customers through Gulf Power's fuel cost recovery rates over the remainder of 2018. Alabama Power Regulatory Assets and Liabilities Regulatory assets and (liabilities) reflected in the balance sheets of Alabama Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,131 $ 947 (a,o) Asset retirement obligations 1,043 147 (b) Deferred income tax charges 245 241 (b,c,d) (Over) under recovered regulatory clause revenues (72 ) 176 (e) Regulatory clauses 142 142 (f) Vacation pay 72 71 (g,o) Loss on reacquired debt 52 56 (h) Nuclear outage 78 49 (i) Remaining net book value of retired assets 649 43 (j) Other regulatory assets 67 57 (k,l) Deferred income tax credits (1,960 ) (2,027 ) (b,d) Other cost of removal obligations (412 ) (497 ) (b) Customer refunds (56 ) (142 ) (m) Natural disaster reserve (150 ) (20 ) (n) Other regulatory liabilities (19 ) (12 ) (l) Total regulatory assets (liabilities), net $ 810 $ (769 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) have been accepted or approved by the Alabama PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 14 years . See Note 11 for additional information. (b) Asset retirement and removal assets and liabilities are recorded, deferred income tax assets are recovered, and deferred income tax credits are amortized over the related property lives, which may range up to 53 years . Asset retirement and other cost of removal assets and liabilities will be settled and trued up following completion of the related activities. (c) Included in the deferred income tax charges are $9 million for 2019 and $10 million for 2018 for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (d) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization. The recovery and amortization of these amounts will occur ratably over the related property lives, which may range up to 53 years . See Note 10 for additional information. (e) Recorded monthly and expected to be recovered or returned within three years . See " Rate CNP PPA ," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) In accordance with an accounting order issued in 2017 by the Alabama PSC, these regulatory assets will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2019 , the remaining amortization periods do not exceed 30 years . (i) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent 18 -month period. (j) Recorded and amortized over remaining periods not exceeding 18 years . (k) Comprised of components including generation site selection/evaluation costs, which are capitalized upon initiation of related construction projects, if applicable, and PPA capacity costs, which are to be recovered over the next 12 months . (l) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three and a half years. Upon final settlement, actual costs incurred are recovered through the energy cost recovery clause. (m) Includes $53 million for 2019 and $109 million for 2018 due to the retail return exceeding the allowed range. The December 31, 2018 balance also includes a $33 million excess deferred tax liability used to increase the Rate NDR balance in 2019. See "Rate RSE," "Rate NDR," and " Tax Reform Accounting Order " herein for additional information. (n) Amortized as expenses are incurred. See "Rate NDR" herein for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Petition for Certificate of Convenience and Necessity On September 6, 2019, Alabama Power filed a petition for a CCN with the Alabama PSC for authorization to procure additional generating capacity through the turnkey construction of a new combined cycle facility and long-term contracts for the purchase of power from others, both as more fully described below, as well as the acquisition of an existing combined cycle facility in Autauga County, Alabama (Autauga Combined Cycle Acquisition). In addition, Alabama Power will pursue approximately 200 MWs of certain demand side management and distributed energy resource programs. This filing 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 regarding the Autauga Combined Cycle Acquisition. The procurement of these resources is subject to the satisfaction or waiver of certain conditions, including, among other customary conditions, approval by the Alabama PSC. The completion of the Autauga Combined Cycle Acquisition is also subject to approval by the FERC. Alabama Power expects to obtain all regulatory approvals by the end of the third quarter 2020. On May 8, 2019, Alabama Power entered into an Agreement for Engineering, Procurement, and Construction with Mitsubishi Hitachi Power Systems Americas, Inc. and Black & Veatch Construction, Inc. to construct an approximately 720 -MW combined cycle facility at Plant Barry (Plant Barry Unit 8), which is expected to be placed in service by the end of 2023. The capital investment associated with the construction of Plant Barry Unit 8 and the Autauga Combined Cycle Acquisition is currently estimated to total approximately $1.1 billion . Alabama Power entered into additional long-term PPAs totaling approximately 640 MWs of generating capacity consisting of approximately 240 MWs of combined cycle generation expected to begin later in 2020 and approximately 400 MWs of solar generation coupled with battery energy storage systems (solar/battery systems) expected to begin in 2022 through 2024. The terms of the agreements for the solar/battery systems permit Alabama Power to use the energy and retire the associated renewable energy credits (REC) in service of customers or to sell RECs, separately or bundled with energy. Upon certification, Alabama Power expects to recover costs associated with Plant Barry Unit 8 pursuant to its Rate CNP New Plant. Additionally, Alabama Power expects to recover costs associated with the Autauga Combined Cycle Acquisition through the inclusion in Rate RSE of revenues from the existing power sales agreement and, on expiration of that agreement, 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 the Autauga Combined Cycle Acquisition and Plant Barry Unit 8 will be incorporated through the annual filing of Rate RSE. The ultimate outcome of these matters cannot be determined at this time. Construction Work in Progress Accounting Order On October 1, 2019, the Alabama PSC acknowledged that Alabama Power would begin certain limited preparatory activities associated with Plant Barry Unit 8 construction to meet the target in-service date by authorizing Alabama Power to record the related costs as CWIP prior to the issuance of an order on the CCN petition. Should a CCN not be granted and Alabama Power does not proceed with the related construction of Plant Barry Unit 8, Alabama Power may transfer those costs and any costs that directly result from the non-issuance of the CCN to a regulatory asset which would be amortized over a five-year period. If the balance of incurred costs reaches 5% of the estimated in-service cost of the total project prior to issuance of an order on the CCN petition, Alabama Power will confer with the Alabama PSC regarding the appropriateness of additional authorization. The Sierra Club subsequently filed a petition for reconsideration of the accounting order. The Alabama PSC voted to deny the petition for reconsideration on January 7, 2020. 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. If Alabama Power's actual retail return is above the allowed WCER range, the excess will be refunded to customers unless otherwise directed by the Alabama PSC; however, there is no provision for additional customer billings should the actual retail return fall below the WCER range. Prior to January 2019, retail rates remained unchanged when the WCER range was between 5.75% and 6.21% . Effective in January 2017, Rate RSE increased 4.48% , or $245 million annually. At December 31, 2017, Alabama Power's actual retail return was within the allowed WCER range. Retail rates under Rate RSE were unchanged for 2018. In conjunction 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. In May 2018, the Alabama PSC approved modifications to Rate RSE and other commitments designed to position Alabama Power to address the growing pressure on its credit quality resulting from the Tax Reform Legislation, without increasing retail rates under Rate RSE in the near term. Alabama Power plans to reduce growth in total debt by increasing equity, with corresponding reductions in debt issuances, thereby de-leveraging its capital structure. Alabama Power's goal is to achieve an equity ratio of approximately 55% by the end of 2025. At December 31, 2019 and 2018, Alabama Power's equity ratio was approximately 50% and 47% , 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. The modifications to the refund mechanism allow Alabama Power to retain a portion of the revenue that causes the actual WCER for a given year to exceed the allowed range. Generally, 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% . In conjunction with these modifications to Rate RSE, in May 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. 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 on February 5, 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. On November 27, 2019, Alabama Power made its required annual Rate RSE submission to the Alabama PSC of projected data for calendar year 2020. Projected earnings were within the specified range; therefore, retail rates under Rate RSE remain unchanged for 2020. 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. The ultimate outcome of this matter cannot be determined at this time. At December 31, 2019, Alabama Power's WCER exceeded 6.15% , resulting in Alabama Power establishing a current regulatory liability of $53 million for Rate RSE refunds, which will be refunded to customers through bill credits in April 2020. 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 2017 through 2019. 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. No adjustments to Rate CNP PPA occurred during the period 2017 through 2019 and no adjustment is expected for 2020. At December 31, 2019 and 2018 , Alabama Power had an under recovered Rate CNP PPA balance of $40 million and $25 million , respectively, which is included in other regulatory assets, deferred on Southern Company's balance sheets and deferred under recovered regulatory clause revenues on Alabama Power's balance sheets. 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, Alabama Power submitted calculations associated with its cost of complying with governmental mandates, as provided under Rate CNP Compliance. The filing reflected a projected under recovered retail revenue requirement for governmental mandates of approximately $205 million , which was recovered in the billing months of January 2019 through December 2019. On November 27, 2019, Alabama Power submitted calculations associated with its cost of complying with governmental mandates, as provided under Rate CNP Compliance. The filing reflected a projected over recovered retail revenue requirement for governmental mandates, which resulted in a rate decrease of approximately $68 million that became effective for the billing month of January 2020. 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, compared to an under recovered balance of $42 million at December 31, 2018 included in customer accounts receivable 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 on February 5, 2019, Alabama Power utilized $78 million of the 2018 Rate RSE refund liability to reduce the Rate ECR under recovered balance. On December 3, 2019, the Alabama PSC approved a decrease to Rate ECR from 2.353 to 2.160 cents per KWH, equal to 1.82% , or approximately $102 million annually, effective January 1, 2020. The rate will adjust to 5.910 cents per KWH in January 2021 absent a further order from the Alabama PSC. 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 Southern Company's and Alabama Power's balance sheets. At December 31, 2018, Alabama Power's under recovered fuel costs totaled $109 million , of which $18 million is included in customer accounts receivable and $91 million is included in deferred under recovered regulatory clause revenues on Southern Company's and Alabama Power's balance sheets. 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 material impact on the timing of any recovery or return of fuel costs. Tax Reform Accounting Order In May 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. On December 3, 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 On February 5, 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. 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 amounts as circumstances warrant. The order allows for reliability-related expenditures to be charged against the additional accruals when the NDR balance exceeds $75 million . Alabama Power may designate a portion of the NDR to reliability-related expenditures as a part of an annual budget process for the following year or during the current year for identified unbudgeted reliability-related expenditures that are incurred. Accruals that have not been designated can be used to offset storm charges. Additional accruals to the NDR enhance Alabama Power's ability to mitigate the financial effects of future natural disasters, promote system reliability, and offset costs retail customers would otherwise bear. There were no such accruals in 2017 and 2018. As discussed herein under "Tax Reform Accounting Order," in accordance with an Alabama PSC order issued on December 3, 2019, Alabama Power applied the remaining excess deferred income tax regulatory liability balance of approximately $39 million to increase the balance in the NDR. Alabama Power also accrued an additional $84 million to the NDR in December 2019 resulting in an accumulated balance of $150 million at December 31, 2019. Of this amount, Alabama Power designated $37 million to be applied to budgeted reliability-related expenditures for 2020, which is included in other regulatory liabilities, current. The remaining NDR balance of $113 million is included in other regulatory liabilities, deferred on the balance sheet. In December 2017, the reserve maintenance charge was suspended and the reserve establishment charge was activated and collected approximately $16 million annually through 2019. Effective with the March 2020 billings, the reserve establishment charge will be suspended and the reserve maintenance charge will be activated as a result of the NDR balance exceeding $75 million . Alabama Power expects to collect approximately $5 million in 2020 and $3 million annually thereafter unless the NDR balance falls below $50 million . As revenue from the Rate NDR charge is recognized, an equal amount of operations and maintenance expenses related to the NDR will also be recognized. As a result, the Rate NDR charge will not have an effect on net income but will impact operating cash flows. Environmental Accounting Order Based on an order from the Alabama PSC (Environmental Accounting Order), Alabama Power is allowed to establish a regulatory asset to record the unrecovered investment costs, including the unrecovered plant asset balance and the unrecovered costs associated with site removal and closure associated with future unit retirements caused by environmental regulations. The regulatory asset is being amortized and recovered over the affected unit's remaining useful life, as established prior to the decision regarding early retirement through Rate CNP Compliance. On April 15, 2019, Alabama Power retired Plant Gorgas Units 8, 9, and 10 and reclassified approximately $654 million of the unrecovered asset balances to regulatory assets, which are being recovered over the units' remaining useful lives, the latest being through 2037, as established prior to the decision to retire. At December 31, 2019, the related regulatory assets totaled $649 million , of which $63 million is included in other regulatory assets, current and $586 million is included in other regulatory assets, deferred on the balance sheet. Additionally, approximately $700 million of net capitalized asset retirement costs were reclassified to a regulatory asset in accordance with accounting guidance provided by the Alabama PSC. The asset retirement costs are being recovered through 2055. Georgia Power Regulatory Assets and Liabilities Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,516 $ 1,295 (a, m) Asset retirement obligations 3,119 2,644 (b, m) Deferred income tax charges 523 522 (b, c, m) Storm damage reserves 410 416 (d) Remaining net book value of retired assets 596 127 (e) Loss on reacquired debt 262 277 (f, m) Vacation pay 93 91 (g, m) Other cost of removal obligations 156 68 (b) Environmental remediation 52 55 (h) Fuel-hedging (realized and unrealized) losses 53 15 (i, m) Other regulatory assets 50 120 (j) Deferred income tax credits (3,078 ) (3,080 ) (b, c) Customer refunds (229 ) (165 ) (k) Other regulatory liabilities (16 ) (7 ) (l, m) Total regulatory assets (liabilities), net $ 3,507 $ 2,378 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the Georgia PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may ra

CONTINGENCIES, COMMITMENTS, AND

CONTINGENCIES, COMMITMENTS, AND GUARANTEES	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
CONTINGENCIES, COMMITMENTS, AND GUARANTEES	CONTINGENCIES, COMMITMENTS, AND GUARANTEES General Litigation Matters The Registrants are involved in various other 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 against Southern Company, certain of its officers, and certain former Mississippi Power officers in the U.S. District Court for the Northern District of Georgia by Monroe County Employees' Retirement System on behalf of all persons who purchased shares of Southern Company's common stock between April 25, 2012 and October 29, 2013. The complaint alleges that Southern Company, certain of its officers, and certain former Mississippi Power officers made materially false and misleading statements regarding the Kemper County energy facility in violation of certain provisions under the Securities Exchange Act of 1934, as amended. The complaint seeks, among other things, compensatory damages and litigation costs and attorneys' fees. In 2017, the plaintiffs filed an amended complaint that provided additional detail about their claims, increased the purported class period by one day, and added certain other former Mississippi Power officers as defendants. Also in 2017, the defendants filed a motion to dismiss the plaintiffs' amended complaint with prejudice, to which the plaintiffs filed an opposition. In March 2018, the court issued an order granting, in part, the defendants' motion to dismiss. The court dismissed certain claims against certain officers of Southern Company and Mississippi Power and dismissed the allegations related to a number of the statements that plaintiffs challenged as being false or misleading. In April 2018, the defendants filed a motion for reconsideration of the court's order, seeking dismissal of the remaining claims in the lawsuit. In August 2018, the court denied the motion for reconsideration and denied a motion to certify the issue for interlocutory appeal. On August 22, 2019, the court certified the plaintiffs' proposed class. On September 5, 2019, the defendants filed a petition for interlocutory appeal of the class certification order with the U.S. Court of Appeals for the Eleventh Circuit. On December 19, 2019, the U.S. District Court for the Northern District of Georgia entered an order staying all deadlines in the case pending mediation. The stay automatically expires on March 31, 2020. 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 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. Each plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and, on each plaintiff's own behalf, attorneys' fees and costs in bringing the lawsuit. Each plaintiff also seeks certain changes to Southern Company's corporate governance and internal processes. In April 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the securities class action. 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 officers, and certain former Mississippi Power officers. The complaint alleges that the individual defendants, among other things, breached their fiduciary duties in connection with schedule delays and cost overruns associated with the construction of the Kemper County energy facility. The complaint further alleges that the individual defendants authorized or failed to correct false and misleading statements regarding the Kemper County energy facility schedule and cost and failed to implement necessary internal controls to prevent harm to Southern Company. The plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and disgorgement of profits and, on its behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiff also seeks certain unspecified changes to Southern Company's corporate governance and internal processes. In May 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the securities class action. On August 5, 2019, the court granted a motion filed by the plaintiff on July 17, 2019 to substitute a new named plaintiff, Martin J. Kobuck, in place of Helen E. Piper Survivor's Trust. 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 tort law claims. In 2016, the Georgia Court of Appeals reversed the trial court's previous dismissal of the case and remanded the case to the trial court. Georgia Power filed a petition for writ of certiorari with the Georgia Supreme Court, which was granted in 2017. In June 2018, the Georgia Supreme Court affirmed the judgment of the Georgia Court of Appeals and remanded the case to the trial court for further proceedings. Following a motion by Georgia Power, on February 13, 2019, the Superior Court of Fulton County ordered the parties to submit petitions to the Georgia PSC for a declaratory ruling to address certain terms the court previously held were ambiguous as used in the Georgia PSC's orders. The order entered by the Superior Court of Fulton County 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. On October 23, 2019, the Georgia PSC issued an order that found and concluded that Georgia Power has appropriately implemented the municipal franchise fee schedule. On March 6, 2019, Georgia Power filed a notice of appeal with the Georgia Court of Appeals regarding the Superior Court of Fulton County's February 2019 order. The amount of any possible losses cannot be calculated at this time because, among other factors, it is unknown whether conditional class certification will be upheld and the ultimate composition of any class and whether any losses would be subject to recovery from any municipalities. Mississippi Power In May 2018, Southern Company and Mississippi Power received a notice of dispute and arbitration demand filed by Martin Product Sales, LLC (Martin) based on two agreements, both related to Kemper IGCC byproducts for which Mississippi Power provided termination notices in 2017. Martin alleges breach of contract, breach of good faith and fair dealing, fraud and misrepresentation, and civil conspiracy and makes a claim for damages in the amount of approximately $143 million , as well as additional unspecified damages, attorney's fees, costs, and interest. A portion of the claim for damages was on behalf of Martin Transport, Inc. (Martin Transport), an affiliate of Martin. In the first quarter 2019, Mississippi Power and Southern Company filed motions to dismiss, which were denied by the arbitration panel on May 10, 2019. On September 27, 2019, Martin Transport filed a separate complaint against Mississippi Power in the Circuit Court of Kemper County, Mississippi alleging claims of fraud, negligent misrepresentation, promissory estoppel, and equitable estoppel, each arising out of the same alleged facts and circumstances that underlie Martin's arbitration demand. Martin Transport seeks compensatory damages of $5 million and punitive damages of $50 million . In November 2019, Martin Transport's claim was combined with the Martin arbitration case and the separate court case was dismissed. On December 16, 2019, Southern Company and Mississippi Power each filed motions for summary judgment on all claims. On February 17, 2020, the arbitration panel granted Southern Company's motion and dismissed Southern Company from the arbitration. An adverse outcome in this proceeding could have a material impact on Southern Company's and Mississippi Power's financial statements. In November 2018, Ray C. Turnage and 10 other individual plaintiffs filed a putative class action complaint against Mississippi Power and three 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 on March 14, 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 have each filed a motion to dismiss the amended complaint. An adverse outcome in this proceeding could have a material impact on Mississippi Power's financial statements. See Note 2 under " Kemper County Energy Facility " for additional information. Southern Power Southern Power indirectly owns a 51% membership interest in RE Roserock LLC (Roserock), the owner of the Roserock facility in Pecos County, Texas. Prior to the facility being placed in service in 2016, certain solar panels were damaged during installation by the construction contractor, McCarthy Building Companies, Inc. (McCarthy), and certain solar panels were damaged by a hail event that also occurred during construction. In connection therewith, Southern Power withheld payment of approximately $26 million to the construction contractor, which placed a lien on the Roserock facility for the same amount. In 2017, Roserock filed a lawsuit in the state district court in Pecos County, Texas against XL Insurance America, Inc. and North American Elite Insurance Company seeking recovery from an insurance policy for damages resulting from the hail event and McCarthy's installation practices. In June 2018, the court granted Roserock's motion for partial summary judgment, finding that the insurers were in breach of contract and in violation of the Texas Insurance Code for failing to pay any monies owed for the hail claim. Separate lawsuits were filed between Roserock and McCarthy, as well as other parties, and that litigation was consolidated in the U.S. District Court for the Western District of Texas. On April 18, 2019, Roserock and the parties to the state and federal lawsuits executed a settlement agreement and mutual release that resolved both lawsuits. Following execution of the agreement, the lawsuits were dismissed, Southern Power paid McCarthy the amounts previously withheld, and McCarthy released its lien. As part of the settlement, Roserock received funds that covered all related legal costs, damages, and the replacement costs of certain solar panels. Funds received by Southern Power in excess of the initial replacement costs were recognized as a gain and included in other income (expense), net, with a portion allocated to noncontrolling interests. As a result, Southern Power recognized a $12 million after-tax gain in the second quarter 2019. 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. 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 compliance costs through regulatory mechanisms. These regulatory mechanisms are adjusted annually or as necessary within limits approved by the state PSCs or other applicable state regulatory agencies. At December 31, 2019 and 2018 , the environmental remediation liabilities of Alabama Power and Mississippi Power were 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 all years presented, Georgia Power recovered approximately $2 million annually through the ECCR tariff. Effective January 1, 2020, Georgia Power is recovering approximately $12 million annually through the ECCR tariff under the 2019 ARP. Georgia Power recognizes a liability for environmental remediation costs only when it determines a loss is probable and reasonably estimable and reduces the reserve as expenditures are incurred. Any difference between the liabilities accrued and costs recovered through rates is deferred as a regulatory asset or liability. The annual recovery amount is expected to be adjusted in future regulatory proceedings. On December 23, 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 paid a civil penalty of $200,000 and 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, 2019 and 2018 was based on the estimated cost of environmental investigation and remediation associated with known current and former MGP operating sites. These environmental remediation expenditures are generally recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies of the natural gas distribution utilities. At December 31, 2019 and 2018 , the environmental remediation liability and the balance of under recovered environmental remediation costs were reflected in the balance sheets as follows: Southern Company Georgia Power Southern Company Gas (in millions) 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 December 31, 2018: Environmental remediation liability: Other current liabilities $ 49 $ 23 $ 26 Accrued environmental remediation 268 — 268 Under recovered environmental remediation costs: Other regulatory assets, current $ 21 $ 2 $ 19 Other regulatory assets, deferred 345 53 292 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 require the DOE to dispose of spent nuclear fuel and high level radioactive waste 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. 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, 2019 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. On-site dry spent fuel storage facilities are operational at all three plants and can be expanded to accommodate spent fuel through the expected life of each plant. 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 $13.9 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, 2019 under the NEIL policies would be $58 million and $85 million , respectively. Claims resulting from terrorist acts are covered under both the ANI and NEIL policies (subject to normal policy limits). The aggregate that NEIL will pay for all claims resulting from terrorist acts in any 12-month period is $3.2 billion 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. Other Matters Southern Company As discussed in Note 1 under " Leveraged Leases ," a subsidiary of Southern Holdings has several leveraged lease agreements. The ability of the lessees to make required payments to the Southern Holdings subsidiary is dependent on the operational performance of the assets. In 2017, the financial and operational performance of one of the 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. While all lease payments through December 31, 2019 have been paid in full due to recent operational improvements, operational and remarketing risks and the resulting cash liquidity challenges persist, and significant concerns continue regarding the lessee's ability to make the remaining semi-annual lease payments. These challenges may also impact the expected residual value of the generation assets. Southern Company has evaluated the recoverability of the lease receivable and the expected residual value of the generation assets under various scenarios. Based on 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 all of the associated rental payments will be received over the term of the lease. As a result, during the fourth quarter 2019, Southern Company revised the estimate of cash flows to be received under the leveraged lease, which resulted in an impairment charge of $17 million ( $13 million after tax). If any future lease payment is 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 from the Southern Holdings subsidiary, in effect terminating the lease and resulting in the write-off of the related lease receivable, which totaled approximately $76 million at December 31, 2019. 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. The ultimate outcome of this matter cannot be determined at this time. Alabama Power On October 16, 2019, Alabama Power agreed to a consent order regarding a fish kill investigation. The consent order required Alabama Power to pay approximately $50,000 to the Alabama Department of Environmental Management in civil penalties and approximately $172,000 to the Alabama Department of Conservation and Natural Resources in fish restocking costs. Alabama Power paid the penalties and restocking costs during the fourth quarter 2019. Mississippi Power In 2013, Mississippi Power submitted a lost revenue claim under the Deepwater Horizon Economic and Property Damages Settlement Agreement associated with the oil spill that occurred in the Gulf of Mexico in 2010. In May 2018, Mississippi Power's claim was settled. The settlement proceeds of $18 million , net of expenses and income tax, were included in Mississippi Power's earnings for 2018. Mississippi Power received half of the settlement proceeds in 2018 and half in 2019. In conjunction with Southern Company's sale of Gulf Power, NextEra Energy held back $75 million of the purchase price pending Mississippi Power and Gulf Power negotiating a mutually acceptable revised operating agreement for Plant Daniel. In addition, Mississippi Power and Gulf Power committed to seek a restructuring of their 50% undivided ownership interests in Plant Daniel such that each of them would, after the restructuring, own 100% of a generating unit. On January 15, 2019, Gulf Power provided notice to Mississippi Power that Gulf Power will retire its share of the generating capacity of Plant Daniel on January 15, 2024. Mississippi Power has the option to purchase Gulf Power's ownership interest for $1 on January 15, 2024, provided that Mississippi Power exercises the option no later than 120 days prior to that date. Mississippi Power is assessing the potential operational and economic effects of Gulf Power's notice. The ultimate outcome of these matters remains subject to completion of Mississippi Power's evaluations and applicable regulatory approvals, including by the FERC and the Mississippi PSC, and cannot be determined at this time. See Note 15 under " Southern Company " for information regarding the sale of Gulf Power. Southern Company Gas Gas Pipeline Projects At December 31, 2019 , Southern Company Gas was involved in two gas pipeline construction projects, the Atlantic Coast Pipeline project and the PennEast Pipeline project. The Atlantic Coast Pipeline has experienced challenges to its permits since construction began in 2018. During the third and fourth quarters 2018, a FERC stop work order, together with delays in obtaining permits necessary for construction and construction delays due to judicial actions, impacted the cost and schedule for the project. Project cost estimates are approximately $8.0 billion ( $400 million for Southern Company Gas), excluding financing costs. On October 4, 2019, the U.S. Supreme Court agreed to hear Atlantic Coast Pipeline's appeal of a lower court ruling that overturned a key permit for the project. On January 7, 2020, the U.S. Court of Appeals for the Fourth Circuit vacated another key permit. The operator of the joint venture has indicated that it currently expects to complete construction by the end of 2021 and place the project in service shortly thereafter. On February 7, 2020, Southern Company Gas entered into an agreement with Dominion Atlantic Coast Pipeline, LLC for the sale of its interest in Atlantic Coast Pipeline. The transaction is expected to be completed in the first half of 2020; however, the ultimate outcome cannot be determined at this time. See Note 15 under "Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline" for additional information. Expected project costs related to the PennEast Pipeline for Southern Company Gas total approximately $300 million , excluding financing costs. In January 2018, the PennEast Pipeline received initial FERC approval. Work continues with state and federal agencies to obtain the required permits to begin construction on the PennEast Pipeline. On September 10, 2019, an appellate court ruled that the PennEast Pipeline does not have federal eminent domain authority over lands in which a state has property rights interests. On February 18, 2020, PennEast Pipeline filed a petition for a writ of certiorari to seek U.S. Supreme Court review of the appellate court decision. On December 30, 2019, PennEast Pipeline filed a two -year extension request with the FERC to complete the project by January 19, 2022. Additionally, on January 30, 2020, Pe

REVENUE FROM CONTRACTS WITH CUS

REVENUE FROM CONTRACTS WITH CUSTOMERS	12 Months Ended
	Dec. 31, 2019
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. ASC 606 became effective on January 1, 2018 and the Registrants adopted it using the modified retrospective method applied to open contracts and only to the version of contracts in effect as of January 1, 2018. In accordance with the modified retrospective method, the Registrants' previously issued financial statements have not been restated to comply with ASC 606 and the Registrants did not have a cumulative-effect adjustment to retained earnings. 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 tables disaggregate revenue from contracts with customers for 2019 and 2018 : 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 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 (a) Other revenue sources primarily relate to revenues from customers accounted for as derivatives and leases, as well as alternative revenues program at Southern Company Gas and other cost recovery mechanisms 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. 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 primarily relate to revenues from customers accounted for as derivatives and leases, as well as alternative revenues program at Southern Company Gas and other cost recovery mechanisms 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, 2019 and 2018 : Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivables As of December 31, 2019 $ 2,413 $ 586 $ 688 $ 79 $ 97 $ 749 As of December 31, 2018 2,630 520 721 100 118 952 Contract Assets As of December 31, 2019 $ 117 $ — $ 69 $ — $ — $ — As of December 31, 2018 102 — 58 — — — Contract Liabilities As of December 31, 2019 $ 52 $ 10 $ 13 $ — $ 1 $ 1 As of December 31, 2018 32 12 7 — 11 2 As of December 31, 2019 and 2018 , Georgia Power had contract assets primarily related to fixed retail customer bill programs, where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term, and unregulated service agreements, where payment is contingent on project completion. Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Contract liabilities for Georgia Power and Southern Power relate to cash collections recognized in advance of revenue for certain unregulated service agreements and certain levelized PPAs, respectively. Southern Company's unregulated distributed generation business had contract assets of $40 million and $39 million at December 31, 2019 and 2018 , respectively, and contract liabilities of $28 million and $11 million at December 31, 2019 and 2018 , respectively, for outstanding performance obligations. The following table reflects revenue from contracts with customers recognized in 2019 included in the contract liability at December 31, 2018 : Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) Revenue Recognized 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, 2019 are expected to be recognized as follows: 2020 2021 2022 2023 2024 2025 and (in millions) Southern Company $ 490 $ 430 $ 336 $ 324 $ 323 $ 2,108 Alabama Power 21 25 22 22 22 118 Georgia Power 60 49 32 32 23 61 Southern Power 287 280 281 271 279 1,948 Revenue expected to be recognized for performance obligations remaining at December 31, 2019 was immaterial for Mississippi Power.

PROPERTY, PLANT, AND EQUIPMENT

PROPERTY, PLANT, AND EQUIPMENT (Notes)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 : 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 At December 31, 2018: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 52,324 $ 16,533 $ 19,145 $ 2,849 $ 13,246 $ — Transmission 11,344 4,380 6,156 769 — — Distribution 18,746 7,389 10,389 968 — — General/other 4,446 2,100 1,985 314 25 — Electric utilities' plant in service 86,860 30,402 37,675 4,900 13,271 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 12,409 — — — — 12,409 Storage facilities 1,640 — — — — 1,640 Other 1,128 — — — — 1,128 Southern Company Gas plant in service 15,177 — — — — 15,177 Other plant in service 1,669 — — — — — Total plant in service $ 103,706 $ 30,402 $ 37,675 $ 4,900 $ 13,271 $ 15,177 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 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. 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. Finance Leases Assets acquired under a finance lease (previously referred to as a capital lease) are included in property, plant, and equipment and are further detailed in the table below for the applicable Registrants at December 31, 2018: At December 31, 2018: Southern Company Georgia Power (in millions) Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 43 — Gas pipeline 7 — Less: Accumulated amortization (75 ) (84 ) Balance, net of amortization $ 191 $ 121 (*) Represents Georgia Power's affiliate PPAs with Southern Power. See Note 1 under " Affiliate Transactions " for additional information. See Note 9 for additional information, including finance lease right-of-use (ROU) assets, net included in property, plant, and equipment at December 31, 2019. 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 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Alabama Power 3.1 % 3.0 % 2.9 % Georgia Power 2.6 % 2.6 % 2.7 % Mississippi Power 3.7 % 4.2 % 3.4 % Southern Company Gas 2.9 % 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 natural gas distribution utilities. Effective January 1, 2020, Georgia Power's and Atlanta Gas Light's depreciation rates were revised by the Georgia PSC in connection with their respective base rate cases. On November 26, 2019, an updated depreciation study was filed with the Mississippi PSC in conjunction with the Mississippi Power 2019 Base Rate Case requesting a $16 million increase in total annual depreciation. 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, 2019 and 2018 , accumulated depreciation for utility plant in service totaled $30.0 billion and $30.3 billion , respectively, for Southern Company and $4.5 billion and $4.3 billion , respectively, for Southern Company Gas. Depreciation of the original cost of other plant in service is provided primarily on a straight-line basis over estimated useful lives, which for Southern Company range up to 65 years and for Southern Company Gas range from five to 15 years for transportation equipment, 40 to 60 years for storage facilities, and up to 65 years for other assets. At December 31, 2019 and 2018 , accumulated depreciation for other plant in service totaled $732 million and $766 million , respectively, for Southern Company and $155 million and $129 million , respectively, for Southern Company Gas. 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 45 years Biomass (*) Up to 40 years Solar Up to 35 years Wind Up to 30 years (*) See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " for information on Southern Power's sale of its biomass facility on June 13, 2019. 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 in the near term. 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. Joint Ownership Agreements At December 31, 2019 , the Registrants' percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation were as follows: Facility (Type) Percent Ownership Plant in Service Accumulated Depreciation CWIP (in millions) Alabama Power Greene County (natural gas) Units 1 and 2 60.0 % (a) $ 182 $ 71 $ 1 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,058 630 65 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,316 $ 603 $ 40 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,565 2,177 96 Plant Scherer (coal) Units 1 and 2 8.4 (c) 266 94 14 Plant Scherer (coal) Unit 3 75.0 (c) 1,267 492 47 Plant Wansley (coal) 53.5 (c) 1,059 367 10 Rocky Mountain (pumped storage) 25.4 (d) 182 139 — Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 118 $ 46 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 750 214 11 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 271 $ 10 $ — (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 " 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 Transco natural gas pipeline system into northwest Georgia. Southern Company Gas leases its 50% undivided ownership for approximately $26 million annually for an initial term 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 $5.8 billion at December 31, 2019 . 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 October 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, with a lease receivable balance of $118 million at December 31, 2019 , 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. On January 17, 2020, Southern Power completed the sale of its equity interests in Plant Mankato to a subsidiary of Xcel. As of December 31, 2019 , under the terms of the PPA and the expansion PPA for Plant Mankato, approximately $547 million of assets, primarily related to property, plant, and equipment, were subject to lien. See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " for additional information. See Note 8 under " Secured Debt " for information regarding debt secured by certain assets of Georgia Power, Mississippi Power, and Southern Company Gas.

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
	Dec. 31, 2019
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. The traditional electric operating companies also have AROs related to various landfill sites, asbestos removal, and underground storage tanks, as well as, for Alabama Power, disposal of polychlorinated biphenyls in certain transformers and sulfur hexafluoride gas in certain substation breakers, for Georgia Power, gypsum cells and restoration of land at the end of long-term land leases for solar facilities, and, for Mississippi Power, mine reclamation and water wells. The ARO liability for Southern Power primarily relates to Southern Power's 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, 2017 $ 4,824 $ 1,709 $ 2,638 $ 174 $ 78 Liabilities incurred 29 — 27 — 2 Liabilities settled (244 ) (55 ) (116 ) (35 ) — Accretion 217 106 94 5 4 Cash flow revisions 4,737 1,450 3,186 16 — Reclassification to held for sale (169 ) — — — — 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 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. In June 2018, Alabama Power recorded an increase of approximately $1.2 billion to its AROs related to the CCR Rule. Mississippi Power also recorded an increase of approximately $11 million to its AROs related to an ash pond at Plant Greene County, which is jointly-owned with Alabama Power. The revised cost estimates were based on information from feasibility studies performed on ash ponds in use at plants operated by Alabama Power, including Plant Greene County. During the second quarter 2018, Alabama Power's management completed its analysis of these studies which indicated that additional closure costs, primarily related to increases in estimated ash volume, water management requirements, and design revisions, will be required to close these ash ponds under the planned closure-in-place methodology. Also in June 2018, Alabama Power completed an updated decommissioning cost site study for Plant Farley. The estimated cost of decommissioning based on the study resulted in an increase in Alabama Power's ARO liability of approximately $300 million . In December 2018, Georgia Power completed updated decommissioning cost site studies for Plant Hatch and Plant Vogtle Units 1 and 2. The estimated cost of decommissioning based on the studies resulted in an increase in Georgia Power's ARO liability of approximately $130 million . See " Nuclear Decommissioning " below for additional information. In December 2018, Georgia Power recorded an increase of approximately $3.1 billion to its AROs related to the CCR Rule and the related state rule. During the second half of 2018, Georgia Power completed a strategic assessment related to its plans to close the ash ponds at all of its generating plants in compliance with the CCR Rule and the related state rule. This assessment included engineering and constructability studies related to design assumptions for ash pond closures and advanced engineering methods. The results indicated that additional closure costs will be required to close these ash ponds, primarily due to changes in closure strategies, the estimated amount of ash to be excavated, and additional water management requirements necessary to support closure strategies. These factors also impact the estimated timing of future cash outlays. The 2018 reclassification of a portion of the ARO liability to liabilities held for sale by Southern Company represents the AROs related to Gulf Power. See Note 15 under " Southern Company " and " Assets Held for Sale " for additional information. 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. The additional estimated costs to close these ash ponds under the planned closure-in-place methodology primarily relate to cost inputs from contractor bids, internal drainage and dewatering system designs, and increases in the estimated ash volumes. Alabama Power anticipates increasing the ARO for its remaining ash pond facility within the next nine months upon completion of a feasibility study and the related cost estimate, and the increase could be material. 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. The cost estimates for AROs related to the CCR Rule and related state rules are based on information at December 31, 2019 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 related state requirements for closure. The traditional electric operating companies expect to continue to update their cost estimates and ARO liabilities periodically as additional information related to these assumptions becomes available. 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, Southern Company's and the traditional electric operating companies' results of operations, cash flows, and financial condition could be materially impacted. The ultimate outcome of this matter cannot be determined at this time. 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, 2019 and 2018 , approximately $28 million and $27 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 $29 million and $28 million at December 31, 2019 and 2018 , 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, 2019 and 2018 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2018: Equity securities $ 919 $ 594 $ 325 Debt securities 726 201 525 Other securities 74 51 23 Total investment securities in the Funds $ 1,719 $ 846 $ 873 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 2019 , 2018 , and 2017 are shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2019 $ 344 $ 194 $ 150 2018 (67 ) (38 ) (29 ) 2017 233 125 108 Unrealized gains (losses) At December 31, 2019 $ 259 $ 149 $ 110 At December 31, 2018 (183 ) (96 ) (87 ) At December 31, 2017 181 98 83 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 $16 million and $17 million at December 31, 2019 and 2018 , 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, 2019 and 2018 , the accumulated provisions for the external decommissioning trust funds were as follows: 2019 2018 (in millions) Alabama Power Plant Farley $ 1,021 $ 846 Georgia Power Plant Hatch $ 634 $ 547 Plant Vogtle Units 1 and 2 379 326 Total $ 1,013 $ 873 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, 2019 based on the most current studies, which were each performed in 2018, were as follows: Plant Farley 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. Under the 2013 ARP, Georgia Power's annual decommissioning cost for ratemaking was a total of $5 million for Plant Hatch and Plant Vogtle Units 1 and 2. Effective January 1, 2020, in connection with the 2019 ARP, this total annual amount was reduced to $4 million . See Note 2 under " Georgia Power – Rate Plans – 2019 ARP " for additional information.

CONSOLIDATED ENTITIES AND EQUIT

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS	12 Months Ended
	Dec. 31, 2019
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. However, the Registrants may also invest in partnerships and limited liability companies that maintain separate ownership accounts. All such investments are required to be accounted for under the equity method unless the interest is so minor that there is virtually no influence over operating and financial policies, as are all investments in joint ventures. 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 $93 million in 2019 , $102 million in 2018 , and $76 million in 2017 for Alabama Power and $95 million in 2019 , $105 million in 2018 , and $78 million in 2017 for Georgia Power. SEGCO paid $14 million of dividends in 2019 , $18 million in 2018 , and $24 million in 2017 , of which one-half of each was 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 May 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, 2019 and 2018, SP Solar had total assets of $6.4 billion and $6.3 billion , respectively, total liabilities of $381 million and $113 million , respectively, and noncontrolling interests of $1.1 billion and $1.2 billion , respectively. 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 December 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, 2019 and 2018, SP Wind had total assets of $2.5 billion and $2.5 billion , respectively, total liabilities of $128 million and $51 million , respectively, and noncontrolling interests of $45 million and $47 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, 2019 and 2018, the other VIEs had total assets of $1.1 billion and $858 million , respectively, total liabilities of $104 million and $80 million , respectively, and noncontrolling interests of $409 million and $241 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. In August 2019, Southern Power completed the acquisition of a majority interest in DSGP and gained control of its most significant activities. As a result, Southern Power became the primary beneficiary of this VIE and began accounting for it as a consolidated entity. Upon consolidation of DSGP, Southern Power recorded an additional $107 million in assets, $51 million in liabilities, and $56 million in noncontrolling interest. There was no cash transferred as a result of this consolidation. From the date of Southern Power's first investment in June 2019 until gaining control in August 2019, Southern Power applied the equity method of accounting. See Note 15 under " Southern Power " for additional information. Equity Method Investments At December 31, 2019 , Southern Power had equity method investments in several wind and battery storage projects totaling $28 million . Redeemable Noncontrolling Interests In 2017, Southern Power reclassified approximately $114 million from redeemable noncontrolling interests to non-redeemable noncontrolling interests due to the expiration of an option allowing SunPower Corporation to require Southern Power to purchase its redeemable noncontrolling interest at fair market value. In addition, in 2017, Turner Renewable Energy, LLC redeemed at fair value its 10% interest of redeemable noncontrolling interest in certain of Southern Power's solar facilities. At December 31, 2019, 2018, and 2017, there were no outstanding redeemable noncontrolling interests. The following table presents the changes in Southern Power's redeemable noncontrolling interests for the year ended December 31, 2017 : 2017 (in millions) Beginning balance $ 164 Net income attributable to redeemable noncontrolling interests 2 Distributions to redeemable noncontrolling interests (2 ) Capital contributions from redeemable noncontrolling interests 2 Redemption of redeemable noncontrolling interests (59 ) Reclassification to non-redeemable noncontrolling interests (114 ) Change in fair value of redeemable noncontrolling interests 7 Ending balance $ — The following table presents the attribution of net income to Southern Power and the noncontrolling interests for the year ended December 31, 2017 : 2017 (in millions) Net income $ 1,117 Less: Net income attributable to noncontrolling interests 44 Less: Net income attributable to redeemable noncontrolling interests 2 Net income attributable to Southern Power $ 1,071 Southern Company Gas Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments at December 31, 2019 and 2018 and related income from those investments for the years ended December 31, 2019 , 2018 , and 2017 were as follows: Investment Balance 2019 2018 (in millions) SNG (a) $ 1,137 $ 1,261 Atlantic Coast Pipeline (b) — 83 PennEast Pipeline 82 71 Pivotal JAX LNG (b) — 53 Other (c) 32 70 Total $ 1,251 $ 1,538 (a) Decrease primarily relates to the continued amortization of deferred tax assets established upon acquisition, as well as distributions in excess of earnings. (b) As a result of the proposed sale of Southern Company Gas' interests in Pivotal LNG and Atlantic Coast Pipeline, these amounts are classified as held for sale at December 31, 2019. See Note 3 under " Other Matters – Southern Company Gas " and Note 15 under " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline " and " Assets Held for Sale ," respectively, for additional information. (c) Decrease primarily relates to the sale of Triton. See Note 15 under " Southern Company Gas " for additional information. Earnings from Equity Method Investments 2019 2018 2017 (in millions) SNG $ 141 $ 131 $ 88 Atlantic Coast Pipeline (a) 13 7 6 PennEast Pipeline (a) 6 5 6 Other (b) (3 ) 5 6 Total $ 157 $ 148 $ 106 (a) Amounts primarily result from AFUDC equity recorded by the project entity. (b) Decrease primarily relates to the sale of Triton. See Note 15 under " Southern Company Gas " for additional information. SNG In 2016, Southern Company Gas, through a wholly-owned, indirect subsidiary, acquired a 50% equity interest in SNG, which is accounted for as an equity method investment. Selected financial information of SNG at December 31, 2019 and 2018 and for the years ended December 31, 2019 , 2018 , and 2017 is as follows: Balance Sheet Information 2019 2018 (in millions) Current assets $ 85 $ 104 Property, plant, and equipment 2,570 2,606 Deferred charges and other assets 158 121 Total Assets $ 2,813 $ 2,831 Current liabilities $ 227 $ 103 Long-term debt 1,214 1,103 Other deferred charges and other liabilities 86 212 Total Liabilities $ 1,527 $ 1,418 Total Stockholders' Equity $ 1,286 $ 1,413 Total Liabilities and Stockholders' Equity $ 2,813 $ 2,831 Income Statement Information 2019 2018 2017 (in millions) Revenues $ 630 $ 604 $ 544 Operating income 335 310 242 Net income 280 261 175 Atlantic Coast and PennEast Pipelines In 2014, Southern Company Gas entered into a joint venture, whereby it holds a 5% ownership interest in the Atlantic Coast Pipeline, an interstate pipeline company formed to develop and operate an approximate 605 -mile natural gas pipeline in North Carolina, Virginia, and West Virginia with expected initial transportation capacity of 1.5 Bcf per day. On February 7, 2020, Southern Company Gas entered into an agreement with Dominion Atlantic Coast Pipeline, LLC for the sale of its interest in Atlantic Coast Pipeline. The transaction is expected to be completed in the first half of 2020; however, the ultimate outcome cannot be determined at this time. See Note 15 under " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline " for additional information. Also in 2014, Southern Company Gas entered into a partnership in which it holds a 20% ownership interest in the PennEast Pipeline, an interstate pipeline company formed to develop and operate an approximate 118 -mile natural gas pipeline between New Jersey and Pennsylvania. The expected initial transportation capacity of 1.0 Bcf per day is under long-term contracts, mainly with public utilities and other market-serving entities, such as electric generation companies, in New Jersey, Pennsylvania, and New York. See Note 3 under " Other Matters – Southern Company Gas – Gas Pipeline Projects " and " Guarantees " for additional information on these pipeline projects. Other On May 29, 2019, Southern Company Gas sold its investment in Triton, a cargo container leasing company that was aggregated into Southern Company Gas' all other segment. See Note 15 under " Southern Company Gas " for additional information. Southern Company Gas owns a 50% equity method investment in a LNG liquefaction and storage facility in Jacksonville, Florida, which was placed in service in October 2018. This facility is outfitted with a 2.0 million gallon storage tank with the capacity to produce in excess of 120,000 gallons of LNG per day. During 2019, net loss from this investment was $2 million . On February 7, 2020, Southern Company Gas entered into an agreement with Dominion Modular LNG Holdings, Inc. for the sale of its interest in Pivotal LNG, which includes the investment in this facility in Jacksonville, Florida. The transaction is expected to be completed in the first half of 2020; however, the ultimate outcome cannot be determined at this time. See Note 15 under " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline " for additional information.

FINANCING

FINANCING	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
FINANCING	FINANCING Long-term Debt Maturities of long-term debt for the next five years are as follows: Southern Company (a)(b) Alabama Power Georgia Power (a) Mississippi Power Southern Power (b) Southern Company Gas (in millions) 2020 $ 2,991 $ 251 $ 1,025 $ 281 $ 825 $ — 2021 3,214 311 397 270 300 330 2022 2,003 751 527 — 677 46 2023 2,413 301 175 — 290 400 2024 492 22 477 — — — (a) Amounts include principal amortization related to the FFB borrowings beginning in February 2020; however, the final maturity date is February 20, 2044. See " DOE Loan Guarantee Borrowings " herein for additional information. (b) Southern Power's 2022 maturity represents euro-denominated debt at the U.S. dollar denominated hedge settlement amount. In addition to the items described herein, long-term debt at December 31, 2019 and 2018 consists of senior notes (for all Registrants), junior subordinated notes (for Southern Company and Georgia Power), first mortgage bonds and medium-term notes (for Southern Company and Southern Company Gas), and bank term loans (for Southern Company and Alabama Power). The traditional electric operating companies also have pollution control revenue bond obligations, which 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. 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 totaling $206 million at December 31, 2019 and 2018 , which constitute substantially all of the assets of this trust and are reflected in the balance sheets as long-term debt payable. 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. At December 31, 2019 and 2018 , 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. 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. The bonds were recorded at fair value at the date of assumption, or $346 million , reflecting a premium of $76 million . See " Secured Debt " herein for additional information. At December 31, 2019 and 2018 , Mississippi Power also had $50 million of tax-exempt revenue bond obligations outstanding representing loans to Mississippi Power from a public authority of funds derived from the sale by such authority of revenue bonds issued to finance a portion of the costs of constructing the Kemper County energy facility. See Note 9 for information related to finance lease obligations. 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 note purchase agreements among the DOE, Georgia Power, and the FFB and related promissory notes which provide for two multi-advance term loan facilities (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 March and December 2019, Georgia Power made borrowings under the FFB Credit Facilities in an aggregate principal amount of $835 million and $383 million , respectively, with applicable interest rates of 3.213% and 2.537% , respectively, both for an interest period that extends to the final maturity date of February 20, 2044. At December 31, 2019 and 2018 , Georgia Power had $3.8 billion and $2.6 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 will begin 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. Outstanding secured debt at December 31, 2019 and 2018 for the applicable Registrants was as follows: Georgia (a) Mississippi Power (b) Southern Company Gas (c) (in millions) December 31, 2019 $ 3,999 $ 270 $ 1,575 December 31, 2018 2,767 270 1,325 (a) Includes Georgia Power's FFB loans that are 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 " Long-term Debt – DOE Loan Guarantee Borrowings " herein for additional information. Also includes finance lease obligations of $156 million and $142 million at December 31, 2019 and 2018 , respectively. See Note 9 for additional information on finance lease obligations. (b) Represents revenue bonds assumed in conjunction with Mississippi Power's purchase of Plant Daniel Units 3 and 4 that are secured by Plant Daniel Units 3 and 4 and certain related personal property. See " Long-term Debt " herein for additional information. (c) Nicor Gas' first mortgage bonds are secured by substantially all of Nicor Gas' properties. 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. A holder's ownership interest in the RSNs is pledged to Southern Company to secure the holder's obligation under the related Stock Purchase Contract. If a holder of a Stock Purchase Contract chooses at any time to have its RSNs released from the pledge, such holder's obligation under such Stock Purchase Contract must be secured by a U.S. Treasury security equal to the aggregate principal amount of the RSNs. At the time of issuance, the RSNs were recorded on Southern Company's consolidated balance sheet as long-term debt and the present value of the contract adjustment payments of $198 million was recorded as a liability, representing the obligation to make contract adjustment payments, with an offsetting reduction to paid-in capital. The liability balance at December 31, 2019 was $185 million , of which $66 million was classified as current. The difference between the face value and present value of the contract adjustment payments will be accreted to interest expense on the consolidated statements of income over the three-year period ending in 2022. The liability recorded for the contract adjustment payments is considered non-cash and excluded from the consolidated statements of cash flows. To settle the Stock Purchase Contracts, Southern Company will be required to issue a maximum of 30.2 million shares of common stock (subject to anti-dilution adjustments and a make-whole adjustment if certain fundamental changes occur). Bank Credit Arrangements At December 31, 2019 , committed credit arrangements with banks were as follows: Expires Company 2020 2022 2024 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power 3 525 800 1,328 1,328 3 Georgia Power — — 1,750 1,750 1,733 — Mississippi Power — 150 — 150 150 — 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 $ 6,900 $ 7,608 $ 7,576 $ 33 (a) Southern Power's subsidiaries are not parties to its bank credit arrangement. (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 or the maintenance of compensating balances with the banks. Commitment fees average less than 1 / 4 of 1% for Southern Company, the traditional electric operating companies, Southern Power, Southern Company Gas, and Nicor Gas. Compensating balances are not legally restricted from withdrawal. 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 Alabama Power, Georgia Power, Southern Power, 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, 2019 , 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, 2019 was approximately $1.4 billion (comprised of approximately $854 million at Alabama Power, $550 million at Georgia Power, and $40 million at Mississippi Power). In addition, at December 31, 2019 , the traditional electric operating companies had approximately $275 million (comprised of approximately $87 million at Alabama Power and $188 million at Georgia Power) of revenue bonds outstanding that are required to be remarketed within the next 12 months . In addition to its credit arrangement described above, at December 31, 2019, Southern Power also had a $120 million continuing letter of credit facility expiring in 2021 for standby letters of credit. At December 31, 2019 , $97 million had been used for letters of credit, primarily as credit support for PPA requirements, and $23 million was unused. At December 31, 2018 , the total amount used under this facility was $103 million . Subsequent to December 31, 2019, Southern Power entered into an additional $60 million continuing letter of credit facility expiring in 2023 for standby letters of credit. Southern Power's subsidiaries are not parties to these letter of credit facilities. Also, at December 31, 2019 and 2018 , Southern Power had $104 million and $103 million , respectively, of cash collateral posted related to PPA requirements, which is included in other deferred charges and assets in 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, 2019 Notes Payable at December 31, 2018 Amount Outstanding Weighted Average Interest Rate Amount Outstanding Weighted Average Interest Rate (in millions) (in millions) Southern Company Commercial paper $ 1,705 2.1 % $ 1,064 3.0 % Short-term bank debt 350 2.3 % 1,851 3.1 % Total $ 2,055 2.1 % $ 2,915 3.1 % Georgia Power Commercial paper $ 115 2.1 % $ 294 3.1 % Short-term bank debt 250 2.2 % — — % Total $ 365 2.2 % $ 294 3.1 % Southern Power Commercial paper $ 449 2.1 % $ — — % Short-term bank debt 100 2.6 % 100 3.1 % Total $ 549 2.2 % $ 100 3.1 % Southern Company Gas Commercial paper: Southern Company Gas Capital $ 372 2.1 % $ 403 3.1 % Nicor Gas 278 1.8 % 247 3.0 % Total $ 650 2.0 % $ 650 3.0 % See " Bank Credit Arrangements " herein for information on bank term loan covenants that limit debt levels and cross-acceleration or cross-default provisions. Outstanding Classes of Capital Stock Southern Company Common Stock Stock Issued During 2019 , Southern Company issued approximately 19.5 million shares of common stock through employee equity compensation plans and received proceeds of approximately $844 million . See " Equity Units " herein for additional information. Shares Reserved At December 31, 2019 , a total of 104 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 104 million shares reserved, 9 million shares are available for awards under the Omnibus Incentive Compensation Plan at December 31, 2019 . Diluted Earnings Per Share For Southern Company, the only difference in computing basic and diluted earnings per share (EPS) is 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 2019 2018 2017 (in millions) As reported shares 1,046 1,020 1,000 Effect of stock-based compensation 8 5 8 Diluted shares 1,054 1,025 1,008 Stock-based compensation awards that were not included in the diluted EPS calculation because they were anti-dilutive were immaterial in all years presented. The Equity Units issued in August 2019 were excluded from the calculation of diluted EPS for 2019 as the dilutive stock price threshold was not met. Redeemable Preferred Stock of Subsidiaries The preferred stock of Alabama Power contains a feature that allows the holders to elect a majority of such subsidiary'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, this preferred stock is presented as "Redeemable Preferred Stock of Subsidiaries" on Southern Company's balance sheets and statements of capitalization in a manner consistent with temporary equity under applicable accounting standards. The following table presents changes during the year in redeemable preferred stock of subsidiaries for Southern Company: Redeemable Preferred Stock of Subsidiaries (in millions) Balance at December 31, 2016: $ 118 Issued (a) 250 Redeemed (a) (38 ) Issuance costs (a) (6 ) Balance at December 31, 2017: 324 Redeemed (b) (33 ) Balance at December 31, 2018 and 2019: $ 291 (a) See " Alabama Power " herein for additional information. (b) See " Mississippi Power " herein for additional information. 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 and statements of capitalization 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 Price Per Share 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 Stated Capital (*) (*) Prior to October 1, 2022: $25.50 ; on or after October 1, 2022: Stated Capital In 2017, Alabama Power issued 10 million shares ( $250 million aggregate stated capital) of 5.00% Class A Preferred Stock, Cumulative, Par Value $1 Per Share (Stated Capital $25 Per Share). The proceeds were used in 2017 to redeem all 2 million shares ( $50 million aggregate stated capital) of 6.50% Series Preference Stock, 6 million shares ( $150 million aggregate stated capital) of 6.45% Series Preference Stock, and 1.52 million shares ( $38 million aggregate stated capital) of 5.83% Class A Preferred Stock and for other general corporate purposes, including Alabama Power's continuous construction program. There were no changes for the years ended December 31, 2019 and 2018 in redeemable preferred stock of Alabama Power. 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, 2019 and 2018 . In 2017, Georgia Power redeemed all of its outstanding shares of Class A preferred stock and preference stock. Mississippi Power Mississippi Power has preferred stock and common stock authorized, but only common stock outstanding as of December 31, 2019 . In October 2018, Mississippi Power completed the redemption of all outstanding shares and depository shares of its Preferred Stock that contained a feature allowing the holders to elect a majority of Mississippi Power's board of directors if preferred dividends were not paid for four consecutive quarters. Because such a potential redemption-triggering event was not solely within the control of Mississippi Power, this preferred stock was presented as "Cumulative Redeemable Preferred Stock" on Mississippi Power's balance sheets and statements of capitalization in a manner consistent with temporary equity under applicable accounting standards. Dividend Restrictions The income of Southern Company is derived primarily from equity in earnings of its subsidiaries. At December 31, 2019 , consolidated retained earnings included $5.3 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, 2019 , the amount of Southern Company Gas' subsidiary retained earnings restricted for dividend payment totaled $951 million . 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 (Notes)

LEASES (Notes)	12 Months Ended
	Dec. 31, 2019
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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 25 years while the land leases have remaining terms of up to 47 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 terms of up to 15 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities at Southern Power and for communication tower leases at Southern Company Gas, 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. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. 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 and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of $624 million at December 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. During 2019, Alabama Power entered into additional long-term PPAs totaling approximately 640 MWs of additional generating capacity consisting of combined cycle generation expected to commence later in 2020 and solar generation coupled with battery energy storage systems expected to commence in 2022 through 2024. Both the combined cycle PPA and the 20 -year term battery energy storage systems of the solar generation PPAs are deemed operating leases. The 28 -year term battery energy storage systems of the solar generation PPAs are deemed finance leases. The estimated minimum lease payments for these agreements, which are contingent upon approval by the Alabama PSC, total $95 million . See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. 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, 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for the year ended December 31, 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) 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. Rent expense and PPA capacity expense related to leases for 2018 and 2017, 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 — — — 2017: Rent expense $ 176 $ 25 $ 31 $ 3 $ 29 $ 15 PPA capacity expense 235 41 225 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million and $73 million for 2018 and 2017 , respectively, of which $29 million in each of 2018 and 2017 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 and $5 million in 2018 and 2017 , respectively. (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: 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 — — — As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas 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 % 3.70 % 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, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — 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, 2019 , Southern Company, Alabama Power, Mississippi Power, and Southern Power have additional leases that have not yet commenced, as detailed in the following table: Southern Company Alabama Power (a) Mississippi Power (b) Southern Power Lease category PPAs, land, pipelines, and aircraft PPAs Pipelines Land Expected commencement date 2020-2024 2020-2024 2020 2020 Longest lease term expiration 40 years 28 years 15 years 40 years Estimated total obligations (in millions) $248 $95 $23 $87 (a) See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. Alabama Power will have variable operating lease payments and variable finance lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. (b) See Note 2 under " Mississippi Power – Kemper County Energy Facility – Lignite Mine and CO 2 Pipeline Facilities " for additional information. Estimated total obligations include non-lease components. 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 term of 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 27 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 23 years. Lease income for the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for Southern Power is included in wholesale revenues. 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. 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. The undiscounted cash flows to be received under the lease are as follows: At December 31, 2019 Southern Company Mississippi Power (in millions) 2020 $ 17 $ 17 2021 15 15 2022 15 15 2023 14 14 2024 14 14 Thereafter 138 138 Total undiscounted cash flows $ 213 $ 213 Lease receivable (*) 118 118 Difference between undiscounted cash flows and discounted cash flows $ 95 $ 95 (*) 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, 2019 Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) 2020 $ 155 $ 26 $ 26 $ 84 $ 35 2021 141 23 19 86 35 2022 125 16 8 87 35 2023 110 7 2 88 34 2024 103 3 — 90 33 Thereafter 1,063 20 — 387 463 Total $ 1,697 $ 95 $ 55 $ 822 $ 635 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. Southern Power allocates 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 25 years while the land leases have remaining terms of up to 47 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 terms of up to 15 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities at Southern Power and for communication tower leases at Southern Company Gas, 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. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. 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 and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of $624 million at December 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. During 2019, Alabama Power entered into additional long-term PPAs totaling approximately 640 MWs of additional generating capacity consisting of combined cycle generation expected to commence later in 2020 and solar generation coupled with battery energy storage systems expected to commence in 2022 through 2024. Both the combined cycle PPA and the 20 -year term battery energy storage systems of the solar generation PPAs are deemed operating leases. The 28 -year term battery energy storage systems of the solar generation PPAs are deemed finance leases. The estimated minimum lease payments for these agreements, which are contingent upon approval by the Alabama PSC, total $95 million . See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. 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, 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for the year ended December 31, 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) 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. Rent expense and PPA capacity expense related to leases for 2018 and 2017, 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 — — — 2017: Rent expense $ 176 $ 25 $ 31 $ 3 $ 29 $ 15 PPA capacity expense 235 41 225 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million and $73 million for 2018 and 2017 , respectively, of which $29 million in each of 2018 and 2017 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 and $5 million in 2018 and 2017 , respectively. (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: 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 — — — As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas 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 % 3.70 % 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, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — 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, 2019 , Southern Company, Alabama Power, Mississippi Power, and Southern Power have additional leases that have not yet commenced, as detailed in the following table: Southern Company Alabama Power (a) Mississippi Power (b) Southern Power Lease category PPAs, land, pipelines, and aircraft PPAs Pipelines Land Expected commencement date 2020-2024 2020-2024 2020 2020 Longest lease term expiration 40 years 28 years 15 years 40 years Estimated total obligations (in millions) $248 $95 $23 $87 (a) See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. Alabama Power will have variable operating lease payments and variable finance lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. (b) See Note 2 under " Mississippi Power – Kemper County Energy Facility – Lignite Mine and CO 2 Pipeline Facilities " for additional information. Estimated total obligations include non-lease components. 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 term of 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 27 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 23 years. Lease income for the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for Southern Power is included in wholesale revenues. 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. 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. The undiscounted cash flows to be received under the lease are as follows: At December 31, 2019 Southern Company Mississippi Power (in millions) 2020 $ 17 $ 17 2021 15 15 2022 15 15 2023 14 14 2024 14 14 Thereafter 138 138 Total undiscounted cash flows $ 213 $ 213 Lease receivable (*) 118 118 Difference between undiscounted cash flows and discounted cash flows $ 95 $ 95 (*) 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, 2019 Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) 2020 $ 155 $ 26 $ 26 $ 84 $ 35 2021 141 23 19 86 35 2022 125 16 8 87 35 2023 110 7 2 88 34 2024 103 3 — 90 33 Thereafter 1,063 20 — 387 463 Total $ 1,697 $ 95 $ 55 $ 822 $ 635 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. Southern Power allocates 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 25 years while the land leases have remaining terms of up to 47 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 terms of up to 15 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities at Southern Power and for communication tower leases at Southern Company Gas, 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. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. 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 and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of $624 million at December 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. During 2019, Alabama Power entered into additional long-term PPAs totaling approximately 640 MWs of additional generating capacity consisting of combined cycle generation expected to commence later in 2020 and solar generation coupled with battery energy storage systems expected to commence in 2022 through 2024. Both the combined cycle PPA and the 20 -year term battery energy storage systems of the solar generation PPAs are deemed operating leases. The 28 -year term battery energy storage systems of the solar generation PPAs are deemed finance leases. The estimated minimum lease payments for these agreements, which are contingent upon approval by the Alabama PSC, total $95 million . See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. 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, 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for the year ended December 31, 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) 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. Rent expense and PPA capacity expense related to leases for 2018 and 2017, 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 — — — 2017: Rent expense $ 176 $ 25 $ 31 $ 3 $ 29 $ 15 PPA capacity expense 235 41 225 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million and $73 million for 2018 and 2017 , respectively, of which $29 million in each of 2018 and 2017 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 and $5 million in 2018 and 2017 , respectively. (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: 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 — — — As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas 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 % 3.70 % 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, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — 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, 2019 , Southern Company, Alabama Power, Mississippi Power, and Southern Power have additional leases that have not yet commenced, as detailed in the following table: Southern Company Alabama Power (a) Mississippi Power (b) Southern Power Lease category PPAs, land, pipelines, and aircraft PPAs Pipelines Land Expected commencement date 2020-2024 2020-2024 2020 2020 Longest lease term expiration 40 years 28 years 15 years 40 years Estimated total obligations (in millions) $248 $95 $23 $87 (a) See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. Alabama Power will have variable operating lease payments and variable finance lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. (b) See Note 2 under " Mississippi Power – Kemper County Energy Facility – Lignite Mine and CO 2 Pipeline Facilities " for additional information. Estimated total obligations include non-lease components. 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 term of 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 27 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 23 years. Lease income for the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for Southern Power is included in wholesale revenues. 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. 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. The undiscounted cash flows to be received under the lease are as follows: At December 31, 2019 Southern Company Mississippi Power (in millions) 2020 $ 17 $ 17 2021 15 15 2022 15 15 2023 14 14 2024 14 14 Thereafter 138 138 Total undiscounted cash flows $ 213 $ 213 Lease receivable (*) 118 118 Difference between undiscounted cash flows and discounted cash flows $ 95 $ 95 (*) 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, 2019 Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) 2020 $ 155 $ 26 $ 26 $ 84 $ 35 2021 141 23 19 86 35 2022 125 16 8 87 35 2023 110 7 2 88 34 2024 103 3 — 90 33 Thereafter 1,063 20 — 387 463 Total $ 1,697 $ 95 $ 55 $ 822 $ 635 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. Southern Power allocates 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 25 years while the land leases have remaining terms of up to 47 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 terms of up to 15 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities at Southern Power and for communication tower leases at Southern Company Gas, 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. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. 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 and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of $624 million at December 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. During 2019, Alabama Power entered into additional long-term PPAs totaling approximately 640 MWs of additional generating capacity consisting of combined cycle generation expected to commence later in 2020 and solar generation coupled with battery energy storage systems expected to commence in 2022 through 2024. Both the combined cycle PPA and the 20 -year term battery energy storage systems of the solar generation PPAs are deemed operating leases. The 28 -year term battery energy storage systems of the solar generation PPAs are deemed finance leases. The estimated minimum lease payments for these agreements, which are contingent upon approval by the Alabama PSC, total $95 million . See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. 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, 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for the year ended December 31, 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) 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. Rent expense and PPA capacity expense related to leases for 2018 and 2017, 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 — — — 2017: Rent expense $ 176 $ 25 $ 31 $ 3 $ 29 $ 15 PPA capacity expense 235 41 225 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million and $73 million for 2018 and 2017 , respectively, of which $29 million in each of 2018 and 2017 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 and $5 million in 2018 and 2017 , respectively. (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: 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 — — — As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas 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 % 3.70 % 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, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ — 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, 2019 , Southern Company, Alabama Power, Mississippi Power, and Southern Power have additional leases that have not yet commenced, as detailed in the following table: Southern Company Alabama Power (a) Mississippi Power (b) Southern Power Lease category PPAs, land, pipelines, and aircraft PPAs Pipelines Land Expected commencement date 2020-2024 2020-2024 2020 2020 Longest lease term expiration 40 years 28 years 15 years 40 years Estimated total obligations (in millions) $248 $95 $23 $87 (a) See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. Alabama Power will have variable operating lease payments and variable finance lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. (b) See Note 2 under " Mississippi Power – Kemper County Energy Facility – Lignite Mine and CO 2 Pipeline Facilities " for additional information. Estimated total obligations include non-lease components. 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 term of 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 27 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 23 years. Lease income for the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 for Southern Power is included in wholesale revenues. 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. 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. The undiscounted cash flows to be received under the lease are as follows: At December 31, 2019 Southern Company Mississippi Power (in millions) 2020 $ 17 $ 17 2021 15 15 2022 15 15 2023 14 14 2024 14 14 Thereafter 138 138 Total undiscounted cash flows $ 213 $ 213 Lease receivable (*) 118 118 Difference between undiscounted cash flows and discounted cash flows $ 95 $ 95 (*) 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, 2019 Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) 2020 $ 155 $ 26 $ 26 $ 84 $ 35 2021 141 23 19 86 35 2022 125 16 8 87 35 2023 110 7 2 88 34 2024 103 3 — 90 33 Thereafter 1,063 20 — 387 463 Total $ 1,697 $ 95 $ 55 $ 822 $ 635 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. Southern Power allocates 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, 2019
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 no subsidiary is allocated more current expense than 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. Due to the complex and comprehensive nature of the enacted tax law changes and their application under GAAP, the Registrants considered all amounts recorded in the financial statements as a result of the Tax Reform Legislation "provisional" as discussed in SAB 118 and subject to revision prior to filing the 2017 tax return in the fourth quarter 2018. As of December 31, 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. Current and Deferred Income Taxes Details of income tax provisions are as follows: 2019 Southern Company Alabama Power Georgia Power 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 Power Mississippi Power 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 2017 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ (62 ) $ 136 $ 256 $ 194 $ (566 ) $ 103 Deferred (6 ) 336 504 (753 ) (312 ) 170 (68 ) 472 760 (559 ) (878 ) 273 State — Current 37 23 116 — (110 ) 27 Deferred 173 73 (46 ) 27 49 67 210 96 70 27 (61 ) 94 Total $ 142 $ 568 $ 830 $ (532 ) $ (939 ) $ 367 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 $51 million for 2019 , $128 million for 2018 , and $316 million for 2017 . Southern Power received $734 million and $5 million of cash related to federal ITCs under renewable energy initiatives in 2019 and 2018, respectively. No cash was received in 2017. 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 2019 , 2018 , and 2017 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) 2019 $ 181 $ 151 2018 87 58 2017 79 57 Southern Power recognized tax credits and reduced the tax basis of the asset 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 in 2019 , $1 million in 2018 , and $18 million in 2017 . See " Unrecognized Tax Benefits " herein for further information. 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 $51 million in 2019 , $21 million in 2018 , and $37 million in 2017 and reduced Southern Power's income tax expense by $32 million in 2017 . 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 $12 million in 2019 , $141 million in 2018 , and $139 million in 2017 . Legal Entity Reorganizations In April 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. In September 2018, Southern Power 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. Each Registrant's effective tax rate for 2018 varied significantly as compared to 2017 due to the 14% lower 2018 federal tax rate resulting from the Tax Reform Legislation. A reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: 2019 Southern Company Alabama Power Georgia Power 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 Power 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 % 2017 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Southern Company Gas Federal statutory rate 35.0 % 35.0 % 35.0 % (35.0 )% 35.0 % 35.0 % State income tax, net of federal deduction 12.5 4.5 2.0 0.6 (22.2 ) 10.0 Employee stock plans' dividend deduction (4.0 ) — — — — — Non-deductible book depreciation 3.1 0.9 0.7 0.1 — — Flowback of excess deferred income taxes (0.3 ) — (0.1 ) — — (0.2 ) AFUDC-Equity (2.6 ) (1.0 ) (0.6 ) — — — AFUDC-Equity portion of Kemper IGCC charge 15.7 — — 5.3 — — ITC basis difference (1.7 ) — — — (10.0 ) — Federal PTCs (12.1 ) — — — (72.5 ) — Amortization of ITC (4.2 ) (0.2 ) (0.1 ) — (20.6 ) (0.2 ) Tax Reform Legislation (25.6 ) 0.3 (0.4 ) 11.9 (416.1 ) 15.0 Noncontrolling interests (1.4 ) — — — (8.6 ) — Other (1.1 ) 0.1 0.2 — (10.7 ) 0.6 Effective income tax (benefit) rate 13.3 % 39.6 % 36.7 % (17.1 )% (525.7 )% 60.2 % (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2017 . 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, 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 — 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 786 173 154 56 46 287 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 December 31, 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,461 $ 2,236 $ 3,005 $ 335 $ 1,483 $ 1,176 Property basis differences 1,807 865 633 162 — 134 Federal effect of net state deferred tax assets — — — 36 — — Leveraged lease basis differences 253 — — — — — Employee benefit obligations 477 149 290 25 6 6 Premium on reacquired debt 88 14 74 — — — Regulatory assets – Storm damage reserves 111 — 111 — — — Employee benefit obligations 975 260 344 45 — 45 Remaining book value of retired assets 56 6 39 11 — — AROs 1,232 276 925 31 — — AROs 1,210 607 575 — — — Other 537 171 102 57 34 132 Total deferred income tax liabilities 15,207 4,584 6,098 702 1,523 1,493 Deferred tax assets — Federal effect of net state deferred tax liabilities 260 155 71 — 22 46 Employee benefit obligations 1,273 286 444 62 7 150 Other property basis differences 251 — 61 — 172 — ITC and PTC carryforward 2,730 11 430 — 2,128 — Alternative minimum tax carryforward 62 — — 32 21 — Other partnership basis difference 162 — — — 162 — Other comprehensive losses 82 10 3 — — — AROs 2,442 883 1,500 31 — — Estimated loss on plants under construction 346 — 283 63 — — Other deferred state tax attributes 415 — 19 251 72 — Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 294 130 127 29 — 8 Other 731 147 140 47 47 285 Total deferred income tax assets 9,048 1,622 3,078 515 2,631 489 Valuation allowance (123 ) — (42 ) (41 ) (27 ) (12 ) Net deferred income tax assets 8,925 1,622 3,036 474 2,604 477 Net deferred income taxes (assets)/liabilities $ 6,282 $ 2,962 $ 3,062 $ 228 $ (1,081 ) $ 1,016 Recognized in the balance sheets: Accumulated deferred income $ (276 ) $ — $ — $ (150 ) $ (1,186 ) $ — Accumulated deferred income taxes – liabilities $ 6,558 $ 2,962 $ 3,062 $ 378 $ 105 $ 1,016 The traditional electric operating companies and 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, 2019 and 2018 . Tax Credit Carryforwards Federal ITC/PTC carryforwards at December 31, 2019 were as follows: Southern Company Alabama Power Georgia Power Southern Power (in millions) Federal ITC/PTC carryforwards $ 1,751 $ 11 $ 88 $ 1,445 Year in which federal ITC/PTC carryforwards begin expiring 2032 2033 2032 2036 Year by which federal ITC/PTC carryforwards are expected to be utilized 2024 2022 2022 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, 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, 2019 , Georgia Power also had approximately $360 million in state investment and other state tax credit carryforwards for the State of Georgia that will expire between 2020 and 2029 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 Southern Company has fully utilized the carryforward from federal NOLs generated in 2016 and 2017. At December 31, 2019 , the state and local NOL carryforwards for Southern Company's subsidiaries were as follows: Company/Jurisdiction Approximate NOL Carryforwards Approximate Net State Income Tax Benefit Tax Year NOL Begins Expiring (in millions) Mississippi Power Mississippi $ 5,099 $ 201 2031 Southern Power Oklahoma 830 39 2035 Florida 258 11 2033 South Carolina 56 2 2034 Other states 21 2 Various Southern Power Total $ 1,165 $ 54 Other (*) Georgia 171 7 2020 New York 220 11 2035 New York City 207 15 2035 Other states 368 18 Various Southern Company Total $ 7,230 $ 306 (*) 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, 2019 . State NOLs for Mississippi, Oklahoma, and Florida are not expected to be fully utilized prior to expiration. At December 31, 2019 , 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 The Registrants had no material changes in unrecognized tax benefits during 2019. Unrecognized tax benefits changes in 2018 and 2017 for Southern Company, Mississippi Power, and Southern Power are provided below. The remaining Registrants did not have any material unrecognized tax benefits for the periods presented. Southern Company Mississippi Power Southern Power (in millions) Unrecognized tax benefits at December 31, 2016 $ 484 $ 465 $ 17 Tax positions changes – Increase from current periods 10 — — Increase from prior periods 10 2 — Decrease from prior periods (196 ) (177 ) (17 ) Reductions due to settlements (290 ) (290 ) — Unrecognized tax benefits at December 31, 2017 18 — — Tax positions changes – Decrease from prior periods (18 ) — — Unrecognized tax benefits at December 31, 2018 $ — $ — $ — Mississippi Power's tax positions changes from prior periods and reductions due to settlements for 2017 related to state tax benefits, deductions for R&E expenditures, and charitable contribution carryforwards that were impacted as a result of the settlement of R&E expenditures associated with the Kemper County energy facility, as well as federal income tax benefits from deferred ITCs. See Note 2 under " Mississippi Power – Kemper County Energy Facility " and " Section 174 Research and Experimental Deduction " herein for more information. Southern Power's decrease from prior periods for 2017 primarily relates to federal income tax benefits from deferred ITCs. The impact on the effective tax rate of Southern Company, if recognized, was as follows for 2017 : Southern Company (in millions) 2017 Tax positions impacting the effective tax rate $ 18 Tax positions not impacting the effective tax rate — Balance of unrecognized tax benefits $ 18 All of the Registrants classify interest on tax uncertainties as interest expense. Accrued interest for all tax positions other than the Section 174 R&E deductions was immaterial for all years presented. None of the Registrants accrued any penalties on uncertain tax positions. It is reasonably possible that the amount of the unrecognized tax benefits could change within 12 months . New audit findings or settlements associated with ongoing audits could result in significant unrecognized tax benefits. At this time, a range of reasonably possible outcomes cannot be determined. The IRS has finalized its audits of Southern Company's consolidated federal income tax returns through 2018. 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. Section 174 Research and Experimental Deduction Southern Company, on behalf of Mississippi Power, reflected deductions for R&E expenditures related to the Kemper County energy facility in its federal income tax returns, as amended, since 2008. In 2017, the U.S. Congress Joint Committee on Taxation approved a settlement between Southern Company and the IRS, resolving a methodology for these deductions. As a result of this approval, Mississippi Power recognized $176 million in 2017 of previously unrecognized tax benefits and reversed $36 million of associated accrued interest.

RETIREMENT BENEFITS

RETIREMENT BENEFITS	12 Months Ended
	Dec. 31, 2019
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). In December 2019, the Registrants voluntarily contributed the following amounts to the qualified pension plan: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Contributions to qualified pension plan $ 1,136 $ 362 $ 200 $ 54 $ 24 $ 145 No mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 2020 . 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, 2020 , no contributions to any other postretirement trusts are expected. In January 2018, the qualified defined benefit pension plan of Southern Company Gas was merged into the Southern Company system's qualified defined benefit pension plan and the pension plan was reopened to all non-union employees of Southern Company Gas. Prior to January 2018, Southern Company Gas had a separate qualified defined benefit, trusteed pension plan covering certain eligible employees, which was closed in 2012 to new employees. Also in January 2018, Southern Company Gas' non-qualified retirement plans were merged into the Southern Company system's non-qualified retirement plan (defined benefit and defined contribution). Effective in December 2017, 538 employees transferred from SCS to Southern Power. Accordingly, Southern Power assumed various compensation and benefit plans including participation in the Southern Company system's qualified defined benefit, trusteed pension plan covering substantially all employees. With the transfer of employees, Southern Power assumed the related benefit obligations from SCS of $139 million for the qualified pension plan (along with trust assets of $138 million ) and $11 million for other postretirement benefit plans, together with $36 million in prior service costs and net gains/losses in OCI. In 2018, Southern Power also began providing certain defined benefits under the non-qualified pension plan for a select group of management and highly compensated employees. No obligation related to these benefits was assumed in the employee transfer; however, obligations for services rendered by employees following the transfer are being recognized by Southern Power and are funded on a cash basis. In addition, Southern Power provides certain medical care and life insurance benefits for retired employees through other postretirement benefit plans that are funded on a cash basis. Prior to the transfer of employees in December 2017, substantially all expenses charged by SCS, including pension and other postretirement benefit costs, were recorded in Southern Power's other operations and maintenance expense. The disclosures included herein exclude Southern Power for periods prior to the transfer of employees in December 2017. On January 1, 2019, Southern Company completed the sale of Gulf Power to NextEra Energy. See Note 15 under " Southern Company " for additional information. The portion of the Southern Company system's pension and other postretirement benefit plans attributable to Gulf Power reflected in Southern Company's consolidated balance sheet as held for sale at December 31, 2018 consisted of: Pension Plans Other Postretirement Benefit Plans (in millions) Projected benefit obligation $ 526 $ 69 Plan assets 492 17 Accrued liability $ (34 ) $ (52 ) All amounts presented in the remainder of 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. 2019 Assumptions used to determine net Southern Company Alabama Power 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 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 2017 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Southern Company Gas Pension plans Discount rate – benefit obligations 4.40 % 4.44 % 4.40 % 4.44 % 4.39 % Discount rate – interest costs 3.77 3.76 3.72 3.81 3.76 Discount rate – service costs 4.81 4.85 4.83 4.83 4.64 Expected long-term return on plan assets 7.92 7.95 7.95 7.95 7.60 Annual salary increase 4.37 4.46 4.46 4.46 3.50 Other postretirement benefit plans Discount rate – benefit obligations 4.23 % 4.27 % 4.23 % 4.22 % 4.15 % Discount rate – interest costs 3.54 3.58 3.55 3.55 3.40 Discount rate – service costs 4.64 4.70 4.63 4.65 4.55 Expected long-term return on plan assets 6.84 6.83 6.79 6.88 6.03 Annual salary increase 4.37 4.46 4.46 4.46 3.50 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 2018 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 4.49 % 4.51 % 4.48 % 4.49 % 4.65 % 4.47 % Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate 4.37 % 4.40 % 4.36 % 4.35 % 4.50 % 4.32 % Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 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. 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, 2019 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 6.50 4.50 2027 Pension Plans The total accumulated benefit obligation for the pension plans at December 31, 2019 and 2018 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2019 $ 13,391 $ 3,053 $ 4,222 $ 615 $ 151 $ 963 December 31, 2018 11,683 2,550 3,613 513 101 842 The actuarial loss of $2.3 billion recorded in the remeasurement of the Southern Company system pension plans at December 31, 2019 was primarily due to a 108 basis point decrease in the overall discount rate used to calculate the benefit obligation as a result of lower market interest rates. The actuarial gain of $1.1 billion recorded in the remeasurement of the Southern Company system pension plans at December 31, 2018 was primarily due to a 69 basis point increase in the overall discount rate used to calculate the benefit obligation as a result of higher market interest rates. Changes in the projected benefit obligations and the fair value of plan assets during the plan years ended December 31, 2019 and 2018 were as follows: 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 ) 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 13,808 $ 2,998 $ 4,188 $ 602 $ 139 $ 1,184 Dispositions (107 ) — — — (3 ) (104 ) Service cost 359 78 87 17 9 34 Interest cost 464 101 139 20 5 39 Benefits paid (618 ) (124 ) (191 ) (24 ) (3 ) (98 ) Actuarial (gain) loss (1,143 ) (237 ) (318 ) (58 ) (24 ) (148 ) Balance at end of year 12,763 2,816 3,905 557 123 907 Change in plan assets Fair value of plan assets at beginning of year 12,992 2,836 4,058 563 138 1,068 Dispositions (107 ) — — — (3 ) (104 ) Actual return (loss) on plan assets (711 ) (150 ) (218 ) (37 ) (9 ) (70 ) Employer contributions 55 13 14 3 — 2 Benefits paid (618 ) (124 ) (191 ) (24 ) (3 ) (98 ) Fair value of plan assets at end of year 11,611 2,575 3,663 505 123 798 Accrued liability $ (1,152 ) $ (241 ) $ (242 ) $ (52 ) $ — $ (109 ) The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2019 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 $ 14,055 $ 3,286 $ 4,480 $ 639 $ 159 $ 999 Non-qualified pension plan 733 118 130 31 26 68 Amounts recognized in the balance sheets at December 31, 2019 and 2018 related to the Registrants' pension plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2018: Prepaid pension costs $ — $ — $ — $ — $ 1 $ — Other regulatory assets, deferred (*) 3,566 955 1,230 167 — 160 Other deferred charges and assets — — — — — 74 Other current liabilities (55 ) (12 ) (15 ) (3 ) — (3 ) Employee benefit obligations (1,097 ) (229 ) (227 ) (49 ) (1 ) (179 ) Other regulatory liabilities, deferred (108 ) — — — — — AOCI 97 — — — 26 (44 ) (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 acquisition by Southern Company. Presented below are the amounts included in regulatory assets at December 31, 2019 and 2018 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, 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 Balance at December 31, 2018 Regulatory assets: Prior service cost $ 17 $ 6 $ 12 $ 2 $ (17 ) Net (gain) loss 3,441 949 1,218 165 83 Regulatory amortization — — — — 94 Total regulatory assets (*) $ 3,458 $ 955 $ 1,230 $ 167 $ 160 (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 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, 2019 and 2018 are presented in the following table: Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): (*) Balance at December 31, 2017 $ 3,155 $ 890 $ 1,105 $ 158 $ 217 Net (gain) loss 498 120 196 19 20 Change in prior service costs 1 — — — (18 ) Dispositions 12 — — — (34 ) Reclassification adjustments: Amortization of prior service costs (4 ) (1 ) (2 ) — 2 Amortization of net gain (loss) (204 ) (54 ) (69 ) (10 ) (12 ) Amortization of regulatory assets (*) — — — — (15 ) Total reclassification adjustments (208 ) (55 ) (71 ) (10 ) (25 ) Total change 303 65 125 9 (57 ) 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 (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 acquisition by Southern Company. Presented below are the amounts included in AOCI at December 31, 2019 and 2018 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 Company Southern Power Southern Company Gas (in millions) Balance at December 31, 2019 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 188 46 (8 ) Total AOCI $ 185 $ 46 $ (14 ) Balance at December 31, 2018 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 100 26 (38 ) Total AOCI $ 97 $ 26 $ (44 ) 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, 2019 and 2018 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2017 $ 107 $ 33 $ (42 ) Net (gain) loss 7 (5 ) 6 Dispositions (8 ) — (8 ) Reclassification adjustments: Amortization of net gain (loss) (9 ) (2 ) — Total reclassification adjustments (9 ) (2 ) — Total change (10 ) (7 ) (2 ) Balance at December 31, 2018 $ 97 $ 26 $ (44 ) Net (gain) loss 88 20 30 Balance at December 31, 2019 $ 185 $ 46 $ (14 ) 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) 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 2017 Service cost $ 293 $ 63 $ 74 $ 15 $ 23 Interest cost 455 98 138 20 42 Expected return on plan assets (897 ) (196 ) (283 ) (40 ) (70 ) Recognized net (gain) loss 162 42 57 7 18 Net amortization 12 2 3 1 1 Net periodic pension cost $ 25 $ 9 $ (11 ) $ 3 $ 14 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. 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, 2019 , estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2020 $ 628 $ 135 $ 204 $ 27 $ 5 $ 62 2021 646 141 208 28 6 62 2022 671 147 214 30 6 64 2023 693 153 220 30 6 62 2024 715 157 226 32 7 62 2025 to 2029 3,868 860 1,209 174 36 316 Other Postretirement Benefits Changes in the APBO and the fair value of the Registrants' plan assets during the plan years ended December 31, 2019 and 2018 were as follows: 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 ) 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 2,339 $ 517 $ 863 $ 97 $ 11 $ 310 Dispositions (18 ) — — — — (18 ) Service cost 24 6 6 1 1 2 Interest cost 75 17 28 3 — 10 Benefits paid (129 ) (28 ) (47 ) (5 ) (1 ) (17 ) Actuarial (gain) loss (432 ) (111 ) (178 ) (15 ) (2 ) (43 ) Retiree drug subsidy 6 2 3 — — — Balance at end of year 1,865 403 675 81 9 244 Change in plan assets Fair value of plan assets at beginning of year 1,053 406 386 25 — 125 Dispositions (18 ) — — — — (18 ) Actual return (loss) on plan assets (57 ) (25 ) (20 ) (1 ) — (5 ) Employer contributions 73 5 22 4 1 13 Benefits paid (123 ) (26 ) (44 ) (5 ) (1 ) (17 ) Fair value of plan assets at end of year 928 360 344 23 — 98 Accrued liability $ (937 ) $ (43 ) $ (331 ) $ (58 ) $ (9 ) $ (146 ) Amounts recognized in the balance sheets at December 31, 2019 and 2018 related to the Registrants' other postretirement benefit plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2018: Other regulatory assets, deferred (a) $ 99 $ — $ 60 $ 6 $ — $ (4 ) Other current liabilities (6 ) — — — — — Employee benefit obligations (b) (931 ) (43 ) (331 ) (58 ) (9 ) 146 Other regulatory liabilities, deferred (77 ) (8 ) — (2 ) — — AOCI (4 ) — — — 1 (4 ) (a) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 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, 2019 and 2018 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, 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 ) Balance at December 31, 2018: Regulatory assets (liabilities): Prior service cost $ 14 $ 8 $ 4 $ — $ 2 Net (gain) loss 8 (16 ) 56 4 (43 ) Regulatory amortization — — — — 37 Total regulatory assets (liabilities) (*) $ 22 $ (8 ) $ 60 $ 4 $ (4 ) (*) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 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, 2019 and 2018 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, 2017 $ 341 $ 56 $ 202 $ 17 $ 46 Net (gain) loss (298 ) (60 ) (132 ) (12 ) (42 ) Change in prior service costs — — — — (2 ) Reclassification adjustments: Amortization of prior service costs (7 ) (4 ) (1 ) — — Amortization of net gain (loss) (14 ) (1 ) (9 ) (1 ) — Amortization of regulatory assets (*) — — — — (6 ) Total reclassification adjustments (21 ) (5 ) (10 ) (1 ) (6 ) Total change (319 ) (65 ) (142 ) (13 ) (50 ) 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 ) (*) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 acquisition by Southern Company. Presented below are the amounts included in AOCI at December 31, 2019 and 2018 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 Power Southern Company Gas (in millions) Balance at December 31, 2019 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 1 2 (5 ) Total AOCI $ 2 $ 2 $ (4 ) Balance at December 31, 2018 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss (5 ) 1 (5 ) Total AOCI $ (4 ) $ 1 $ (4 ) The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2019 and 2018 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2017 $ 4 $ 3 $ (3 ) Net (gain) loss (8 ) (2 ) (2 ) Change from employee transfer — — 1 Total change (8 ) (2 ) (1 ) 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 ) 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) 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 2017 Service cost $ 24 $ 6 $ 7 $ 1 $ 2 Interest cost 79 17 29 3 10 Expected return on plan assets (66 ) (25 ) (25 ) (1 ) (7 ) Net amortization 20 5 9 1 1 Net periodic postretirement benefit cost $ 57 $ 3 $ 20 $ 4 $ 6 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, reflect expected future service and are estimated based on assumptions used to measure the APBO for the other postretirement benefit plans. The Registrants' estimated benefit payments are reduced by drug subsidy receipts expected as a result of the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit payments: 2020 $ 130 $ 29 $ 49 $ 6 $ — $ 18 2021 129 29 49 6 — 18 2022 129 29 49 6 1 18 2023 130 29 49 6 1 19 2024 129 29 48 6 1 18 2025 to 2029 630 145 238 29 3 83 Subsidy receipts: 2020 $ (5 ) $ (1 ) $ (2 ) $ — $ — $ — 2021 (6 ) (2 ) (2 ) — — — 2022 (6 ) (2 ) (3 ) — — — 2023 (6 ) (2 ) (3 ) — — — 2024 (6 ) (2 ) (3 ) (1 ) — — 2025 to 2029 (30 ) (9 ) (13 ) (2 ) — — Total: 2020 $ 125 $ 28 $ 47 $ 6 $ — $ 18 2021 123 27 47 6 — 18 2022 123 27 46 6 1 18 2023 124 27 46 6 1 19 2024 123 27 45 5 1 18 2025 to 2029 600 136 225 27 3 83 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 (such as commingled/pooled funds) are valued as Level 2 when the underlying holdings are comprised of Level 1 or Level 2 equity securities. Fixed income: A mix of domestic and

STOCK COMPENSATION

STOCK COMPENSATION	12 Months Ended
	Dec. 31, 2019
Equity [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. Southern Company Gas and Southern Power had no employee participants in the stock-based compensation plans until 2017 and 2018, respectively. In conjunction with the Merger, stock-based compensation in the form of Southern Company RSUs and PSUs was granted to certain executives of Southern Company Gas through the Southern Company Omnibus Incentive Compensation Plan. At December 31, 2019 , 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 2,320 307 370 89 50 285 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 -year performance period as compared to a group of industry peers; ROE awards based on Southern Company's equity-weighted return over the performance period; and EPS awards based on Southern Company's cumulative EPS over the performance period. EPS awards were last granted in 2017. The fair value of TSR awards is determined as of the grant date using a Monte Carlo simulation model to estimate the TSR of Southern Company's common stock among industry peers over the performance period. 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 2019 2018 2017 Expected volatility 15.6% 14.9% 15.6% Expected term (in years) 3 3 3 Interest rate 2.4% 2.4% 1.4% Weighted average grant-date fair value $62.71 $43.75 $49.08 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 awards granted during 2019 , 2018 , and 2017 was $49.38 , $43.49 , and $49.21 , 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, 2018 . In February 2019, the PSUs that vested for the three -year performance period ended December 31, 2018 were converted into 1.7 million shares outstanding at a share price of $49.24 . During 2019 , Southern Company granted 1.2 million PSUs and 1.2 million PSUs were vested or forfeited, resulting in 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 . Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 (in millions) Southern Company Compensation cost recognized in income $ 77 $ 91 $ 74 Tax benefit of compensation cost recognized in income 20 24 29 Southern Company Gas Compensation cost recognized in income $ 14 $ 11 $ 8 Tax benefit of compensation cost recognized in income 4 3 3 Total PSU compensation cost and the related tax benefit recognized in income were immaterial for all periods presented for Alabama Power, Georgia Power, Mississippi Power, and Southern Power. 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, 2019 , Southern Company's total unrecognized compensation cost related to PSUs was $31 million and is expected to be recognized over a weighted-average period of approximately 12 months . The total unrecognized compensation cost related to PSUs as of December 31, 2019 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 2019 , 2018 , and 2017 were $50.44 , $43.81 , and $49.25 , 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 -, or three -year vesting period. Shares of Southern Company common stock are delivered to employees at the end of each vesting period. Southern Company had 1.1 million RSUs outstanding at December 31, 2018 . During 2019 , Southern Company granted 0.6 million RSUs and 0.4 million RSUs were vested or forfeited, resulting in 1.3 million unvested RSUs outstanding at December 31, 2019 , including RSUs related to employee retention agreements. For the years ended December 31, 2019 , 2018 , and 2017 , Southern Company's total compensation cost for RSUs recognized in income was $28 million , $27 million , and $25 million , respectively. The related tax benefit also recognized in income was $7 million , $7 million , and $10 million for the years ended December 31, 2019 , 2018 , and 2017 , respectively. Total unrecognized compensation cost related to RSUs as of December 31, 2019 for Southern Company of $14 million will be recognized over a weighted-average period of approximately 10 months . Total RSUs outstanding and total compensation cost and related tax benefit for the RSUs recognized in income for the years ended December 31, 2019 , 2018 , and 2017 , as well as the total unrecognized compensation cost as of December 31, 2019 , 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. 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, 2019 , the weighted average remaining contractual term for the options outstanding and exercisable was approximately three years . As of December 31, 2017, all stock option awards are vested and compensation cost fully recognized. Total compensation cost for stock option awards and the related tax benefits recognized in income for the year ended December 31, 2017 were immaterial for Southern Company, Alabama Power, Georgia Power, and Mississippi Power. Southern Company's activity in the stock option program for 2019 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2018 17.5 $ 41.92 Exercised 11.6 41.62 Outstanding and Exercisable at December 31, 2019 5.9 $ 42.52 Southern Company's cash receipts from issuances related to stock options exercised under the share-based payment arrangements for the years ended December 31, 2019 , 2018 , and 2017 were $482 million , $41 million , and $239 million , respectively. At December 31, 2019 , the aggregate intrinsic value for the options outstanding and exercisable was as follows: Southern Company Alabama Power Georgia Power Mississippi Power (in millions) Total intrinsic value for outstanding and exercisable options $ 124 $ 14 $ 35 $ 6 Total intrinsic value of options exercised, and the related tax benefit, for the years ended December 31, 2019 , 2018 , and 2017 are presented below: Year Ended December 31 2019 2018 2017 (in millions) Southern Company Intrinsic value of options exercised $ 167 $ 9 $ 64 Tax benefit of options exercised 35 2 25 Alabama Power Intrinsic value of options exercised $ 21 $ 2 $ 12 Tax benefit of options exercised 4 — 5 Georgia Power Intrinsic value of options exercised $ 30 $ 2 $ 13 Tax benefit of options exercised 6 — 5 Mississippi Power Intrinsic value of options exercised $ 4 $ 1 $ 2 Tax benefit of options exercised 1 — 1 Total intrinsic value of options exercised, and the related tax benefit recognized in income, for the years ended December 31, 2019 and 2018 was immaterial for Southern Power and Southern Company Gas. Merger Stock Compensation Southern Company Restricted Stock Awards At the effective time of the Merger, each outstanding award of existing Southern Company Gas PSUs was converted into an award of Southern Company RSUs. Under the terms of the restricted stock awards, the employees received Southern Company stock when they satisfied the requisite service period by being continuously employed through the original three -year vesting schedule of the award being replaced. Southern Company issued 0.7 million RSUs with a grant-date fair value of $53.83 , based on the closing stock price of Southern Company common stock on the date of the grant. Approximately $13 million of the grant date fair value, which was related to pre-combination service, was accounted for as Merger consideration. Southern Company Gas recognized the remaining fair value as compensation expense on a straight-line basis over the remaining vesting period. The compensation cost related to the grant of RSUs to Southern Company Gas employees is recognized in Southern Company Gas' financial statements with a corresponding credit to equity, representing a capital contribution from Southern Company. As of December 31, 2018, all RSUs were vested. For the years ended December 31, 2018 and 2017, total compensation cost for RSUs recognized in income and the related tax benefit were immaterial. Southern Company Gas Change in Control Awards Southern Company awarded PSUs to certain Southern Company Gas employees who continued their employment with the Southern Company in lieu of certain change in control benefits the employee was entitled to receive following the Merger (change in control awards). Shares of Southern Company common stock and/or cash equal to the dollar value of the change in control benefit vested and were issued one-third each year as long as the employee remained in service with Southern Company or its subsidiaries at each vest date. In addition to the change in control benefit, Southern Company common stock was issued to the employees at the end of a performance period based on achievement of certain Southern Company common stock price metrics, as well performance goals established by the Compensation Committee of the Southern Company Board of Directors (achievement shares). The change in control benefits were accounted for as a liability award with the fair value equal to the guaranteed dollar value of the change in control benefit. The compensation cost of the change in control benefit was recognized in Southern Company Gas' financial statements with a corresponding credit to a liability. The grant-date fair value of the achievement portion of the award was determined using a Monte Carlo simulation model to estimate the number of achievement shares expected to vest based on the Southern Company common stock price. The compensation cost of the achievement shares was recognized in Southern Company Gas' financial statements with a corresponding credit to equity, representing a capital contribution from Southern Company. The expected payout was reevaluated annually with expense recognized to date increased or decreased proportionately based on the expected performance. The compensation cost ultimately recognized for the achievement shares was based on the actual performance. As of December 31, 2019 , all change in control awards are vested. For the year ended December 31, 2017, total compensation cost and the related tax benefit for the change in control awards recognized in income was $12 million and $6 million , respectively. Total compensation cost and the related tax benefit for the change in control awards recognized in income were immaterial for all other periods presented.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2019
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 determinative fair values. Fund managers value the assets using various inputs and techniques depending on the nature of the underlying investments. 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)(b) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (c)(d) 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)(b) $ 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: (c) 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: (c)(d) 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)(b) $ 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) Energy-related derivatives exclude $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude 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. At December 31, 2018 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 469 $ 292 $ — $ — $ 761 Foreign currency derivatives — 75 — — 75 Investments in trusts: (c)(d) Domestic equity 601 107 — — 708 Foreign equity 53 173 — — 226 U.S. Treasury and government agency securities — 261 — — 261 Municipal bonds — 83 — — 83 Pooled funds – fixed income — 14 — — 14 Corporate bonds 24 290 — — 314 Mortgage and asset backed securities — 68 — — 68 Private equity — — — 45 45 Cash and cash equivalents 16 — — — 16 Other 34 4 — — 38 Cash equivalents 765 1 — — 766 Other investments — 12 — — 12 Total $ 1,962 $ 1,380 $ — $ 45 $ 3,387 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 316 $ — $ — $ 964 Interest rate derivatives — 49 — — 49 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ 648 $ 388 $ 21 $ — $ 1,057 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c) Domestic equity 396 95 — — 491 Foreign equity 53 50 — — 103 U.S. Treasury and government agency securities — 18 — — 18 Municipal bonds — 1 — — 1 Corporate bonds 24 135 — — 159 Mortgage and asset backed securities — 23 — — 23 Private equity — — — 45 45 Other 6 — — — 6 Cash equivalents 116 1 — — 117 Other investments — 12 — — 12 Total $ 595 $ 341 $ — $ 45 $ 981 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c)(d) Domestic equity 205 1 — — 206 Foreign equity — 119 — — 119 U.S. Treasury and government agency securities — 243 — — 243 Municipal bonds — 82 — — 82 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 45 — — 45 Other 19 4 — — 23 Total $ 224 $ 655 $ — $ — $ 879 Liabilities: Energy-related derivatives $ — $ 21 $ — $ — $ 21 Interest rate derivatives — 2 — — 2 Total $ — $ 23 $ — $ — $ 23 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 255 — — — 255 Total $ 255 $ 3 $ — $ — $ 258 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Foreign currency derivatives — 75 — — 75 Cash equivalents 46 — — — 46 Total $ 46 $ 79 $ — $ — $ 125 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ — $ 31 $ 21 $ — $ 52 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 469 $ 272 $ — $ — $ 741 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 14 — — 14 Cash equivalents 4 — — — 4 Cash equivalents 40 — — — 40 Total $ 513 $ 301 $ — $ — $ 814 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 261 $ — $ — $ 909 (a) Energy-related derivatives exclude $8 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude cash collateral of $277 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 Southern Power 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 obligation is categorized as Level 3 under Fair Value Measurements as the fair value is determined using significant unobservable inputs for the forecasted facility generation in MW-hours, as well as other inputs such as a fixed dollar amount per MW-hour, and a discount rate. The fair value of contingent consideration reflects the net present value of expected payments and any periodic change arising from forecasted generation is expected to be immaterial. "Other investments" include investments 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, 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 $56 million and $45 million at December 31, 2019 and 2018 , respectively. Unfunded commitments related to the private equity investments totaled $70 million and $50 million at December 31, 2019 and 2018 , 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, 2019 and 2018 , other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company (a)(b) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (b) (in millions) 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 At December 31, 2018: Long-term debt, including securities due within one year: Carrying amount $ 45,023 $ 8,120 $ 9,838 $ 1,579 $ 5,017 $ 5,940 Fair value 44,824 8,370 9,800 1,546 4,980 5,965 (a) Amounts at December 31, 2018 include long-term debt of Gulf Power, which was classified as liabilities held for sale on Southern Company's balance sheet at December 31, 2018. See Note 15 under " Southern Company " and " Assets Held for Sale " for additional information. (b) The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the Merger. Southern Company Gas amortizes the fair value adjustments over the lives of the respective bonds. 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.

DERIVATIVES

DERIVATIVES	12 Months Ended
	Dec. 31, 2019
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 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 the respective fuel cost recovery clauses. • Cash Flow Hedges – Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in 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, 2019 , 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 Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 589 2023 2029 Alabama Power 88 2022 — Georgia Power 175 2023 — Mississippi Power 101 2023 — Southern Power 7 2020 2020 Southern Company Gas (*) 218 2022 2029 (*) 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 4,096 million mmBtu and short natural gas positions of 3,878 million mmBtu at December 31, 2019 , which is also included in Southern Company's total volume. At December 31, 2019 , 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 2020 . 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 23 million mmBtu for Southern Company, which includes 6 million mmBtu for Alabama Power, 7 million mmBtu for Georgia Power, 3 million mmBtu for Mississippi Power, and 7 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, 2020 are immaterial for Southern Power. 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, 2019 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Georgia Power $ 250 3-month LIBOR 2.23% March 2025 $ (6 ) Georgia Power 250 3-month LIBOR 2.40% March 2030 (11 ) Southern Company Gas 200 3-month LIBOR 1.81% September 2030 2 Fair Value Hedges of Existing Debt Southern Company parent 300 2.75% 3-month LIBOR + 0.92% June 2020 — Southern Company parent 1,500 2.35% 1-month LIBOR + 0.87% July 2021 (7 ) Southern Company $ 2,500 $ (22 ) The estimated pre-tax gains (losses) related to interest rate derivatives expected to be reclassified from AOCI to interest expense for the year ending December 31, 2020 total $(22) 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, 2019 , 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 $ (7 ) Southern Power 564 3.78% 500 1.85% June 2026 (1 ) Total $ 1,241 € 1,100 $ (8 ) 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, 2020 are $(24) 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, 2019 and 2018 , the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2019 2018 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: Other current assets/Other current liabilities $ 3 $ 70 $ 8 $ 23 Other deferred charges and assets/Other deferred credits and liabilities 6 44 9 26 Assets held for sale, current/Liabilities held for sale, current — — — 6 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 114 $ 17 $ 55 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 6 $ 3 $ 7 Other deferred charges and assets/Other deferred credits and liabilities — — 1 2 Interest rate derivatives: Other current assets/Other current liabilities 2 23 — 19 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 30 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 16 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 19 $ 54 $ 79 $ 81 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 461 $ 358 $ 561 $ 575 Other deferred charges and assets/Other deferred credits and liabilities 207 225 180 325 Total derivatives not designated as hedging instruments $ 668 $ 583 $ 741 $ 900 Gross amounts recognized $ 696 $ 751 $ 837 $ 1,036 Gross amounts offset (a) $ (463 ) $ (562 ) $ (524 ) $ (801 ) Net amounts recognized in the Balance Sheets (b) $ 233 $ 189 $ 313 $ 235 2019 2018 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 $ 2 $ 14 $ 3 $ 4 Other deferred charges and assets/Other deferred credits and liabilities 2 10 3 6 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 24 $ 6 $ 10 Gross amounts recognized $ 4 $ 24 $ 6 $ 10 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 2 $ 22 $ 2 $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 32 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 3 21 4 13 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 53 $ 6 $ 21 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 17 $ — $ 2 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 17 $ — $ 2 Gross amounts recognized $ 4 $ 70 $ 6 $ 23 Gross amounts offset $ (3 ) $ (3 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ 1 $ 67 $ — $ 17 2019 2018 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 $ — $ 15 $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 1 12 2 6 Total derivatives designated as hedging instruments for regulatory purposes $ 1 $ 27 $ 3 $ 9 Gross amounts recognized $ 1 $ 27 $ 3 $ 9 Gross amounts offset $ (1 ) $ (1 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 26 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ 3 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — — 1 2 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 16 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 17 $ 26 $ 79 $ 31 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 1 $ — $ — Total derivatives not designated as hedging instruments $ 2 $ 1 $ — $ — Gross amounts recognized $ 19 $ 27 $ 79 $ 31 Gross amounts offset $ — $ — $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 19 $ 27 $ 76 $ 28 2019 2018 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/Liabilities from risk management activities-current $ — $ 9 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 1 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 10 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 4 $ — $ 1 Interest rate derivatives: Assets from risk management activities/Liabilities from risk management activities-current 2 — — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 4 $ — $ 1 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 459 $ 357 $ 559 $ 574 Other deferred charges and assets/Other deferred credits and liabilities 207 225 180 325 Total derivatives not designated as hedging instruments $ 666 $ 582 $ 739 $ 899 Gross amounts recognized $ 668 $ 596 $ 741 $ 909 Gross amounts offset (a) $ (456 ) $ (555 ) $ (508 ) $ (785 ) Net amounts recognized in the Balance Sheets (b) $ 212 $ 41 $ 233 $ 124 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $99 million and $277 million at December 31, 2019 and 2018 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $4 million and $8 million at December 31, 2019 and 2018 , respectively. Energy-related derivatives not designated as hedging instruments were immaterial for the traditional electric operating companies at December 31, 2019 and 2018 . At December 31, 2019 and 2018 , 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, 2019 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power 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 Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2018 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (3 ) $ (6 ) $ (2 ) $ (8 ) Other regulatory assets, deferred (16 ) (3 ) (9 ) (4 ) — Assets held for sale, current (6 ) — — — — Other regulatory liabilities, current 1 — — — 1 Total energy-related derivative gains (losses) $ (40 ) $ (6 ) $ (15 ) $ (6 ) $ (7 ) For the years ended December 31, 2019 , 2018 , and 2017 , 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 2019 2018 2017 (in millions) Southern Company Energy-related derivatives $ (13 ) $ 17 $ (47 ) Interest rate derivatives (57 ) (1 ) (2 ) Foreign currency derivatives (84 ) (78 ) 140 Total $ (154 ) $ (62 ) $ 91 Georgia Power Interest rate derivatives $ (59 ) $ — $ 1 Southern Power Energy-related derivatives $ (4 ) $ 10 $ (38 ) Foreign currency derivatives (84 ) (78 ) 140 Total $ (88 ) $ (68 ) $ 102 Southern Company Gas Energy-related derivatives $ (9 ) $ 7 $ (9 ) Interest rate derivatives 2 — — Total $ (7 ) $ 7 $ (9 ) For all years presented, the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments on AOCI were immaterial for the other Registrants. In addition, for the year ended December 31, 2017 , there was no material ineffectiveness recorded in earnings for any Registrant. Upon the adoption of ASU 2017-12, beginning in 2018, ineffectiveness was no longer separately measured and recorded in earnings. The pre-tax effects of cash flow and fair value hedge accounting on income for the years ended December 31, 2019 , 2018 , and 2017 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2019 2018 2017 (in millions) Southern Company Total cost of natural gas $ 1,319 $ 1,539 $ 1,601 Gain (loss) on energy-related cash flow hedges (a) (2 ) 2 (2 ) Total depreciation and amortization 3,038 3,131 3,010 Gain (loss) on energy-related cash flow hedges (a) (6 ) 7 (16 ) Total interest expense, net of amounts capitalized (1,736 ) (1,842 ) (1,694 ) Gain (loss) on interest rate cash flow hedges (a) (20 ) (21 ) (21 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (24 ) (23 ) Gain (loss) on interest rate fair value hedges (b) 42 (12 ) (22 ) Total other income (expense), net 252 114 163 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) (60 ) 160 Alabama Power Total interest expense, net of amounts capitalized $ (336 ) $ (323 ) $ (305 ) Gain (loss) on interest rate cash flow hedges (a) (6 ) (6 ) (6 ) Georgia Power Total interest expense, net of amounts capitalized $ (409 ) $ (397 ) $ (419 ) Gain (loss) on interest rate cash flow hedges (a) (3 ) (4 ) (4 ) Gain (loss) on interest rate fair value hedges (b) 2 2 (3 ) Mississippi Power Total interest expense, net of amounts capitalized $ (69 ) $ (76 ) $ (42 ) Gain (loss) on interest rate cash flow hedges (a) (2 ) (2 ) (2 ) Southern Power Total depreciation and amortization $ 479 $ 493 $ 503 Gain (loss) on energy-related cash flow hedges (a) (6 ) 7 (17 ) Total interest expense, net of amounts capitalized (169 ) (183 ) (191 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (24 ) (23 ) Total other income (expense), net 47 23 1 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) (60 ) 159 Southern Company Gas Total cost of natural gas $ 1,319 $ 1,539 $ 1,601 Gain (loss) on energy-related cash flow hedges (a) (2 ) 2 (2 ) (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 were immaterial for Southern Company Gas for all years presented. At December 31, 2019 and 2018 , 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, 2019 At December 31, 2018 At December 31, 2019 At December 31, 2018 (in millions) (in millions) Southern Company Securities due within one year $ — $ (498 ) $ — $ 2 Long-term debt (2,093 ) (2,052 ) 3 41 Georgia Power Securities due within one year $ — $ (498 ) $ — $ 2 The pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income for the years ended December 31, 2019 , 2018 , and 2017 for the applicable Registrants were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2019 2018 2017 (in millions) Southern Company Energy-related derivatives Natural gas revenues (*) $ 223 $ (122 ) $ (80 ) Cost of natural gas 10 (6 ) (2 ) Wholesale electric revenues 2 2 (4 ) Total derivatives in non-designated hedging relationships $ 235 $ (126 ) $ (86 ) Southern Company Gas Energy-related derivatives Natural gas revenues (*) $ 223 $ (122 ) $ (80 ) Cost of natural gas 10 (6 ) (2 ) Total derivatives in non-designated hedging relationships $ 233 $ (128 ) $ (82 ) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $3 million , $5 million , and $23 million for the years ended December 31, 2019 , 2018 , and 2017 , 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, 2019 , the Registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the Registrants with interest rate derivatives at December 31, 2019 , the fair value of interest rate derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, was immaterial. At December 31, 2019 , 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. Based on the value of the positions in these accounts and the associated margin requirements, Alabama Power and Southern Power may be required to post collateral. At December 31, 2019 , 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, 2019 , cash collateral held on deposit in broker margin accounts was $99 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. Prior to entering into a physical transaction, Southern Company Gas assigns physical wholesale 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. In addition, Southern Company Gas conducts credit evaluations and obtains appropriate internal approvals for the counterparty's line of credit before any transaction with the counterparty is executed. In most cases, the counterparty must have an investment grade rating, which includes a minimum long-term debt rating of Baa3 from Moody's and BBB- from S&P. Generally, Southern Company Gas requires credit enhancements by way of a guaranty, cash deposit, or letter of credit for transaction counterparties that do not have investment grade ratings. Southern Company Gas also utilizes master netting agreements whenever possible to mitigate exposure to counterparty credit risk. When Southern Company Gas is engaged in more than one outstanding derivative transaction with the same counterparty and it also has a legally enforceable netting agreement with that counterparty, the "net" mark-to-market exposure represents the netting of the positive and negative exposures with that counterparty and a reasonable measure of Southern Company Gas' credit risk. Southern Company Gas also uses other netting agreements with certain counterparties with whom it conducts significant transactions. Master netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty. Southern Company Gas also nets across product lines and against cash collateral provided the master netting and cash collateral agreements include such provisions. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. 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, 2019
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS Southern Company On January 1, 2019, Southern Company completed the sale of all of the capital stock of Gulf Power to 700 Universe, LLC, 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). The assets and liabilities of Gulf Power were classified as assets held for sale and liabilities held for sale on Southern Company's balance sheet as of December 31, 2018. See " Assets Held for Sale " herein for additional information. On July 22, 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. On December 30, 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. On December 31, 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. Alabama Power On September 6, 2019, Alabama Power entered into the Autauga Combined Cycle Acquisition, a purchase and sale agreement to acquire all of the equity interests in Tenaska Alabama II Partners, L.P. Tenaska Alabama II Partners, L.P. owns and operates an approximately 885 -MW combined cycle generation facility in Autauga County, Alabama. The transaction is expected to close by September 1, 2020. As part of the Autauga Combined Cycle Acquisition, Alabama Power will assume an existing power sales agreement under which the full output of the generating facility remains committed to another third party for its remaining term of approximately three years . The estimated revenues from the power sales agreement are expected to offset the associated costs of operation during the remaining term. The completion of the Autauga Combined Cycle Acquisition is subject to the satisfaction or waiver of certain conditions, including, among other customary conditions, approval by the Alabama PSC and the FERC. Alabama Power expects to obtain all regulatory approvals by the end of the third quarter 2020. The ultimate outcome of this matter cannot be determined at this time. Southern Power During 2019 and 2018 , Southern Power or one of its wholly-owned subsidiaries acquired, completed, or continued construction of the facilities discussed below. Acquisition-related costs were expensed as incurred and were not material for any of the years presented. Acquisitions During 2019 During 2019 , Southern Power acquired a controlling interest in the fuel cell generation facility listed below and acquired the Skookumchuck wind facility discussed under " Construction Projects " below. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Remaining Period DSGP (a) Fuel Cell Bloom Energy 28 Delaware 100% of Class B N/A (b) 15 years (a) During 2019, Southern Power made a total investment of approximately $167 million in DSGP and now holds a controlling interest and consolidates 100% of DSGP's operating results. Southern Power records net income attributable to noncontrolling interests for approximately 10 MWs of the facility. (b) 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. In connection with the Class C member joining the partnership, the original fuel cells (before repower), which had a carrying value of approximately $55 million , were distributed to the Class A member in a non-cash transaction that was excluded from the statements of cash flows. Acquisitions During 2018 During 2018, Southern Power acquired and completed the project below and acquired the Wildhorse Mountain and Reading wind facilities discussed under " Construction Projects " below. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC 20 Kern County, CA 100% of Class B (*) March 20 years (*) Southern Power owns 100% of the Class B membership interests under a tax equity partnership. The Gaskell West 1 facility did not have operating revenues or activities prior to being placed in service during March 2018. Construction Projects During 2019 , Southern Power completed construction of and placed in service the 385 -MW Plant Mankato expansion and the Wildhorse Mountain facility, acquired and continued construction of the Skookumchuck facility, and continued construction of the Reading facility. Total aggregate construction costs, excluding acquisition costs, are expected to be between $490 million and $535 million for the two facilities under construction. At December 31, 2019 , total costs of construction incurred for the two facilities under construction were $417 million and are included in CWIP. The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Completed During the Year Ended December 31, 2019 Mankato expansion (a) Natural Gas 385 Mankato, MN May 2019 20 years Wildhorse Mountain (b) Wind 100 Pushmataha County, OK December 2019 20 years Projects Under Construction at December 31, 2019 Reading (c) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 12 years Skookumchuck (d) Wind 136 Lewis and Thurston Counties, WA Second quarter 2020 20 years (a) Southern Power completed the sale of its equity interests in Plant Mankato, including the expansion, to a subsidiary of Xcel on January 17, 2020. The expansion unit started providing energy under a PPA with Northern States Power on June 1, 2019. See " Sales of Natural Gas and Biomass Plants " below and " Assets Held for Sale " herein for additional information. (b) In May 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, as a result, owns 100% of the Class B membership interests. (c) In August 2018, Southern Power purchased 100% of the membership interests of the Reading facility pursuant to a joint development arrangement. Southern Power may enter into a tax equity partnership, in which case it would then own 100% of the Class B membership interests. The ultimate outcome of this matter cannot be determined at this time. (d) In October 2019, Southern Power purchased 100% of the membership interests of the Skookumchuck facility pursuant to a joint development arrangement. In December 2019, Southern Power entered into a tax equity agreement as the Class B member with funding of the tax equity amounts expected to occur upon commercial operation. Shortly after commercial operation, Southern Power may sell a noncontrolling interest in these Class B membership interests to another partner. The ultimate outcome of this matter cannot be determined at this time. 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 2020 and 2021, are expected to qualify for 100% and 80% PTCs, respectively. The significant majority of this equipment either has been deployed to completed projects, projects under construction, or projects that are probable of being completed 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. Sales during 2019 resulted in gains totaling approximately $17 million . 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 through its wholly-owned general partner, 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 the Florida Plants to NextEra Energy for $203 million , including 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 May 2018. On June 13, 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 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 estimated working capital adjustments. The sale resulted in a gain of approximately $39 million ( $23 million after tax) in 2020. The assets and liabilities of Plant Mankato are classified as held for sale on Southern Company's and Southern Power's balance sheets as of December 31, 2019 and 2018. 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 the first quarter 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 through November 4, 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 will provide certain administrative and operational services through no later than July 31, 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 will provide certain administrative and operational services through no later than July 29, 2020. Sale of Triton On May 29, 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. Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline On February 7, 2020, Southern Company Gas entered into agreements with Dominion Modular LNG Holdings, Inc. and Dominion Atlantic Coast Pipeline, LLC for the sale of its interests in Pivotal LNG and Atlantic Coast Pipeline, respectively, for an aggregate purchase price of $165 million , including estimated working capital and timing adjustments. Southern Company Gas may also receive two payments of $5 million each, contingent upon certain milestones related to Pivotal LNG being met by Dominion Modular LNG Holdings, Inc. after the completion of the sale. Based on the terms of these pending 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 completion of each transaction is subject to the satisfaction or waiver of certain conditions, including, among other customary closing conditions, the completion of the other transaction and, for the sale of the interest in Atlantic Coast Pipeline, the expiration or termination of any applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. The transactions are expected to be completed in the first half of 2020; however, the ultimate outcome cannot be determined at this time. The assets and liabilities of Pivotal LNG and the interest in Atlantic Coast Pipeline are classified as held for sale as of December 31, 2019. See Notes 3 and 7 under "Southern Company Gas – Gas Pipeline Projects" and "Southern Company Gas – Equity Method Investments," respectively, and " Assets Held for Sale " herein for additional information. Assets Held for Sale As discussed previously, Southern Company, Southern Power, and Southern Company Gas each have assets and liabilities held for sale on their balance sheets at December 31, 2019 and/or 2018. Assets and liabilities held for sale have been classified separately on each company's balance sheet at the lower of carrying value or fair value less costs to sell at the time the criteria for held-for-sale classification were met. For assets and liabilities held for sale recorded at fair value on a nonrecurring basis, the fair value of assets held for sale is based primarily on unobservable inputs (Level 3), which includes the agreed upon sales prices in executed sales agreements. 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, 2019 and/or 2018: Southern Company Southern Power Southern Company Gas At December 31, At December 31, At December 31, 2019 2018 2019 2018 2019 (in millions) (in millions) (in millions) Assets Held for Sale: Current assets $ 19 $ 393 $ 17 $ 8 $ 2 Total property, plant, and equipment 565 4,583 547 536 18 Goodwill and other intangible assets 40 40 40 40 — Equity investments in unconsolidated subsidiaries 151 — — — 151 Other non-current assets 14 727 14 — — Total Assets Held for Sale $ 789 $ 5,743 $ 618 $ 584 $ 171 Liabilities Held for Sale: Current liabilities $ 5 $ 425 $ 3 $ 15 $ 2 Long-term debt — 1,286 — — — Accumulated deferred income taxes — 618 — — — Other non-current liabilities — 932 — — — Total Liabilities Held for Sale $ 5 $ 3,261 $ 3 $ 15 $ 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; therefore, pre-tax income for these components for the years ended December 31, 2019 , 2018 , and 2017 are presented below: 2019 2018 2017 (in millions) Earnings before income taxes: (a) Gulf Power N/A $ 140 $ 229 Southern Power's Florida Plants (b) N/A $ 49 $ 37 Southern Power's Plant Nacogdoches (c) $ 13 $ 27 $ 25 Southern Power's Plant Mankato $ 29 N/M N/M N/M - Not material (a) Earnings before income taxes for Southern Power's components reflect the cessation of depreciation and amortization on the long-lived assets being sold upon classification as held for sale. (b) Earnings before income taxes for the Florida Plants in 2018 represents the period from January 1, 2018 to December 4, 2018 (the divestiture date). (c) Earnings before income taxes for Plant Nacogdoches in 2019 represents January 1, 2019 through June 13, 2019 (the divestiture date).

SEGMENT AND RELATED INFORMATION

SEGMENT AND RELATED INFORMATION (Notes)	12 Months Ended
	Dec. 31, 2019
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 $398 million , $435 million , and $392 million in 2019 , 2018 , and 2017 , respectively. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies and Southern Power were $14 million and $64 million , respectively, in 2019 , $32 million and $119 million , respectively, in 2018 , and $23 million and $119 million , respectively, in 2017 . 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, 2019 , 2018 , and 2017 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) 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)(b)(c)(d)(e) 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 Gross property additions 5,748 489 — 6,237 1,418 159 — 7,814 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)(f)(g) 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 Gross property additions 6,077 315 — 6,392 1,399 414 — 8,205 2017 Operating revenues $ 16,884 $ 2,075 $ (419 ) $ 18,540 $ 3,920 $ 741 $ (170 ) $ 23,031 Depreciation and amortization 1,954 503 — 2,457 501 52 — 3,010 Interest income 14 7 — 21 3 11 (9 ) 26 Earnings from equity method investments 1 — — 1 106 (1 ) — 106 Interest expense 820 191 — 1,011 200 490 (7 ) 1,694 Income taxes (benefit) 1,021 (939 ) — 82 367 (307 ) — 142 Segment net income (loss) (a)(b)(h)(i) (193 ) 1,071 — 878 243 (279 ) — 842 Goodwill — 2 — 2 5,967 299 — 6,268 Total assets 72,204 15,206 (325 ) 87,085 22,987 2,552 (1,619 ) 111,005 Gross property additions 3,836 268 — 4,104 1,525 355 — 5,984 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $24 million ( $24 million after tax) in 2019 , $1.1 billion ( $722 million after tax) in 2018 , and $3.4 billion ( $2.4 billion after tax) in 2017 . See Note 2 under " Georgia Power – Nuclear Construction " and " Mississippi Power – Kemper County Energy Facility – Schedule and Cost Estimate " for additional information. (c) Segment net income (loss) for Southern Power includes a $23 million pre-tax gain ( $88 million gain after tax) on the sale of Plant Nacogdoches in 2019. See Note 15 under "Southern Power" for additional information. (d) Segment net income (loss) for Southern Company Gas in 2019 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 – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. (e) Segment net income (loss) for the "All Other" column in 2019 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. (f) Segment net income (loss) for Southern Power includes pre-tax impairment charges of $156 million ( $117 million after tax) in 2018. See Note 15 under " Southern Power " for additional information. (g) Segment net income (loss) for Southern Company Gas includes a net gain on dispositions of $291 million ( $51 million loss after tax) in 2018 related to the Southern Company Gas Dispositions and a goodwill impairment charge of $42 million in 2018 related to the sale of Pivotal Home Solutions. See Note 15 under " Southern Company Gas " for additional information. (h) Segment net income (loss) for the traditional electric operating companies includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) in 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. (i) Segment net income (loss) includes income tax expense of $367 million for the traditional electric operating companies, income tax benefit of $743 million for Southern Power, and income tax expense of $93 million for Southern Company Gas in 2017 related to the Tax Reform Legislation. Products and Services Electric Utilities' Revenues Year Retail Wholesale Other Total (in millions) 2019 $ 14,084 $ 2,152 $ 859 $ 17,095 2018 15,222 2,516 833 18,571 2017 15,330 2,426 784 18,540 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2019 $ 3,001 $ 456 $ 335 $ 3,792 2018 3,155 568 186 3,909 2017 3,024 860 36 3,920 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. During 2018, Southern Company Gas changed its reportable segments to further align the way its Chief Operating Decision Maker reviews operating results and reclassified prior year data to conform to the new reportable segment presentation. This change resulted in a new reportable segment, gas pipeline investments, which was formerly included in gas midstream operations. 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. See Note 15 under " Southern Company Gas " for additional information. Gas pipeline investments consists of joint ventures in natural gas pipeline investments including a 50% interest in SNG, two significant pipeline construction projects, 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. See Notes 3 , 5 , 7 , and 15 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. See Note 15 under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. The all other column includes segments below the quantitative threshold for separate disclosure, including storage and fuels operations, Pivotal LNG, the investment in Triton through its sale on May 29, 2019, and other subsidiaries that fall below the quantitative threshold for separate disclosure. See Note 15 under " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline " for additional information. Financial data for business segments for the years ended December 31, 2019 , 2018 , and 2017 was as follows: Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other (e) Eliminations Consolidated (in millions) 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 Gross property additions 1,433 1 1 4 1,439 27 — 1,466 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 Gross property additions 1,429 32 — 6 1,467 54 — 1,521 Total assets at December 31, 2018 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) 21,448 2017 Operating revenues $ 3,207 $ 17 $ 6 $ 860 $ 4,090 $ 64 $ (234 ) $ 3,920 Depreciation and amortization 391 2 2 62 457 44 — 501 Operating income (loss) 645 10 (51 ) 113 717 (57 ) — 660 Earnings from equity method investments — 103 — — 103 3 — 106 Interest expense (153 ) (26 ) (7 ) (5 ) (191 ) (9 ) — (200 ) Income taxes (f) 178 109 — 24 311 56 — 367 Segment net income (loss) (f) 353 (22 ) (57 ) 84 358 (115 ) — 243 Gross property additions 1,330 117 1 9 1,457 51 — 1,508 Total assets at December 31, 2017 19,358 1,699 1,096 2,147 24,300 12,726 (14,039 ) 22,987 (a) Operating revenues for the three gas distribution operations dispositions were $244 million and $399 million for 2018 and 2017, respectively. See Note 15 under " Southern Company Gas " for additional information. (b) Segment net income for gas distribution operations includes a gain on dispositions of $324 million ( $16 million after tax) 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. See Note 15 under " Southern Company Gas " for additional information. (c) 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) 2019 $ 5,703 $ 275 $ 5,978 $ 5,684 $ 294 2018 6,955 451 7,406 7,262 144 2017 6,152 481 6,633 6,627 6 (d) Operating revenues for the gas marketing services disposition were $55 million and $129 million in 2018 and 2017, respectively. See Note 15 under " Southern Company Gas " for additional information. (e) Segment net income (loss) for the "All Other" column in 2019 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 – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. (f) Includes the impact of the Tax Reform Legislation and new income tax apportionment factors in several states resulting from Southern Company Gas' inclusion in the consolidated Southern Company state tax filings.

QUARTERLY FINANCIAL INFORMATION

QUARTERLY FINANCIAL INFORMATION (UNAUDITED)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY FINANCIAL INFORMATION (UNAUDITED)	QUARTERLY FINANCIAL INFORMATION (UNAUDITED) The tables below provide summarized quarterly financial information for each Registrant for 2019 and 2018 . Each Registrant's business is influenced by seasonal weather conditions. Quarter Ended Southern Company (a) Alabama Power Georgia Power Mississippi Power (b) Southern Power (c) Southern Company Gas (d) (in millions) March 2019 Operating Revenues $ 5,412 $ 1,408 $ 1,833 $ 287 $ 443 $ 1,474 Operating Income (Loss) 3,691 338 448 56 60 353 Net Income (Loss) 2,059 217 311 37 27 270 Net Income (Loss) Attributable to Registrant 2,084 217 311 37 56 270 June 2019 Operating Revenues $ 5,098 $ 1,513 $ 2,117 $ 313 $ 510 $ 689 Operating Income (Loss) 1,342 445 647 54 153 134 Net Income (Loss) 931 296 448 37 203 106 Net Income (Loss) Attributable to Registrant 899 296 448 37 174 106 September 2019 Operating Revenues $ 5,995 $ 1,841 $ 2,755 $ 370 $ 574 $ 498 Operating Income (Loss) 2,013 676 1,161 93 167 (35 ) Net Income (Loss) 1,345 469 839 65 111 (29 ) Net Income (Loss) Attributable to Registrant 1,316 469 839 65 86 (29 ) December 2019 Operating Revenues $ 4,914 $ 1,363 $ 1,703 $ 294 $ 411 $ 1,131 Operating Income (Loss) 690 134 205 22 15 318 Net Income (Loss) 409 88 122 — (12 ) 238 Net Income (Loss) Attributable to Registrant 440 88 122 — 23 238 (a) Southern Company recorded a preliminary pre-tax gain associated with the sale of Gulf Power of $2.5 billion ( $1.3 billion after tax) in the first quarter 2019 and recorded subsequent adjustments of $(15) million ( $(11) million after tax) in the second quarter 2019, $4 million ( $4 million after tax) in the third quarter 2019, and $70 million ( $102 million after tax) in the fourth quarter 2019. In addition, Southern Company recorded a pre-tax loss, including related impairment charges, on the sales of certain PowerSecure business units totaling $32 million in the second quarter 2019, $14 million ( $15 million after tax) in the third quarter 2019, and $12 million ( $5 million after tax) in the fourth quarter 2019, as well as a pre-tax impairment charge of $17 million ( $13 million after tax) in the fourth quarter 2019 related to a leveraged lease investment. See Notes 3 and 15 under " Other Matters – Southern Company " and " Southern Company ," respectively, for additional information. Also see notes (b), (c), and (d) below. (b) Mississippi Power recorded total pre-tax charges to income of $2 million ( $1 million after tax) in the first quarter 2019, $4 million ( $3 million after tax) in the second quarter 2019, $4 million ( $3 million after tax) in the third quarter 2019, and $14 million ( $17 million after tax) in the fourth quarter 2019 as a result of 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. The fourth quarter charges include impacts associated with the expected close out of a DOE contract related to the Kemper County energy facility, as well as an adjustment related to the tax abandonment of the Kemper IGCC following the filing of the 2018 tax return. See Note 2 under " Mississippi Power – Kemper County Energy Facility " for additional information. (c) Southern Power recorded a pre-tax gain of $23 million ( $88 million gain after tax) in the second quarter 2019 on the sale of Plant Nacogdoches. See Note 15 under " Southern Power " for additional information. (d) Southern Company Gas recorded pre-tax impairment charges of $92 million ( $65 million after tax) in the third quarter 2019, and a subsequent adjustment of $(1) million ( $4 million after tax) in the fourth quarter 2019, related to a natural gas storage facility in Louisiana and $24 million ( $17 million after tax) in the fourth quarter 2019 in contemplation of the sale of its interests in Pivotal LNG and Atlantic Coast Pipeline. See Notes 3 and 15 under " Other Matters – Southern Company Gas " and " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. Quarter Ended Southern Company (a) Alabama Power Georgia Power (b) Mississippi Power (c) Southern Power (d) Southern Company Gas (e) (in millions) March 2018 Operating Revenues $ 6,372 $ 1,473 $ 1,961 $ 302 $ 509 $ 1,639 Operating Income (Loss) 1,376 372 513 7 60 388 Net Income (Loss) 936 225 352 (7 ) 115 279 Net Income (Loss) Attributable to Registrant 938 225 352 (7 ) 121 279 June 2018 Operating Revenues $ 5,627 $ 1,503 $ 2,048 $ 297 $ 555 $ 730 Operating Income (Loss) 63 380 (472 ) 54 16 49 Net Income (Loss) (127 ) 259 (396 ) 46 45 (31 ) Net Income (Loss) Attributable to Registrant (154 ) 259 (396 ) 46 22 (31 ) September 2018 Operating Revenues $ 6,159 $ 1,740 $ 2,593 $ 358 $ 635 $ 492 Operating Income (Loss) 2,174 561 991 80 136 374 Net Income (Loss) 1,222 373 664 47 146 46 Net Income (Loss) Attributable to Registrant 1,164 373 664 47 92 46 December 2018 Operating Revenues $ 5,337 $ 1,316 $ 1,818 $ 308 $ 506 $ 1,048 Operating Income (Loss) 578 164 257 52 30 104 Net Income (Loss) 269 73 173 149 (60 ) 78 Net Income (Loss) Attributable to Registrant 278 73 173 149 (48 ) 78 (a) See notes (b), (c), (d), and (e) below. (b) Georgia Power recorded an estimated probable loss of $1.1 billion in the second quarter 2018 to reflect its revised estimate to complete construction and start-up of Plant Vogtle Units 3 and 4. See Note 2 under " Georgia Power – Nuclear Construction " for additional information. (c) As a result of the abandonment and related closure activities for the mine and gasifier-related assets at the Kemper County energy facility, Mississippi Power recorded total pre-tax charges to income of $44 million ( $33 million after tax) in the first quarter 2018, immaterial amounts in the second and third quarters 2018, and a pre-tax credit to income of $9 million in the fourth quarter 2018. In addition, Mississippi Power recorded a credit to earnings of $95 million in the fourth quarter 2018 primarily resulting from the reduction of a valuation allowance for a state income tax NOL carryforward associated with the Kemper County energy facility. See Note 2 under " Mississippi Power – Kemper County Energy Facility " and Note 10 for additional information. (d) Southern Power recorded pre-tax impairment charges of $119 million ( $89 million after tax) in the second quarter 2018 in contemplation of the sale of the Florida Plants and $36 million ( $27 million after tax) in the third quarter 2018 related to wind turbine equipment. See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " and " – Development Projects " for additional information. As a result of the Tax Reform Legislation, Southern Power recorded income tax expense of $75 million in the fourth quarter 2018. See Note 10 for additional information. (e) Southern Company Gas recorded a goodwill impairment charge of $42 million in the first quarter 2018 in contemplation of the sale of Pivotal Home Solutions. Southern Company Gas also recorded gains (losses) on dispositions in the second, third, and fourth quarters 2018 of $(36) million ( $(76) million after tax), $353 million ( $40 million after tax), and $(27) million ( $(15) million after tax), respectively. See Note 15 under " Southern Company Gas " for additional information. The table below provides quarterly earnings per share financial information for Southern Company common stock for 2019 and 2018 . Earnings Per Common Share (*) Quarter Ended Basic Diluted March 2019 $ 2.01 $ 1.99 June 2019 0.86 0.85 September 2019 1.26 1.25 December 2019 0.42 0.42 March 2018 $ 0.93 $ 0.92 June 2018 (0.15 ) (0.15 ) September 2018 1.14 1.13 December 2018 0.27 0.27 (*) See the notes below the two preceding tables for additional information.

VALUATION AND QUALIFYING ACCOUN

VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions Reclassified to Held for Sale (c) Balance at End of Period Provision for uncollectible accounts (a) 2019 $ 50 $ 68 $ — $ 69 $ — $ 49 2018 44 69 (1 ) 61 1 50 2017 43 56 — 55 — 44 Tax valuation allowance (net state) (b) 2019 $ 100 $ 13 $ — $ — $ — $ 113 2018 148 (38 ) — 10 — 100 2017 22 126 — — — 148 (a) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (b) In 2017, Mississippi Power established a valuation allowance for the State of Mississippi net operating loss carryforward expected to expire prior to being fully utilized. This valuation allowance was reduced in 2018 as a result of higher projected state taxable income. 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. (c) Represents provision for uncollectible accounts at Gulf Power presented on Southern Company's balance sheet at December 31, 2018 as assets held for sale, current. See Note 15 to the financial statements under " Southern Company " and " Assets Held for Sale " in Item 8 herein for additional information. ALABAMA POWER COMPANY SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions (*) Balance at End of Period Provision for uncollectible accounts 2019 $ 10 $ 24 $ — $ 12 $ 22 2018 9 13 — 12 10 2017 10 10 — 11 9 (*) 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, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions Balance at End of Period Provision for uncollectible accounts (a) 2019 $ 2 $ 13 $ — $ 13 $ 2 2018 3 11 — 12 2 2017 3 11 — 11 3 Tax valuation allowance (net state) (b) 2019 $ 33 $ (5 ) $ — $ — $ 28 2018 — 39 — 6 33 2017 — — — — — (a) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (b) 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, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions Balance at End of Period Provision for uncollectible accounts (a) 2019 $ 1 $ 2 $ — $ 2 $ 1 2018 1 1 — 1 1 2017 — 2 — 1 1 Tax valuation allowance (net state) (b) 2019 $ 32 $ — $ — $ — $ 32 2018 124 (92 ) — — 32 2017 — 124 — — 124 (a) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. (b) In 2017, Mississippi Power established a valuation allowance for the State of Mississippi net operating loss carryforward expected to expire prior to being fully utilized, which was reduced in 2018 as a result of higher projected state taxable income. 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, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions Balance at End of Period Tax valuation allowance (net state) 2019 $ 22 $ 7 $ — $ — $ 29 2018 10 12 — — 22 2017 — 10 — — 10 SOUTHERN COMPANY GAS AND SUBSIDIARY COMPANIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2019 , 2018 , AND 2017 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Deductions Balance at End of Period Provision for uncollectible accounts (a) 2019 $ 30 $ 29 $ — $ 41 $ 18 2018 28 33 (1 ) 30 30 2017 27 28 — 27 28 Tax valuation allowance (net state) (b) 2019 $ 12 $ (8 ) $ — $ — $ 4 2018 11 1 — — 12 2017 19 — — 8 11 (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, 2019
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. On January 1, 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 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 of and developing 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 at Southern Power and Southern Company Gas, as well as additional information regarding 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 partial 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 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 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.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards See Note 4 for information on the Registrants' adoption of ASC 606, Revenue from Contracts with Customers (ASC 606) effective January 1, 2018. In 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged and there is no change to the accounting for existing leveraged leases. The Registrants adopted the new standard effective January 1, 2019. See Note 9 for additional information and related disclosures.
Affiliate Transactions	Affiliate Transactions
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities The traditional electric operating companies and 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 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 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 ASC 606, lease, derivative, and regulatory accounting. Other than the timing of recognition of guaranteed and fixed billing arrangements at Southern Company Gas, the adoption of ASC 606 in 2018 had no impact on the timing or amount of revenue recognized under previous guidance. See Note 4 for information regarding the Registrants' adoption of ASC 606 and related disclosures. Traditional Electric Operating Companies The majority of the revenues of the traditional electric operating companies are generated from contracts with retail electric customers. Retail revenues recognized under ASC 606 are consistent with prior revenue recognition policies. 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 billings 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 either on a levelized basis over the appropriate contract period or the amount billable under the contract terms. Energy and other revenues are generally recognized as services are provided. The accounting for these revenues under ASC 606 is consistent with prior revenue recognition policies. 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 generally have a right to consideration in an amount that corresponds directly with the value to the customer of the entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice and has elected to recognize revenue for its sales of electricity and capacity using the invoice practical expedient. In addition, payment for goods and services rendered is typically due in the subsequent month following satisfaction of the Registrants' performance obligation. 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 entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice. In addition, 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. The natural gas market for Atlanta Gas Light was deregulated in 1997. Accordingly, Marketers, 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 is recognized as a single performance obligation satisfied over time and is 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 generally has a right to consideration in an amount that corresponds directly with the value to the customer of the entity's performance completed to date and may recognize revenue in the amount to which the entity has a right to invoice and has elected to recognize revenue for its sales of natural gas using the invoice practical expedient. In addition, payment for goods and services rendered is typically due in the subsequent month following satisfaction of 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 monthly 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. Prior to the sale of Pivotal Home Solutions in 2018, revenues for warranty and repair contracts were recognized on a straight-line basis over the contract term while revenues for maintenance services were recognized at the time such services were performed. See Note 15 under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. Concentration of Revenue Southern Company, Alabama Power, Georgia Power, Mississippi Power (with the exception of its 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 serves long-term contracts with rural electric cooperative associations and municipalities located in southeastern Mississippi under cost-based MRA electric tariffs, which are subject to regulation by the FERC. The contracts with these wholesale customers represent ed 15.7% of Mississippi Power 's total operating revenues in 2019 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.
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 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. Under the deferred method, 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 2019 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, 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 accounted for under ASC 606.
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, with the exception of Elizabethtown Gas and Elkton Gas prior to their sales, 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
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, 2019 and 2018
Storm Damage Reserves and Environmental Remediation Recovery	Storm Damage Reserves
Leveraged Leases	Leveraged Leases A subsidiary of Southern Holdings has several leveraged lease agreements, with original terms ranging up to 45 years , which relate to international and domestic energy generation, distribution, and transportation assets. 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 Note 3 under " Other Matters – Southern Company " for information regarding an impairment charge associated with one of the leveraged leases.
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, biomass, 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, 2019 , the Nicor Gas LIFO inventory balance was $161 million . Based on the average cost of gas purchased in December 2019 , the estimated replacement cost of Nicor Gas' inventory at December 31, 2019 was $214 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, 2019 and 2018 , the required collateral in the event of a credit rating downgrade was $11 million and $30 million , respectively. Credit policies were established 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 Southern Company Gas' wholesale gas services is engaged in more than one outstanding derivative transaction with the same counterparty and it also has a legally enforceable netting agreement with that counterparty, the "net" mark-to-market exposure represents the netting of the positive and negative exposures with that counterparty combined with a reasonable measure of Southern Company Gas' credit risk. 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.
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, 2019 , the top 20 counterparties represented 59% , or $218 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 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.
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. For 2017, ineffectiveness arising from cash flow hedges was recognized in net income. Upon the adoption of ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12) in 2018, ineffectiveness is no longer separately measured and recorded in earnings. 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, 2019 . 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 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 the respective fuel cost recovery clauses. • Cash Flow Hedges – Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in 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. 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. 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.
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. The traditional electric operating companies also have AROs related to various landfill sites, asbestos removal, and underground storage tanks, as well as, for Alabama Power, disposal of polychlorinated biphenyls in certain transformers and sulfur hexafluoride gas in certain substation breakers, for Georgia Power, gypsum cells and restoration of land at the end of long-term land leases for solar facilities, and, for Mississippi Power, mine reclamation and water wells. The ARO liability for Southern Power primarily relates to Southern Power's 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, 2017 $ 4,824 $ 1,709 $ 2,638 $ 174 $ 78 Liabilities incurred 29 — 27 — 2 Liabilities settled (244 ) (55 ) (116 ) (35 ) — Accretion 217 106 94 5 4 Cash flow revisions 4,737 1,450 3,186 16 — Reclassification to held for sale (169 ) — — — — 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 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets. In June 2018, Alabama Power recorded an increase of approximately $1.2 billion to its AROs related to the CCR Rule. Mississippi Power also recorded an increase of approximately $11 million to its AROs related to an ash pond at Plant Greene County, which is jointly-owned with Alabama Power. The revised cost estimates were based on information from feasibility studies performed on ash ponds in use at plants operated by Alabama Power, including Plant Greene County. During the second quarter 2018, Alabama Power's management completed its analysis of these studies which indicated that additional closure costs, primarily related to increases in estimated ash volume, water management requirements, and design revisions, will be required to close these ash ponds under the planned closure-in-place methodology. Also in June 2018, Alabama Power completed an updated decommissioning cost site study for Plant Farley. The estimated cost of decommissioning based on the study resulted in an increase in Alabama Power's ARO liability of approximately $300 million . In December 2018, Georgia Power completed updated decommissioning cost site studies for Plant Hatch and Plant Vogtle Units 1 and 2. The estimated cost of decommissioning based on the studies resulted in an increase in Georgia Power's ARO liability of approximately $130 million . See " Nuclear Decommissioning " below for additional information. In December 2018, Georgia Power recorded an increase of approximately $3.1 billion to its AROs related to the CCR Rule and the related state rule. During the second half of 2018, Georgia Power completed a strategic assessment related to its plans to close the ash ponds at all of its generating plants in compliance with the CCR Rule and the related state rule. This assessment included engineering and constructability studies related to design assumptions for ash pond closures and advanced engineering methods. The results indicated that additional closure costs will be required to close these ash ponds, primarily due to changes in closure strategies, the estimated amount of ash to be excavated, and additional water management requirements necessary to support closure strategies. These factors also impact the estimated timing of future cash outlays. The 2018 reclassification of a portion of the ARO liability to liabilities held for sale by Southern Company represents the AROs related to Gulf Power. See Note 15 under " Southern Company " and " Assets Held for Sale " for additional information. 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. The additional estimated costs to close these ash ponds under the planned closure-in-place methodology primarily relate to cost inputs from contractor bids, internal drainage and dewatering system designs, and increases in the estimated ash volumes. Alabama Power anticipates increasing the ARO for its remaining ash pond facility within the next nine months upon completion of a feasibility study and the related cost estimate, and the increase could be material. 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. The cost estimates for AROs related to the CCR Rule and related state rules are based on information at December 31, 2019 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 related state requirements for closure. The traditional electric operating companies expect to continue to update their cost estimates and ARO liabilities periodically as additional information related to these assumptions becomes available. 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, Southern Company's and the traditional electric operating companies' results of operations, cash flows, and financial condition could be materially impacted. The ultimate outcome of this matter cannot be determined at this time.
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, 2019 and 2018 , approximately $28 million and $27 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 $29 million and $28 million at December 31, 2019 and 2018 , 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, 2019 and 2018 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2018: Equity securities $ 919 $ 594 $ 325 Debt securities 726 201 525 Other securities 74 51 23 Total investment securities in the Funds $ 1,719 $ 846 $ 873 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 2019 , 2018 , and 2017 are shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2019 $ 344 $ 194 $ 150 2018 (67 ) (38 ) (29 ) 2017 233 125 108 Unrealized gains (losses) At December 31, 2019 $ 259 $ 149 $ 110 At December 31, 2018 (183 ) (96 ) (87 ) At December 31, 2017 181 98 83 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 $16 million and $17 million at December 31, 2019 and 2018 , 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, 2019 and 2018 , the accumulated provisions for the external decommissioning trust funds were as follows: 2019 2018 (in millions) Alabama Power Plant Farley $ 1,021 $ 846 Georgia Power Plant Hatch $ 634 $ 547 Plant Vogtle Units 1 and 2 379 326 Total $ 1,013 $ 873 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, 2019 based on the most current studies, which were each performed in 2018, were as follows: Plant Farley 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.
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 Southern Power 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 obligation is categorized as Level 3 under Fair Value Measurements as the fair value is determined using significant unobservable inputs for the forecasted facility generation in MW-hours, as well as other inputs such as a fixed dollar amount per MW-hour, and a discount rate. The fair value of contingent consideration reflects the net present value of expected payments and any periodic change arising from forecasted generation is expected to be immaterial. "Other investments" include investments 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, treasury bonds, and/or agency bonds.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of costs for affiliate transactions	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 Power Southern Power (in millions) 2019 $ 3 $ 14 2018 15 41 2017 16 27 2019 , 2018 , and 2017 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2019 $ 17 $ 99 $ 28 $ 31 2018 8 101 25 32 2017 9 102 25 32 In November 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 2019 , 2018 , and 2017 : Georgia Southern Power (in millions) 2019 $ 4 $ 64 2018 21 119 2017 22 119 2019 , 2018 , and 2017 were as follows: Alabama Georgia Mississippi Southern Power (*) Southern Company Gas (in millions) 2019 $ 527 $ 704 $ 118 $ 90 $ 183 2018 508 653 104 98 194 2017 479 625 140 218 63 (*) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Alabama Power 3.1 % 3.0 % 2.9 % Georgia Power 2.6 % 2.6 % 2.7 % Mississippi Power 3.7 % 4.2 % 3.4 % Southern Company Gas 2.9 % 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: 2019 2018 2017 Georgia Power 9.0 % 9.8 % 11.3 % Duke Energy Corporation N/A 6.8 % 6.7 % Southern California Edison 6.8 % 6.2 % N/A Morgan Stanley Capital Group 4.9 % N/A 4.5 %
Schedule of total AFUDC and interest capitalized	Total AFUDC and interest capitalized for the Registrants in 2019 , 2018 , and 2017 was as follows: Southern Company Alabama Georgia (*) Mississippi Southern Power Southern Company Gas (in millions) 2019 $ 202 $ 71 $ 103 $ — $ 15 $ 13 2018 210 84 94 — 17 14 2017 249 54 63 72 11 19 (*) 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 2019 , 2018 , and 2017 for the traditional electric operating companies and the natural gas distribution utilities were as follows: 2019 2018 2017 Alabama Power 8.4 % 8.3 % 8.3 % Georgia Power (*) 6.9 % 7.3 % 5.6 % Mississippi Power 7.3 % 3.3 % 6.7 % Southern Company Gas: Atlanta Gas Light 7.8 % 7.9 % 8.1 % Chattanooga Gas 7.1 % 7.4 % 7.4 % Nicor Gas 2.3 % 2.1 % 1.2 % (*) 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, 2019 and 2018 , goodwill was as follows: At December 31, 2019 At December 31, 2018 (in millions) Southern Company $ 5,280 $ 5,315 Southern Company Gas: Gas distribution operations $ 4,034 $ 4,034 Gas marketing services 981 981 Southern Company Gas total $ 5,015 $ 5,015
Schedule of intangible assets subject to amortization	At December 31, 2019 and 2018 , other intangible assets were as follows: At December 31, 2019 At December 31, 2018 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 (a) $ 212 $ (116 ) $ 96 $ 223 $ (94 ) $ 129 Trade names (a) 64 (25 ) 39 70 (21 ) 49 Storage and transportation contracts 64 (62 ) 2 64 (54 ) 10 PPA fair value adjustments (b) 390 (69 ) 321 405 (61 ) 344 Other 11 (8 ) 3 11 (5 ) 6 Total other intangible assets subject to amortization $ 741 $ (280 ) $ 461 $ 773 $ (235 ) $ 538 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 816 $ (280 ) $ 536 $ 848 $ (235 ) $ 613 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments (b) $ 390 $ (69 ) $ 321 $ 405 $ (61 ) $ 344 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (104 ) $ 52 $ 156 $ (84 ) $ 72 Trade names 26 (10 ) 16 26 (7 ) 19 Wholesale gas services Storage and transportation contracts 64 (62 ) 2 64 (54 ) 10 Total other intangible assets subject to amortization $ 246 $ (176 ) $ 70 $ 246 $ (145 ) $ 101 (a) The decrease in the gross carrying amount during 2019 primarily reflects the sales of two PowerSecure business units. See Note 15 for additional information. (b) The decrease in the gross carrying amount during 2019 reflects the sale of Plant Nacogdoches, partially offset by additional PPA fair value adjustments related to the acquisition of DSGP. See Note 15 under " Southern Power " for additional information.
Schedule of intangible assets not subject to amortization	At December 31, 2019 and 2018 , other intangible assets were as follows: At December 31, 2019 At December 31, 2018 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 (a) $ 212 $ (116 ) $ 96 $ 223 $ (94 ) $ 129 Trade names (a) 64 (25 ) 39 70 (21 ) 49 Storage and transportation contracts 64 (62 ) 2 64 (54 ) 10 PPA fair value adjustments (b) 390 (69 ) 321 405 (61 ) 344 Other 11 (8 ) 3 11 (5 ) 6 Total other intangible assets subject to amortization $ 741 $ (280 ) $ 461 $ 773 $ (235 ) $ 538 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 816 $ (280 ) $ 536 $ 848 $ (235 ) $ 613 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments (b) $ 390 $ (69 ) $ 321 $ 405 $ (61 ) $ 344 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (104 ) $ 52 $ 156 $ (84 ) $ 72 Trade names 26 (10 ) 16 26 (7 ) 19 Wholesale gas services Storage and transportation contracts 64 (62 ) 2 64 (54 ) 10 Total other intangible assets subject to amortization $ 246 $ (176 ) $ 70 $ 246 $ (145 ) $ 101 (a) The decrease in the gross carrying amount during 2019 primarily reflects the sales of two PowerSecure business units. See Note 15 for additional information. (b) The decrease in the gross carrying amount during 2019 reflects the sale of Plant Nacogdoches, partially offset by additional PPA fair value adjustments related to the acquisition of DSGP. See Note 15 under " Southern Power " for additional information.
Schedule of amortization associated with other intangible assets	Amortization associated with other intangible assets in 2019 , 2018 , and 2017 was as follows: 2019 2018 2017 (in millions) Southern Company (a) $ 61 $ 89 $ 124 Southern Power (b) 19 25 25 Southern Company Gas: Gas marketing services $ 23 $ 32 $ 54 Wholesale gas services (b) 8 20 32 Southern Company Gas total $ 31 $ 52 $ 86 (a) Includes $27 million , $45 million , and $57 million in 2019 , 2018 , and 2017 , 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, 2019 , the estimated amortization associated with other intangible assets for the next five years is as follows: 2020 2021 2022 2023 2024 (in millions) Southern Company (*) $ 48 $ 42 $ 38 $ 37 $ 35 Southern Power (*) 20 20 20 20 20 Southern Company Gas 19 13 10 9 7 (*) Excludes amounts related to held for sale assets. See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " for additional information.
Reconciliation of cash, and cash equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that total to the amounts shown in the statements of cash flows for the Registrants that had restricted cash at December 31, 2019 and/or 2018 : Southern Company Southern Company Gas (in millions) At December 31, 2019 Cash and cash equivalents $ 1,975 $ 46 Restricted cash: Other accounts and notes receivable 3 3 Total cash, cash equivalents, and restricted cash $ 1,978 $ 49 Southern Georgia Power Southern (in millions) At December 31, 2018 Cash and cash equivalents $ 1,396 $ 4 $ 64 Cash and cash equivalents classified as assets held for sale 9 — — Restricted cash: Restricted cash — 108 — Other accounts and notes receivable 114 — 6 Total cash, cash equivalents, and restricted cash $ 1,519 $ 112 $ 70
Reconciliation of restricted cash and cash equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets that total to the amounts shown in the statements of cash flows for the Registrants that had restricted cash at December 31, 2019 and/or 2018 : Southern Company Southern Company Gas (in millions) At December 31, 2019 Cash and cash equivalents $ 1,975 $ 46 Restricted cash: Other accounts and notes receivable 3 3 Total cash, cash equivalents, and restricted cash $ 1,978 $ 49 Southern Georgia Power Southern (in millions) At December 31, 2018 Cash and cash equivalents $ 1,396 $ 4 $ 64 Cash and cash equivalents classified as assets held for sale 9 — — Restricted cash: Restricted cash — 108 — Other accounts and notes receivable 114 — 6 Total cash, cash equivalents, and restricted cash $ 1,519 $ 112 $ 70
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 reserves in 2019 , 2018 , and 2017 : Southern Company (a)(b) Alabama (b) Georgia Mississippi (in millions) 2019 $ 170 $ 139 $ 30 $ 1 2018 74 16 30 1 2017 41 4 30 3 (a) Includes accruals at Gulf Power of $26.9 million in 2018 and $3.5 million in 2017. 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 domestic and international leveraged leases consists of the following at December 31: 2019 2018 (in millions) Net rentals receivable $ 1,410 $ 1,563 Unearned income (622 ) (765 ) Investment in leveraged leases 788 798 Deferred taxes from leveraged leases (238 ) (255 ) Net investment in leveraged leases $ 550 $ 543
Summary of the components of income from leveraged leases	A summary of the components of income from the leveraged leases follows: 2019 2018 2017 (in millions) Pretax leveraged lease income $ 11 $ 25 $ 25 Net impact of Tax Reform Legislation — — 48 Income tax expense — (6 ) (9 ) Net leveraged lease income $ 11 $ 19 $ 64
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 Hedges Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss) (in millions) Southern Company Balance at December 31, 2018 $ (121 ) $ (82 ) $ (203 ) Current period change (58 ) (60 ) (118 ) Balance at December 31, 2019 $ (179 ) $ (142 ) $ (321 ) Southern Power Balance at December 31, 2018 $ 36 $ (20 ) $ 16 Current period change (25 ) (17 ) (42 ) Balance at December 31, 2019 $ 11 $ (37 ) $ (26 ) Southern Company Gas Balance at December 31, 2018 $ (3 ) $ 29 $ 26 Current period change (3 ) (16 ) (19 ) Balance at December 31, 2019 $ (6 ) $ 13 $ 7

REGULATORY MATTERS (Tables)

REGULATORY MATTERS (Tables)	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
Schedule of regulatory assets	Regulatory assets and (liabilities) reflected in the consolidated balance sheets of Southern Company at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 4,423 $ 3,658 (a,o) Asset retirement obligations-asset 4,381 2,933 (b,o) Remaining net book value of retired assets 1,275 211 (c) Deferred income tax charges 803 799 (b,n) Property damage reserves-asset 410 416 (d) Environmental remediation-asset 349 366 (e,o) Loss on reacquired debt 323 346 (f) Under recovered regulatory clause revenues 254 407 (g) Vacation pay 186 182 (h,o) Long-term debt fair value adjustment 107 121 (i) Other regulatory assets 492 581 (j) Deferred income tax credits (6,301 ) (6,455 ) (b,n) Other cost of removal obligations (2,084 ) (2,297 ) (b) Customer refunds (285 ) (293 ) (k) Over recovered regulatory clause revenues (205 ) (47 ) (g) Property damage reserves-liability (204 ) (76 ) (l) Other regulatory liabilities (86 ) (132 ) (m) Total regulatory assets (liabilities), net $ 3,838 $ 720 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the respective PSC or regulatory agency and are as follows: (a) Recovered and amortized over the average remaining service period, which may range up to 15 years . See Note 11 for additional information. (b) AROs and other cost of removal obligations are recorded, deferred income tax assets are recovered, and deferred income tax liabilities are amortized over the related property lives, which may range up to 80 years . Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. Included in the deferred income tax assets is $23 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Amortized over periods not exceeding 18 years . (d) Effective January 1, 2020, Georgia Power is recovering approximately $213 million annually for storm damage. See " Georgia Power – Rate Plans – 2019 ARP " and " – Storm Damage Recovery " herein for additional information. (e) Recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 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, 2019 , the remaining amortization periods do not exceed 34 years . (g) Recorded and recovered or amortized over periods generally not exceeding six years . (h) Recorded as earned by employees and recovered as paid, generally within one year . (i) Recovered over the remaining life of the original debt issuances at acquisition, which range up to 19 years as of December 31, 2019 . (j) Comprised of numerous immaterial components including nuclear outage costs, fuel-hedging losses, cancelled construction projects, property tax, and other miscellaneous assets. These costs are amortized over remaining periods generally not exceeding eight years as of December 31, 2019 . (k) At December 31, 2019 and 2018, primarily includes approximately $53 million and $109 million , respectively, at Alabama Power and $110 million and $100 million , respectively, at Georgia Power as a result of each company exceeding its allowed retail return range, as well as approximately $105 million and $55 million , respectively, pursuant to the Georgia Power Tax Reform Settlement Agreement. See " Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (l) Amortized as related expenses are incurred. See " Alabama Power – Rate NDR " and " Mississippi Power – System Restoration Rider " herein for additional information. (m) Comprised of numerous components including building leases, fuel-hedging gains, and other liabilities that are recovered over remaining periods not exceeding 20 years . (n) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, including $778 million of liabilities being amortized over periods not exceeding six years as of December 31, 2019 . See " Georgia Power ," " Mississippi Power ," and " Southern Company Gas " herein and Note 10 for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Alabama Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,131 $ 947 (a,o) Asset retirement obligations 1,043 147 (b) Deferred income tax charges 245 241 (b,c,d) (Over) under recovered regulatory clause revenues (72 ) 176 (e) Regulatory clauses 142 142 (f) Vacation pay 72 71 (g,o) Loss on reacquired debt 52 56 (h) Nuclear outage 78 49 (i) Remaining net book value of retired assets 649 43 (j) Other regulatory assets 67 57 (k,l) Deferred income tax credits (1,960 ) (2,027 ) (b,d) Other cost of removal obligations (412 ) (497 ) (b) Customer refunds (56 ) (142 ) (m) Natural disaster reserve (150 ) (20 ) (n) Other regulatory liabilities (19 ) (12 ) (l) Total regulatory assets (liabilities), net $ 810 $ (769 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) have been accepted or approved by the Alabama PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 14 years . See Note 11 for additional information. (b) Asset retirement and removal assets and liabilities are recorded, deferred income tax assets are recovered, and deferred income tax credits are amortized over the related property lives, which may range up to 53 years . Asset retirement and other cost of removal assets and liabilities will be settled and trued up following completion of the related activities. (c) Included in the deferred income tax charges are $9 million for 2019 and $10 million for 2018 for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (d) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization. The recovery and amortization of these amounts will occur ratably over the related property lives, which may range up to 53 years . See Note 10 for additional information. (e) Recorded monthly and expected to be recovered or returned within three years . See " Rate CNP PPA ," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) In accordance with an accounting order issued in 2017 by the Alabama PSC, these regulatory assets will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2019 , the remaining amortization periods do not exceed 30 years . (i) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent 18 -month period. (j) Recorded and amortized over remaining periods not exceeding 18 years . (k) Comprised of components including generation site selection/evaluation costs, which are capitalized upon initiation of related construction projects, if applicable, and PPA capacity costs, which are to be recovered over the next 12 months . (l) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three and a half years. Upon final settlement, actual costs incurred are recovered through the energy cost recovery clause. (m) Includes $53 million for 2019 and $109 million for 2018 due to the retail return exceeding the allowed range. The December 31, 2018 balance also includes a $33 million excess deferred tax liability used to increase the Rate NDR balance in 2019. See "Rate RSE," "Rate NDR," and " Tax Reform Accounting Order " herein for additional information. (n) Amortized as expenses are incurred. See "Rate NDR" herein for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,516 $ 1,295 (a, m) Asset retirement obligations 3,119 2,644 (b, m) Deferred income tax charges 523 522 (b, c, m) Storm damage reserves 410 416 (d) Remaining net book value of retired assets 596 127 (e) Loss on reacquired debt 262 277 (f, m) Vacation pay 93 91 (g, m) Other cost of removal obligations 156 68 (b) Environmental remediation 52 55 (h) Fuel-hedging (realized and unrealized) losses 53 15 (i, m) Other regulatory assets 50 120 (j) Deferred income tax credits (3,078 ) (3,080 ) (b, c) Customer refunds (229 ) (165 ) (k) Other regulatory liabilities (16 ) (7 ) (l, m) Total regulatory assets (liabilities), net $ 3,507 $ 2,378 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the Georgia PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 13 years . See Note 11 for additional information. (b) Effective January 1, 2020, Georgia Power is recovering CCR AROs through its Environmental Compliance Cost Recovery (ECCR) tariff and approximately $5 million annually for other AROs through its traditional base tariffs. See " Rate Plans – 2019 ARP " and " Integrated Resource Plan " herein for additional information on recovery of compliance costs for CCR AROs. Other cost of removal obligations, non-CCR AROs, and deferred income tax assets are recovered and deferred income tax liabilities are amortized over the related property lives, which may range up to 60 years . Included in the deferred income tax assets is $13 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2022. See Note 6 for additional information on AROs. (c) As a result of the Tax Reform Legislation, these balances include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $660 million of deferred income tax liabilities, neither of which are subject to normalization. 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. See " Rate Plans " herein and Note 10 for additional information. (d) Effective January 1, 2020, Georgia Power is recovering $213 million annually for storm damage. See " Rate Plans – 2019 ARP " and " Storm Damage Recovery " herein and Note 1 under " Storm Damage Reserves " for additional information. (e) The net book values of Plant Hammond Units 1 through 4 ( $488 million at December 31, 2019 ) and Plant Branch Units 1 through 4 ( $69 million and $87 million at December 31, 2019 and 2018 , respectively) are being amortized over the units' remaining useful lives, which vary between 2020 and 2035. The net book values of Plant McIntosh Unit 1 ( $30 million at December 31, 2019 ) and Plant Mitchell Unit 3 ( $8 million and $9 million at December 31, 2019 and 2018 , respectively) are being amortized through 2022. The balance at December 31, 2018 also includes $31 million related to obsolete inventories of certain retired units, which was fully amortized under the 2019 ARP. See " Rate Plans – 2019 ARP " and " Integrated Resource Plan " herein 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, 2019 , the amortization periods do not exceed 33 years . (g) Recorded as earned by employees and recovered as paid, generally within one year . (h) Effective January 1, 2020, Georgia Power is recovering $12 million annually for environmental remediation. See Note 3 under " Environmental Remediation " for additional information. (i) Recovered through Georgia Power's fuel cost recovery mechanism upon final settlement, within four years . (j) Comprised of several components including deferred nuclear outage costs and cancelled construction projects. Nuclear outage costs are recorded as incurred and recovered over the outage cycles of each nuclear unit, which do not exceed 24 months . Approximately $22 million of costs associated with construction of environmental controls that will not be completed as a result of unit retirements are being amortized through 2022. (k) At December 31, 2019 and 2018 , includes approximately $110 million and $100 million , respectively, as a result of the retail ROE exceeding the allowed retail ROE range and approximately $105 million and $55 million , respectively, related to the Georgia Power Tax Reform Settlement Agreement. See " Rate Plans " herein for additional information. (l) Comprised of Demand-Side Management (DSM) tariffs over recovery, building lease, and fuel-hedging gains. DSM tariffs over recovery of $10 million at December 31, 2019 is being amortized through 2022. The building lease is being amortized through 2030. Fuel-hedging gains are refunded through Georgia Power's fuel cost recovery mechanism upon final settlement, within four years . (m) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Mississippi Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans – regulatory assets $ 213 $ 171 (a) Asset retirement obligations 210 143 (b) Kemper County energy facility assets, net 61 69 (c) Remaining net book value of retired assets 30 41 (d) Property tax 47 44 (e) Deferred charges related to income taxes 33 34 (b) Plant Daniel Units 3 and 4 34 36 (f) ECO Plan carryforward — 26 (g) Other regulatory assets 48 28 (h) Deferred credits related to income taxes (358 ) (377 ) (i) Other cost of removal obligations (189 ) (185 ) (b) Property damage (55 ) (56 ) (j) Other regulatory liabilities (10 ) (9 ) (k) Total regulatory assets (liabilities), net $ 64 $ (35 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the Mississippi PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 14 years . See Note 11 for additional information. (b) Asset retirement and other cost of removal obligations will be settled and trued up upon completion of removal activities over a period to be determined by the Mississippi PSC. Asset retirement and other cost of removal obligations and deferred charges related to income taxes are generally recovered over the related property lives, which may range up to 48 years . (c) Includes $78 million of regulatory assets and $18 million of regulatory liabilities that are expected to be fully amortized by 2025 and 2023, respectively. For additional information, see " Kemper County Energy Facility – Rate Recovery" herein. (d) Retail portion includes approximately $16 million being recovered over a five-year period through 2021 and 2022 for Plant Watson and Plant Greene County, respectively. Wholesale portion includes approximately $14 million being recovered over a 12 -year period through 2031 for Plant Watson and Plant Greene County. (e) Recovered through the ad valorem tax adjustment clause over a 12 -month period beginning in April of the following year. See " Ad Valorem Tax Adjustment " herein for additional information. (f) Represents the difference between the revenue requirement under purchase accounting and operating lease accounting, which will be amortized over a 10 -year period beginning October 2021. (g) Generally recovered through the ECO Plan clause in the year following the deferral. See " Environmental Compliance Overview Plan " herein. (h) Includes $9 million related to vacation pay and $5 million related to other miscellaneous assets, all of which are recorded and recovered over periods not exceeding one year ; $6 million related to loss on reacquired debt, which is recorded and amortized over either the remaining life of the original issue, or if refinanced, over the remaining life of the new issue (at December 31, 2019, the amortization periods did not exceed 22 years ); and $27 million related to fuel-hedging assets, which are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three years , and are recovered through Mississippi Power's energy cost management clause upon settlement. (i) Includes excess deferred income taxes primarily associated with Tax Reform Legislation of $358 million , of which $252 million is related to protected deferred income taxes being recovered over the related property lives, which may range up to 48 years , and $106 million related to unprotected deferred income taxes (not subject to normalization). The unprotected retail portion includes $28 million associated with the Kemper County energy facility being amortized over an eight -year period through 2025. The unprotected wholesale portion includes $18 million of excess deferred income taxes being amortized over three-year periods through 2022. An additional $8 million associated with the System Restoration Rider is being amortized over an eight -year period through 2025. The amortization period for the remaining unprotected deferred income taxes is expected to be determined in the Mississippi Power 2019 Base Rate Case. See " Kemper County Energy Facility " and " Municipal and Rural Associations Tariff " herein and Note 10 for additional information. (j) See " System Restoration Rider " herein. (k) Refunded or amortized generally over periods not exceeding one year . Regulatory assets and (liabilities) reflected in the balance sheets of Southern Company Gas at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Environmental remediation $ 296 $ 311 (a,b) Retiree benefit plans 167 161 (a,c) Long-term debt fair value adjustment 107 121 (d) Under recovered regulatory clause revenues 72 90 (e) Other regulatory assets 68 59 (f) Other cost of removal obligations (1,606 ) (1,585 ) (g) Deferred income tax credits (874 ) (940 ) (g,i) Over recovered regulatory clause revenues (82 ) (43 ) (e) Other regulatory liabilities (22 ) (46 ) (h) Total regulatory assets (liabilities), net $ (1,874 ) $ (1,872 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) have been approved or accepted by the relevant state PSC or other regulatory body and are as follows: (a) Not earning a return as offset in rate base by a corresponding asset or liability. (b) Recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 for additional information. (c) Recovered and amortized over the average remaining service period which range up to 15 years . See Note 11 for additional information. (d) Recovered over the remaining life of the original debt issuances at acquisition, which range up to 19 years as of December 31, 2019. (e) Recorded and recovered or amortized over periods generally not exceeding six 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. (f) Includes financial instrument-hedging assets totaling $11 million and $8 million at December 31, 2019 and 2018 , respectively, which are recorded over the life of the underlying hedged purchase contracts generally not exceeding two years , vacation pay assets totaling $11 million at both December 31, 2019 and 2018 , which are recorded as earned by employees and recovered as paid, generally within one year , and several other miscellaneous components, which are recovered or amortized over periods generally not exceeding eight years . (g) Other cost of removal obligations are recorded and deferred income tax liabilities are amortized over the related property lives, which may range up to 80 years . Cost of removal liabilities will be settled and trued up following completion of the related activities. (h) Comprised of numerous components, including amounts to be refunded to customers as a result of the Tax Reform Legislation and energy efficiency programs, which are recovered or amortized over remaining periods generally not exceeding 20 years . Upon final settlement, actual energy efficiency program costs incurred are recovered, and actual income earned is refunded through the energy cost recovery clause. See " Rate Proceedings " herein for additional information regarding customer refunds resulting from the Tax Reform Legislation. (i) As of December 31, 2019, includes $12 million of excess deferred income tax liabilities not subject to normalization as a result of the Tax Reform Legislation which are being amortized through 2024 . See " Rate Proceedings " herein and Note 10 for additional details. Infrastructure Replacement Programs and Capital Projects December 31, 2019 December 31, 2018 (in millions) Atlanta Gas Light $ 70 $ 95 Virginia Natural Gas 10 11 Nicor Gas 2 4 Total $ 82 $ 110
Schedule of regulatory liabilities	Regulatory assets and (liabilities) reflected in the consolidated balance sheets of Southern Company at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 4,423 $ 3,658 (a,o) Asset retirement obligations-asset 4,381 2,933 (b,o) Remaining net book value of retired assets 1,275 211 (c) Deferred income tax charges 803 799 (b,n) Property damage reserves-asset 410 416 (d) Environmental remediation-asset 349 366 (e,o) Loss on reacquired debt 323 346 (f) Under recovered regulatory clause revenues 254 407 (g) Vacation pay 186 182 (h,o) Long-term debt fair value adjustment 107 121 (i) Other regulatory assets 492 581 (j) Deferred income tax credits (6,301 ) (6,455 ) (b,n) Other cost of removal obligations (2,084 ) (2,297 ) (b) Customer refunds (285 ) (293 ) (k) Over recovered regulatory clause revenues (205 ) (47 ) (g) Property damage reserves-liability (204 ) (76 ) (l) Other regulatory liabilities (86 ) (132 ) (m) Total regulatory assets (liabilities), net $ 3,838 $ 720 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the respective PSC or regulatory agency and are as follows: (a) Recovered and amortized over the average remaining service period, which may range up to 15 years . See Note 11 for additional information. (b) AROs and other cost of removal obligations are recorded, deferred income tax assets are recovered, and deferred income tax liabilities are amortized over the related property lives, which may range up to 80 years . Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. Included in the deferred income tax assets is $23 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Amortized over periods not exceeding 18 years . (d) Effective January 1, 2020, Georgia Power is recovering approximately $213 million annually for storm damage. See " Georgia Power – Rate Plans – 2019 ARP " and " – Storm Damage Recovery " herein for additional information. (e) Recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 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, 2019 , the remaining amortization periods do not exceed 34 years . (g) Recorded and recovered or amortized over periods generally not exceeding six years . (h) Recorded as earned by employees and recovered as paid, generally within one year . (i) Recovered over the remaining life of the original debt issuances at acquisition, which range up to 19 years as of December 31, 2019 . (j) Comprised of numerous immaterial components including nuclear outage costs, fuel-hedging losses, cancelled construction projects, property tax, and other miscellaneous assets. These costs are amortized over remaining periods generally not exceeding eight years as of December 31, 2019 . (k) At December 31, 2019 and 2018, primarily includes approximately $53 million and $109 million , respectively, at Alabama Power and $110 million and $100 million , respectively, at Georgia Power as a result of each company exceeding its allowed retail return range, as well as approximately $105 million and $55 million , respectively, pursuant to the Georgia Power Tax Reform Settlement Agreement. See " Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (l) Amortized as related expenses are incurred. See " Alabama Power – Rate NDR " and " Mississippi Power – System Restoration Rider " herein for additional information. (m) Comprised of numerous components including building leases, fuel-hedging gains, and other liabilities that are recovered over remaining periods not exceeding 20 years . (n) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization, including $778 million of liabilities being amortized over periods not exceeding six years as of December 31, 2019 . See " Georgia Power ," " Mississippi Power ," and " Southern Company Gas " herein and Note 10 for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Alabama Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,131 $ 947 (a,o) Asset retirement obligations 1,043 147 (b) Deferred income tax charges 245 241 (b,c,d) (Over) under recovered regulatory clause revenues (72 ) 176 (e) Regulatory clauses 142 142 (f) Vacation pay 72 71 (g,o) Loss on reacquired debt 52 56 (h) Nuclear outage 78 49 (i) Remaining net book value of retired assets 649 43 (j) Other regulatory assets 67 57 (k,l) Deferred income tax credits (1,960 ) (2,027 ) (b,d) Other cost of removal obligations (412 ) (497 ) (b) Customer refunds (56 ) (142 ) (m) Natural disaster reserve (150 ) (20 ) (n) Other regulatory liabilities (19 ) (12 ) (l) Total regulatory assets (liabilities), net $ 810 $ (769 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) have been accepted or approved by the Alabama PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 14 years . See Note 11 for additional information. (b) Asset retirement and removal assets and liabilities are recorded, deferred income tax assets are recovered, and deferred income tax credits are amortized over the related property lives, which may range up to 53 years . Asset retirement and other cost of removal assets and liabilities will be settled and trued up following completion of the related activities. (c) Included in the deferred income tax charges are $9 million for 2019 and $10 million for 2018 for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (d) As a result of the Tax Reform Legislation, these accounts include certain deferred income tax assets and liabilities not subject to normalization. The recovery and amortization of these amounts will occur ratably over the related property lives, which may range up to 53 years . See Note 10 for additional information. (e) Recorded monthly and expected to be recovered or returned within three years . See " Rate CNP PPA ," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) In accordance with an accounting order issued in 2017 by the Alabama PSC, these regulatory assets will be amortized concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue. At December 31, 2019 , the remaining amortization periods do not exceed 30 years . (i) Nuclear outage costs are deferred to a regulatory asset when incurred and amortized over a subsequent 18 -month period. (j) Recorded and amortized over remaining periods not exceeding 18 years . (k) Comprised of components including generation site selection/evaluation costs, which are capitalized upon initiation of related construction projects, if applicable, and PPA capacity costs, which are to be recovered over the next 12 months . (l) Fuel-hedging assets and liabilities are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three and a half years. Upon final settlement, actual costs incurred are recovered through the energy cost recovery clause. (m) Includes $53 million for 2019 and $109 million for 2018 due to the retail return exceeding the allowed range. The December 31, 2018 balance also includes a $33 million excess deferred tax liability used to increase the Rate NDR balance in 2019. See "Rate RSE," "Rate NDR," and " Tax Reform Accounting Order " herein for additional information. (n) Amortized as expenses are incurred. See "Rate NDR" herein for additional information. (o) Not earning a return as offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans $ 1,516 $ 1,295 (a, m) Asset retirement obligations 3,119 2,644 (b, m) Deferred income tax charges 523 522 (b, c, m) Storm damage reserves 410 416 (d) Remaining net book value of retired assets 596 127 (e) Loss on reacquired debt 262 277 (f, m) Vacation pay 93 91 (g, m) Other cost of removal obligations 156 68 (b) Environmental remediation 52 55 (h) Fuel-hedging (realized and unrealized) losses 53 15 (i, m) Other regulatory assets 50 120 (j) Deferred income tax credits (3,078 ) (3,080 ) (b, c) Customer refunds (229 ) (165 ) (k) Other regulatory liabilities (16 ) (7 ) (l, m) Total regulatory assets (liabilities), net $ 3,507 $ 2,378 Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the Georgia PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 13 years . See Note 11 for additional information. (b) Effective January 1, 2020, Georgia Power is recovering CCR AROs through its Environmental Compliance Cost Recovery (ECCR) tariff and approximately $5 million annually for other AROs through its traditional base tariffs. See " Rate Plans – 2019 ARP " and " Integrated Resource Plan " herein for additional information on recovery of compliance costs for CCR AROs. Other cost of removal obligations, non-CCR AROs, and deferred income tax assets are recovered and deferred income tax liabilities are amortized over the related property lives, which may range up to 60 years . Included in the deferred income tax assets is $13 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2022. See Note 6 for additional information on AROs. (c) As a result of the Tax Reform Legislation, these balances include $145 million of deferred income tax assets related to CWIP for Plant Vogtle Units 3 and 4 and approximately $660 million of deferred income tax liabilities, neither of which are subject to normalization. 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. See " Rate Plans " herein and Note 10 for additional information. (d) Effective January 1, 2020, Georgia Power is recovering $213 million annually for storm damage. See " Rate Plans – 2019 ARP " and " Storm Damage Recovery " herein and Note 1 under " Storm Damage Reserves " for additional information. (e) The net book values of Plant Hammond Units 1 through 4 ( $488 million at December 31, 2019 ) and Plant Branch Units 1 through 4 ( $69 million and $87 million at December 31, 2019 and 2018 , respectively) are being amortized over the units' remaining useful lives, which vary between 2020 and 2035. The net book values of Plant McIntosh Unit 1 ( $30 million at December 31, 2019 ) and Plant Mitchell Unit 3 ( $8 million and $9 million at December 31, 2019 and 2018 , respectively) are being amortized through 2022. The balance at December 31, 2018 also includes $31 million related to obsolete inventories of certain retired units, which was fully amortized under the 2019 ARP. See " Rate Plans – 2019 ARP " and " Integrated Resource Plan " herein 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, 2019 , the amortization periods do not exceed 33 years . (g) Recorded as earned by employees and recovered as paid, generally within one year . (h) Effective January 1, 2020, Georgia Power is recovering $12 million annually for environmental remediation. See Note 3 under " Environmental Remediation " for additional information. (i) Recovered through Georgia Power's fuel cost recovery mechanism upon final settlement, within four years . (j) Comprised of several components including deferred nuclear outage costs and cancelled construction projects. Nuclear outage costs are recorded as incurred and recovered over the outage cycles of each nuclear unit, which do not exceed 24 months . Approximately $22 million of costs associated with construction of environmental controls that will not be completed as a result of unit retirements are being amortized through 2022. (k) At December 31, 2019 and 2018 , includes approximately $110 million and $100 million , respectively, as a result of the retail ROE exceeding the allowed retail ROE range and approximately $105 million and $55 million , respectively, related to the Georgia Power Tax Reform Settlement Agreement. See " Rate Plans " herein for additional information. (l) Comprised of Demand-Side Management (DSM) tariffs over recovery, building lease, and fuel-hedging gains. DSM tariffs over recovery of $10 million at December 31, 2019 is being amortized through 2022. The building lease is being amortized through 2030. Fuel-hedging gains are refunded through Georgia Power's fuel cost recovery mechanism upon final settlement, within four years . (m) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. Regulatory assets and (liabilities) reflected in the balance sheets of Mississippi Power at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Retiree benefit plans – regulatory assets $ 213 $ 171 (a) Asset retirement obligations 210 143 (b) Kemper County energy facility assets, net 61 69 (c) Remaining net book value of retired assets 30 41 (d) Property tax 47 44 (e) Deferred charges related to income taxes 33 34 (b) Plant Daniel Units 3 and 4 34 36 (f) ECO Plan carryforward — 26 (g) Other regulatory assets 48 28 (h) Deferred credits related to income taxes (358 ) (377 ) (i) Other cost of removal obligations (189 ) (185 ) (b) Property damage (55 ) (56 ) (j) Other regulatory liabilities (10 ) (9 ) (k) Total regulatory assets (liabilities), net $ 64 $ (35 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) are approved by the Mississippi PSC and are as follows: (a) Recovered and amortized over the average remaining service period which may range up to 14 years . See Note 11 for additional information. (b) Asset retirement and other cost of removal obligations will be settled and trued up upon completion of removal activities over a period to be determined by the Mississippi PSC. Asset retirement and other cost of removal obligations and deferred charges related to income taxes are generally recovered over the related property lives, which may range up to 48 years . (c) Includes $78 million of regulatory assets and $18 million of regulatory liabilities that are expected to be fully amortized by 2025 and 2023, respectively. For additional information, see " Kemper County Energy Facility – Rate Recovery" herein. (d) Retail portion includes approximately $16 million being recovered over a five-year period through 2021 and 2022 for Plant Watson and Plant Greene County, respectively. Wholesale portion includes approximately $14 million being recovered over a 12 -year period through 2031 for Plant Watson and Plant Greene County. (e) Recovered through the ad valorem tax adjustment clause over a 12 -month period beginning in April of the following year. See " Ad Valorem Tax Adjustment " herein for additional information. (f) Represents the difference between the revenue requirement under purchase accounting and operating lease accounting, which will be amortized over a 10 -year period beginning October 2021. (g) Generally recovered through the ECO Plan clause in the year following the deferral. See " Environmental Compliance Overview Plan " herein. (h) Includes $9 million related to vacation pay and $5 million related to other miscellaneous assets, all of which are recorded and recovered over periods not exceeding one year ; $6 million related to loss on reacquired debt, which is recorded and amortized over either the remaining life of the original issue, or if refinanced, over the remaining life of the new issue (at December 31, 2019, the amortization periods did not exceed 22 years ); and $27 million related to fuel-hedging assets, which are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three years , and are recovered through Mississippi Power's energy cost management clause upon settlement. (i) Includes excess deferred income taxes primarily associated with Tax Reform Legislation of $358 million , of which $252 million is related to protected deferred income taxes being recovered over the related property lives, which may range up to 48 years , and $106 million related to unprotected deferred income taxes (not subject to normalization). The unprotected retail portion includes $28 million associated with the Kemper County energy facility being amortized over an eight -year period through 2025. The unprotected wholesale portion includes $18 million of excess deferred income taxes being amortized over three-year periods through 2022. An additional $8 million associated with the System Restoration Rider is being amortized over an eight -year period through 2025. The amortization period for the remaining unprotected deferred income taxes is expected to be determined in the Mississippi Power 2019 Base Rate Case. See " Kemper County Energy Facility " and " Municipal and Rural Associations Tariff " herein and Note 10 for additional information. (j) See " System Restoration Rider " herein. Regulatory assets and (liabilities) reflected in the balance sheets of Southern Company Gas at December 31, 2019 and 2018 relate to: 2019 2018 Note (in millions) Environmental remediation $ 296 $ 311 (a,b) Retiree benefit plans 167 161 (a,c) Long-term debt fair value adjustment 107 121 (d) Under recovered regulatory clause revenues 72 90 (e) Other regulatory assets 68 59 (f) Other cost of removal obligations (1,606 ) (1,585 ) (g) Deferred income tax credits (874 ) (940 ) (g,i) Over recovered regulatory clause revenues (82 ) (43 ) (e) Other regulatory liabilities (22 ) (46 ) (h) Total regulatory assets (liabilities), net $ (1,874 ) $ (1,872 ) Note: Unless otherwise noted, the recovery and amortization periods for these regulatory assets and (liabilities) have been approved or accepted by the relevant state PSC or other regulatory body and are as follows: (a) Not earning a return as offset in rate base by a corresponding asset or liability. (b) Recovered through environmental cost recovery mechanisms when the remediation work is performed. See Note 3 for additional information. (c) Recovered and amortized over the average remaining service period which range up to 15 years . See Note 11 for additional information. (d) Recovered over the remaining life of the original debt issuances at acquisition, which range up to 19 years as of December 31, 2019. (e) Recorded and recovered or amortized over periods generally not exceeding six 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. (f) Includes financial instrument-hedging assets totaling $11 million and $8 million at December 31, 2019 and 2018 , respectively, which are recorded over the life of the underlying hedged purchase contracts generally not exceeding two years , vacation pay assets totaling $11 million at both December 31, 2019 and 2018 , which are recorded as earned by employees and recovered as paid, generally within one year , and several other miscellaneous components, which are recovered or amortized over periods generally not exceeding eight years . (g) Other cost of removal obligations are recorded and deferred income tax liabilities are amortized over the related property lives, which may range up to 80 years . Cost of removal liabilities will be settled and trued up following completion of the related activities. (h) Comprised of numerous components, including amounts to be refunded to customers as a result of the Tax Reform Legislation and energy efficiency programs, which are recovered or amortized over remaining periods generally not exceeding 20 years . Upon final settlement, actual energy efficiency program costs incurred are recovered, and actual income earned is refunded through the energy cost recovery clause. See " Rate Proceedings " herein for additional information regarding customer refunds resulting from the Tax Reform Legislation. (i) As of December 31, 2019, includes $12 million of excess deferred income tax liabilities not subject to normalization as a result of the Tax Reform Legislation which are being amortized through 2024 . See " Rate Proceedings " herein and Note 10 for additional details.
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) $ 8.2 Construction contingency estimate 0.2 Total project capital cost forecast (a)(b) 8.4 Net investment as of December 31, 2019 (b) (5.9 ) Remaining estimate to complete (a) $ 2.5 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $300 million , of which $23 million had been accrued through December 31, 2019 . (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	On December 17, 2019, the Georgia PSC voted to approve the 2019 ARP, under which Georgia Power increased its rates on January 1, 2020 and will increase rates annually for 2021 and 2022 as detailed below based on compliance filings to be made at least 90 days prior to the effective date. Georgia Power will recover estimated increases through its existing tariffs as follows: Tariff 2020 2021 2022 (in millions) Traditional base $ — $ 120 $ 192 ECCR (a) 318 55 184 DSM 12 1 1 Municipal Franchise Fee 12 4 9 Total (b) $ 342 $ 181 $ 386 (a) Effective January 1, 2020, CCR AROs will be recovered through the ECCR tariff. See "Integrated Resource Plan" herein for additional information on recovery of compliance costs for CCR AROs. (b) Totals may not add due to rounding.

CONTINGENCIES, COMMITMENTS, A_2

CONTINGENCIES, COMMITMENTS, AND GUARANTEES (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of regulatory assets and liabilities	At December 31, 2019 and 2018 , the environmental remediation liability and the balance of under recovered environmental remediation costs were reflected in the balance sheets as follows: Southern Company Georgia Power Southern Company Gas (in millions) 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 December 31, 2018: Environmental remediation liability: Other current liabilities $ 49 $ 23 $ 26 Accrued environmental remediation 268 — 268 Under recovered environmental remediation costs: Other regulatory assets, current $ 21 $ 2 $ 19 Other regulatory assets, deferred 345 53 292
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, 2019 were as follows: Pipeline Charges, Storage Capacity, and Gas Supply (in millions) 2020 $ 725 2021 559 2022 526 2023 454 2024 330 2025 and thereafter 1,677 Total $ 4,271

REVENUE FROM CONTRACTS WITH C_2

REVENUE FROM CONTRACTS WITH CUSTOMERS (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	The following tables disaggregate revenue from contracts with customers for 2019 and 2018 : 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 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 (a) Other revenue sources primarily relate to revenues from customers accounted for as derivatives and leases, as well as alternative revenues program at Southern Company Gas and other cost recovery mechanisms 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. 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 primarily relate to revenues from customers accounted for as derivatives and leases, as well as alternative revenues program at Southern Company Gas and other cost recovery mechanisms 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 revenue from contracts with customers recognized in 2019 included in the contract liability at December 31, 2018 : Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) Revenue Recognized 2019 $ 30 $ 11 $ 6 $ 11 $ 2 The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at December 31, 2019 and 2018 : Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Accounts Receivables As of December 31, 2019 $ 2,413 $ 586 $ 688 $ 79 $ 97 $ 749 As of December 31, 2018 2,630 520 721 100 118 952 Contract Assets As of December 31, 2019 $ 117 $ — $ 69 $ — $ — $ — As of December 31, 2018 102 — 58 — — — Contract Liabilities As of December 31, 2019 $ 52 $ 10 $ 13 $ — $ 1 $ 1 As of December 31, 2018 32 12 7 — 11 2
Revenue, remaining performance obligation, expected timing of satisfaction	Revenues from contracts with customers related to these performance obligations remaining at December 31, 2019 are expected to be recognized as follows: 2020 2021 2022 2023 2024 2025 and (in millions) Southern Company $ 490 $ 430 $ 336 $ 324 $ 323 $ 2,108 Alabama Power 21 25 22 22 22 118 Georgia Power 60 49 32 32 23 61 Southern Power 287 280 281 271 279 1,948

PROPERTY, PLANT, AND EQUIPMEN_2

PROPERTY, PLANT, AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, plant and equipment	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 45 years Biomass (*) Up to 40 years Solar Up to 35 years Wind Up to 30 years (*) See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " for information on Southern Power's sale of its biomass facility on June 13, 2019. The Registrants' property, plant, and equipment in service consisted of the following at December 31, 2019 and 2018 : 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 At December 31, 2018: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 52,324 $ 16,533 $ 19,145 $ 2,849 $ 13,246 $ — Transmission 11,344 4,380 6,156 769 — — Distribution 18,746 7,389 10,389 968 — — General/other 4,446 2,100 1,985 314 25 — Electric utilities' plant in service 86,860 30,402 37,675 4,900 13,271 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 12,409 — — — — 12,409 Storage facilities 1,640 — — — — 1,640 Other 1,128 — — — — 1,128 Southern Company Gas plant in service 15,177 — — — — 15,177 Other plant in service 1,669 — — — — — Total plant in service $ 103,706 $ 30,402 $ 37,675 $ 4,900 $ 13,271 $ 15,177
Assets acquired under a capital lease	Assets acquired under a finance lease (previously referred to as a capital lease) are included in property, plant, and equipment and are further detailed in the table below for the applicable Registrants at December 31, 2018: At December 31, 2018: Southern Company Georgia Power (in millions) Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 43 — Gas pipeline 7 — Less: Accumulated amortization (75 ) (84 ) Balance, net of amortization $ 191 $ 121 (*) Represents Georgia Power's affiliate PPAs with Southern Power. See Note 1 under " Affiliate Transactions " for additional information.
Composite straight-line rates	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 Power Southern Power (in millions) 2019 $ 3 $ 14 2018 15 41 2017 16 27 2019 , 2018 , and 2017 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2019 $ 17 $ 99 $ 28 $ 31 2018 8 101 25 32 2017 9 102 25 32 In November 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 2019 , 2018 , and 2017 : Georgia Southern Power (in millions) 2019 $ 4 $ 64 2018 21 119 2017 22 119 2019 , 2018 , and 2017 were as follows: Alabama Georgia Mississippi Southern Power (*) Southern Company Gas (in millions) 2019 $ 527 $ 704 $ 118 $ 90 $ 183 2018 508 653 104 98 194 2017 479 625 140 218 63 (*) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Alabama Power 3.1 % 3.0 % 2.9 % Georgia Power 2.6 % 2.6 % 2.7 % Mississippi Power 3.7 % 4.2 % 3.4 % Southern Company Gas 2.9 % 2.9 % 2.9 %
Ownership and investment in jointly-owned facilities	At December 31, 2019 , the Registrants' percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation were as follows: Facility (Type) Percent Ownership Plant in Service Accumulated Depreciation CWIP (in millions) Alabama Power Greene County (natural gas) Units 1 and 2 60.0 % (a) $ 182 $ 71 $ 1 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,058 630 65 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,316 $ 603 $ 40 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,565 2,177 96 Plant Scherer (coal) Units 1 and 2 8.4 (c) 266 94 14 Plant Scherer (coal) Unit 3 75.0 (c) 1,267 492 47 Plant Wansley (coal) 53.5 (c) 1,059 367 10 Rocky Mountain (pumped storage) 25.4 (d) 182 139 — Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 118 $ 46 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 750 214 11 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 271 $ 10 $ — (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 " 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 Transco natural gas pipeline system into northwest Georgia. Southern Company Gas leases its 50% undivided ownership for approximately $26 million annually for an initial term 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, 2019
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, 2017 $ 4,824 $ 1,709 $ 2,638 $ 174 $ 78 Liabilities incurred 29 — 27 — 2 Liabilities settled (244 ) (55 ) (116 ) (35 ) — Accretion 217 106 94 5 4 Cash flow revisions 4,737 1,450 3,186 16 — Reclassification to held for sale (169 ) — — — — 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 (*) Included in other deferred credits and liabilities on Southern Power's consolidated balance sheets.
Investment securities in the Funds	nvestment securities in the Funds for December 31, 2019 and 2018 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2018: Equity securities $ 919 $ 594 $ 325 Debt securities 726 201 525 Other securities 74 51 23 Total investment securities in the Funds $ 1,719 $ 846 $ 873
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 2019 , 2018 , and 2017 are shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2019 $ 344 $ 194 $ 150 2018 (67 ) (38 ) (29 ) 2017 233 125 108 Unrealized gains (losses) At December 31, 2019 $ 259 $ 149 $ 110 At December 31, 2018 (183 ) (96 ) (87 ) At December 31, 2017 181 98 83 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)(b) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (c)(d) 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)(b) $ 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: (c) 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: (c)(d) 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)(b) $ 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) Energy-related derivatives exclude $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude 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. At December 31, 2018 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 469 $ 292 $ — $ — $ 761 Foreign currency derivatives — 75 — — 75 Investments in trusts: (c)(d) Domestic equity 601 107 — — 708 Foreign equity 53 173 — — 226 U.S. Treasury and government agency securities — 261 — — 261 Municipal bonds — 83 — — 83 Pooled funds – fixed income — 14 — — 14 Corporate bonds 24 290 — — 314 Mortgage and asset backed securities — 68 — — 68 Private equity — — — 45 45 Cash and cash equivalents 16 — — — 16 Other 34 4 — — 38 Cash equivalents 765 1 — — 766 Other investments — 12 — — 12 Total $ 1,962 $ 1,380 $ — $ 45 $ 3,387 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 316 $ — $ — $ 964 Interest rate derivatives — 49 — — 49 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ 648 $ 388 $ 21 $ — $ 1,057 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c) Domestic equity 396 95 — — 491 Foreign equity 53 50 — — 103 U.S. Treasury and government agency securities — 18 — — 18 Municipal bonds — 1 — — 1 Corporate bonds 24 135 — — 159 Mortgage and asset backed securities — 23 — — 23 Private equity — — — 45 45 Other 6 — — — 6 Cash equivalents 116 1 — — 117 Other investments — 12 — — 12 Total $ 595 $ 341 $ — $ 45 $ 981 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c)(d) Domestic equity 205 1 — — 206 Foreign equity — 119 — — 119 U.S. Treasury and government agency securities — 243 — — 243 Municipal bonds — 82 — — 82 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 45 — — 45 Other 19 4 — — 23 Total $ 224 $ 655 $ — $ — $ 879 Liabilities: Energy-related derivatives $ — $ 21 $ — $ — $ 21 Interest rate derivatives — 2 — — 2 Total $ — $ 23 $ — $ — $ 23 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 255 — — — 255 Total $ 255 $ 3 $ — $ — $ 258 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Foreign currency derivatives — 75 — — 75 Cash equivalents 46 — — — 46 Total $ 46 $ 79 $ — $ — $ 125 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ — $ 31 $ 21 $ — $ 52 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 469 $ 272 $ — $ — $ 741 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 14 — — 14 Cash equivalents 4 — — — 4 Cash equivalents 40 — — — 40 Total $ 513 $ 301 $ — $ — $ 814 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 261 $ — $ — $ 909 (a) Energy-related derivatives exclude $8 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude cash collateral of $277 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	t December 31, 2019 and 2018 , the accumulated provisions for the external decommissioning trust funds were as follows: 2019 2018 (in millions) Alabama Power Plant Farley $ 1,021 $ 846 Georgia Power Plant Hatch $ 634 $ 547 Plant Vogtle Units 1 and 2 379 326 Total $ 1,013 $ 873
Estimated costs of decommissioning	he estimated costs of decommissioning at December 31, 2019 based on the most current studies, which were each performed in 2018, were as follows: Plant Farley 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, 2019
Equity Method Investments and Joint Ventures [Abstract]
Redeemable noncontrolling interest	The following table presents the changes in Southern Power's redeemable noncontrolling interests for the year ended December 31, 2017 : 2017 (in millions) Beginning balance $ 164 Net income attributable to redeemable noncontrolling interests 2 Distributions to redeemable noncontrolling interests (2 ) Capital contributions from redeemable noncontrolling interests 2 Redemption of redeemable noncontrolling interests (59 ) Reclassification to non-redeemable noncontrolling interests (114 ) Change in fair value of redeemable noncontrolling interests 7 Ending balance $ —
Condensed income statement	The following table presents the attribution of net income to Southern Power and the noncontrolling interests for the year ended December 31, 2017 : 2017 (in millions) Net income $ 1,117 Less: Net income attributable to noncontrolling interests 44 Less: Net income attributable to redeemable noncontrolling interests 2 Net income attributable to Southern Power $ 1,071
Equity method investments	Selected financial information of SNG at December 31, 2019 and 2018 and for the years ended December 31, 2019 , 2018 , and 2017 is as follows: Balance Sheet Information 2019 2018 (in millions) Current assets $ 85 $ 104 Property, plant, and equipment 2,570 2,606 Deferred charges and other assets 158 121 Total Assets $ 2,813 $ 2,831 Current liabilities $ 227 $ 103 Long-term debt 1,214 1,103 Other deferred charges and other liabilities 86 212 Total Liabilities $ 1,527 $ 1,418 Total Stockholders' Equity $ 1,286 $ 1,413 Total Liabilities and Stockholders' Equity $ 2,813 $ 2,831 Income Statement Information 2019 2018 2017 (in millions) Revenues $ 630 $ 604 $ 544 Operating income 335 310 242 Net income 280 261 175 The carrying amounts of Southern Company Gas' equity method investments at December 31, 2019 and 2018 and related income from those investments for the years ended December 31, 2019 , 2018 , and 2017 were as follows: Investment Balance 2019 2018 (in millions) SNG (a) $ 1,137 $ 1,261 Atlantic Coast Pipeline (b) — 83 PennEast Pipeline 82 71 Pivotal JAX LNG (b) — 53 Other (c) 32 70 Total $ 1,251 $ 1,538 (a) Decrease primarily relates to the continued amortization of deferred tax assets established upon acquisition, as well as distributions in excess of earnings. (b) As a result of the proposed sale of Southern Company Gas' interests in Pivotal LNG and Atlantic Coast Pipeline, these amounts are classified as held for sale at December 31, 2019. See Note 3 under " Other Matters – Southern Company Gas " and Note 15 under " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline " and " Assets Held for Sale ," respectively, for additional information. (c) Decrease primarily relates to the sale of Triton. See Note 15 under " Southern Company Gas " for additional information.
Equity method investments related income	Earnings from Equity Method Investments 2019 2018 2017 (in millions) SNG $ 141 $ 131 $ 88 Atlantic Coast Pipeline (a) 13 7 6 PennEast Pipeline (a) 6 5 6 Other (b) (3 ) 5 6 Total $ 157 $ 148 $ 106 (a) Amounts primarily result from AFUDC equity recorded by the project entity. (b) Decrease primarily relates to the sale of Triton. See Note 15 under " Southern Company Gas " for additional information.

FINANCING (Tables)

FINANCING (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
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)(b) Alabama Power Georgia Power (a) Mississippi Power Southern Power (b) Southern Company Gas (in millions) 2020 $ 2,991 $ 251 $ 1,025 $ 281 $ 825 $ — 2021 3,214 311 397 270 300 330 2022 2,003 751 527 — 677 46 2023 2,413 301 175 — 290 400 2024 492 22 477 — — — (a) Amounts include principal amortization related to the FFB borrowings beginning in February 2020; however, the final maturity date is February 20, 2044. See " DOE Loan Guarantee Borrowings " herein for additional information. (b) Southern Power's 2022 maturity represents euro-denominated debt at the U.S. dollar denominated hedge settlement amount.
Summary of debt	Outstanding secured debt at December 31, 2019 and 2018 for the applicable Registrants was as follows: Georgia (a) Mississippi Power (b) Southern Company Gas (c) (in millions) December 31, 2019 $ 3,999 $ 270 $ 1,575 December 31, 2018 2,767 270 1,325 (a) Includes Georgia Power's FFB loans that are 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 " Long-term Debt – DOE Loan Guarantee Borrowings " herein for additional information. Also includes finance lease obligations of $156 million and $142 million at December 31, 2019 and 2018 , respectively. See Note 9 for additional information on finance lease obligations. (b) Represents revenue bonds assumed in conjunction with Mississippi Power's purchase of Plant Daniel Units 3 and 4 that are secured by Plant Daniel Units 3 and 4 and certain related personal property. See " Long-term Debt " herein for additional information. (c) Nicor Gas' first mortgage bonds are secured by substantially all of Nicor Gas' properties.
Summary of committed credit arrangements	At December 31, 2019 , committed credit arrangements with banks were as follows: Expires Company 2020 2022 2024 Total Unused Due within One Year (in millions) Southern Company parent $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — Alabama Power 3 525 800 1,328 1,328 3 Georgia Power — — 1,750 1,750 1,733 — Mississippi Power — 150 — 150 150 — 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 $ 6,900 $ 7,608 $ 7,576 $ 33 (a) Southern Power's subsidiaries are not parties to its bank credit arrangement. (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, 2019 Notes Payable at December 31, 2018 Amount Outstanding Weighted Average Interest Rate Amount Outstanding Weighted Average Interest Rate (in millions) (in millions) Southern Company Commercial paper $ 1,705 2.1 % $ 1,064 3.0 % Short-term bank debt 350 2.3 % 1,851 3.1 % Total $ 2,055 2.1 % $ 2,915 3.1 % Georgia Power Commercial paper $ 115 2.1 % $ 294 3.1 % Short-term bank debt 250 2.2 % — — % Total $ 365 2.2 % $ 294 3.1 % Southern Power Commercial paper $ 449 2.1 % $ — — % Short-term bank debt 100 2.6 % 100 3.1 % Total $ 549 2.2 % $ 100 3.1 % Southern Company Gas Commercial paper: Southern Company Gas Capital $ 372 2.1 % $ 403 3.1 % Nicor Gas 278 1.8 % 247 3.0 % Total $ 650 2.0 % $ 650 3.0 %
Shares used to compute diluted EPS	Shares used to compute diluted EPS were as follows: Average Common Stock Shares 2019 2018 2017 (in millions) As reported shares 1,046 1,020 1,000 Effect of stock-based compensation 8 5 8 Diluted shares 1,054 1,025 1,008
Schedule of temporary equity	The following table presents changes during the year in redeemable preferred stock of subsidiaries for Southern Company: Redeemable Preferred Stock of Subsidiaries (in millions) Balance at December 31, 2016: $ 118 Issued (a) 250 Redeemed (a) (38 ) Issuance costs (a) (6 ) Balance at December 31, 2017: 324 Redeemed (b) (33 ) Balance at December 31, 2018 and 2019: $ 291 (a) See " Alabama Power " herein for additional information. (b) See " Mississippi Power " herein for additional information. Preferred Stock Par Value/Stated Capital Per Share Shares Outstanding Redemption Price Per Share 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 Stated Capital (*) (*) Prior to October 1, 2022: $25.50 ; on or after October 1, 2022: Stated Capital

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Major categories of lease obligations	The major categories of lease obligations are as follows: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 the year ended December 31, 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) 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 and 2017, 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 — — — 2017: Rent expense $ 176 $ 25 $ 31 $ 3 $ 29 $ 15 PPA capacity expense 235 41 225 — — — (a) Georgia Power's energy-only solar PPAs accounted for as leases contained contingent rent expense of $72 million and $73 million for 2018 and 2017 , respectively, of which $29 million in each of 2018 and 2017 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 and $5 million in 2018 and 2017 , respectively. (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: 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 — — — As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas 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 % 3.70 % 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, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ —
Maturities of finance lease liabilities	Maturities of lease liabilities are as follows: As of December 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2020 $ 289 $ 54 $ 205 $ 2 $ 26 $ 18 2021 268 52 198 1 23 17 2022 260 53 197 1 23 14 2023 208 4 198 1 24 11 2024 163 1 161 — 24 10 Thereafter 1,514 1 831 2 812 44 Total 2,702 165 1,790 7 932 114 Less: Present value discount 858 9 364 1 534 22 Operating lease obligations $ 1,844 $ 156 $ 1,426 $ 6 $ 398 $ 92 Finance leases: 2020 $ 31 $ 1 $ 28 $ — $ — $ — 2021 25 1 24 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — 2024 15 — 25 — — — Thereafter 246 — 134 — — — Total 357 4 261 — — — Less: Present value discount 131 — 105 — Finance lease obligations $ 226 $ 4 $ 156 $ — $ — $ —
Leases not yet commenced	As of December 31, 2019 , Southern Company, Alabama Power, Mississippi Power, and Southern Power have additional leases that have not yet commenced, as detailed in the following table: Southern Company Alabama Power (a) Mississippi Power (b) Southern Power Lease category PPAs, land, pipelines, and aircraft PPAs Pipelines Land Expected commencement date 2020-2024 2020-2024 2020 2020 Longest lease term expiration 40 years 28 years 15 years 40 years Estimated total obligations (in millions) $248 $95 $23 $87 (a) See Note 2 under " Alabama Power – Petition for Certificate of Convenience and Necessity " for additional information. Alabama Power will have variable operating lease payments and variable finance lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. (b) See Note 2 under " Mississippi Power – Kemper County Energy Facility – Lignite Mine and CO 2 Pipeline Facilities " for additional information. Estimated total obligations include non-lease components.
Lease income, operating leases	Lease income for the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 the year ended December 31, 2019 is as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 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 under the lease are as follows: At December 31, 2019 Southern Company Mississippi Power (in millions) 2020 $ 17 $ 17 2021 15 15 2022 15 15 2023 14 14 2024 14 14 Thereafter 138 138 Total undiscounted cash flows $ 213 $ 213 Lease receivable (*) 118 118 Difference between undiscounted cash flows and discounted cash flows $ 95 $ 95 (*) 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, 2019 Southern Company Alabama Power Georgia Power Southern Power Southern Company Gas (in millions) 2020 $ 155 $ 26 $ 26 $ 84 $ 35 2021 141 23 19 86 35 2022 125 16 8 87 35 2023 110 7 2 88 34 2024 103 3 — 90 33 Thereafter 1,063 20 — 387 463 Total $ 1,697 $ 95 $ 55 $ 822 $ 635

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Details of income tax provisions	Details of income tax provisions are as follows: 2019 Southern Company Alabama Power Georgia Power 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 Power Mississippi Power 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 2017 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Federal — Current $ (62 ) $ 136 $ 256 $ 194 $ (566 ) $ 103 Deferred (6 ) 336 504 (753 ) (312 ) 170 (68 ) 472 760 (559 ) (878 ) 273 State — Current 37 23 116 — (110 ) 27 Deferred 173 73 (46 ) 27 49 67 210 96 70 27 (61 ) 94 Total $ 142 $ 568 $ 830 $ (532 ) $ (939 ) $ 367
Summary of amortization of tax credits	ITCs amortized in 2019 , 2018 , and 2017 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) 2019 $ 181 $ 151 2018 87 58 2017 79 57
Schedule of effective income tax reconciliation	A reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: 2019 Southern Company Alabama Power Georgia Power 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 Power 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 % 2017 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Southern Company Gas Federal statutory rate 35.0 % 35.0 % 35.0 % (35.0 )% 35.0 % 35.0 % State income tax, net of federal deduction 12.5 4.5 2.0 0.6 (22.2 ) 10.0 Employee stock plans' dividend deduction (4.0 ) — — — — — Non-deductible book depreciation 3.1 0.9 0.7 0.1 — — Flowback of excess deferred income taxes (0.3 ) — (0.1 ) — — (0.2 ) AFUDC-Equity (2.6 ) (1.0 ) (0.6 ) — — — AFUDC-Equity portion of Kemper IGCC charge 15.7 — — 5.3 — — ITC basis difference (1.7 ) — — — (10.0 ) — Federal PTCs (12.1 ) — — — (72.5 ) — Amortization of ITC (4.2 ) (0.2 ) (0.1 ) — (20.6 ) (0.2 ) Tax Reform Legislation (25.6 ) 0.3 (0.4 ) 11.9 (416.1 ) 15.0 Noncontrolling interests (1.4 ) — — — (8.6 ) — Other (1.1 ) 0.1 0.2 — (10.7 ) 0.6 Effective income tax (benefit) rate 13.3 % 39.6 % 36.7 % (17.1 )% (525.7 )% 60.2 % (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2017 .
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, 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 — 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 786 173 154 56 46 287 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 December 31, 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 8,461 $ 2,236 $ 3,005 $ 335 $ 1,483 $ 1,176 Property basis differences 1,807 865 633 162 — 134 Federal effect of net state deferred tax assets — — — 36 — — Leveraged lease basis differences 253 — — — — — Employee benefit obligations 477 149 290 25 6 6 Premium on reacquired debt 88 14 74 — — — Regulatory assets – Storm damage reserves 111 — 111 — — — Employee benefit obligations 975 260 344 45 — 45 Remaining book value of retired assets 56 6 39 11 — — AROs 1,232 276 925 31 — — AROs 1,210 607 575 — — — Other 537 171 102 57 34 132 Total deferred income tax liabilities 15,207 4,584 6,098 702 1,523 1,493 Deferred tax assets — Federal effect of net state deferred tax liabilities 260 155 71 — 22 46 Employee benefit obligations 1,273 286 444 62 7 150 Other property basis differences 251 — 61 — 172 — ITC and PTC carryforward 2,730 11 430 — 2,128 — Alternative minimum tax carryforward 62 — — 32 21 — Other partnership basis difference 162 — — — 162 — Other comprehensive losses 82 10 3 — — — AROs 2,442 883 1,500 31 — — Estimated loss on plants under construction 346 — 283 63 — — Other deferred state tax attributes 415 — 19 251 72 — Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 294 130 127 29 — 8 Other 731 147 140 47 47 285 Total deferred income tax assets 9,048 1,622 3,078 515 2,631 489 Valuation allowance (123 ) — (42 ) (41 ) (27 ) (12 ) Net deferred income tax assets 8,925 1,622 3,036 474 2,604 477 Net deferred income taxes (assets)/liabilities $ 6,282 $ 2,962 $ 3,062 $ 228 $ (1,081 ) $ 1,016 Recognized in the balance sheets: Accumulated deferred income $ (276 ) $ — $ — $ (150 ) $ (1,186 ) $ — Accumulated deferred income taxes – liabilities $ 6,558 $ 2,962 $ 3,062 $ 378 $ 105 $ 1,016
Summary of tax credit carryforwards	Federal ITC/PTC carryforwards at December 31, 2019 were as follows: Southern Company Alabama Power Georgia Power Southern Power (in millions) Federal ITC/PTC carryforwards $ 1,751 $ 11 $ 88 $ 1,445 Year in which federal ITC/PTC carryforwards begin expiring 2032 2033 2032 2036 Year by which federal ITC/PTC carryforwards are expected to be utilized 2024 2022 2022 2024
Summary of operating loss carryforward	At December 31, 2019 , the state and local NOL carryforwards for Southern Company's subsidiaries were as follows: Company/Jurisdiction Approximate NOL Carryforwards Approximate Net State Income Tax Benefit Tax Year NOL Begins Expiring (in millions) Mississippi Power Mississippi $ 5,099 $ 201 2031 Southern Power Oklahoma 830 39 2035 Florida 258 11 2033 South Carolina 56 2 2034 Other states 21 2 Various Southern Power Total $ 1,165 $ 54 Other (*) Georgia 171 7 2020 New York 220 11 2035 New York City 207 15 2035 Other states 368 18 Various Southern Company Total $ 7,230 $ 306 (*) 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, 2019 .
Changes in unrecognized tax benefits	Unrecognized tax benefits changes in 2018 and 2017 for Southern Company, Mississippi Power, and Southern Power are provided below. The remaining Registrants did not have any material unrecognized tax benefits for the periods presented. Southern Company Mississippi Power Southern Power (in millions) Unrecognized tax benefits at December 31, 2016 $ 484 $ 465 $ 17 Tax positions changes – Increase from current periods 10 — — Increase from prior periods 10 2 — Decrease from prior periods (196 ) (177 ) (17 ) Reductions due to settlements (290 ) (290 ) — Unrecognized tax benefits at December 31, 2017 18 — — Tax positions changes – Decrease from prior periods (18 ) — — Unrecognized tax benefits at December 31, 2018 $ — $ — $ —
Impact on effective tax rate	The impact on the effective tax rate of Southern Company, if recognized, was as follows for 2017 : Southern Company (in millions) 2017 Tax positions impacting the effective tax rate $ 18 Tax positions not impacting the effective tax rate — Balance of unrecognized tax benefits $ 18

RETIREMENT BENEFITS (Tables)

RETIREMENT BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Schedule of defined benefit plan	In December 2019, the Registrants voluntarily contributed the following amounts to the qualified pension plan: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Contributions to qualified pension plan $ 1,136 $ 362 $ 200 $ 54 $ 24 $ 145 Pension Plans Other Postretirement Benefit Plans (in millions) Projected benefit obligation $ 526 $ 69 Plan assets 492 17 Accrued liability $ (34 ) $ (52 )
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. 2019 Assumptions used to determine net Southern Company Alabama Power 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 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 2017 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Southern Company Gas Pension plans Discount rate – benefit obligations 4.40 % 4.44 % 4.40 % 4.44 % 4.39 % Discount rate – interest costs 3.77 3.76 3.72 3.81 3.76 Discount rate – service costs 4.81 4.85 4.83 4.83 4.64 Expected long-term return on plan assets 7.92 7.95 7.95 7.95 7.60 Annual salary increase 4.37 4.46 4.46 4.46 3.50 Other postretirement benefit plans Discount rate – benefit obligations 4.23 % 4.27 % 4.23 % 4.22 % 4.15 % Discount rate – interest costs 3.54 3.58 3.55 3.55 3.40 Discount rate – service costs 4.64 4.70 4.63 4.65 4.55 Expected long-term return on plan assets 6.84 6.83 6.79 6.88 6.03 Annual salary increase 4.37 4.46 4.46 4.46 3.50 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 2018 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 4.49 % 4.51 % 4.48 % 4.49 % 4.65 % 4.47 % Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07 Other postretirement benefit plans Discount rate 4.37 % 4.40 % 4.36 % 4.35 % 4.50 % 4.32 % Annual salary increase 4.34 4.46 4.46 4.46 4.46 3.07
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, 2019 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 6.50 4.50 2027
Schedule of accumulated and projected benefit obligations	The total accumulated benefit obligation for the pension plans at December 31, 2019 and 2018 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2019 $ 13,391 $ 3,053 $ 4,222 $ 615 $ 151 $ 963 December 31, 2018 11,683 2,550 3,613 513 101 842 The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2019 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 $ 14,055 $ 3,286 $ 4,480 $ 639 $ 159 $ 999 Non-qualified pension plan 733 118 130 31 26 68
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, 2019 and 2018 were as follows: 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 ) 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 13,808 $ 2,998 $ 4,188 $ 602 $ 139 $ 1,184 Dispositions (107 ) — — — (3 ) (104 ) Service cost 359 78 87 17 9 34 Interest cost 464 101 139 20 5 39 Benefits paid (618 ) (124 ) (191 ) (24 ) (3 ) (98 ) Actuarial (gain) loss (1,143 ) (237 ) (318 ) (58 ) (24 ) (148 ) Balance at end of year 12,763 2,816 3,905 557 123 907 Change in plan assets Fair value of plan assets at beginning of year 12,992 2,836 4,058 563 138 1,068 Dispositions (107 ) — — — (3 ) (104 ) Actual return (loss) on plan assets (711 ) (150 ) (218 ) (37 ) (9 ) (70 ) Employer contributions 55 13 14 3 — 2 Benefits paid (618 ) (124 ) (191 ) (24 ) (3 ) (98 ) Fair value of plan assets at end of year 11,611 2,575 3,663 505 123 798 Accrued liability $ (1,152 ) $ (241 ) $ (242 ) $ (52 ) $ — $ (109 )
Amounts recognized in balance sheets	Amounts recognized in the balance sheets at December 31, 2019 and 2018 related to the Registrants' pension plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2018: Prepaid pension costs $ — $ — $ — $ — $ 1 $ — Other regulatory assets, deferred (*) 3,566 955 1,230 167 — 160 Other deferred charges and assets — — — — — 74 Other current liabilities (55 ) (12 ) (15 ) (3 ) — (3 ) Employee benefit obligations (1,097 ) (229 ) (227 ) (49 ) (1 ) (179 ) Other regulatory liabilities, deferred (108 ) — — — — — AOCI 97 — — — 26 (44 ) (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 acquisition by Southern Company. Presented below are the amounts included in regulatory assets at December 31, 2019 and 2018 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, 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 Balance at December 31, 2018 Regulatory assets: Prior service cost $ 17 $ 6 $ 12 $ 2 $ (17 ) Net (gain) loss 3,441 949 1,218 165 83 Regulatory amortization — — — — 94 Total regulatory assets (*) $ 3,458 $ 955 $ 1,230 $ 167 $ 160 (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 acquisition by Southern Company. Amounts recognized in the balance sheets at December 31, 2019 and 2018 related to the Registrants' other postretirement benefit plans consist of the following: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2018: Other regulatory assets, deferred (a) $ 99 $ — $ 60 $ 6 $ — $ (4 ) Other current liabilities (6 ) — — — — — Employee benefit obligations (b) (931 ) (43 ) (331 ) (58 ) (9 ) 146 Other regulatory liabilities, deferred (77 ) (8 ) — (2 ) — — AOCI (4 ) — — — 1 (4 ) (a) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 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, 2019 and 2018 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, 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 ) Balance at December 31, 2018: Regulatory assets (liabilities): Prior service cost $ 14 $ 8 $ 4 $ — $ 2 Net (gain) loss 8 (16 ) 56 4 (43 ) Regulatory amortization — — — — 37 Total regulatory assets (liabilities) (*) $ 22 $ (8 ) $ 60 $ 4 $ (4 ) (*) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 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, 2019 and 2018 are presented in the following table: Southern Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): (*) Balance at December 31, 2017 $ 3,155 $ 890 $ 1,105 $ 158 $ 217 Net (gain) loss 498 120 196 19 20 Change in prior service costs 1 — — — (18 ) Dispositions 12 — — — (34 ) Reclassification adjustments: Amortization of prior service costs (4 ) (1 ) (2 ) — 2 Amortization of net gain (loss) (204 ) (54 ) (69 ) (10 ) (12 ) Amortization of regulatory assets (*) — — — — (15 ) Total reclassification adjustments (208 ) (55 ) (71 ) (10 ) (25 ) Total change 303 65 125 9 (57 ) 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 (*) Amounts for Southern Company exclude regulatory assets of $252 million and $268 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' pension plans prior to its 2016 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, 2019 and 2018 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, 2017 $ 341 $ 56 $ 202 $ 17 $ 46 Net (gain) loss (298 ) (60 ) (132 ) (12 ) (42 ) Change in prior service costs — — — — (2 ) Reclassification adjustments: Amortization of prior service costs (7 ) (4 ) (1 ) — — Amortization of net gain (loss) (14 ) (1 ) (9 ) (1 ) — Amortization of regulatory assets (*) — — — — (6 ) Total reclassification adjustments (21 ) (5 ) (10 ) (1 ) (6 ) Total change (319 ) (65 ) (142 ) (13 ) (50 ) 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 ) (*) Amounts for Southern Company exclude regulatory assets of $50 million and $57 million at December 31, 2019 and 2018 , respectively, associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its 2016 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, 2019 and 2018 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 Company Southern Power Southern Company Gas (in millions) Balance at December 31, 2019 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 188 46 (8 ) Total AOCI $ 185 $ 46 $ (14 ) Balance at December 31, 2018 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 100 26 (38 ) Total AOCI $ 97 $ 26 $ (44 ) Presented below are the amounts included in AOCI at December 31, 2019 and 2018 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 Power Southern Company Gas (in millions) Balance at December 31, 2019 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss 1 2 (5 ) Total AOCI $ 2 $ 2 $ (4 ) Balance at December 31, 2018 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss (5 ) 1 (5 ) Total AOCI $ (4 ) $ 1 $ (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, 2019 and 2018 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2017 $ 107 $ 33 $ (42 ) Net (gain) loss 7 (5 ) 6 Dispositions (8 ) — (8 ) Reclassification adjustments: Amortization of net gain (loss) (9 ) (2 ) — Total reclassification adjustments (9 ) (2 ) — Total change (10 ) (7 ) (2 ) Balance at December 31, 2018 $ 97 $ 26 $ (44 ) Net (gain) loss 88 20 30 Balance at December 31, 2019 $ 185 $ 46 $ (14 ) The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2019 and 2018 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2017 $ 4 $ 3 $ (3 ) Net (gain) loss (8 ) (2 ) (2 ) Change from employee transfer — — 1 Total change (8 ) (2 ) (1 ) 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 )
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) 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 2017 Service cost $ 293 $ 63 $ 74 $ 15 $ 23 Interest cost 455 98 138 20 42 Expected return on plan assets (897 ) (196 ) (283 ) (40 ) (70 ) Recognized net (gain) loss 162 42 57 7 18 Net amortization 12 2 3 1 1 Net periodic pension cost $ 25 $ 9 $ (11 ) $ 3 $ 14 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) 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 2017 Service cost $ 24 $ 6 $ 7 $ 1 $ 2 Interest cost 79 17 29 3 10 Expected return on plan assets (66 ) (25 ) (25 ) (1 ) (7 ) Net amortization 20 5 9 1 1 Net periodic postretirement benefit cost $ 57 $ 3 $ 20 $ 4 $ 6
Estimated pension benefit payments	At December 31, 2019 , estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2020 $ 628 $ 135 $ 204 $ 27 $ 5 $ 62 2021 646 141 208 28 6 62 2022 671 147 214 30 6 64 2023 693 153 220 30 6 62 2024 715 157 226 32 7 62 2025 to 2029 3,868 860 1,209 174 36 316 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit payments: 2020 $ 130 $ 29 $ 49 $ 6 $ — $ 18 2021 129 29 49 6 — 18 2022 129 29 49 6 1 18 2023 130 29 49 6 1 19 2024 129 29 48 6 1 18 2025 to 2029 630 145 238 29 3 83 Subsidy receipts: 2020 $ (5 ) $ (1 ) $ (2 ) $ — $ — $ — 2021 (6 ) (2 ) (2 ) — — — 2022 (6 ) (2 ) (3 ) — — — 2023 (6 ) (2 ) (3 ) — — — 2024 (6 ) (2 ) (3 ) (1 ) — — 2025 to 2029 (30 ) (9 ) (13 ) (2 ) — — Total: 2020 $ 125 $ 28 $ 47 $ 6 $ — $ 18 2021 123 27 47 6 — 18 2022 123 27 46 6 1 18 2023 124 27 46 6 1 19 2024 123 27 45 5 1 18 2025 to 2029 600 136 225 27 3 83
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, 2019 and 2018 were as follows: 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 ) 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 2,339 $ 517 $ 863 $ 97 $ 11 $ 310 Dispositions (18 ) — — — — (18 ) Service cost 24 6 6 1 1 2 Interest cost 75 17 28 3 — 10 Benefits paid (129 ) (28 ) (47 ) (5 ) (1 ) (17 ) Actuarial (gain) loss (432 ) (111 ) (178 ) (15 ) (2 ) (43 ) Retiree drug subsidy 6 2 3 — — — Balance at end of year 1,865 403 675 81 9 244 Change in plan assets Fair value of plan assets at beginning of year 1,053 406 386 25 — 125 Dispositions (18 ) — — — — (18 ) Actual return (loss) on plan assets (57 ) (25 ) (20 ) (1 ) — (5 ) Employer contributions 73 5 22 4 1 13 Benefits paid (123 ) (26 ) (44 ) (5 ) (1 ) (17 ) Fair value of plan assets at end of year 928 360 344 23 — 98 Accrued liability $ (937 ) $ (43 ) $ (331 ) $ (58 ) $ (9 ) $ (146 )
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 (such as commingled/pooled funds) are valued as Level 2 when the underlying holdings are comprised of Level 1 or Level 2 equity securities. Fixed income: A mix of domestic and international bonds. Investments in fixed income securities 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	These fair values exclude cash, receivables related to investment income and pending investment sales, and payables related to pending investment purchases. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs 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 % Liabilities: Derivatives (1 ) — — (1 ) Total $ 6,435 $ 5,157 $ 2,526 $ 14,118 100 % 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 Other Observable Inputs 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 Other Observable Inputs 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 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Equity: 51 % 53 % Domestic equity $ 2,102 $ 1,030 $ — $ 3,132 International equity 1,344 1,325 — 2,669 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 930 — 930 Mortgage- and asset-backed securities — 7 — 7 Corporate bonds — 1,195 — 1,195 Pooled funds — 654 — 654 Cash equivalents and other 270 2 — 272 Real estate investments 419 — 1,361 1,780 14 15 Special situations — — 171 171 3 1 Private equity — — 821 821 9 7 Total $ 4,135 $ 5,143 $ 2,353 $ 11,631 100 % 100 % Alabama Power Assets: Equity: 51 % 53 % Domestic equity $ 466 $ 228 $ — $ 694 International equity 298 293 — 591 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 206 — 206 Mortgage- and asset-backed securities — 2 — 2 Corporate bonds — 265 — 265 Pooled funds — 145 — 145 Cash equivalents and other 60 1 — 61 Real estate investments 93 — 302 395 14 15 Special situations — — 38 38 3 1 Private equity — — 182 182 9 7 Total $ 917 $ 1,140 $ 522 $ 2,579 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Equity: 51 % 53 % Domestic equity $ 663 $ 325 $ — $ 988 International equity 424 418 — 842 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 294 — 294 Mortgage- and asset-backed securities — 2 — 2 Corporate bonds — 377 — 377 Pooled funds — 206 — 206 Cash equivalents and other 85 1 — 86 Real estate investments 132 — 429 561 14 15 Special situations — — 54 54 3 1 Private equity — — 259 259 9 7 Total $ 1,304 $ 1,623 $ 742 $ 3,669 100 % 100 % Mississippi Power Assets: Equity: 51 % 53 % Domestic equity $ 91 $ 45 $ — $ 136 International equity 59 59 — 118 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 40 — 40 Corporate bonds — 52 — 52 Pooled funds — 28 — 28 Cash equivalents and other 12 — — 12 Real estate investments 18 — 59 77 14 15 Special situations — — 7 7 3 1 Private equity — — 36 36 9 7 Total $ 180 $ 224 $ 102 $ 506 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Southern Power Assets: Equity: 51 % 53 % Domestic equity $ 22 $ 11 $ — $ 33 International equity 14 14 — 28 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 10 — 10 Corporate bonds — 13 — 13 Pooled funds — 7 — 7 Cash equivalents and other 3 — — 3 Real estate investments 4 — 15 19 14 15 Special situations — — 2 2 3 1 Private equity — — 9 9 9 7 Total $ 43 $ 55 $ 26 $ 124 100 % 100 % Southern Company Gas Assets: Equity: 51 % 53 % Domestic equity $ 145 $ 71 $ — $ 216 International equity 92 91 — 183 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 64 — 64 Corporate bonds — 82 — 82 Pooled funds — 45 — 45 Cash equivalents and other 19 — — 19 Real estate investments 29 — 94 123 14 15 Special situations — — 12 12 3 1 Private equity — — 56 56 9 7 Total $ 285 $ 353 $ 162 $ 800 100 % 100 % The fair values of the applicable Registrants' other postretirement benefit plan assets at December 31, 2019 and 2018 are presented below. The Registrants did not have any investments classified as Level 3 at December 31, 2019 or 2018 . These fair value measurements exclude cash, receivables related to investment income, pending investment sales, and payables related to pending investment purchases. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) (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 Other Observable Inputs Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) (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 Other Observable Inputs Net Asset Value as a Practical Expedient Total Target Allocation Actual Allocation At December 31, 2019: (Level 1) (Level 2) (NAV) (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 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Equity: 62 % 62 % Domestic equity $ 100 $ 76 $ — $ 176 International equity 45 75 — 120 Fixed income: 29 30 U.S. Treasury, government, and agency bonds — 34 — 34 Corporate bonds — 35 — 35 Pooled funds — 81 — 81 Cash equivalents and other 13 — — 13 Trust-owned life insurance — 386 — 386 Real estate investments 13 — 40 53 5 5 Special situations — — 4 4 1 — Private equity — — 24 24 3 3 Total $ 171 $ 687 $ 68 $ 926 100 % 100 % Alabama Power Assets: Equity: 64 % 66 % Domestic equity $ 35 $ 10 $ — $ 45 International equity 12 12 — 24 Fixed income: 28 28 U.S. Treasury, government, and agency bonds — 10 — 10 Corporate bonds — 11 — 11 Pooled funds — 6 — 6 Cash equivalents and other 3 — — 3 Trust-owned life insurance — 233 — 233 Real estate investments 4 — 13 17 4 4 Special situations — — 2 2 1 — Private equity — — 8 8 3 2 Total $ 54 $ 282 $ 23 $ 359 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Equity: 60 % 59 % Domestic equity $ 41 $ 9 $ — $ 50 International equity 17 32 — 49 Fixed income: 33 35 U.S. Treasury, government, and agency bonds — 7 — 7 Corporate bonds — 10 — 10 Pooled funds — 44 — 44 Cash equivalents and other 5 — — 5 Trust-owned life insurance — 153 — 153 Real estate investments 4 — 11 15 4 4 Special situations — — 2 2 1 — Private equity — — 7 7 2 2 Total $ 67 $ 255 $ 20 $ 342 100 % 100 % Mississippi Power Assets: Equity: 41 % 42 % Domestic equity $ 3 $ 2 $ — $ 5 International equity 2 2 — 4 Fixed income: 38 39 U.S. Treasury, government, and agency bonds — 6 — 6 Corporate bonds — 2 — 2 Pooled funds — 1 — 1 Cash equivalents and other 1 — — 1 Real estate investments 1 — 2 3 11 12 Special situations — — — — 3 1 Private equity — — 1 1 7 6 Total $ 7 $ 13 $ 3 $ 23 100 % 100 % Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Net Asset Value as a Practical Expedient Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Gas Assets: Equity: 71 % 69 % Domestic equity $ 2 $ 47 $ — $ 49 International equity 1 17 — 18 Fixed income: 25 28 U.S. Treasury, government, and agency bonds — 1 — 1 Corporate bonds — 1 — 1 Pooled funds — 24 — 24 Cash equivalents and other 1 — — 1 Real estate investments — — 1 1 2 2 Special situations — — — — 1 — Private equity — — 1 1 1 1 Total $ 4 $ 90 $ 2 $ 96 100 % 100 %
Total matching contributions	Total matching contributions made to the plans for 2019 , 2018 , and 2017 were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2019 $ 113 $ 25 $ 27 $ 4 $ 2 $ 15 2018 119 24 26 5 3 18 2017 118 23 26 5 N/A 19

STOCK COMPENSATION (Tables)

STOCK COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of employees participating in stock-based compensation programs	At December 31, 2019 , 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 2,320 307 370 89 50 285
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 2019 2018 2017 Expected volatility 15.6% 14.9% 15.6% Expected term (in years) 3 3 3 Interest rate 2.4% 2.4% 1.4% Weighted average grant-date fair value $62.71 $43.75 $49.08
Schedule of compensation costs and related tax benefits	Total intrinsic value of options exercised, and the related tax benefit, for the years ended December 31, 2019 , 2018 , and 2017 are presented below: Year Ended December 31 2019 2018 2017 (in millions) Southern Company Intrinsic value of options exercised $ 167 $ 9 $ 64 Tax benefit of options exercised 35 2 25 Alabama Power Intrinsic value of options exercised $ 21 $ 2 $ 12 Tax benefit of options exercised 4 — 5 Georgia Power Intrinsic value of options exercised $ 30 $ 2 $ 13 Tax benefit of options exercised 6 — 5 Mississippi Power Intrinsic value of options exercised $ 4 $ 1 $ 2 Tax benefit of options exercised 1 — 1 Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 (in millions) Southern Company Compensation cost recognized in income $ 77 $ 91 $ 74 Tax benefit of compensation cost recognized in income 20 24 29 Southern Company Gas Compensation cost recognized in income $ 14 $ 11 $ 8 Tax benefit of compensation cost recognized in income 4 3 3
Share-based compensation, stock options, activity	Southern Company's activity in the stock option program for 2019 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2018 17.5 $ 41.92 Exercised 11.6 41.62 Outstanding and Exercisable at December 31, 2019 5.9 $ 42.52
Schedule of aggregate and total intrinsic value of options exercised	At December 31, 2019 , the aggregate intrinsic value for the options outstanding and exercisable was as follows: Southern Company Alabama Power Georgia Power Mississippi Power (in millions) Total intrinsic value for outstanding and exercisable options $ 124 $ 14 $ 35 $ 6

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2019
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 2019 , 2018 , and 2017 are shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2019 $ 344 $ 194 $ 150 2018 (67 ) (38 ) (29 ) 2017 233 125 108 Unrealized gains (losses) At December 31, 2019 $ 259 $ 149 $ 110 At December 31, 2018 (183 ) (96 ) (87 ) At December 31, 2017 181 98 83 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)(b) $ 388 $ 267 $ 22 $ — $ 677 Interest rate derivatives — 2 — — 2 Foreign currency derivatives — 16 — — 16 Investments in trusts: (c)(d) 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)(b) $ 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: (c) 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: (c)(d) 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)(b) $ 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) Energy-related derivatives exclude $4 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude 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. At December 31, 2018 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 469 $ 292 $ — $ — $ 761 Foreign currency derivatives — 75 — — 75 Investments in trusts: (c)(d) Domestic equity 601 107 — — 708 Foreign equity 53 173 — — 226 U.S. Treasury and government agency securities — 261 — — 261 Municipal bonds — 83 — — 83 Pooled funds – fixed income — 14 — — 14 Corporate bonds 24 290 — — 314 Mortgage and asset backed securities — 68 — — 68 Private equity — — — 45 45 Cash and cash equivalents 16 — — — 16 Other 34 4 — — 38 Cash equivalents 765 1 — — 766 Other investments — 12 — — 12 Total $ 1,962 $ 1,380 $ — $ 45 $ 3,387 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 316 $ — $ — $ 964 Interest rate derivatives — 49 — — 49 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ 648 $ 388 $ 21 $ — $ 1,057 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c) Domestic equity 396 95 — — 491 Foreign equity 53 50 — — 103 U.S. Treasury and government agency securities — 18 — — 18 Municipal bonds — 1 — — 1 Corporate bonds 24 135 — — 159 Mortgage and asset backed securities — 23 — — 23 Private equity — — — 45 45 Other 6 — — — 6 Cash equivalents 116 1 — — 117 Other investments — 12 — — 12 Total $ 595 $ 341 $ — $ 45 $ 981 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c)(d) Domestic equity 205 1 — — 206 Foreign equity — 119 — — 119 U.S. Treasury and government agency securities — 243 — — 243 Municipal bonds — 82 — — 82 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 45 — — 45 Other 19 4 — — 23 Total $ 224 $ 655 $ — $ — $ 879 Liabilities: Energy-related derivatives $ — $ 21 $ — $ — $ 21 Interest rate derivatives — 2 — — 2 Total $ — $ 23 $ — $ — $ 23 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, 2018: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 255 — — — 255 Total $ 255 $ 3 $ — $ — $ 258 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Foreign currency derivatives — 75 — — 75 Cash equivalents 46 — — — 46 Total $ 46 $ 79 $ — $ — $ 125 Liabilities: Energy-related derivatives $ — $ 8 $ — $ — $ 8 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 21 — 21 Total $ — $ 31 $ 21 $ — $ 52 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 469 $ 272 $ — $ — $ 741 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds - fixed income — 14 — — 14 Cash equivalents 4 — — — 4 Cash equivalents 40 — — — 40 Total $ 513 $ 301 $ — $ — $ 814 Liabilities: Energy-related derivatives (a)(b) $ 648 $ 261 $ — $ — $ 909 (a) Energy-related derivatives exclude $8 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Energy-related derivatives exclude cash collateral of $277 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, 2019 and 2018 , other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company (a)(b) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (b) (in millions) 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 At December 31, 2018: Long-term debt, including securities due within one year: Carrying amount $ 45,023 $ 8,120 $ 9,838 $ 1,579 $ 5,017 $ 5,940 Fair value 44,824 8,370 9,800 1,546 4,980 5,965 (a) Amounts at December 31, 2018 include long-term debt of Gulf Power, which was classified as liabilities held for sale on Southern Company's balance sheet at December 31, 2018. See Note 15 under " Southern Company " and " Assets Held for Sale " for additional information. (b) The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the Merger. Southern Company Gas amortizes the fair value adjustments over the lives of the respective bonds.
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. 2019 (in millions) Beginning balance $ — Transfers to Level 3 (32 ) Transfers from Level 3 3 Instruments realized or otherwise settled during period (4 ) Changes in fair value 47 Ending balance $ 14

DERIVATIVES (Tables)

DERIVATIVES (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of energy-related derivatives	At December 31, 2019 , 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 Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 589 2023 2029 Alabama Power 88 2022 — Georgia Power 175 2023 — Mississippi Power 101 2023 — Southern Power 7 2020 2020 Southern Company Gas (*) 218 2022 2029 (*) 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 4,096 million mmBtu and short natural gas positions of 3,878 million mmBtu at December 31, 2019 , which is also included in Southern Company's total volume.
Notional amount of interest rate derivatives	At December 31, 2019 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value (in millions) (in millions) Cash Flow Hedges of Forecasted Debt Georgia Power $ 250 3-month LIBOR 2.23% March 2025 $ (6 ) Georgia Power 250 3-month LIBOR 2.40% March 2030 (11 ) Southern Company Gas 200 3-month LIBOR 1.81% September 2030 2 Fair Value Hedges of Existing Debt Southern Company parent 300 2.75% 3-month LIBOR + 0.92% June 2020 — Southern Company parent 1,500 2.35% 1-month LIBOR + 0.87% July 2021 (7 ) Southern Company $ 2,500 $ (22 )
Schedule of foreign exchange contracts	At December 31, 2019 , 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 $ (7 ) Southern Power 564 3.78% 500 1.85% June 2026 (1 ) Total $ 1,241 € 1,100 $ (8 )
Fair value of energy-related derivatives and interest rate derivatives	At December 31, 2019 and 2018 , the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2019 2018 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: Other current assets/Other current liabilities $ 3 $ 70 $ 8 $ 23 Other deferred charges and assets/Other deferred credits and liabilities 6 44 9 26 Assets held for sale, current/Liabilities held for sale, current — — — 6 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 114 $ 17 $ 55 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 6 $ 3 $ 7 Other deferred charges and assets/Other deferred credits and liabilities — — 1 2 Interest rate derivatives: Other current assets/Other current liabilities 2 23 — 19 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 30 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 16 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 19 $ 54 $ 79 $ 81 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 461 $ 358 $ 561 $ 575 Other deferred charges and assets/Other deferred credits and liabilities 207 225 180 325 Total derivatives not designated as hedging instruments $ 668 $ 583 $ 741 $ 900 Gross amounts recognized $ 696 $ 751 $ 837 $ 1,036 Gross amounts offset (a) $ (463 ) $ (562 ) $ (524 ) $ (801 ) Net amounts recognized in the Balance Sheets (b) $ 233 $ 189 $ 313 $ 235 2019 2018 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 $ 2 $ 14 $ 3 $ 4 Other deferred charges and assets/Other deferred credits and liabilities 2 10 3 6 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 24 $ 6 $ 10 Gross amounts recognized $ 4 $ 24 $ 6 $ 10 Gross amounts offset $ (2 ) $ (2 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 2 $ 22 $ 2 $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 32 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 3 21 4 13 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 53 $ 6 $ 21 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 17 $ — $ 2 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 17 $ — $ 2 Gross amounts recognized $ 4 $ 70 $ 6 $ 23 Gross amounts offset $ (3 ) $ (3 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ 1 $ 67 $ — $ 17 2019 2018 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 $ — $ 15 $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 1 12 2 6 Total derivatives designated as hedging instruments for regulatory purposes $ 1 $ 27 $ 3 $ 9 Gross amounts recognized $ 1 $ 27 $ 3 $ 9 Gross amounts offset $ (1 ) $ (1 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 26 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ 3 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — — 1 2 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 16 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 17 $ 26 $ 79 $ 31 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 1 $ — $ — Total derivatives not designated as hedging instruments $ 2 $ 1 $ — $ — Gross amounts recognized $ 19 $ 27 $ 79 $ 31 Gross amounts offset $ — $ — $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 19 $ 27 $ 76 $ 28 2019 2018 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/Liabilities from risk management activities-current $ — $ 9 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — 1 Total derivatives designated as hedging instruments for regulatory purposes $ — $ 10 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 4 $ — $ 1 Interest rate derivatives: Assets from risk management activities/Liabilities from risk management activities-current 2 — — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 4 $ — $ 1 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 459 $ 357 $ 559 $ 574 Other deferred charges and assets/Other deferred credits and liabilities 207 225 180 325 Total derivatives not designated as hedging instruments $ 666 $ 582 $ 739 $ 899 Gross amounts recognized $ 668 $ 596 $ 741 $ 909 Gross amounts offset (a) $ (456 ) $ (555 ) $ (508 ) $ (785 ) Net amounts recognized in the Balance Sheets (b) $ 212 $ 41 $ 233 $ 124 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $99 million and $277 million at December 31, 2019 and 2018 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $4 million and $8 million at December 31, 2019 and 2018 , respectively.
Pre-tax effects on the balance sheets	At December 31, 2019 and 2018 , 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, 2019 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power 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 Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2018 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (3 ) $ (6 ) $ (2 ) $ (8 ) Other regulatory assets, deferred (16 ) (3 ) (9 ) (4 ) — Assets held for sale, current (6 ) — — — — Other regulatory liabilities, current 1 — — — 1 Total energy-related derivative gains (losses) $ (40 ) $ (6 ) $ (15 ) $ (6 ) $ (7 )
Pre-tax effects of interest rate derivatives, designated as cash flow hedging instruments	For the years ended December 31, 2019 , 2018 , and 2017 , 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 2019 2018 2017 (in millions) Southern Company Energy-related derivatives $ (13 ) $ 17 $ (47 ) Interest rate derivatives (57 ) (1 ) (2 ) Foreign currency derivatives (84 ) (78 ) 140 Total $ (154 ) $ (62 ) $ 91 Georgia Power Interest rate derivatives $ (59 ) $ — $ 1 Southern Power Energy-related derivatives $ (4 ) $ 10 $ (38 ) Foreign currency derivatives (84 ) (78 ) 140 Total $ (88 ) $ (68 ) $ 102 Southern Company Gas Energy-related derivatives $ (9 ) $ 7 $ (9 ) Interest rate derivatives 2 — — Total $ (7 ) $ 7 $ (9 )
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, 2019 , 2018 , and 2017 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2019 2018 2017 (in millions) Southern Company Total cost of natural gas $ 1,319 $ 1,539 $ 1,601 Gain (loss) on energy-related cash flow hedges (a) (2 ) 2 (2 ) Total depreciation and amortization 3,038 3,131 3,010 Gain (loss) on energy-related cash flow hedges (a) (6 ) 7 (16 ) Total interest expense, net of amounts capitalized (1,736 ) (1,842 ) (1,694 ) Gain (loss) on interest rate cash flow hedges (a) (20 ) (21 ) (21 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (24 ) (23 ) Gain (loss) on interest rate fair value hedges (b) 42 (12 ) (22 ) Total other income (expense), net 252 114 163 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) (60 ) 160 Alabama Power Total interest expense, net of amounts capitalized $ (336 ) $ (323 ) $ (305 ) Gain (loss) on interest rate cash flow hedges (a) (6 ) (6 ) (6 ) Georgia Power Total interest expense, net of amounts capitalized $ (409 ) $ (397 ) $ (419 ) Gain (loss) on interest rate cash flow hedges (a) (3 ) (4 ) (4 ) Gain (loss) on interest rate fair value hedges (b) 2 2 (3 ) Mississippi Power Total interest expense, net of amounts capitalized $ (69 ) $ (76 ) $ (42 ) Gain (loss) on interest rate cash flow hedges (a) (2 ) (2 ) (2 ) Southern Power Total depreciation and amortization $ 479 $ 493 $ 503 Gain (loss) on energy-related cash flow hedges (a) (6 ) 7 (17 ) Total interest expense, net of amounts capitalized (169 ) (183 ) (191 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (24 ) (23 ) Total other income (expense), net 47 23 1 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) (60 ) 159 Southern Company Gas Total cost of natural gas $ 1,319 $ 1,539 $ 1,601 Gain (loss) on energy-related cash flow hedges (a) (2 ) 2 (2 ) (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, 2019 and 2018 , 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, 2019 At December 31, 2018 At December 31, 2019 At December 31, 2018 (in millions) (in millions) Southern Company Securities due within one year $ — $ (498 ) $ — $ 2 Long-term debt (2,093 ) (2,052 ) 3 41 Georgia Power Securities due within one year $ — $ (498 ) $ — $ 2
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 for the years ended December 31, 2019 , 2018 , and 2017 for the applicable Registrants were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2019 2018 2017 (in millions) Southern Company Energy-related derivatives Natural gas revenues (*) $ 223 $ (122 ) $ (80 ) Cost of natural gas 10 (6 ) (2 ) Wholesale electric revenues 2 2 (4 ) Total derivatives in non-designated hedging relationships $ 235 $ (126 ) $ (86 ) Southern Company Gas Energy-related derivatives Natural gas revenues (*) $ 223 $ (122 ) $ (80 ) Cost of natural gas 10 (6 ) (2 ) Total derivatives in non-designated hedging relationships $ 233 $ (128 ) $ (82 ) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $3 million , $5 million , and $23 million for the years ended December 31, 2019 , 2018 , and 2017 , 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, 2019
Business Combinations [Abstract]
Schedule of business acquisitions, by acquisition	During 2019 , Southern Power acquired a controlling interest in the fuel cell generation facility listed below and acquired the Skookumchuck wind facility discussed under " Construction Projects " below. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Remaining Period DSGP (a) Fuel Cell Bloom Energy 28 Delaware 100% of Class B N/A (b) 15 years (a) During 2019, Southern Power made a total investment of approximately $167 million in DSGP and now holds a controlling interest and consolidates 100% of DSGP's operating results. Southern Power records net income attributable to noncontrolling interests for approximately 10 MWs of the facility. (b) 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. In connection with the Class C member joining the partnership, the original fuel cells (before repower), which had a carrying value of approximately $55 million , were distributed to the Class A member in a non-cash transaction that was excluded from the statements of cash flows. Acquisitions During 2018 During 2018, Southern Power acquired and completed the project below and acquired the Wildhorse Mountain and Reading wind facilities discussed under " Construction Projects " below. Project Facility Resource Seller Approximate Nameplate Capacity ( MW ) Location Southern Power Ownership Percentage COD PPA Contract Period Gaskell West 1 Solar Recurrent Energy Development Holdings, LLC 20 Kern County, CA 100% of Class B (*) March 20 years (*) Southern Power owns 100% of the Class B membership interests under a tax equity partnership.
Schedule of construction projects	During 2019 , Southern Power completed construction of and placed in service the 385 -MW Plant Mankato expansion and the Wildhorse Mountain facility, acquired and continued construction of the Skookumchuck facility, and continued construction of the Reading facility. Total aggregate construction costs, excluding acquisition costs, are expected to be between $490 million and $535 million for the two facilities under construction. At December 31, 2019 , total costs of construction incurred for the two facilities under construction were $417 million and are included in CWIP. The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Contract Period Projects Completed During the Year Ended December 31, 2019 Mankato expansion (a) Natural Gas 385 Mankato, MN May 2019 20 years Wildhorse Mountain (b) Wind 100 Pushmataha County, OK December 2019 20 years Projects Under Construction at December 31, 2019 Reading (c) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 12 years Skookumchuck (d) Wind 136 Lewis and Thurston Counties, WA Second quarter 2020 20 years (a) Southern Power completed the sale of its equity interests in Plant Mankato, including the expansion, to a subsidiary of Xcel on January 17, 2020. The expansion unit started providing energy under a PPA with Northern States Power on June 1, 2019. See " Sales of Natural Gas and Biomass Plants " below and " Assets Held for Sale " herein for additional information. (b) In May 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, as a result, owns 100% of the Class B membership interests. (c) In August 2018, Southern Power purchased 100% of the membership interests of the Reading facility pursuant to a joint development arrangement. Southern Power may enter into a tax equity partnership, in which case it would then own 100% of the Class B membership interests. The ultimate outcome of this matter cannot be determined at this time. (d)
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, 2019 and/or 2018: Southern Company Southern Power Southern Company Gas At December 31, At December 31, At December 31, 2019 2018 2019 2018 2019 (in millions) (in millions) (in millions) Assets Held for Sale: Current assets $ 19 $ 393 $ 17 $ 8 $ 2 Total property, plant, and equipment 565 4,583 547 536 18 Goodwill and other intangible assets 40 40 40 40 — Equity investments in unconsolidated subsidiaries 151 — — — 151 Other non-current assets 14 727 14 — — Total Assets Held for Sale $ 789 $ 5,743 $ 618 $ 584 $ 171 Liabilities Held for Sale: Current liabilities $ 5 $ 425 $ 3 $ 15 $ 2 Long-term debt — 1,286 — — — Accumulated deferred income taxes — 618 — — — Other non-current liabilities — 932 — — — Total Liabilities Held for Sale $ 5 $ 3,261 $ 3 $ 15 $ 2 Gulf Power and Southern Power's Florida Plants, Plant Nacogdoches, and Plant Mankato represented individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax income for these components for the years ended December 31, 2019 , 2018 , and 2017 are presented below: 2019 2018 2017 (in millions) Earnings before income taxes: (a) Gulf Power N/A $ 140 $ 229 Southern Power's Florida Plants (b) N/A $ 49 $ 37 Southern Power's Plant Nacogdoches (c) $ 13 $ 27 $ 25 Southern Power's Plant Mankato $ 29 N/M N/M N/M - Not material (a) Earnings before income taxes for Southern Power's components reflect the cessation of depreciation and amortization on the long-lived assets being sold upon classification as held for sale. (b) Earnings before income taxes for the Florida Plants in 2018 represents the period from January 1, 2018 to December 4, 2018 (the divestiture date). (c)

SEGMENT AND RELATED INFORMATI_2

SEGMENT AND RELATED INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Financial data for business segments	Financial data for business segments and products and services for the years ended December 31, 2019 , 2018 , and 2017 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) 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)(b)(c)(d)(e) 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 Gross property additions 5,748 489 — 6,237 1,418 159 — 7,814 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)(f)(g) 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 Gross property additions 6,077 315 — 6,392 1,399 414 — 8,205 2017 Operating revenues $ 16,884 $ 2,075 $ (419 ) $ 18,540 $ 3,920 $ 741 $ (170 ) $ 23,031 Depreciation and amortization 1,954 503 — 2,457 501 52 — 3,010 Interest income 14 7 — 21 3 11 (9 ) 26 Earnings from equity method investments 1 — — 1 106 (1 ) — 106 Interest expense 820 191 — 1,011 200 490 (7 ) 1,694 Income taxes (benefit) 1,021 (939 ) — 82 367 (307 ) — 142 Segment net income (loss) (a)(b)(h)(i) (193 ) 1,071 — 878 243 (279 ) — 842 Goodwill — 2 — 2 5,967 299 — 6,268 Total assets 72,204 15,206 (325 ) 87,085 22,987 2,552 (1,619 ) 111,005 Gross property additions 3,836 268 — 4,104 1,525 355 — 5,984 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $24 million ( $24 million after tax) in 2019 , $1.1 billion ( $722 million after tax) in 2018 , and $3.4 billion ( $2.4 billion after tax) in 2017 . See Note 2 under " Georgia Power – Nuclear Construction " and " Mississippi Power – Kemper County Energy Facility – Schedule and Cost Estimate " for additional information. (c) Segment net income (loss) for Southern Power includes a $23 million pre-tax gain ( $88 million gain after tax) on the sale of Plant Nacogdoches in 2019. See Note 15 under "Southern Power" for additional information. (d) Segment net income (loss) for Southern Company Gas in 2019 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 – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. (e) Segment net income (loss) for the "All Other" column in 2019 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. (f) Segment net income (loss) for Southern Power includes pre-tax impairment charges of $156 million ( $117 million after tax) in 2018. See Note 15 under " Southern Power " for additional information. (g) Segment net income (loss) for Southern Company Gas includes a net gain on dispositions of $291 million ( $51 million loss after tax) in 2018 related to the Southern Company Gas Dispositions and a goodwill impairment charge of $42 million in 2018 related to the sale of Pivotal Home Solutions. See Note 15 under " Southern Company Gas " for additional information. (h) Segment net income (loss) for the traditional electric operating companies includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) in 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. (i) Segment net income (loss) includes income tax expense of $367 million for the traditional electric operating companies, income tax benefit of $743 million for Southern Power, and income tax expense of $93 million for Southern Company Gas in 2017 related to the Tax Reform Legislation. Financial data for business segments for the years ended December 31, 2019 , 2018 , and 2017 was as follows: Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other (e) Eliminations Consolidated (in millions) 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 Gross property additions 1,433 1 1 4 1,439 27 — 1,466 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 Gross property additions 1,429 32 — 6 1,467 54 — 1,521 Total assets at December 31, 2018 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) 21,448 2017 Operating revenues $ 3,207 $ 17 $ 6 $ 860 $ 4,090 $ 64 $ (234 ) $ 3,920 Depreciation and amortization 391 2 2 62 457 44 — 501 Operating income (loss) 645 10 (51 ) 113 717 (57 ) — 660 Earnings from equity method investments — 103 — — 103 3 — 106 Interest expense (153 ) (26 ) (7 ) (5 ) (191 ) (9 ) — (200 ) Income taxes (f) 178 109 — 24 311 56 — 367 Segment net income (loss) (f) 353 (22 ) (57 ) 84 358 (115 ) — 243 Gross property additions 1,330 117 1 9 1,457 51 — 1,508 Total assets at December 31, 2017 19,358 1,699 1,096 2,147 24,300 12,726 (14,039 ) 22,987 (a) Operating revenues for the three gas distribution operations dispositions were $244 million and $399 million for 2018 and 2017, respectively. See Note 15 under " Southern Company Gas " for additional information. (b) Segment net income for gas distribution operations includes a gain on dispositions of $324 million ( $16 million after tax) 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. See Note 15 under " Southern Company Gas " for additional information. (c) 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) 2019 $ 5,703 $ 275 $ 5,978 $ 5,684 $ 294 2018 6,955 451 7,406 7,262 144 2017 6,152 481 6,633 6,627 6 (d) Operating revenues for the gas marketing services disposition were $55 million and $129 million in 2018 and 2017, respectively. See Note 15 under " Southern Company Gas " for additional information. (e) Segment net income (loss) for the "All Other" column in 2019 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 – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. (f) Includes the impact of the Tax Reform Legislation and new income tax apportionment factors in several states resulting from Southern Company Gas' inclusion in the consolidated Southern Company state tax filings.
Financial data for products and services	Products and Services Electric Utilities' Revenues Year Retail Wholesale Other Total (in millions) 2019 $ 14,084 $ 2,152 $ 859 $ 17,095 2018 15,222 2,516 833 18,571 2017 15,330 2,426 784 18,540 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2019 $ 3,001 $ 456 $ 335 $ 3,792 2018 3,155 568 186 3,909 2017 3,024 860 36 3,920
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) 2019 $ 5,703 $ 275 $ 5,978 $ 5,684 $ 294 2018 6,955 451 7,406 7,262 144 2017 6,152 481 6,633 6,627 6

QUARTERLY FINANCIAL INFORMATI_2

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Summarized quarterly financial data	The tables below provide summarized quarterly financial information for each Registrant for 2019 and 2018 . Each Registrant's business is influenced by seasonal weather conditions. Quarter Ended Southern Company (a) Alabama Power Georgia Power Mississippi Power (b) Southern Power (c) Southern Company Gas (d) (in millions) March 2019 Operating Revenues $ 5,412 $ 1,408 $ 1,833 $ 287 $ 443 $ 1,474 Operating Income (Loss) 3,691 338 448 56 60 353 Net Income (Loss) 2,059 217 311 37 27 270 Net Income (Loss) Attributable to Registrant 2,084 217 311 37 56 270 June 2019 Operating Revenues $ 5,098 $ 1,513 $ 2,117 $ 313 $ 510 $ 689 Operating Income (Loss) 1,342 445 647 54 153 134 Net Income (Loss) 931 296 448 37 203 106 Net Income (Loss) Attributable to Registrant 899 296 448 37 174 106 September 2019 Operating Revenues $ 5,995 $ 1,841 $ 2,755 $ 370 $ 574 $ 498 Operating Income (Loss) 2,013 676 1,161 93 167 (35 ) Net Income (Loss) 1,345 469 839 65 111 (29 ) Net Income (Loss) Attributable to Registrant 1,316 469 839 65 86 (29 ) December 2019 Operating Revenues $ 4,914 $ 1,363 $ 1,703 $ 294 $ 411 $ 1,131 Operating Income (Loss) 690 134 205 22 15 318 Net Income (Loss) 409 88 122 — (12 ) 238 Net Income (Loss) Attributable to Registrant 440 88 122 — 23 238 (a) Southern Company recorded a preliminary pre-tax gain associated with the sale of Gulf Power of $2.5 billion ( $1.3 billion after tax) in the first quarter 2019 and recorded subsequent adjustments of $(15) million ( $(11) million after tax) in the second quarter 2019, $4 million ( $4 million after tax) in the third quarter 2019, and $70 million ( $102 million after tax) in the fourth quarter 2019. In addition, Southern Company recorded a pre-tax loss, including related impairment charges, on the sales of certain PowerSecure business units totaling $32 million in the second quarter 2019, $14 million ( $15 million after tax) in the third quarter 2019, and $12 million ( $5 million after tax) in the fourth quarter 2019, as well as a pre-tax impairment charge of $17 million ( $13 million after tax) in the fourth quarter 2019 related to a leveraged lease investment. See Notes 3 and 15 under " Other Matters – Southern Company " and " Southern Company ," respectively, for additional information. Also see notes (b), (c), and (d) below. (b) Mississippi Power recorded total pre-tax charges to income of $2 million ( $1 million after tax) in the first quarter 2019, $4 million ( $3 million after tax) in the second quarter 2019, $4 million ( $3 million after tax) in the third quarter 2019, and $14 million ( $17 million after tax) in the fourth quarter 2019 as a result of 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. The fourth quarter charges include impacts associated with the expected close out of a DOE contract related to the Kemper County energy facility, as well as an adjustment related to the tax abandonment of the Kemper IGCC following the filing of the 2018 tax return. See Note 2 under " Mississippi Power – Kemper County Energy Facility " for additional information. (c) Southern Power recorded a pre-tax gain of $23 million ( $88 million gain after tax) in the second quarter 2019 on the sale of Plant Nacogdoches. See Note 15 under " Southern Power " for additional information. (d) Southern Company Gas recorded pre-tax impairment charges of $92 million ( $65 million after tax) in the third quarter 2019, and a subsequent adjustment of $(1) million ( $4 million after tax) in the fourth quarter 2019, related to a natural gas storage facility in Louisiana and $24 million ( $17 million after tax) in the fourth quarter 2019 in contemplation of the sale of its interests in Pivotal LNG and Atlantic Coast Pipeline. See Notes 3 and 15 under " Other Matters – Southern Company Gas " and " Southern Company Gas – Proposed Sale of Pivotal LNG and Atlantic Coast Pipeline ," respectively, for additional information. Quarter Ended Southern Company (a) Alabama Power Georgia Power (b) Mississippi Power (c) Southern Power (d) Southern Company Gas (e) (in millions) March 2018 Operating Revenues $ 6,372 $ 1,473 $ 1,961 $ 302 $ 509 $ 1,639 Operating Income (Loss) 1,376 372 513 7 60 388 Net Income (Loss) 936 225 352 (7 ) 115 279 Net Income (Loss) Attributable to Registrant 938 225 352 (7 ) 121 279 June 2018 Operating Revenues $ 5,627 $ 1,503 $ 2,048 $ 297 $ 555 $ 730 Operating Income (Loss) 63 380 (472 ) 54 16 49 Net Income (Loss) (127 ) 259 (396 ) 46 45 (31 ) Net Income (Loss) Attributable to Registrant (154 ) 259 (396 ) 46 22 (31 ) September 2018 Operating Revenues $ 6,159 $ 1,740 $ 2,593 $ 358 $ 635 $ 492 Operating Income (Loss) 2,174 561 991 80 136 374 Net Income (Loss) 1,222 373 664 47 146 46 Net Income (Loss) Attributable to Registrant 1,164 373 664 47 92 46 December 2018 Operating Revenues $ 5,337 $ 1,316 $ 1,818 $ 308 $ 506 $ 1,048 Operating Income (Loss) 578 164 257 52 30 104 Net Income (Loss) 269 73 173 149 (60 ) 78 Net Income (Loss) Attributable to Registrant 278 73 173 149 (48 ) 78 (a) See notes (b), (c), (d), and (e) below. (b) Georgia Power recorded an estimated probable loss of $1.1 billion in the second quarter 2018 to reflect its revised estimate to complete construction and start-up of Plant Vogtle Units 3 and 4. See Note 2 under " Georgia Power – Nuclear Construction " for additional information. (c) As a result of the abandonment and related closure activities for the mine and gasifier-related assets at the Kemper County energy facility, Mississippi Power recorded total pre-tax charges to income of $44 million ( $33 million after tax) in the first quarter 2018, immaterial amounts in the second and third quarters 2018, and a pre-tax credit to income of $9 million in the fourth quarter 2018. In addition, Mississippi Power recorded a credit to earnings of $95 million in the fourth quarter 2018 primarily resulting from the reduction of a valuation allowance for a state income tax NOL carryforward associated with the Kemper County energy facility. See Note 2 under " Mississippi Power – Kemper County Energy Facility " and Note 10 for additional information. (d) Southern Power recorded pre-tax impairment charges of $119 million ( $89 million after tax) in the second quarter 2018 in contemplation of the sale of the Florida Plants and $36 million ( $27 million after tax) in the third quarter 2018 related to wind turbine equipment. See Note 15 under " Southern Power – Sales of Natural Gas and Biomass Plants " and " – Development Projects " for additional information. As a result of the Tax Reform Legislation, Southern Power recorded income tax expense of $75 million in the fourth quarter 2018. See Note 10 for additional information. (e) Southern Company Gas recorded a goodwill impairment charge of $42 million in the first quarter 2018 in contemplation of the sale of Pivotal Home Solutions. Southern Company Gas also recorded gains (losses) on dispositions in the second, third, and fourth quarters 2018 of $(36) million ( $(76) million after tax), $353 million ( $40 million after tax), and $(27) million ( $(15) million after tax), respectively. See Note 15 under " Southern Company Gas " for additional information. The table below provides quarterly earnings per share financial information for Southern Company common stock for 2019 and 2018 . Earnings Per Common Share (*) Quarter Ended Basic Diluted March 2019 $ 2.01 $ 1.99 June 2019 0.86 0.85 September 2019 1.26 1.25 December 2019 0.42 0.42 March 2018 $ 0.93 $ 0.92 June 2018 (0.15 ) (0.15 ) September 2018 1.14 1.13 December 2018 0.27 0.27 (*) See the notes below the two preceding tables for additional information.

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - General (Narrative) (Details)	Dec. 31, 2019stateelectric_company
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 527	$ 508	$ 479
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	17	8	9
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	704	653	625
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	99	101	102
Georgia Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	4	21	22
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	118	104	140
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	3	15	16
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	90	98	218
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	14	41	27
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	28	25	25
Southern Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	64	119	119
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	183	194	63
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 31	$ 32	$ 32

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Affiliate Transactions (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Southern Nuclear Operating Company, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		$ 256	$ 247	$ 248
Southern Nuclear Operating Company, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services		760	780	675
Southern Natural Gas Company, LLC | Alabama Power
Related Party Transaction [Line Items]
Costs for services		17	8	9
Southern Natural Gas Company, LLC | Georgia Power
Related Party Transaction [Line Items]
Costs for services		99	101	102
Southern Natural Gas Company, LLC | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services		31	32	32
Southern Natural Gas Company, LLC | Southern Power
Related Party Transaction [Line Items]
Costs for services		28	25	25
Gulf Power | Alabama Power
Related Party Transaction [Line Items]
Amounts received related to tariff			11	11
Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services			8	11
Gulf Power | Mississippi Power
Related Party Transaction [Line Items]
Costs for services			31	31
PowerSecure International, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		7	24	11
Southern Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services		177	216	235
Southern Company Services, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services		527	508	479
Southern Company Services, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services		704	653	625
Southern Company Services, Inc. | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services		183	194	63
Southern Company Services, Inc. | Mississippi Power
Related Party Transaction [Line Items]
Costs for services		118	104	140
Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services		90	98	218
Non-Fuel Expense | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services		9	8	9
Purchased Power from Affiliates | Southern Power
Related Party Transaction [Line Items]
Costs for services		174	215	233
Operating Lease PPA | Southern Power
Related Party Transaction [Line Items]
Costs for services		116	65	81
Electric Transmission | Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services		$ 15	$ 12	$ 13
Plant Scherer (coal) Unit 3 | Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Proportionate share of related non-fuel expenses (percent)		25.00%
Subsequent Event | Southern Company Gas
Related Party Transaction [Line Items]
Proceeds from affiliate	$ 71
Subsequent Event | Southern Natural Gas Company, LLC | Georgia Power
Related Party Transaction [Line Items]
Proceeds from affiliate	$ 142

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenues (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019
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 Revenue (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Feb. 19, 2020USD ($)	Jan. 29, 2019facilityMW	Dec. 31, 2018USD ($)
Concentration Risk [Line Items]
Outstanding accounts receivable	$ 2,413			$ 2,630
Mississippi Power
Concentration Risk [Line Items]
Wholesale customers representing total operating revenues (percent)	15.70%
Period of cancellation notices	10 years
Outstanding accounts receivable	$ 79			100
PG&E
Concentration Risk [Line Items]
Number of solar facilities | facility			4
Capacity of natural gas facility (mw) | MW			207
Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	97			$ 118
PPAs | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	2
Transmission Interconnections | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	33
Other accounts and notes receivable | Transmission Interconnections | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	27
Other Noncurrent Assets | Transmission Interconnections | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	$ 6
Subsequent Event | Transmission Interconnections | Southern Power
Concentration Risk [Line Items]
Bankruptcy claims, amount received		$ 15

SUMMARY OF SIGNIFICANT ACCOUN_9

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Georgia Power
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	9.00%	9.80%	11.30%
Duke Energy Corporation
Concentration Risk [Line Items]
Percentage of total revenues for top three customers		6.80%	6.70%
Southern California Edison
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	6.80%	6.20%
Morgan Stanley Capital Group
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	4.90%		4.50%

SUMMARY OF SIGNIFICANT ACCOU_10

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income and Other Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 117	$ 114	$ 100
Included In Operating Expenses | Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected	$ 114	$ 111	$ 98

SUMMARY OF SIGNIFICANT ACCOU_11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Total AFUDC and Interest Capitalized (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 202	$ 210	$ 249
Alabama Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	71	84	54
Georgia Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	103	94	63
Mississippi Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	0	0	72
Southern Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	15	17	11
Southern Company Gas
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 13	$ 14	$ 19

SUMMARY OF SIGNIFICANT ACCOU_12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Average AFUDC Composite Rates (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Alabama Power
Capitalized Contract Cost [Line Items]
Composite rate	8.40%	8.30%	8.30%
Georgia Power
Capitalized Contract Cost [Line Items]
Composite rate	6.90%	7.30%	5.60%
Mississippi Power
Capitalized Contract Cost [Line Items]
Composite rate	7.30%	3.30%	6.70%
Atlanta Gas Light
Capitalized Contract Cost [Line Items]
Composite rate	7.80%	7.90%	8.10%
Chattanooga Gas
Capitalized Contract Cost [Line Items]
Composite rate	7.10%	7.40%	7.40%
Nicor Gas
Capitalized Contract Cost [Line Items]
Composite rate	2.30%	2.10%	1.20%

SUMMARY OF SIGNIFICANT ACCOU_13

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill and Other Intangible Assets and Liabilities (Narrative) (Details) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0
Intangible liabilities included in other deferred credits and liabilities	609,000,000			$ 609,000,000	$ 465,000,000
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	0			115,000,000	42,000,000	$ 0
Intangible liabilities included in other deferred credits and liabilities	51,000,000			51,000,000	$ 105,000,000
Intangible liabilities | Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Intangible liabilities included in other deferred credits and liabilities	$ 91,000,000			$ 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 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_14

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Goodwill Balances (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 5,280	$ 5,315	$ 6,268
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_15

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Intangible Assets (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)business_unit	Dec. 31, 2018USD ($)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 741	$ 773
Accumulated Amortization	(280)	(235)
Other Intangible Assets, Net	461	538
Intangible assets, gross	816	848
Intangible assets, net	536	613
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	223
Accumulated Amortization	(116)	(94)
Other Intangible Assets, Net	96	129
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	70
Accumulated Amortization	(25)	(21)
Other Intangible Assets, Net	39	49
Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(62)	(54)
Other Intangible Assets, Net	2	10
PPA fair value adjustments(b)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	405
Accumulated Amortization	(69)	(61)
Other Intangible Assets, Net	321	344
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11	11
Accumulated Amortization	(8)	(5)
Other Intangible Assets, Net	3	6
Southern Power
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(69)	(61)
Southern Power | PPA fair value adjustments(b)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	390	405
Accumulated Amortization	(69)	(61)
Other Intangible Assets, Net	321	344
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	246	246
Accumulated Amortization	(176)	(145)
Other Intangible Assets, Net	70	101
Intangible assets, net	70	101
Southern Company Gas | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	156	156
Accumulated Amortization	(104)	(84)
Other Intangible Assets, Net	52	72
Southern Company Gas | Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26	26
Accumulated Amortization	(10)	(7)
Other Intangible Assets, Net	16	19
Southern Company Gas | Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(62)	(54)
Other Intangible Assets, Net	$ 2	$ 10
PowerSecure International, Inc.
Finite-Lived Intangible Assets [Line Items]
Number of business units sold | business_unit	2

SUMMARY OF SIGNIFICANT ACCOU_16

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 61	$ 89	$ 124
Estimated future amortization, 2020	48
Estimated future amortization, 2021	42
Estimated future amortization, 2022	38
Estimated future amortization, 2023	37
Estimated future amortization, 2024	35
Southern Power
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	19	25	25
Estimated future amortization, 2020	20
Estimated future amortization, 2021	20
Estimated future amortization, 2022	20
Estimated future amortization, 2023	20
Estimated future amortization, 2024	20
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	31	52	86
Estimated future amortization, 2020	19
Estimated future amortization, 2021	13
Estimated future amortization, 2022	10
Estimated future amortization, 2023	9
Estimated future amortization, 2024	7
Southern Company Gas | Gas marketing services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	23	32	54
Southern Company Gas | Wholesale gas services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	8	20	32
Operating Revenues
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 27	$ 45	$ 57

SUMMARY OF SIGNIFICANT ACCOU_17

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Transmission Receivables/Prepayments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019
Southern Power
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Period of reimbursement for transmission costs	5 years

SUMMARY OF SIGNIFICANT ACCOU_18

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,975	$ 1,396
Restricted cash:
Restricted cash		0
Total cash, cash equivalents, and restricted cash	1,978	1,519	$ 2,147	$ 1,992
Georgia Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	52	4
Restricted cash:
Restricted cash		108
Total cash, cash equivalents, and restricted cash	52	112	852	3
Southern Company Gas
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	46	64
Restricted cash:
Restricted cash		0
Total cash, cash equivalents, and restricted cash	$ 49	70	$ 78	$ 24
Cash and cash equivalents classified as assets held for sale
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents		9
Cash and cash equivalents classified as assets held for sale | Georgia Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents		0
Cash and cash equivalents classified as assets held for sale | Southern Company Gas
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents		$ 0

SUMMARY OF SIGNIFICANT ACCOU_19

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Storm Damage Reserves (Details) - Major storms - USD ($)	Dec. 03, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			$ 170,000,000	$ 74,000,000	$ 41,000,000
Alabama Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs			84,000,000	0	0
Storm damage reserves		$ 84,000,000	139,000,000	16,000,000	4,000,000
Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			30,000,000	30,000,000	30,000,000
Mississippi Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs			0	0	0
Storm damage reserves			$ 1,000,000	1,000,000	3,000,000
Gulf Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves				$ 26,900,000	$ 3,500,000
Accumulated Deferred Income Taxes | Alabama Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 39,000,000

SUMMARY OF SIGNIFICANT ACCOU_20

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leveraged Leases (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019leveraged_lease	Dec. 30, 2019USD ($)leveraged_lease
Leveraged Lease [Line Items]
Number of leveraged leases | leveraged_lease	1	1
Maximum
Leveraged Lease [Line Items]
Original term (up to) (years)	45 years
Leveraged Lease Investment | Disposal Group, Held-for-sale, Not Discontinued Operations
Leveraged Lease [Line Items]
Consideration for sale | $		$ 20

SUMMARY OF SIGNIFICANT ACCOU_21

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, 2019	Dec. 31, 2018
Leveraged Lease [Line Items]
Net rentals receivable	$ 1,410	$ 1,563
Unearned income	(622)	(765)
Investment in leveraged leases	788	798
Deferred taxes from leveraged leases	(238)	(255)
Net investment in leveraged leases	$ 550	$ 543

SUMMARY OF SIGNIFICANT ACCOU_22

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Leveraged Lease [Line Items]
Pretax leveraged lease income	$ 11	$ 25	$ 25
Net impact of Tax Reform Legislation	0	0	48
Income tax expense	0	(6)	(9)
Net leveraged lease income	$ 11	$ 19	$ 64

SUMMARY OF SIGNIFICANT ACCOU_23

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Natural Gas for Sale (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Nicor Gas
Inventory [Line Items]
LIFO inventory balance	$ 161
Estimated replacement cost of inventory	214
Southern Company Gas
Inventory [Line Items]
LOCOM adjustments	$ 21	$ 10	$ 0

SUMMARY OF SIGNIFICANT ACCOU_24

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Energy Marketing Receivables and Payables (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Required collateral in the event of a credit rating downgrade	$ 11	$ 30

SUMMARY OF SIGNIFICANT ACCOU_25

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Uncollectible accounts, average percent of revenues (less than)	1.00%

SUMMARY OF SIGNIFICANT ACCOU_26

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Credit Risk (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)counterpartycustomer	Dec. 31, 2018USD ($)
Concentration Risk [Line Items]
Receivables	$ 2,413	$ 2,630
Southern Company Gas
Concentration Risk [Line Items]
Receivables	$ 749	$ 952
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)	59.00%
Receivables	$ 218

SUMMARY OF SIGNIFICANT ACCOU_27

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Financial Instruments (Narrative) (Details)	Dec. 31, 2019USD ($)
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, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 29,039	$ 25,528	$ 26,612
Current period change	(118)	26	(9)
Ending balance	31,759	29,039	25,528
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(121)
Ending balance		(121)
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Current period change	(58)
Ending balance	(179)
Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(82)
Current period change	(60)
Ending balance	(142)	(82)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(203)	(189)	(180)
Current period change	(118)
Ending balance	(321)	(203)	(189)
Southern Power
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	7,284	6,498	5,675
Current period change	(42)	14	(10)
Ending balance	6,622	7,284	6,498
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	36
Ending balance		36
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Current period change	(25)
Ending balance	11
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(20)
Current period change	(17)
Ending balance	(37)	(20)
Southern Power | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	16	(2)	35
Current period change	(42)
Ending balance	(26)	16	(2)
Southern Company Gas
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	8,570	9,022	9,109
Current period change	(19)	2	(5)
Ending balance	9,506	8,570	9,022
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3)
Ending balance		(3)
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Current period change	(3)
Ending balance	(6)
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	29
Current period change	(16)
Ending balance	13	29
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	26	20	26
Current period change	(19)
Ending balance	$ 7	$ 26	$ 20

REGULATORY MATTERS - Schedule o

REGULATORY MATTERS - Schedule of SO Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Jan. 01, 2020	Oct. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 3,838	$ 720
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			34 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 3,507	2,378
Customer refund liability, current			105
Customer refund			$ 55
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			33 years
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (1,874)	(1,872)
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 810	(769)
Regulatory amortization period		5 years
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			30 years
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (6,301)	(6,455)
Deferred tax liabilities			$ 778
Deferred income tax credits | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liability amortization period			6 years
Deferred income tax credits | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (3,078)	(3,080)
Deferred income tax credits | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(874)	(940)
Deferred income tax credits | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(1,960)	(2,027)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(2,084)	(2,297)
Other cost of removal obligations | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(1,606)	(1,585)
Other cost of removal obligations | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(412)	(497)
Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(285)	(293)
Customer refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(229)	(165)
Customer refund liability, current			105	55
Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(205)	(47)
Over recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(82)	(43)
Property damage reserves-liability
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(204)	(76)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (86)	(132)
Other regulatory liabilities | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liability amortization period			20 years
Other regulatory liabilities | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (16)	(7)
Other regulatory liabilities | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (22)	(46)
Other regulatory liabilities | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			20 years
Other regulatory liabilities | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (19)	(12)
Customer refunds - RSE portion | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			53	109
Customer refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			110	100
Customer refunds | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(56)	(142)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			4,423	3,658
Regulatory asset			$ 23
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			15 years
Retiree benefit plans | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,516	1,295
Retiree benefit plans | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			13 years
Retiree benefit plans | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 167	161
Retiree benefit plans | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			15 years
Retiree benefit plans | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,131	947
Retiree benefit plans | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			14 years
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 4,381	2,933
Asset retirement obligations-asset | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			3,119	2,644
Asset retirement obligations-asset | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			1,043	147
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,275	211
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			18 years
Remaining net book value of retired assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 596	127
Remaining net book value of retired assets | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			3 years
Remaining net book value of retired assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			18 years
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 803	799
Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			80 years
Deferred income tax charges | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 523	522
Deferred tax liabilities			660
Deferred income tax charges | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 245	241
Regulatory amortization period			53 years
Deferred income tax charges | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			53 years
Property damage reserves-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 410	416
Environmental remediation-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			349	366
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			323	346
Loss on reacquired debt | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			262	277
Loss on reacquired debt | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			52	56
Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			254	407
Under recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 72	90
Regulatory amortization period			6 years
Under recovered regulatory clause revenues | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 142	142
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 186	182
Regulatory amortization period			1 year
Vacation pay | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 93	91
Regulatory amortization period			1 year
Vacation pay | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 11	11
Regulatory amortization period			1 year
Vacation pay | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 72	71
Regulatory amortization period			1 year
Long-term debt fair value adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 107	121
Long-term debt fair value adjustment | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 107	121
Long-term debt fair value adjustment | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			19 years
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 492	581
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			8 years
Other regulatory assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 50	120
Regulatory amortization period			24 months
Other regulatory assets | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 68	59
Other regulatory assets | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			8 years
Other regulatory assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 67	$ 57
Regulatory amortization period			12 months
Asset Group 1 | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			6 years
Subsequent Event | Major storms | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Recoveries for storm damage	$ 213

REGULATORY MATTERS - Gulf Power

REGULATORY MATTERS - Gulf Power Regulatory Matters (Details) - Gulf Power - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Jul. 31, 2017	Mar. 31, 2017	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount	$ 54
Rate case settlement annual increase base rates	62
Purchased power capacity cost recovery clause credit	$ 8
Tax reform settlement agreement, annual reduction of revenue from base rates			$ 18
Tax reform settlement agreement, annual reduction of revenue from environmental cost recovery rates			16
Tax reform settlement agreement, refund			$ 69
Plant Scherer Unit 3
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss on Plant Scherer Unit 3		$ 32.5

REGULATORY MATTERS - Schedule_2

REGULATORY MATTERS - Schedule of APC Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Oct. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,838	$ 720
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(6,301)	(6,455)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(2,084)	(2,297)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(86)	(132)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,423	3,658
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		15 years
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,381	2,933
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 803	799
Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		80 years
Regulatory clauses
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 254	407
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 186	182
Regulatory amortization period		1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 323	346
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 492	581
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		8 years
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 810	(769)
Regulatory amortization period	5 years
Medicare drug subsidy obligation related to subsidiary		$ 9	10
Fuel hedging assets and liabilities, amortization period		3 years 6 months
Alabama Power | Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (1,960)	(2,027)
Alabama Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(412)	(497)
Alabama Power | Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(56)	(142)
Alabama Power | Natural disaster reserve
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(150)	(20)
Alabama Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(19)	(12)
Alabama Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		33
Alabama Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,131	947
Alabama Power | Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		14 years
Alabama Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,043	147
Alabama Power | Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 245	241
Regulatory amortization period		53 years
Alabama Power | Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		53 years
Alabama Power | (Over) under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (72)	176
Regulatory amortization period		3 years
Alabama Power | Regulatory clauses
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 142	142
Alabama Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 72	71
Regulatory amortization period		1 year
Alabama Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 52	56
Alabama Power | Nuclear outage
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 78	49
Regulatory amortization period		18 months
Alabama Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 649	43
Alabama Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 67	$ 57
Regulatory amortization period		12 months

REGULATORY MATTERS - APC Regula

REGULATORY MATTERS - APC Regulatory Matters (Details)	Jan. 01, 2021USD ($)	Dec. 03, 2019USD ($)$ / KWH_Kilowatt_hour	Dec. 02, 2019$ / KWH_Kilowatt_hour	Oct. 01, 2019	May 01, 2018USD ($)	Jan. 31, 2021$ / KWH_Kilowatt_hour	Dec. 31, 2019USD ($)MW	Jan. 31, 2019	Dec. 31, 2025	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)$ / KWH_Kilowatt_hourMW	Dec. 31, 2018USD ($)$ / KWH_Kilowatt_hour	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)MW	Mar. 31, 2020USD ($)	Sep. 06, 2019MW	May 08, 2019MW	Apr. 15, 2019USD ($)	Feb. 06, 2019USD ($)	Feb. 05, 2019USD ($)	Jan. 31, 2017USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Contract with customer, liability, bill credits											$ 50,000,000
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period											8 years
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Additional generating capacity, petitioned megawatts | MW																200
Additional generating capacity, petitioned megawatts, total | MW																2,400
Capital investment, construction and acquisition							$ 1,100,000,000				$ 1,100,000,000			$ 1,100,000,000
PPA, additional generating capacity (in MWs) | MW							640				640			640
Regulatory amortization period				5 years
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%				5.98%			5.98%
Percent of basis points							0.07%				0.07%			0.07%
Percent of designated customer value benchmark survey							33.33%				33.33%			33.33%
Rate RSE refund liability													$ 53,000,000						$ 78,000,000	$ 78,000,000
Rate RSE increase																					4.48%
Rate RSE increase amount																					$ 245,000,000
Contract with customer, liability, bill credits											$ 267,000,000
Public utilities, approved return on equity											50.00%	47.00%
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%
Under recovered certified power purchase agreements							$ 40,000,000				$ 40,000,000	$ 25,000,000		$ 40,000,000
Over (under) recovered environmental clause							62,000,000				62,000,000	$ (42,000,000)		62,000,000
Retail revenue requirement for environmental compliance											$ 205,000,000
Current billing rates under rate ECR (usd per KWH) | $ / KWH_Kilowatt_hour		0.02160	0.02353								0.05910	0.02015
Current billing rates under rate ECR, percentage decrease		1.82%
Current billing rates under rate ECR, decrease, amount		$ 102,000,000
Under recovered fuel cost							49,000,000				$ 49,000,000	$ 109,000,000		49,000,000
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
Minimum natural disaster reserve balance, triggering establishment charge							50,000,000				50,000,000			50,000,000
Natural disaster reserve authorized limit							75,000,000				$ 75,000,000			75,000,000
Annual recovery amount														16,000,000
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			10
Maximum rate NDR charge per month, monthly residential customer account							5				5			5
Alabama Power | Plant Barry Unit 8
Schedule of Regulatory Assets and Liabilities [Line Items]
Approximate nameplate capacity (in MW) | MW																	720
Costs incurred, percentage of estimated in-service cost				5.00%
Alabama Power | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved return on equity									55.00%
Retail revenue requirement for environmental compliance										$ 68,000,000
Current billing rates under rate ECR (usd per KWH) | $ / KWH_Kilowatt_hour						0.05910
Natural disaster reserve authorized limit	$ 50,000,000														$ 75,000,000
Annual recovery amount	$ 3,000,000									5,000,000
Alabama Power | Regulatory Liabilities, Current
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered environmental clause							(55,000,000)				(55,000,000)			(55,000,000)
Alabama Power | Regulatory Liabilities, Noncurrent
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered environmental clause							(7,000,000)				(7,000,000)			(7,000,000)
Alabama Power | Other regulatory liabilities, current
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered fuel cost							32,000,000				32,000,000			32,000,000
Alabama Power | Other regulatory liabilities, deferred
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered fuel cost							$ 17,000,000				$ 17,000,000			$ 17,000,000
Alabama Power | Minimum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity							5.75%				5.75%			5.75%
Public utilities, actual weighted common equity return, threshold, percentage											6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche one											6.15%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche two											6.65%
Public utilities, actual weighted common equity return, threshold for customer refundable fees, refund payments, percentage, tranche three											7.15%
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%
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity							6.21%				6.21%			6.21%
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%
Alabama Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period											12 months
Under recovered fuel cost												18,000,000
Alabama Power | Unrecovered Investment Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset							$ 649,000,000				$ 649,000,000			$ 649,000,000
Regulatory assets, current							63,000,000				63,000,000			63,000,000
Regulatory assets, noncurrent							586,000,000				586,000,000			586,000,000
Alabama Power | Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities							$ 109,000,000				109,000,000			$ 109,000,000
Alabama Power | Rate ECR refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Contract with customer, liability, bill credits											$ 31,000,000
Alabama Power | (Over) under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered fuel cost												91,000,000
Year 2020 | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
PPA, additional generating capacity (in MWs) | MW							240				240			240
Years 2022 Through 2024 | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
PPA, additional generating capacity (in MWs) | MW							400				400			400
Major storms
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves											$ 170,000,000	74,000,000	41,000,000
Major storms | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset, amortization period							$ 150,000,000				150,000,000			$ 150,000,000
Storm damage reserves							84,000,000				139,000,000	$ 16,000,000	$ 4,000,000
Major storms | Alabama Power | Other regulatory liabilities, current
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset, amortization period							$ 113,000,000				$ 113,000,000			$ 113,000,000
Major storms | Alabama Power | Other regulatory liabilities, current | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset, amortization period										$ 37,000,000
Restatement Adjustment | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided																		$ 700,000,000
Net capitalized asset retirement costs																		700,000,000
Restatement Adjustment | Alabama Power | Plant Gorgas Units 8, 9, And 10
Schedule of Regulatory Assets and Liabilities [Line Items]
Net investment costs to be transferred upon retirement																		654,000,000
Remaining amounts of regulatory assets for which no return on investment during recovery period is provided																		$ 654,000,000

REGULATORY MATTERS - Schedule_3

REGULATORY MATTERS - Schedule of GPC Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,838	$ 720
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue		34 years
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (6,301)	(6,455)
Deferred tax liabilities		778
Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(285)	(293)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(86)	(132)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,423	3,658
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		15 years
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 4,381	2,933
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 803	799
Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		80 years
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,275	211
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		18 years
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 323	346
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 186	182
Regulatory amortization period		1 year
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 492	581
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		8 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,507	2,378
Costs recovered annually		2	2	$ 2
Portion of actual earnings above approved ROE band refunded to customers, value		60
Customer refund liability, current		$ 105
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue		33 years
Cost recovery, estimate, nuclear fuel		$ 50
Georgia Power | Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(3,078)	(3,080)
Georgia Power | Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(229)	(165)
Portion of actual earnings above approved ROE band refunded to customers, value		110	100
Customer refund liability, current		105	55
Georgia Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(16)	(7)
Amortization of regulatory assets		10
Costs associated with construction to be completed		22
Georgia Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,516	1,295
Georgia Power | Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		13 years
Georgia Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,119	2,644
ARO annual recovery		5
Georgia Power | Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		523	522
Deferred tax assets related to CWIP		145
Deferred tax liabilities		660
Georgia Power | Storm damage reserves
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		410	416
Georgia Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 596	127
Georgia Power | Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		3 years
Georgia Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 262	277
Georgia Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 93	91
Regulatory amortization period		1 year
Georgia Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 156	68
Georgia Power | Environmental remediation
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		52	55
Georgia Power | Fuel-hedging (realized and unrealized) losses
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 53	15
Regulatory amortization period		4 years
Georgia Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 50	120
Regulatory amortization period		24 months
Georgia Power | Deferred Income Tax Charge, AROs, Cost Of Removal Obligations, Deferred Income Tax Credits | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		60 years
Georgia Power | Retiree Medicare Drug Subsidy
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 13
Georgia Power | Obsolete Inventories of Retired Units
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			31
Plant Hammond Units 1 through 4 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		488
Plant Branch Units 1 Through 4 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		69	87
Plant McIntosh Unit 1 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		30
Plant Mitchell Unit 3 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		$ 8	$ 9
Subsequent Event | Major storms | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Recoveries for storm damage	$ 213

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	181
Rate increase 2022	386
Traditional base
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	0
Rate increase 2021	120
Rate increase 2022	192
ECCR
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	318
Rate increase 2021	55
Rate increase 2022	184
DSM
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	12
Rate increase 2021	1
Rate increase 2022	1
Municipal Franchise Fee
Public Utilities, General Disclosures [Line Items]
Rate increase 2020	12
Rate increase 2021	4
Rate increase 2022	$ 9

REGULATORY MATTERS - GPC Regu_2

REGULATORY MATTERS - GPC Regulatory Matters (Details) $ in Millions	Dec. 17, 2019	Dec. 16, 2019	Jan. 31, 2019MW	Apr. 03, 2018	Feb. 29, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)MW	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2022USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2013
Schedule of Regulatory Assets and Liabilities [Line Items]
Contract with customer, liability, bill credits							$ 50
Effective income tax rate							27.50%	16.30%	13.30%
Deferred income taxes							$ 611	$ 89	$ 166
Total regulatory assets (liabilities), net							3,838	720
Other regulatory assets							885	525
Other regulatory assets, deferred							6,805	5,375
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net							$ 1,275	$ 211
Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period							18 years
Scenario, Forecast | Customers
Schedule of Regulatory Assets and Liabilities [Line Items]
Percentage basis net merger savings										60.00%
Georgia Power
Schedule of Regulatory Assets and Liabilities [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 (percent)	20.00%
Portion of actual earnings above approved ROE band refunded to customers (percent)	40.00%	66.67%					50.00%
Portion of actual earnings above approved ROE band refunded to customers, used to reduce regulatory assets (percent)							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							60
Customer refund liability, noncurrent							330
Customer refund							55
Customer refund liability in absence of base rate case							110		$ 4
Contract with customer, liability, bill credits							$ 95	$ 130
Effective income tax rate							21.50%	21.30%	36.70%
Deferred income taxes							$ 179	$ (260)	$ 458
Under recovered CCR rule							$ 175
Proposed capacity of units for certification (in mw) | MW							25
Approved capacity of units for solar generation resources (mw) | MW							2,210
Proposed capacity of units for investment portfolio (mw) | MW							80
Approved increase (decrease) in annual billing based on fuel cost recovery rate												$ 313
Adjustment to fuel cost recovery rate if under recovered fuel balance exceeds budget thereafter							$ 200
Over recovered fuel balance							$ 73	115
Required period for options and hedges							48 months
Total regulatory assets (liabilities), net							$ 3,507	2,378
Other regulatory assets							263	169
Other regulatory assets, deferred							2,716	2,258
Georgia Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net							596	127
Georgia Power | Storm damage reserves
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net							410	416
Georgia Power | Property damage reserves-liability
Schedule of Regulatory Assets and Liabilities [Line Items]
Other regulatory assets							213	30
Other regulatory assets, deferred							$ 197	$ 386
Georgia Power | Minimum
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail rate of return on common equity							9.50%						10.00%
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail rate of return on common equity							12.00%						12.00%
Retail regulatory equity ratio	0.56	0.55
Cost recovery, estimate, nuclear fuel							$ 50
Georgia Power | Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period							3 years
Georgia Power | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Percentage basis net merger savings										40.00%
Portion of actual earnings above approved ROE band refunded to customers (percent)						50.00%
Portion of actual earnings above approved ROE band refunded to customers, value						$ 50
Contract with customer, liability, bill credits					$ 105
Recovery estimate of under recovered CCR rule costs						$ 265				$ 390	$ 290
Georgia Power | Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities							$ 659
Regulatory liability amortization period							3 years
Georgia Power | State and Local Jurisdiction
Schedule of Regulatory Assets and Liabilities [Line Items]
Effective income tax rate				6.00%			5.75%
Plant Hammond Units 1 through 4 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units (mw) | MW			840
Net book value of planned units retirements							$ 488
Plant McIntosh Unit 1 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units (mw) | MW			142.5
Net book value of planned units retirements							30
Plant Hammond and Plant McIntosh Units | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements							295
Unusable materials and supplies inventory							$ 20

REGULATORY MATTERS - Nuclear Co

REGULATORY MATTERS - Nuclear Construction (Details) - Georgia Power $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2009utilityMW	Jun. 30, 2018USD ($)
Loss Contingencies [Line Items]
Number of construction units approved | utility			2
Electric generating capacity (mw) | MW			1,100
Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Percent ownership		45.70%
Construction contingency estimate, subject to rate recovery evaluation		$ 140		$ 366
Construction financing costs		2,200
Additional base capital costs per month		50
AFUDC per month		$ 12
Plant Vogtle Units 3 And 4 | Scenario, Forecast
Loss Contingencies [Line Items]
Construction financing costs	$ 3,100
Vogtle Owners | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed		30 days

REGULATORY MATTERS - Schedule_4

REGULATORY MATTERS - Schedule of Nuclear Construction Cost and Schedule (Details) - USD ($) $ in Millions	Feb. 18, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments [Line Items]
Total AFUDC and interest capitalized		$ 202	$ 210	$ 249
Georgia Power
Commitments [Line Items]
Total AFUDC and interest capitalized		103	$ 94	$ 63
Customer refund		55
Georgia Power | Plant Vogtle Units 3 And 4
Commitments [Line Items]
Base project capital cost forecast		8,200
Construction contingency estimate		200
Total project capital cost forecast		8,400
Net investment		(5,900)
Remaining estimate to complete		2,500
Total AFUDC and interest capitalized		300
Total AFUDC and interest capitalized, accrual amount		$ 23
Subsequent Event | Twenty First Vogtle Construction Monitoring Report | Georgia Power | Plant Vogtle Units 3 And 4
Commitments [Line Items]
Maximum guarantee	$ 1,700
Customer refund	$ 188

REGULATORY MATTERS - Nuclear _2

REGULATORY MATTERS - Nuclear Construction Joint Owner Contracts (Details)	Aug. 31, 2018
Georgia Power | Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Ownership interest percentage required for voting for continuing construction	90.00%

REGULATORY MATTERS - Nuclear _3

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

Jan. 01, 2021

Feb. 19, 2020

Feb. 18, 2020

Jan. 01, 2020

Dec. 18, 2018

Jan. 01, 2018

Jan. 01, 2016

Dec. 31, 2022

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2015

Dec. 31, 2009

Dec. 31, 2016

Jan. 01, 2013

Loss Contingencies [Line Items]

Retail rate of return on common equity

10.50%

10.95%

Potential decrease each month, percentage

0.01%

Customer refund

$ 55

Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Estimated in-service capital cost

$ 4,418

Proceeds from recovery of financing costs

2,200

Project capital cost forecast

7,300

Increase (decrease) in tariff

$ 62

Additional construction capital costs

$ 3,300

Amendment to estimated in-service capital cost

5,680

Retail rate of return on common equity

10.95%

Public utilities, approved return on equity

10.00%

10.00%

Return on equity reduction, negative impact on earnings

$ 75

$ 100

$ 25

Plant Vogtle Units 3 And 4 | Scenario, Forecast

Loss Contingencies [Line Items]

Public utilities, approved return on equity

5.30%

8.30%

Return on equity reduction, negative impact on earnings

$ 190

$ 240

$ 140

Subsequent Event | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Approval of construction capital costs

$ 674

Minimum

Loss Contingencies [Line Items]

Retail rate of return on common equity

9.50%

10.00%

Twentieth Vogtle Construction Monitoring Report | Subsequent Event | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Approval of construction capital costs

$ 1,200

Expenditures related to Georgia Power's portion of an administrative claim filed in the Westinghouse bankruptcy proceedings

21.5

Twenty First Vogtle Construction Monitoring Report | Subsequent Event | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Maximum guarantee

1,700

Approval of construction capital costs

6,700

Customer refund

$ 188

REGULATORY MATTERS - Schedule_5

REGULATORY MATTERS - Schedule of MPC Regulatory Assets and Labilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 3,838	$ 720
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,084)	(2,297)
Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(204)	(76)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(86)	(132)
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	4,381	2,933
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	1,275	211
Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	803	799
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	492	581
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	4,423	3,658
Regulatory asset	23
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 186	182
Regulatory amortization period	1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 323	346
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 64	(35)
Regulatory amortization period	5 years
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Mississippi Power | Deferred credits related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (358)	(377)
Regulatory amortization period	8 years
Tax Cuts and Jobs Act of 2017, deferred tax assets	$ 358
Tax Cuts and Jobs Act of 2017, protected deferred tax assets	252
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	106
System Restoration Rider, deferred tax assets	$ 8
Mississippi Power | Deferred credits related to income taxes | Retail electric revenues | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	$ 28
Mississippi Power | Deferred credits related to income taxes | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	3 years
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	$ 18
Mississippi Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(189)	(185)
Mississippi Power | Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(55)	(56)
Mississippi Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (10)	(9)
Regulatory amortization period	1 year
Mississippi Power | Retiree benefit plans – regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 213	171
Mississippi Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 210	143
Regulatory amortization period	48 years
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 61	69
Regulatory amortization period	8 years
Regulatory asset	$ 78
Regulatory liabilities	18
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	30	41
Mississippi Power | Remaining net book value of retired assets | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 16
Regulatory amortization period	5 years
Mississippi Power | Remaining net book value of retired assets | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 14
Regulatory amortization period	12 years
Mississippi Power | Property tax
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 47	44
Regulatory amortization period	12 months
Mississippi Power | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 33	34
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	34	36
Mississippi Power | ECO carryforward
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	0	26
Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 48	$ 28
Regulatory amortization period	3 years
Mississippi Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	14 years
Mississippi Power | Kemper Retail
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	6 years
Mississippi Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 9
Mississippi Power | Other Miscellaneous Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 5
Regulatory amortization period	1 year
Mississippi Power | Fuel-hedging Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 27
Mississippi Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 6
Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	18 years
Maximum | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	80 years
Maximum | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Maximum | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Maximum | Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	22 years

REGULATORY MATTERS - MPC Regula

REGULATORY MATTERS - MPC Regulatory Matters (Details)

Jan. 01, 2020USD ($)

Nov. 26, 2019USD ($)

Jan. 01, 2019USD ($)

May 08, 2018USD ($)

Feb. 14, 2018USD ($)

Feb. 07, 2018USD ($)

Feb. 06, 2018USD ($)

Feb. 29, 2020USD ($)

Feb. 28, 2019USD ($)

Feb. 28, 2018USD ($)

Dec. 31, 2019USD ($)filing

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Oct. 24, 2019USD ($)

Aug. 07, 2018USD ($)

Jul. 31, 2017USD ($)

Jul. 31, 2016USD ($)

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 3,838,000,000

$ 720,000,000

Major storms

Schedule of Regulatory Assets and Liabilities [Line Items]

Storm damage reserves

170,000,000

74,000,000

$ 41,000,000

Remaining net book value of retired assets

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 1,275,000,000

211,000,000

Remaining net book value of retired assets | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory amortization period

18 years

Mississippi Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, requested rate increase (decrease), amount

$ 5,800,000

Base rate case filing, rate decrease percentage

0.60%

Base rate case filing, measurement input, average equity ratio

53.00%

Base rate case filing, measurement input, return on investment

7.728%

Performance evaluation plan, number of filings per calendar year | filing

2

Annual PEP filing rate increase amount

$ 26,000,000

Public utilities, approved return on equity

9.33%

Regulatory equity ratio

55.00%

Increase in annual base rate revenues

$ 21,600,000

Amount approved for recovery

$ 2,000,000

Net regulatory assets

$ 64,000,000

(35,000,000)

Retail rate of return on common equity

9.31%

Allowed equity ratio

50.00%

50.00%

Actual average equity ratio variance (more than)

1.00%

Percent ownership

50.00%

Public utilities, requested cost to complete environmental compliance projects

$ 66,000,000

Regulatory amortization period

5 years

PSC retail increase (decrease)

$ 2,000,000

7,000,000

(8,000,000)

Threshold above which actual damages are charged to the reserve

50,000

Wholesale accrual per annual SSR rate

$ 300,000

SRR rate

0.00%

Psc approved annual property damage reserve accrual

$ 1,000,000

2,000,000

4,000,000

Mississippi Power | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Proposed property damage reserve

54,000,000

Mississippi Power | Wholesale

Schedule of Regulatory Assets and Liabilities [Line Items]

Proposed property damage reserve

1,000,000

Mississippi Power | Major storms

Schedule of Regulatory Assets and Liabilities [Line Items]

Storm damage reserves

$ 1,000,000

1,000,000

$ 3,000,000

Mississippi Power | Mississippi Public Service Commission

Schedule of Regulatory Assets and Liabilities [Line Items]

Period to agree on system restoration rider

3 years

Mississippi Power | MRA Revenue

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (16,000,000)

Over recovered fuel cost

$ 6,000,000

6,000,000

Mississippi Power | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 3,000,000

$ (35,000,000)

$ 39,000,000

Over recovered fuel cost

$ 23,000,000

8,000,000

Mississippi Power | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, requested rate increase (decrease), amount

$ 17,000,000

Allowed equity ratio

51.00%

Public utilities approved rate increase (decrease)

2.00%

Mississippi Power | Kemper IGCC

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

8.60%

Public utilities, approved rate increase (decrease), amount

$ 99,300,000

Mississippi Power | Plant Greene County Units 1 And 2

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory asset

$ 17,000,000

Mississippi Power | Plant Watson

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory asset

$ 41,000,000

Mississippi Power | Plant Daniel Units 1 & 2 (coal)

Schedule of Regulatory Assets and Liabilities [Line Items]

Percent ownership

50.00%

Mississippi Power | Remaining net book value of retired assets

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 30,000,000

41,000,000

Mississippi Power | Remaining net book value of retired assets | Wholesale

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 14,000,000

Regulatory amortization period

12 years

Mississippi Power | Remaining net book value of retired assets | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 16,000,000

Regulatory amortization period

5 years

Mississippi Power | Contested Compensation Costs

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 4,000,000

Mississippi Power | Subsequent Event | MRA Revenue

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 1,000,000

Mississippi Power | Deferred credits related to income taxes

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ (358,000,000)

$ (377,000,000)

Regulatory amortization period

8 years

Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets

$ 106,000,000

Mississippi Power | Deferred credits related to income taxes | Wholesale

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory amortization period

3 years

Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets

$ 18,000,000

Mississippi Power | Deferred credits related to income taxes | Kemper IGCC | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory amortization period

8 years

Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets

$ 28,000,000

Mississippi Power | Deferred charges related to income taxes

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory liabilities

44,000,000

Mississippi Power | Performance Settlement Agreement, Average Equity Ratio Differential

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory liabilities

4,000,000

Mississippi Power | ECO Settlement Agreement, Average Equity Ratio Differential

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory liabilities

$ 2,000,000

Mississippi Power And Gulf Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, requested cost to complete environmental compliance projects

125,000,000

Ash Pond Closure | Mississippi Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, requested cost to complete environmental compliance projects

$ 17,000,000

Scenario, Forecast | Mississippi Power | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (24,000,000)

REGULATORY MATTERS - Kemper Reg

REGULATORY MATTERS - Kemper Regulatory Matters (Details) $ in Millions

Dec. 31, 2019

Feb. 07, 2018

Feb. 06, 2018USD ($)

Apr. 30, 2018USD ($)

Jun. 30, 2017USD ($)

Dec. 31, 2018USD ($)

Mar. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2024USD ($)

Dec. 31, 2020USD ($)

Dec. 31, 2019USD ($)MW

Dec. 31, 2018USD ($)

Dec. 31, 2012USD ($)

Dec. 31, 2023USD ($)

May 31, 2017USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2010USD ($)

Schedule of Regulatory Assets and Liabilities [Line Items]

Period costs

$ 37

$ 29

Mississippi Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Plant capacity under coal gasification combined cycle technology | MW

582

Maximum cap construction costs

$ 2,880

Pre-tax charge to income

$ (9)

After tax charge to income

$ (95)

Period costs

$ 1

0

Public utilities, approved return on equity

9.33%

Mississippi Power | Kemper IGCC

Schedule of Regulatory Assets and Liabilities [Line Items]

Firm transportation agreement, term

15 years

Maximum cap construction costs

$ 5,950

Estimated cost

7,380

Cost related to grant funding

137

Pre-tax charge to income

2,800

$ 44

$ 242

$ 24

37

$ 3,070

After tax charge to income

$ 2,000

$ 33

206

$ 1,890

After tax charge to income, cost during suspension period

$ 164

Period costs, net of tax

$ 68

Public utilities, approved rate increase (decrease), amount

$ 99.3

Public utilities, approved return on equity

8.60%

Amortization of regulatory assets

8 years

Amortization of regulatory liabilities

6 years

Disallowance pre-tax charge to income

$ 78

Pre-tax charge to income before accumulated depreciation

85

Pre-tax charge to income, accumulated depreciation

7

Disallowance after tax charge to income

$ 48

Reduction in customer rates annually

$ 26.8

Government grants expected

$ 137

$ 270

Government grants received

$ 387

Mississippi Power | Kemper IGCC | Scenario, Forecast

Schedule of Regulatory Assets and Liabilities [Line Items]

Period costs

$ 5

$ 17

Minimum | Mississippi Power | Kemper IGCC | Scenario, Forecast

Schedule of Regulatory Assets and Liabilities [Line Items]

Period costs

$ 15

Maximum | Mississippi Power | Kemper IGCC | Scenario, Forecast

Schedule of Regulatory Assets and Liabilities [Line Items]

Period costs

$ 16

Department Of Energy, Initial Grants | Mississippi Power | Kemper IGCC

Schedule of Regulatory Assets and Liabilities [Line Items]

Government grants received

382

Department Of Energy, Additional Grants For Future Rate Impacts | Mississippi Power | Kemper IGCC

Schedule of Regulatory Assets and Liabilities [Line Items]

Government grants received

$ 5

REGULATORY MATTERS - MPC Wholes

REGULATORY MATTERS - MPC Wholesale Regulatory Matters (Details) - Mississippi Power - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2019
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
MRA Revenue
Public Utilities, General Disclosures [Line Items]
Decrease in base rate under cost based electric tariff due to settlement	$ 3.7

REGULATORY MATTERS - Schedule_6

REGULATORY MATTERS - Schedule of GAS Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 3,838	$ 720
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,084)	(2,297)
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(6,301)	(6,455)
Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(205)	(47)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(86)	(132)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 4,423	3,658
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Long-term debt fair value adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 107	121
Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	254	407
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 492	581
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 186	182
Regulatory amortization period	1 year
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (1,874)	(1,872)
Southern Company Gas | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(1,606)	(1,585)
Southern Company Gas | Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(874)	(940)
Southern Company Gas | Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(82)	(43)
Southern Company Gas | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (22)	(46)
Southern Company Gas | Other regulatory liabilities | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	20 years
Southern Company Gas | Excess Deferred Income Tax Liabilities Not Subject To Normalization
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 12
Southern Company Gas | Environmental remediation
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	296	311
Southern Company Gas | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 167	161
Southern Company Gas | Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Southern Company Gas | Long-term debt fair value adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 107	121
Southern Company Gas | Long-term debt fair value adjustment | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	19 years
Southern Company Gas | Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 72	90
Regulatory amortization period	6 years
Southern Company Gas | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 68	59
Southern Company Gas | Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Southern Company Gas | Financial Instrument Hedging
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 11	8
Southern Company Gas | Financial Instrument Hedging | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	2 years
Southern Company Gas | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 11	$ 11
Regulatory amortization period	1 year
Southern Company Gas | Deferred Income Tax Charges and Other Cost of Removal Obligations | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	80 years

REGULATORY MATTERS - GAS Regula

REGULATORY MATTERS - GAS Regulatory Matters (Details) - USD ($) $ in Millions

Jan. 31, 2020

Dec. 19, 2019

Oct. 02, 2019

Dec. 31, 2018

Dec. 17, 2018

May 15, 2018

May 05, 2018

Feb. 23, 2018

Dec. 21, 2017

Oct. 10, 2017

Oct. 31, 2018

Jul. 31, 2018

Jan. 31, 2018

Jun. 30, 2020

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Sep. 30, 2019

Schedule of Regulatory Assets and Liabilities [Line Items]

Contract with customer, liability, bill credits

$ 50

Nicor Gas

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), recovery of investment amount

$ 65

Public utilities, approved rate increase (decrease), amount

$ 168

$ (44)

$ 137

Public utilities, approved return on equity

9.73%

9.80%

Public utilities, approved equity capital structure, percentage

54.20%

Nicor Gas | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Infrastructure investment, annual customer rate increase

4.00%

Infrastructure investment, annual customer rate increase in any given year

5.50%

Nicor Gas | Regulatory Infrastructure Program

Schedule of Regulatory Assets and Liabilities [Line Items]

Program duration period

9 years

Nicor Gas | Investing In Illinois

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease) amount recovery of investments

$ 65

$ 93

Virginia Natural Gas

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (14)

$ 34

Public utilities, approved return on equity

9.50%

Contract with customer, liability, bill credits

$ 14

Virginia Natural Gas | Minimum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

9.00%

Virginia Natural Gas | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

10.00%

Virginia Natural Gas | SAVE

Schedule of Regulatory Assets and Liabilities [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

Public utilities, approved rate increase (decrease) amount recovery of investments

$ 13

Virginia Natural Gas | Year 2018 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

35

Virginia Natural Gas | Year 2019 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

40

Virginia Natural Gas | Year 2020 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

50

Virginia Natural Gas | Year 2021 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

60

Virginia Natural Gas | Year 2022 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

70

Virginia Natural Gas | Year 2023 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

70

Virginia Natural Gas | Year 2024 | SAVE

Schedule of Regulatory Assets and Liabilities [Line Items]

Approved infrastructure replacement program, approved investment amount, current fiscal year

$ 70

Atlanta Gas Light

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 65

$ 16

Public utilities, approved return on equity

10.25%

Public utilities, approved equity capital structure, percentage

56.00%

Annual proceeds from strategic economic development projects

$ 15

Public utilities, maximum base rate percentage

5.00%

Regulatory equity ratio

55.00%

Contract with customer, liability, bill credits

$ 8

$ 8

Public utilities approved rate increase (decrease)

4.00%

Atlanta Gas Light | Minimum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

10.05%

10.55%

Atlanta Gas Light | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

10.45%

10.95%

Atlanta Gas Light | Favorable Regulatory Action

Schedule of Regulatory Assets and Liabilities [Line Items]

Proceeds from legal settlements

$ 7

$ 20

Atlanta Gas Light | True Up Recovery

Schedule of Regulatory Assets and Liabilities [Line Items]

Gain contingency, unrecorded amount

$ 135

Atlanta Gas Light | True-Up Recovery, Unrecognized Equity

Schedule of Regulatory Assets and Liabilities [Line Items]

Gain contingency, unrecorded amount

70

Southern Company Gas

Schedule of Regulatory Assets and Liabilities [Line Items]

Under recovered fuel cost

$ 15

$ 74

$ 15

Subsequent Event | Atlanta Gas Light

Schedule of Regulatory Assets and Liabilities [Line Items]

Comprehensive capacity supply and related infrastructure delivery plan, term

10 years

Updated comprehensive capacity supply and related infrastructure delivery plan, at least once every third year, term

10 years

Scenario, Forecast | Virginia Natural Gas

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, estimated project costs

$ 346

REGULATORY MATTERS - Schedule_7

REGULATORY MATTERS - Schedule of GAS Unrecognized Ratemaking Amounts (Details) - Regulatory Asset Off Balance Sheet - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 70	$ 95
Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	10	11
Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	2	4
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 82	$ 110

CONTINGENCIES, COMMITMENTS, A_3

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Litigation (Details) - Pending Litigation - lawsuit	May 04, 2018	Apr. 25, 2018	Dec. 31, 2017	Aug. 31, 2017
Putative Securities Class Action
Loss Contingencies [Line Items]
Class action complaint, increase in purported class period			1 day
Shareholder Derivative Lawsuits
Loss Contingencies [Line Items]
Number of claims				2
Stay period	30 days	30 days

CONTINGENCIES, COMMITMENTS, A_4

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - MPC Litigation (Details) $ in Millions	Sep. 27, 2019USD ($)	Mar. 14, 2019plaintiff	Nov. 21, 2018plaintiff	May 18, 2018USD ($)	Nov. 30, 2018USD ($)defendant	May 31, 2018agreement
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of plaintiffs | plaintiff			10
Martin Product Sales, LLC Litigation
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss contingency, damages sought, value				$ 143
Purported Violations Of Mississippi Consumer Protection Act | Pending Litigation | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss contingency, number of agreements | agreement						2
Number of plaintiffs | plaintiff		4
Loss contingency, number of defendants | defendant					3
Public utilities, underpayment of refunds					$ 23.5
Martin Product Sales, LLC Litigation | Martin Product Sales, LLC Litigation
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss contingency, damages sought, value	$ 50
Loss contingency, damages sought, compensatory value	$ 5

CONTINGENCIES, COMMITMENTS, A_5

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SPC Litigation (Details) - Southern Power - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Construction contract payment withheld		$ 26
Gain on funds received in excess of initial replacement costs, net of allocation to noncontrolling interests, net of tax	$ 12
RE Roserock, LLC
Loss Contingencies [Line Items]
Noncontrolling ownership percentage held by parent		51.00%

CONTINGENCIES, COMMITMENTS, A_6

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GPC and GAS Environmental Remediation (Details) $ in Thousands	Dec. 23, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)statesite	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Accrued environmental remediation			$ 234,000	$ 268,000
Georgia Power
Environmental Exit Cost [Line Items]
Costs recovered annually			2,000	2,000	$ 2,000
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current			15,000	23,000
Accrued environmental remediation			0	0
Under recovered environmental remediation costs, other regulatory assets, current			12,000	2,000
Under recovered environmental remediation costs, other regulatory assets, deferred			40,000	53,000
Southern Company Gas
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current			36,000	26,000
Accrued environmental remediation			233,000	268,000
Under recovered environmental remediation costs, other regulatory assets, current			37,000	19,000
Under recovered environmental remediation costs, other regulatory assets, deferred			$ 260,000	292,000
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
Southern Company
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current			$ 51,000	49,000
Accrued environmental remediation			234,000	268,000
Under recovered environmental remediation costs, other regulatory assets, current			49,000	21,000
Under recovered environmental remediation costs, other regulatory assets, deferred			$ 300,000	$ 345,000
Scenario, Forecast | Georgia Power
Environmental Exit Cost [Line Items]
Costs recovered annually		$ 12,000
Mississippi Commission On Environmental Quality | Mississippi Power
Environmental Exit Cost [Line Items]
Civil penalties	$ 200

CONTINGENCIES, COMMITMENTS, A_7

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Nuclear Fuel Disposal Costs and Nuclear Insurance (Details)	12 Months Ended
	Dec. 31, 2019USD ($)plant
Jointly Owned Utility Plant Interests [Line Items]
Maximum fund for public liability claims arising from a single nuclear incident under price-anderson amendments act	$ 13,900,000,000
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
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	58,000,000
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	$ 85,000,000
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	12-week

CONTINGENCIES, COMMITMENTS, A_8

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SO Other Matters (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2017lessee
Commitments and Contingencies Disclosure [Abstract]
Number of lessees | lessee		1
Lease, impairment loss	$ 17
Lease, impairment loss, after tax	13
Leveraged lease investment	$ 76

CONTINGENCIES, COMMITMENTS, A_9

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - APC Other Matters (Details) - Alabama Power - Fish Kill Investigation	Oct. 16, 2019USD ($)
Alabama Department of Environmental Management (ADEM)
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party	$ 50,000
Alabama Department Of Conservation And Natural Resources
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party	$ 172,000

CONTINGENCIES, COMMITMENTS, _10

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - MPC Other Matters (Details) - USD ($)	Jan. 01, 2019	May 31, 2018	Jan. 15, 2024
Mississippi Power | Deepwater Horizon Oil Spill Litigation Case
Loss Contingencies [Line Items]
Litigation settlement		$ 18,000,000
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]
Percent ownership			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, _11

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GAS Other Matters (Details)	Dec. 30, 2019	Dec. 31, 2019USD ($)facilitycavernpipeline	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 30, 2020phasemi
Loss Contingencies [Line Items]
Impairment charges		$ 168,000,000	$ 210,000,000	$ 0
Southern Company Gas
Loss Contingencies [Line Items]
Impairment of long-lived assets		$ 0
Pipelines | Southern Company Gas
Loss Contingencies [Line Items]
Number of gas construction projects | pipeline		2
PennEast Pipeline
Loss Contingencies [Line Items]
Extension request, term	2 years
Maximum | Pipelines
Loss Contingencies [Line Items]
Construction contingency estimate		$ 8,000,000,000
Maximum | Pipelines | Southern Company Gas
Loss Contingencies [Line Items]
Construction contingency estimate		400,000,000
Maximum | PennEast Pipeline | Southern Company Gas
Loss Contingencies [Line Items]
Construction contingency estimate		$ 300,000,000
Natural Gas Storage - Salt Dome Caverns
Loss Contingencies [Line Items]
Number of salt dome caverns | cavern		2
Natural Gas Storage Facility | Southern Company Gas
Loss Contingencies [Line Items]
Impairment charges		$ 91,000,000
After tax impairment charges		69,000,000
Public utilities, property, plant and equipment, net		$ 326,000,000
Subsequent Event | PennEast Pipeline
Loss Contingencies [Line Items]
Construction amendment, number of phases | phase					2
Construction amendment, number of miles of pipe, phase one | mi					68
California and Texas | Natural Gas Storage Facility | Southern Company Gas
Loss Contingencies [Line Items]
Public utilities, number of facilities | facility		2

CONTINGENCIES, COMMITMENTS, _12

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Commitments (Details) - Georgia Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
MEAG Power
Loss Contingencies [Line Items]
Percent ownership	5.00%
Plant Vogtle Units 1 and 2
Loss Contingencies [Line Items]
Capacity payments	$ 6	$ 8	$ 9
Recorded unconditional purchase obligation	56
2020	5
2021	5
2022	4
2023	3
2024	4
2025 and thereafter	$ 35

CONTINGENCIES, COMMITMENTS, _13

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GAS Commitments (Details) - Southern Company Gas MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)MMBTU
Long-term Purchase Commitment [Line Items]
Natural gas pipeline capacity | MMBTU	45
Long-term purchase commitment amount	$ 84
Pipeline Charges, Storage Capacity, and Gas Supply
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2020	725
2021	559
2022	526
2023	454
2024	330
2025 and thereafter	1,677
Total	$ 4,271

CONTINGENCIES, COMMITMENTS, _14

CONTINGENCIES, COMMITMENTS, AND GUARANTEES - Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2017	Dec. 31, 2014
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	$ 2,055	$ 2,915
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Jointly owned affiliate equity	87
Jointly owned affiliate long term debt	$ 100
Ownership percentage, equity method investment	50.00%
Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	$ 650	$ 650
SEGCO | Maturity December 1, 2018 | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Guarantee of unsecured senior notes	100
SEGCO | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	26
Atlantic Coast Pipeline | Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Ownership percentage, equity method investment				5.00%
Maximum guarantee	$ 88
Revolving Credit Facility | Atlantic Coast Pipeline | Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Revolving credit facility executed			$ 3,400

REVENUE FROM CONTRACTS WITH C_3

REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 21,419	$ 23,495	$ 23,031
Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	14,445	15,087
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	6,164	6,586
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	5,065	5,255
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	3,126	3,152
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	90	94
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2,989	3,175
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,413	1,525
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	389	436
Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	907	944
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	35	40
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	245	230
Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,518	1,711
PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	833	950
PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	453	498
Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	232	263
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2,609	3,739
Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	32	32
Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	2,095	3,083
Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	440	571
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	42	53
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,035	1,529
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	22,596	25,241
Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	4,266	5,108
Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	(5,443)	(6,854)
Alabama Power
Disaggregation of Revenue [Line Items]
Total operating revenues	6,125	6,032	6,039
Alabama Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	5,671	5,215
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	2,509	2,285
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,677	1,541
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,460	1,364
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	25	25
Alabama Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	328	378
Alabama Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	145	158
Alabama Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	102	101
Alabama Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	81	119
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Alabama Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	153	210
Alabama Power | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	6,152	5,803
Alabama Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	(27)	229
Alabama Power | Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power
Disaggregation of Revenue [Line Items]
Total operating revenues	8,408	8,420	8,310
Georgia Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	7,888	7,697
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	3,377	3,295
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	3,097	3,025
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,360	1,321
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	54	56
Georgia Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	123	158
Georgia Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	60	81
Georgia Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	54	53
Georgia Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	9	24
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Georgia Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	407	236
Georgia Power | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	8,418	8,091
Georgia Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	(10)	329
Georgia Power | Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power
Disaggregation of Revenue [Line Items]
Total operating revenues	1,264	1,265	1,187
Mississippi Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	886	902
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	278	277
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	291	290
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	306	326
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	11	9
Mississippi Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	366	350
Mississippi Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	11	15
Mississippi Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	3	6
Mississippi Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	352	329
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Mississippi Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	19	22
Mississippi Power | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	1,271	1,274
Mississippi Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	(7)	(9)
Mississippi Power | Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power
Disaggregation of Revenue [Line Items]
Total operating revenues	1,938	2,205	2,075
Southern Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,208	1,351
Southern Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	648	727
Southern Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	322	394
Southern Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	238	230
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	12	13
Southern Power | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	1,220	1,364
Southern Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	718	841
Southern Power | Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	3,792	3,909	$ 3,920
Southern Company Gas | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2,989	3,175
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,413	1,525
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	389	436
Southern Company Gas | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	907	944
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	35	40
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	245	230
Southern Company Gas | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2,609	3,739
Southern Company Gas | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	32	32
Southern Company Gas | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues	2,095	3,083
Southern Company Gas | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	440	571
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	42	53
Southern Company Gas | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Southern Company Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total operating revenues	5,598	6,914
Southern Company Gas | Other revenue sources
Disaggregation of Revenue [Line Items]
Total operating revenues	3,637	3,849
Southern Company Gas | Other adjustments
Disaggregation of Revenue [Line Items]
Total operating revenues	$ (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, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,413	$ 2,630
Contract Assets	117	102
Contract Liabilities	52	32
Contract with Customer, Liability, Revenue Recognized	30
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	40	39
Contract Liabilities	28	11
Alabama Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	586	520
Contract Assets	0	0
Contract Liabilities	10	12
Contract with Customer, Liability, Revenue Recognized	11
Georgia Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	688	721
Contract Assets	69	58
Contract Liabilities	$ 13	7
Performance obligation, expected timing of satisfaction	Georgia Power had contract assets primarily related to fixed retail customer bill programs, where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term, and unregulated service agreements, where payment is contingent on project completion. Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Contract liabilities for Georgia Power and Southern Power relate to cash collections recognized in advance of revenue for certain unregulated service agreements and
Contract with Customer, Liability, Revenue Recognized	$ 6
Mississippi Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	79	100
Contract Assets	0	0
Contract Liabilities	0	0
Southern Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	97	118
Contract Assets	0	0
Contract Liabilities	1	11
Contract with Customer, Liability, Revenue Recognized	11
Southern Company Gas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	749	952
Contract Assets	0	0
Contract Liabilities	1	$ 2
Contract with Customer, Liability, Revenue Recognized	$ 2

REVENUE FROM CONTRACTS WITH C_5

REVENUE FROM CONTRACTS WITH CUSTOMERS - Performance Obligations (Details) $ in Millions	Dec. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 490
Expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 430
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	$ 336
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	$ 324
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	$ 323
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	$ 2,108
Expected timing of satisfaction
Alabama Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 21
Expected timing of satisfaction	1 year
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	$ 25
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	$ 22
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	$ 22
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	$ 22
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	$ 118
Expected timing of satisfaction
Georgia Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 60
Expected timing of satisfaction	1 year
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	$ 49
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	$ 32
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	$ 32
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	$ 23
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	$ 61
Expected timing of satisfaction
Southern Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 287
Expected timing of satisfaction	1 year
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	$ 280
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	$ 281
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	$ 271
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	$ 279
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	$ 1,948
Expected timing of satisfaction

PROPERTY, PLANT, AND EQUIPMEN_3

PROPERTY, PLANT, AND EQUIPMENT - Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Electric utilities:
Generation	$ 50,329	$ 52,324
Transmission	12,157	11,344
Distribution	19,846	18,746
General/other	4,650	4,446
Electric utilities' plant in service	86,982	86,860
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	13,518	12,409
Storage facilities	1,634	1,640
Other	1,192	1,128
Southern Company Gas plant in service	16,344	15,177
Other plant in service	1,788	1,669
Total plant in service	105,114	103,706
Alabama Power
Electric utilities:
Generation	15,329	16,533
Transmission	4,719	4,380
Distribution	7,798	7,389
General/other	2,177	2,100
Electric utilities' plant in service	30,023	30,402
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	30,023	30,402
Georgia Power
Electric utilities:
Generation	18,341	19,145
Transmission	6,590	6,156
Distribution	11,024	10,389
General/other	2,182	1,985
Electric utilities' plant in service	38,137	37,675
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	38,137	37,675
Mississippi Power
Electric utilities:
Generation	2,786	2,849
Transmission	808	769
Distribution	1,024	968
General/other	239	314
Electric utilities' plant in service	4,857	4,900
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	4,857	4,900
Southern Power
Electric utilities:
Generation	13,241	13,246
Transmission	0	0
Distribution	0	0
General/other	29	25
Electric utilities' plant in service	13,270	13,271
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	13,270	13,271
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	13,518	12,409
Storage facilities	1,634	1,640
Other	1,192	1,128
Southern Company Gas plant in service	16,344	15,177
Other plant in service	0	0
Total plant in service	$ 16,344	$ 15,177

PROPERTY, PLANT, AND EQUIPMEN_4

PROPERTY, PLANT, AND EQUIPMENT - Additional Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019
Alabama Power
Property, Plant and Equipment [Line Items]
Period to amortize costs	18 months
Plant Vogtle Units 1 and 2 | Georgia Power
Property, Plant and Equipment [Line Items]
Unit operating cycle (term)	18 months
Plant Hatch Units 1 and 2 | Georgia Power
Property, Plant and Equipment [Line Items]
Unit operating cycle (term)	24 months

PROPERTY, PLANT, AND EQUIPMEN_5

PROPERTY, PLANT, AND EQUIPMENT - Assets Acquired Under a Capital Lease (Details) $ in Millions	Dec. 31, 2018USD ($)
Capital Leased Assets [Line Items]
Less: Accumulated amortization	$ (75)
Balance, net of amortization	191
Office buildings
Capital Leased Assets [Line Items]
Capital leased assets, gross	216
PPAs
Capital Leased Assets [Line Items]
Capital leased assets, gross	0
Computer-related equipment
Capital Leased Assets [Line Items]
Capital leased assets, gross	43
Gas pipeline
Capital Leased Assets [Line Items]
Capital leased assets, gross	7
Georgia Power
Capital Leased Assets [Line Items]
Less: Accumulated amortization	(84)
Balance, net of amortization	121
Georgia Power | Office buildings
Capital Leased Assets [Line Items]
Capital leased assets, gross	61
Georgia Power | PPAs
Capital Leased Assets [Line Items]
Capital leased assets, gross	144
Georgia Power | Computer-related equipment
Capital Leased Assets [Line Items]
Capital leased assets, gross	0
Georgia Power | Gas pipeline
Capital Leased Assets [Line Items]
Capital leased assets, gross	$ 0

PROPERTY, PLANT, AND EQUIPMEN_6

PROPERTY, PLANT, AND EQUIPMENT - Composite Straight-Line Rates (Details) - Utility plant in service	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Alabama Power
Property, Plant and Equipment [Line Items]
Composite rate	3.10%	3.00%	2.90%
Georgia Power
Property, Plant and Equipment [Line Items]
Composite rate	2.60%	2.60%	2.70%
Mississippi Power
Property, Plant and Equipment [Line Items]
Composite rate	3.70%	4.20%	3.40%
Southern Company Gas
Property, Plant and Equipment [Line Items]
Composite rate	2.90%	2.90%	2.90%

PROPERTY, PLANT, AND EQUIPMEN_7

PROPERTY, PLANT, AND EQUIPMENT - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	Nov. 26, 2019	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Accumulated depreciation		$ 30,765	$ 31,038
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation		30,000	30,300
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation		$ 732	766
Other plant in service | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		65 years
Mississippi Power
Property, Plant and Equipment [Line Items]
Base rate case filing, annual depreciation increase requested	$ 16
Accumulated depreciation		$ 1,463	1,429
Southern Company Gas
Property, Plant and Equipment [Line Items]
Accumulated depreciation		4,650	4,400
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation		4,500	4,300
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation		$ 155	$ 129
Southern Company Gas | Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		5 years
Southern Company Gas | Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		15 years
Southern Company Gas | Storage facilities | Minimum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		40 years
Southern Company Gas | Storage facilities | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		60 years
Southern Company Gas | Other assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciation period of original cost		65 years

PROPERTY, PLANT, AND EQUIPMEN_8

PROPERTY, PLANT, AND EQUIPMENT - Southern Power Useful Lives (Details) - Southern Power - Maximum	12 Months Ended
	Dec. 31, 2019
Natural Gas Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	45 years
Biomass Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	40 years
Solar Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	35 years
Wind Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	30 years

PROPERTY, PLANT, AND EQUIPMEN_9

PROPERTY, PLANT, AND EQUIPMENT - Ownership and Investment in Jointly-Owned Facilities (Details) $ in Millions	1 Months Ended	60 Months Ended
	Aug. 31, 2017USD ($)	Jan. 15, 2024	Dec. 31, 2019USD ($)mi	Oct. 24, 2019
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			$ 182
Accumulated Depreciation			71
CWIP			$ 1
Alabama Power | Plant Miller (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership			91.80%
Plant in Service			$ 2,058
Accumulated Depreciation			630
CWIP			$ 65
Georgia Power | Plant Hatch (nuclear)
Other Ownership Interests [Line Items]
Percent Ownership			50.10%
Plant in Service			$ 1,316
Accumulated Depreciation			603
CWIP			$ 40
Georgia Power | Plant Vogtle (nuclear) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership			45.70%
Plant in Service			$ 3,565
Accumulated Depreciation			2,177
CWIP			$ 96
Georgia Power | Plant Scherer (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership			8.40%
Plant in Service			$ 266
Accumulated Depreciation			94
CWIP			$ 14
Georgia Power | Plant Scherer (coal) Unit 3
Other Ownership Interests [Line Items]
Percent Ownership			75.00%
Plant in Service			$ 1,267
Accumulated Depreciation			492
CWIP			$ 47
Georgia Power | Plant Wansley (coal)
Other Ownership Interests [Line Items]
Percent Ownership			53.50%
Plant in Service			$ 1,059
Accumulated Depreciation			367
CWIP			$ 10
Georgia Power | Rocky Mountain (pumped storage)
Other Ownership Interests [Line Items]
Percent Ownership			25.40%
Plant in Service			$ 182
Accumulated Depreciation			139
CWIP			$ 0
Mississippi Power
Other Ownership Interests [Line Items]
Percent Ownership				50.00%
Mississippi Power | Plant Daniel (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership			50.00%
Plant in Service			$ 750
Accumulated Depreciation			214
CWIP			$ 11
Southern Company Gas | Dalton Pipeline (natural gas pipeline)
Other Ownership Interests [Line Items]
Percent Ownership			50.00%
Plant in Service			$ 271
Accumulated Depreciation			10
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			$ 118
Accumulated Depreciation			46
CWIP			$ 1
Plant Daniel | Scenario, Forecast | Gulf Power
Other Ownership Interests [Line Items]
Ownership interest to be sold (percent)		50.00%

PROPERTY, PLANT, AND EQUIPME_10

PROPERTY, PLANT, AND EQUIPMENT - Joint Ownership Agreements (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 7,880	$ 7,254
Georgia Power
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 5,650	$ 4,833
Plant Vogtle Units 3 And 4 | Georgia Power
Property, Plant and Equipment [Line Items]
Percent ownership	45.70%
Construction work in progress	$ 5,800

PROPERTY, PLANT, AND EQUIPME_11

PROPERTY, PLANT, AND EQUIPMENT - Assets Subject to Lien (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	$ 118,700	$ 116,914	$ 111,005
Mississippi Power
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	5,035	4,886
Mississippi Power | Chevron
Property, Plant and Equipment [Line Items]
Net book value of co-generation assets	118
Southern Power
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	14,300	$ 14,883
Southern Power | Senior Lien
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	$ 547

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Details of AROs Included in the Balance Sheets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 9,394	$ 4,824
Liabilities incurred	37	29
Liabilities settled	(328)	(244)
Accretion	402	217
Cash flow revisions	281	4,737
Reclassification to held for sale		(169)
Balance at end of year	9,786	9,394
Alabama Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	3,210	1,709
Liabilities incurred	0	0
Liabilities settled	(127)	(55)
Accretion	145	106
Cash flow revisions	312	1,450
Reclassification to held for sale		0
Balance at end of year	3,540	3,210
Georgia Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	5,829	2,638
Liabilities incurred	35	27
Liabilities settled	(151)	(116)
Accretion	243	94
Cash flow revisions	(172)	3,186
Reclassification to held for sale		0
Balance at end of year	5,784	5,829
Mississippi Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	160	174
Liabilities incurred	1	0
Liabilities settled	(35)	(35)
Accretion	7	5
Cash flow revisions	57	16
Reclassification to held for sale		0
Balance at end of year	190	160
Southern Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	84	78
Liabilities incurred	1	2
Liabilities settled	0	0
Accretion	4	4
Cash flow revisions	0	0
Reclassification to held for sale		0
Balance at end of year	$ 89	$ 84

ASSET RETIREMENT OBLIGATIONS _2

ASSET RETIREMENT OBLIGATIONS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2014
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs			$ 1,200	$ 312
Estimated inflation rate (percentage)				4.50%
Estimated trust earnings rate (percentage)				7.00%
Alabama Power | Internal reserves
Jointly Owned Utility Plant Interests [Line Items]
Accumulated provisions for decommissioning	$ 16	$ 17		$ 16
Alabama Power | Plant Farley
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs			300
Mississippi Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs				57
Mississippi Power | Plant Greene County
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs			$ 11
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs	(174)	3,100
Fair market value of securities on loan and pledged to creditors	28	27		28
Fair value of collateral received	$ 29	28		$ 29
Estimated inflation rate (percentage)				2.75%
Estimated trust earnings rate (percentage)				4.75%
Georgia Power | Plant Hatch and Plant Vogtle Units 1 And 2
Jointly Owned Utility Plant Interests [Line Items]
Increase (decrease) to AROs		$ 130
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, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 2,034	$ 1,719
Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	1,159	919
Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	798	726
Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	77	74
Alabama Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,021	846
Alabama Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	743	594
Alabama Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	218	201
Alabama Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	60	51
Georgia Power
Marketable Securities [Line Items]
Total investment securities in the Funds	1,013	873
Georgia Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	416	325
Georgia Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	580	525
Georgia Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 17	$ 23

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value increases (decreases)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ 344	$ (67)	$ 233
Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	259	(183)	181
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	194	(38)	125
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	149	(96)	98
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	150	(29)	108
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	$ 110	$ (87)	$ 83

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, 2019	Dec. 31, 2018
Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 1,013	$ 873
Plant Farley | Alabama Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	1,021	846
Plant Hatch | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	634	547
Plant Vogtle Units 1 and 2 | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 379	$ 326

ASSET RETIREMENT OBLIGATIONS _6

ASSET RETIREMENT OBLIGATIONS - Estimated Costs of Decommissioning (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
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, 2019USD ($)MW	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
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 | MW	1,020
Share of purchased power	$ 93	$ 102	$ 76
Alabama Power | SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Dividends paid by equity method investment	$ 14	18	24
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	$ 95	$ 105	$ 78
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)	Dec. 11, 2018wind_farminvestor	May 22, 2018	Aug. 31, 2019USD ($)	Dec. 31, 2018USD ($)wind_farm	Sep. 30, 2018operating_facility	Dec. 31, 2019USD ($)	Dec. 31, 2017USD ($)	Oct. 31, 2017
Redeemable Noncontrolling Interest [Line Items]
Equity method investments in wind and battery storage projects				$ 269,000,000		$ 391,000,000
Southern Power
Redeemable Noncontrolling Interest [Line Items]
Equity method investments in wind and battery storage projects				0		28,000,000
Number of wind facilities | operating_facility					8
Reclassification from redeemable noncontrolling interest				$ 0		$ 0	$ 0
SunPower Corp | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Reclassification from redeemable noncontrolling interest							(114,000,000)
Reclassification to nonredeemable noncontrolling interest							$ 114,000,000
SP Solar Holdings I, LP | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership		33.00%
Distribution made to limited partner, cash distributions paid, percentage						67.00%
SP Solar Holdings I, LP | Global Atlantic
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage						33.00%
SP Solar Holdings I, LP | Wholly Owned Subsidiary Of Southern Power | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Ownership interest		66.00%
SP Wind
Redeemable Noncontrolling Interest [Line Items]
Number of wind facilities | wind_farm	8			8
SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership	100.00%
Distribution made to limited partner, cash distributions paid, percentage						60.00%
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%
SP Wind | Wholly Owned Subsidiary Of Southern Power | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Ownership interest	100.00%
General Partner | SP Solar Holdings I, LP | Wholly Owned Subsidiary Of Southern Power | Southern Power
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				$ 6,300,000,000		$ 6,400,000,000
Liabilities				113,000,000		381,000,000
Noncontrolling interests related to other partners' interest				1,200,000,000		1,100,000,000
Variable Interest Entity, Primary Beneficiary | SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets				2,500,000,000		2,500,000,000
Liabilities				51,000,000		128,000,000
Noncontrolling interests related to other partners' interest				47,000,000		45,000,000
Variable Interest Entity, Primary Beneficiary | Other Variable Interest Entities | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets				858,000,000		1,100,000,000
Liabilities				80,000,000		104,000,000
Noncontrolling interests related to other partners' interest				$ 241,000,000		$ 409,000,000
Variable Interest Entity, Primary Beneficiary | DSGP | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets			$ 107,000,000
Liabilities			51,000,000
Noncontrolling interests related to other partners' interest			56,000,000
Cash transferred as a result of this reconsideration event			$ 0
Southern Power Solar Facilities | Turner Renewable Energy | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest								10.00%

CONSOLIDATED ENTITIES AND EQU_5

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,303	$ 1,580
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,251	1,538
SNG | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,137	1,261
Current assets	85	104
Property, plant, and equipment	2,570	2,606
Deferred charges and other assets	158	121
Total Assets	2,813	2,831
Current liabilities	227	103
Long-term debt	1,214	1,103
Other deferred charges and other liabilities	86	212
Total Liabilities	1,527	1,418
Total Stockholders' Equity	1,286	1,413
Total Liabilities and Stockholders' Equity	2,813	2,831
PennEast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	82	71
Pivotal JAX LNG, LLC | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	0	53
Atlantic Coast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	0	83
Other | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 32	$ 70

CONSOLIDATED ENTITIES AND EQU_6

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Income Statement Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 162	$ 148	$ 106
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	157	148	106
Southern Company Gas | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	141	131	88
Revenues	630	604	544
Operating income	335	310	242
Net income	280	261	175
Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	13	7	6
Southern Company Gas | PennEast Pipeline(a)
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	6	5	6
Southern Company Gas | Other
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ (3)	$ 5	$ 6

CONSOLIDATED ENTITIES AND EQU_7

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - GAS Equity Method Investments Narrative (Details) - Southern Company Gas $ in Millions	May 29, 2019USD ($)	Dec. 31, 2019gal	Dec. 31, 2016	Dec. 31, 2014miBcf
Southern Natural Gas Company, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment		50.00%
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment				5.00%
Pipeline infrastructure | mi				605
PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment				20.00%
Pipeline infrastructure | mi				118
Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment		50.00%
Dominion Modular LNG Holdings, Inc.
Schedule of Equity Method Investments [Line Items]
Realized loss on disposal, net of tax | $	$ 2
Minimum | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas pipeline capacity (volume) | Bcf				1.5
Minimum | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas pipeline capacity (volume) | Bcf				1
Liquefied Natural Gas (LNG) | Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Storage facility capacity | gal		2,000,000
Liquefied Natural Gas (LNG) | Minimum | Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Storage facility production capacity | gal		120,000
Southern Natural Gas Company, LLC | Southern Natural Gas Company, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment			50.00%

CONSOLIDATED ENTITIES AND EQU_8

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Redeemable Noncontrolling Interest (Details) - Southern Power $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Noncontrolling Interest [Roll Forward]
Beginning balance	$ 164
Net income attributable to redeemable noncontrolling interests	2
Distributions to redeemable noncontrolling interests	(2)
Capital contributions from redeemable noncontrolling interests	2
Redemption of redeemable noncontrolling interests	(59)
Reclassification to non-redeemable noncontrolling interests	(114)
Change in fair value of redeemable noncontrolling interests	7
Ending balance	$ 0

CONSOLIDATED ENTITIES AND EQU_9

CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Net income									$ 4,744	$ 2,300	$ 926
Less: Net income attributable to noncontrolling interests									10	(58)	(44)
Net income attributable to Southern Power	$ 440	$ 1,316	$ 899	$ 2,084	$ 278	$ 1,164	$ (154)	$ 938
Southern Power
Noncontrolling Interest [Line Items]
Net income									329	246	1,117
Less: Net income attributable to noncontrolling interests									$ (10)	$ 59	44
Less: Net income attributable to redeemable noncontrolling interests											2
Net income attributable to Southern Power	$ 23	$ 86	$ 174	$ 56	$ (48)	$ 92	$ 22	$ 121			$ 1,071

FINANCING - Maturities of Long-

FINANCING - Maturities of Long-Term Debt (Details) $ in Millions	Dec. 31, 2019USD ($)
Debt Disclosure [Line Items]
2020	$ 2,991
2021	3,214
2022	2,003
2023	2,413
2024	492
Alabama Power
Debt Disclosure [Line Items]
2020	251
2021	311
2022	751
2023	301
2024	22
Georgia Power
Debt Disclosure [Line Items]
2020	1,025
2021	397
2022	527
2023	175
2024	477
Mississippi Power
Debt Disclosure [Line Items]
2020	281
2021	270
2022	0
2023	0
2024	0
Southern Power
Debt Disclosure [Line Items]
2020	825
2021	300
2022	677
2023	290
2024	0
Southern Company Gas
Debt Disclosure [Line Items]
2020	0
2021	330
2022	46
2023	400
2024	$ 0

FINANCING - Long-Term Debt (Det

FINANCING - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Alabama Power | Trust Preferred Securities
Debt Disclosure [Line Items]
Long-term debt	$ 206	$ 206
Mississippi Power | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	270	270
Mississippi Business Finance Corporation Taxable Revenue Bonds Series 1999A Due 2021 | Mississippi Power | Corporate bonds
Debt Disclosure [Line Items]
Long-term debt	$ 270	$ 270
Fixed stated interest rate of debt obligation	7.13%	7.13%
Long-term debt, fair value	$ 346
Unamortized premium	76
Tax-exempt Revenue Bonds | Mississippi Power | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	$ 50	$ 50

FINANCING - DOE Loan Guarantee

FINANCING - DOE Loan Guarantee Borrowings (Details)	1 Months Ended		12 Months Ended
	Dec. 31, 2019USD ($)	Mar. 31, 2019USD ($)loan	Dec. 31, 2014USD ($)	Dec. 31, 2018USD ($)	Aug. 31, 2018
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 7,608,000,000
Georgia Power
Debt Instrument [Line Items]
Percent of eligible project costs (may not exceed)		70.00%
Line of credit facility, maximum borrowing capacity	$ 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%
Term Loan | Georgia Power
Debt Instrument [Line Items]
Number of term loan facilities | loan		2
FFB Loan | Georgia Power
Debt Instrument [Line Items]
Eligible project costs to be reimbursed			$ 5,130,000,000
Proceeds from lines of credit	$ 383,000,000	$ 835,000,000
Fixed stated interest rate of debt obligation	2.537%	3.213%
Line of credit facility, maximum borrowing capacity	$ 3,800,000,000			$ 2,600,000,000
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%
Ownership interest percentage required for voting for continuing construction					90.00%

FINANCING - Secured Debt (Detai

FINANCING - Secured Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Oct. 24, 2019	Dec. 31, 2018
Debt Disclosure [Line Items]
Finance lease obligations	$ 226
Finance lease obligations			$ 197
Georgia Power
Debt Disclosure [Line Items]
Finance lease obligations	$ 156
Finance lease obligations			142
Georgia Power | Plant Vogtle Units 3 And 4
Debt Disclosure [Line Items]
Percent ownership	45.70%
Georgia Power | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	$ 3,999		2,767
Mississippi Power
Debt Disclosure [Line Items]
Percent ownership		50.00%
Finance lease obligations	0
Mississippi Power | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	270		270
Southern Company Gas
Debt Disclosure [Line Items]
Finance lease obligations	0
Southern Company Gas | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	$ 1,575		$ 1,325

FINANCING - Equity Units (Detai

FINANCING - Equity Units (Details) - USD ($)	1 Months Ended
	Aug. 31, 2019	Dec. 31, 2019
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 Debt
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity units, settlement terms, contract adjustment payments, accretion period	3 years
Series 2019A Remarketable Junior Subordinated Notes | Junior Subordinated Debt
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 2019A And Series 2019B Remarketable Junior Subordinated Notes | Junior Subordinated Debt
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	$ 185,000,000
Purchase contract adjustment liability, current		$ 66,000,000
Series 2019B Remarketable Junior Subordinated Notes | Junior Subordinated Debt
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, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Expires, 2020	$ 33,000,000
Expires, 2022	675,000,000
Expires, 2024	6,900,000,000
Total	7,608,000,000
Unused	7,576,000,000
Due within One Year	33,000,000
Southern Company
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	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, 2020	3,000,000
Expires, 2022	525,000,000
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, 2020	0
Expires, 2022	0
Expires, 2024	1,750,000,000
Total	1,750,000,000
Unused	1,733,000,000
Due within One Year	0
Mississippi Power
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	150,000,000
Expires, 2024	0
Total	150,000,000
Unused	150,000,000
Due within One Year	0
Southern Power
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	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
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	97,000,000	$ 103,000,000
Southern Company Gas
Line of Credit Facility [Line Items]
Expires, 2020	0
Expires, 2022	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, 2020	30,000,000
Expires, 2022	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 ($)	12 Months Ended
	Dec. 31, 2019	Feb. 19, 2020	Dec. 31, 2018
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	$ 1,400,000,000
Remarketed pollution control bonds	275,000,000
Line of credit facility, maximum borrowing capacity	7,608,000,000
Unused credit with banks	$ 7,576,000,000
Other Subsidiaries
Debt Disclosure [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	65.00%
Line of credit facility, maximum borrowing capacity	$ 30,000,000
Unused credit with banks	30,000,000
Alabama Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	854,000,000
Remarketed pollution control bonds	87,000,000
Line of credit facility, maximum borrowing capacity	1,328,000,000
Unused credit with banks	1,328,000,000
Georgia Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	550,000,000
Remarketed pollution control bonds	188,000,000
Line of credit facility, maximum borrowing capacity	1,750,000,000
Unused credit with banks	1,733,000,000
Mississippi Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	40,000,000
Line of credit facility, maximum borrowing capacity	150,000,000
Unused credit with banks	150,000,000
Southern Power
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity	600,000,000
Unused credit with banks	591,000,000
Southern Power | Continuing Letter of Credit Facility
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity	120,000,000
Unused credit with banks	97,000,000		$ 103,000,000
Southern Power | Continuing Letter of Credit Facility | Subsequent Event
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity		$ 60,000,000
Southern Power | Power Purchase Agreement
Debt Disclosure [Line Items]
Unused credit with banks	23,000,000
Debt instrument, collateral amount	$ 104,000,000		$ 103,000,000

FINANCING - Notes Payable (Deta

FINANCING - Notes Payable (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount Outstanding	$ 2,055	$ 2,915
Weighted Average Interest Rate	2.10%	3.10%
Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 1,705	$ 1,064
Weighted Average Interest Rate	2.10%	3.00%
Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 350	$ 1,851
Weighted Average Interest Rate	2.30%	3.10%
Georgia Power
Short-term Debt [Line Items]
Amount Outstanding	$ 365	$ 294
Weighted Average Interest Rate	2.20%	3.10%
Georgia Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 115	$ 294
Weighted Average Interest Rate	2.10%	3.10%
Georgia Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 250	$ 0
Weighted Average Interest Rate	2.20%	0.00%
Southern Power
Short-term Debt [Line Items]
Amount Outstanding	$ 549	$ 100
Weighted Average Interest Rate	2.20%	3.10%
Southern Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 449	$ 0
Weighted Average Interest Rate	2.10%	0.00%
Southern Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 100	$ 100
Weighted Average Interest Rate	2.60%	3.10%
Southern Company Gas
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 650
Southern Company Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 650
Weighted Average Interest Rate	2.00%	3.00%
Southern Company Gas Capital | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 372	$ 403
Weighted Average Interest Rate	2.10%	3.10%
Nicor Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 278	$ 247
Weighted Average Interest Rate	1.80%	3.00%

FINANCING - Outstanding Classes

FINANCING - Outstanding Classes of Capital Stock Narrative (Details)	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares
Debt Instrument [Line Items]
Stock issued employee and director stock plans (in shares)	19,500,000
Proceeds from issuance of shares under share-based compensation plans | $	$ 844,000,000
Number of shares reserved for issuance to stock-based compensation plan (in shares)	104,000,000
Southern Company Common Stock
Debt Instrument [Line Items]
Remaining shares available for awards (in shares)	9,000,000
Alabama Power | 5.00% Class A Preferred Stock
Debt Instrument [Line Items]
Shares outstanding (in shares)	10,000,000	10,000,000
Temporary equity, dividend rate percentage	0.05	0.0500
Preferred stock, par value (in dollars per share) | $ / shares		$ 1
Temporary equity, par value (in dollars per share) | $ / shares	$ 25	$ 25
Alabama Power | 5.00% Class A Preferred Stock | Aggregate Stated Capital
Debt Instrument [Line Items]
Debt instrument, face amount | $		$ 250,000,000
Alabama Power | 5.30% Class A Preferred Stock
Debt Instrument [Line Items]
Shares outstanding (in shares)		2,000,000
Temporary equity, dividend rate percentage		0.0650
Alabama Power | 5.30% Class A Preferred Stock | Aggregate Stated Capital
Debt Instrument [Line Items]
Debt instrument, face amount | $		$ 50,000,000
Alabama Power | 5.625% Preference Stock
Debt Instrument [Line Items]
Shares outstanding (in shares)		6,000,000
Temporary equity, dividend rate percentage		0.0645
Alabama Power | 5.625% Preference Stock | Aggregate Stated Capital
Debt Instrument [Line Items]
Debt instrument, face amount | $		$ 150,000,000
Alabama Power | 5.83% Class A Preferred Stock
Debt Instrument [Line Items]
Shares outstanding (in shares)		1,520,000
Temporary equity, dividend rate percentage		0.0583
Alabama Power | 5.83% Class A Preferred Stock | Aggregate Stated Capital
Debt Instrument [Line Items]
Debt instrument, face amount | $		$ 38,000,000

FINANCING - Diluted Earnings Pe

FINANCING - Diluted Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
As reported shares	1,046	1,020	1,000
Effect of stock-based compensation	8	5	8
Diluted shares	1,054	1,025	1,008

FINANCING - Schedule of Tempora

FINANCING - Schedule of Temporary Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	$ 291
Redeemed	0	$ (33)	$ (658)
Ending balance	291	291
Redeemable Preferred Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	291	324	118
Issued			250
Redeemed		(33)	(38)
Issuance costs			(6)
Ending balance	$ 291	$ 291	$ 324

FINANCING - Preferred Stock Red

FINANCING - Preferred Stock Redemption (Details) - Alabama Power	12 Months Ended
	Dec. 31, 2019$ / sharesshares	Dec. 31, 2017$ / sharesshares	Oct. 02, 2022$ / shares
4.92% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage	0.0492
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.0472
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.0464
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.046
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.0452
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.042
Temporary equity, par value (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]
Temporary equity, dividend rate percentage	0.05	0.0500
Temporary equity, par value (in dollars per share)	$ 25	$ 25
Shares outstanding (in shares) | shares	10,000,000	10,000,000
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, 2019USD ($)
Variable Interest Entity [Line Items]
Undistributed retained earnings of subsidiaries	$ 5,300
Southern Company Gas
Variable Interest Entity [Line Items]
Retained earnings, unappropriated	$ 951
Southern Company Gas | Southern Company Gas Capital | 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) $ in Millions	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Lease obligations	$ 2,070
Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	160
Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,582
Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	6
Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	398
Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	92
Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	990
Electric generating units | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	125
Electric generating units | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,487
Electric generating units | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Electric generating units | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Electric generating units | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0
Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	782
Real estate/land | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	4
Real estate/land | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	54
Real estate/land | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	2
Real estate/land | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	398
Real estate/land | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	74
Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	154
Communication towers | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	2
Communication towers | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	3
Communication towers | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Communication towers | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Communication towers | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	18
Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	51
Railcars | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	21
Railcars | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	26
Railcars | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	3
Railcars | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Railcars | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0
Other
Lessee, Lease, Description [Line Items]
Lease obligations	93
Other | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	8
Other | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	12
Other | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	1
Other | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0
Other | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	$ 0

LEASES - Narrative (Details)

LEASES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)MW
Lessee, Lease, Description [Line Items]
Operating leases	14 years 2 months 12 days
Operating lease obligations	$ 1,844
Minimum lease payments	$ 2,702
Maximum | Real estate
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
Maximum | Communication towers
Lessee, Lease, Description [Line Items]
Lessee, lease term	15 years
Lessee, renewal period	20 years
Maximum | Fuel cells
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	15 years
Georgia Power
Lessee, Lease, Description [Line Items]
Operating leases	10 years 2 months 12 days
Operating lease obligations	$ 1,426
Minimum lease payments	$ 1,790
Southern Company Gas
Lessee, Lease, Description [Line Items]
Operating leases	9 years 10 months 24 days
Operating lease obligations	$ 92
Minimum lease payments	$ 114
Southern Company Gas | Maximum
Lessee, Lease, Description [Line Items]
Lessor, remaining term	23 years
Southern Power
Lessee, Lease, Description [Line Items]
Operating leases	32 years 9 months 18 days
Operating lease obligations	$ 398
Minimum lease payments	$ 932
Southern Power | Maximum | Land
Lessee, Lease, Description [Line Items]
Lessee, lease term	47 years
Southern Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	27 years
Alabama Power
Lessee, Lease, Description [Line Items]
Operating leases	3 years 1 month 6 days
Operating lease obligations	$ 156
PPA, additional generating capacity (in MWs) | MW	640
Operating lease, term of contract	20 years
Finance lease, term of contract	28 years
Minimum lease payments	$ 165
Alabama Power | Electric generating units
Lessee, Lease, Description [Line Items]
Minimum lease payments	$ 95
Alabama Power | Minimum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating leases	3 years
Alabama Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating leases	18 years
Mississippi Power
Lessee, Lease, Description [Line Items]
Operating leases	7 years
Operating lease obligations	$ 6
Minimum lease payments	$ 7
Mississippi Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, lease term, sales-type lease	20 years
Affiliate | Georgia Power | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 624
Traditional Electric Operating Companies | Maximum | Outdoor lighting
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	7 years

LEASES - Balance Sheet Amounts

LEASES - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) $ in Millions	Dec. 31, 2019USD ($)
Operating Leases
Operating lease ROU assets, net	$ 1,800
Operating lease obligations - current	229
Operating lease obligations - non-current	1,615
Total operating lease obligations	1,844
Finance Leases
Finance lease ROU assets, net	216
Finance lease obligations - current	21
Finance lease obligations - non-current	205
Total finance lease obligations	226
Alabama Power
Operating Leases
Operating lease ROU assets, net	132
Operating lease obligations - current	49
Operating lease obligations - non-current	107
Total operating lease obligations	156
Finance Leases
Finance lease ROU assets, net	4
Finance lease obligations - current	1
Finance lease obligations - non-current	3
Total finance lease obligations	4
Georgia Power
Operating Leases
Operating lease ROU assets, net	1,428
Operating lease obligations - current	144
Operating lease obligations - non-current	1,282
Total operating lease obligations	1,426
Finance Leases
Finance lease ROU assets, net	130
Finance lease obligations - current	11
Finance lease obligations - non-current	145
Total finance lease obligations	156
Mississippi Power
Operating Leases
Operating lease ROU assets, net	6
Operating lease obligations - current	2
Operating lease obligations - non-current	4
Total operating lease obligations	6
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	0
Southern Power
Operating Leases
Operating lease ROU assets, net	369
Operating lease obligations - current	22
Operating lease obligations - non-current	376
Total operating lease obligations	398
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	0
Southern Company Gas
Operating Leases
Operating lease ROU assets, net	93
Operating lease obligations - current	14
Operating lease obligations - non-current	78
Total operating lease obligations	92
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	$ 0

LEASES - Lease Costs (Details)

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

LEASES - Rent Expense and PPA C

LEASES - Rent Expense and PPA Capacity Expense Related to Leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Lessee, Lease, Description [Line Items]
Rent expense	$ 192	$ 176
PPA capacity expense	231	235
Alabama Power
Lessee, Lease, Description [Line Items]
Rent expense	23	25
PPA capacity expense	44	41
Georgia Power
Lessee, Lease, Description [Line Items]
Rent expense	34	31
PPA capacity expense	206	225
Operating leases, contingent rent expense (2018 - Immaterial)	72,000,000	73,000,000
Mississippi Power
Lessee, Lease, Description [Line Items]
Rent expense	4	3
PPA capacity expense	0	0
Operating leases, contingent rent expense (2018 - Immaterial)	10,000,000	5,000,000
Southern Power
Lessee, Lease, Description [Line Items]
Rent expense	31	29
PPA capacity expense	0	0
Southern Company Gas
Lessee, Lease, Description [Line Items]
Rent expense	15	15
PPA capacity expense	0	0
Affiliate Operating Lease PPA | Georgia Power
Lessee, Lease, Description [Line Items]
Operating leases, contingent rent expense (2018 - Immaterial)	$ 29,000,000	$ 29,000,000

LEASES - Other Information (Det

LEASES - Other Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 323
Operating cash flows from finance leases	10
Financing cash flows from finance leases	32
ROU assets obtained in exchange for new operating lease obligations	118
ROU assets obtained in exchange for new finance lease obligations	$ 35
Weighted-average remaining lease term in years:
Operating leases	14 years 2 months 12 days
Finance leases	18 years 9 months 18 days
Weighted-average discount rate:
Operating leases	4.53%
PPA capacity expense	5.04%
Alabama Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 54
Operating cash flows from finance leases	0
Financing cash flows from finance leases	1
ROU assets obtained in exchange for new operating lease obligations	7
ROU assets obtained in exchange for new finance lease obligations	$ 2
Weighted-average remaining lease term in years:
Operating leases	3 years 1 month 6 days
Finance leases	12 years 1 month 6 days
Weighted-average discount rate:
Operating leases	3.33%
PPA capacity expense	3.60%
Georgia Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 210
Operating cash flows from finance leases	19
Financing cash flows from finance leases	13
ROU assets obtained in exchange for new operating lease obligations	21
ROU assets obtained in exchange for new finance lease obligations	$ 24
Weighted-average remaining lease term in years:
Operating leases	10 years 2 months 12 days
Finance leases	10 years 6 months
Weighted-average discount rate:
Operating leases	4.46%
PPA capacity expense	10.76%
Mississippi Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 3
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	7 years
Weighted-average discount rate:
Operating leases	4.02%
Southern Power
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 27
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	2
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	32 years 9 months 18 days
Weighted-average discount rate:
Operating leases	5.66%
Southern Company Gas
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 18
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	19
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	9 years 10 months 24 days
Weighted-average discount rate:
Operating leases	3.70%

LEASES - Maturities of Lease Li

LEASES - Maturities of Lease Liabilities (Details) $ in Millions	Dec. 31, 2019USD ($)
Operating leases:
2020	$ 289
2021	268
2022	260
2023	208
2024	163
Thereafter	1,514
Total	2,702
Less: Present value discount	858
Operating lease obligations, including held for sale	1,844
Operating lease obligations	1,844
Finance leases:
2020	31
2021	25
2022	22
2023	18
2024	15
Thereafter	246
Total	357
Less: Present value discount	131
Finance lease obligations	226
Alabama Power
Operating leases:
2020	54
2021	52
2022	53
2023	4
2024	1
Thereafter	1
Total	165
Less: Present value discount	9
Operating lease obligations	156
Finance leases:
2020	1
2021	1
2022	1
2023	1
2024	0
Thereafter	0
Total	4
Less: Present value discount	0
Finance lease obligations	4
Georgia Power
Operating leases:
2020	205
2021	198
2022	197
2023	198
2024	161
Thereafter	831
Total	1,790
Less: Present value discount	364
Operating lease obligations	1,426
Finance leases:
2020	28
2021	24
2022	25
2023	25
2024	25
Thereafter	134
Total	261
Less: Present value discount	105
Finance lease obligations	156
Mississippi Power
Operating leases:
2020	2
2021	1
2022	1
2023	1
2024	0
Thereafter	2
Total	7
Less: Present value discount	1
Operating lease obligations	6
Finance leases:
2020	0
2021	0
2022	0
2023	0
2024	0
Thereafter	0
Total	0
Less: Present value discount
Finance lease obligations	0
Southern Power
Operating leases:
2020	26
2021	23
2022	23
2023	24
2024	24
Thereafter	812
Total	932
Less: Present value discount	534
Operating lease obligations	398
Finance leases:
2020	0
2021	0
2022	0
2023	0
2024	0
Thereafter	0
Total	0
Less: Present value discount
Finance lease obligations	0
Southern Company Gas
Operating leases:
2020	18
2021	17
2022	14
2023	11
2024	10
Thereafter	44
Total	114
Less: Present value discount	22
Operating lease obligations	92
Finance leases:
2020	0
2021	0
2022	0
2023	0
2024	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	$ 0

LEASES - Leases Not Yet Commenc

LEASES - Leases Not Yet Commenced (Details) $ in Millions	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Longest lease term expiration	40 years
Estimated total obligations	$ 248
Alabama Power
Lessee, Lease, Description [Line Items]
Estimated total obligations	95
Mississippi Power
Lessee, Lease, Description [Line Items]
Estimated total obligations	23
Southern Power
Lessee, Lease, Description [Line Items]
Estimated total obligations	$ 87
Minimum
Lessee, Lease, Description [Line Items]
Longest lease term expiration	15 years
Maximum
Lessee, Lease, Description [Line Items]
Longest lease term expiration	40 years
Maximum | Alabama Power
Lessee, Lease, Description [Line Items]
Longest lease term expiration	28 years
Maximum | Mississippi Power
Lessee, Lease, Description [Line Items]
Longest lease term expiration	15 years
Maximum | Southern Power
Lessee, Lease, Description [Line Items]
Longest lease term expiration	40 years

LEASES - Lease Income (Details)

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

LEASES - Undiscounted Cash Flow

LEASES - Undiscounted Cash Flows to be Received Under Tolling Arrangements Accounted for as Sales-type Leases (Details) $ in Millions	Dec. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
2020	$ 17
2021	15
2022	15
2023	14
2024	14
Thereafter	138
Total undiscounted cash flows	213
Lease receivable()	118
Difference between undiscounted cash flows and discounted cash flows	95
Mississippi Power
Lessor, Lease, Description [Line Items]
2020	17
2021	15
2022	15
2023	14
2024	14
Thereafter	138
Total undiscounted cash flows	213
Lease receivable()	118
Difference between undiscounted cash flows and discounted cash flows	$ 95

LEASES - Undiscounted Cash Fl_2

LEASES - Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases (Details) $ in Millions	Dec. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
2020	$ 155
2021	141
2022	125
2023	110
2024	103
Thereafter	1,063
Total	1,697
Alabama Power
Lessor, Lease, Description [Line Items]
2020	26
2021	23
2022	16
2023	7
2024	3
Thereafter	20
Total	95
Georgia Power
Lessor, Lease, Description [Line Items]
2020	26
2021	19
2022	8
2023	2
2024	0
Thereafter	0
Total	55
Southern Power
Lessor, Lease, Description [Line Items]
2020	84
2021	86
2022	87
2023	88
2024	90
Thereafter	387
Total	822
Southern Company Gas
Lessor, Lease, Description [Line Items]
2020	35
2021	35
2022	35
2023	34
2024	33
Thereafter	463
Total	$ 635

INCOME TAXES - Current and Defe

INCOME TAXES - Current and Deferred Income Tax Provisions (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal —
Current		$ 156	$ 167	$ (62)
Deferred		1,237	231	(6)
Total federal taxes		1,393	398	(68)
State —
Current		275	188	37
Deferred		130	(137)	173
Total state taxes		405	51	210
Income taxes		1,798	449	142
Alabama Power
Federal —
Current		61	91	136
Deferred		125	123	336
Total federal taxes		186	214	472
State —
Current		12	26	23
Deferred		72	51	73
Total state taxes		84	77	96
Income taxes		270	291	568
Georgia Power
Federal —
Current		264	393	256
Deferred		180	(249)	504
Total federal taxes		444	144	760
State —
Current		6	81	116
Deferred		22	(11)	(46)
Total state taxes		28	70	70
Income taxes		472	214	830
Mississippi Power
Federal —
Current		(6)	(567)	194
Deferred		26	575	(753)
Total federal taxes		20	8	(559)
State —
Current		(1)	(10)	0
Deferred		11	(100)	27
Total state taxes		10	(110)	27
Income taxes		30	(102)	(532)
Southern Power
Federal —
Current		(717)	85	(566)
Deferred		647	(154)	(312)
Total federal taxes		(70)	(69)	(878)
State —
Current		1	(9)	(110)
Deferred		13	(86)	49
Total state taxes		14	(95)	(61)
Income taxes	$ 75	(56)	(164)	(939)
Southern Company Gas
Federal —
Current		(120)	334	103
Deferred		195	33	170
Total federal taxes		75	367	273
State —
Current		37	131	27
Deferred		18	(34)	67
Total state taxes		55	97	94
Income taxes		$ 130	$ 464	$ 367

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)operating_facility	Sep. 30, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Income Tax Disclosure [Line Items]
Deferred income tax assets			$ 9,048,000,000	$ 8,680,000,000	$ 9,048,000,000
Income tax benefit				$ (1,798,000,000)	(449,000,000)	$ (142,000,000)
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern				12 months
Unrecognized tax benefits			0		0	18,000,000	$ 484,000,000
Decrease in unrecognized tax benefits from prior periods					18,000,000	196,000,000
ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,730,000,000	$ 2,098,000,000	2,730,000,000
Southern Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,631,000,000	$ 1,917,000,000	2,631,000,000
Percentage reduction in tax basis of assets				50.00%
Number of wind facilities | operating_facility	8
Income tax benefit			(75,000,000)	$ 56,000,000	164,000,000	939,000,000
Unrecognized tax benefits			0		0	0	17,000,000
Decrease in unrecognized tax benefits from prior periods					0	17,000,000
Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				734,000,000	5,000,000	0
Southern Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,128,000,000	1,445,000,000	2,128,000,000
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				5,000,000	1,000,000	18,000,000
Southern Power | Production Tax Credit Carryforward
Income Tax Disclosure [Line Items]
Effective income tax rate reconciliation, tax credit, production, amount				12,000,000	141,000,000	139,000,000
Georgia Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			3,078,000,000	3,123,000,000	3,078,000,000
Income tax benefit				(472,000,000)	(214,000,000)	(830,000,000)
State investment tax credit carryforward				360,000,000
Georgia Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			430,000,000	435,000,000	430,000,000
Mississippi Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			515,000,000	451,000,000	515,000,000
Income tax benefit				(30,000,000)	102,000,000	532,000,000
Unrecognized tax benefits			0		0	0	$ 465,000,000
Decrease in unrecognized tax benefits from prior periods					0	177,000,000
Mississippi Power | Kemper IGCC
Income Tax Disclosure [Line Items]
Unrecognized tax benefits						176,000,000
Decrease in unrecognized tax benefits from prior periods		$ 36,000,000
Mississippi Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			0	0	0
State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Income tax benefit	$ 65,000,000
State and Local Jurisdiction | Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits						32,000,000
State and Local Jurisdiction | Georgia Power
Income Tax Disclosure [Line Items]
Valuation allowance				28,000,000
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				51,000,000	21,000,000	37,000,000
Deferred Charges Related To Income Taxes, Current | Other Noncurrent Assets | Southern Power | Unrealized Tax Credits
Income Tax Disclosure [Line Items]
Deferred income tax assets			$ 128,000,000	51,000,000	$ 128,000,000	$ 316,000,000
Mississippi | State and Local Jurisdiction | Mississippi Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance				32,000,000
Oklahoma | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance				16,000,000
Florida | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance				$ 11,000,000

INCOME TAXES - Amortization of

INCOME TAXES - Amortization of Deferred Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 181	$ 87	$ 79
Southern Power
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 151	$ 58	$ 57

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	4.90%	1.80%	12.50%
Employee stock plans' dividend deduction	(0.40%)	(1.00%)	(4.00%)
Non-deductible book depreciation	0.30%	0.80%	3.10%
Flowback of excess deferred income taxes	(2.10%)	(4.00%)	(0.30%)
AFUDC-Equity	(0.40%)	(1.00%)	(2.60%)
ITC basis difference	(0.10%)	(0.60%)	(1.70%)
AFUDC-Equity portion of Kemper IGCC charge			15.70%
Federal PTCs		(4.70%)	(12.10%)
Amortization of ITC	(0.80%)	(2.00%)	(4.20%)
Tax impact on sale of subsidiaries	5.10%	8.60%
Tax Reform Legislation		(1.40%)	(25.60%)
Noncontrolling interests	0.00%	(0.40%)	(1.40%)
Other	0.00%	(0.80%)	(1.10%)
Effective income tax (benefit) rate	27.50%	16.30%	13.30%
Alabama Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	4.90%	5.00%	4.50%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.60%	0.60%	0.90%
Flowback of excess deferred income taxes	(5.30%)	(1.80%)	0.00%
AFUDC-Equity	(0.80%)	(1.00%)	(1.00%)
ITC basis difference	0.00%	0.00%	0.00%
AFUDC-Equity portion of Kemper IGCC charge			0.00%
Federal PTCs		0.00%	0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.20%)
Tax impact on sale of subsidiaries	0.00%	0.00%
Tax Reform Legislation		0.00%	0.30%
Noncontrolling interests	0.00%	0.00%	0.00%
Other	(0.40%)	(0.10%)	0.10%
Effective income tax (benefit) rate	19.90%	23.60%	39.60%
Georgia Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	1.00%	5.50%	2.00%
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.50%	1.20%	0.70%
Flowback of excess deferred income taxes	0.00%	0.00%	(0.10%)
AFUDC-Equity	(0.60%)	(1.40%)	(0.60%)
ITC basis difference	0.00%	0.00%	0.00%
AFUDC-Equity portion of Kemper IGCC charge			0.00%
Federal PTCs		0.00%	0.00%
Amortization of ITC	(0.10%)	(0.20%)	(0.10%)
Tax impact on sale of subsidiaries	0.00%	0.00%
Tax Reform Legislation		(4.90%)	(0.40%)
Noncontrolling interests	0.00%	0.00%	0.00%
Other	(0.30%)	0.10%	0.20%
Effective income tax (benefit) rate	21.50%	21.30%	36.70%
Mississippi Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	4.30%	(65.10%)	(0.60%)
Employee stock plans' dividend deduction	0.00%	0.00%	0.00%
Non-deductible book depreciation	0.40%	0.70%	(0.10%)
Flowback of excess deferred income taxes	(12.60%)	(4.10%)	0.00%
AFUDC-Equity	(0.10%)	0.00%	0.00%
ITC basis difference	0.00%	0.00%	0.00%
AFUDC-Equity portion of Kemper IGCC charge			(5.30%)
Federal PTCs		0.00%	0.00%
Amortization of ITC	(0.10%)	(0.20%)	0.00%
Tax impact on sale of subsidiaries	0.00%	0.00%
Tax Reform Legislation		(26.30%)	(11.90%)
Noncontrolling interests	0.00%	0.00%	0.00%
Other	4.90%	(1.40%)	0.00%
Effective income tax (benefit) rate	17.80%	(75.40%)	17.10%
Southern Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	4.00%	(90.80%)	(22.20%)
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	0.00%	0.00%	0.00%
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference	(1.90%)	(0.20%)	(10.00%)
AFUDC-Equity portion of Kemper IGCC charge			0.00%
Federal PTCs		(156.60%)	(72.50%)
Amortization of ITC	(16.10%)	(55.40%)	(20.60%)
Tax impact on sale of subsidiaries	(27.60%)	0.00%
Tax Reform Legislation		96.10%	(416.10%)
Noncontrolling interests	0.80%	(14.90%)	(8.60%)
Other	(0.60%)	2.00%	(10.70%)
Effective income tax (benefit) rate	(20.40%)	(198.80%)	(525.70%)
Southern Company Gas
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	21.00%	21.00%	35.00%
State income tax, net of federal deduction	6.10%	9.20%	10.00%
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	(6.00%)	(3.00%)	(0.20%)
AFUDC-Equity	0.00%	0.00%	0.00%
ITC basis difference	0.00%	0.00%	0.00%
AFUDC-Equity portion of Kemper IGCC charge			0.00%
Federal PTCs		0.00%	0.00%
Amortization of ITC	(0.10%)	(0.10%)	(0.20%)
Tax impact on sale of subsidiaries	(1.40%)	28.50%
Tax Reform Legislation		(0.40%)	15.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Other	(1.40%)	0.30%	0.60%
Effective income tax (benefit) rate	18.20%	55.50%	60.20%

INCOME TAXES - Deferred Tax Ass

INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred tax liabilities —
Deferred income tax liabilities	$ 16,261	$ 15,207
Deferred tax assets —
Deferred income tax assets	8,680	9,048
Valuation allowance	(137)	(123)
Net deferred income tax assets	8,543	8,925
Net deferred income taxes liabilities	7,718	6,282
Accumulated deferred income taxes – assets	(170)	(276)
Accumulated deferred income taxes – liabilities	7,888	6,558
Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	8,711	8,461
Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	1,843	1,807
Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	277	260
Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	236	253
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	704	477
Deferred tax assets —
Deferred income tax assets	1,385	1,273
Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	83	88
Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	109	111
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	1,174	975
Regulatory assets associated with remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	341	56
AROs
Deferred tax liabilities —
Deferred income tax liabilities	1,723	1,232
AROs
Deferred tax liabilities —
Deferred income tax liabilities	814	1,210
Other
Deferred tax liabilities —
Deferred income tax liabilities	523	537
Other property basis differences
Deferred tax assets —
Deferred income tax assets	230	251
ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	2,098	2,730
Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		62
Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	169	162
Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	112	82
AROs
Deferred tax assets —
Deferred income tax assets	2,537	2,442
Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	283	346
Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	402	415
Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	401	294
Other
Deferred tax assets —
Deferred income tax assets	786	731
Alabama Power
Deferred tax liabilities —
Deferred income tax liabilities	5,161	4,584
Deferred tax assets —
Deferred income tax assets	1,901	1,622
Valuation allowance	0	0
Net deferred income tax assets	1,901	1,622
Net deferred income taxes liabilities	3,260	2,962
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,260	2,962
Alabama Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	2,402	2,236
Alabama Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	912	865
Alabama Power | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	162	155
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	242	149
Deferred tax assets —
Deferred income tax assets	334	286
Alabama Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	13	14
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	311	260
Alabama Power | Regulatory assets associated with remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	174	6
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	613	276
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	360	607
Alabama Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	134	171
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	11	11
Alabama Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		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	8	10
Alabama Power | AROs
Deferred tax assets —
Deferred income tax assets	973	883
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	240	130
Alabama Power | Other
Deferred tax assets —
Deferred income tax assets	173	147
Georgia Power
Deferred tax liabilities —
Deferred income tax liabilities	6,345	6,098
Deferred tax assets —
Deferred income tax assets	3,123	3,078
Valuation allowance	(35)	(42)
Net deferred income tax assets	3,088	3,036
Net deferred income taxes liabilities	3,257	3,062
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,257	3,062
Georgia Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	3,058	3,005
Georgia Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	643	633
Georgia Power | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	63	71
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	351	290
Deferred tax assets —
Deferred income tax assets	488	444
Georgia Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	70	74
Georgia Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	109	111
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	403	344
Georgia Power | Regulatory assets associated with remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	159	39
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	1,066	925
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	405	575
Georgia Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	81	102
Georgia Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	65	61
Georgia Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	435	430
Georgia Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		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	18	3
Georgia Power | AROs
Deferred tax assets —
Deferred income tax assets	1,471	1,500
Georgia Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	283	283
Georgia Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	13	19
Georgia Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	133	127
Georgia Power | Other
Deferred tax assets —
Deferred income tax assets	154	140
Mississippi Power
Deferred tax liabilities —
Deferred income tax liabilities	695	702
Deferred tax assets —
Deferred income tax assets	451	515
Valuation allowance	(41)	(41)
Net deferred income tax assets	410	474
Net deferred income taxes liabilities	285	228
Accumulated deferred income taxes – assets	(139)	(150)
Accumulated deferred income taxes – liabilities	424	378
Mississippi Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	315	335
Mississippi Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	143	162
Mississippi Power | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	24	36
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	38	25
Deferred tax assets —
Deferred income tax assets	72	62
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	55	45
Mississippi Power | Regulatory assets associated with remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	8	11
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	44	31
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	68	57
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 | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		32
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	44	31
Mississippi Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	63
Mississippi Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	251	251
Mississippi Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	28	29
Mississippi Power | Other
Deferred tax assets —
Deferred income tax assets	56	47
Southern Power
Deferred tax liabilities —
Deferred income tax liabilities	1,445	1,523
Deferred tax assets —
Deferred income tax assets	1,917	2,631
Valuation allowance	(36)	(27)
Net deferred income tax assets	1,881	2,604
Net deferred income taxes assets	(436)	(1,081)
Accumulated deferred income taxes – assets	(551)	(1,186)
Accumulated deferred income taxes – liabilities	115	105
Southern Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,422	1,483
Southern Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	24	22
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	6
Deferred tax assets —
Deferred income tax assets	5	7
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 | Regulatory assets associated with 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	11	34
Southern Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	146	172
Southern Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	1,445	2,128
Southern Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		21
Southern Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	169	162
Southern Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	10	0
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	72	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	46	47
Southern Company Gas
Deferred tax liabilities —
Deferred income tax liabilities	1,676	1,493
Deferred tax assets —
Deferred income tax assets	462	489
Valuation allowance	(5)	(12)
Net deferred income tax assets	457	477
Net deferred income taxes liabilities	1,219	1,016
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	1,219	1,016
Southern Company Gas | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,288	1,176
Southern Company Gas | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	133	134
Southern Company Gas | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	56	46
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	12	6
Deferred tax assets —
Deferred income tax assets	111	150
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 | Regulatory assets associated with 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	198	132
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 | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		0
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	8	0
Southern Company Gas | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	0	8
Southern Company Gas | Other
Deferred tax assets —
Deferred income tax assets	$ 287	$ 285

INCOME TAXES - Federal ITC_PTC

INCOME TAXES - Federal ITC/PTC Carryforwards (Details) - ITC and PTC carryforward $ in Millions	Dec. 31, 2019USD ($)
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 1,751
Alabama Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	11
Georgia Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	88
Southern Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 1,445

INCOME TAXES - NOL Carryforward

INCOME TAXES - NOL Carryforwards (Details) $ in Millions	Dec. 31, 2019USD ($)
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	$ 306
Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	201
Southern Power
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	54
Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	39
Southern Power | Florida
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	11
Southern Power | South Carolina
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	2
Southern Power | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	2
Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	18
Other Subsidiaries | Georgia
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	7
Other Subsidiaries | New York
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	11
Other Subsidiaries | New York City
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	15
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	7,230
State and Local Jurisdiction | Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	5,099
State and Local Jurisdiction | Southern Power
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	1,165
State and Local Jurisdiction | Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	830
State and Local Jurisdiction | Southern Power | Florida
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	258
State and Local Jurisdiction | Southern Power | South Carolina
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	56
State and Local Jurisdiction | Southern Power | Other states
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	21
State and Local Jurisdiction | Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	368
State and Local Jurisdiction | Other Subsidiaries | Georgia
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	171
State and Local Jurisdiction | Other Subsidiaries | New York
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	220
State and Local Jurisdiction | Other Subsidiaries | New York City
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	$ 207

INCOME TAXES - Changes in Unrec

INCOME TAXES - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 18	$ 484
Increase from current periods		10
Increase from prior periods		10
Decrease from prior periods	(18)	(196)
Reductions due to settlements		(290)
Balance at end of year	0	18
Mississippi Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	465
Increase from current periods		0
Increase from prior periods		2
Decrease from prior periods	0	(177)
Reductions due to settlements		(290)
Balance at end of year	0	0
Southern Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	17
Increase from current periods		0
Increase from prior periods		0
Decrease from prior periods	0	(17)
Reductions due to settlements		0
Balance at end of year	$ 0	$ 0

INCOME TAXES - Impact of Unreco

INCOME TAXES - Impact of Unrecognized Tax Benefits on Effective Tax Rate, If Recognized (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Impact on effective tax rate
Tax positions impacting the effective tax rate		$ 18
Tax positions not impacting the effective tax rate		0
Balance of unrecognized tax benefits	$ 0	$ 18	$ 484

RETIREMENT BENEFITS - Schedule

RETIREMENT BENEFITS - Schedule of Voluntarily Contributions (Details) - Pension plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	$ 1,208	$ 55
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	383	13
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	243	14
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	59	3
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	7	0
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	144	$ 2
Qualified pension plan
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	1,136
Qualified pension plan | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	362
Qualified pension plan | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	200
Qualified pension plan | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	54
Qualified pension plan | Southern Power
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	24
Qualified pension plan | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Contributions to qualified pension plan	$ 145

RETIREMENT BENEFITS - Narrative

RETIREMENT BENEFITS - Narrative (Details)	1 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)employee	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Defined Benefit Plan Disclosure [Line Items]
Plan asset amortization period		5 years
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Prior service costs and net gains/losses in OCI	$ 36,000,000
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	13,808,000,000	$ 14,788,000,000	$ 12,763,000,000
Plan assets	$ 12,992,000,000	14,057,000,000	11,611,000,000
Actuarial gain (loss)		$ (2,346,000,000)	$ 1,143,000,000
Change in discount rate		1.08%	0.69%
Pension plans | Qualified pension plan
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year		$ 0
Projected benefit obligation		14,055,000,000
Pension plans | Southern Company Services, Inc.
Defined Benefit Plan Disclosure [Line Items]
Number of employees transferred | employee	538
Pension plans | Southern Power
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 139,000,000	185,000,000	$ 123,000,000
Plan assets	138,000,000	169,000,000	123,000,000
Actuarial gain (loss)		(54,000,000)	24,000,000
Pension plans | Southern Power | Qualified pension plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		159,000,000
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year		0
Projected benefit obligation	2,339,000,000	1,985,000,000	1,865,000,000
Plan assets	1,053,000,000	1,061,000,000	928,000,000
Actuarial gain (loss)		(223,000,000)	432,000,000
Other postretirement benefit plans | Southern Power
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	11,000,000	11,000,000	9,000,000
Plan assets	$ 0	0	0
Actuarial gain (loss)		$ (2,000,000)	$ 2,000,000

RETIREMENT BENEFITS - Defined B

RETIREMENT BENEFITS - Defined Benefit Plan Related to Gulf Power (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 14,788	$ 12,763	$ 13,808
Plan assets	14,057	11,611	12,992
Accrued liability	(731)	(1,152)
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	1,985	1,865	2,339
Plan assets	1,061	928	$ 1,053
Accrued liability	(924)	$ (937)
Gulf Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	526
Plan assets	492
Accrued liability	(34)
Gulf Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	69
Plan assets	17
Accrued liability	$ (52)

RETIREMENT BENEFITS - Actuarial

RETIREMENT BENEFITS - Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.49%	3.80%	4.40%
Expected long-term return on plan assets	7.75%	7.95%	7.92%
Annual salary increase, net periodic costs	4.34%	4.34%	4.37%
Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.12%	3.45%	3.77%
Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.70%	3.98%	4.81%
Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.41%	4.49%
Annual salary increase	4.73%	4.34%
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.37%	3.68%	4.23%
Expected long-term return on plan assets	6.86%	6.83%	6.84%
Annual salary increase, net periodic costs	4.34%	4.34%	4.37%
Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.98%	3.29%	3.54%
Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.63%	3.91%	4.64%
Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.24%	4.37%
Annual salary increase	4.73%	4.34%
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.51%	3.81%	4.44%
Expected long-term return on plan assets	7.75%	7.95%	7.95%
Annual salary increase, net periodic costs	4.46%	4.46%	4.46%
Alabama Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.14%	3.45%	3.76%
Alabama Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.73%	4.00%	4.85%
Alabama Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.44%	4.51%
Annual salary increase	4.73%	4.46%
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.40%	3.71%	4.27%
Expected long-term return on plan assets	6.76%	6.83%	6.83%
Annual salary increase, net periodic costs	4.46%	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	4.01%	3.31%	3.58%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.67%	3.93%	4.70%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.28%	4.40%
Annual salary increase	4.73%	4.46%
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.48%	3.79%	4.40%
Expected long-term return on plan assets	7.75%	7.95%	7.95%
Annual salary increase, net periodic costs	4.46%	4.46%	4.46%
Georgia Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.10%	3.42%	3.72%
Georgia Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.72%	3.99%	4.83%
Georgia Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.40%	4.48%
Annual salary increase	4.73%	4.46%
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.36%	3.68%	4.23%
Expected long-term return on plan assets	6.85%	6.80%	6.79%
Annual salary increase, net periodic costs	4.46%	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	3.97%	3.29%	3.55%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.64%	3.91%	4.63%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.22%	4.36%
Annual salary increase	4.73%	4.46%
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.49%	3.80%	4.44%
Expected long-term return on plan assets	7.75%	7.95%	7.95%
Annual salary increase, net periodic costs	4.46%	4.46%	4.46%
Mississippi Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.12%	3.46%	3.81%
Mississippi Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.73%	3.99%	4.83%
Mississippi Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.41%	4.49%
Annual salary increase	4.73%	4.46%
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.35%	3.68%	4.22%
Expected long-term return on plan assets	6.79%	6.99%	6.88%
Annual salary increase, net periodic costs	4.46%	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	3.95%	3.29%	3.55%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.64%	3.91%	4.65%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.22%	4.35%
Annual salary increase	4.73%	4.46%
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.65%	3.94%
Expected long-term return on plan assets	7.75%	7.95%
Annual salary increase, net periodic costs	4.46%	4.46%
Southern Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.35%	3.69%
Southern Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.75%	4.01%
Southern Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.52%	4.65%
Annual salary increase	4.73%	4.46%
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.50%	3.81%
Expected long-term return on plan assets	0.00%	0.00%
Annual salary increase, net periodic costs	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	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	4.65%	3.93%
Southern Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.39%	4.50%
Annual salary increase	4.73%	4.46%
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.47%	3.74%	4.39%
Expected long-term return on plan assets	7.75%	7.95%	7.60%
Annual salary increase, net periodic costs	3.07%	3.07%	3.50%
Southern Company Gas | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.11%	3.41%	3.76%
Southern Company Gas | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.57%	3.84%	4.64%
Southern Company Gas | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.39%	4.47%
Annual salary increase	4.73%	3.07%
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.32%	3.62%	4.15%
Expected long-term return on plan assets	6.49%	5.89%	6.03%
Annual salary increase, net periodic costs	3.07%	3.07%	3.50%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.91%	3.21%	3.40%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.56%	3.82%	4.55%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	3.19%	4.32%
Annual salary increase	4.73%	3.07%

RETIREMENT BENEFITS - Schedul_2

RETIREMENT BENEFITS - Schedule of Health Care Cost Trend Rates (Details) - Other postretirement benefit plans	Dec. 31, 2019
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	6.50%
Ultimate Cost Trend Rate	4.50%

RETIREMENT BENEFITS - Accumulat

RETIREMENT BENEFITS - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 13,391	$ 11,683
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	3,053	2,550
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	4,222	3,613
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	615	513
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	151	101
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 963	$ 842

RETIREMENT BENEFITS - Changes i

RETIREMENT BENEFITS - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	$ 12,763	$ 13,808
Dispositions	(509)	(107)
Service cost	292	359	$ 293
Interest cost	492	464	455
Benefits paid	(596)	(618)
Actuarial (gain) loss	2,346	(1,143)
Balance at end of year	14,788	12,763	13,808
Change in plan assets
Fair value of plan assets at beginning of year	11,611	12,992
Dispositions	(509)	(107)
Actual return (loss) on plan assets	2,343	(711)
Employer contributions	1,208	55
Benefits paid	(596)	(618)
Fair value of plan assets at end of year	14,057	11,611	12,992
Accrued liability	(731)	(1,152)
Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	1,865	2,339
Dispositions	(69)	(18)
Service cost	18	24	24
Interest cost	69	75	79
Benefits paid	(126)	(129)
Actuarial (gain) loss	223	(432)
Retiree drug subsidy	5	6
Balance at end of year	1,985	1,865	2,339
Change in plan assets
Fair value of plan assets at beginning of year	928	1,053
Dispositions	(18)	(18)
Actual return (loss) on plan assets	189	(57)
Employer contributions	83	73
Benefits paid	(121)	(123)
Fair value of plan assets at end of year	1,061	928	1,053
Accrued liability	(924)	(937)
Alabama Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	2,816	2,998
Dispositions	0	0
Service cost	69	78	63
Interest cost	114	101	98
Benefits paid	(125)	(124)
Actuarial (gain) loss	530	(237)
Balance at end of year	3,404	2,816	2,998
Change in plan assets
Fair value of plan assets at beginning of year	2,575	2,836
Dispositions	0	0
Actual return (loss) on plan assets	524	(150)
Employer contributions	383	13
Benefits paid	(125)	(124)
Fair value of plan assets at end of year	3,357	2,575	2,836
Accrued liability	(47)	(241)
Alabama Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	403	517
Dispositions	0	0
Service cost	5	6	6
Interest cost	16	17	17
Benefits paid	(27)	(28)
Actuarial (gain) loss	63	(111)
Retiree drug subsidy	2	2
Balance at end of year	462	403	517
Change in plan assets
Fair value of plan assets at beginning of year	360	406
Dispositions	0	0
Actual return (loss) on plan assets	76	(25)
Employer contributions	2	5
Benefits paid	(25)	(26)
Fair value of plan assets at end of year	413	360	406
Accrued liability	(49)	(43)
Georgia Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	3,905	4,188
Dispositions	0	0
Service cost	74	87	74
Interest cost	156	139	138
Benefits paid	(194)	(191)
Actuarial (gain) loss	669	(318)
Balance at end of year	4,610	3,905	4,188
Change in plan assets
Fair value of plan assets at beginning of year	3,663	4,058
Dispositions	0	0
Actual return (loss) on plan assets	730	(218)
Employer contributions	243	14
Benefits paid	(194)	(191)
Fair value of plan assets at end of year	4,442	3,663	4,058
Accrued liability	(168)	(242)
Georgia Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	675	863
Dispositions	0	0
Service cost	5	6	7
Interest cost	26	28	29
Benefits paid	(47)	(47)
Actuarial (gain) loss	80	(178)
Retiree drug subsidy	3	3
Balance at end of year	742	675	863
Change in plan assets
Fair value of plan assets at beginning of year	344	386
Dispositions	0	0
Actual return (loss) on plan assets	68	(20)
Employer contributions	35	22
Benefits paid	(44)	(44)
Fair value of plan assets at end of year	403	344	386
Accrued liability	(339)	(331)
Mississippi Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	557	602
Dispositions	0	0
Service cost	12	17	15
Interest cost	22	20	20
Benefits paid	(26)	(24)
Actuarial (gain) loss	106	(58)
Balance at end of year	671	557	602
Change in plan assets
Fair value of plan assets at beginning of year	505	563
Dispositions	0	0
Actual return (loss) on plan assets	103	(37)
Employer contributions	59	3
Benefits paid	(26)	(24)
Fair value of plan assets at end of year	641	505	563
Accrued liability	(30)	(52)
Mississippi Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	81	97
Dispositions	0	0
Service cost	1	1	1
Interest cost	3	3	3
Benefits paid	(6)	(5)
Actuarial (gain) loss	8	(15)
Retiree drug subsidy	0	0
Balance at end of year	87	81	97
Change in plan assets
Fair value of plan assets at beginning of year	23	25
Dispositions	0	0
Actual return (loss) on plan assets	4	(1)
Employer contributions	5	4
Benefits paid	(6)	(5)
Fair value of plan assets at end of year	26	23	25
Accrued liability	(61)	(58)
Southern Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	123	139
Dispositions	0	(3)
Service cost	7	9
Interest cost	5	5
Benefits paid	(4)	(3)
Actuarial (gain) loss	54	(24)
Balance at end of year	185	123	139
Change in plan assets
Fair value of plan assets at beginning of year	123	138
Dispositions	0	(3)
Actual return (loss) on plan assets	43	(9)
Employer contributions	7	0
Benefits paid	(4)	(3)
Fair value of plan assets at end of year	169	123	138
Accrued liability	(16)	0
Southern Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	9	11
Dispositions	0	0
Service cost	1	1
Interest cost	0	0
Benefits paid	(1)	(1)
Actuarial (gain) loss	2	(2)
Retiree drug subsidy	0	0
Balance at end of year	11	9	11
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Dispositions	0	0
Actual return (loss) on plan assets	0	0
Employer contributions	1	1
Benefits paid	(1)	(1)
Fair value of plan assets at end of year	0	0	0
Accrued liability	(11)	(9)
Southern Company Gas | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year	907	1,184
Dispositions	0	(104)
Service cost	25	34	23
Interest cost	36	39	42
Benefits paid	(64)	(98)
Actuarial (gain) loss	163	(148)
Balance at end of year	1,067	907	1,184
Change in plan assets
Fair value of plan assets at beginning of year	798	1,068
Dispositions	0	(104)
Actual return (loss) on plan assets	172	(70)
Employer contributions	144	2
Benefits paid	(64)	(98)
Fair value of plan assets at end of year	1,050	798	1,068
Accrued liability	(17)	(109)
Southern Company Gas | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year	244	310
Dispositions	0	(18)
Service cost	1	2	2
Interest cost	9	10	10
Benefits paid	(17)	(17)
Actuarial (gain) loss	13	(43)
Retiree drug subsidy	0	0
Balance at end of year	250	244	310
Change in plan assets
Fair value of plan assets at beginning of year	98	125
Dispositions	0	(18)
Actual return (loss) on plan assets	21	(5)
Employer contributions	13	13
Benefits paid	(17)	(17)
Fair value of plan assets at end of year	115	98	$ 125
Accrued liability	(135)	$ (146)
Qualified pension plan | Pension plans
Change in benefit obligation
Balance at end of year	14,055
Change in plan assets
Employer contributions	1,136
Qualified pension plan | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year	3,286
Change in plan assets
Employer contributions	362
Qualified pension plan | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year	4,480
Change in plan assets
Employer contributions	200
Qualified pension plan | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year	639
Change in plan assets
Employer contributions	54
Qualified pension plan | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year	159
Change in plan assets
Employer contributions	24
Qualified pension plan | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year	999
Change in plan assets
Employer contributions	145
Non-qualified pension plan | Pension plans
Change in benefit obligation
Balance at end of year	733
Non-qualified pension plan | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year	118
Non-qualified pension plan | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year	130
Non-qualified pension plan | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year	31
Non-qualified pension plan | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year	26
Non-qualified pension plan | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year	$ 68

RETIREMENT BENEFITS - Amounts R

RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	$ 6,805	$ 5,375
Other deferred charges and assets	1,071	1,463
Other current liabilities	(830)	(852)
Employee benefit obligations	(1,814)	(2,147)
Other regulatory liabilities, deferred	(256)	(169)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	2	0
Other regulatory assets, deferred	4,072	3,566
Other deferred charges and assets	0	0
Other current liabilities	(54)	(55)
Employee benefit obligations	(679)	(1,097)
Other regulatory liabilities, deferred	(79)	(108)
AOCI	185	97
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	183	99
Other current liabilities	(5)	(6)
Employee benefit obligations	(919)	(931)
Other regulatory liabilities, deferred	(62)	(77)
AOCI	2	(4)
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	1,976	1,240
Other deferred charges and assets	269	188
Other current liabilities	(105)	(45)
Employee benefit obligations	(206)	(314)
Other regulatory liabilities, deferred	(146)	(69)
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	71	0
Other regulatory assets, deferred	1,130	955
Other deferred charges and assets	0	0
Other current liabilities	(8)	(12)
Employee benefit obligations	(110)	(229)
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	3	0
Other current liabilities	0	0
Employee benefit obligations	(49)	(43)
Other regulatory liabilities, deferred	(2)	(8)
AOCI	0	0
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	2,716	2,258
Other deferred charges and assets	500	514
Other current liabilities	(187)	(183)
Employee benefit obligations	(540)	(599)
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	1,416	1,230
Other deferred charges and assets	0	0
Other current liabilities	(11)	(15)
Employee benefit obligations	(157)	(227)
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	96	60
Other current liabilities	0	0
Employee benefit obligations	(339)	(331)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	360	331
Other deferred charges and assets	34	3
Other current liabilities	(49)	(28)
Employee benefit obligations	(99)	(115)
Other regulatory liabilities, deferred	(76)	(81)
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	2	0
Other regulatory assets, deferred	204	167
Other deferred charges and assets	0	0
Other current liabilities	(2)	(3)
Employee benefit obligations	(30)	(49)
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	10	6
Other current liabilities	0	0
Employee benefit obligations	(61)	(58)
Other regulatory liabilities, deferred	0	(2)
AOCI	0	0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Other deferred charges and assets	216	373
Other current liabilities	(132)	(121)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	10	1
Other regulatory assets, deferred	0	0
Other deferred charges and assets	0	0
Other current liabilities	(2)	0
Employee benefit obligations	(24)	(1)
Other regulatory liabilities, deferred	0	0
AOCI	46	26
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	(11)	(9)
Other regulatory liabilities, deferred	0	0
AOCI	2	1
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	618	669
Other deferred charges and assets	207	193
Other current liabilities	(128)	(130)
Employee benefit obligations	(265)	(357)
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	172	160
Other deferred charges and assets	82	74
Other current liabilities	(2)	(3)
Employee benefit obligations	(97)	(179)
Other regulatory liabilities, deferred	0	0
AOCI	(14)	(44)
Regulatory asset	252	268
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	(11)	(4)
Other current liabilities	0	0
Employee benefit obligations	(135)	146
Other regulatory liabilities, deferred	0	0
AOCI	(4)	(4)
Regulatory asset	$ 50	$ 57

RETIREMENT BENEFITS - Component

RETIREMENT BENEFITS - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 29,039	$ 25,528	$ 26,612
Total other comprehensive income (loss)	(118)	26	(9)
Ending balance	31,759	29,039	25,528
Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(82)
Total other comprehensive income (loss)	(60)
Ending balance	(142)	(82)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(3)	(3)
Net (gain) loss	188	100
Total AOCI	185	97
Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	13	17
Net (gain) loss	3,980	3,441
Regulatory amortization	0	0
Regulatory asset	3,993	3,458
Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	97	107
Reclassification adjustments		(9)
Total other comprehensive income (loss)		(10)
Ending balance	185	97	107
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3,458	3,155
Reclassification adjustments	(122)	(208)
Total other comprehensive income (loss)	535	303
Ending balance	3,993	3,458	3,155
Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(88)	(7)
Reclassification adjustments		(9)
Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(801)	(498)
Reclassification adjustments	(119)	(204)
Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(1)
Reclassification adjustments	(3)	(4)
Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		8
Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		(12)
Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Pension plans | Change in prior year service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	144
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	1	(5)
Total AOCI	2	(4)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	1
Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	11	14
Net (gain) loss	110	8
Regulatory amortization	0	0
Regulatory asset	121	22
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)	6	(8)
Ending balance	2	(4)	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	22	341
Reclassification adjustments	(1)	(21)
Total other comprehensive income (loss)	99	(319)
Ending balance	121	22	341
Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	5	(8)
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	(90)	298
Reclassification adjustments	2	(14)
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)	0
Reclassification adjustments	(3)	(7)
Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
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 | 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	7,477	6,829	6,323
Total other comprehensive income (loss)	4	4	4
Ending balance	8,955	7,477	6,829
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	6	6
Net (gain) loss	1,124	949
Regulatory amortization	0	0
Regulatory asset	1,130	955
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	955	890
Reclassification adjustments	(38)	(55)
Total other comprehensive income (loss)	175	65
Ending balance	1,130	955	890
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	(213)	(120)
Reclassification adjustments	(37)	(54)
Alabama Power | Pension 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)	(1)
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 | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power | Pension plans | Change in prior year service costs | 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
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	8
Net (gain) loss	(2)	(16)
Regulatory amortization	0	0
Regulatory asset	1
Regulatory liabilities		(8)
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	(9)	56
Reclassification adjustments	(4)	(5)
Total other comprehensive income (loss)	10	(65)
Ending balance	1	(9)	56
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	(14)	60
Reclassification adjustments	0	(1)
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	0
Reclassification adjustments	(4)	(4)
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 | 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	14,323	11,931	11,356
Total other comprehensive income (loss)	(42)	3	3
Ending balance	15,065	14,323	11,931
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	10	12
Net (gain) loss	1,406	1,218
Regulatory amortization	0	0
Regulatory asset	1,416	1,230
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	1,230	1,105
Reclassification adjustments	(45)	(71)
Total other comprehensive income (loss)	186	125
Ending balance	1,416	1,230	1,105
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	(231)	(196)
Reclassification adjustments	(44)	(69)
Georgia Power | Pension 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)	(2)
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 | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power | Pension plans | Change in prior year service costs | 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
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	4	4
Net (gain) loss	92	56
Regulatory amortization	0	0
Regulatory asset	96	60
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	60	202
Reclassification adjustments	(1)	(10)
Total other comprehensive income (loss)	36	(142)
Ending balance	96	60	202
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	(37)	132
Reclassification adjustments	(1)	(9)
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	0
Reclassification adjustments	0	(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 | 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	1,609	1,358	2,943
Total other comprehensive income (loss)	1	0	0
Ending balance	1,652	1,609	1,358
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	201	165
Regulatory amortization	0	0
Regulatory asset	203	167
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	167	158
Reclassification adjustments	(6)	(10)
Total other comprehensive income (loss)	36	9
Ending balance	203	167	158
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	(42)	(19)
Reclassification adjustments	(6)	(10)
Mississippi Power | Pension 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 | 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 | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Pension plans | Change in prior year service costs | 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
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	10	4
Regulatory amortization	0	0
Regulatory asset	10	4
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	4	17
Reclassification adjustments	0	(1)
Total other comprehensive income (loss)	6	(13)
Ending balance	10	4	17
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	(6)	12
Reclassification adjustments	0	(1)
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	0
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 | 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	7,284	6,498	5,675
Total other comprehensive income (loss)	(42)	14	(10)
Ending balance	6,622	7,284	6,498
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(20)
Total other comprehensive income (loss)	(17)
Ending balance	(37)	(20)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	46	26
Total AOCI	46	26
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	26	33
Reclassification adjustments		(2)
Total other comprehensive income (loss)		(7)
Ending balance	46	26	33
Southern Power | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(20)	5
Reclassification adjustments		(2)
Southern Power | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net (gain) loss	2	1
Total AOCI	2	1
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	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	1	3
Total other comprehensive income (loss)	1	(2)
Ending balance	2	1	3
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	(2)
Southern Power | Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		0
Southern Company Gas
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	8,570	9,022	9,109
Total other comprehensive income (loss)	(19)	2	(5)
Ending balance	9,506	8,570	9,022
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	29
Total other comprehensive income (loss)	(16)
Ending balance	13	29
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(6)	(6)
Net (gain) loss	(8)	(38)
Total AOCI	(14)	(44)
Regulatory asset	252	268
Southern Company Gas | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(15)	(17)
Net (gain) loss	113	83
Regulatory amortization	74	94
Regulatory asset	172	160
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	(44)	(42)
Reclassification adjustments		0
Total other comprehensive income (loss)		(2)
Ending balance	(14)	(44)	(42)
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	160	217
Reclassification adjustments	(18)	(25)
Total other comprehensive income (loss)	12	(57)
Ending balance	172	160	217
Southern Company Gas | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss	(30)	(6)
Reclassification adjustments		0
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	(30)	(20)
Reclassification adjustments	0	(12)
Southern Company Gas | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		18
Reclassification adjustments	2	2
Southern Company Gas | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		8
Southern Company Gas | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		34
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	(20)	(15)
Southern Company Gas | Pension plans | Change in prior year service costs | 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
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net (gain) loss	(5)	(5)
Total AOCI	(4)	(4)
Regulatory asset	50	57
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	2
Net (gain) loss	(43)	(43)
Regulatory amortization	31	37
Regulatory liabilities	(11)	(4)
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)	(3)
Total other comprehensive income (loss)	0	(1)
Ending balance	(4)	(4)	(3)
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	(4)	46
Reclassification adjustments	(6)	(6)
Total other comprehensive income (loss)	(7)	(50)
Ending balance	(11)	(4)	$ 46
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	(2)
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	1	42
Reclassification adjustments	0	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	2
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss		1
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 | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	$ (6)	$ (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, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Components of net periodic
Service cost	$ 292	$ 359	$ 293
Interest cost	492	464	455
Expected return on plan assets	(885)	(943)	(897)
Recognized net (gain) loss	120	213	162
Net amortization	2	4	12
Prior service cost	0	0
Total change	21	97	25
Benefit payments:
2020	628
2021	646
2022	671
2023	693
2024	715
2025 to 2029	3,868
Other postretirement benefit plans
Components of net periodic
Service cost	18	24	24
Interest cost	69	75	79
Expected return on plan assets	(65)	(69)	(66)
Prior service cost	0	21	20
Total change	22	51	57
Benefit payments:
2020	130
2021	129
2022	129
2023	130
2024	129
2025 to 2029	630
Subsidy receipts:
2020	(5)
2021	(6)
2022	(6)
2023	(6)
2024	(6)
2025 to 2029	(30)
Benefit Payments and Subsidy Receipts, Total:
2020	125
2021	123
2022	123
2023	124
2024	123
2025 to 2029	600
Alabama Power | Pension plans
Components of net periodic
Service cost	69	78	63
Interest cost	114	101	98
Expected return on plan assets	(206)	(207)	(196)
Recognized net (gain) loss	37	54	42
Net amortization	0	1	2
Prior service cost	0	0
Total change	14	27	9
Benefit payments:
2020	135
2021	141
2022	147
2023	153
2024	157
2025 to 2029	860
Alabama Power | Other postretirement benefit plans
Components of net periodic
Service cost	5	6	6
Interest cost	16	17	17
Expected return on plan assets	(26)	(26)	(25)
Prior service cost	4	5	5
Total change	(1)	2	3
Benefit payments:
2020	29
2021	29
2022	29
2023	29
2024	29
2025 to 2029	145
Subsidy receipts:
2020	(1)
2021	(2)
2022	(2)
2023	(2)
2024	(2)
2025 to 2029	(9)
Benefit Payments and Subsidy Receipts, Total:
2020	28
2021	27
2022	27
2023	27
2024	27
2025 to 2029	136
Georgia Power | Pension plans
Components of net periodic
Service cost	74	87	74
Interest cost	156	139	138
Expected return on plan assets	(292)	(296)	(283)
Recognized net (gain) loss	44	69	57
Net amortization	1	2	3
Prior service cost	0	0
Total change	(17)	1	(11)
Benefit payments:
2020	204
2021	208
2022	214
2023	220
2024	226
2025 to 2029	1,209
Georgia Power | Other postretirement benefit plans
Components of net periodic
Service cost	5	6	7
Interest cost	26	28	29
Expected return on plan assets	(25)	(25)	(25)
Prior service cost	1	10	9
Total change	7	19	20
Benefit payments:
2020	49
2021	49
2022	49
2023	49
2024	48
2025 to 2029	238
Subsidy receipts:
2020	(2)
2021	(2)
2022	(3)
2023	(3)
2024	(3)
2025 to 2029	(13)
Benefit Payments and Subsidy Receipts, Total:
2020	47
2021	47
2022	46
2023	46
2024	45
2025 to 2029	225
Mississippi Power | Pension plans
Components of net periodic
Service cost	12	17	15
Interest cost	22	20	20
Expected return on plan assets	(40)	(41)	(40)
Recognized net (gain) loss	6	10	7
Net amortization	0	0	1
Prior service cost	0	0
Total change	0	6	3
Benefit payments:
2020	27
2021	28
2022	30
2023	30
2024	32
2025 to 2029	174
Mississippi Power | Other postretirement benefit plans
Components of net periodic
Service cost	1	1	1
Interest cost	3	3	3
Expected return on plan assets	(2)	(2)	(1)
Prior service cost	0	1	1
Total change	2	3	4
Benefit payments:
2020	6
2021	6
2022	6
2023	6
2024	6
2025 to 2029	29
Subsidy receipts:
2020	0
2021	0
2022	0
2023	0
2024	(1)
2025 to 2029	(2)
Benefit Payments and Subsidy Receipts, Total:
2020	6
2021	6
2022	6
2023	6
2024	5
2025 to 2029	27
Southern Power | Pension plans
Components of net periodic
Service cost	7	9
Interest cost	5	5
Expected return on plan assets	(10)	(10)
Recognized net (gain) loss	1	1
Net amortization	0	0
Prior service cost	0	0
Total change	3	5
Benefit payments:
2020	5
2021	6
2022	6
2023	6
2024	7
2025 to 2029	36
Southern Power | Other postretirement benefit plans
Components of net periodic
Service cost	1	1
Interest cost	0	0
Expected return on plan assets	0	0
Prior service cost	0	0
Total change	1	1
Benefit payments:
2020	0
2021	0
2022	1
2023	1
2024	1
2025 to 2029	3
Subsidy receipts:
2020	0
2021	0
2022	0
2023	0
2024	0
2025 to 2029	0
Benefit Payments and Subsidy Receipts, Total:
2020	0
2021	0
2022	1
2023	1
2024	1
2025 to 2029	3
Southern Company Gas | Pension plans
Components of net periodic
Service cost	25	34	23
Interest cost	36	39	42
Expected return on plan assets	(60)	(75)	(70)
Recognized net (gain) loss	2	12	18
Net amortization	14	15	1
Prior service cost	(3)	(2)
Total change	14	23	14
Benefit payments:
2020	62
2021	62
2022	64
2023	62
2024	62
2025 to 2029	316
Southern Company Gas | Other postretirement benefit plans
Components of net periodic
Service cost	1	2	2
Interest cost	9	10	10
Expected return on plan assets	(7)	(7)	(7)
Prior service cost	6	6	1
Total change	9	$ 11	$ 6
Benefit payments:
2020	18
2021	18
2022	18
2023	19
2024	18
2025 to 2029	83
Subsidy receipts:
2020	0
2021	0
2022	0
2023	0
2024	0
2025 to 2029	0
Benefit Payments and Subsidy Receipts, Total:
2020	18
2021	18
2022	18
2023	19
2024	18
2025 to 2029	$ 83

RETIREMENT BENEFITS - Fair Valu

RETIREMENT BENEFITS - Fair Values of Pension Plan and Other Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Liabilities Fair Value
Target plan asset allocations	100.00%
Actual plan asset allocations	100.00%
Pension plans
Assets Fair Value
Fair value, plan assets	$ 14,119	$ 11,631
Liabilities Fair Value
Derivatives	(1)
Total	$ 14,118
Target plan asset allocations		100.00%
Actual plan asset allocations		100.00%
Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	51.00%	53.00%
Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 3,118	$ 3,132
Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 3,646	$ 2,669
Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	29.00%	24.00%
Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 965	$ 930
Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	9	7
Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1,315	1,195
Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	684	654
Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	1,317	272
Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 1,957	$ 1,780
Liabilities Fair Value
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	12.00%	15.00%
Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 155	$ 171
Liabilities Fair Value
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 953	$ 821
Liabilities Fair Value
Target plan asset allocations	9.00%	9.00%
Actual plan asset allocations	7.00%	7.00%
Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 1,060	$ 926
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Other postretirement benefit plans | Equity
Liabilities Fair Value
Target plan asset allocations	63.00%	62.00%
Actual plan asset allocations	64.00%	62.00%
Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 176	$ 176
Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 149	$ 120
Other postretirement benefit plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	28.00%	29.00%
Actual plan asset allocations	30.00%	30.00%
Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 31	$ 34
Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	35	35
Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	82	81
Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	42	13
Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	463	386
Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 53	$ 53
Liabilities Fair Value
Target plan asset allocations	5.00%	5.00%
Actual plan asset allocations	4.00%	5.00%
Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 4	$ 4
Liabilities Fair Value
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
Fair value, plan assets	$ 25	$ 24
Liabilities Fair Value
Target plan asset allocations	3.00%	3.00%
Actual plan asset allocations	2.00%	3.00%
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Fair value, plan assets	$ 6,436	$ 4,135
Liabilities Fair Value
Derivatives	(1)
Total	6,435
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	2,220	2,102
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	2,360	1,344
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
Fair value, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	1,317	270
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	539	419
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	221	171
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	95	100
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	69	45
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
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
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
Fair value, plan assets	42	13
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
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
Fair value, plan assets	15	13
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
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
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	5,157	5,143
Liabilities Fair Value
Derivatives	0
Total	5,157
Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	898	1,030
Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	1,286	1,325
Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	965	930
Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	9	7
Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1,315	1,195
Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	684	654
Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	2
Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	772	687
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	81	76
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	80	75
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	31	34
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	35	35
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	82	81
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	463	386
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	2,526	2,353
Liabilities Fair Value
Derivatives	0
Total	2,526
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	1,418	1,361
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	155	171
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	953	821
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	67	68
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity
Assets Fair Value
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
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
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
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
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	38	40
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	4	4
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	25	24
Alabama Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 3,372	$ 2,579
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Alabama Power | Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	51.00%	53.00%
Alabama Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 744	$ 694
Alabama Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 871	$ 591
Alabama Power | Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	29.00%	24.00%
Alabama Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 230	$ 206
Alabama Power | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	2	2
Alabama Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	314	265
Alabama Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	163	145
Alabama Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	315	61
Alabama Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 468	$ 395
Liabilities Fair Value
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	12.00%	15.00%
Alabama Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 37	$ 38
Liabilities Fair Value
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
Fair value, plan assets	$ 228	$ 182
Liabilities Fair Value
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
Fair value, plan assets	$ 412	$ 359
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Alabama Power | Other postretirement benefit plans | Equity
Liabilities Fair Value
Target plan asset allocations	68.00%	64.00%
Actual plan asset allocations	67.00%	66.00%
Alabama Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 34	$ 45
Alabama Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 32	$ 24
Alabama Power | Other postretirement benefit plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	24.00%	28.00%
Actual plan asset allocations	27.00%	28.00%
Alabama Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 10	$ 10
Alabama Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	11
Alabama Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	6	6
Alabama Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	12	3
Alabama Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	281	233
Alabama Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 17	$ 17
Liabilities Fair Value
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
Fair value, plan assets	$ 1	$ 2
Liabilities Fair Value
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
Fair value, plan assets	$ 8	$ 8
Liabilities Fair Value
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
Fair value, plan assets	$ 1,538	$ 917
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	530	466
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	564	298
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
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
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
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
Fair value, plan assets	315	60
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	129	93
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
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
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
Fair value, plan assets	64	54
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	26	35
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	21	12
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
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
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
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
Fair value, plan assets	12	3
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
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
Fair value, plan assets	5	4
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
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
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	1,230	1,140
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	214	228
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	307	293
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	230	206
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	2	2
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	314	265
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	163	145
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	1
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	327	282
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	8	10
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	11	12
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	10	10
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	11
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	6	6
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
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
Fair value, plan assets	281	233
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	604	522
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
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
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	339	302
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	37	38
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	228	182
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	21	23
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
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
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
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
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
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
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
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
Fair value, plan assets	12	13
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	1	2
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	8	8
Georgia Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 4,461	$ 3,669
Liabilities Fair Value
Target plan asset allocations	100.00%
Actual plan asset allocations	100.00%	100.00%
Georgia Power | Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	51.00%	53.00%
Georgia Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 985	$ 988
Georgia Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 1,153	$ 842
Georgia Power | Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%
Actual plan asset allocations	29.00%	24.00%
Georgia Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 305	$ 294
Georgia Power | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	3	2
Georgia Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	415	377
Georgia Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	216	206
Georgia Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	416	86
Georgia Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 618	$ 561
Liabilities Fair Value
Target plan asset allocations	14.00%
Actual plan asset allocations	12.00%	15.00%
Georgia Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 49	$ 54
Liabilities Fair Value
Target plan asset allocations	3.00%
Actual plan asset allocations	1.00%	1.00%
Georgia Power | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 301	$ 259
Liabilities Fair Value
Target plan asset allocations	9.00%
Actual plan asset allocations	7.00%	7.00%
Georgia Power | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 402	$ 342
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Georgia Power | Other postretirement benefit plans | Equity
Liabilities Fair Value
Target plan asset allocations	60.00%	60.00%
Actual plan asset allocations	61.00%	59.00%
Georgia Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 55	$ 50
Georgia Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 61	$ 49
Georgia Power | Other postretirement benefit plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	33.00%	33.00%
Actual plan asset allocations	34.00%	35.00%
Georgia Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 7	$ 7
Georgia Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	10
Georgia Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	45	44
Georgia Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	16	5
Georgia Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	182	153
Georgia Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 16	$ 15
Liabilities Fair Value
Target plan asset allocations	4.00%	4.00%
Actual plan asset allocations	3.00%	4.00%
Georgia Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 1	$ 2
Liabilities Fair Value
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
Fair value, plan assets	$ 8	$ 7
Liabilities Fair Value
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
Fair value, plan assets	$ 2,033	$ 1,304
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	701	663
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	746	424
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
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
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
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
Fair value, plan assets	416	85
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	170	132
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
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
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
Fair value, plan assets	94	67
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	48	41
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	25	17
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
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
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
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
Fair value, plan assets	16	5
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
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
Fair value, plan assets	5	4
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
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
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	1,630	1,623
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	284	325
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	407	418
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	305	294
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	3	2
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	415	377
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	216	206
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	1
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	288	255
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	7	9
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	36	32
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	7	7
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	10
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	45	44
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
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
Fair value, plan assets	182	153
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	798	742
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
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
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	448	429
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	49	54
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	301	259
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	20	20
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
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
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
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
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
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
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
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
Fair value, plan assets	11	11
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	1	2
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	8	7
Mississippi Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 644	$ 506
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Mississippi Power | Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%
Actual plan asset allocations	51.00%
Mississippi Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 142	$ 136
Mississippi Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 167	$ 118
Mississippi Power | Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	29.00%	24.00%
Mississippi Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 44	$ 40
Mississippi Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	60	52
Mississippi Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	31	28
Mississippi Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	60	12
Mississippi Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 90	$ 77
Liabilities Fair Value
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	12.00%	15.00%
Mississippi Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 7	$ 7
Liabilities Fair Value
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
Fair value, plan assets	$ 43	$ 36
Liabilities Fair Value
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
Fair value, plan assets	$ 25	$ 23
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Mississippi Power | Other postretirement benefit plans | Equity
Liabilities Fair Value
Target plan asset allocations	43.00%	41.00%
Actual plan asset allocations	41.00%	42.00%
Mississippi Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 4	$ 5
Mississippi Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 6	$ 4
Mississippi Power | Other postretirement benefit plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	37.00%	38.00%
Actual plan asset allocations	42.00%	39.00%
Mississippi Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 6	$ 6
Mississippi Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	2	2
Mississippi Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	1	1
Mississippi Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	2	1
Mississippi Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 3	$ 3
Liabilities Fair Value
Target plan asset allocations	11.00%	11.00%
Actual plan asset allocations	10.00%	12.00%
Mississippi Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 0	$ 0
Liabilities Fair Value
Target plan asset allocations	2.00%	3.00%
Actual plan asset allocations	1.00%	1.00%
Mississippi Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 1	$ 1
Liabilities Fair Value
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
Fair value, plan assets	$ 294	$ 180
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	101	91
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	108	59
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
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
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
Fair value, plan assets	60	12
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	25	18
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
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
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
Fair value, plan assets	10	7
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	3	3
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	4	2
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
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
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
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
Fair value, plan assets	2	1
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
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
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
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	235	224
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	41	45
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	59	59
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	44	40
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	60	52
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	31	28
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	12	13
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	1	2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
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
Fair value, plan assets	6	6
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	2	2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	115	102
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	65	59
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	7	7
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	43	36
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	3	3
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
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
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
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
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
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
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
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
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
Fair value, plan assets	1	1
Southern Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 170	$ 124
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Power | Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	51.00%	53.00%
Southern Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 38	$ 33
Southern Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 44	$ 28
Southern Power | Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	29.00%	24.00%
Southern Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 12	$ 10
Southern Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	16	13
Southern Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	8	7
Southern Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	16	3
Southern Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 23	$ 19
Liabilities Fair Value
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	12.00%	15.00%
Southern Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 2	$ 2
Liabilities Fair Value
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
Fair value, plan assets	$ 11	$ 9
Liabilities Fair Value
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
Fair value, plan assets	$ 77	$ 43
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	27	22
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	28	14
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
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
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
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
Fair value, plan assets	16	3
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	6	4
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
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
Fair value, plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	63	55
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	11	11
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	16	14
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	12	10
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	16	13
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	8	7
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	30	26
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
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
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	17	15
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	2	2
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	11	9
Southern Company Gas | Pension plans
Assets Fair Value
Fair value, plan assets	$ 1,054	$ 800
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Company Gas | Pension plans | Equity
Liabilities Fair Value
Target plan asset allocations	51.00%	51.00%
Actual plan asset allocations	51.00%	53.00%
Southern Company Gas | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 233	$ 216
Southern Company Gas | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 272	$ 183
Southern Company Gas | Pension plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	23.00%	23.00%
Actual plan asset allocations	29.00%	24.00%
Southern Company Gas | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 72	$ 64
Southern Company Gas | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	1
Southern Company Gas | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	98	82
Southern Company Gas | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	51	45
Southern Company Gas | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	98	19
Southern Company Gas | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 146	$ 123
Liabilities Fair Value
Target plan asset allocations	14.00%	14.00%
Actual plan asset allocations	12.00%	15.00%
Southern Company Gas | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 12	$ 12
Liabilities Fair Value
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
Fair value, plan assets	$ 71	$ 56
Liabilities Fair Value
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
Fair value, plan assets	$ 114	$ 96
Liabilities Fair Value
Target plan asset allocations	100.00%	100.00%
Actual plan asset allocations	100.00%	100.00%
Southern Company Gas | Other postretirement benefit plans | Equity
Liabilities Fair Value
Target plan asset allocations	72.00%	71.00%
Actual plan asset allocations	73.00%	69.00%
Southern Company Gas | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 60	$ 49
Southern Company Gas | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 23	$ 18
Southern Company Gas | Other postretirement benefit plans | Fixed income
Liabilities Fair Value
Target plan asset allocations	26.00%	25.00%
Actual plan asset allocations	25.00%	28.00%
Southern Company Gas | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 1	$ 1
Southern Company Gas | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1	1
Southern Company Gas | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	25	24
Southern Company Gas | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	2	1
Southern Company Gas | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 1	$ 1
Liabilities Fair Value
Target plan asset allocations	1.00%	2.00%
Actual plan asset allocations	1.00%	2.00%
Southern Company Gas | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets		$ 0
Liabilities Fair Value
Target plan asset allocations		1.00%
Actual plan asset allocations		0.00%
Southern Company Gas | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 1	$ 1
Liabilities Fair Value
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
Fair value, plan assets	$ 480	$ 285
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	166	145
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	176	92
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
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
Fair value, plan assets	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds
Assets Fair Value
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
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
Fair value, plan assets	98	19
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	40	29
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations
Assets Fair Value
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
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
Fair value, plan assets	6	4
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
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
Fair value, plan assets	2	1
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
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
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
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
Fair value, plan assets	2	1
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets		0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	385	353
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	67	71
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	96	91
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	72	64
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	98	82
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	51	45
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	106	90
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	58	47
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	21	17
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	1	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	25	24
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
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
Fair value, plan assets	0	0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets		0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans
Assets Fair Value
Fair value, plan assets	189	162
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity
Assets Fair Value
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
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
Fair value, plan assets	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds
Assets Fair Value
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
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
Fair value, plan assets	106	94
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	12	12
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	71	56
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans
Assets Fair Value
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
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
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
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
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
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
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
Fair value, plan assets	1	1
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets		0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity
Assets Fair Value
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 113	$ 119	$ 118
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	25	24	23
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	27	26	26
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	4	5	5
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	2	3
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 15	$ 18	$ 19

STOCK COMPENSATION - Schedule o

STOCK COMPENSATION - Schedule of Employees Participating in Stock-Based Compensation Programs (Details)	Dec. 31, 2019employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	2,320
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	307
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	370
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	89
Southern Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	50
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	285

STOCK COMPENSATION - Performanc

STOCK COMPENSATION - Performance Shares Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Feb. 29, 2020$ / sharesshares	Feb. 28, 2019$ / sharesshares	Dec. 31, 2019USD ($)type$ / sharesshares	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares converted (in shares)		1,700,000
Shares converted (in dollars per share) | $ / shares		$ 49.24
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
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)			2,500,000	2,500,000
Equity instruments, vested (in shares)			1,200,000
Equity instrument, granted (in shares)			1,200,000
Unrecognized compensation cost | $			$ 31
Total unrecognized compensation cost related to award, weighted average period			12 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			$ 49.38	$ 43.49	$ 49.21
Subsequent Event
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

STOCK COMPENSATION - Performa_2

STOCK COMPENSATION - Performance Shares, Assumptions Used (Details) - Performance Shares - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	15.60%	14.90%	15.60%
Expected term (in years)	3 years	3 years	3 years
Interest rate	2.40%	2.40%	1.40%
Weighted average grant-date fair value (in dollars per share)	$ 62.71	$ 43.75	$ 49.08

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	$ 77	$ 91	$ 74
Tax benefit of compensation cost recognized in income	20	24	29
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	14	11	8
Tax benefit of compensation cost recognized in income	$ 4	$ 3	$ 3

STOCK COMPENSATION - Restricted

STOCK COMPENSATION - Restricted Stock Units Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period (years)		3 years
Shares vested and issued each year employee remains in service		33.00%
Total unrecognized compensation cost related to award, weighted average period		10 months
Restricted stock units, unvested (in shares)		1.3	1.1
Equity instrument, granted (in shares)		0.6
Vested or forfeited (in shares)		0.4
Total compensation cost for award recognized in income		$ 28	$ 27	$ 25
Total compensation cost for award recognized in income, tax benefit		7	$ 7	$ 10
Total unrecognized compensation cost related to award		$ 14
Parent Company | Restricted Stock Units (RSUs)
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)	$ 53.83	$ 50.44	$ 43.81	$ 49.25
Equity instrument, granted (in shares)	0.7
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash received from issuance related to option exercise	$ 482	$ 41	$ 239
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term for options outstanding	3 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, 2019$ / sharesshares
Shares Subject to Option
Outstanding at December 31, 2018 (in shares) | shares	17.5
Exercised (in shares) | shares	11.6
Outstanding and Exercisable at December 31, 2019 (in shares) | shares	5.9
Weighted Average Exercise Price
Outstanding at December 31, 2017 (in dollars per share) | $ / shares	$ 41.92
Exercised (in dollars per share) | $ / shares	41.62
Outstanding and Exercisable at December 31, 2018 (in dollars per share) | $ / shares	$ 42.52

STOCK COMPENSATION - Aggregate

STOCK COMPENSATION - Aggregate Intrinsic Value for Options Exercised (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 124
Aggregate intrinsic value for options exercisable	124
Intrinsic value of options exercised	167	$ 9	$ 64
Tax benefit of options exercised	35	2	25
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	14
Aggregate intrinsic value for options exercisable	14
Intrinsic value of options exercised	21	2	12
Tax benefit of options exercised	4	0	5
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	35
Aggregate intrinsic value for options exercisable	35
Intrinsic value of options exercised	30	2	13
Tax benefit of options exercised	6	0	5
Mississippi Power
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
Intrinsic value of options exercised	4	1	2
Tax benefit of options exercised	$ 1	$ 0	$ 1

STOCK COMPENSATION - Merger Sto

STOCK COMPENSATION - Merger Stock Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period (years)		3 years
Equity instrument, granted (in shares)		0.6
Total compensation cost for award recognized in income		$ 28	$ 27	$ 25
Total compensation cost for award recognized in income, tax benefit		$ 7	$ 7	$ 10
Parent Company | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instrument, granted (in shares)	0.7
Equity instrument granted in period, weighted average grant date fair value (in dollars per share)	$ 53.83	$ 50.44	$ 43.81	$ 49.25
Merger-related expenses				$ 13
Southern Company Gas | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period (years)		3 years
Southern Company Gas | Change In Control Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.00%
Total compensation cost for award recognized in income				12
Tax credit carryforward				$ 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, 2019	Dec. 31, 2018
Liabilities:
Weather derivative premium	$ 4	$ 8
Collateral already posted, aggregate fair value	99	277
Recurring
Assets:
Cash equivalents	1,395	766
Other investments	30	12
Total	4,189	3,387
Liabilities:
Contingent consideration	19	21
Total	770	1,057
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	1,393	765
Other investments	9	0
Total	2,650	1,962
Liabilities:
Contingent consideration	0	0
Total	442	648
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	2	1
Other investments	21	12
Total	1,461	1,380
Liabilities:
Contingent consideration	0	0
Total	302	388
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Other investments	0	0
Total	22	0
Liabilities:
Contingent consideration	19	21
Total	26	21
Recurring | Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Total	56	45
Alabama Power
Assets:
Derivative asset	2	2
Liabilities:
Derivative liability	22	6
Alabama Power | Recurring
Assets:
Cash equivalents	693	117
Other investments	21	12
Total	1,739	981
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	691	116
Other investments	0	0
Total	1,273	595
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	2	1
Other investments	21	12
Total	410	341
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	56	45
Georgia Power
Assets:
Derivative asset	1	0
Liabilities:
Derivative liability	67	17
Georgia Power | Recurring
Assets:
Total	1,017	879
Liabilities:
Total	70	23
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	276	224
Liabilities:
Total	0	0
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Total	741	655
Liabilities:
Total	70	23
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Liabilities:
Total	0	0
Mississippi Power
Assets:
Derivative asset	0	1
Liabilities:
Derivative liability	26	7
Mississippi Power | Recurring
Assets:
Cash equivalents	281	255
Total	282	258
Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	281	255
Total	281	255
Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total	1	3
Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total	0	0
Southern Power
Assets:
Derivative asset	19	76
Liabilities:
Derivative liability	27	28
Southern Power | Recurring
Assets:
Cash equivalents	113	46
Total	132	125
Liabilities:
Contingent consideration	19	21
Total	46	52
Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	113	46
Total	113	46
Liabilities:
Contingent consideration	0	0
Total	0	0
Southern Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total	19	79
Liabilities:
Contingent consideration	0	0
Total	27	31
Southern Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total	0	0
Liabilities:
Contingent consideration	19	21
Total	19	21
Southern Company Gas
Assets:
Derivative asset	212	233
Liabilities:
Derivative liability	41	124
Weather derivative premium	4	8
Collateral already posted, aggregate fair value	99	277
Southern Company Gas | Recurring
Assets:
Cash equivalents	8	40
Total	708	814
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	8	40
Total	397	513
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total	289	301
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total	22	0
Energy-related derivatives | Recurring
Assets:
Derivative asset	677	761
Liabilities:
Derivative liability	703	964
Energy-related derivatives | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	388	469
Liabilities:
Derivative liability	442	648
Energy-related derivatives | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	267	292
Liabilities:
Derivative liability	254	316
Energy-related derivatives | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	22	0
Liabilities:
Derivative liability	7	0
Energy-related derivatives | Alabama Power | Recurring
Assets:
Derivative asset	4	6
Liabilities:
Derivative liability	24	10
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	4	6
Liabilities:
Derivative liability	24	10
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	4	6
Liabilities:
Derivative liability	53	21
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	4	6
Liabilities:
Derivative liability	53	21
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	1	3
Liabilities:
Derivative liability	27	9
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	1	3
Liabilities:
Derivative liability	27	9
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	3	4
Liabilities:
Derivative liability	3	8
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	3	4
Liabilities:
Derivative liability	3	8
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	665	741
Liabilities:
Derivative liability	596	909
Energy-related derivatives | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	388	469
Liabilities:
Derivative liability	442	648
Energy-related derivatives | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	255	272
Liabilities:
Derivative liability	147	261
Energy-related derivatives | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	22	0
Liabilities:
Derivative liability	7	0
Interest rate derivatives | Recurring
Assets:
Derivative asset	2
Liabilities:
Derivative liability	24	49
Interest rate derivatives | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0
Liabilities:
Derivative liability	0	0
Interest rate derivatives | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	2
Liabilities:
Derivative liability	24	49
Interest rate derivatives | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0
Liabilities:
Derivative liability	0	0
Interest rate derivatives | Georgia Power | Recurring
Liabilities:
Derivative liability	17	2
Interest rate derivatives | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Derivative liability	0	0
Interest rate derivatives | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivative liability	17	2
Interest rate derivatives | Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liability	0	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	16	75
Liabilities:
Derivative liability	24	23
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	16	75
Liabilities:
Derivative liability	24	23
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	16	75
Liabilities:
Derivative liability	24	23
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	16	75
Liabilities:
Derivative liability	24	23
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	886	708
Domestic equity | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	751	601
Domestic equity | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	135	107
Domestic equity | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	611	491
Domestic equity | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	488	396
Domestic equity | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	123	95
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	264	206
Domestic equity | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	263	205
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	11	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	11	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	288	226
Foreign equity | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	68	53
Foreign equity | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	220	173
Foreign equity | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	132	103
Foreign equity | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	68	53
Foreign equity | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	64	50
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	152	119
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	152	119
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	4	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	4	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	307	261
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	307	261
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	18
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	18
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	286	243
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	286	243
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	83
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	83
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	82
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	82
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	14
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	14
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	14
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	14
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	320	314
Corporate bonds | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	23	24
Corporate bonds | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	297	290
Corporate bonds | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Corporate bonds | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	167	159
Corporate bonds | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	23	24
Corporate bonds | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	144	135
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	153	155
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	153	155
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	87	68
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	87	68
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	23
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	23
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	57	45
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	57	45
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	56	45
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	56	45
Private equity | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	56	45
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	56	45
Cash and cash equivalents | Recurring
Assets:
Nuclear decommissioning trusts	1	16
Cash and cash equivalents | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	1	16
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	4
Cash equivalents | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	1	4
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	22	38
Other | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	17	34
Other | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	5	4
Other | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Other | Alabama Power | Recurring
Assets:
Nuclear decommissioning trusts	4	6
Other | Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	3	6
Other | Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	1	0
Other | Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Other | Georgia Power | Recurring
Assets:
Nuclear decommissioning trusts	17	23
Other | Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	13	19
Other | Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	4	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, 2019USD ($)$ / MMBTU	Dec. 31, 2018USD ($)
Private equity | Alabama Power
Fair Value, Option, Quantitative Disclosures [Line Items]
Alternative investment	$ 56	$ 45
Unfunded commitments	70	$ 50
Energy-related derivatives | Significant Unobservable Inputs (Level 3) | Southern Company Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, at fair value, net	$ 14
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	1.54
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	2.92

FAIR VALUE MEASUREMENTS - Finan

FAIR VALUE MEASUREMENTS - Financial Instruments, Carrying Amount Not Equal to Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$ 44,561	$ 45,023
Fair Value	48,339	44,824
Alabama Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	8,517	8,120
Fair Value	9,525	8,370
Georgia Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	11,660	9,838
Fair Value	12,680	9,800
Mississippi Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	1,589	1,579
Fair Value	1,671	1,546
Southern Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	4,398	5,017
Fair Value	4,708	4,980
Southern Company Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	5,845	5,940
Fair Value	$ 6,509	$ 5,965

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, 2019USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 0
Transfers to Level 3	(32)
Transfers from Level 3	3
Instruments realized or otherwise settled during period	(4)
Changes in fair value	47
Ending balance	$ 14

DERIVATIVES - Energy-Related De

DERIVATIVES - Energy-Related Derivative Contracts (Details) - Energy-related, Natural Gas MMBTU in Millions	Dec. 31, 2019MMBTU
Derivative [Line Items]
Net Purchased mmBtu	589
Alabama Power
Derivative [Line Items]
Net Purchased mmBtu	88
Georgia Power
Derivative [Line Items]
Net Purchased mmBtu	175
Mississippi Power
Derivative [Line Items]
Net Purchased mmBtu	101
Southern Power
Derivative [Line Items]
Net Purchased mmBtu	7
Southern Company Gas
Derivative [Line Items]
Net Purchased mmBtu	218
Long | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	4,096
Short | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	3,878

DERIVATIVES - Narrative (Detail

DERIVATIVES - Narrative (Details) MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)MMBTUMWh	Dec. 31, 2018USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	23
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period | $	$ (22)
Collateral already posted, aggregate fair value | $	$ 99	$ 277
Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	589
Southern Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	7
Southern Power | Public Utilities, Inventory, Power Position
Derivative [Line Items]
Net Purchased mmBtu | MWh	1
Southern Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	7
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	6
Alabama Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	88
Georgia Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	7
Georgia Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	175
Mississippi Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	3
Mississippi Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	101
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ (24)

DERIVATIVES - Interest Rate Der

DERIVATIVES - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Derivative [Line Items]
Notional Amount	$ 2,500
Fair Value Gain (Loss) December 31, 2019	(22)
Georgia Power | Maturity Date March 2025 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 250
Weighted Average Interest Rate Paid	2.23%
Fair Value Gain (Loss) December 31, 2019	$ (6)
Georgia Power | Maturity Date March 2030 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 250
Weighted Average Interest Rate Paid	2.40%
Fair Value Gain (Loss) December 31, 2019	$ (11)
Southern Company Gas | Maturity Date September 2030 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 200
Weighted Average Interest Rate Paid	1.81%
Fair Value Gain (Loss) December 31, 2019	$ 2
Southern Company | Maturity Date June 2020 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 300
Weighted Average Interest Rate Paid	0.92%
Fair Value Gain (Loss) December 31, 2019	$ 0
Interest Rate Received	2.75%
Southern Company | Maturity Date June 2021 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Weighted Average Interest Rate Paid	0.87%
Fair Value Gain (Loss) December 31, 2019	$ (7)
Interest Rate Received	2.35%

DERIVATIVES - Foreign Currency

DERIVATIVES - Foreign Currency Derivatives (Details) - 12 months ended Dec. 31, 2019 - Foreign currency derivatives - Cash Flow Hedges of Existing Debt € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) December 31, 2019	(8)
Southern Power | Maturity Date June 2022
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain (Loss) December 31, 2019	$ (7)
Southern Power | Maturity Date June 2026
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) December 31, 2019	$ (1)

DERIVATIVES - Financial Stateme

DERIVATIVES - Financial Statement Presentation (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value	$ 99	$ 277
Weather derivative premium	4	8
Parent Company
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	696	837
Derivative asset, gross amount offset	(463)	(524)
Derivative asset, net amounts recognized in the balance sheets	233	313
Derivative liability, gross amounts recognized	751	1,036
Derivative liability, gross amounts offset	(562)	(801)
Derivative liability, gross amounts recognized in balance sheets	189	235
Parent Company | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	668	741
Derivative liability, gross amounts recognized	583	900
Parent Company | 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	461	561
Parent Company | 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	358	575
Parent Company | 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	207	180
Parent Company | 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	225	325
Alabama Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	4	6
Derivative asset, gross amount offset	(2)	(4)
Derivative asset, net amounts recognized in the balance sheets	2	2
Derivative liability, gross amounts recognized	24	10
Derivative liability, gross amounts offset	(2)	(4)
Derivative liability, gross amounts recognized in balance sheets	22	6
Georgia Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	4	6
Derivative asset, gross amount offset	(3)	(6)
Derivative asset, net amounts recognized in the balance sheets	1	0
Derivative liability, gross amounts recognized	70	23
Derivative liability, gross amounts offset	(3)	(6)
Derivative liability, gross amounts recognized in balance sheets	67	17
Mississippi Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	1	3
Derivative asset, gross amount offset	(1)	(2)
Derivative asset, net amounts recognized in the balance sheets	0	1
Derivative liability, gross amounts recognized	27	9
Derivative liability, gross amounts offset	(1)	(2)
Derivative liability, gross amounts recognized in balance sheets	26	7
Southern Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	19	79
Derivative asset, gross amount offset	0	(3)
Derivative asset, net amounts recognized in the balance sheets	19	76
Derivative liability, gross amounts recognized	27	31
Derivative liability, gross amounts offset	0	(3)
Derivative liability, gross amounts recognized in balance sheets	27	28
Southern Power | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	2	0
Derivative liability, gross amounts recognized	1	0
Southern Power | 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	2	0
Southern Power | 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	1	0
Southern Company Gas
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	668	741
Derivative asset, gross amount offset	(456)	(508)
Derivative asset, net amounts recognized in the balance sheets	212	233
Derivative liability, gross amounts recognized	596	909
Derivative liability, gross amounts offset	(555)	(785)
Derivative liability, gross amounts recognized in balance sheets	41	124
Collateral already posted, aggregate fair value	99	277
Weather derivative premium	4	8
Southern Company Gas | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	666	739
Derivative liability, gross amounts recognized	582	899
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	207	180
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	225	325
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	459	559
Southern Company Gas | 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	357	574
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	9	17
Derivative liability, gross amounts recognized	114	55
Hedging Instruments for Regulatory Purposes | Parent Company | 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	3	8
Hedging Instruments for Regulatory Purposes | Parent Company | 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	70	23
Hedging Instruments for Regulatory Purposes | Parent Company | 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	6	9
Hedging Instruments for Regulatory Purposes | Parent Company | 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	44	26
Hedging Instruments for Regulatory Purposes | Parent Company | Energy-related derivatives | Assets held for sale, current | 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 | Parent Company | Energy-related derivatives | Liabilities held for sale, current | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	6
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	4	6
Derivative liability, gross amounts recognized	24	10
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	2	3
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	14	4
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	2	3
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	10	6
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	4	6
Derivative liability, gross amounts recognized	53	21
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	1	2
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	32	8
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	3	4
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	21	13
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	1	3
Derivative liability, gross amounts recognized	27	9
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	0	1
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	15	3
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	1	2
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	12	6
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	0	2
Derivative liability, gross amounts recognized	10	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	1	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	0	2
Hedging Instruments for Regulatory Purposes | Southern Company Gas | 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	9	8
Cash Flow and Fair Value Hedging | Parent Company | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	19	79
Derivative liability, gross amounts recognized	54	81
Cash Flow and Fair Value Hedging | Parent Company | 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	1	3
Cash Flow and Fair Value Hedging | Parent Company | 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	6	7
Cash Flow and Fair Value Hedging | Parent Company | 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	1
Cash Flow and Fair Value Hedging | Parent Company | 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	2
Cash Flow and Fair Value Hedging | Parent Company | 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	2	0
Cash Flow and Fair Value Hedging | Parent Company | 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	23	19
Cash Flow and Fair Value Hedging | Parent Company | 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 | Parent Company | 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	1	30
Cash Flow and Fair Value Hedging | Parent Company | 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 | Parent Company | 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	24	23
Cash Flow and Fair Value Hedging | Parent Company | 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	16	75
Cash Flow and Fair Value Hedging | Parent Company | 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 | Georgia Power | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Derivative liability, gross amounts recognized	17	2
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	17	2
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	17	79
Derivative liability, gross amounts recognized	26	31
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	1	3
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	6
Cash Flow and Fair Value Hedging | Southern 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	0	1
Cash Flow and Fair Value Hedging | Southern 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	0	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	24	23
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	16	75
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	2	0
Derivative liability, gross amounts recognized	4	1
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	0	0
Cash Flow and Fair Value Hedging | Southern Company Gas | 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	4	1
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	2	0
Cash Flow and Fair Value Hedging | Southern Company Gas | 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	$ 0

DERIVATIVES - Pre-Tax Effects o

DERIVATIVES - Pre-Tax Effects of Unrealized Derivative Gains (Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 99	$ 277
Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(94)	(40)
Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(63)	(19)
Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(37)	(16)
Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		(6)
Energy-related derivatives | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	6	1
Alabama Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(20)	(6)
Alabama Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(14)	(3)
Alabama Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(8)	(3)
Alabama Power | Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Alabama Power | Energy-related derivatives | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	2	0
Georgia Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(49)	(15)
Georgia Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(31)	(6)
Georgia Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(18)	(9)
Georgia Power | Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Georgia Power | Energy-related derivatives | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	0
Mississippi Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(26)	(6)
Mississippi Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(15)	(2)
Mississippi Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(11)	(4)
Mississippi Power | Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Mississippi Power | Energy-related derivatives | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	0
Southern Company Gas
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	99	277
Southern Company Gas | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	1	(7)
Southern Company Gas | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(3)	(8)
Southern Company Gas | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	0	0
Southern Company Gas | Energy-related derivatives | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Southern Company Gas | Energy-related derivatives | Other regulatory liabilities, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	$ 4	$ 1

DERIVATIVES - Pre-Tax Effects_2

DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Cash Flow Hedging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (154)
Gain (Loss) Recognized in OCI on Derivative		$ (62)	$ 91
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(13)
Gain (Loss) Recognized in OCI on Derivative		17	(47)
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(57)
Gain (Loss) Recognized in OCI on Derivative		(1)	(2)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(84)
Gain (Loss) Recognized in OCI on Derivative		(78)	140
Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(59)
Gain (Loss) Recognized in OCI on Derivative		0	1
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(88)
Gain (Loss) Recognized in OCI on Derivative		(68)	102
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(4)
Gain (Loss) Recognized in OCI on Derivative		10	(38)
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(84)
Gain (Loss) Recognized in OCI on Derivative		(78)	140
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(7)
Gain (Loss) Recognized in OCI on Derivative		7	(9)
Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(9)
Gain (Loss) Recognized in OCI on Derivative		7	(9)
Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ 2
Gain (Loss) Recognized in OCI on Derivative		$ 0	$ 0

DERIVATIVES - Pre-Tax Effects_3

DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Cash Flow and Fair Value Hedging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (154)
Gain (Loss) Recognized in OCI on Derivative		$ (62)	$ 91
Depreciation and amortization	3,038	3,131	3,010
Interest expense, net of amounts capitalized	(1,736)	(1,842)	(1,694)
Other income (expense), net	252	114	163
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(13)
Gain (Loss) Recognized in OCI on Derivative		17	(47)
Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(2)
Gain (Loss) Recognized in OCI on Derivative		2	(2)
Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(6)
Gain (Loss) Recognized in OCI on Derivative		7	(16)
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(57)
Gain (Loss) Recognized in OCI on Derivative		(1)	(2)
Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(20)
Gain (Loss) Recognized in OCI on Derivative		(21)	(21)
Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	42
Gain (Loss) Recognized in OCI on Derivative		(12)	(22)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(84)
Gain (Loss) Recognized in OCI on Derivative		(78)	140
Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(24)
Gain (Loss) Recognized in OCI on Derivative		(24)	(23)
Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(24)
Gain (Loss) Recognized in OCI on Derivative		(60)	160
Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenue	1,319	1,539	1,601
Alabama Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	793	764	736
Interest expense, net of amounts capitalized	(336)	(323)	(305)
Other income (expense), net	46	20	43
Alabama Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(6)
Gain (Loss) Recognized in OCI on Derivative		(6)	(6)
Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(59)
Gain (Loss) Recognized in OCI on Derivative		0	1
Depreciation and amortization	981	923	895
Interest expense, net of amounts capitalized	(409)	(397)	(419)
Other income (expense), net	140	115	104
Georgia Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(3)
Gain (Loss) Recognized in OCI on Derivative		(4)	(4)
Georgia Power | Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	2
Gain (Loss) Recognized in OCI on Derivative		2	(3)
Mississippi Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	192	169	161
Interest expense, net of amounts capitalized	(69)	(76)	(42)
Other income (expense), net	12	17	1
Mississippi Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(2)
Gain (Loss) Recognized in OCI on Derivative		(2)	(2)
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(88)
Gain (Loss) Recognized in OCI on Derivative		(68)	102
Depreciation and amortization	479	493	503
Interest expense, net of amounts capitalized	(169)	(183)	(191)
Other income (expense), net	47	23	1
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(4)
Gain (Loss) Recognized in OCI on Derivative		10	(38)
Southern Power | Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(6)
Gain (Loss) Recognized in OCI on Derivative		7	(17)
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(84)
Gain (Loss) Recognized in OCI on Derivative		(78)	140
Southern Power | Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(24)
Gain (Loss) Recognized in OCI on Derivative		(24)	(23)
Southern Power | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(24)
Gain (Loss) Recognized in OCI on Derivative		(60)	159
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(7)
Gain (Loss) Recognized in OCI on Derivative		7	(9)
Interest expense, net of amounts capitalized	(232)	(228)	(200)
Other income (expense), net	20	1	44
Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(9)
Gain (Loss) Recognized in OCI on Derivative		7	(9)
Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	2
Gain (Loss) Recognized in OCI on Derivative		0	0
Southern Company Gas | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(2)
Gain (Loss) Recognized in OCI on Derivative		2	(2)
Southern Company Gas | Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenue	$ 1,319	$ 1,539	$ 1,601

DERIVATIVES - Cumulative Basis

DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Securities due within one year
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	$ 0	$ (498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	2
Securities due within one year | Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	0	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	0	2
Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(2,093)	(2,052)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 3	$ 41

DERIVATIVES - Pre-Tax Effects_4

DERIVATIVES - Pre-Tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Energy-related derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 235	$ (126)	$ (86)
Energy-related derivatives | Natural Gas Revenues | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	223	(122)	(80)
Energy-related derivatives | Cost of Natural Gas | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	10	(6)	(2)
Energy-related derivatives | Wholesale electric revenues | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	2	2	(4)
Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	3	5	23
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	56	19	24
Southern Company Gas | Energy-related derivatives | Natural Gas Revenues | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	223	(122)	(80)
Southern Company Gas | Energy-related derivatives | Cost of Natural Gas | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	233	(128)	(82)
Southern Company Gas | Energy-related derivatives | Other revenues | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 10	$ (6)	$ (2)

ACQUISITIONS AND DISPOSITIONS -

ACQUISITIONS AND DISPOSITIONS - SO Dispositions Narrative (Details) - USD ($)	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2019	Jul. 22, 2019
Business Acquisition [Line Items]
Gain (loss) on dispositions							$ (2,569,000,000)	$ (291,000,000)	$ (40,000,000)
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	70,000,000	$ 4,000,000	$ (15,000,000)	$ 2,500,000,000	2,600,000,000
Gain on dispositions, after tax		$ 1,400,000,000	102,000,000	4,000,000	(11,000,000)	$ 1,300,000,000	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				5,000,000
Gain (loss) on dispositions							(58,000,000)
Gain on dispositions, after tax							(52,000,000)
Consideration for sale	$ 9,000,000		$ 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 | Leveraged Lease Investment
Business Acquisition [Line Items]
Consideration for sale										$ 20,000,000
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

ACQUISITIONS AND DISPOSITIONS_2

ACQUISITIONS AND DISPOSITIONS - Alabama Power Narrative (Details) - Alabama Power - Autauga Combined Cycle Acquisition - MW	Sep. 06, 2019	Sep. 01, 2020
Business Acquisition [Line Items]
Power sales agreement, remaining term	3 years
Scenario, Forecast
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW)		885

ACQUISITIONS AND DISPOSITIONS_3

ACQUISITIONS AND DISPOSITIONS - Schedule of Acquisitions (Details) - Southern Power $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2018MW	Dec. 31, 2019USD ($)MW	Dec. 31, 2018
DSGP
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		28
PPA Contract Period		15 years
Payments to acquire businesses | $		$ 167
Results of operations, percentage consolidated		100.00%
Noncontrolling interest, approximate nameplate capacity (in MW)		10
Approximate nameplate capacity, repowered amount (in MW)		18
Fuel cells, before repower, carrying value | $		$ 55
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	20
PPA Contract Period	20 years
Results of operations, percentage consolidated			100.00%
DSGP | Class B Membership Interest | DSGP
Business Acquisition [Line Items]
Ownership Percentage		100.00%
Gaskell West 1 | Class B Membership Interest | Gaskell West 1
Business Acquisition [Line Items]
Ownership Percentage	100.00%

ACQUISITIONS AND DISPOSITIONS_4

ACQUISITIONS AND DISPOSITIONS - SPC Acquisitions and Dispositions Narrative (Details) $ in Millions

Jan. 17, 2020USD ($)

Jun. 13, 2019USD ($)MW

Dec. 11, 2018wind_farminvestor

May 22, 2018

Dec. 31, 2018USD ($)wind_farminvestor

Sep. 30, 2018operating_facility

May 31, 2018USD ($)

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2019USD ($)facilityMW

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

May 31, 2019MW

Business Acquisition [Line Items]

Construction work in progress

$ 7,254

$ 7,880

$ 7,254

Impairment charges

168

210

$ 0

Assets held for sale

393

188

393

Sale of noncontrolling interests

1,273

Gain (loss) on dispositions

(2,569)

(291)

(40)

Southern Power

Business Acquisition [Line Items]

Construction work in progress

$ 430

515

430

Impairment charges

$ 3

156

$ 0

Sale of noncontrolling interests

[1]

1,273

Number of wind facilities | operating_facility

8

Southern Power | Mankato

Business Acquisition [Line Items]

Approximate nameplate capacity (in MW) | MW

385

385

Southern Power | Series of Business Acquisitions

Business Acquisition [Line Items]

Number of facilities under construction | facility

2

Construction work in progress

$ 417

Southern Power | Minimum | Series of Business Acquisitions

Business Acquisition [Line Items]

Aggregate construction costs

490

Southern Power | Maximum | Series of Business Acquisitions

Business Acquisition [Line Items]

Aggregate construction costs

535

Wind Generating Facility | Southern Power

Business Acquisition [Line Items]

Impairment charges

36

Assets held for sale

$ 17

Scenario, Forecast | Wind Generating Facility | Southern Power

Business Acquisition [Line Items]

Project qualification for production tax credits, percentage

80.00%

100.00%

SP Solar Holdings I, LP | Southern Power

Business Acquisition [Line Items]

Sale of equity interest in limited partnership

33.00%

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]

Sale of equity interest in limited partnership

100.00%

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

(410)

$ (417)

[1]

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

After tax impairment charges

$ 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 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

Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mankato | Southern Power

Business Acquisition [Line Items]

Consideration for sale

$ 663

Gain (loss) on dispositions

39

Gain on dispositions, after tax

$ 23

[1]

See Note 15 under " Southern Power - Sales of Renewable Facility Interests " for additional information.

ACQUISITIONS AND DISPOSITIONS_5

ACQUISITIONS AND DISPOSITIONS - Construction Projects (Details) - Southern Power - MW	1 Months Ended		3 Months Ended
	Dec. 31, 2019	May 31, 2019	Jun. 30, 2020	Oct. 31, 2019	Aug. 31, 2018	May 31, 2018
Mankato
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	385	385
PPA Contract Period		20 years
Wild Horse Mountain
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	100
PPA Contract Period	20 years
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%
Reading | Reading
Business Acquisition [Line Items]
Noncontrolling ownership percentage held by parent					100.00%
Reading | Class B Membership Interest | Reading
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%
Scenario, Forecast | Reading
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			200
PPA Contract Period			12 years
Scenario, Forecast | Skookumchuck
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			136
PPA Contract Period			20 years

ACQUISITIONS AND DISPOSITIONS_6

ACQUISITIONS AND DISPOSITIONS - GAS Acquisitions and Dispositions Narrative (Details)	Feb. 07, 2020USD ($)payment	May 29, 2019USD ($)	Jul. 31, 2018USD ($)utility	Jun. 30, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Impairment charges					$ 0
Gain (loss) on dispositions										$ (2,569,000,000)	$ (291,000,000)	$ (40,000,000)
Southern Company Gas
Business Acquisition [Line Items]
Impairment charges					$ 0					115,000,000	42,000,000	0
Number of natural gas distribution utilities sold | utility			3
Gain (loss) on dispositions										0	$ (291,000,000)	$ 0
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
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax						$ (15,000,000)	$ 40,000,000	$ (76,000,000)
Gain (loss) on dispositions						$ (27,000,000)	$ 353,000,000	$ (36,000,000)
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				$ 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
Subsequent Event | Southern Company Gas | Pivotal LNG And Atlantic Coast Pipeline
Business Acquisition [Line Items]
Number of contingent milestone payments | payment	2
Contingent milestone payment, amount	$ 5,000,000
Subsequent Event | 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	$ 165,000,000

ACQUISITIONS AND DISPOSITIONS_7

ACQUISITIONS AND DISPOSITIONS - Held For Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets Held for Sale:
Current assets	$ 19	$ 393
Total property, plant, and equipment	565	4,583
Goodwill and other intangible assets	40	40
Equity investments in unconsolidated subsidiaries	151	0
Other non-current assets	14	727
Total Assets Held for Sale	789	5,743
Liabilities Held for Sale:
Current liabilities	5	425
Long-term debt	0	1,286
Accumulated deferred income taxes	0	618
Other non-current liabilities	0	932
Total Liabilities Held for Sale	5	3,261
Southern Power
Assets Held for Sale:
Current assets	17	8
Total property, plant, and equipment	547	536
Goodwill and other intangible assets	40	40
Equity investments in unconsolidated subsidiaries	0	0
Other non-current assets	14	0
Total Assets Held for Sale	618	584
Liabilities Held for Sale:
Current liabilities	3	15
Long-term debt	0	0
Accumulated deferred income taxes	0	0
Other non-current liabilities	0	0
Total Liabilities Held for Sale	3	$ 15
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
Other non-current assets	0
Total Assets Held for Sale	171
Liabilities Held for Sale:
Current liabilities	2
Long-term debt	0
Accumulated deferred income taxes	0
Other non-current liabilities	0
Total Liabilities Held for Sale	$ 2

ACQUISITIONS AND DISPOSITIONS_8

ACQUISITIONS AND DISPOSITIONS - Pre-tax Profit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gulf Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes		$ 140	$ 229
Florida Plants | Southern Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes		49	37
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	$ 25
Mankato | Southern Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 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, 2019USD ($)statepipelinesegment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Total operating revenues		$ 21,419	$ 23,495	$ 23,031
Traditional Operating Companies
Segment Reporting Information [Line Items]
Number of states in which entity operates (states) | state		3
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues		$ 1,938	2,205	2,075
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues		$ 3,792	3,909	3,920
Number of states in which entity operates (states) | state		4
Number of natural gas distribution utilities sold | utility	3
Number of reportable segments | segment		4
Southern Natural Gas Company, LLC | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		50.00%
Dalton Pipeline | Southern Company Gas
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment		50.00%
Southern Power | Southern Company Gas
Segment Reporting Information [Line Items]
Natural gas revenues		$ 64	119	119
Traditional Electric Operating Companies | Southern Company Gas
Segment Reporting Information [Line Items]
Natural gas revenues		14	32	23
Wholesale revenues, affiliates | Southern Power
Segment Reporting Information [Line Items]
Total operating revenues		$ 398	$ 435	$ 392
Pipelines | Southern Company Gas
Segment Reporting Information [Line Items]
Number of pipeline construction projects | pipeline		2

SEGMENT AND RELATED INFORMATI_4

SEGMENT AND RELATED INFORMATION - Financial Data for Business Segments (Details)	Jan. 01, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2019USD ($)utility	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2019USD ($)utility	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Total operating revenues												$ 21,419,000,000	$ 23,495,000,000	$ 23,031,000,000
Depreciation and amortization												3,038,000,000	3,131,000,000	3,010,000,000
Interest income												60,000,000	38,000,000	26,000,000
Earnings from equity method investments												162,000,000	148,000,000	106,000,000
Interest expense												1,736,000,000	1,842,000,000	1,694,000,000
Income taxes												1,798,000,000	449,000,000	142,000,000
Segment net income (loss)			$ 409,000,000	$ 1,345,000,000	$ 931,000,000	$ 2,059,000,000	$ 269,000,000	$ 1,222,000,000	$ (127,000,000)	$ 936,000,000		4,739,000,000	2,226,000,000	842,000,000
Goodwill			5,280,000,000				5,315,000,000					5,280,000,000	5,315,000,000	6,268,000,000
Total Assets			118,700,000,000				116,914,000,000					118,700,000,000	116,914,000,000	111,005,000,000
Gross property additions												7,814,000,000	8,205,000,000	5,984,000,000
Depreciation and amortization												3,331,000,000	3,549,000,000	3,457,000,000
Operating Income			690,000,000	2,013,000,000	1,342,000,000	3,691,000,000	578,000,000	2,174,000,000	63,000,000	1,376,000,000		7,736,000,000	4,191,000,000	2,333,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on plants under construction												24,000,000	1,097,000,000	3,362,000,000
Gain (loss) on dispositions												(2,569,000,000)	(291,000,000)	(40,000,000)
Impairment charges												168,000,000	210,000,000	0
Lease, impairment loss			17,000,000
Lease, impairment loss, after tax			13,000,000
Gain (loss) on asset sales												2,588,000,000	301,000,000	42,000,000
Impairment charges			0
Plant Scherer Unit 3
Segment and Related Information (Textual) [Abstract]
After tax charge to income											$ 20,000,000
Pre-tax charge to income											$ 33,000,000
Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												17,095,000,000	18,571,000,000	18,540,000,000
Depreciation and amortization												2,472,000,000	2,565,000,000	2,457,000,000
Interest income												47,000,000	31,000,000	21,000,000
Earnings from equity method investments												5,000,000	(1,000,000)	1,000,000
Interest expense												987,000,000	1,035,000,000	1,011,000,000
Income taxes												708,000,000	207,000,000	82,000,000
Segment net income (loss)												3,268,000,000	2,304,000,000	878,000,000
Goodwill			2,000,000				2,000,000					2,000,000	2,000,000	2,000,000
Total Assets			94,650,000,000				93,959,000,000					94,650,000,000	93,959,000,000	87,085,000,000
Gross property additions												6,237,000,000	6,392,000,000	4,104,000,000
Traditional Operating Companies
Segment and Related Information (Textual) [Abstract]
Pre-tax charge to income												24,000,000	1,100,000,000	3,400,000,000
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)													367,000,000
Traditional Operating Companies | Kemper IGCC
Segment and Related Information (Textual) [Abstract]
After tax charge to income												24,000,000	722,000,000	2,400,000,000
Traditional Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												15,569,000,000	16,843,000,000	16,884,000,000
Depreciation and amortization												1,993,000,000	2,072,000,000	1,954,000,000
Interest income												38,000,000	23,000,000	14,000,000
Earnings from equity method investments												2,000,000	(1,000,000)	1,000,000
Interest expense												818,000,000	852,000,000	820,000,000
Income taxes												764,000,000	371,000,000	1,021,000,000
Segment net income (loss)												2,929,000,000	2,117,000,000	(193,000,000)
Goodwill			0				0					0	0	0
Total Assets			81,063,000,000				79,382,000,000					81,063,000,000	79,382,000,000	72,204,000,000
Gross property additions												5,748,000,000	6,077,000,000	3,836,000,000
Southern Power
Segment and Related Information (Textual) [Abstract]
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)													743,000,000
Southern Power | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												1,938,000,000	2,205,000,000	2,075,000,000
Depreciation and amortization												479,000,000	493,000,000	503,000,000
Interest income												9,000,000	8,000,000	7,000,000
Earnings from equity method investments												3,000,000	0	0
Interest expense												169,000,000	183,000,000	191,000,000
Income taxes												(56,000,000)	(164,000,000)	(939,000,000)
Segment net income (loss)												339,000,000	187,000,000	1,071,000,000
Goodwill			2,000,000				2,000,000					2,000,000	2,000,000	2,000,000
Total Assets			14,300,000,000				14,883,000,000					14,300,000,000	14,883,000,000	15,206,000,000
Gross property additions												489,000,000	315,000,000	268,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues												3,792,000,000	3,909,000,000	3,920,000,000
Depreciation and amortization												487,000,000	500,000,000	501,000,000
Interest income												3,000,000	4,000,000	3,000,000
Earnings from equity method investments												157,000,000	148,000,000	106,000,000
Interest expense												232,000,000	228,000,000	200,000,000
Income taxes												130,000,000	464,000,000	367,000,000
Segment net income (loss)												585,000,000	372,000,000	243,000,000
Goodwill			5,015,000,000				5,015,000,000					5,015,000,000	5,015,000,000	5,967,000,000
Total Assets			21,687,000,000				21,448,000,000					21,687,000,000	21,448,000,000	22,987,000,000
Gross property additions												1,418,000,000	1,399,000,000	1,525,000,000
Segment and Related Information (Textual) [Abstract]
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)													93,000,000
All other
Segment Reporting Information [Line Items]
Total operating revenues												690,000,000	1,213,000,000	741,000,000
Depreciation and amortization												79,000,000	66,000,000	52,000,000
Interest income												16,000,000	8,000,000	11,000,000
Earnings from equity method investments												0	2,000,000	(1,000,000)
Interest expense												517,000,000	580,000,000	490,000,000
Income taxes												960,000,000	(222,000,000)	(307,000,000)
Segment net income (loss)												908,000,000	(453,000,000)	(279,000,000)
Goodwill			263,000,000				298,000,000					263,000,000	298,000,000	299,000,000
Total Assets			3,511,000,000				3,285,000,000					3,511,000,000	3,285,000,000	2,552,000,000
Gross property additions												159,000,000	414,000,000	355,000,000
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues												(158,000,000)	(198,000,000)	(170,000,000)
Depreciation and amortization												0	0	0
Interest income												(6,000,000)	(5,000,000)	(9,000,000)
Earnings from equity method investments												0	(1,000,000)	0
Interest expense												0	(1,000,000)	(7,000,000)
Income taxes												0	0	0
Segment net income (loss)												(22,000,000)	3,000,000	0
Goodwill			0				0					0	0	0
Total Assets			(1,148,000,000)				(1,778,000,000)					(1,148,000,000)	(1,778,000,000)	(1,619,000,000)
Gross property additions												0	0	0
Intersegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												(412,000,000)	(477,000,000)	(419,000,000)
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												0	0	0
Segment net income (loss)												0	0	0
Goodwill			0				0					0	0	0
Total Assets			(713,000,000)				(306,000,000)					(713,000,000)	(306,000,000)	(325,000,000)
Gross property additions												0	0	0
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues												1,938,000,000	2,205,000,000	2,075,000,000
Depreciation and amortization												479,000,000	493,000,000	503,000,000
Interest expense												169,000,000	183,000,000	191,000,000
Income taxes							75,000,000					(56,000,000)	(164,000,000)	(939,000,000)
Segment net income (loss)			(12,000,000)	111,000,000	203,000,000	27,000,000	(60,000,000)	146,000,000	45,000,000	115,000,000		339,000,000	187,000,000	1,071,000,000
Total Assets			14,300,000,000				14,883,000,000					14,300,000,000	14,883,000,000
Depreciation and amortization												505,000,000	524,000,000	536,000,000
Operating Income			15,000,000	167,000,000	153,000,000	60,000,000	30,000,000	136,000,000	16,000,000	60,000,000		395,000,000	242,000,000	368,000,000
Segment and Related Information (Textual) [Abstract]
Impairment charges												3,000,000	156,000,000	0
After tax impairment charges													117,000,000
Gain (loss) on asset sales												(23,000,000)	(2,000,000)	0
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues												3,792,000,000	3,909,000,000	3,920,000,000
Earnings from equity method investments												157,000,000	148,000,000	106,000,000
Interest expense												232,000,000	228,000,000	200,000,000
Income taxes												130,000,000	464,000,000	367,000,000
Segment net income (loss)			238,000,000	(29,000,000)	106,000,000	270,000,000	78,000,000	46,000,000	(31,000,000)	279,000,000		585,000,000	372,000,000	243,000,000
Goodwill			5,015,000,000				5,015,000,000					5,015,000,000	5,015,000,000
Total Assets			21,687,000,000				21,448,000,000					21,687,000,000	21,448,000,000	22,987,000,000
Gross property additions												1,466,000,000	1,521,000,000	1,508,000,000
Depreciation and amortization												487,000,000	500,000,000	501,000,000
Operating Income			318,000,000	(35,000,000)	134,000,000	353,000,000	104,000,000	374,000,000	49,000,000	388,000,000		770,000,000	915,000,000	660,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions												0	(291,000,000)	0
Gain (loss) on asset sales												0	291,000,000	0
Impairment charges			0									115,000,000	42,000,000	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
Segment and Related Information (Textual) [Abstract]
Gain (loss) on asset sales												324,000,000
Net gain (loss) on dispositions, net of tax												16,000,000
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Goodwill			981,000,000				981,000,000					981,000,000	981,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on asset sales												(33,000,000)
Net gain (loss) on dispositions, net of tax												(67,000,000)
Southern Company Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues												(62,000,000)	(76,000,000)	(234,000,000)
Earnings from equity method investments												0	0	0
Interest expense												0	0	0
Income taxes												0	0	0
Segment net income (loss)												0	0	0
Total Assets			(11,300,000,000)				(11,582,000,000)					(11,300,000,000)	(11,582,000,000)	(14,039,000,000)
Gross property additions												0	0	0
Depreciation and amortization												0	0	0
Operating Income												0	0	0
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues												3,810,000,000	3,930,000,000	4,090,000,000
Earnings from equity method investments												162,000,000	145,000,000	103,000,000
Interest expense												225,000,000	227,000,000	191,000,000
Income taxes												200,000,000	495,000,000	311,000,000
Segment net income (loss)												677,000,000	435,000,000	358,000,000
Total Assets			22,228,000,000				21,918,000,000					22,228,000,000	21,918,000,000	24,300,000,000
Gross property additions												1,439,000,000	1,467,000,000	1,457,000,000
Depreciation and amortization												454,000,000	453,000,000	457,000,000
Operating Income												924,000,000	1,013,000,000	717,000,000
Southern Company Gas | Operating Segments | All other
Segment Reporting Information [Line Items]
Total operating revenues												44,000,000	55,000,000	64,000,000
Earnings from equity method investments												(5,000,000)	3,000,000	3,000,000
Interest expense												7,000,000	1,000,000	9,000,000
Income taxes												(70,000,000)	(31,000,000)	56,000,000
Segment net income (loss)												(92,000,000)	(63,000,000)	(115,000,000)
Total Assets			10,759,000,000				11,112,000,000					10,759,000,000	11,112,000,000	12,726,000,000
Gross property additions												27,000,000	54,000,000	51,000,000
Depreciation and amortization												33,000,000	47,000,000	44,000,000
Operating Income												(154,000,000)	(98,000,000)	(57,000,000)
Southern Company Gas | Operating Segments | Gas Distribution Operations
Segment Reporting Information [Line Items]
Total operating revenues												3,028,000,000	3,186,000,000	3,207,000,000
Earnings from equity method investments												0	0	0
Interest expense												187,000,000	178,000,000	153,000,000
Income taxes												63,000,000	409,000,000	178,000,000
Segment net income (loss)												337,000,000	334,000,000	353,000,000
Total Assets			18,204,000,000				17,266,000,000					18,204,000,000	17,266,000,000	19,358,000,000
Gross property additions												1,433,000,000	1,429,000,000	1,330,000,000
Depreciation and amortization												422,000,000	409,000,000	391,000,000
Operating Income												573,000,000	904,000,000	645,000,000
Segment and Related Information (Textual) [Abstract]
Disposal group, including discontinued operation, revenue												244,000,000	399,000,000
Southern Company Gas | Operating Segments | Gas Pipeline Investments
Segment Reporting Information [Line Items]
Total operating revenues												32,000,000	32,000,000	17,000,000
Earnings from equity method investments												162,000,000	145,000,000	103,000,000
Interest expense												30,000,000	34,000,000	26,000,000
Income taxes												58,000,000	28,000,000	109,000,000
Segment net income (loss)												94,000,000	103,000,000	(22,000,000)
Total Assets			1,678,000,000				1,763,000,000					1,678,000,000	1,763,000,000	1,699,000,000
Gross property additions												1,000,000	32,000,000	117,000,000
Depreciation and amortization												5,000,000	5,000,000	2,000,000
Operating Income												20,000,000	20,000,000	10,000,000
Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues												294,000,000	144,000,000	6,000,000
Earnings from equity method investments												0	0	0
Interest expense												5,000,000	9,000,000	7,000,000
Income taxes												52,000,000	4,000,000	0
Segment net income (loss)												163,000,000	38,000,000	(57,000,000)
Total Assets			850,000,000				1,302,000,000					850,000,000	1,302,000,000	1,096,000,000
Gross property additions												1,000,000	0	1,000,000
Less Gross Gas Costs												5,684,000,000	7,262,000,000	6,627,000,000
Depreciation and amortization												1,000,000	2,000,000	2,000,000
Operating Income												219,000,000	70,000,000	(51,000,000)
Southern Company Gas | Operating Segments | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues												456,000,000	568,000,000	860,000,000
Earnings from equity method investments												0	0	0
Interest expense												3,000,000	6,000,000	5,000,000
Income taxes												27,000,000	54,000,000	24,000,000
Segment net income (loss)												83,000,000	(40,000,000)	84,000,000
Total Assets			$ 1,496,000,000				1,587,000,000					1,496,000,000	1,587,000,000	2,147,000,000
Gross property additions												4,000,000	6,000,000	9,000,000
Depreciation and amortization												26,000,000	37,000,000	62,000,000
Operating Income												112,000,000	19,000,000	113,000,000
Segment and Related Information (Textual) [Abstract]
Disposal group, including discontinued operation, revenue												55,000,000	129,000,000
Third Party Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues												5,703,000,000	6,955,000,000	6,152,000,000
Intercompany Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues												275,000,000	451,000,000	481,000,000
Total Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues												$ 5,978,000,000	$ 7,406,000,000	$ 6,633,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Number of distribution utilities | utility			3,000,000,000									3,000,000,000
Gain (loss) on dispositions							(27,000,000)	353,000,000	(36,000,000)
Gain (loss) on dispositions, after tax							$ (15,000,000)	$ 40,000,000	$ (76,000,000)
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							$ 23,000,000
Gain (loss) on dispositions, after tax					88,000,000							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		$ 70,000,000	4,000,000	(15,000,000)	2,500,000,000						2,600,000,000
Gain (loss) on dispositions, after tax	$ 1,400,000,000		102,000,000	4,000,000	(11,000,000)	$ 1,300,000,000						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)
Impairment charges			12,000,000	14,000,000	$ 32,000,000
After tax impairment charges			$ 5,000,000	$ 15,000,000
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)
Gain (loss) on asset sales												291,000,000
Net gain (loss) on dispositions, net of tax												(51,000,000)
Impairment charges										$ 42,000,000		42,000,000
Natural Gas Storage Facility | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Impairment charges												115,000,000
After tax impairment charges												$ 86,000,000

SEGMENT AND RELATED INFORMATI_5

SEGMENT AND RELATED INFORMATION - Electric Utilities' Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Total operating revenues	$ 21,419	$ 23,495	$ 23,031
Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	14,084	15,222	15,330
Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	636	664	681
Electric Utilities
Revenue from External Customer [Line Items]
Total operating revenues	17,095	18,571	18,540
Electric Utilities | Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	14,084	15,222	15,330
Electric Utilities | Wholesale
Revenue from External Customer [Line Items]
Total operating revenues	2,152	2,516	2,426
Electric Utilities | Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	$ 859	$ 833	$ 784

SEGMENT AND RELATED INFORMATI_6

SEGMENT AND RELATED INFORMATION - Gas Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total operating revenues	$ 21,419	$ 23,495	$ 23,031
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	3,792	3,909	3,920
Southern Company Gas | Gas Distribution Operations
Segment Reporting Information [Line Items]
Total operating revenues	3,001	3,155	3,024
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues	456	568	860
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Total operating revenues	$ 335	$ 186	$ 36

QUARTERLY FINANCIAL INFORMATI_3

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($)	Jan. 01, 2019	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2017
Summarized quarterly financial information
Operating revenues				$ 4,914,000,000	$ 5,995,000,000	$ 5,098,000,000	$ 5,412,000,000	$ 5,337,000,000	$ 6,159,000,000	$ 5,627,000,000	$ 6,372,000,000
Operating Income				690,000,000	2,013,000,000	1,342,000,000	3,691,000,000	578,000,000	2,174,000,000	63,000,000	1,376,000,000		$ 7,736,000,000	$ 4,191,000,000	$ 2,333,000,000
Net Income (Loss)				409,000,000	1,345,000,000	931,000,000	2,059,000,000	269,000,000	1,222,000,000	(127,000,000)	936,000,000		4,739,000,000	2,226,000,000	842,000,000
Consolidated Net Income Attributable to Southern Company				440,000,000	$ 1,316,000,000	$ 899,000,000	$ 2,084,000,000	$ 278,000,000	$ 1,164,000,000	$ (154,000,000)	$ 938,000,000
Gain (loss) on dispositions													(2,569,000,000)	(291,000,000)	(40,000,000)
Impairment charges													168,000,000	210,000,000	0
Lease, impairment loss				17,000,000
Lease, impairment loss, after tax				13,000,000
Income taxes													$ 1,798,000,000	$ 449,000,000	$ 142,000,000
Impairment charges				$ 0
Basic (in dollars per share)				$ 0.42	$ 1.26	$ 0.86	$ 2.01	$ 0.27	$ 1.14	$ (0.15)	$ 0.93		$ 4.53	$ 2.18	$ 0.84
Diluted (in dollars per share)				$ 0.42	$ 1.25	$ 0.85	$ 1.99	$ 0.27	$ 1.13	$ (0.15)	$ 0.92		$ 4.50	$ 2.17	$ 0.84
Alabama Power
Summarized quarterly financial information
Operating revenues				$ 1,363,000,000	$ 1,841,000,000	$ 1,513,000,000	$ 1,408,000,000	$ 1,316,000,000	$ 1,740,000,000	$ 1,503,000,000	$ 1,473,000,000
Operating Income				134,000,000	676,000,000	445,000,000	338,000,000	164,000,000	561,000,000	380,000,000	372,000,000		$ 1,593,000,000	$ 1,477,000,000	$ 1,657,000,000
Net Income (Loss)				88,000,000	469,000,000	296,000,000	217,000,000	73,000,000	373,000,000	259,000,000	225,000,000		1,070,000,000	930,000,000	848,000,000
Consolidated Net Income Attributable to Southern Company				88,000,000	469,000,000	296,000,000	217,000,000	73,000,000	373,000,000	259,000,000	225,000,000
Income taxes													270,000,000	291,000,000	568,000,000
Georgia Power
Summarized quarterly financial information
Operating revenues				1,703,000,000	2,755,000,000	2,117,000,000	1,833,000,000	1,818,000,000	2,593,000,000	2,048,000,000	1,961,000,000
Operating Income				205,000,000	1,161,000,000	647,000,000	448,000,000	257,000,000	991,000,000	(472,000,000)	513,000,000		2,461,000,000	1,289,000,000	2,573,000,000
Net Income (Loss)				122,000,000	839,000,000	448,000,000	311,000,000	173,000,000	664,000,000	(396,000,000)	352,000,000		1,720,000,000	793,000,000	1,414,000,000
Consolidated Net Income Attributable to Southern Company				122,000,000	839,000,000	448,000,000	311,000,000	173,000,000	664,000,000	(396,000,000)	352,000,000
Income taxes													472,000,000	214,000,000	830,000,000
Mississippi Power
Summarized quarterly financial information
Operating revenues				294,000,000	370,000,000	313,000,000	287,000,000	308,000,000	358,000,000	297,000,000	302,000,000
Operating Income				22,000,000	93,000,000	54,000,000	56,000,000	52,000,000	80,000,000	54,000,000	7,000,000		225,000,000	193,000,000	(3,151,000,000)
Net Income (Loss)				0	65,000,000	37,000,000	37,000,000	149,000,000	47,000,000	46,000,000	(7,000,000)		139,000,000	235,000,000	(2,590,000,000)
Consolidated Net Income Attributable to Southern Company				0	65,000,000	37,000,000	37,000,000	149,000,000	47,000,000	46,000,000	(7,000,000)
Pre-tax charge (credit) to income								(9,000,000)
After tax charge (credit) to income								(95,000,000)
Income taxes													30,000,000	(102,000,000)	(532,000,000)
Southern Power
Summarized quarterly financial information
Operating revenues				411,000,000	574,000,000	510,000,000	443,000,000	506,000,000	635,000,000	555,000,000	509,000,000
Operating Income				15,000,000	167,000,000	153,000,000	60,000,000	30,000,000	136,000,000	16,000,000	60,000,000		395,000,000	242,000,000	368,000,000
Net Income (Loss)				(12,000,000)	111,000,000	203,000,000	27,000,000	(60,000,000)	146,000,000	45,000,000	115,000,000		339,000,000	187,000,000	1,071,000,000
Consolidated Net Income Attributable to Southern Company				23,000,000	86,000,000	174,000,000	56,000,000	(48,000,000)	92,000,000	22,000,000	121,000,000				1,071,000,000
Impairment charges													3,000,000	156,000,000	0
After tax impairment charges														117,000,000
Income taxes								75,000,000					(56,000,000)	(164,000,000)	(939,000,000)
Southern Company Gas
Summarized quarterly financial information
Operating revenues				1,131,000,000	498,000,000	689,000,000	1,474,000,000	1,048,000,000	492,000,000	730,000,000	1,639,000,000
Operating Income				318,000,000	(35,000,000)	134,000,000	353,000,000	104,000,000	374,000,000	49,000,000	388,000,000		770,000,000	915,000,000	660,000,000
Net Income (Loss)				238,000,000	(29,000,000)	106,000,000	270,000,000	78,000,000	46,000,000	(31,000,000)	279,000,000		585,000,000	372,000,000	243,000,000
Consolidated Net Income Attributable to Southern Company				238,000,000	(29,000,000)	106,000,000	270,000,000	78,000,000	46,000,000	(31,000,000)	279,000,000
Gain (loss) on dispositions													0	(291,000,000)	0
Income taxes													130,000,000	464,000,000	367,000,000
Impairment charges				0									115,000,000	42,000,000	$ 0
Plant Vogtle Units 3 And 4 | Georgia Power
Summarized quarterly financial information
Estimated loss on plants under construction										1,100,000,000
Kemper IGCC | Mississippi Power
Summarized quarterly financial information
Pre-tax charge (credit) to income			$ 2,800,000,000								44,000,000	$ 242,000,000	24,000,000	$ 37,000,000		$ 3,070,000,000
After tax charge (credit) to income			$ 2,000,000,000								33,000,000	$ 206,000,000				$ 1,890,000,000
Florida Plants | Southern Power
Summarized quarterly financial information
Impairment charges										119,000,000
After tax impairment charges										89,000,000
Natural Gas Storage Facility | Southern Company Gas
Summarized quarterly financial information
Impairment charges													115,000,000
After tax impairment charges													86,000,000
Wind Turbine Equipment | Southern Power
Summarized quarterly financial information
Impairment charges									36,000,000
After tax impairment charges									27,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Summarized quarterly financial information
Gain (loss) on dispositions								(27,000,000)	353,000,000	(36,000,000)
Gain (loss) on dispositions, after tax								$ (15,000,000)	$ 40,000,000	$ (76,000,000)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Summarized quarterly financial information
Gain (loss) on dispositions	$ 2,600,000,000			70,000,000	4,000,000	(15,000,000)	2,500,000,000						2,600,000,000
Gain (loss) on dispositions, after tax	$ 1,400,000,000			102,000,000	4,000,000	(11,000,000)	1,300,000,000						1,400,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PowerSecure International, Inc. Lighting Business
Summarized quarterly financial information
Gain (loss) on dispositions													(58,000,000)
Gain (loss) on dispositions, after tax													(52,000,000)
Impairment charges				12,000,000	14,000,000	32,000,000
After tax impairment charges				5,000,000	15,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Plant Nacogdoches | Southern Power
Summarized quarterly financial information
Gain (loss) on dispositions						23,000,000							23,000,000
Gain (loss) on dispositions, after tax						88,000,000							88,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Pivotal Home Solutions | Southern Company Gas
Summarized quarterly financial information
Gain (loss) on dispositions													(24,000,000)
Gain (loss) on dispositions, after tax		$ (67,000,000)											(17,000,000)
Impairment charges											$ 42,000,000		$ 42,000,000
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations | Gasifier-Related Assets | Mississippi Power
Summarized quarterly financial information
Pre-tax charge (credit) to income				14,000,000	4,000,000	4,000,000	2,000,000
After tax charge (credit) to income				17,000,000	3,000,000	$ 3,000,000	$ 1,000,000
LOUISIANA | Natural Gas Storage Facility | Southern Company Gas
Summarized quarterly financial information
Impairment charges				(1,000,000)	92,000,000
After tax impairment charges				$ 4,000,000	$ 65,000,000

VALUATION AND QUALIFYING ACCO_2

VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Millions	May 29, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 50	$ 44	$ 43
Charged to Income		68	69	56
Charged to Other Accounts		0	(1)	0
Deductions		69	61	55
Reclassified to Held for Sale		0	1	0
Balance at End of Period		49	50	44
Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		100	148	22
Charged to Income		13	(38)	126
Charged to Other Accounts		0	0	0
Deductions		0	10	0
Reclassified to Held for Sale		0	0	0
Balance at End of Period		113	100	148
Alabama Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		10	9	10
Charged to Income		24	13	10
Charged to Other Accounts		0	0	0
Deductions		12	12	11
Balance at End of Period		22	10	9
Georgia Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2	3	3
Charged to Income		13	11	11
Charged to Other Accounts		0	0	0
Deductions		13	12	11
Balance at End of Period		2	2	3
Georgia Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		33	0	0
Charged to Income		(5)	39	0
Charged to Other Accounts		0	0	0
Deductions		0	6	0
Balance at End of Period		28	33	0
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	0
Charged to Income		2	1	2
Charged to Other Accounts		0	0	0
Deductions		2	1	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	124	0
Charged to Income		0	(92)	124
Charged to Other Accounts		0	0	0
Deductions		0	0	0
Balance at End of Period		32	32	124
Southern Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		22	10	0
Charged to Income		7	12	10
Charged to Other Accounts		0	0	0
Deductions		0	0	0
Balance at End of Period		29	22	10
Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		30	28	27
Charged to Income		29	33	28
Charged to Other Accounts		0	(1)	0
Deductions		41	30	27
Balance at End of Period		18	30	28
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		12	11	19
Charged to Income		(8)	1	0
Charged to Other Accounts		0	0	0
Deductions		0	0	8
Balance at End of Period		4	$ 12	$ 11
Triton | Southern Company Gas
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Reversal of federal income tax valuation allowance	$ 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

Uncategorized Items - so10-k123

Label	Element	Value
Other Accounts And Notes Receivable [Member]
Restricted Cash	us-gaap_RestrictedCash	$ 3,000,000
Restricted Cash	us-gaap_RestrictedCash	114,000,000
Georgia Power [Member] | Other Accounts And Notes Receivable [Member]
Restricted Cash	us-gaap_RestrictedCash	0
Southern Company Gas [Member] | Other Accounts And Notes Receivable [Member]
Restricted Cash	us-gaap_RestrictedCash	3,000,000
Restricted Cash	us-gaap_RestrictedCash	$ 6,000,000