Georgia Power (GPJA) 10-K 20 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 29, 2018
Document Information [Line Items]
Entity Registrant Name	SOUTHERN CO
Entity Central Index Key	92,122
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 47
Entity Common Stock, Shares Outstanding		1,034,564,279
Alabama Power
Document Information [Line Items]
Entity Registrant Name	ALABAMA POWER CO
Entity Central Index Key	3,153
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		30,537,500
Georgia Power
Document Information [Line Items]
Entity Registrant Name	GEORGIA POWER CO
Entity Central Index Key	41,091
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		9,261,500
Mississippi Power
Document Information [Line Items]
Entity Registrant Name	MISSISSIPPI POWER CO
Entity Central Index Key	66,904
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,121,000
Southern Power
Document Information [Line Items]
Entity Registrant Name	SOUTHERN POWER CO
Entity Central Index Key	1,160,661
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,000
Southern Company Gas
Document Information [Line Items]
Entity Registrant Name	SOUTHERN Co GAS
Entity Central Index Key	1,004,155
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		100

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Revenues:
Total operating revenues			$ 23,495,000,000	$ 23,031,000,000	$ 19,896,000,000
Operating Expenses:
Other operations and maintenance			5,889,000,000	5,739,000,000	5,382,000,000
Depreciation and amortization			3,131,000,000	3,010,000,000	2,502,000,000
Taxes other than income taxes			1,315,000,000	1,250,000,000	1,113,000,000
Estimated loss on plants			1,097,000,000	3,362,000,000	428,000,000
Goodwill impairment			42,000,000
Impairment charges			210,000,000	0	0
Gain on dispositions, net			(291,000,000)	(40,000,000)	1,000,000
Gain on disposition			301,000,000	42,000,000	2,000,000
Depreciation and amortization			3,549,000,000	3,457,000,000	2,923,000,000
Total operating expenses			19,304,000,000	20,698,000,000	15,410,000,000
Operating Income			4,191,000,000	2,333,000,000	4,486,000,000
Other Income and (Expense):
Allowance for equity funds used during construction			138,000,000	160,000,000	202,000,000
Earnings from equity method investments			148,000,000	106,000,000	59,000,000
Interest expense, net of amounts capitalized			(1,842,000,000)	(1,694,000,000)	(1,317,000,000)
Other income (expense), net			114,000,000	163,000,000	50,000,000
Total other income and (expense)			(1,442,000,000)	(1,265,000,000)	(1,006,000,000)
Earnings Before Income Taxes			2,749,000,000	1,068,000,000	3,480,000,000
Income taxes			449,000,000	142,000,000	951,000,000
Net Income			2,300,000,000	926,000,000	2,529,000,000
Dividends on preferred and preference stock of subsidiaries			16,000,000	38,000,000	45,000,000
Net income attributable to noncontrolling interests			58,000,000	46,000,000	36,000,000
Net Income (Loss)			$ 2,226,000,000	$ 842,000,000	$ 2,448,000,000
Earnings per share —
Basic (in dollars per share)			$ 2.18	$ 0.84	$ 2.57
Diluted (in dollars per share)			$ 2.17	$ 0.84	$ 2.55
Average number of shares of common stock outstanding — (in millions)
Basic (in shares)			1,020	1,000	951
Diluted (in shares)			1,025	1,008	958
Retail electric revenues
Operating Revenues:
Total operating revenues			$ 15,222,000,000	$ 15,330,000,000	$ 15,234,000,000
Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues			2,516,000,000	2,426,000,000	1,926,000,000
Other electric revenues
Operating Revenues:
Total operating revenues			664,000,000	681,000,000	698,000,000
Fuel
Operating Expenses:
Cost of revenue			4,637,000,000	4,400,000,000	4,361,000,000
Purchased power
Operating Expenses:
Cost of revenue			971,000,000	863,000,000	750,000,000
Natural gas revenues
Operating Revenues:
Total operating revenues			3,854,000,000	3,791,000,000	1,596,000,000
Operating Expenses:
Cost of revenue			1,539,000,000	1,601,000,000	613,000,000
Other revenues
Operating Revenues:
Total operating revenues			1,239,000,000	803,000,000	442,000,000
Operating Expenses:
Cost of revenue			806,000,000	513,000,000	260,000,000
Alabama Power
Operating Revenues:
Total operating revenues			6,032,000,000	6,039,000,000	5,889,000,000
Operating Expenses:
Other operations and maintenance			1,669,000,000	1,709,000,000	1,557,000,000
Depreciation and amortization			764,000,000	736,000,000	703,000,000
Taxes other than income taxes			389,000,000	384,000,000	380,000,000
Purchased power, non-affiliates			216,000,000	170,000,000	166,000,000
Purchased power, affiliates			216,000,000	158,000,000	168,000,000
Depreciation and amortization			917,000,000	888,000,000	844,000,000
Total operating expenses			4,555,000,000	4,382,000,000	4,271,000,000
Operating Income			1,477,000,000	1,657,000,000	1,618,000,000
Other Income and (Expense):
Allowance for equity funds used during construction			62,000,000	39,000,000	28,000,000
Interest expense, net of amounts capitalized			(323,000,000)	(305,000,000)	(302,000,000)
Other income (expense), net			20,000,000	43,000,000	26,000,000
Total other income and (expense)			(241,000,000)	(223,000,000)	(248,000,000)
Earnings Before Income Taxes			1,236,000,000	1,434,000,000	1,370,000,000
Income taxes			291,000,000	568,000,000	531,000,000
Net Income			945,000,000	866,000,000	839,000,000
Dividends on preferred and preference stock of subsidiaries			15,000,000	18,000,000	17,000,000
Net Income (Loss)			930,000,000	848,000,000	822,000,000
Alabama Power | Retail electric revenues
Operating Revenues:
Total operating revenues			5,367,000,000	5,458,000,000	5,322,000,000
Alabama Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues			279,000,000	276,000,000	283,000,000
Alabama Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues			119,000,000	97,000,000	69,000,000
Alabama Power | Fuel
Operating Expenses:
Cost of revenue			1,301,000,000	1,225,000,000	1,297,000,000
Alabama Power | Other revenues
Operating Revenues:
Total operating revenues			267,000,000	208,000,000	215,000,000
Georgia Power
Operating Revenues:
Total operating revenues			8,420,000,000	8,310,000,000	8,383,000,000
Operating Expenses:
Other operations and maintenance			1,860,000,000	1,724,000,000	2,003,000,000
Depreciation and amortization			923,000,000	895,000,000	855,000,000
Taxes other than income taxes			437,000,000	409,000,000	405,000,000
Estimated loss on plants			1,060,000,000	0	0
Purchased power, non-affiliates			430,000,000	416,000,000	361,000,000
Purchased power, affiliates			723,000,000	622,000,000	518,000,000
Depreciation and amortization			1,142,000,000	1,100,000,000	1,063,000,000
Total operating expenses			7,131,000,000	5,737,000,000	5,949,000,000
Operating Income			1,289,000,000	2,573,000,000	2,434,000,000
Other Income and (Expense):
Interest expense, net of amounts capitalized			(397,000,000)	(419,000,000)	(388,000,000)
Other income (expense), net			115,000,000	104,000,000	81,000,000
Total other income and (expense)			(282,000,000)	(315,000,000)	(307,000,000)
Earnings Before Income Taxes			1,007,000,000	2,258,000,000	2,127,000,000
Income taxes			214,000,000	830,000,000	780,000,000
Net Income			793,000,000	1,428,000,000	1,347,000,000
Dividends on preferred and preference stock of subsidiaries			0	14,000,000	17,000,000
Net Income (Loss)			793,000,000	1,414,000,000	1,330,000,000
Georgia Power | Retail electric revenues
Operating Revenues:
Total operating revenues			7,752,000,000	7,738,000,000	7,772,000,000
Georgia Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues			163,000,000	163,000,000	175,000,000
Georgia Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues			24,000,000	26,000,000	42,000,000
Georgia Power | Fuel
Operating Expenses:
Cost of revenue			1,698,000,000	1,671,000,000	1,807,000,000
Georgia Power | Other revenues
Operating Revenues:
Total operating revenues			481,000,000	383,000,000	394,000,000
Mississippi Power
Operating Revenues:
Total operating revenues			1,265,000,000	1,187,000,000	1,163,000,000
Operating Expenses:
Other operations and maintenance			313,000,000	291,000,000	317,000,000
Depreciation and amortization			169,000,000	161,000,000	132,000,000
Taxes other than income taxes			107,000,000	104,000,000	109,000,000
Estimated loss on plants			37,000,000	3,362,000,000	428,000,000
Purchased power, affiliates			41,000,000	25,000,000	34,000,000
Depreciation and amortization			177,000,000	198,000,000	157,000,000
Total operating expenses			1,072,000,000	4,338,000,000	1,363,000,000
Operating Income			193,000,000	(3,151,000,000)	(200,000,000)
Other Income and (Expense):
Allowance for equity funds used during construction			0	72,000,000	124,000,000
Interest expense, net of amounts capitalized			(76,000,000)	(42,000,000)	(74,000,000)
Other income (expense), net			17,000,000	1,000,000	(2,000,000)
Total other income and (expense)			(59,000,000)	31,000,000	48,000,000
Earnings Before Income Taxes			134,000,000	(3,120,000,000)	(152,000,000)
Income taxes			(102,000,000)	(532,000,000)	(104,000,000)
Net Income			236,000,000	(2,588,000,000)	(48,000,000)
Dividends on preferred and preference stock of subsidiaries			1,000,000	2,000,000	2,000,000
Net Income (Loss)			235,000,000	(2,590,000,000)	(50,000,000)
Mississippi Power | Retail electric revenues
Operating Revenues:
Total operating revenues			889,000,000	854,000,000	859,000,000
Mississippi Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues			263,000,000	259,000,000	261,000,000
Mississippi Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues			91,000,000	56,000,000	26,000,000
Mississippi Power | Fuel
Operating Expenses:
Cost of revenue			405,000,000	395,000,000	343,000,000
Mississippi Power | Other revenues
Operating Revenues:
Total operating revenues			22,000,000	18,000,000	17,000,000
Southern Power
Operating Revenues:
Total operating revenues			2,205,000,000	2,075,000,000	1,577,000,000
Operating Expenses:
Other operations and maintenance			395,000,000	386,000,000	354,000,000
Depreciation and amortization			493,000,000	503,000,000	352,000,000
Taxes other than income taxes			46,000,000	48,000,000	23,000,000
Impairment charges			156,000,000	0	0
Gain on disposition			(2,000,000)	0	0
Purchased power, non-affiliates			176,000,000	149,000,000	102,000,000
Depreciation and amortization			524,000,000	536,000,000	370,000,000
Total operating expenses			1,963,000,000	1,707,000,000	1,287,000,000
Operating Income			242,000,000	368,000,000	290,000,000
Other Income and (Expense):
Interest expense, net of amounts capitalized			(183,000,000)	(191,000,000)	(117,000,000)
Other income (expense), net			23,000,000	1,000,000	6,000,000
Total other income and (expense)			(160,000,000)	(190,000,000)	(111,000,000)
Earnings Before Income Taxes			82,000,000	178,000,000	179,000,000
Income taxes			(164,000,000)	(939,000,000)	(195,000,000)
Net Income			246,000,000	1,117,000,000	374,000,000
Net income attributable to noncontrolling interests			59,000,000	46,000,000	36,000,000
Net Income (Loss)			187,000,000	1,071,000,000	338,000,000
Southern Power | Wholesale revenues, non-affiliates
Operating Revenues:
Total operating revenues			1,757,000,000	1,671,000,000	1,146,000,000
Southern Power | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues			435,000,000	392,000,000	419,000,000
Southern Power | Fuel
Operating Expenses:
Cost of revenue			699,000,000	621,000,000	456,000,000
Southern Power | Other revenues
Operating Revenues:
Total operating revenues				12,000,000	$ 12,000,000
Southern Company Gas
Operating Revenues:
Total operating revenues	$ 1,652,000,000		3,909,000,000	3,920,000,000
Operating Expenses:
Other operations and maintenance	480,000,000		981,000,000	945,000,000
Taxes other than income taxes	71,000,000		211,000,000	184,000,000
Goodwill impairment	0		42,000,000	0
Gain on dispositions, net	0		(291,000,000)	0
Gain on disposition	0		291,000,000	0
Depreciation and amortization	238,000,000		500,000,000	501,000,000
Merger-related expenses	41,000,000		0	0
Total operating expenses	1,453,000,000		2,994,000,000	3,260,000,000
Operating Income	199,000,000		915,000,000	660,000,000
Other Income and (Expense):
Earnings from equity method investments	60,000,000		148,000,000	106,000,000
Interest expense, net of amounts capitalized	(81,000,000)		(228,000,000)	(200,000,000)
Other income (expense), net	12,000,000		1,000,000	44,000,000
Total other income and (expense)	(9,000,000)		(79,000,000)	(50,000,000)
Earnings Before Income Taxes	190,000,000		836,000,000	610,000,000
Income taxes	76,000,000		464,000,000	367,000,000
Net Income	114,000,000		372,000,000	243,000,000
Net income attributable to noncontrolling interests	0		0	0
Net Income (Loss)	114,000,000		372,000,000	243,000,000
Southern Company Gas | Natural gas revenues
Operating Revenues:
Total operating revenues	1,591,000,000		3,874,000,000	3,787,000,000
Operating Expenses:
Cost of revenue	613,000,000		1,539,000,000	1,601,000,000
Southern Company Gas | Alternative revenue programs
Operating Revenues:
Total operating revenues	5,000,000		(20,000,000)	4,000,000
Southern Company Gas | Other revenues
Operating Revenues:
Total operating revenues	56,000,000		55,000,000	129,000,000
Operating Expenses:
Cost of revenue	$ 10,000,000		$ 12,000,000	$ 29,000,000
Predecessor | Southern Company Gas
Operating Revenues:
Total operating revenues		$ 1,905,000,000
Operating Expenses:
Other operations and maintenance		452,000,000
Taxes other than income taxes		99,000,000
Goodwill impairment		0
Gain on dispositions, net		0
Gain on disposition		0
Depreciation and amortization		206,000,000
Merger-related expenses		56,000,000
Total operating expenses		1,582,000,000
Operating Income		323,000,000
Other Income and (Expense):
Earnings from equity method investments		2,000,000
Interest expense, net of amounts capitalized		(96,000,000)
Other income (expense), net		3,000,000
Total other income and (expense)		(91,000,000)
Earnings Before Income Taxes		232,000,000
Income taxes		87,000,000
Net Income		145,000,000
Net income attributable to noncontrolling interests		14,000,000
Net Income (Loss)		131,000,000
Predecessor | Southern Company Gas | Natural gas revenues
Operating Revenues:
Total operating revenues		1,845,000,000
Operating Expenses:
Cost of revenue		755,000,000
Predecessor | Southern Company Gas | Alternative revenue programs
Operating Revenues:
Total operating revenues		(4,000,000)
Predecessor | Southern Company Gas | Other revenues
Operating Revenues:
Total operating revenues		64,000,000
Operating Expenses:
Cost of revenue		$ 14,000,000

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - Southern Company Gas - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Excise taxes collected	$ 32		$ 114	$ 100
Predecessor
Excise taxes collected		$ 57

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Net Income			$ 2,300	$ 926	$ 2,529
Qualifying hedges:
Changes in fair value, net of tax			(47)
Changes in fair value, net of tax				57	(136)
Reclassification adjustment for amounts included in net income, net of tax			72
Reclassification adjustment for amounts included in net income, net of tax				(60)	69
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax			(5)	17	13
Reclassification adjustment for amounts included in net income, net of tax			6	(23)	4
Total other comprehensive income (loss)			26	(9)	(50)
Dividends on preferred and preference stock of subsidiaries			16	38	45
Comprehensive income attributable to noncontrolling interests			58	46	36
Current period change			2,252	833	2,398
Alabama Power
Consolidated Net Income			945	866	839
Qualifying hedges:
Changes in fair value, net of tax			0
Changes in fair value, net of tax				1	(2)
Reclassification adjustment for amounts included in net income, net of tax			4
Reclassification adjustment for amounts included in net income, net of tax				3	4
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)			4	4	2
Dividends on preferred and preference stock of subsidiaries			15	18	17
Current period change			949	870	841
Georgia Power
Consolidated Net Income			793	1,428	1,347
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax			3
Reclassification adjustment for amounts included in net income, net of tax				3	2
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)			3	3	2
Dividends on preferred and preference stock of subsidiaries			0	14	17
Current period change			796	1,431	1,349
Mississippi Power
Consolidated Net Income			236	(2,588)	(48)
Qualifying hedges:
Changes in fair value, net of tax			(1)
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)			0	0	2
Dividends on preferred and preference stock of subsidiaries			1	2	2
Current period change			236	(2,588)	(46)
Southern Power
Consolidated Net Income			246	1,117	374
Qualifying hedges:
Changes in fair value, net of tax			(51)
Changes in fair value, net of tax				63	(27)
Reclassification adjustment for amounts included in net income, net of tax			58
Reclassification adjustment for amounts included in net income, net of tax				(73)	58
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax			5	0	0
Reclassification adjustment for amounts included in net income, net of tax			2	0	0
Total other comprehensive income (loss)			14	(10)	31
Comprehensive income attributable to noncontrolling interests			59	46	36
Current period change			201	1,061	$ 369
Southern Company Gas
Consolidated Net Income	$ 114		372	243
Qualifying hedges:
Changes in fair value, net of tax			5
Changes in fair value, net of tax	(1)			(5)
Reclassification adjustment for amounts included in net income, net of tax			(1)
Reclassification adjustment for amounts included in net income, net of tax	0			1
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax	27		0	(1)
Reclassification adjustment for amounts included in net income, net of tax	0		(2)	0
Total other comprehensive income (loss)	26		2	(5)
Comprehensive income attributable to noncontrolling interests	0		0	0
Current period change	$ 140		$ 374	$ 238
Predecessor | Southern Company Gas
Consolidated Net Income		$ 145
Qualifying hedges:
Changes in fair value, net of tax		(41)
Reclassification adjustment for amounts included in net income, net of tax		1
Pension and other postretirement benefit plans:
Benefit plan net gain (loss), net of tax		0
Reclassification adjustment for amounts included in net income, net of tax		5
Total other comprehensive income (loss)		(35)
Comprehensive income attributable to noncontrolling interests		14
Current period change		$ 96

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Qualifying hedges, change in fair value, tax			$ (16)
Qualifying hedges, change in fair value, tax				$ 34	$ (84)
Qualifying hedges, reclassification adjustment, tax			24
Qualifying hedges, reclassification adjustment, tax				(37)	43
Pension and other postretirement benefit plans, gain (loss), tax			(2)	6	10
Pension and other postretirement benefit plans, reclassification adjustment, tax			5	(6)	3
Alabama Power
Qualifying hedges, change in fair value, tax			0
Qualifying hedges, change in fair value, tax				(1)	(1)
Qualifying hedges, reclassification adjustment, tax			2
Qualifying hedges, reclassification adjustment, tax				2	2
Georgia Power
Qualifying hedges, reclassification adjustment, tax			1
Qualifying hedges, reclassification adjustment, tax				1	2
Mississippi Power
Qualifying hedges, change in fair value, tax			(1)
Qualifying hedges, change in fair value, tax				(1)	1
Qualifying hedges, reclassification adjustment, tax			0
Qualifying hedges, reclassification adjustment, tax				1	1
Southern Power
Qualifying hedges, change in fair value, tax			(17)
Qualifying hedges, change in fair value, tax				39	(17)
Qualifying hedges, reclassification adjustment, tax			19
Qualifying hedges, reclassification adjustment, tax				(46)	36
Pension and other postretirement benefit plans, gain (loss), tax			2	0	0
Pension and other postretirement benefit plans, reclassification adjustment, tax			0	0	$ 0
Southern Company Gas
Qualifying hedges, change in fair value, tax			2
Qualifying hedges, change in fair value, tax	$ (1)			(3)
Qualifying hedges, reclassification adjustment, tax			(1)
Qualifying hedges, reclassification adjustment, tax	0			0
Pension and other postretirement benefit plans, gain (loss), tax	19		0	0
Pension and other postretirement benefit plans, reclassification adjustment, tax	$ 0		$ 3	$ 0
Predecessor | Southern Company Gas
Qualifying hedges, change in fair value, tax		$ (23)
Qualifying hedges, reclassification adjustment, tax		0
Pension and other postretirement benefit plans, gain (loss), tax		0
Pension and other postretirement benefit plans, reclassification adjustment, tax		$ 4

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Consolidated net income	$ 2,300,000,000	$ 926,000,000	$ 2,529,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	3,549,000,000	3,457,000,000	2,923,000,000
Deferred income taxes	94,000,000	166,000,000	(127,000,000)
Amortization of investment tax credits	(87,000,000)	(79,000,000)	(59,000,000)
Collateral deposits	17,000,000	(4,000,000)	(102,000,000)
Allowance for equity funds used during construction	(138,000,000)	(160,000,000)	(202,000,000)
Pension and postretirement funding	(4,000,000)	(2,000,000)	(1,029,000,000)
Settlement of asset retirement obligations	(244,000,000)	(177,000,000)	(171,000,000)
Stock based compensation expense	125,000,000	109,000,000	121,000,000
Hedge settlements	(10,000,000)	6,000,000	(233,000,000)
Estimated loss on plants under construction	1,093,000,000	3,179,000,000	428,000,000
Impairment charges	210,000,000	0	0
Goodwill impairment	42,000,000
Gain on dispositions, net	(301,000,000)	(42,000,000)	(2,000,000)
Other, net	(22,000,000)	(112,000,000)	(219,000,000)
Changes in certain current assets and liabilities —
-Receivables	(426,000,000)	(202,000,000)	(544,000,000)
-Fossil fuel for generation	123,000,000	36,000,000	178,000,000
-Natural gas for sale	49,000,000	36,000,000	(226,000,000)
-Other current assets	(127,000,000)	(143,000,000)	(206,000,000)
-Accounts payable	291,000,000	(280,000,000)	301,000,000
-Accrued taxes	267,000,000	(142,000,000)	1,456,000,000
-Retail fuel cost over recovery	36,000,000	(212,000,000)	(231,000,000)
-Other current liabilities	63,000,000	(45,000,000)	250,000,000
Net cash provided from operating activities	6,945,000,000	6,394,000,000	4,894,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(65,000,000)	(1,054,000,000)	(10,680,000,000)
Property additions	(8,001,000,000)	(7,423,000,000)	(7,310,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	1,682,000,000	0
Nuclear decommissioning trust fund purchases	(1,117,000,000)	(811,000,000)	(1,160,000,000)
Nuclear decommissioning trust fund sales	1,111,000,000	805,000,000	1,154,000,000
Proceeds from dispositions	2,956,000,000	97,000,000	15,000,000
Cost of removal, net of salvage	(388,000,000)	(313,000,000)	(245,000,000)
Change in construction payables, net	50,000,000	259,000,000	(121,000,000)
Investment in unconsolidated subsidiaries	(114,000,000)	(152,000,000)	(1,444,000,000)
Payments pursuant to LTSAs	(186,000,000)	(227,000,000)	(134,000,000)
Other investing activities	(6,000,000)	(53,000,000)	(122,000,000)
Net cash used for investing activities	(5,760,000,000)	(7,190,000,000)	(20,047,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(774,000,000)	(401,000,000)	1,228,000,000
Proceeds —
Long-term debt	2,478,000,000	5,858,000,000	16,368,000,000
Common stock	1,090,000,000	793,000,000	3,758,000,000
Preferred stock	0	250,000,000	0
Short-term borrowings	3,150,000,000	1,259,000,000	0
Redemptions and repurchases —
Long-term debt	(5,533,000,000)	(2,930,000,000)	(3,145,000,000)
Preferred and preference stock	(33,000,000)	(658,000,000)	0
Short-term borrowings	(1,900,000,000)	(659,000,000)	(478,000,000)
Other long-term debt	(100,000,000)	0	0
Distributions to noncontrolling interests	(153,000,000)	(119,000,000)	(72,000,000)
Capital contributions from noncontrolling interests	2,551,000,000	80,000,000	682,000,000
Payment of common stock dividends	(2,425,000,000)	(2,300,000,000)	(2,104,000,000)
Other financing activities	(264,000,000)	(222,000,000)	(512,000,000)
Net cash provided from (used for) financing activities	(1,813,000,000)	951,000,000	15,725,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(628,000,000)	155,000,000	572,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	2,147,000,000	1,992,000,000	1,420,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	1,519,000,000	2,147,000,000	1,992,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	1,794,000,000	1,676,000,000	1,066,000,000
Income taxes (net of refunds)	172,000,000	(410,000,000)	(148,000,000)
Noncash transactions —
Accrued property additions at year-end	1,103,000,000	985,000,000	1,262,000,000
Alabama Power
Operating Activities:
Consolidated net income	945,000,000	866,000,000	839,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	917,000,000	888,000,000	844,000,000
Deferred income taxes	174,000,000	409,000,000	407,000,000
Allowance for equity funds used during construction	(62,000,000)	(39,000,000)	(28,000,000)
Pension and postretirement funding	(4,000,000)	(2,000,000)	(133,000,000)
Settlement of asset retirement obligations	(55,000,000)	(26,000,000)	(25,000,000)
Other, net	(1,000,000)	13,000,000	(77,000,000)
Changes in certain current assets and liabilities —
-Receivables	(149,000,000)	(168,000,000)	94,000,000
-Prepayments	(2,000,000)	(2,000,000)	1,000,000
-Other current assets	30,000,000	20,000,000	38,000,000
-Accounts payable	24,000,000	71,000,000	73,000,000
-Accrued taxes	10,000,000	(84,000,000)	93,000,000
-Retail fuel cost over recovery	0	(76,000,000)	(162,000,000)
-Other current liabilities	128,000,000	3,000,000	11,000,000
-Materials and supplies	(82,000,000)	(34,000,000)	(38,000,000)
-Accrued compensation	8,000,000	(2,000,000)	12,000,000
Net cash provided from operating activities	1,881,000,000	1,837,000,000	1,949,000,000
Investing Activities:
Property additions	(2,158,000,000)	(1,882,000,000)	(1,272,000,000)
Nuclear decommissioning trust fund purchases	(279,000,000)	(237,000,000)	(352,000,000)
Nuclear decommissioning trust fund sales	278,000,000	237,000,000	351,000,000
Cost of removal, net of salvage	(130,000,000)	(112,000,000)	(94,000,000)
Change in construction payables, net	26,000,000	161,000,000	(37,000,000)
Other investing activities	(26,000,000)	(43,000,000)	(34,000,000)
Net cash used for investing activities	(2,289,000,000)	(1,876,000,000)	(1,438,000,000)
Proceeds —
Preferred stock	0	250,000,000	0
Senior notes	500,000,000	1,100,000,000	400,000,000
Pollution control revenue bonds	120,000,000	0	0
Other long-term debt	0	0	45,000,000
Capital contributions from parent company	511,000,000	361,000,000	260,000,000
Redemptions and repurchases —
Preferred and preference stock	0	(238,000,000)	0
Senior notes	0	(525,000,000)	(200,000,000)
Pollution control revenue bonds	(120,000,000)	(36,000,000)	0
Payment of common stock dividends	(801,000,000)	(714,000,000)	(765,000,000)
Other financing activities	(33,000,000)	(35,000,000)	(25,000,000)
Net cash provided from (used for) financing activities	177,000,000	163,000,000	(285,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(231,000,000)	124,000,000	226,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	544,000,000	420,000,000	194,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	313,000,000	544,000,000	420,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	284,000,000	285,000,000	277,000,000
Income taxes (net of refunds)	106,000,000	236,000,000	(108,000,000)
Noncash transactions —
Accrued property additions at year-end	272,000,000	245,000,000	84,000,000
Georgia Power
Operating Activities:
Consolidated net income	793,000,000	1,428,000,000	1,347,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	1,142,000,000	1,100,000,000	1,063,000,000
Deferred income taxes	(260,000,000)	458,000,000	383,000,000
Pension, postretirement, and other employee benefits	(75,000,000)	(68,000,000)	(33,000,000)
Pension and postretirement funding	0	0	(287,000,000)
Settlement of asset retirement obligations	(116,000,000)	(120,000,000)	(123,000,000)
Other deferred charges — affiliated	0	0	(111,000,000)
Estimated loss on plants under construction	1,060,000,000	0	0
Other, net	(21,000,000)	(83,000,000)	(25,000,000)
Changes in certain current assets and liabilities —
-Receivables	8,000,000	(256,000,000)	60,000,000
-Fossil fuel for generation	83,000,000	(16,000,000)	104,000,000
-Other current assets	(43,000,000)	(28,000,000)	(38,000,000)
-Accounts payable	95,000,000	(219,000,000)	(42,000,000)
-Accrued taxes	58,000,000	1,000,000	131,000,000
-Retail fuel cost over recovery	0	(84,000,000)	(32,000,000)
-Other current liabilities	(107,000,000)	(33,000,000)	28,000,000
-Prepaid income taxes	152,000,000	(168,000,000)	0
Net cash provided from operating activities	2,769,000,000	1,912,000,000	2,425,000,000
Investing Activities:
Property additions	(3,116,000,000)	(2,704,000,000)	(2,223,000,000)
Proceeds pursuant to the Toshiba Guarantee, net of joint owner portion	0	1,682,000,000	0
Nuclear decommissioning trust fund purchases	(839,000,000)	(574,000,000)	(808,000,000)
Nuclear decommissioning trust fund sales	833,000,000	568,000,000	803,000,000
Cost of removal, net of salvage	(107,000,000)	(100,000,000)	(83,000,000)
Payments pursuant to LTSAs	(54,000,000)	(64,000,000)	(34,000,000)
Change in construction payables, net of joint owner portion	68,000,000	223,000,000	(35,000,000)
Proceeds from asset dispositions	138,000,000	96,000,000	10,000,000
Other investing activities	(32,000,000)	(39,000,000)	23,000,000
Net cash used for investing activities	(3,109,000,000)	(912,000,000)	(2,347,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	294,000,000	(391,000,000)	234,000,000
Proceeds —
Short-term borrowings	0	700,000,000	0
Senior notes	0	1,350,000,000	650,000,000
Pollution control revenue bonds	108,000,000	65,000,000	0
Other long-term debt	0	370,000,000	0
Capital contributions from parent company	2,985,000,000	431,000,000	594,000,000
FFB loan	0	0	425,000,000
Redemptions and repurchases —
Preferred and preference stock	0	(270,000,000)	0
Short-term borrowings	(150,000,000)	(550,000,000)	0
Senior notes	(1,500,000,000)	(450,000,000)	(700,000,000)
Pollution control revenue bonds	(469,000,000)	(65,000,000)	(4,000,000)
Payment of common stock dividends	(1,396,000,000)	(1,281,000,000)	(1,305,000,000)
Premiums on redemption and repurchases of senior notes	(152,000,000)	0	0
Other financing activities	(20,000,000)	(60,000,000)	(36,000,000)
Net cash provided from (used for) financing activities	(400,000,000)	(151,000,000)	(142,000,000)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(740,000,000)	849,000,000	(64,000,000)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	852,000,000	3,000,000	67,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	112,000,000	852,000,000	3,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	408,000,000	386,000,000	375,000,000
Income taxes (net of refunds)	300,000,000	496,000,000	170,000,000
Noncash transactions —
Accrued property additions at year-end	683,000,000	550,000,000	336,000,000
Mississippi Power
Operating Activities:
Consolidated net income	236,000,000	(2,588,000,000)	(48,000,000)
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	177,000,000	198,000,000	157,000,000
Deferred income taxes	475,000,000	(727,000,000)	(67,000,000)
Allowance for equity funds used during construction	0	(72,000,000)	(124,000,000)
Pension and postretirement funding	0	0	(47,000,000)
Settlement of asset retirement obligations	(35,000,000)	(23,000,000)	(23,000,000)
Estimated loss on plants under construction	33,000,000	3,179,000,000	428,000,000
Other, net	18,000,000	(8,000,000)	(9,000,000)
Changes in certain current assets and liabilities —
-Receivables	(19,000,000)	540,000,000	13,000,000
-Fossil fuel for generation	(3,000,000)	24,000,000	4,000,000
-Other current assets	(7,000,000)	(13,000,000)	(12,000,000)
-Accounts payable	15,000,000	(3,000,000)	(14,000,000)
-Accrued taxes	(46,000,000)	80,000,000	14,000,000
-Other current liabilities	(41,000,000)	(3,000,000)	9,000,000
-Prepaid income taxes	(12,000,000)	0	39,000,000
-Accrued interest	(1,000,000)	(29,000,000)	27,000,000
-Over recovered regulatory clause revenues	14,000,000	(51,000,000)	(45,000,000)
-Customer liability associated with Kemper refunds	0	(1,000,000)	(73,000,000)
Net cash provided from operating activities	804,000,000	503,000,000	229,000,000
Investing Activities:
Property additions	(188,000,000)	(429,000,000)	(798,000,000)
Change in construction payables, net	4,000,000	(47,000,000)	(26,000,000)
Payments pursuant to LTSAs	(29,000,000)	(10,000,000)	10,000,000
Government grant proceeds	0	0	137,000,000
Other investing activities	(19,000,000)	(18,000,000)	(20,000,000)
Net cash used for investing activities	(232,000,000)	(504,000,000)	(697,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(4,000,000)	(18,000,000)	0
Proceeds —
Short-term borrowings	300,000,000	109,000,000	0
Senior notes	600,000,000	0	0
Other long-term debt	0	0	1,200,000,000
Capital contributions from parent company	15,000,000	1,002,000,000	627,000,000
Long-term debt issuance to parent company	0	40,000,000	200,000,000
Redemptions and repurchases —
Preferred and preference stock	(33,000,000)	0	0
Short-term borrowings	(300,000,000)	(109,000,000)	(478,000,000)
Senior notes	(155,000,000)	(35,000,000)	(300,000,000)
Pollution control revenue bonds	(43,000,000)	0	0
Long-term debt to parent company	0	(591,000,000)	(225,000,000)
Capital leases	0	(71,000,000)	(3,000,000)
Other long-term debt	(900,000,000)	(300,000,000)	(425,000,000)
Other financing activities	(7,000,000)	(2,000,000)	(2,000,000)
Net cash provided from (used for) financing activities	(527,000,000)	25,000,000	594,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	45,000,000	24,000,000	126,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	248,000,000	224,000,000	98,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	293,000,000	248,000,000	224,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	80,000,000	65,000,000	50,000,000
Income taxes (net of refunds)	(525,000,000)	(424,000,000)	(97,000,000)
Noncash transactions —
Accrued property additions at year-end	35,000,000	32,000,000	78,000,000
Southern Power
Operating Activities:
Consolidated net income	246,000,000	1,117,000,000	374,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	524,000,000	536,000,000	370,000,000
Deferred income taxes	(239,000,000)	(263,000,000)	(1,063,000,000)
Amortization of investment tax credits	(58,000,000)	(57,000,000)	(37,000,000)
Collateral deposits	17,000,000	(4,000,000)	(102,000,000)
Income taxes receivable, non-current	42,000,000	(61,000,000)	(13,000,000)
Impairment charges	156,000,000	0	0
Gain on dispositions, net	2,000,000	0	0
Accrued income taxes, non-current	(14,000,000)	14,000,000	(109,000,000)
Other, net	(10,000,000)	(9,000,000)	12,000,000
Changes in certain current assets and liabilities —
-Receivables	(20,000,000)	(60,000,000)	(54,000,000)
-Other current assets	(26,000,000)	(28,000,000)	4,000,000
-Accrued taxes	7,000,000	(55,000,000)	940,000,000
-Other current liabilities	(19,000,000)	1,000,000	46,000,000
-Prepaid income taxes	25,000,000	24,000,000	(29,000,000)
Net cash provided from operating activities	631,000,000	1,155,000,000	339,000,000
Investing Activities:
Business acquisitions, net of cash acquired	(65,000,000)	(1,016,000,000)	(2,284,000,000)
Property additions	(315,000,000)	(268,000,000)	(2,114,000,000)
Proceeds from dispositions	203,000,000	0	0
Change in construction payables, net of joint owner portion	(6,000,000)	(153,000,000)	(57,000,000)
Payments pursuant to LTSAs and for equipment not yet received	(75,000,000)	(203,000,000)	(350,000,000)
Other investing activities	31,000,000	15,000,000	16,000,000
Net cash used for investing activities	(227,000,000)	(1,625,000,000)	(4,789,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(105,000,000)	(104,000,000)	73,000,000
Proceeds —
Short-term borrowings	200,000,000	0	0
Senior notes	0	525,000,000	2,831,000,000
Other long-term debt	0	43,000,000	65,000,000
Capital contributions from parent company	2,000,000	0	1,850,000,000
Redemptions and repurchases —
Short-term borrowings	(100,000,000)	0	0
Senior notes	(350,000,000)	(500,000,000)	(200,000,000)
Other long-term debt	(420,000,000)	(18,000,000)	(86,000,000)
Return of capital	(1,650,000,000)	0	0
Distributions to noncontrolling interests	(153,000,000)	(119,000,000)	(57,000,000)
Capital contributions from noncontrolling interests	2,551,000,000	80,000,000	682,000,000
Purchase of membership interests from noncontrolling interests	0	(59,000,000)	(129,000,000)
Payment of common stock dividends	(312,000,000)	(317,000,000)	(272,000,000)
Other financing activities	(26,000,000)	(33,000,000)	(30,000,000)
Net cash provided from (used for) financing activities	(363,000,000)	(502,000,000)	4,727,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	41,000,000	(972,000,000)	277,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	140,000,000	1,112,000,000	835,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	181,000,000	140,000,000	1,112,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	173,000,000	189,000,000	89,000,000
Income taxes (net of refunds)	79,000,000	(487,000,000)	116,000,000
Noncash transactions —
Accrued property additions at year-end	31,000,000	32,000,000	251,000,000
Accrued acquisitions at year-end	0	0	461,000,000
Southern Company Gas
Operating Activities:
Consolidated net income	372,000,000	243,000,000
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	500,000,000	501,000,000
Deferred income taxes	(1,000,000)	236,000,000
Pension and postretirement funding	0	0
Hedge settlements	0	0
Goodwill impairment	42,000,000	0
Gain on dispositions, net	(291,000,000)	0
Mark-to-market adjustments	(19,000,000)	(24,000,000)
Other, net	(24,000,000)	(51,000,000)
Changes in certain current assets and liabilities —
-Receivables	(218,000,000)	(94,000,000)
-Natural gas for sale	49,000,000	36,000,000
-Other current assets	4,000,000	(24,000,000)
-Accounts payable	372,000,000	(20,000,000)
-Accrued taxes	10,000,000	110,000,000
-Other current liabilities	(22,000,000)	(8,000,000)
-Prepaid income taxes	(42,000,000)	(39,000,000)
-Accrued compensation	32,000,000	15,000,000
Net cash provided from operating activities	764,000,000	881,000,000
Investing Activities:
Property additions	(1,388,000,000)	(1,514,000,000)
Proceeds from dispositions	2,609,000,000	0
Cost of removal, net of salvage	(96,000,000)	(66,000,000)
Change in construction payables, net	(37,000,000)	72,000,000
Investment in unconsolidated subsidiaries	(110,000,000)	(145,000,000)
Returned investment in unconsolidated subsidiaries	20,000,000	80,000,000
Other investing activities	0	5,000,000
Net cash used for investing activities	998,000,000	(1,568,000,000)
Financing Activities:
Increase (decrease) in notes payable, net	(868,000,000)	262,000,000
Proceeds —
First mortgage bonds	300,000,000	400,000,000
Senior notes	0	450,000,000
Capital contributions from parent company	24,000,000	103,000,000
Redemptions and repurchases —
Gas facility revenue bonds	(200,000,000)	0
Medium-term notes	0	(22,000,000)
Senior notes	(155,000,000)	0
First mortgage bonds	0	0
Return of capital	(400,000,000)	0
Distributions to noncontrolling interests	0	0
Purchase of 15% noncontrolling interest in SouthStar	0	0
Payment of common stock dividends	(468,000,000)	(443,000,000)
Other financing activities	(3,000,000)	(9,000,000)
Net cash provided from (used for) financing activities	(1,770,000,000)	741,000,000
Net Change in Cash, Cash Equivalents, and Restricted Cash	(8,000,000)	54,000,000
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	78,000,000	24,000,000
Cash, Cash Equivalents, and Restricted Cash at End of Year	70,000,000	78,000,000	24,000,000
Supplemental Cash Flow Information:
Interest, net of amounts capitalized	249,000,000	223,000,000
Income taxes (net of refunds)	524,000,000	72,000,000
Noncash transactions —
Accrued property additions at year-end	$ 97,000,000	$ 135,000,000
Predecessor | Southern Company Gas
Redemptions and repurchases —
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year			$ 22,000,000

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net cash paid for capitalized interest			$ 72	$ 89	$ 128
Alabama Power
Net cash paid for capitalized interest			22	15	11
Georgia Power
Net cash paid for capitalized interest			26	23	20
Mississippi Power
Net cash paid for capitalized interest			0	29	49
Southern Power
Net cash paid for capitalized interest			17	11	$ 44
Southern Company Gas
Net cash paid for capitalized interest	$ 4		$ 7	$ 11
Southern Company Gas | Southstar
Ownership percentage of noncontrolling interest	15.00%
Predecessor | Southern Company Gas
Net cash paid for capitalized interest		$ 3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 1,396	$ 2,130
Receivables —
Customer accounts receivable	1,726	1,806
Energy marketing receivable	801	607
Unbilled revenues	654	810
Under recovered fuel clause revenues	115	171
Other accounts and notes receivable	813	698
Accumulated provision for uncollectible accounts	(50)	(44)
Materials and supplies	1,465	1,438
Fossil fuel for generation	405	594
Natural gas for sale	524	595
Prepaid expenses	432	452
Assets from risk management activities, net of collateral	222	137
Other regulatory assets, current	525	604
Assets held for sale, current	393	12
Other current assets	162	62
Total current assets	9,583	10,072
Property, Plant, and Equipment:
In service	103,706	103,542
Less: Accumulated depreciation	31,038	31,457
Plant in service, net of depreciation	72,668	72,085
Nuclear fuel, at amortized cost	875	883
Construction work in progress	7,254	6,904
Total property, plant, and equipment	80,797	79,872
Other Property and Investments:
Goodwill	5,315	6,268
Equity investments in unconsolidated subsidiaries	1,580	1,513
Other intangible assets, net of amortization	613	873
Nuclear decommissioning trusts, at fair value	1,721	1,832
Leveraged leases	798	775
Miscellaneous property and investments	269	249
Total other property and investments	10,296	11,510
Deferred Charges and Other Assets:
Deferred charges related to income taxes	794	825
Unamortized loss on reacquired debt	323	206
Other regulatory assets	8,308	6,943
Disposal Group, Including Discontinued Operation, Assets, Noncurrent	5,350	0
Other deferred charges and assets	1,463	1,577
Total deferred charges and other assets	16,238	9,551
Total Assets	116,914	111,005
Current Liabilities:
Securities due within one year	3,198	3,892
Notes payable	2,915	2,439
Accounts payable —
Energy marketing trade payables	856	546
Accounts payable	2,580	2,530
Customer deposits	522	542
Accrued taxes	656	636
Accrued interest	472	488
Accrued compensation	1,030	959
Asset retirement obligations, current	404	351
Other regulatory liabilities, current	376	337
Liabilities held for sale, current	425	0
Other current liabilities	852	874
Total current liabilities	14,286	13,594
Long-Term Debt:
Unamortized debt issuance expense	(208)	(226)
Total long-term debt	40,736	44,462
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	6,558	6,842
Deferred credits related to income taxes	6,460	7,256
Accumulated deferred ITCs	2,372	2,267
Employee benefit obligations	2,147	2,256
Asset retirement obligations	8,990	4,473
Accrued environmental remediation	268	389
Other cost of removal obligations	2,297	2,684
Other regulatory liabilities	169	239
Liabilities held for sale	2,836	0
Other deferred credits and liabilities	465	691
Total deferred credits and other liabilities	32,562	27,097
Total Liabilities	87,584	85,153
Common Stockholder's Equity:
Common stock	5,164	5,038
Paid-in capital	11,094	10,469
Retained earnings	8,706	8,885
Accumulated other comprehensive income (loss)	(203)	(189)
Total common stockholders' equity	24,723	24,167
Redeemable Preferred Stock of Subsidiaries	291	324
Total Stockholders' Equity	29,039	25,528
Total Liabilities and Stockholder's Equity	116,914	111,005
Commitments and Contingent Matters
Alabama Power
Current Assets:
Cash and cash equivalents	313	544
Receivables —
Customer accounts receivable	403	355
Unbilled revenues	150	162
Other accounts and notes receivable	51	55
Affiliated	94	43
Accumulated provision for uncollectible accounts	(10)	(9)
Materials and supplies	546	458
Fossil fuel for generation	141	184
Prepaid expenses	66	85
Other regulatory assets, current	137	124
Other current assets	18	5
Total current assets	1,909	2,006
Property, Plant, and Equipment:
In service	30,402	27,326
Less: Accumulated depreciation	9,988	9,563
Plant in service, net of depreciation	20,414	17,763
Nuclear fuel, at amortized cost	324	339
Construction work in progress	1,113	908
Total property, plant, and equipment	21,851	19,010
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	65	67
Nuclear decommissioning trusts, at fair value	847	903
Miscellaneous property and investments	127	124
Total other property and investments	1,039	1,094
Deferred Charges and Other Assets:
Deferred charges related to income taxes	240	239
Deferred under recovered regulatory clause revenues	116	54
Other regulatory assets	1,386	1,272
Other deferred charges and assets	189	189
Total deferred charges and other assets	1,931	1,754
Total Assets	26,730	23,864
Current Liabilities:
Securities due within one year	201	0
Accounts payable —
Affiliated	364	327
Other	614	585
Customer deposits	96	92
Accrued taxes	44	54
Accrued interest	89	77
Accrued compensation	227	205
Asset retirement obligations, current	163	7
Other current liabilities	161	53
Total current liabilities	1,959	1,400
Long-Term Debt:
Unamortized debt premium (discount), net	(12)	(11)
Unamortized debt issuance expense	(54)	(51)
Total long-term debt	7,923	7,628
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,962	2,760
Deferred credits related to income taxes	2,027	2,082
Accumulated deferred ITCs	106	112
Employee benefit obligations	314	304
Asset retirement obligations	3,047	1,702
Other cost of removal obligations	497	609
Other regulatory liabilities	69	84
Other deferred credits and liabilities	58	63
Total deferred credits and other liabilities	9,080	7,716
Total Liabilities	18,962	16,744
Redeemable Preferred Stock	291	291
Common Stockholder's Equity:
Common stock	1,222	1,222
Paid-in capital	3,508	2,986
Retained earnings	2,775	2,647
Accumulated other comprehensive income (loss)	(28)	(26)
Total common stockholders' equity	7,477	6,829
Redeemable Preferred Stock of Subsidiaries	291	291
Total Stockholders' Equity	7,477	6,829
Total Liabilities and Stockholder's Equity	26,730	23,864
Commitments and Contingent Matters
Georgia Power
Current Assets:
Cash and cash equivalents	4	852
Restricted cash	108	0
Receivables —
Customer accounts receivable	591	544
Unbilled revenues	208	255
Under recovered fuel clause revenues	115	165
Joint owner accounts receivable	170	262
Other accounts and notes receivable	80	76
Affiliated	39	24
Accumulated provision for uncollectible accounts	(2)	(3)
Materials and supplies	519	504
Fossil fuel for generation	231	314
Prepaid expenses	142	216
Other regulatory assets, current	199	205
Other current assets	70	14
Total current assets	2,474	3,428
Property, Plant, and Equipment:
In service	37,675	34,861
Less: Accumulated depreciation	12,096	11,704
Plant in service, net of depreciation	25,579	23,157
Nuclear fuel, at amortized cost	550	544
Construction work in progress	4,833	4,613
Total property, plant, and equipment	30,962	28,314
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	51	53
Nuclear decommissioning trusts, at fair value	873	929
Miscellaneous property and investments	72	59
Total other property and investments	996	1,041
Deferred Charges and Other Assets:
Deferred charges related to income taxes	517	516
Other regulatory assets	4,902	2,932
Other deferred charges and assets	514	548
Total deferred charges and other assets	5,933	3,996
Total Assets	40,365	36,779
Current Liabilities:
Securities due within one year	617	857
Notes payable	294	150
Accounts payable —
Affiliated	575	493
Other	890	834
Customer deposits	276	270
Other accrued taxes	377	344
Accrued interest	105	123
Accrued compensation	221	219
Asset retirement obligations, current	202	270
Other regulatory liabilities, current	169	191
Other current liabilities	183	198
Total current liabilities	3,909	3,949
Long-Term Debt:
Unamortized debt premium (discount), net	(6)	(12)
Unamortized debt issuance expense	(108)	(124)
Total long-term debt	9,364	11,073
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,062	3,175
Deferred credits related to income taxes	3,080	3,248
Accumulated deferred ITCs	262	248
Employee benefit obligations	599	659
Asset retirement obligations	5,627	2,368
Accrued environmental remediation	0	0
Other deferred credits and liabilities	139	128
Total deferred credits and other liabilities	12,769	9,826
Total Liabilities	26,042	24,848
Common Stockholder's Equity:
Common stock	398	398
Paid-in capital	10,322	7,328
Retained earnings	3,612	4,215
Accumulated other comprehensive income (loss)	(9)	(10)
Total common stockholders' equity	14,323	11,931
Total Stockholders' Equity	14,323	11,931
Total Liabilities and Stockholder's Equity	40,365	36,779
Commitments and Contingent Matters
Mississippi Power
Current Assets:
Cash and cash equivalents	293	248
Receivables —
Customer accounts receivable	34	36
Unbilled revenues	41	41
Other accounts and notes receivable	31	16
Affiliated	21	16
Materials and supplies	53	44
Fossil fuel for generation	20	17
Other regulatory assets, current	116	125
Prepaid income taxes	12	0
Other current assets	7	9
Total current assets	628	552
Property, Plant, and Equipment:
In service	4,900	4,773
Less: Accumulated depreciation	1,429	1,325
Plant in service, net of depreciation	3,471	3,448
Construction work in progress	103	84
Total property, plant, and equipment	3,574	3,532
Other Property and Investments:
Total other property and investments	24	30
Deferred Charges and Other Assets:
Deferred charges related to income taxes	33	35
Other regulatory assets	474	437
Accumulated deferred income taxes	150	247
Other deferred charges and assets	3	33
Total deferred charges and other assets	660	752
Total Assets	4,886	4,866
Current Liabilities:
Securities due within one year	40	989
Notes payable	0	4
Accounts payable —
Affiliated	60	59
Other	90	96
Accrued taxes	0	40
Other accrued taxes	95	101
Accrued interest	15	16
Accrued compensation	38	39
Accrued plant closure costs	29	35
Asset retirement obligations, current	34	37
Over recovered regulatory clause liabilities	14	0
Other current liabilities	40	47
Total current liabilities	455	1,463
Long-Term Debt:
Unamortized debt issuance expense	(8)	(7)
Total long-term debt	1,539	1,097
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	378	0
Deferred credits related to income taxes	382	372
Employee benefit obligations	115	116
Asset retirement obligations	126	137
Other cost of removal obligations	185	178
Other regulatory liabilities	81	79
Other deferred credits and liabilities	16	33
Total deferred credits and other liabilities	1,283	915
Total Liabilities	3,277	3,475
Redeemable Preferred Stock	0	33
Common Stockholder's Equity:
Common stock	38	38
Paid-in capital	4,546	4,529
Retained earnings	(2,971)	(3,205)
Accumulated other comprehensive income (loss)	(4)	(4)
Total common stockholders' equity	1,609	1,358
Redeemable Preferred Stock of Subsidiaries	0	33
Total Stockholders' Equity	1,609	1,358
Total Liabilities and Stockholder's Equity	4,886	4,866
Commitments and Contingent Matters
Southern Power
Current Assets:
Cash and cash equivalents	181	129
Receivables —
Customer accounts receivable	111	117
Other accounts and notes receivable	116	98
Affiliated	55	50
Materials and supplies	220	278
Prepaid income taxes	25	50
Other current assets	37	36
Total current assets	745	758
Property, Plant, and Equipment:
In service	13,271	13,755
Less: Accumulated depreciation	2,171	1,910
Plant in service, net of depreciation	11,100	11,845
Construction work in progress	430	511
Total property, plant, and equipment	11,530	12,356
Other Property and Investments:
Intangible assets, net of amortization	345	411
Total other property and investments	345	411
Deferred Charges and Other Assets:
Prepaid LTSAs	98	118
Income taxes receivable, non-current	30	72
Disposal Group, Including Discontinued Operation, Assets, Noncurrent	576	0
Accumulated deferred income taxes	1,186	925
Other deferred charges and assets	373	566
Total deferred charges and other assets	2,263	1,681
Total Assets	14,883	15,206
Current Liabilities:
Securities due within one year	599	770
Notes payable	100	105
Accounts payable —
Affiliated	92	102
Other	77	103
Accrued taxes	6	4
Liabilities held for sale, current	15	0
Other current liabilities	142	148
Total current liabilities	1,031	1,232
Long-Term Debt:
Unamortized debt premium (discount), net	(9)	(10)
Unamortized debt issuance expense	(23)	(28)
Total long-term debt	4,418	5,071
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	105	199
Accumulated deferred ITCs	1,832	1,884
Other deferred credits and liabilities	213	322
Total deferred credits and other liabilities	2,150	2,405
Total Liabilities	7,599	8,708
Common Stockholder's Equity:
Common stock	0	0
Paid-in capital	1,600	3,662
Retained earnings	1,352	1,478
Accumulated other comprehensive income (loss)	16	(2)
Total common stockholders' equity	2,968	5,138
Noncontrolling Interests	4,316	1,360
Total Stockholders' Equity	7,284	6,498
Total Liabilities and Stockholder's Equity	14,883	15,206
Commitments and Contingent Matters
Southern Power | 1.95% due 2019
Long-Term Debt:
Senior notes	0	600
Southern Power | 2.375% due 2020
Long-Term Debt:
Senior notes	300	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	687	720
Southern Power | 2.75% due 2023
Long-Term Debt:
Senior notes	290	290
Southern Power | 1.85% to 5.25% due 2025-2046
Long-Term Debt:
Senior notes	2,348	2,374
Southern Power | Variable rate (3.34% at 12/31/18) due 2020
Long-Term Debt:
Other long-term debt	525	525
Southern Company Gas
Current Assets:
Cash and cash equivalents	64	73
Receivables —
Customer accounts receivable	370	400
Energy marketing receivable	801	607
Unbilled revenues	213	285
Other accounts and notes receivable	142	91
Affiliated	11	12
Accumulated provision for uncollectible accounts	(30)	(28)
Natural gas for sale	524	595
Prepaid expenses	118	79
Assets from risk management activities, net of collateral	219	135
Other regulatory assets, current	73	94
Other current assets	50	52
Total current assets	2,555	2,395
Property, Plant, and Equipment:
In service	15,177	15,833
Less: Accumulated depreciation	4,400	4,596
Plant in service, net of depreciation	10,777	11,237
Construction work in progress	580	491
Total property, plant, and equipment	11,357	11,728
Other Property and Investments:
Goodwill	5,015	5,967
Equity investments in unconsolidated subsidiaries	1,538	1,477
Other intangible assets, net of amortization	101	280
Miscellaneous property and investments	20	21
Total other property and investments	6,674	7,745
Deferred Charges and Other Assets:
Other regulatory assets	669	901
Other deferred charges and assets	193	218
Total deferred charges and other assets	862	1,119
Total Assets	21,448	22,987
Current Liabilities:
Securities due within one year	357	157
Notes payable	650	1,518
Accounts payable —
Affiliated	45	21
Other	402	425
Energy marketing trade payables	856	546
Customer deposits	133	128
Accrued taxes	66	40
Other accrued taxes	75	78
Accrued interest	55	51
Accrued compensation	100	74
Other regulatory liabilities, current	79	135
Liabilities from risk management activities	76	69
Other current liabilities	130	159
Total current liabilities	3,024	3,401
Long-Term Debt:
Total long-term debt	5,583	5,891
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,016	1,089
Deferred credits related to income taxes	940	1,063
Employee benefit obligations	357	415
Accrued environmental remediation	268	342
Other cost of removal obligations	1,585	1,646
Other deferred credits and liabilities	105	118
Total deferred credits and other liabilities	4,271	4,673
Total Liabilities	12,878	13,965
Common Stockholder's Equity:
Paid-in capital	8,856	9,214
Retained earnings	(312)	(212)
Accumulated other comprehensive income (loss)	26	20
Total common stockholders' equity	8,570	9,022
Total Stockholders' Equity	8,570	9,022
Total Liabilities and Stockholder's Equity	21,448	22,987
Commitments and Contingent Matters
Securities due within one year | Mississippi Power
Current Liabilities:
Securities due within one year	$ 40	$ 989

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accumulated Amortization	$ 235	$ 186
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Southern Power
Accumulated Amortization	$ 61	$ 47
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares outstanding (in shares)	1,000	1,000
Southern Power | 1.95% due 2019
Fixed stated interest rate of debt obligation	1.95%	1.95%
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 Company Gas
Accumulated Amortization	$ 145	$ 120
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 | Southern Power | 1.85% to 5.25% due 2025-2046
Fixed stated interest rate of debt obligation	1.85%	1.85%
Maximum | Southern Power | 1.85% to 5.25% due 2025-2046
Fixed stated interest rate of debt obligation	5.25%	5.25%

Consolidated Statements of Capi

Consolidated Statements of Capitalization - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Long-Term Debt:
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042	$ 206	$ 206
Maturity
2,019	3,156
2,020	4,041
2,021	3,186
2,022	1,974
2,023	2,388
Total long-term senior notes and debt	34,025	36,820
Pollution control revenue bonds —
Pollution control revenue bonds	2,585	3,297
Total other long-term debt	10,684	10,987
Unamortized fair value adjustment of long-term debt	474	525
Capitalized lease obligations	197	204
Unamortized debt premium	36	44
Unamortized debt discount	(194)	(206)
Unamortized debt issuance expense	(208)	(226)
Total long-term debt	45,220	48,354
Amount due within one year	3,198	3,892
Amount held for sale	1,286	0
Long-term debt excluding amounts due within one year and held for sale	$ 40,736	$ 44,462
Percent capitalization	58.10%	63.20%
Cumulative preferred stock
Redeemable preferred stock	$ 291	$ 324
Total redeemable preferred stock - percent capitalization	0.40%	0.50%
Common Stockholders' Equity:
Common stock	$ 5,164	$ 5,038
Paid-in capital	11,094	10,469
Treasury, at cost	(38)	(36)
Retained earnings	8,706	8,885
Accumulated other comprehensive loss	(203)	(189)
Total common stockholders' equity	$ 24,723	$ 24,167
Total common stockholders' equity - percent capitalization	35.30%	34.40%
Total preferred and preference stock of subsidiaries - percent capitalization	6.20%	1.90%
Total Stockholders' Equity	$ 29,039	$ 25,528
Total Capitalization	$ 70,066	$ 70,314
Percent capitalization	100.00%	100.00%
Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Cumulative preferred stock
Redeemable preferred stock	$ 48	$ 81
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	4,316	1,361
Senior Notes
Maturity
2,018	0	2,352
2,019	2,948	3,074
2,020	2,271	2,273
2,021	2,638	2,643
2,022	1,983	2,016
2,023	2,290	2,290
Thereafter	19,895	19,902
Adjustable Rate Loans
Maturity
2,018	0	1,420
2,020	1,875	825
2,021	125	25
Pollution control revenue bonds due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	25	25
Pollution control revenue bonds due 2022
Pollution control revenue bonds —
Pollution control revenue bonds	90	90
Pollution control revenue bonds due 2023
Pollution control revenue bonds —
Pollution control revenue bonds	33	33
Pollution control revenue bonds due 2025 through 2049
Pollution control revenue bonds —
Pollution control revenue bonds	1,112	1,346
Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	148	148
Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Pollution control revenue bonds —
Pollution control revenue bonds	65	65
Pollution control revenue bonds - variable rates (1.76% at 12/31/18) due 2022
Pollution control revenue bonds —
Pollution control revenue bonds	4	4
Pollution control revenue bonds - variable rates (1.70% to 1.87% at 12/31/18) due 2024 to 2053
Pollution control revenue bonds —
Pollution control revenue bonds	1,417	1,585
Plant Daniel revenue bonds (7.13%) due 2021
Pollution control revenue bonds —
Plant Daniel revenue bonds (7.13%) due 2021	270	270
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Pollution control revenue bonds —
Gas facility revenue bonds	0	47
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Pollution control revenue bonds —
Gas facility revenue bonds	0	154
FFB loans — 2.57% to 3.86% due 2020
Pollution control revenue bonds —
FFB loans	44	44
FFB loans — 2.57% to 3.86% due 2021
Pollution control revenue bonds —
FFB loans	44	44
FFB loans — 2.57% to 3.86% due 2022
Pollution control revenue bonds —
FFB loans	44	44
FFB loans — 2.57% to 3.86% due 2023
Pollution control revenue bonds —
FFB loans	44	44
FFB loans — 2.57% to 3.86% due 2024 to 2044
Pollution control revenue bonds —
FFB loans	2,449	2,449
First mortgage bonds — 4.70% due 2019
Pollution control revenue bonds —
First mortgage bonds	50	50
First mortgage bonds - 5.80% due 2023
Pollution control revenue bonds —
First mortgage bonds	50	50
First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Pollution control revenue bonds —
First mortgage bonds	1,225	925
Alabama Power
Long-Term Debt:
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042	206	206
Maturity
2,019	200	200
2,020	250	250
2,021	310
2,022	750	750
2,023	300	300
Thereafter	5,175	4,675
Total long-term notes payable	6,920	6,420
Pollution control revenue bonds —
Pollution control revenue bonds	1,060	1,060
Total other long-term debt	1,060	1,060
Capitalized lease obligations	4	4
Unamortized debt premium (discount), net	(12)	(11)
Unamortized debt issuance expense	(54)	(51)
Total long-term debt	8,124	7,628
Amount due within one year	201	0
Long-term debt excluding amounts due within one year and held for sale	$ 7,923	$ 7,628
Percent capitalization	50.40%	51.70%
Cumulative preferred stock
Redeemable preferred stock	$ 291	$ 291
Total redeemable preferred stock - percent capitalization	1.90%	2.00%
Common Stockholders' Equity:
Common stock	$ 1,222	$ 1,222
Paid-in capital	3,508	2,986
Retained earnings	2,775	2,647
Accumulated other comprehensive loss	(28)	(26)
Total common stockholders' equity	$ 7,477	$ 6,829
Total common stockholders' equity - percent capitalization	47.70%	46.30%
Total Stockholders' Equity	$ 7,477	$ 6,829
Total Capitalization	$ 15,691	$ 14,748
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 | Adjustable Rate Loans
Maturity
2,021	25	25
Alabama Power | Long-term senior notes and debt maturing 2021
Maturity
2,021	220	220
Alabama Power | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Pollution control revenue bonds —
Pollution control revenue bonds	65	65
Alabama Power | Pollution control revenue bonds due 2034
Pollution control revenue bonds —
Pollution control revenue bonds	207	207
Alabama Power | Pollution control revenue bonds - variable rates (1.70% to 1.80% at 12/31/18) due 2024-2038
Pollution control revenue bonds —
Pollution control revenue bonds	788	788
Georgia Power
Maturity
2,018	0	747
2,019	621
2,020	1,006
2,021	375
2,022	505
2,023	153
Thereafter	3,325	4,075
Total long-term notes payable	5,598	7,196
Pollution control revenue bonds —
Pollution control revenue bonds	1,460	1,821
Total other long-term debt	4,355	4,716
Capitalized lease obligations	142	154
Unamortized debt premium (discount), net	(6)	(12)
Unamortized debt issuance expense	(108)	(124)
Total long-term debt	9,981	11,930
Amount due within one year	617	857
Long-term debt excluding amounts due within one year and held for sale	$ 9,364	$ 11,073
Percent capitalization	39.50%	48.10%
Common Stockholders' Equity:
Common stock	$ 398	$ 398
Paid-in capital	10,322	7,328
Retained earnings	3,612	4,215
Accumulated other comprehensive loss	(9)	(10)
Total common stockholders' equity	$ 14,323	$ 11,931
Total common stockholders' equity - percent capitalization	60.50%	51.90%
Total Stockholders' Equity	$ 14,323	$ 11,931
Total Capitalization	$ 23,687	$ 23,004
Percent capitalization	100.00%	100.00%
Georgia Power | Adjustable Rate Loans
Maturity
2,018	$ 0	$ 100
Georgia Power | Long-term senior notes and debt maturing 2020
Maturity
2,020	950	950
Georgia Power | Long-term senior notes and debt maturing 2019
Maturity
2,019	498	499
Georgia Power | Long-term senior notes and debt maturing 2021
Maturity
2,021	325	325
Georgia Power | Long-term senior notes and debt maturing 2022
Maturity
2,022	400	400
Georgia Power | Long-term senior notes and debt maturing 2023
Maturity
2,023	100	100
Georgia Power | Pollution control revenue bonds due 2022
Pollution control revenue bonds —
Pollution control revenue bonds	53	53
Georgia Power | Pollution control revenue bonds due 2025 through 2049
Pollution control revenue bonds —
Pollution control revenue bonds	748	940
Georgia Power | Pollution control revenue bonds - variable rates (1.77% to 1.78% at 12/31/18) due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	108	108
Georgia Power | Pollution control revenue bonds - variable rates (0.00% to 0.00% at 12/31/18) due 2026-2052
Pollution control revenue bonds —
Pollution control revenue bonds	551	720
Georgia Power | FFB loans — 2.57% to 3.86% due 2020
Pollution control revenue bonds —
FFB loans	44	44
Georgia Power | FFB loans — 2.57% to 3.86% due 2021
Pollution control revenue bonds —
FFB loans	44	44
Georgia Power | FFB loans — 2.57% to 3.86% due 2022
Pollution control revenue bonds —
FFB loans	44	44
Georgia Power | FFB loans — 2.57% to 3.86% due 2023
Pollution control revenue bonds —
FFB loans	44	44
Georgia Power | FFB loans — 2.57% to 3.86% due 2024 to 2044
Pollution control revenue bonds —
FFB loans	2,449	2,449
Georgia Power | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Pollution control revenue bonds —
Junior subordinated notes	270	270
Mississippi Power
Maturity
2,019	0	125
2,020	307
2,021	270
2,022	0
2,023	0
Thereafter	950	680
Total long-term notes payable	1,250	1,705
Pollution control revenue bonds —
Pollution control revenue bonds	40	83
Total other long-term debt	310	353
Unamortized debt premium	29	36
Unamortized debt discount	(2)	(1)
Unamortized debt issuance expense	(8)	(7)
Total long-term debt	1,579	2,086
Amount due within one year	40	989
Long-term debt excluding amounts due within one year and held for sale	$ 1,539	$ 1,097
Percent capitalization	48.90%	44.10%
Cumulative preferred stock
Redeemable preferred stock	$ 0	$ 33
Total redeemable preferred stock - percent capitalization	0.00%	1.30%
Common Stockholders' Equity:
Common stock	$ 38	$ 38
Paid-in capital	4,546	4,529
Retained earnings	(2,971)	(3,205)
Accumulated other comprehensive loss	(4)	(4)
Total common stockholders' equity	$ 1,609	$ 1,358
Total common stockholders' equity - percent capitalization	51.10%	54.60%
Total Stockholders' Equity	$ 1,609	$ 1,358
Total Capitalization	$ 3,148	$ 2,488
Percent capitalization	100.00%	100.00%
Mississippi Power | Adjustable Rate Loans
Maturity
2,018	$ 0	$ 900
2,020	300	0
Mississippi Power | Pollution control revenue bonds due 2028
Pollution control revenue bonds —
Pollution control revenue bonds	0	43
Mississippi Power | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Pollution control revenue bonds —
Pollution control revenue bonds	40	40
Mississippi Power | Plant Daniel revenue bonds (7.13%) due 2021
Pollution control revenue bonds —
Plant Daniel revenue bonds (7.13%) due 2021	270	270
Southern Company Gas
Maturity
2,018	0	155
2,019	350
2,020	0
2,021	330	330
2,022	46	46
2,023	400
Thereafter	3,134	3,134
Total long-term notes payable	4,160	4,315
Pollution control revenue bonds —
Total other long-term debt	1,325	1,225
Unamortized fair value adjustment of long-term debt	474	525
Unamortized debt discount	(19)	(17)
Total long-term debt	5,940	6,048
Amount due within one year	357	157
Long-term debt excluding amounts due within one year and held for sale	$ 5,583	$ 5,891
Percent capitalization	39.40%	39.50%
Common Stockholders' Equity:
Paid-in capital	$ 8,856	$ 9,214
Retained earnings	(312)	(212)
Accumulated other comprehensive loss	26	20
Total common stockholders' equity	$ 8,570	$ 9,022
Total common stockholders' equity - percent capitalization	60.60%	60.50%
Total Stockholders' Equity	$ 8,570	$ 9,022
Total Capitalization	$ 14,153	$ 14,913
Percent capitalization	100.00%	100.00%
Southern Company Gas | Long-term senior notes and debt maturing 2019
Maturity
2,019	$ 300	$ 300
Southern Company Gas | Long-term senior notes and debt maturing 2023
Maturity
2,023	350	350
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Pollution control revenue bonds —
Gas facility revenue bonds	0	47
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Pollution control revenue bonds —
Gas facility revenue bonds	0	153
Southern Company Gas | First mortgage bonds — 4.70% due 2019
Pollution control revenue bonds —
First mortgage bonds	50	50
Southern Company Gas | First mortgage bonds - 5.80% due 2023
Pollution control revenue bonds —
First mortgage bonds	50	50
Southern Company Gas | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Pollution control revenue bonds —
First mortgage bonds	$ 1,225	$ 925

Consolidated Statements of Ca_3

Consolidated Statements of Capitalization (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Annual interest requirement	$ 1,700
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, shares issued (in shares)	1,000,000,000	1,000,000,000
Treasury shares (in shares)	1,000,000	900,000
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)	20,000,000	20,000,000
Redeemable cumulative preferred stock, shares outstanding (in shares)	475,115	809,325
Redeemable Preferred Stock, $1 par value
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, dividend rate	5.83%	5.83%
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	$ 15
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042
Fixed stated interest rate of debt obligation	5.50%
Pollution control revenue bonds - 4.55%
Fixed stated interest rate of debt obligation	4.55%	4.55%
Pollution control revenue bonds - variable rates (1.76% at 12/31/18) due 2022
Fixed stated interest rate of debt obligation	1.76%
Plant Daniel revenue bonds (7.13%) due 2021
Fixed stated interest rate of debt obligation	7.13%	7.13%
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Fixed stated interest rate of debt obligation		1.71%
Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Fixed stated interest rate of debt obligation		1.71%
First mortgage bonds — 4.70% due 2019
Fixed stated interest rate of debt obligation	4.70%	4.70%
First mortgage bonds - 5.80% due 2023
Fixed stated interest rate of debt obligation	5.80%	5.80%
Alabama Power
Annual interest requirement	$ 330
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
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
Alabama Power | Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042
Fixed stated interest rate of debt obligation	5.50%	5.50%
Alabama Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.125%	5.125%
Alabama Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.375%	3.375%
Alabama Power | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	3.55%	3.55%
Georgia Power
Annual interest requirement	$ 356	$ 356
Common stock, shares authorized (in shares)	20,000,000	20,000,000
Common stock, shares outstanding (in shares)	9,261,500	9,261,500
Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		2.29%
Georgia Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	4.25%	4.25%
Georgia Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	2.00%	2.00%
Georgia Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.40%	2.40%
Georgia Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	2.85%	2.85%
Georgia Power | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	5.75%	5.75%
Georgia Power | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.35%	2.35%
Mississippi Power
Fixed stated interest rate of debt obligation	7.13%
Annual interest requirement	$ 70	$ 70
Preferred stock, par value (in dollars per share)	$ 100	$ 100
Redeemable cumulative preferred stock, shares authorized (in shares)	1,244,139	1,244,139
Redeemable cumulative preferred stock, shares outstanding (in shares)	0	334,210
Common stock, shares authorized (in shares)	1,130,000	1,130,000
Common stock, shares outstanding (in shares)	1,121,000	1,121,000
Mississippi Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		3.05%
Mississippi Power | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.55%	5.55%
Mississippi Power | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.47%
Mississippi Power | Pollution control revenue bonds - 5.15% due 2028
Fixed stated interest rate of debt obligation	5.15%	5.15%
Mississippi Power | Plant Daniel revenue bonds (7.13%) due 2021
Fixed stated interest rate of debt obligation	7.13%	7.13%
Southern Company Gas
Annual interest requirement	$ 244	$ 244
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
Southern Company Gas | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	3.50%	3.50%
Southern Company Gas | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.25%	5.25%
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2022
Fixed stated interest rate of debt obligation		1.71%
Southern Company Gas | Gas facility revenue bonds - variable rate (1.71% at 12/31/17) due 2024 to 2033
Fixed stated interest rate of debt obligation		1.71%
Southern Company Gas | First mortgage bonds — 4.70% due 2019
Fixed stated interest rate of debt obligation	4.70%	4.70%
Southern Company Gas | First mortgage bonds - 5.80% due 2023
Fixed stated interest rate of debt obligation	5.80%	5.80%
Minimum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%	4.20%
Minimum | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	1.50%	1.50%
Minimum | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	1.85%	1.85%
Minimum | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	2.00%	2.00%
Minimum | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.35%	2.35%
Minimum | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	1.00%	1.00%
Minimum | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	2.45%	0.00%
Minimum | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	1.63%	1.625%
Minimum | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.10%	2.10%
Minimum | Pollution control revenue bonds - 1.15% to 2.60% due 2023
Fixed stated interest rate of debt obligation	1.15%	1.15%
Minimum | Pollution control revenue bonds - 1.38% to 4.00% due 2025-2049
Fixed stated interest rate of debt obligation	1.40%	1.40%
Minimum | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.77%
Minimum | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.76%
Minimum | Pollution control revenue bonds - variable rates (1.70% to 1.87% at 12/31/18) due 2024 to 2053
Fixed stated interest rate of debt obligation		1.70%
Minimum | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	2.66%	2.66%
Minimum | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	5.00%	5.00%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		2.29%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.10%
Minimum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.34%
Minimum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.20%	4.20%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	2.38%	2.38%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Alabama Power | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	2.80%	2.80%
Minimum | Alabama Power | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.76%	1.76%
Minimum | Alabama Power | Pollution control revenue bonds - 1.625% to 2.90% due 2034
Fixed stated interest rate of debt obligation	1.625%	1.625%
Minimum | Alabama Power | Pollution control revenue bonds - variable rates (1.70% to 1.80% at 12/31/18) due 2024-2038
Fixed stated interest rate of debt obligation	1.70%	1.70%
Minimum | Alabama Power | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.70%	3.70%
Minimum | Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	1.95%	1.95%
Minimum | Georgia Power | Long-term senior notes and debt maturing 2026-2043
Fixed stated interest rate of debt obligation	3.25%	3.25%
Minimum | Georgia Power | Pollution control revenue bonds - 1.55% to 4.00% due 2025 to 2049
Fixed stated interest rate of debt obligation	1.55%	1.55%
Minimum | Georgia Power | Pollution control revenue bonds - variable rates (1.77% to 1.78% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.77%
Minimum | Georgia Power | Pollution control revenue bonds - variable rates (1.70% to 1.83% at 12/31/18) due 2026-2052
Fixed stated interest rate of debt obligation	1.70%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	2.57%	2.57%
Minimum | Georgia Power | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	5.00%	5.00%
Minimum | Mississippi Power
Preferred stock, dividend rate	4.40%	4.40%
Minimum | Mississippi Power | Long-term senior notes and debt maturing 2028-2042
Fixed stated interest rate of debt obligation	3.95%	3.95%
Minimum | Mississippi Power | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.20%	2.20%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.50%	3.50%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.55%	8.55%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Southern Company Gas | Long-term senior notes and debt maturing 2025-2047
Fixed stated interest rate of debt obligation	2.45%	2.45%
Minimum | Southern Company Gas | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	2.66%	2.66%
Maximum | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	5.44%	5.44%
Maximum | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Long-term senior notes and debt maturing 2019
Fixed stated interest rate of debt obligation	5.55%	5.55%
Maximum | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	4.75%	4.75%
Maximum | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	9.10%	9.10%
Maximum | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.70%	8.70%
Maximum | Long-term senior notes and debt maturing 2023
Fixed stated interest rate of debt obligation	5.75%	0.00%
Maximum | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	7.30%	7.30%
Maximum | Pollution control revenue bonds - 2.10% to 2.35% due 2022
Fixed stated interest rate of debt obligation	2.35%	2.35%
Maximum | Pollution control revenue bonds - 1.15% to 2.60% due 2023
Fixed stated interest rate of debt obligation	2.60%	2.60%
Maximum | Pollution control revenue bonds - 1.38% to 4.00% due 2025-2049
Fixed stated interest rate of debt obligation	5.15%	5.15%
Maximum | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.23%
Maximum | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.87%
Maximum | Pollution control revenue bonds - variable rates (1.70% to 1.87% at 12/31/18) due 2024 to 2053
Fixed stated interest rate of debt obligation		1.87%
Maximum | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	6.58%	6.58%
Maximum | Junior subordinated notes (5.00% to 6.25%) due 2057 to 2077
Fixed stated interest rate of debt obligation	6.25%	6.25%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation		3.05%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2020
Fixed stated interest rate of debt obligation	3.50%
Maximum | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.91%
Maximum | Alabama Power | Redeemable Preferred Stock, $100 par or stated value | Cumulative preferred stock
Preferred stock, dividend rate	4.92%	4.92%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.95%	3.95%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	5.875%	5.875%
Maximum | Alabama Power | Long-term senior notes and debt maturing 2025-2048
Fixed stated interest rate of debt obligation	6.125%	6.125%
Maximum | Alabama Power | Pollution control revenue bonds - variable rates (1.76% to 1.87% at 12/31/18) due 2021
Fixed stated interest rate of debt obligation	1.87%	1.87%
Maximum | Alabama Power | Pollution control revenue bonds - 1.625% to 2.90% due 2034
Fixed stated interest rate of debt obligation	2.90%	2.90%
Maximum | Alabama Power | Pollution control revenue bonds - variable rates (1.70% to 1.80% at 12/31/18) due 2024-2038
Fixed stated interest rate of debt obligation	1.80%	1.80%
Maximum | Alabama Power | Adjustable Rate Loans | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	3.91%	3.91%
Maximum | Georgia Power | Long-term senior notes and debt maturing 2018
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Georgia Power | Long-term senior notes and debt maturing 2026-2043
Fixed stated interest rate of debt obligation	5.95%	5.95%
Maximum | Georgia Power | Pollution control revenue bonds - 1.55% to 4.00% due 2025 to 2049
Fixed stated interest rate of debt obligation	4.00%	4.00%
Maximum | Georgia Power | Pollution control revenue bonds - variable rates (1.77% to 1.78% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	1.78%
Maximum | Georgia Power | Pollution control revenue bonds - variable rates (1.70% to 1.83% at 12/31/18) due 2026-2052
Fixed stated interest rate of debt obligation	1.83%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2020
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2021
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2022
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2023
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Georgia Power | FFB loans — 2.57% to 3.86% due 2024 to 2044
Fixed stated interest rate of debt obligation	3.86%	3.86%
Maximum | Mississippi Power
Preferred stock, dividend rate	5.25%	5.25%
Maximum | Mississippi Power | Long-term senior notes and debt maturing 2028-2042
Fixed stated interest rate of debt obligation	5.40%	5.40%
Maximum | Mississippi Power | Pollution control revenue bonds - variable rates (1.77 to 2.23% at 12/31/18) due 2019
Fixed stated interest rate of debt obligation	2.23%	2.23%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2021
Fixed stated interest rate of debt obligation	9.10%	9.10%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2022
Fixed stated interest rate of debt obligation	8.70%	8.70%
Maximum | Southern Company Gas | Long-term senior notes and debt maturing 2025-2047
Fixed stated interest rate of debt obligation	7.30%	7.30%
Maximum | Southern Company Gas | First mortgage bonds — 2.66% to 6.58% due 2026 to 2057
Fixed stated interest rate of debt obligation	6.58%	6.58%

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions		Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Preferred and Preference Stock of Subsidiaries	Noncontrolling Interests		Alabama Power	Alabama PowerCommon Stock	Alabama PowerPaid-In Capital	Alabama PowerRetained Earnings	Alabama PowerAccumulated Other Comprehensive Income (Loss)	Georgia Power	Georgia PowerCommon Stock	Georgia PowerPaid-In Capital	Georgia PowerRetained Earnings	Georgia PowerAccumulated Other Comprehensive Income (Loss)	Mississippi Power	Mississippi PowerCommon Stock	Mississippi PowerPaid-In Capital	Mississippi PowerRetained Earnings	Mississippi PowerAccumulated Other Comprehensive Income (Loss)	Southern Power		Southern PowerCommon Stock	Southern PowerPaid-In Capital		Southern PowerRetained Earnings	Southern PowerAccumulated Other Comprehensive Income (Loss)	Southern PowerTotal Common Stockholder's Equity		Southern PowerNoncontrolling Interests	[1]	Southern Company Gas	Southern Company GasCommon Stock	Southern Company GasTreasury	Southern Company GasPaid-In Capital	Southern Company GasRetained Earnings	Southern Company GasAccumulated Other Comprehensive Income (Loss)	Southern Company GasNoncontrolling Interests
Beginning balance (in shares) (Predecessor) at Dec. 31, 2015																																						120,377	217
Beginning balance (in shares) at Dec. 31, 2015			915,073	3,352								31,000					9,000					1,000						0
Beginning balance (Predecessor) at Dec. 31, 2015																																					$ 3,975	$ 603	$ (8)	$ 2,099	$ 1,421	$ (186)	$ 46
Beginning balance at Dec. 31, 2015		$ 21,982	$ 4,572	$ (142)	$ 6,282	$ 10,010	$ (130)	$ 609	$ 781	[1]	$ 5,992	$ 1,222	$ 2,341	$ 2,461	$ (32)	$ 10,719	$ 398	$ 6,275	$ 4,061	$ (15)	$ 2,359	$ 38	$ 2,893	$ (566)	$ (6)	$ 3,264		$ 0	$ 1,822		$ 657	$ 4	$ 2,483		$ 781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock | Predecessor																																					131				131
Return of capital | Predecessor																																					0
Other comprehensive income (loss) | Predecessor																																					(35)					(35)
Stock issued (in shares) | Predecessor																																						95
Stock issued | Predecessor																																					6			6
Stock-based compensation (in shares) | Predecessor																																						270
Stock-based compensation | Predecessor																																					30	$ 2		28
Cash dividends on common stock | Predecessor																																					(128)				(128)
Reclassification of noncontrolling interest | Predecessor																																					(46)						(46)
Ending balance (in shares) (Predecessor) at Jun. 30, 2016																																						120,742	217
Ending balance (in shares) at Jun. 30, 2016																																						0	0
Ending balance (Predecessor) at Jun. 30, 2016																																					3,933	$ 605	$ (8)	2,133	1,424	(221)	0
Ending balance at Jun. 30, 2016																																					8,001	$ 0	$ 0	8,001	0	0	0
Beginning balance (in shares) (Predecessor) at Dec. 31, 2015																																						120,377	217
Beginning balance (in shares) at Dec. 31, 2015			915,073	3,352								31,000					9,000					1,000						0
Beginning balance (Predecessor) at Dec. 31, 2015																																					3,975	$ 603	$ (8)	2,099	1,421	(186)	46
Beginning balance at Dec. 31, 2015		21,982	$ 4,572	$ (142)	6,282	10,010	(130)	609	781	[1]	5,992	$ 1,222	2,341	2,461	(32)	10,719	$ 398	6,275	4,061	(15)	2,359	$ 38	2,893	(566)	(6)	3,264		$ 0	1,822		657	4	2,483		781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock		2,448				2,448					822			822		1,330			1,330		(50)			(50)		338					338		338
Return of capital																										0
Capital contributions from (to) parent company											272		272			610		610			632		632			1,850			1,850				1,850
Other comprehensive income (loss)		(50)					(50)				2				2	2				2	2				2	31						31	31
Stock issued (in shares)			76,140	2,599
Stock issued		3,758	$ 380	$ 115	3,263
Stock-based compensation		120			120
Cash dividends on common stock		(2,104)				(2,104)					(765)			(765)		(1,305)			(1,305)							(272)					(272)		(272)
Contributions from noncontrolling interests		618							618	[1]																618									618
Distributions to noncontrolling interests		(57)							(57)	[1]																(57)									(57)
Purchase of membership interests from noncontrolling interests		(129)							(129)	[1]																(129)									(129)
Net income attributable to noncontrolling interests		(32)							(32)	[1]																32									32
Other (in shares)				(66)
Other		(6)		$ (4)	(4)	2																				0			(1)		1
Ending balance (in shares) at Dec. 31, 2016			991,213	819								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	[1]	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	$ 0	9,095	(12)	26	0
Beginning balance (in shares) (Predecessor) at Jun. 30, 2016																																						120,742	217
Beginning balance (in shares) at Jun. 30, 2016																																						0	0
Beginning balance (Predecessor) at Jun. 30, 2016																																					3,933	$ 605	$ (8)	2,133	1,424	(221)	0
Beginning balance at Jun. 30, 2016																																					8,001	$ 0	$ 0	8,001	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock																																					114				114
Return of capital																																					0
Capital contributions from (to) parent company																																					1,094			1,094
Other comprehensive income (loss)																																					26					26
Cash dividends on common stock																																					(126)				(126)
Ending balance (in shares) at Dec. 31, 2016			991,213	819								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2016		26,612	$ 4,952	$ (31)	9,661	10,356	(180)	609	1,245	[1]	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	$ 0	9,095	(12)	26	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock		842				842					848			848		1,414			1,414		(2,590)			(2,590)		1,071					1,071		1,071				243				243
Return of capital																										0											0
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)			17,319
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 transfer from SCS	[2]																									(27)						(27)	(27)
Preference stock redemption		(609)						(609)
Contributions from noncontrolling interests		79							79	[1]																79									79
Distributions to noncontrolling interests		(122)							(122)	[1]																(122)									(122)
Purchase of membership interests from noncontrolling interests																										(59)
Net income attributable to noncontrolling interests		(44)							(44)	[1]																44									44
Reclassification from redeemable noncontrolling interests		114							114	[1]																114									114
Other (in shares)				(110)
Other		(21)		$ (5)	(4)	(13)			1	[1]	(5)			(5)		(4)			(4)		1			1		(7)			(7)				(7)				1			2		(1)
Ending balance (in shares) at Dec. 31, 2017			1,008,532	929								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2017		25,528	$ 5,038	$ (36)	10,469	8,885	(189)	0	1,361	[1]	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	$ 0	9,214	(212)	20	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) after dividends on preferred and preference stock		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)			26,209
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]																1,372									1,372
Distributions to noncontrolling interests		(164)							(164)	[1]																(164)									(164)
Net income attributable to noncontrolling interests		(58)							(58)	[1]																59									59
Sale of noncontrolling interests		1,273			(417)				1,690																	1,273	[3]		(417)	[3]			(417)	[3]	1,690	[3]
Other (in shares)				(24)
Other		(29)		$ (2)	(6)	20	(40)		(1)	[1]	(7)			(1)	(6)	(2)				(2)	(1)			(1)		5			3		(1)	4	6		(1)		0				(4)	4
Ending balance (in shares) at Dec. 31, 2018			1,034,741	953								31,000					9,000					1,000						0										0	0
Ending balance at Dec. 31, 2018		$ 29,039	$ 5,164	$ (38)	$ 11,094	$ 8,706	$ (203)	$ 0	$ 4,316	[1]	$ 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	$ 0	$ 8,856	$ (312)	$ 26	$ 0
[1]	Excludes redeemable noncontrolling interests. See Note 7 to the financial statements under "Noncontrolling Interests" for additional information.
[2]	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.
[3]	See Note 15 under "Southern Power - Sales of Renewable Facility Interests" for additional information.

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)$ / shares
Cash dividends (in dollars per share) | $ / shares	$ 2.3800
Other comprehensive income (loss), net of tax	$ 26
Pension and Other Postretirement Benefit Plans
Other comprehensive income (loss), net of tax	2
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, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General Southern Company is the parent company of the traditional electric operating companies, Southern Power, Southern Company Gas (as of July 1, 2016), SCS, Southern Linc, Southern Holdings, Southern Nuclear, PowerSecure (as of May 9, 2016), and other direct and indirect subsidiaries. The traditional electric operating companies – Alabama Power, Georgia Power, Gulf Power (through December 31, 2018), and Mississippi Power – are vertically integrated utilities providing electric service in four Southeastern states. On January 1, 2019, Southern Company completed the sale of Gulf Power 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. On May 22, 2018, Southern Power sold a noncontrolling 33% equity interest in SP Solar, a limited partnership indirectly owning substantially all of Southern Power's solar facilities, and, on December 11, 2018, Southern Power sold a noncontrolling tax equity interest in SP Wind, a holding company owning a portfolio of eight operating wind facilities. On November 5, 2018, Southern Power entered into an agreement to sell all of its equity interests in Plant Mankato (including the 385 -MW expansion currently under construction). On December 4, 2018, Southern Power sold all of its equity interests in Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) to NextEra Energy. Southern Company Gas distributes natural gas through natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. In July 2018, Southern Company Gas completed sales of three of its natural gas distribution utilities (Elizabethtown Gas (New Jersey), Florida City Gas, and Elkton Gas (Maryland)). The remaining natural gas distribution utilities include Nicor Gas (Illinois), Atlanta Gas Light (Georgia), Virginia Natural Gas, and Chattanooga Gas (Tennessee). In June 2018, Southern Company Gas also completed the sale of Pivotal Home Solutions, which provided home equipment protection products and 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 investments in leveraged leases and for other electric services. 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 is a provider of energy solutions, including distributed energy infrastructure, energy efficiency products and services, and utility infrastructure services, to customers. See Note 15 for additional information regarding disposition activities. 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 control and for VIEs where a registrant has an equity investment but is not the primary beneficiary. Southern Power has consolidated renewable generation projects that are partially funded by tax equity investors. The related contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. Therefore, the noncontrolling interest is accounted for under a balance sheet approach utilizing the 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 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, Southern Company Gas has recast its reportable segments. See Note 16 under " Southern Company Gas " for additional information. At December 31, 2018, Southern Company and Southern Power each had assets and liabilities held for sale on their balance sheets. Unless otherwise noted, the disclosures herein related to specific asset and liability balances at December 31, 2018 exclude assets and liabilities held for sale. See Note 15 under " Assets Held for Sale " for additional information including Southern Company's and Southern Power's major classes of assets and liabilities classified as held for sale. Southern Company Gas Pursuant to the Merger, Southern Company pushed down the application of the acquisition method of accounting to the financial statements of Southern Company Gas such that the assets and liabilities are recorded at their respective fair values, and goodwill was established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout Southern Company Gas' financial statements and the combined notes to the financial statements, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor." Certain predecessor period data presented in Southern Company Gas' financial statements has been modified or reclassified to conform to the presentation used by Southern Company. Changes to Southern Company Gas' statements of income include classifying operating revenues as natural gas revenues and other revenues, as well as classifying cost of goods sold as cost of natural gas and cost of other sales and presenting interest expense and AFUDC on a gross basis. Changes to Southern Company Gas' statements of cash flows include revised financial statement line item descriptions to align with the new balance sheet descriptions and expanded line items within each category of cash flow activity. Recently Adopted Accounting Standards Revenue In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers (ASC 606), replacing the existing accounting standard and industry-specific guidance for revenue recognition with a five-step model for recognizing and measuring revenue from contracts with customers. The underlying principle of the standard is to recognize revenue to depict the transfer of goods or services to customers at the amount expected to be collected. ASC 606 became effective on January 1, 2018 and the registrants adopted it using the modified retrospective method applied to open contracts and only to the version of contracts in effect as of January 1, 2018. In accordance with the modified retrospective method, the registrants' previously issued financial statements have not been restated to comply with ASC 606 and the registrants did not have a cumulative-effect adjustment to retained earnings. The adoption of ASC 606 had no significant impact on the timing of revenue recognition compared to previously reported results; however, it requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers, which are included herein and in Note 4 . ASC 606 provided additional clarity on financial statement presentation that resulted in reclassifications into other revenues and other operations and maintenance from other income/(expense), net at Alabama Power and Georgia Power primarily related to certain unregulated sales of products and services. In addition, contract assets related to certain fixed retail revenues at Georgia Power and Southern Company's unregulated distributed generation business have been reclassified from unbilled revenue in accordance with the guidance in ASC 606. These reclassifications did not affect the timing or amount of revenues recognized or cash flows. ASC 606 also provided additional guidance on revenue recognized over time, resulting in a change in the timing of revenue recognized from guaranteed and fixed billing arrangements at Southern Company Gas. The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Year Ended December 31, 2018 Statements of Income As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Natural gas revenues $ 3,854 $ 3,852 $ 2 Other revenues 1,239 1,234 5 Other operations and maintenance 5,889 5,830 59 Operating Income 4,191 4,243 (52 ) Other income (expense), net 114 60 54 Earnings Before Income Taxes 2,749 2,747 2 Income taxes 449 448 1 Consolidated Net Income 2,300 2,299 1 Consolidated Net Income Attributable to Southern Company 2,226 2,225 1 Alabama Power Other revenues $ 267 $ 230 $ 37 Other operations and maintenance 1,669 1,625 44 Taxes other than income taxes 389 388 1 Operating Income 1,477 1,485 (8 ) Other income (expense), net 20 12 8 Georgia Power Other revenues $ 481 $ 387 $ 94 Other operations and maintenance 1,860 1,772 88 Operating Income 1,289 1,283 6 Other income (expense), net 115 121 (6 ) Southern Company Gas Natural gas revenues $ 3,874 $ 3,872 $ 2 Operating Income 915 913 2 Earnings Before Income Taxes 836 834 2 Income taxes 464 463 1 Net Income 372 371 1 For the Year Ended December 31, 2018 Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 2,300 $ 2,299 $ 1 Changes in certain current assets and liabilities: Receivables (426 ) (472 ) 46 Other current assets (127 ) (81 ) (46 ) Accrued taxes 267 268 (1 ) Other current liabilities 63 61 2 Georgia Power Changes in certain current assets and liabilities: Receivables $ 8 $ 1 $ 7 Other current assets (43 ) (36 ) (7 ) Southern Company Gas Net income $ 372 $ 371 $ 1 Changes in certain current assets and liabilities: Accrued taxes 10 11 (1 ) Other current liabilities (22 ) (24 ) 2 At December 31, 2018 Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 654 $ 728 $ (74 ) Other accounts and notes receivable 813 814 (1 ) Other current assets 162 87 75 Accrued taxes 656 655 1 Other current liabilities 852 854 (2 ) Total Stockholders' Equity 29,039 29,038 1 Georgia Power Unbilled revenues $ 208 $ 243 $ (35 ) Other accounts and notes receivable 80 81 (1 ) Other current assets 70 34 36 Southern Company Gas Accrued income taxes $ 66 $ 65 $ 1 Other current liabilities 130 132 (2 ) Common Stockholder's Equity 8,570 8,569 1 Other In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18). ASU 2016-18 eliminates the need to reflect transfers between cash and restricted cash in operating, investing, and financing activities in the statements of cash flows. In addition, the net change in cash and cash equivalents during the period includes amounts generally described as restricted cash or restricted cash equivalents. The registrants adopted ASU 2016-18 retrospectively effective January 1, 2018. Southern Company, Southern Power, and Southern Company Gas have restated prior periods in the statements of cash flows by immaterial amounts. The change in restricted cash in the statements of cash flows was previously disclosed in operating activities for Southern Company and Southern Company Gas and in investing activities for Southern Company and Southern Power. See " Restricted Cash " herein for additional information. In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 removes the requirement to compare the implied fair value of goodwill with the carrying amount as part of Step 2 of the goodwill impairment test. Under the new standard, the goodwill impairment loss will be measured as the excess of a reporting unit's carrying amount over its fair value, not exceeding the total amount of goodwill allocated to that reporting unit, which may increase the frequency of goodwill impairment charges if a future goodwill impairment test does not pass the Step 1 evaluation. ASU 2017-04 is effective prospectively for periods beginning on or after December 15, 2019, with early adoption permitted. The registrants adopted ASU 2017-04 effective January 1, 2018 with no impact on their respective financial statements. In March 2017, the FASB issued ASU No. 2017-07, Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (ASU 2017-07). ASU 2017-07 requires that an employer report the service cost component in the same line item or items as other compensation costs and requires the other components of net periodic pension and postretirement benefit costs to be separately presented in the statements of income outside of income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. The registrants adopted ASU 2017-07 effective January 1, 2018 with no material impact on their respective financial statements. ASU 2017-07 has been applied retrospectively, with the service cost component of net periodic benefit costs included in operations and maintenance expenses and all other components of net periodic benefit costs included in other income (expense), net in the statements of income for all periods presented for Southern Company, the traditional electric operating companies, and Southern Company Gas. The impacted registrants used the practical expedient provided by ASU 2017-07, which permits an employer to use the amounts disclosed in its retirement benefits note for prior comparative periods as the estimation basis for applying the retrospective presentation requirements to those periods. The amounts of the other components of net periodic benefit costs reclassified for the prior periods are presented in Note 11 . The presentation changes resulted in a decrease in operating income and an increase in other income for the years ended December 31, 2017 and 2016 for each of the impacted registrants. Since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017, no retrospective presentation of Southern Power's net periodic benefit costs is required. The requirement to limit capitalization to the service cost component of net periodic benefit costs has been applied on a prospective basis from the date of adoption for all registrants. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12). ASU 2017-12 makes more financial and non-financial hedging strategies eligible for hedge accounting, amends the related presentation and disclosure requirements, and simplifies hedge effectiveness assessment requirements. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The registrants adopted ASU 2017-12 effective January 1, 2018 with no material impact on their respective financial statements. See Note 14 for disclosures required by ASU 2017-12. On February 14, 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (ASU 2018-02) to address the application of ASC 740, Income Taxes (ASC 740) to certain provisions of the Tax Reform Legislation. ASU 2018-02 specifically addresses the ASC 740 requirement that the effect of a change in tax laws or rates on deferred tax assets and liabilities be included in income from continuing operations, even when the tax effects were initially recognized directly in OCI at the previous rate, which strands the income tax rate differential in accumulated OCI. The amendments in ASU 2018-02 allow a reclassification from accumulated OCI to retained earnings for stranded tax effects resulting from the Tax Reform Legislation. The registrants adopted ASU 2018-02 effective January 1, 2018 with no material impact on their respective financial statements. On August 28, 2018, the FASB issued ASU No. 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General (Topic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans (ASU 2018-14). ASU 2018-14 amends ASC 715 to add, remove, and clarify disclosure requirements related to defined benefit pension and other postretirement plans. The registrants adopted ASU 2018-14 effective December 31, 2018 with no material impact on their respective financial statements. See Note 11 for disclosures required by ASU 2018-14. 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 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 2018 , 2017 , and 2016 were as follows: Alabama Georgia Mississippi Southern Power (a) Southern Company Gas (b) (in millions) 2018 $ 508 $ 653 $ 104 $ 98 $ 194 2017 479 625 140 218 63 2016 460 606 231 193 17 (a) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. (b) Southern Company Gas' 2016 costs represent services provided subsequent to the Merger. 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 2018 , 2017 , and 2016 amounted to $247 million , $248 million , and $249 million , respectively, for Alabama Power and $780 million , $675 million , and $666 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 total power purchased from affiliates through the power pool is included in purchased power, affiliates on their respective statements of income. Mississippi Power's and Southern Power's total power purchased from affiliates through the power pool is included in purchased power on their respective statements of income and was as follows: Mississippi Power Southern Power (in millions) 2018 $ 15 $ 41 2017 16 27 2016 29 21 SCS, as agent for Alabama Power, Georgia Power, Southern Power, and Southern Company Gas, has 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 Notes 7 and 15 under " Southern Company Gas – Equity Method Investments – SNG " and " Southern Company Gas – Investment in SNG ," respectively, for additional information. Transportation costs under these agreements in 2018 , 2017 , and 2016 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2018 $ 8 $ 101 $ 25 $ 32 2017 9 102 25 32 2016 (*) 2 35 7 15 (*) Represents costs incurred for the period subsequent to Southern Company Gas' investment in SNG. On November 16, 2018, SNG completed its purchase of Georgia Power's natural gas lateral pipeline serving Plant McDonough Units 4 through 6 at net book value, as approved by the Georgia PSC on January 16, 2018. SNG expects to pay $142 million to Georgia Power in the first quarter 2020. During the interim period, Georgia Power will receive a discounted shipping rate to reflect the delayed consideration. Southern Company Gas' portion of the expected capital expenditures for the purchase of this pipeline and additional construction is $122 million . 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 2018 , 2017 , and 2016 : Georgia Southern Power (in millions) 2018 $ 21 $ 119 2017 22 119 2016 (*) 10 17 (*) Represents costs incurred for the period subsequent to Southern Company's acquisition of Southern Company Gas. 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 expenses, which totaled $8 million , $9 million , and $13 million in 2018 , 2017 , and 2016 , respectively. Mississippi Power also reimburses Alabama Power for any direct fuel purchases delivered from one of Alabama Power's transfer facilities. There were no such fuel purchases in 2018 , 2017 , and 2016 . 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 2018 , $11 million in 2017 , and $12 million in 2016 . See Note 15 under " Southern Company's Sale of Gulf Power " 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 $24 million in 2018 and $11 million in 2017 and were immaterial in 2016 . 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 entered into several PPAs with Southern Power for capacity and energy. Total expenses associated with these PPAs were $216 million , $235 million , and $265 million in 2018 , 2017 , and 2016 , respectively. See Note 8 under " Long-term Debt – Capital Leases – Georgia Power " and Note 9 under " Fuel and Power Purchase Agreements – Affiliate " for additional information. 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 , $11 million , and $8 million in 2018 , 2017 , and 2016 , respectively. See Note 5 under " Joint Ownership Agreements " and Note 15 under " Southern Company's Sale of Gulf Power " 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 expenditures and costs, which totaled $31 million , $31 million , and $26 million in 2018 , 2017 , and 2016 , respectively. See Note 5 under " Joint Ownership Agreements " and Note 15 under " Southern Company's Sale of Gulf Power " for additional information. In 2014, prior to Southern Company's 2016 acquisition of PowerSecure, Georgia Power entered into agreements with PowerSecure to build solar power generation facilities at two U.S. Army bases, as approved by the Georgia PSC. In October 2016, the two facilities began commercial operation. Payments of $32 million made by Georgia Power to PowerSecure under the agreements since Southern Company's acquisition of PowerSecure are included in plant in service at December 31, 2018 . 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 $215 million , $233 million , and $258 million for 2018 , 2017 , and 2016 , respectively. Included within these revenues were affiliate PPAs accounted for as operating leases, which totaled $65 million , $81 million , and $109 million for 2018 , 2017 , and 2016 , respectively. Southern Power has several agreements with SCS for transmission services. Transmission services purchased by Southern Power from SCS totaled $12 million , $13 million , and $11 million for 2018 , 2017 , and 2016 , respectively, and were charged to other operations and maintenance 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 9 under " Fuel and Power Purchase Agreements " 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 2018 , 2017 , or 2016 . 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 had no impact on the timing or amount of revenue recognized under previous guidance. See " Recently Adopted Accounting Standards – Revenue " herein and 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

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 3,658 $ 3,931 (a,p) Asset retirement obligations-asset 2,933 1,133 (b,p) Deferred income tax charges 799 814 (b,o) Property damage reserves-asset 416 333 (c) Under recovered regulatory clause revenues 407 317 (d) Environmental remediation-asset 366 511 (e,p) Loss on reacquired debt 346 223 (f) Remaining net book value of retired assets 211 306 (g) Vacation pay 182 183 (h,p) Long-term debt fair value adjustment 121 138 (i) Deferred PPA charges — 119 (j,p) Other regulatory assets 581 625 (k) Deferred income tax credits (6,455 ) (7,261 ) (b,o) Other cost of removal obligations (2,297 ) (2,684 ) (b) Customer refunds (293 ) (188 ) (n) Property damage reserves-liability (76 ) (135 ) (l) Over recovered regulatory clause revenues (47 ) (155 ) (d) Other regulatory liabilities (132 ) (104 ) (m) Total regulatory assets (liabilities), net $ 720 $ (1,894 ) 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) Asset retirement 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 $28 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Georgia Power – Storm Damage Recovery " herein for additional information. (d) Recorded and recovered or amortized over periods generally not exceeding 10 years . (e) Recovered through environmental cost recovery mechanisms when the remediation is performed or the work is performed. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue, which may range up to 50 years . (g) Amortized over periods not exceeding eight years . (h) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (i) Recovered over the remaining life of the original debt issuances, which range up to 20 years . For additional information see Note 15 under " Southern Company Merger with Southern Company Gas ." (j) Related to Gulf Power and reclassified as assets held for sale at December 31, 2018. See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power. (k) Comprised of numerous immaterial components including nuclear outage, fuel-hedging losses, cancelled construction projects, building and generating plant leases, property tax, and other miscellaneous assets. These costs are recorded and recovered or amortized over periods generally not exceeding 50 years . (l) Amortized as storm restoration and potential reliability-related expenses are incurred. (m) Comprised of numerous components including retiree benefit plans, fuel-hedging gains, AROs, and other liabilities that are recorded and recovered or amortized over periods not exceeding 20 years . (n) At December 31, 2018, represents amounts accrued and outstanding for refund, including approximately $109 million as a result of Alabama Power's 2018 retail return exceeding the allowed range, approximately $55 million pursuant to the Georgia Power Tax Reform Settlement Agreement, and approximately $100 million , subject to review and approval by the Georgia PSC, as a result of Georgia Power's 2018 retail ROE exceeding the allowed retail ROE range. See "Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (o) 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 be determined in future rate proceedings. See "Georgia Power," "Mississippi Power," and "Southern Company Gas" herein and Note 10 for additional information. (p) 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's Sale of Gulf Power " 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), including a $62 million increase in base revenues, less an $8 million purchased power capacity cost recovery clause credit. The 2017 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, on March 26, 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 in 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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 947 $ 946 (a,p) Deferred income tax charges 241 240 (b,c,d,) Under recovered regulatory clause revenues 176 53 (e) Asset retirement obligations 147 (33 ) (b) Regulatory clauses 142 142 (f) Vacation pay 71 70 (g,p) Loss on reacquired debt 56 62 (h) Nuclear outage 49 56 (i) Remaining net book value of retired assets 43 54 (j) Other regulatory assets 57 58 (k,l) Deferred income tax credits (2,027 ) (2,082 ) (b,d) Other cost of removal obligations (497 ) (609 ) (b) Rate RSE refund (109 ) — (m) Natural disaster reserve (20 ) (38 ) (n) Other regulatory liabilities (45 ) (7 ) (l,o) Total regulatory assets (liabilities), net $ (769 ) $ (1,088 ) 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 15 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 50 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 $10 million for 2018 and $13 million for 2017 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 50 years . See Note 10 for additional information. (e) Recorded and recovered or amortized over periods not exceeding 10 years . See "Rate CNP PPA," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study. See " Rate RSE " herein for additional information. (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 the remaining life of the original issue, which may range up to 50 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 up to 8 years . (k) Comprised of components including generation site selection/evaluation costs, PPA capacity (to be recovered over the next 12 months ), and other miscellaneous assets. Capitalized upon initialization of related construction projects, if applicable. (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) Refund accrued as a result of the 2018 retail return exceeding the allowed range. See " Rate RSE " herein for additional information. (n) Amortized as storm restoration and potential reliability-related expenses are incurred. (o) Comprised of several components, primarily $33 million deferred as a result of the Alabama PSC accounting order regarding the Tax Reform Legislation. See "Tax Reform Accounting Order" herein for additional information. (p) Not earning a return as offset in rate base by a corresponding asset or liability. 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% . At December 31, 2016, Alabama Power's retail return exceeded the allowed WCER range which resulted in Alabama Power establishing a $73 million Rate RSE refund liability. In accordance with an Alabama PSC order issued in February 2017, Alabama Power applied the full amount of the refund to reduce the under recovered balance of Rate CNP PPA as discussed further below. 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. On May 1, 2018, the Alabama PSC approved modifications to Rate RSE and other commitments designed to position Alabama Power to address the growing pressure on its credit quality resulting from the Tax Reform Legislation, without increasing retail rates under Rate RSE in the near term. Alabama Power plans to reduce growth in total debt by increasing equity, with corresponding reductions in debt issuances, thereby de-leveraging its capital structure. Alabama Power's goal is to achieve an equity ratio of approximately 55% by the end of 2025. At December 31, 2018, Alabama Power's equity ratio was approximately 47% . 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, 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% . In conjunction with these modifications to Rate RSE, on May 8, 2018, Alabama Power consented to a moratorium on any upward adjustments under Rate RSE for 2019 and 2020 and will also return $50 million to customers through bill credits in 2019. On November 30, 2018, Alabama Power made its required annual Rate RSE submission to the Alabama PSC of projected data for calendar year 2019. Projected earnings were within the specified range; therefore, retail rates under Rate RSE remain unchanged for 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 will apply $75 million to reduce the Rate ECR under recovered balance and the remaining $34 million will be refunded to customers through bill credits in July through September 2019. Rate CNP PPA Alabama Power's retail rates, approved by the Alabama PSC, provide for adjustments under Rate CNP to recognize the placing of new generating facilities into retail service. Alabama Power may also recover retail costs associated with certificated PPAs under Rate CNP PPA. No adjustments to Rate CNP PPA occurred during the period 2016 through 2018 and no adjustment is expected in 2019. At December 31, 2018 and 2017 , Alabama Power had an under recovered Rate CNP PPA balance of $25 million and $12 million , respectively, which is included in deferred under recovered regulatory clause revenues in the balance sheet. In accordance with an accounting order issued in February 2017 by the Alabama PSC, Alabama Power eliminated the under recovered balance in Rate CNP PPA at December 31, 2016, which totaled approximately $142 million . As discussed herein under "Rate RSE," Alabama Power utilized the full amount of its $73 million Rate RSE refund liability to reduce the amount of the Rate CNP PPA under recovery and reclassified the remaining $69 million to a separate regulatory asset. The amortization of the new regulatory asset through Rate RSE will begin concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. Alabama Power's current depreciation study became effective January 1, 2017. 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 a factor that is calculated annually. 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 Southern Company's or Alabama Power's net income. In accordance with an accounting order issued in February 2017 by the Alabama PSC, Alabama Power reclassified $36 million of its under recovered balance in Rate CNP Compliance to a separate regulatory asset. The amortization of the new regulatory asset through Rate RSE will begin concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. Alabama Power's current depreciation study became effective January 1, 2017. In December 2017, the Alabama PSC issued a consent order that Alabama Power leave in effect for 2018 the factors associated with Alabama Power's compliance costs for the year 2017, with any under-collected amount for prior years deemed recovered before any current year amounts. On November 30, 2018, Alabama Power submitted calculations associated with its cost of complying with environmental mandates, as provided under Rate CNP Compliance. The filing reflected a projected unrecovered retail revenue requirement for environmental compliance of approximately $205 million , which is being recovered in the billing months of January 2019 through December 2019. At December 31, 2018 , Alabama Power had an under recovered Rate CNP Compliance balance of $42 million , which is included in customer accounts receivable, and $17 million at December 31, 2017 included in deferred under recovered regulatory clause revenues in the balance sheet. Rate ECR Alabama Power has established energy cost recovery rates under Alabama Power's Rate ECR as approved by the Alabama PSC. Rates are 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 give 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. In accordance with an accounting order issued in February 2017 by the Alabama PSC, Alabama Power reclassified $36 million of its under recovered balance in Rate ECR to a separate regulatory asset. The amortization of the new regulatory asset through Rate RSE will begin concurrently with the effective date of Alabama Power's next depreciation study, which is expected to occur no later than 2022. Alabama Power's current depreciation study became effective January 1, 2017. In December 2017, the Alabama PSC issued a consent order that Alabama Power leave in effect for 2018 the energy cost recovery rates which began in 2017. On May 1, 2018, the Alabama PSC approved an increase to Rate ECR from 2.015 cents per KWH to 2.353 cents per KWH effective July 2018 through December 2018. On December 4, 2018, the Alabama PSC issued a consent order to leave this rate in effect through December 31, 2019. This change is expected to increase collections by approximately $183 million in 2019. Absent any further order from the Alabama PSC, in January 2020, the rates will return to the originally authorized 5.910 cents per KWH. As discussed herein under "Rate RSE," in accordance with an Alabama PSC order issued on February 5, 2019, Alabama Power will utilize $75 million of the 2018 Rate RSE refund liability to reduce the Rate ECR under recovered balance. 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. At December 31, 2017, Alabama Power had an under recovered fuel balance of $25 million , which was 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 On May 1, 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 estimated deferrals for the year ended December 31, 2018 totaled approximately $63 million , subject to adjustment following the filing of the 2018 tax return, of which $30 million was used to offset the Rate ECR under recovered balance and $33 million is recorded in other regulatory liabilities, deferred on the balance sheet to be used for the benefit of customers as determined by the Alabama PSC at a future date. See 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 . In December 2017, the reserve maintenance charge was suspended and the reserve establishment charge was activated as a result of the NDR balance falling below $50 million . Alabama Power expects to collect approximately $16 million annually until the reserve balance is restored to $75 million . The NDR balance at December 31, 2018 was $20 million and is included in other regulatory liabilities, deferred on the balance sheet. 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 will enhance Alabama Power's ability to deal with the financial effects of future natural disasters, promote system reliability, and offset costs retail customers would otherwise bear. No such accruals were recorded or designated in any period presented. 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. At December 31, 2018, this regulatory asset had a balance of $42 million , of which $10 million is included in other regulatory assets, current and $32 million is included in other regulatory assets, deferred on the balance sheet. Subsequent to December 31, 2018, Alabama Power determined that Plant Gorgas Units 8, 9, and 10 (approximately 1,000 MWs) will be retired by April 15, 2019 due to the expected costs of compliance with federal and state environmental regulations. In accordance with the Environmental Accounting Order, approximately $740 million of net investment costs will be transferred to a regulatory asset at the retirement date and recovered over the affected units' remaining useful lives, as established prior to the decision to retire. Georgia Power Regulatory Assets and Liabilities Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 1,295 $ 1,313 (a, l) Asset retirement obligations 2,644 945 (b, l) Deferred income tax charges 522 521 (b, c, l) Storm damage reserves 416 333 (d) Remaining net book value of retired assets 127 146 (e) Loss on reacquired debt 277 127 (f, l) Vacation pay 91 91 (g, l) Other cost of removal obligations 68 40 (b) Environmental remediation 55 49 (h) Other regulatory assets 135 106 (i) Deferred income tax credits (3,080 ) (3,248 ) (b, c) Customer refunds (165 ) (188 ) (j) Other regulatory liabilities (7 ) (3 ) (k, l) Total regulatory assets (liabilities), net $ 2,378 $ 232 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 14 years . See Note 11 for additional information. (b) Through 2019, Georgia Power is recovering approximately $60 million annually for AROs, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. See Note 6 for additional information on AROs. Other cost of removal obligations and deferred income tax assets are recovered and deferred income tax liabilities are amortized over the related property lives, which may range up to 65 years . Included in the deferred income tax assets is $17 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2022. (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 $610 million of deferred income tax liabilities, neither of which are subject to normalization. The recovery and amortization of these amounts is expected to be determined in the Georgia Power 2019 Base Rate Case. See " Rate Plans " herein and Note 10 for additional information. (d) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Storm Damage Recovery " herein and Note 1 under "Storm Damage Reserves" for additional information. (e) The net book value of Plant Branch Units 1 through 4 at December 31, 2018 was $87 million , which is being amortized over the units' remaining useful lives through 2024. The net book value of Plant Mitchell Unit 3 at December 31, 2018 was $9 million , which will continue to be amortized through December 31, 2019 as provided in the 2013 ARP. Amortization of the remaining approximately $4 million net book value of Plant Mitchell Unit 3 at December 31, 2019 and a total of approximately $31 million related to obsolete inventories of certain retired units is expected to be determined in the Georgia Power 2019 Base Rate Case. See " 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, which currently does not exceed 34 years . (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Through 2019, Georgia Power is recovering approximately $2 million annually for environmental remediation, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See Note 3 under Environmental Remediation for additional information. (i) Comprised of several components including future generation costs, deferred nuclear outage costs, cancelled construction projects, building lease, and fuel-hedging losses. The timing of recovery of approximately $50 million for a future generation site is expected to be determined in the Georgia Power 2019 Base Rate Case. Nuclear outage costs are recorded and recovered or amortized over the outage cycles of each nuclear unit, which do not exceed 24 months . Approximately $30 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. The building lease is recorded and recovered or amortized through 2020. Fuel-hedging losses are recovered through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Integrated Resource Plan " herein for additional information on future generation costs. (j) At December 31, 2018, approximately $55 million was accrued and outstanding for refund pursuant to the Georgia Power Tax Reform Settlement Agreement and approximately $100 million was accrued for refund, subject to review and approval by the Georgia PSC, as a result of the 2018 retail ROE exceeding the allowed retail ROE range. See " Rate Plans " herein for additional information. (k) Comprised of Demand-Side Management (DSM) tariff over recovery and fuel-hedging gains. The amortization of DSM tariff over recovery of $3 million at December 31, 2018 is expected to be determined in the Georgia Power 2019 Base Rate Case. Fuel-hedging gains are refunded through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Rate Plans " herein for additional information on customer refunds and DSM tariffs. (l) Generally not earning a return as they are excluded from rate base or are offset in rate base by a corresponding asset or liability. Rate Pl

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies	CONTINGENCIES General Litigation Matters Each registrant is subject to certain claims and legal actions arising in the ordinary course of business. In addition, the business activities of Southern Company's subsidiaries are subject to extensive governmental regulation related to public health and the environment, such as laws and regulations governing air, water, land, and protection of other natural resources. Litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental laws and regulations has occurred throughout the U.S. This litigation has included claims for damages alleged to have been caused by CO 2 and other emissions, CCR, and alleged exposure to hazardous materials, and/or requests for injunctive relief in connection with such matters. The ultimate outcome of such pending or potential litigation against each registrant and any subsidiaries cannot be predicted at this time; however, for current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on such registrant's financial statements. Southern Company In January 2017, a putative securities class action complaint was filed against Southern Company, certain of its officers, and certain former Mississippi Power officers in the U.S. District Court for the Northern District of Georgia, Atlanta Division, by Monroe County Employees' Retirement System on behalf of all persons who purchased shares of Southern Company's common stock between April 25, 2012 and October 29, 2013. The complaint alleges that Southern Company, certain of its officers, and certain former Mississippi Power officers made materially false and misleading statements regarding the Kemper County energy facility in violation of certain provisions under the Securities Exchange Act of 1934, as amended. The complaint seeks, among other things, compensatory damages and litigation costs and attorneys' fees. In June 2017, the plaintiffs filed an amended complaint that provided additional detail about their claims, increased the purported class period by one day, and added certain other former Mississippi Power officers as defendants. In July 2017, the defendants filed a motion to dismiss the plaintiffs' amended complaint with prejudice, to which the plaintiffs filed an opposition in September 2017. On March 29, 2018, the U.S. District Court for the Northern District of Georgia, Atlanta Division, issued an order granting, in part, the defendants' motion to dismiss. The court dismissed certain claims against certain officers of Southern Company and Mississippi Power and dismissed the allegations related to a number of the statements that plaintiffs challenged as being false or misleading. On April 26, 2018, the defendants filed a motion for reconsideration of the court's order, seeking dismissal of the remaining claims in the lawsuit. On August 10, 2018, the court denied the motion for reconsideration and denied a motion to certify the issue for interlocutory appeal. In February 2017, Jean Vineyard filed a shareholder derivative lawsuit and, in May 2017, Judy Mesirov filed a shareholder derivative lawsuit, each in the U.S. District Court for the Northern District of Georgia. Each of these lawsuits names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. In August 2017, these two shareholder derivative lawsuits were consolidated in the U.S. District Court for the Northern District of Georgia. The complaints allege that the defendants caused Southern Company to make false or misleading statements regarding the Kemper County energy facility cost and schedule. Further, the complaints allege that the defendants were unjustly enriched and caused the waste of corporate assets and also allege that the individual defendants violated their fiduciary duties. Each plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and, on each plaintiff's own behalf, attorneys' fees and costs in bringing the lawsuit. Each plaintiff also seeks certain changes to Southern Company's corporate governance and internal processes. On April 25, 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the putative securities class action. In May 2017, Helen E. Piper Survivor's Trust filed a shareholder derivative lawsuit in the Superior Court of Gwinnett County, State of Georgia that names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. The complaint alleges that the individual defendants, among other things, breached their fiduciary duties in connection with schedule delays and cost overruns associated with the construction of the Kemper County energy facility. The complaint further alleges that the individual defendants authorized or failed to correct false and misleading statements regarding the Kemper County energy facility schedule and cost and failed to implement necessary internal controls to prevent harm to Southern Company. The plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and disgorgement of profits and, on its behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiff also seeks certain unspecified changes to Southern Company's corporate governance and internal processes. On May 4, 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the putative securities class action. Southern Company believes these legal challenges have no merit; however, an adverse outcome in any of these proceedings could have an impact on Southern Company's results of operations, financial condition, and liquidity. Southern Company will vigorously defend itself in these matters, the ultimate outcome of which cannot be determined at this time. Alabama Power On March 2, 2018, the Alabama Department of Environmental Management (ADEM) issued proposed administrative orders assessing a penalty of $1.25 million to Alabama Power for unpermitted discharge of fluids and/or pollutants to groundwater at five electric generating plants. The orders were finalized and Alabama Power paid the penalty on September 27, 2018. This matter is now concluded. 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 August 2017. On June 18, 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 entered an order staying this lawsuit for 60 days and ordered the parties to submit petitions to the Georgia PSC within 20 days 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. Georgia Power believes the plaintiffs' claims have no merit and will continue to vigorously defend itself in this matter. The amount of any possible losses cannot be calculated at this time because, among other factors, it is unknown whether 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. The ultimate outcome of this matter cannot be determined at this time. Mississippi Power In 2016, a complaint against Mississippi Power was filed in Harrison County Circuit Court (Circuit Court) by Biloxi Freezing & Processing Inc., Gulfside Casino Partnership, and John Carlton Dean, which was amended and refiled to include, among other things, Southern Company as a defendant. The individual plaintiff alleged that Mississippi Power and Southern Company violated the Mississippi Unfair Trade Practices Act. All plaintiffs alleged that Mississippi Power and Southern Company concealed, falsely represented, and failed to fully disclose important facts concerning the cost and schedule of the Kemper County energy facility and that these alleged breaches unjustly enriched Mississippi Power and Southern Company. The plaintiffs sought unspecified actual damages and punitive damages; asked the Circuit Court to appoint a receiver to oversee, operate, manage, and otherwise control all affairs relating to the Kemper County energy facility; asked the Circuit Court to revoke any licenses or certificates authorizing Mississippi Power or Southern Company to engage in any business related to the Kemper County energy facility in Mississippi; and sought attorney's fees, costs, and interest. The plaintiffs also sought an injunction to prevent any Kemper County energy facility costs from being charged to customers through electric rates. In June 2017, the Circuit Court ruled in favor of motions by Southern Company and Mississippi Power and dismissed the case. In July 2017, the plaintiffs filed notice of an appeal. On July 13, 2018, Mississippi Power and Southern Company reached a settlement agreement with the plaintiffs and the plaintiffs' appeal was dismissed with prejudice. The settlement had no material impact on Southern Company's or Mississippi Power's financial statements. On May 18, 2018, Southern Company and Mississippi Power received a notice of dispute and arbitration demand filed by Martin Product Sales, LLC (Martin) based on two agreements, both related to Kemper IGCC byproducts for which Mississippi Power provided termination notices in September 2017. Martin alleges breach of contract, breach of good faith and fair dealing, fraud and misrepresentation, and civil conspiracy and makes a claim for damages in the amount of approximately $143 million , as well as additional unspecified damages, attorney's fees, costs, and interest. In the first quarter 2019, Mississippi Power and Southern Company filed motions to dismiss. Southern Company and Mississippi Power believe this legal challenge has no merit; however, an adverse outcome in this proceeding could have a material impact on Southern Company's and Mississippi Power's results of operations, financial condition, and liquidity. Southern Company and Mississippi Power will vigorously defend themselves in this matter, the ultimate outcome of which cannot be determined at this time. On November 21, 2018, Ray C. Turnage and 10 other individual plaintiffs filed a putative class action complaint against Mississippi Power and the three current 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 in the refund process because it applied the wrong interest rate to the payments. 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. Mississippi Power believes this legal challenge has no merit; however, an adverse outcome in this proceeding could have a material impact on Mississippi Power's results of operations, financial condition, and liquidity. Mississippi Power will vigorously defend itself in this matter, the ultimate outcome of which cannot be determined at this time. Southern Power Southern Power indirectly owns a 51% membership interest in RE Roserock LLC (Roserock), the owner of the Roserock facility in Pecos County, Texas. Prior to the facility being placed in service in November 2016, certain solar panels were damaged during installation by the construction contractor, McCarthy Building Companies, Inc. (McCarthy), and certain solar panels were damaged by a hail event that also occurred during construction. In connection therewith, Southern Power is withholding payments of approximately $26 million from the construction contractor, which has placed a lien on the Roserock facility for the same amount. In May 2017, Roserock filed a lawsuit in the state district court in Pecos County, Texas, (State Court lawsuit) against XL Insurance America, Inc. (XL) and North American Elite Insurance Company (North American Elite) seeking recovery from an insurance policy for damages resulting from the hail storm and McCarthy's installation practices. On June 1, 2018, the court in the State Court lawsuit granted Roserock's motion for partial summary judgment, finding that the insurers were in breach of contract and in violation of the Texas Insurance Code for failing to pay any monies owed for the hail claim. In addition to the State Court lawsuit, lawsuits were filed between Roserock and McCarthy, as well as other parties, and that litigation has been consolidated in the U.S. District Court for the Western District of Texas. Southern Power intends to vigorously pursue and defend these matters, the ultimate outcome of which cannot be determined at this time. Southern Company Gas Nicor Energy Services Company, doing business as Pivotal Home Solutions, formerly a wholly-owned subsidiary of Southern Company Gas, was a defendant in a putative class action initially filed in 2017 in the state court in Indiana. The plaintiffs purported to represent a class of the customers who purchased products from Nicor Energy Services Company and alleged that the marketing, sale, and billing of the products violated the Indiana Consumer Fraud and Deceptive Business Practices Act, constituting common law fraud and resulting in unjust enrichment of these entities. In 2018, Nicor Energy Services Company was named in a second class action filed in the state court of Ohio asserting nearly identical allegations and legal claims. The plaintiffs sought, on behalf of the classes they purported to represent, actual and punitive damages, interest costs, attorney fees, and injunctive relief. To facilitate the sale of Pivotal Home Solutions, Southern Company Gas retained most of the financial responsibility for these lawsuits following the completion of the sale. On June 12, 2018, the parties settled these claims and Southern Company Gas recorded an $11 million charge, which is included in other operations and maintenance expenses for the year ended December 31, 2018 . Southern Company Gas is involved in litigation relating to an incident that occurred in one of its prior service territories that resulted in several deaths, injuries, and property damage. Southern Company Gas has resolved all claims for personal injuries or death, but it is continuing to defend litigation seeking to recover alleged property damages. Southern Company Gas has insurance that provides full coverage of the expected financial exposure in excess of $11 million per incident. During the successor period ended December 31, 2016, Southern Company Gas recorded reserves for substantially all of its potential exposure from these cases. 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, 2018 and 2017 , 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. In 2013, the Georgia PSC approved the 2013 ARP including the recovery of approximately $2 million annually through the ECCR tariff. 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 as part of the Georgia Power 2019 Base Rate Case and further adjusted in future regulatory proceedings. 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, 2018 and 2017 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 recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies of the natural gas distribution utilities, with the exception of one site representing $2 million of the accrued remediation costs. At December 31, 2018 and 2017 , 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, 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 December 31, 2017: Environmental remediation liability: Other current liabilities $ 73 $ 22 $ 46 Accrued environmental remediation (*) 389 — 342 Under recovered environmental remediation costs: Other regulatory assets, current $ 38 $ 2 $ 31 Other regulatory assets, deferred 473 47 379 (*) At December 31, 2017, $85 million of Southern Company Gas' total environmental remediation liability related to Elizabethtown Gas, which was sold on July 1, 2018. See Note 15 under " Southern Company Gas " for more information regarding Southern Company Gas' sale of Elizabethtown Gas. The ultimate outcome of these matters cannot be determined at this time; however, as a result of the regulatory treatment for environmental remediation expenses described above, the final disposition of these matters is not expected to have a material impact on the financial statements of Southern Company, Georgia Power, or Southern Company Gas. 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. In October 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, 2018 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 back for the benefit of customers in accordance with direction from their respective PSC and, 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 $14.1 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 September 10, 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, 2018 under the NEIL policies would be $56 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, however, 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 Mississippi Power In 2013, Mississippi Power submitted a lost revenue claim under the Deep Horizon Economic and Property Damages Settlement Agreement associated with the oil spill that occurred in the Gulf of Mexico in 2010. On May 14, 2018, Mississippi Power's claim was settled. The settlement proceeds of $18 million , net of expenses and income tax, are included in Mississippi Power's earnings for 2018. As of December 31, 2018, Mississippi Power had received half of the settlement proceeds. Southern Company Gas A wholly-owned subsidiary of Southern Company Gas owns and operates a natural gas storage facility consisting of two salt dome caverns in Louisiana. Periodic integrity tests are required in accordance with rules of the Louisiana Department of Natural Resources (DNR). In August 2017, in connection with an ongoing integrity project, updated seismic mapping indicated the proximity of one of the caverns to the edge of the salt dome may be less than the required minimum and could result in Southern Company Gas retiring the cavern early. At December 31, 2018 , the facility's property, plant, and equipment had a net book value of $109 million , of which the cavern itself represents approximately 20% . A potential early retirement of this cavern is dependent upon several factors including compliance with an order from the Louisiana DNR detailing the requirements to place the cavern back in service, which includes, among other things, obtaining core samples to determine the composition of the sheath surrounding the edge of the salt dome. The cavern continues to maintain its pressures and overall structural integrity. These events were considered in connection with Southern Company Gas' annual long-lived asset impairment analysis, which determined there was no impairment as of December 31, 2018 . Any changes in results of monitoring activities, rates at which expiring capacity contracts are re-contracted, timing of placing the cavern back in service, or Louisiana DNR requirements could trigger impairment. Further, early retirement of the cavern could trigger impairment of other long-lived assets associated with the natural gas storage facility. The ultimate outcome of this matter cannot be determined at this time, but could have a significant impact on Southern Company's or Southern Company Gas' financial statements.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	REVENUE FROM CONTRACTS WITH CUSTOMERS The registrants generate revenues from a variety of sources, some of which are excluded from the scope of ASC 606, such as leases, derivatives, and certain cost recovery mechanisms. See Note 1 under " Recently Adopted Accounting Standards – Revenue " for additional information on the adoption of ASC 606 for revenue from contracts with customers and under "Revenues" for additional information on the revenue policies of the registrants. The following tables disaggregate revenue sources for the year ended December 31, 2018 : 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 6,608 Commercial 5,266 Industrial 3,224 Other 124 Natural gas distribution revenues 3,175 Alternative revenue programs (b) (20 ) Total retail electric and gas distribution revenues $ 18,377 Wholesale energy revenues (c)(d) 1,896 Wholesale capacity revenues (d) 620 Other natural gas revenues (e) 699 Other revenues (f) 1,903 Total operating revenues $ 23,495 (a) Retail electric revenues include $75 million of leases and a net increase of $60 million from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 2 for additional information on cost recovery mechanisms. (b) See Note 1 under " Revenues " for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (c) Wholesale energy revenues include $299 million of revenues accounted for as derivatives, primarily related to short-term physical energy sales in the wholesale electricity market. See Note 1 under " Revenues – Southern Power " and Note 14 for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $384 million and $121 million , respectively, of PPA contracts accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $7.0 billion of which $3.9 billion relates to contracts that are accounted for as derivatives. See Note 16 under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other revenues include $322 million of revenues not accounted for under ASC 606. 2018 Alabama Power Georgia Power Mississippi Power (in millions) Operating revenues Retail revenues (a)(b) Residential $ 2,335 $ 3,301 $ 273 Commercial 1,578 3,023 286 Industrial 1,428 1,344 321 Other 26 84 9 Total retail electric revenues $ 5,367 $ 7,752 $ 889 Wholesale energy revenues (c) 297 133 348 Wholesale capacity revenues 101 54 6 Other revenues (b)(d) 267 481 22 Total operating revenues $ 6,032 $ 8,420 $ 1,265 (a) Retail revenues at Alabama Power, Georgia Power, and Mississippi Power include a net increase or (net reduction) of $152 million , $(19) million , and $(13) million , respectively, related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 2 for additional information on cost recovery mechanisms. (b) Retail revenues and other revenues at Georgia Power include $74 million and $135 million , respectively, of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, and Mississippi Power include $20 million , $29 million , and $4 million , respectively, accounted for as derivatives primarily related to short-term physical energy sales in the wholesale electricity market. See Note 14 for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power and Georgia Power include $57 million and $109 million , respectively, of revenues not accounted for under ASC 606. 2018 (in millions) Southern Power PPA capacity revenues (a) $ 580 PPA energy revenues (a) 1,140 Non-PPA revenues (b) 472 Other revenues 13 Total operating revenues $ 2,205 (a) PPA capacity revenues and PPA energy revenues include $186 million and $413 million , respectively, related to PPAs accounted for as leases. See Note 1 under " Revenues – Southern Power " for additional information on capacity revenues accounted for as leases. (b) Non-PPA revenues include $242 million of revenues from short-term sales related to physical energy sales in the wholesale electricity market accounted for as derivatives. See Note 1 under " Revenues – Southern Power " and Note 14 for additional information on energy-related derivative contracts. 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 1,525 Commercial 436 Transportation 944 Industrial 40 Other 230 Alternative revenue programs (a) (20 ) Total natural gas distribution revenues $ 3,155 Gas pipeline investments 32 Wholesale gas services (b) 101 Gas marketing services (c) 568 Other revenues 53 Total operating revenues $ 3,909 (a) See Note 1 under " Revenues – Southern Company Gas " for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $7.0 billion of which $3.9 billion relates to contracts that are accounted for as derivatives. See Note 16 under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues and Note 14 for additional information on energy-related derivative contracts. (c) Gas marketing services includes $3 million of revenues not accounted for under ASC 606. 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, 2018 : Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,630 $ 102 $ 32 Alabama Power 520 — 12 Georgia Power 721 58 7 Mississippi Power 100 — — Southern Power 118 — 11 Southern Company Gas 952 — 2 As of December 31, 2018 , Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Georgia Power had contract assets primarily related to fixed retail customer bill programs where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term and to unregulated service agreements where payment is contingent upon project completion. Georgia Power also had contract liabilities for outstanding performance obligations primarily related to unregulated service agreements. Southern Power's contract liabilities relate to collections recognized in advance of revenue for certain levelized PPAs with Georgia Power. Southern Company's unregulated distributed generation business had $39 million and $11 million of contract assets and contract liabilities, respectively, at December 31, 2018 remaining for outstanding performance obligations. Remaining Performance Obligations The traditional electric operating companies and Southern Power have long-term contracts with customers in which revenues are recognized as performance obligations are satisfied over the contract term. These contracts primarily relate to PPAs whereby the traditional electric operating companies and Southern Power provide electricity and generation capacity to a customer. The revenue recognized for the delivery of electricity is variable; however, certain PPAs include a fixed payment for fixed generation capacity over the term of the contract. Southern Company's unregulated distributed generation business also has partially satisfied performance obligations related to certain fixed price contracts. Revenues from contracts with customers related to these performance obligations remaining at December 31, 2018 are expected to be recognized as follows: 2019 2020 2021 2022 2023 2024 and (in millions) Southern Company (*) $ 487 $ 341 $ 315 $ 315 $ 306 $ 2,103 Alabama Power 23 22 26 23 22 140 Georgia Power 41 38 40 30 31 82 Mississippi Power 3 3 1 — — — Southern Power 323 295 270 281 275 2,028 (*) Excludes amounts related to held for sale assets. See Note 15 under " Southern Company's Sale of Gulf Power " for additional information.

Property, Plant, and Equipment

Property, Plant, and Equipment (Notes)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 : 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 At December 31, 2017: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 51,279 $ 14,213 $ 17,038 $ 2,801 $ 13,737 $ — Transmission 11,562 4,119 5,947 737 — — Distribution 19,239 7,034 9,978 946 — — General/other 4,402 1,960 1,898 289 18 — Electric utilities' plant in service 86,482 27,326 34,861 4,773 13,755 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 13,079 — — — — 13,079 Storage facilities 1,599 — — — — 1,599 Other 1,155 — — — — 1,155 Southern Company Gas plant in service 15,833 — — — — 15,833 Other plant in service 1,227 — — — — — Total plant in service $ 103,542 $ 27,326 $ 34,861 $ 4,773 $ 13,755 $ 15,833 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 recorded as depreciable property, plant, and equipment, while the recoverable or retained portion is recorded as non-depreciable property, plant, and equipment. Capital Leases Assets acquired under a capital lease are included in property, plant, and equipment and are further detailed in the table below for the applicable registrants: Southern Company Georgia Power (in millions) At December 31, 2018: Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 43 — Gas pipeline 7 — Less: Accumulated amortization (75 ) (84 ) Balance, net of amortization $ 191 $ 121 At December 31, 2017: Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 51 — Gas pipeline 6 — Less: Accumulated amortization (72 ) (68 ) Balance, net of amortization $ 201 $ 137 (*) Represents Georgia Power's affiliate PPAs with Southern Power. See Note 1 under " Affiliate Transactions " and Note 9 under " Fuel and Power Purchase Agreements – Affiliate " for additional information. See Note 8 under " Long-term Debt – Capital Leases " for additional information. 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 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 (percent) Alabama Power 3.0 % 2.9 % 3.0 % Georgia Power 2.6 % 2.7 % 2.8 % Mississippi Power (*) 4.1 % 3.7 % 4.2 % Southern Company Gas 2.9 % 2.9 % 2.8 % (*) Mississippi Power's decrease in 2017 is primarily the result of recording a loss on its lignite mine in June 2017. 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. In 2016, Alabama Power submitted an updated depreciation study to the FERC and received authorization to use the recommended rates beginning January 2017. The study was also provided to the Alabama PSC. Under the terms of the 2013 ARP, Georgia Power amortized approximately $14 million annually from 2014 through 2016 of its remaining regulatory liability related to other cost of removal obligations. Southern Company's 2017 depreciation includes $34 million of reductions in depreciation recognized by Gulf Power under the terms of its 2013 rate case settlement agreement with the Florida PSC. 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, 2018 and 2017 , accumulated depreciation for utility plant in service totaled $30.3 billion and $30.8 billion , respectively, for Southern Company and $4.3 billion and $4.5 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, 2018 and 2017 , accumulated depreciation for other plant in service totaled $766 million and $673 million , respectively, for Southern Company and $129 million and $75 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 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, 2018 , 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) $ 274 $ 71 $ 1 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,056 619 138 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,569 $ 615 $ 54 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,804 2,150 84 Plant Scherer (coal) Units 1 and 2 8.4 (c) 266 96 14 Plant Scherer (coal) Unit 3 75.0 (c) 1,238 493 66 Plant Wansley (coal) 53.5 (c) 1,179 362 160 Rocky Mountain (pumped storage) 25.4 (d) 184 135 — Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 180 $ 93 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 723 201 7 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 270 $ 6 $ — (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. (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 also entered into an agreement to lease its 50% undivided ownership in the Dalton Pipeline that became effective when it was placed in service in August 2017. Under the lease, Southern Company Gas will receive approximately $26 million annually for an initial term of 25 years . 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 $4.5 billion at December 31, 2018 . See Note 2 under " Georgia Power – Nuclear Construction " for additional information. On December 4, 2018, Southern Power completed the sale of its 65% ownership interest in Plant Stanton Unit A, which Southern Power previously jointly-owned with OUC, the FMPA, and the KUA, to NextEra Energy. See Note 15 under " Southern Power – Sales of Natural Gas Plants " for additional information. In conjunction with Southern Company's sale of Gulf Power, Mississippi Power and Gulf Power have 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 the FERC and the Mississippi PSC, and cannot now be determined. See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power. 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 On October 2, 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 net book value of approximately $101 million at December 31, 2018 , 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. Under the terms of the PPA and the expansion PPA for Southern Power's Plant Mankato, which was acquired in 2016, approximately $563 million of assets, primarily related to property, plant, and equipment, are subject to lien at December 31, 2018 . See Note 15 under " Southern Power – Sales of Natural Gas Plants " for additional information regarding the proposed sale of Plant Mankato. See Note 3 under " General Litigation Matters – Southern Power " for information regarding liens on Southern Power's Roserock facility. 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, 2018
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, 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 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, 2016 $ 4,514 $ 1,533 $ 2,532 $ 179 $ 64 Liabilities incurred 16 — 4 — 6 Liabilities settled (177 ) (26 ) (120 ) (23 ) — Accretion 179 77 89 5 4 Cash flow revisions 292 125 133 13 4 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 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. As the level of work becomes more defined in the next 12 months, it is likely that these cost estimates will change and the change could be material. 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. 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. 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's Sale of Gulf Power " and " Assets Held for Sale " for additional information. In 2017 , Alabama Power's and Georgia Power's cash flow revisions were primarily related to changes in closure strategy for ash ponds and landfills. Georgia Power's cash flow revisions in 2017 also related to changes in closure strategy for gypsum cells. Mississippi Power's cash flow revisions in 2017 primarily related to a revision in the closure date of its lignite mine. The liabilities settled in 2017 for Alabama Power, Georgia Power, and Mississippi Power were primarily related to ash pond closure activity. The cost estimates for AROs related to the CCR Rule are based on information at December 31, 2018 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 requirements for closure. The traditional electric operating companies expect to continue to periodically update their ARO cost estimates, which could increase further, as additional information becomes available. 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, 2018 and 2017 , approximately $27 million and $76 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 $28 million and $77 million at December 31, 2018 and 2017 , 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, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2017: Equity securities $ 1,059 $ 644 $ 415 Debt securities 725 223 502 Other securities 47 35 12 Total investment securities in the Funds $ 1,831 $ 902 $ 929 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 reinvested interest and dividends and excluding the Funds' expenses, for 2018 , 2017 , and 2016 are shown in the table below. The fair value increases (decreases) included unrealized gains (losses) on securities held in the Funds at each of December 31, 2018 , 2017 , and 2016 , which are also shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2018 $ (67 ) $ (38 ) $ (29 ) 2017 233 125 108 2016 114 76 38 Unrealized gains (losses) At December 31, 2018 $ (183 ) $ (96 ) $ (87 ) At December 31, 2017 181 98 83 At December 31, 2016 48 34 14 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 $17 million and $18 million at December 31, 2018 and 2017 , 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, 2018 and 2017 , the accumulated provisions for the external decommissioning trust funds were as follows: 2018 2017 (in millions) Alabama Power Plant Farley $ 846 $ 902 Georgia Power Plant Hatch $ 547 $ 583 Plant Vogtle Units 1 and 2 326 346 Total $ 873 $ 929 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, 2018 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 2012. Significant assumptions used to determine these costs for ratemaking were an estimated inflation rate of 4.5% and 2.4% for Alabama Power and Georgia Power, respectively, and an estimated trust earnings rate of 7.0% and 4.4% 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, the Georgia PSC approved Georgia Power's annual decommissioning cost for ratemaking of $4 million and $2 million for Plant Hatch and Plant Vogtle Units 1 and 2, respectively. Georgia Power expects the Georgia PSC to review and adjust, if necessary, the amounts collected in rates for nuclear decommissioning costs in the Georgia Power 2019 Base Rate Case.

Consolidated Entities and Equit

Consolidated Entities and Equity Method Investments	12 Months Ended
	Dec. 31, 2018
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. SEGCO uses natural gas as the primary fuel source for 1,000 MWs of its generating capacity. 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 $102 million in 2018 , $76 million in 2017 , and $55 million in 2016 for Alabama Power and $105 million in 2018 , $78 million in 2017 , and $57 million in 2016 for Georgia Power. SEGCO paid $18 million of dividends in 2018 and $24 million in each of 2017 and 2016 , 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 9 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 wholly-owned 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 On May 22, 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. Southern Power previously consolidated SP Solar and will continue to do so as the primary beneficiary of the VIE since it controls the most significant activities of the partnership, including operating and maintaining its assets. At December 31, 2018, SP Solar had total assets of $6.3 billion , total liabilities of $113 million , and noncontrolling interests of $1.2 billion . Cash distributions from SP Solar are allocated 67% to Southern Power and 33% to Global Atlantic in accordance with their partnership interest percentage. Under the terms of the limited partnership agreement, distributions without limited partner consent are limited to available cash and SP Solar is obligated to distribute all such available cash to its partners each quarter. Available cash includes all cash generated in the quarter subject to the maintenance of appropriate operating reserves. Transfers and sales of the assets in the VIE are subject to limited partner consent and the liabilities do not have recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. SP Wind On December 11, 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. Southern Power previously consolidated SP Wind and will continue to do so as the primary beneficiary of the VIE since it controls the most significant activities of the entity, including operating and maintaining its assets. At December 31, 2018, SP Wind had total assets of $2.5 billion , total liabilities of $51 million , and noncontrolling interests of $47 million . 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. Transfers and sales of the assets in the VIE are subject to Class A member consent and the liabilities do not have recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. Redeemable Noncontrolling Interests In April 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 October 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, 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 years ended December 31, 2017 and 2016 : 2017 2016 (in millions) Beginning balance $ 164 $ 43 Net income attributable to redeemable noncontrolling interests 2 4 Distributions to redeemable noncontrolling interests (2 ) (1 ) Capital contributions from redeemable noncontrolling interests 2 118 Redemption of redeemable noncontrolling interests (59 ) — Reclassification to non-redeemable noncontrolling interests (114 ) — Change in fair value of redeemable noncontrolling interests 7 — Ending balance $ — $ 164 The following table presents the attribution of net income to Southern Power and the noncontrolling interests for the years ended December 31, 2017 and 2016 : 2017 2016 (in millions) Net income $ 1,117 $ 374 Less: Net income attributable to noncontrolling interests 44 32 Less: Net income attributable to redeemable noncontrolling interests 2 4 Net income attributable to Southern Power $ 1,071 $ 338 Southern Company Gas SouthStar, previously a joint venture owned 85% by Southern Company Gas and 15% by Piedmont, was the only VIE for which Southern Company Gas was the primary beneficiary, prior to October 2016 when Southern Company Gas completed its purchase of Piedmont's remaining interest in SouthStar. In 2015, Georgia Natural Gas Company (GNG), a 100% -owned, direct subsidiary of Southern Company Gas, notified Piedmont of its election, pursuant to a change in control of SouthStar, to purchase Piedmont's 15% interest in SouthStar at fair market value. This purchase was contingent upon the closing of the merger between Piedmont and Duke Energy Corporation (Duke Energy). In October 2016, after Piedmont and Duke Energy completed their merger, GNG completed its purchase of Piedmont's interest in SouthStar and paid a purchase price of $160 million and $15 million for Piedmont's share of SouthStar's 2016 earnings through the date of acquisition. Southern Company Gas' cash flows used for financing activities included SouthStar's distribution to Piedmont for its portion of SouthStar's annual earnings from the previous year. For the successor period of July 1, 2016 through December 31, 2016 , SouthStar made a distribution of $15 million upon completion of the purchase of Piedmont's interest in SouthStar. For the predecessor period of January 1, 2016 through June 30, 2016 , SouthStar distributed $19 million to Piedmont. Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments at December 31, 2018 and 2017 and related income from those investments for the successor years ended December 31, 2018 and 2017 , the successor period of July 1, 2016 through December 31, 2016 , and the predecessor period of January 1, 2016 through June 30, 2016 were as follows: Investment Balance December 31, 2018 December 31, 2017 (in millions) SNG $ 1,261 $ 1,262 PennEast Pipeline 71 57 Atlantic Coast Pipeline 83 41 Other 123 117 Total $ 1,538 $ 1,477 Successor Predecessor Earnings from Equity Method Investments Year ended December 31, 2018 Year ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) SNG $ 131 $ 88 $ 56 $ — PennEast Pipeline 5 6 — — Atlantic Coast Pipeline 7 6 1 — Other 5 6 3 2 Total $ 148 $ 106 $ 60 $ 2 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. See Note 15 under " Southern Company Gas – Investment in SNG " for additional information. Selected financial information of SNG at December 31, 2018 and 2017 and for the years ended December 31, 2018 and 2017 and for the period September 1, 2016 through December 31, 2016 is as follows: At December 31, Balance Sheet Information 2018 2017 (in millions) Current assets $ 104 $ 82 Property, plant, and equipment 2,606 2,439 Deferred charges and other assets 121 121 Total Assets $ 2,831 $ 2,642 Current liabilities $ 103 $ 110 Long-term debt 1,103 1,102 Other deferred charges and other liabilities 212 76 Total Liabilities $ 1,418 $ 1,288 Total Stockholders' Equity $ 1,413 $ 1,354 Total Liabilities and Stockholders' Equity $ 2,831 $ 2,642 Income Statement Information Year ended December 31, 2018 Year ended December 31, 2017 September 1, 2016 (in millions) Revenues $ 604 $ 544 $ 230 Operating income 310 242 137 Net income 261 175 115 Other Investments Pipelines 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 a 118 -mile natural gas pipeline between New Jersey and Pennsylvania. The 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. Also in 2014, Southern Company Gas entered into a project in which it holds a 5% ownership interest in the Atlantic Coast Pipeline, an interstate pipeline company formed to develop and operate a 594 -mile natural gas pipeline in North Carolina, Virginia, and West Virginia with initial transportation capacity of 1.5 Bcf per day. See Note 2 under "FERC Matters – Southern Company Gas" for additional information on these pipeline projects. Pivotal JAX LNG, LLC Southern Company Gas owns a 50% interest 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.

Financing

Financing	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
FINANCING	FINANCING Securities Due Within One Year A summary of long-term securities due within one year at each of December 31, 2018 and 2017 is as follows: December 31, 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Senior notes $ 2,950 $ 200 $ 500 $ — $ 600 $ 300 Revenue bonds (a) 173 — 108 40 — — First mortgage bonds 50 — — — — 50 Capitalized leases 24 1 13 — — — Other (b) 1 — (4 ) — (1 ) 7 Total $ 3,198 $ 201 $ 617 $ 40 $ 599 $ 357 (a) For Southern Company and Mississippi Power, includes $40 million in pollution control revenue bonds classified as short term since they are variable rate demand obligations supported by short-term credit facilities; however, the final maturity dates range from 2020 to 2028. (b) Represents unamortized debt related amounts, acquisition accounting fair value adjustments, and/or fair value hedges. See Note 14 for additional information regarding fair value hedges. December 31, 2017 Southern Company Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Senior notes $ 2,354 $ 750 $ — $ 350 $ 155 Long-term bank term loans 1,420 100 900 420 — Revenue bonds (a) 90 — 90 — — Capitalized leases 31 11 — — — Other (b) (3 ) (4 ) (1 ) — 2 Total $ 3,892 $ 857 $ 989 $ 770 $ 157 (a) For Southern Company and Mississippi Power, includes $50 million in revenue bonds classified as short term at December 31, 2017 that were remarketed in an index rate mode subsequent to December 31, 2017. Also for Southern Company and Mississippi Power, includes $40 million in pollution control revenue bonds classified as short term since they are variable rate demand obligations supported by short-term credit facilities; however, the final maturity dates range from 2020 to 2028. (b) Represents unamortized debt related amounts, acquisition accounting fair value adjustments, and fair value hedges. See Note 14 for additional information regarding fair value hedges. Maturities of long-term debt for the next five years are as follows: Southern Company (a) Alabama Power Georgia Power (a) Mississippi Power Southern Power (b) Southern Company Gas (in millions) 2019 $ 3,156 $ 200 $ 621 $ — $ 600 $ 350 2020 4,041 250 1,006 307 825 — 2021 3,186 310 375 270 300 330 2022 1,974 750 505 — 677 46 2023 2,388 300 153 — 290 400 (a) Amounts include principal amortization related to the FFB borrowings beginning in 2020; however, the final maturity date is February 20, 2044. See " Long-term Debt – 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. Long-term Debt Senior Notes Total senior notes (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern (a) Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (b) (in millions) December 31, 2018 $ 32,725 $ 6,875 $ 5,600 $ 1,200 $ 5,050 $ 4,000 December 31, 2017 35,148 6,375 7,100 755 5,459 4,157 (a) Includes $10.0 billion and $10.2 billion of senior notes at the Southern Company parent entity at December 31, 2018 and 2017 , respectively. (b) Represents senior notes issued by Southern Company Gas Capital, which are fully and unconditionally guaranteed by Southern Company Gas. See " Structural Considerations " herein for additional information. See Note 14 for information regarding fair value hedges of existing senior notes. Except as otherwise described herein, Southern Company and its subsidiaries used the proceeds of 2018 senior note issuances for long-term debt redemptions and maturities, to repay short-term indebtedness, and for general corporate purposes, including working capital. The subsidiaries also used the proceeds for their construction programs. In August 2018, Southern Company issued $750 million aggregate principal amount of Series 2018A Floating Rate Senior Notes due February 14, 2020 bearing interest based on three -month LIBOR. Subsequent to December 31, 2018, through cash tender offers, Southern Company repurchased and retired approximately $522 million of the $1.0 billion aggregate principal amount outstanding of its 1.85% Senior Notes due July 1, 2019 ( 1.85% Notes), approximately $180 million of the $350 million aggregate principal amount outstanding of its Series 2014B 2.15% Senior Notes due September 1, 2019 (Series 2014B Notes), and approximately $504 million of the $750 million aggregate principal amount outstanding of its Series 2018A Floating Rate Notes due February 14, 2020 (Series 2018A Notes), for an aggregate purchase price, excluding accrued and unpaid interest, of approximately $1.2 billion . In addition, subsequent to December 31, 2018, and following the completion of the cash tender offers, Southern Company completed the redemption of all of the Series 2018A Notes remaining outstanding and called for redemption all of the 1.85% Notes and Series 2014B Notes remaining outstanding. In June 2018, Alabama Power issued $500 million aggregate principal amount of Series 2018A 4.30% Senior Notes due July 15, 2048. In April 2018, Georgia Power redeemed all $250 million aggregate principal amount of its Series 2008B 5.40% Senior Notes due June 1, 2018. In May 2018, through cash tender offers, Georgia Power repurchased and retired $89 million of the $250 million aggregate principal amount outstanding of its Series 2007A 5.65% Senior Notes due March 1, 2037, $326 million of the $500 million aggregate principal amount outstanding of its Series 2009A 5.95% Senior Notes due February 1, 2039, and $335 million of the $600 million aggregate principal amount outstanding of its Series 2010B 5.40% Senior Notes due June 1, 2040, for an aggregate purchase price, excluding accrued and unpaid interest, of $902 million . In March 2018, Mississippi Power issued $300 million aggregate principal amount of Series 2018A Floating Rate Senior Notes due March 27, 2020 bearing interest based on three -month LIBOR and $300 million aggregate principal amount of Series 2018B 3.95% Senior Notes due March 30, 2028. In October 2018, Mississippi Power completed the redemption of all $30 million aggregate principal amount outstanding of its Series G 5.40% Senior Notes due July 1, 2035 and all $125 million aggregate principal amount outstanding of its Series 2009A 5.55% Senior Notes due March 1, 2019. Junior Subordinated Notes Total junior subordinated notes outstanding for Southern Company and Georgia Power at December 31, 2018 and 2017 were as follows: Southern (*) Georgia Power (in millions) December 31, 2018 $ 3,570 $ 270 December 31, 2017 3,570 270 (*) Includes $3.3 billion of junior subordinated notes at the Southern Company parent entity at both December 31, 2018 and 2017 . Pollution Control Revenue Bonds Pollution control revenue bond obligations represent loans to the traditional electric operating companies from public authorities of funds derived from sales by such authorities of revenue bonds issued to finance pollution control and solid waste disposal facilities. In some cases, the pollution control revenue bond obligations represent obligations under installment sales agreements with respect to facilities constructed with the proceeds of revenue bonds issued by public authorities. The traditional electric operating companies are required to make payments sufficient for the authorities to meet principal and interest requirements of such bonds. Proceeds from certain issuances are restricted until qualifying expenditures are incurred. Total tax-exempt pollution control revenue bond obligations (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Mississippi Power (in millions) December 31, 2018 $ 2,585 $ 1,060 $ 1,460 $ 40 December 31, 2017 3,297 1,060 1,821 83 In October 2018, Alabama Power purchased and held $120 million aggregate principal amount of The Industrial Development Board of the City of Mobile, Alabama Pollution Control Revenue Bonds (Alabama Power Company Plant Barry Project), Series 2008. Alabama Power reoffered these bonds to the public in November 2018. During 2018, Georgia Power purchased and held the following pollution control revenue bonds, which may be reoffered to the public at a later date: • approximately $105 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2013 • $173 million aggregate principal amount of Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 2009 • $55 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994 • $65 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 2008 • approximately $72 million aggregate principal amount of Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 2013 In December 2018, the Development Authority of Burke County (Georgia) issued approximately $108 million aggregate principal amount of Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2018 due November 1, 2052 for the benefit of Georgia Power. The proceeds were used to redeem, in January 2019, approximately $13 million , $20 million , and $75 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 1992, Eighth Series 1994, and Second Series 1995, respectively. In July 2018, Mississippi Power purchased and held approximately $43 million aggregate principal amount of Mississippi Business Finance Corporation Pollution Control Revenue Refunding Bonds, Series 2002. Mississippi Power may reoffer these bonds to the public at a later date. Bank Term Loans Total long-term bank term loans (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) December 31, 2018 $ 145 $ 45 $ — $ — $ — December 31, 2017 1,465 45 100 900 420 See " Notes Payable " herein for additional information regarding bank term loans. In January 2018, Georgia Power repaid its outstanding $100 million floating rate bank loan due October 26, 2018. In March 2018, Mississippi Power repaid at maturity a $900 million unsecured term loan. In May 2018, Southern Power repaid $420 million aggregate principal amount of long-term floating rate bank loans. In November 2018, SEGCO, as borrower, and Alabama Power, as guarantor, entered into a $100 million long-term delayed draw floating rate bank term loan bearing interest based on three-month LIBOR, which SEGCO used to repay at maturity $100 million aggregate principal amount of Series 2013A Senior Notes. See Note 9 under " Guarantees " for additional information. 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 the Loan Guarantee Agreement in 2014, under which the DOE agreed to guarantee the obligations of Georgia Power under a note purchase agreement (FFB Note Purchase Agreement) among the DOE, Georgia Power, and the FFB and a related promissory note (FFB Promissory Note). The FFB Note Purchase Agreement and the FFB Promissory Note provide for a multi-advance term loan facility (FFB Credit Facility), under which Georgia Power may make term loan borrowings through the FFB. In July 2017, Georgia Power entered into an amendment to the Loan Guarantee Agreement (LGA Amendment) in connection with the DOE's consent to Georgia Power's entry into the Vogtle Services Agreement and the related intellectual property licenses (IP Licenses). Under the terms of the Loan Guarantee Agreement, upon termination of the Vogtle 3 and 4 Agreement, further advances are conditioned upon the DOE's approval of any agreements entered into in replacement of the Vogtle 3 and 4 Agreement. Under the terms of the LGA Amendment, Georgia Power will not request any advances unless and until certain conditions are satisfied, including (i) receipt of the DOE's approval of the Bechtel Agreement (together with the Vogtle Services Agreement and the IP Licenses, the Replacement EPC Arrangements) and (ii) Georgia Power's entry into a further amendment to the Loan Guarantee Agreement with the DOE to reflect the Replacement EPC Arrangements. Proceeds of advances made under the FFB Credit Facility are used to reimburse Georgia Power for Eligible Project Costs. Aggregate borrowings under the FFB Credit Facility may not exceed the lesser of (i) 70% of Eligible Project Costs or (ii) approximately $3.46 billion . In September 2017, the DOE issued a conditional commitment to Georgia Power for up to approximately $1.67 billion of additional guaranteed loans under the Loan Guarantee Agreement. This conditional commitment expires on March 31, 2019 , subject to any further extension approved by the DOE. Final approval and issuance of these additional loan guarantees by the DOE cannot be assured and are subject to the negotiation of definitive agreements, completion of due diligence by the DOE, receipt of any necessary regulatory approvals, and satisfaction of other conditions. All borrowings under the FFB Credit Facility 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 the 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 under the FFB Credit Facility on a quarterly basis through 2020. The final maturity date for each advance under the FFB Credit Facility is February 20, 2044. Interest is payable quarterly and principal payments will begin on February 20, 2020. Borrowings under the FFB Credit Facility will bear interest at the applicable U.S. Treasury rate plus a spread equal to 0.375% . At both December 31, 2018 and 2017 , Georgia Power had $2.6 billion of borrowings outstanding under the FFB Credit Facility. Under the Loan Guarantee Agreement, Georgia Power is subject to customary borrower affirmative and negative covenants and events of default. In addition, Georgia Power is subject to project-related reporting requirements and other project-specific covenants and events of default. In the event certain mandatory prepayment events (including any decision not to continue construction of Plant Vogtle Units 3 and 4) occur, the FFB's commitment to make further advances under the FFB Credit Facility will terminate and Georgia Power will be required to prepay the outstanding principal amount of all borrowings under the FFB Credit Facility over a period of five years (with level principal amortization). Among other things, these mandatory prepayment events include (i) the termination of the Vogtle Services Agreement or rejection of the Vogtle Services Agreement in bankruptcy if Georgia Power does not maintain access to intellectual property rights under the IP Licenses; (ii) a decision by Georgia Power not to continue construction of Plant Vogtle Units 3 and 4; (iii) cancellation of Plant Vogtle Units 3 and 4 by the Georgia PSC, or by Georgia Power if authorized by the Georgia PSC; and (iv) cost disallowances by the Georgia PSC that could have a material adverse effect on completion of Plant Vogtle Units 3 and 4 or Georgia Power's ability to repay the outstanding borrowings under the FFB Credit Facility. Under certain circumstances, insurance proceeds and any proceeds from an event of taking must be applied to immediately prepay outstanding borrowings under the FFB Credit Facility. In addition, if Georgia Power discontinues construction of Plant Vogtle Units 3 and 4, Georgia Power would be obligated to immediately repay a portion of the outstanding borrowings under the FFB Credit Facility to the extent such outstanding borrowings exceed 70% of Eligible Project Costs, net of the proceeds received by Georgia Power under the Guarantee Settlement Agreement. Georgia Power also may voluntarily prepay outstanding borrowings under the FFB Credit Facility. Under the FFB Credit Facility, any prepayment (whether mandatory or optional) will be made with a make-whole premium or discount, as applicable. In connection with any cancellation of Plant Vogtle Units 3 and 4 that results in a mandatory prepayment event, 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. Other Long-Term Debt Alabama Power 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 outstanding at December 31, 2018 and 2017 , 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. At December 31, 2018 and 2017 , trust preferred securities of $200 million were outstanding. See Note 1 under " Variable Interest Entities " for additional information on the accounting treatment for this trust and the related securities. Mississippi Power At December 31, 2018 and 2017 , 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, 2018 and 2017 , Mississippi Power 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. Southern Company Gas At December 31, 2018 and 2017 , Nicor Gas had $1.3 billion and $1.0 billion , respectively, of first mortgage bonds outstanding. These bonds have been issued with maturities ranging from 2019 to 2058. See " Secured Debt " herein for additional information. Prior to its sale, in the second quarter 2018, Pivotal Utility Holdings caused $200 million aggregate principal amount of gas facility revenue bonds to be redeemed. Nicor Gas issued $300 million aggregate principal amount of first mortgage bonds in a private placement, of which $100 million was issued in August 2018 and $200 million was issued in November 2018. At both December 31, 2018 and 2017 , Atlanta Gas Light had $159 million of medium-term notes outstanding. Capital Leases Assets acquired under capital leases are recorded in the balance sheets as property, plant, and equipment and the related obligations are classified as long-term debt. See Note 5 under " Capital Leases " for additional information. Southern Company At December 31, 2018 and 2017 , SCS had capital lease obligations of approximately $178 million and $177 million , respectively, for an office building and certain computer equipment including desktops, laptops, servers, printers, and storage devices with annual interest rates that range from 1.6% to 4.7% . Georgia Power At December 31, 2018 and 2017 , Georgia Power had a capital lease obligation for its corporate headquarters building of $15 million and $22 million , respectively, with an annual interest rate of 7.9% . For ratemaking purposes, the Georgia PSC has allowed the lease payments in cost of service with no return on the capital lease asset. The difference between the depreciation and the lease payments allowed for ratemaking purposes is recovered as operating expenses as ordered by the Georgia PSC. The annual operating expense incurred for this capital lease was not material for any year presented. At December 31, 2018 and 2017 , Georgia Power had capital lease obligations related to two affiliate PPAs with Southern Power of $128 million and $132 million , respectively. The annual interest rates range from 11% to 12% for these two capital lease PPAs. For ratemaking purposes, the Georgia PSC has included the capital lease asset amortization in cost of service and the interest in Georgia Power's cost of debt. See Note 1 under " Affiliate Transactions " and Note 9 under " Fuel and Power Purchase Agreements – Affiliate " for additional information. 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, 2018 and 2017 for the applicable registrants was as follows: Georgia (a) Mississippi Power (b) Southern Company Gas (c) (in millions) December 31, 2018 $ 2,767 $ 270 $ 1,325 December 31, 2017 2,779 270 1,025 (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. These borrowings totaled $2.6 billion at both December 31, 2018 and 2017 . See " Long-term Debt – DOE Loan Guarantee Borrowings " herein for additional information. Also includes capital lease obligations of $142 million and $154 million at December 31, 2018 and 2017 , respectively. See " Long-term Debt – Capital Leases – Georgia Power " herein for additional information. (b) The revenue bonds assumed in conjunction with Mississippi Power's purchase of Plant Daniel Units 3 and 4 are secured by Plant Daniel Units 3 and 4 and certain related personal property. See " Long-term Debt – Other Long-Term Debt " herein for additional information. (c) Nicor Gas' first mortgage bonds are secured by substantially all of Nicor Gas' properties. See " Long-term Debt – Other Long-Term Debt – Southern Company Gas " herein for additional information. At December 31, 2018 and 2017 , Gulf Power had $41 million of secured debt related to a lien on its property at Plant Daniel in connection with the issuance of two series of its pollution control revenue bonds, which are included in liabilities held for sale on Southern Company's balance sheet at December 31, 2018. On January 1, 2019, Southern Company completed its sale of Gulf Power to NextEra Energy. See Note 15 under " Southern Company's Sale of Gulf Power " for additional information. 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. Bank Credit Arrangements At December 31, 2018 , committed credit arrangements with banks were as follows: Expires Executable Term Loans Expires Within One Year Company 2019 2020 2022 Total Unused (d) One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — $ — Alabama Power 33 500 800 1,333 1,333 — — — 33 Georgia Power — — 1,750 1,750 1,736 — — — — Mississippi Power 100 — — 100 100 — — — 100 Southern Power (b) — — 750 750 727 — — — — Southern Company Gas (c) — — 1,900 1,900 1,895 — — — — Other 30 — — 30 30 — — — 30 Southern Company Consolidated (e) $ 163 $ 500 $ 7,200 $ 7,863 $ 7,820 $ — $ — $ — $ 163 (a) Represents the Southern Company parent entity. (b) Southern Power's subsidiaries are not parties to its bank credit arrangement. (c) Southern Company Gas provides a parent guarantee of the obligations of its subsidiary Southern Company Gas Capital, which is the borrower of $1.4 billion ( $1.395 billion unused) of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 million (all unused) 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. (d) Amounts used are for letters of credit. (e) Excludes $280 million of committed credit arrangements of Gulf Power, which was sold on January 1, 2019. See Note 15 under " Southern Company's Sale of Gulf Power " for additional information. Most of 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. 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 most of 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 would exclude any project debt incurred by certain subsidiaries of Southern Power to the extent such debt is non-recourse to Southern Power and capitalization would exclude the capital stock or other equity attributable to such subsidiaries. At December 31, 2018 , Southern Company, the traditional electric operating companies, Southern Power, Southern Company Gas, and Nicor Gas were each in compliance with their respective debt limit covenants. 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 Southern Company, the traditional electric operating companies, Southern Power, Southern Company Gas, and Nicor Gas. The amount of variable rate revenue bonds of the traditional electric operating companies outstanding requiring liquidity support at December 31, 2018 was approximately $1.6 billion (comprised of approximately $854 million at Alabama Power, $659 million at Georgia Power, $82 million at Gulf Power, and $40 million at Mississippi Power). In addition, at December 31, 2018 , the traditional electric operating companies had approximately $403 million (comprised of approximately $345 million at Georgia Power and $58 million at Gulf Power) of revenue bonds outstanding that are required to be remarketed within the next 12 months . See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power on January 1, 2019. Subsequent to December 31, 2018, Georgia Power redeemed approximately $108 million of obligations related to outstanding variable rate pollution control revenue bonds. In addition to its credit arrangement described above, Southern Power also has a $120 million continuing letter of credit facility expiring in 2021 for standby letters of credit. At December 31, 2018 , $103 million has been used for letters of credit, primarily as credit support for PPA requirements, and $17 million was unused. At December 31, 2017 , the total amount available under this facility was $19 million . Southern Power's subsidiaries are not parties to this letter of credit facility. Also, at December 31, 2018 and 2017 , Southern Power had $ 103 million and $113 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 Southern Company, Alabama Power, Georgia Power, Southern Power, Southern Company Gas, 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 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 were as follows: Notes Payable at December 31, 2018 Notes Payable at December 31, 2017 Amount Outstanding Weighted Average Interest Rate Amount Outstanding Weighted Average Interest Rate (in millions) (in millions) Southern Company Commercial paper $ 1,064 3.0 % $ 1,832 1.8 % Short-term bank debt 1,851 3.1 % 607 2.3 % Total $ 2,915 3.1 % $ 2,439 1.9 % Alabama Power Short-term bank debt $ — — % $ 3 3.7 % Georgia Power Commercial paper $ 294 3.1 % $ — — % Short-term bank debt — — % 150 2.2 % Total $ 294 3.1 % $ 150 2.2 % Mississippi Power Short-term bank debt $ — — % $ 4 3.8 % Southern Power Commercial paper $ — — % $ 105 2.0 % Short-term bank debt 100

Commitments

Commitments	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS	COMMITMENTS Fuel and Power Purchase Agreements Non-Affiliate To supply a portion of the fuel requirements of the Southern Company system's electric generating plants, the Southern Company system has entered into various long-term commitments not recognized on the balance sheets for the procurement and delivery of fossil fuel and, for Alabama Power and Georgia Power, nuclear fuel. Fuel expense in 2018 , 2017 , and 2016 for the Southern Company system is shown below, the majority of which was purchased under long-term commitments. Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) 2018 $ 4,637 $ 1,301 $ 1,698 $ 405 $ 699 2017 4,400 1,225 1,671 395 621 2016 4,361 1,297 1,807 343 456 Each registrant expects that a substantial amount of its future fuel needs will continue to be purchased under long-term commitments. The traditional electric operating companies have entered into various non-affiliate long-term PPAs, some of which are accounted for as leases. For Alabama Power and Georgia Power, most long-term PPAs include capacity and energy components. Mississippi Power's long-term PPAs are associated with solar facilities and only include an energy component. For the traditional electric operating companies, the energy-related costs associated with PPAs are recoverable through fuel cost recovery provisions. Total capacity expense under these non-affiliate PPAs accounted for as operating leases in 2018 , 2017 , and 2016 was as follows: Southern Company Alabama Power Georgia Power (in millions) 2018 $ 231 $ 44 $ 113 2017 235 41 118 2016 232 42 113 In addition, Georgia Power's non-affiliate energy-only solar PPAs accounted for as leases contained contingent rent expense of $43 million , $44 million , and $18 million for 2018 , 2017 , and 2016 , respectively. Mississippi Power's energy-only solar PPAs accounted for as operating leases contained contingent rent expense of $10 million , $5 million , and an immaterial amount for 2018 , 2017 , and 2016 , respectively. Contingent rents are recognized as services are performed. Estimated total obligations under non-affiliate PPAs accounted for as operating leases at December 31, 2018 were as follows: Southern Company Alabama Power Georgia Power (in millions) 2019 $ 161 $ 41 $ 120 2020 164 42 122 2021 168 44 124 2022 171 46 125 2023 127 — 127 2024 and thereafter 642 — 642 Total $ 1,433 $ 173 $ 1,260 In addition, Georgia Power has commitments regarding a portion of a 5% interest in the original cost of Plant Vogtle Units 1 and 2 owned by MEAG Power that are in effect until the latter of the retirement of the plant or the latest stated maturity date of MEAG Power's bonds issued to finance such ownership interest. The payments for capacity are required whether or not any capacity is available. The energy cost is a function of each unit's variable operating costs. Portions of the capacity payments relate to costs in excess of MEAG Power's Plant Vogtle Units 1 and 2 allowed investment for ratemaking purposes. The present value of these portions at the time of the disallowance was written off. Generally, the cost of such capacity and energy is included in purchased power in Southern Company's statements of income and in purchased power, non-affiliates in Georgia Power's statements of income. Georgia Power's capacity payments related to this commitment totaled $8 million , $9 million , and $11 million in 2018 , 2017 , and 2016 , respectively. At December 31, 2018 , Georgia Power's estimated long-term obligations related to this commitment totaled $59 million , consisting of $6 million for 2019 , $5 million for 2020 , $5 million for 2021 , $4 million for 2022 , $3 million for 2023 , and $36 million for 2024 and thereafter . SCS may enter into various types of wholesale energy and natural gas contracts acting as an agent for the traditional electric operating companies and Southern Power. Under these agreements, each of the traditional electric operating companies and Southern Power may be jointly and severally liable. Accordingly, Southern Company has entered into keep-well agreements with each of the traditional electric operating companies to ensure they will not subsidize or be responsible for any costs, losses, liabilities, or damages resulting from the inclusion of Southern Power as a contracting party under these agreements. Affiliate Georgia Power has also entered into affiliate long-term PPAs with Southern Power, some of which Georgia Power accounts for as leases. Georgia Power's total capacity expense under these affiliate PPAs accounted for as leases was $93 million , $107 million , and $133 million in 2018 , 2017 , and 2016 , respectively. In addition, Georgia Power's energy-only solar PPAs with Southern Power accounted for as leases contained contingent rent expense of $29 million , $29 million , and $21 million for 2018 , 2017 , and 2016 , respectively. Georgia Power's estimated total obligations under affiliate PPAs accounted for as leases at December 31, 2018 were as follows: Georgia Power Affiliate Capital Lease PPAs Affiliate Operating Lease PPAs (in millions) 2019 $ 23 $ 64 2020 23 65 2021 24 66 2022 24 68 2023 25 69 2024 and thereafter 158 349 Total $ 277 $ 681 Less: amounts representing executory costs (a) 42 Net minimum lease payments 235 Less: amounts representing interest (b) 105 Present value of net minimum lease payments $ 130 (a) Executory costs such as taxes, maintenance, and insurance (including the estimated profit thereon) a re estimated and included in total minimum lease payments. (b) Calculated using an adjusted incremental borrowing rate to reduce the present value of the net minimum lease payments to fair value. See Note 8 under " Long-term Debt – Capital Leases – Georgia Power " for additional information. Pipeline Charges, Storage Capacity, and Gas Supply Southern Company Gas has commitments for pipeline charges, storage capacity, and gas supply, which include charges recoverable through natural gas cost recovery mechanisms, or alternatively, billed to marketers selling retail natural gas, as well as demand charges associated with Southern Company Gas' wholesale gas services. Gas supply commitments include amounts for gas commodity purchases associated with Southern Company Gas' gas marketing services of 47 million mmBtu at floating gas prices calculated using forward natural gas prices at December 31, 2018 and valued at $150 million . Southern Company Gas provides guarantees to certain gas suppliers for certain of its subsidiaries in support of payment 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, 2018 were as follows: Pipeline Charges, Storage Capacity, and Gas Supply (in millions) 2019 $ 781 2020 584 2021 520 2022 489 2023 412 2024 and thereafter 1,871 Total $ 4,657 Operating Leases In addition to the operating lease PPAs discussed previously, the Southern Company system has operating lease agreements with various terms and expiration dates. The traditional electric operating companies' operating leases primarily relate to facilities, coal railcars, vehicles, cellular tower space, and other equipment. Southern Power's operating leases primarily relate to land for solar and wind facilities and are recognized on a straight-line basis over the minimum lease term, plus any renewal periods necessary to cover the expected life of the respective facility. Southern Company Gas' operating leases primarily relate to facilities and vehicles. Total rent expense for 2018 , 2017 , and 2016 was as follows: Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power (*) (in millions) 2018 $ 192 $ 23 $ 34 $ 4 $ 31 2017 176 25 31 3 29 2016 169 18 28 3 22 (*) 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. Southern Company Gas (in millions) 2018 $ 15 2017 15 Successor – July 1, 2016 through December 31, 2016 8 Predecessor – January 1, 2016 through June 30, 2016 6 The registrants exclude contingent rent but include any step rents, fixed escalations, lease concessions, and lease extensions to cover the expected life of the facility in the computation of minimum lease payments. At December 31, 2018 , estimated minimum lease payments under operating leases were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2019 $ 156 $ 12 $ 23 $ 3 $ 23 $ 18 2020 134 10 18 2 24 16 2021 110 7 9 1 24 15 2022 98 6 6 1 24 13 2023 79 3 5 1 26 10 2024 and thereafter 1,040 1 13 2 874 34 Total $ 1,617 $ 39 $ 74 $ 10 $ 995 $ 106 For the traditional electric operating companies, a majority of the railcar and barge lease expenses are recoverable through fuel cost recovery provisions. In addition to the above rental commitments, Alabama Power and Georgia Power have potential obligations upon expiration of certain railcar leases with respect to the residual value of the leased property. These leases have terms expiring in 2023 for Alabama Power and in 2024 for Georgia Power with maximum obligations under these leases of $12 million for Alabama Power and $9 million for Georgia Power. At the termination of the leases, Alabama Power and Georgia Power may renew the leases, exercise their purchase options, or the property can be sold to a third party. Alabama Power and Georgia Power expect that the fair market value of the leased property would substantially reduce or, for Alabama Power, potentially eliminate the loss under the residual value obligations. Guarantees Alabama Power has guaranteed unconditionally the obligation of SEGCO under an installment sale agreement for the purchase of certain pollution control facilities at SEGCO's generating units, pursuant to which $25 million principal amount of pollution control revenue bonds are outstanding and mature in June 2019. Alabama Power also guaranteed a $100 million principal amount long-term bank loan entered into by SEGCO on November 28, 2018. Georgia Power has agreed to reimburse Alabama Power for the portion of such obligations corresponding to Georgia Power's proportionate ownership of SEGCO's stock if Alabama Power is called upon to make such payment under its guarantee. At December 31, 2018 , the capitalization of SEGCO consisted of $90 million of equity and $125 million of long-term debt, on which the annual interest requirement is $4 million . In addition, SEGCO had short-term debt outstanding of $5 million . See Note 7 under " SEGCO " for additional information. In 2013, Georgia Power entered into an agreement that requires Georgia Power to guarantee certain payments of a gas supplier for Plant McIntosh for a period up to 15 years . The agreement was subsequently amended on May 31, 2018. The guarantee is expected to be terminated if certain events occur by October 2019. In the event the gas supplier defaults on payments, the maximum potential exposure under the guarantee and amendment is approximately $30 million . In October 2017, Atlantic Coast Pipeline executed a $3.4 billion revolving credit facility with a stated maturity date of October 2021. Southern Company Gas entered into a guarantee agreement to support its share of the revolving credit facility. Southern Company Gas' maximum exposure to loss under the terms of the guarantee is limited to 5% of the outstanding borrowings under the credit facility, and totaled $72 million as of December 31, 2018. See Note 2 under "FERC Matters – Southern Company Gas" for additional information regarding the Atlantic Coast Pipeline. As discussed above under " Operating Leases ," Alabama Power and Georgia Power have entered into certain residual value guarantees related to railcar leases.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
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. PowerSecure and Southern Company Gas became participants in the income tax allocation agreement as of May 9, 2016 and July 1, 2016, respectively. See Note 15 for additional information on these acquisitions, as well as disposition activity during 2018. In accordance with IRS regulations, each company is jointly and severally liable for the federal tax liability. Prior to the Merger, Southern Company Gas filed a U.S. federal consolidated income tax return and various state income tax returns. 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. However, the IRS continues to issue regulations that provide further interpretation and guidance on the law and each respective state's adoption of the provisions contained in the Tax Reform Legislation remains uncertain. In addition, the regulatory treatment of certain impacts of the Tax Reform Legislation is subject to the discretion of the FERC and each state regulatory commission. The ultimate impact of these matters cannot be determined at this time. See Note 2 for additional information. Current and Deferred Income Taxes Details of income tax provisions are as follows: 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ 167 $ 91 $ 393 $ (567 ) $ 85 Deferred 231 123 (249 ) 575 (154 ) 398 214 144 8 (69 ) State — Current 188 26 81 (10 ) (9 ) Deferred (137 ) 51 (11 ) (100 ) (86 ) 51 77 70 (110 ) (95 ) Total $ 449 $ 291 $ 214 $ (102 ) $ (164 ) 2017 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ (62 ) $ 136 $ 256 $ 194 $ (566 ) Deferred (6 ) 336 504 (753 ) (312 ) (68 ) 472 760 (559 ) (878 ) State — Current 37 23 116 — (110 ) Deferred 173 73 (46 ) 27 49 210 96 70 27 (61 ) Total $ 142 $ 568 $ 830 $ (532 ) $ (939 ) 2016 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ 1,184 $ 103 $ 391 $ (31 ) $ 928 Deferred (342 ) 339 319 (60 ) (1,098 ) 842 442 710 (91 ) (170 ) State — Current (108 ) 20 6 (6 ) (60 ) Deferred 217 69 64 (7 ) 35 109 89 70 (13 ) (25 ) Total $ 951 $ 531 $ 780 $ (104 ) $ (195 ) Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Federal — Current $ 334 $ 103 $ — $ 67 Deferred 33 170 65 8 367 273 65 75 State — Current 131 27 (16 ) 12 Deferred (34 ) 67 27 — 97 94 11 12 Total $ 464 $ 367 $ 76 $ 87 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 $128 million for 2018 , $316 million for 2017 , and $1.13 billion for 2016 . These ITCs and PTCs for Southern Company and Southern Power are included in " Deferred Tax Assets and Liabilities " herein. In accordance with regulatory requirements, federal ITCs for the traditional electric operating companies and the natural gas distribution utilities, as well as certain state ITCs for Nicor Gas, are deferred, and, upon utilization, amortized over the average life of the related property with such amortization normally applied as a credit to reduce depreciation in the statements of income. Southern Power's deferred federal ITCs are amortized to income tax expense over the life of the respective asset. ITCs amortized in 2018 , 2017 , and 2016 were immaterial for Alabama Power, Georgia Power, Mississippi Power, and Southern Company Gas and were as follows for Southern Company and Southern Power: Southern Company Southern Power (in millions) 2018 $ 87 $ 58 2017 79 57 2016 59 37 Southern Power received $5 million of cash related to federal ITCs under renewable energy initiatives in 2018. No cash was received in 2017 or 2016. 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 $1 million in 2018 , $18 million in 2017 , and $173 million in 2016 . 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 $21 million in 2018, $37 million in 2017, and $31 million in 2016 and reduced Southern Power's income tax expense by $32 million in 2017 and $7 million in 2016. 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 $141 million in 2018 , $139 million in 2017 , and $50 million in 2016 . 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: 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Federal statutory rate 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 ) 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 ) — 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 ) Tax impact from sale of subsidiaries 8.6 — — — — Tax Reform Legislation (1.4 ) — (4.9 ) (26.3 ) 96.1 Noncontrolling interests (0.4 ) — — — (14.9 ) Other (0.8 ) (0.1 ) 0.1 (1.4 ) 2.0 Effective income tax (benefit) rate 16.3 % 23.6 % 21.3 % (75.4 )% (198.8 )% 2017 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Federal statutory rate 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 ) 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 ) — — 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 ) Tax Reform Legislation (25.6 ) 0.3 (0.4 ) 11.9 (416.1 ) Noncontrolling interests (1.4 ) — — — (8.6 ) Other (1.1 ) 0.1 0.2 — (10.7 ) Effective income tax (benefit) rate 13.3 % 39.6 % 36.7 % (17.1 )% (525.7 )% (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2017. 2016 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Federal statutory rate 35.0 % 35.0 % 35.0 % (35.0 )% 35.0 % State income tax, net of federal deduction 2.0 4.2 2.1 (5.7 ) (9.1 ) Employee stock plans' dividend deduction (1.2 ) — — — — Non-deductible book depreciation 0.9 1.0 0.8 0.7 — Flowback of excess deferred income taxes (0.1 ) — (0.1 ) (0.3 ) — AFUDC-Equity (2.0 ) (0.7 ) (0.8 ) (28.5 ) — ITC basis difference (5.0 ) — — — (96.3 ) Federal PTCs (1.2 ) — — — (23.3 ) Amortization of ITC (0.9 ) (0.2 ) (0.2 ) (0.1 ) (13.4 ) Noncontrolling interests (0.3 ) — — — (6.2 ) Other 0.1 (0.5 ) (0.1 ) 0.4 4.7 Effective income tax (benefit) rate 27.3 % 38.8 % 36.7 % (68.5 )% (108.6 )% (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2016. Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 Federal statutory rate 21.0% 35.0% 35.0% 35.0% State income tax, net of federal deduction 9.2 10.0 3.6 3.5 Flowback of excess deferred income taxes (3.0) (0.2) — — Amortization of ITC (0.1) (0.2) (0.4) — Tax impact on sale of subsidiaries 28.5 — — — Tax Reform Legislation (0.4) 15.0 — — Other 0.3 0.6 1.8 (0.9) Effective income tax rate 55.5% 60.2% 40.0% 37.6% 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, 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 AROs 1,232 276 925 31 — — AROs 1,210 607 575 — — — Other 593 177 141 68 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 taxes – assets $ (276 ) $ — $ — $ (150 ) $ (1,186 ) $ — Accumulated deferred income taxes – liabilities $ 6,558 $ 2,962 $ 3,062 $ 378 $ 105 $ 1,016 December 31, 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 9,059 $ 2,135 $ 2,889 $ 303 $ 1,922 $ 1,150 Property basis differences 1,853 725 606 207 2 204 Federal effect of net state deferred tax assets — — — 9 — — Leveraged lease basis differences 251 — — — — — Employee benefit obligations 527 162 287 28 7 4 Premium on reacquired debt 54 16 34 — — — Regulatory assets – Storm damage reserves 89 — 89 — — — Employee benefit obligations 1,044 260 349 46 — 75 AROs 821 249 501 33 — — AROs 370 220 130 — — — Other 689 147 140 73 30 208 Total deferred income tax liabilities 14,757 3,914 5,025 699 1,961 1,641 Deferred tax assets — Federal effect of net state deferred tax liabilities 330 143 85 — 42 54 Employee benefit obligations 1,339 286 448 62 8 185 Other property basis differences 343 — 59 — 184 — ITC and PTC carryforward 2,414 9 403 — 2,002 — Federal NOL carryforward 518 — — 40 333 92 Alternative minimum tax carryforward 69 — — 32 21 — Other partnership basis difference 23 — — — 23 — Other comprehensive losses 84 10 4 — 1 — AROs 1,191 469 631 33 — — Estimated loss on plants under construction 722 — — 722 — — Other deferred state tax attributes 330 — 6 133 77 — Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 304 126 123 27 — 9 Other 538 111 91 54 9 223 Total deferred income tax assets 8,205 1,154 1,850 1,103 2,700 563 Valuation allowance (184 ) — — (157 ) (13 ) (11 ) Net deferred income tax assets 8,021 1,154 1,850 946 2,687 552 Net deferred income taxes (assets)/liabilities $ 6,736 $ 2,760 $ 3,175 $ (247 ) $ (726 ) $ 1,089 Recognized in the balance sheets: Accumulated deferred income $ (106 ) $ — $ — $ (247 ) $ (925 ) $ — Accumulated deferred income taxes – liabilities $ 6,842 $ 2,760 $ 3,175 $ — $ 199 $ 1,089 The implementation of the Tax Reform Legislation significantly reduced accumulated deferred income taxes in 2017, partially offset by bonus depreciation provisions in the PATH Act. 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, 2018 and 2017 . Tax Credit Carryforwards Federal ITC/PTC carryforwards at December 31, 2018 were as follows: Southern Company Alabama Power Georgia Power Southern Power (in millions) Federal ITC/PTC carryforwards $ 2,410 $ 11 $ 108 $ 2,128 Year in which federal ITC/PTC carryforwards begin expiring 2032 2033 2032 2034 Year by which federal ITC/PTC carryforwards are expected to be utilized 2022 2021 2021 2022 The estimated tax credit utilization reflects the 2018 abandonment loss related to certain Kemper County energy facility expenditures as well as the projected taxable gains on the various sale transactions described in Note 15 and "Legal Entity Reorganizations" herein. The expected utilization of tax credit carryforwards could be further delayed by numerous factors, including the acquisition of additional renewable projects, the purchase of rights to additional PTCs of Plant Vogtle Units 3 and 4 pursuant to the MEAG Funding Agreement or the Global Amendments, 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, 2018 , Georgia Power also had approximately $341 million in state investment and other state tax credit carryforwards for the State of Georgia that will expire between 2020 and 2028 and are not expected to be fully utilized. Georgia Power has a net state valuation allowance of $33 million associated with these carryforwards. The ultimate outcome of these matters cannot be determined at this time. Net Operating Loss Carryforwards In the 2018 tax year, Southern Company expects to fully utilize the carryforward from federal NOLs generated in 2016 and 2017. At December 31, 2018 , 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 $ 5,062 $ 200 2031 Southern Power Oklahoma 846 40 2035 Florida 264 11 2033 South Carolina 62 2 2034 Other states 42 3 2029 Southern Power Total $ 1,214 $ 56 Other (*) Georgia 358 16 2019 New York 223 11 2036 New York City 208 15 2036 Other states 278 14 Various Southern Company Total $ 7,343 $ 312 (*) Represents other Southern Company subsidiaries. Alabama Power, Georgia Power, and Southern Company Gas did not have state NOL carryforwards at December 31, 2018 . State NOLs for Mississippi, Oklahoma, and Florida are not expected to be fully utilized prior to expiration. At December 31, 2018, Mississippi Power had a net state valuation allowance of $32 million for the Mississippi NOL and Southern Power had a net state valuation allowance of $9 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 Unrecognized tax benefits changes in 2018 , 2017 , and 2016 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, 2015 $ 433 $ 421 $ 8 Tax positions changes – Increase from current periods 45 26 17 Increase from prior periods 21 18 — Decrease from prior periods (15 ) — (8 ) 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 increase from current and prior periods for 2017 and 2016 relate 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. Mississippi Power's tax positions decrease from prior periods and the reductions due to settlements for 2017 relate primarily to the settlement of R&E expenditures associated with the Kemper County energy facility. See Note 2 under " Mississippi Power – Kemper County Energy Facility " and " Section 174 Research and Experimental Deduction " herein for more information. Southern Power's increase in unrecognized tax benefits from current periods for 2016, and the decrease from prior periods for 2017 and 2016, primarily relate to federal income tax benefits from deferred ITCs. There were no unrecognized tax benefits at December 31, 2018. The impact on the effective tax rate of Southern Company, Mississippi Power, and Southern Power, if recognized, was as follows for 2017 and 2016: Southern Company Mississippi Power Southern Power (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 $ — $ — 2016 Tax positions impacting the effective tax rate $ 20 $ 1 $ 17 Tax positions not impacting the effective tax rate 464 464 — Balance of unrecognized tax benefits $ 484 $ 465 $ 17 Mississippi Power's tax positions not impacting the effective tax rate for 2016 relate to deductions for R&E expenditures associated with the Kemper County energy facility. See " Section 174 Research and Experimental Deduction " herein for more information. These amounts are presented on a gross basis without considering the related federal or state income tax impact. Southern Power's impact on the effective tax rate was determined based on the amount of ITCs, which were uncertain. 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 2017, as well as the pre-Merger Southern Company Gas tax returns. Southern Company is a participant in the Compliance Assurance Process of the IRS. The audits for the registrants' state income tax returns have either been concluded, or the statute of limitations has expired, for years prior to 2012. Section 174 Research and Experimental Deduction Southern Company, on behalf of Mississippi Power, has reflected deductions for R&E expenditures related to the Kemper County energy facility in its federal income tax calculations since 2013 and filed amended federal income tax returns for 2008 through 2013 to also include such deductions. In September 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, 2018
Retirement Benefits [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS The Southern Company system has a qualified defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at PowerSecure. The qualified defined benefit pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No contributions to the qualified pension plan were made for the year ended December 31, 2018 and no mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 2019 . 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, 2019 , no other postretirement trust contributions are expected. On January 1, 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 1, 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 on January 1, 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's Sale of Gulf Power " for additional information. The portion of the Southern Company system's pension and other postretirement benefit plans attributable to Gulf Power that is reflected in Southern Company's consolidated balance sheet as held for sale at December 31, 2018 consists 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. 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. 2018 Assumptions used to determine net Southern Company Alabama Power Georgia Mississippi Power Southern Power Pension plans Discount rate – benefit obligations 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % Discount rate – interest costs 3.45 3.45 3.42 3.46 3.69 Discount rate – service costs 3.98 4.00 3.99 3.99 4.01 Expected long-term return on plan assets 7.95 7.95 7.95 7.95 7.95 Annual salary increase 4.34 4.46 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % Discount rate – interest costs 3.29 3.31 3.29 3.29 3.47 Discount rate – service costs 3.91 3.93 3.91 3.91 3.93 Expected long-term return on plan assets 6.83 6.83 6.80 6.99 — Annual salary increase 4.34 4.46 4.46 4.46 4.46 2017 Assumptions used to determine net Southern Company Alabama Georgia Mississippi Power Pension plans Discount rate – benefit obligations 4.40 % 4.44 % 4.40 % 4.44 % Discount rate – interest costs 3.77 3.76 3.72 3.81 Discount rate – service costs 4.81 4.85 4.83 4.83 Expected long-term return on plan assets 7.92 7.95 7.95 7.95 Annual salary increase 4.37 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 4.23 % 4.27 % 4.23 % 4.22 % Discount rate – interest costs 3.54 3.58 3.55 3.55 Discount rate – service costs 4.64 4.70 4.63 4.65 Expected long-term return on plan assets 6.84 6.83 6.79 6.88 Annual salary increase 4.37 4.46 4.46 4.46 2016 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Pension plans Discount rate – benefit obligations 4.58 % 4.67 % 4.65 % 4.69 % Discount rate – interest costs 3.88 3.90 3.86 3.97 Discount rate – service costs 4.98 5.07 5.03 5.04 Expected long-term return on plan assets 8.16 8.20 8.20 8.20 Annual salary increase 4.37 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 4.38 % 4.51 % 4.49 % 4.47 % Discount rate – interest costs 3.66 3.69 3.67 3.66 Discount rate – service costs 4.85 4.96 4.88 4.88 Expected long-term return on plan assets 6.66 6.83 6.27 7.07 Annual salary increase 4.37 4.46 4.46 4.46 Southern Company Gas Successor Predecessor Assumptions used to determine net periodic costs: Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 Pension plans Discount rate – benefit obligations 3.74 % 4.39 % 3.85 % 4.60 % Discount rate – interest costs 3.41 3.76 3.21 4.00 Discount rate – service costs 3.84 4.64 4.07 4.80 Expected long-term return on plan assets 7.95 7.60 7.75 7.80 Annual salary increase 3.07 3.50 3.50 3.70 Pension band increase (*) N/A N/A 2.00 2.00 Other postretirement benefit plans Discount rate - benefit obligations 3.62 % 4.15 % 3.61 % 4.40 % Discount rate – interest costs 3.21 3.40 2.84 3.60 Discount rate – service costs 3.82 4.55 3.96 4.70 Expected long-term return on plan assets 5.89 6.03 5.93 6.60 Annual salary increase 3.07 3.50 3.50 3.70 (*) Only applicable to Nicor Gas union employees. The pension bands for the former Nicor Gas plan reflect the negotiated rates in accordance with the union agreements. 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 2017 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % 3.74 % Annual salary increase 4.32 4.46 4.46 4.46 4.46 2.88 Other postretirement benefit plans Discount rate 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % 3.62 % Annual salary increase 4.32 4.46 4.46 4.46 4.46 2.56 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, 2018 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Pre-65 6.50 % 4.50 % 2028 Post-65 medical 5.00 4.50 2028 Post-65 prescription 8.00 4.50 2028 Pension Plans The total accumulated benefit obligation for the pension plans at December 31, 2018 and 2017 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2018 $ 11,683 $ 2,550 $ 3,613 $ 513 $ 101 $ 842 December 31, 2017 12,577 2,696 3,847 541 111 1,139 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. The actuarial loss of $1.3 billion recorded in the remeasurement of the Southern Company system pension plans at December 31, 2017 was primarily due to a 60 basis point decrease in the overall discount rate used to calculate the benefit obligation as a result of lower market interest rates. Changes in the projected benefit obligations and the fair value of plan assets during the plan years ended December 31, 2018 and 2017 were as follows: 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 ) 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 12,385 $ 2,663 $ 3,800 $ 534 $ — $ 1,133 Service cost 293 63 74 15 — 23 Interest cost 455 98 138 20 — 42 Benefits paid (596 ) (120 ) (187 ) (22 ) — (91 ) Plan amendments (26 ) — — — — (26 ) Actuarial (gain) loss 1,297 294 363 55 — 103 Obligations assumed from employee transfer — — — — 139 — Balance at end of year 13,808 2,998 4,188 602 139 1,184 Change in plan assets Fair value of plan assets at beginning of year 11,583 2,517 3,621 499 — 983 Actual return (loss) on plan assets 1,953 427 610 84 — 175 Employer contributions 52 12 14 2 — 1 Benefits paid (596 ) (120 ) (187 ) (22 ) — (91 ) Assets assumed from employee transfer — — — — 138 — Fair value of plan assets at end of year 12,992 2,836 4,058 563 138 1,068 Accrued liability $ (816 ) $ (162 ) $ (130 ) $ (39 ) $ (1 ) $ (116 ) The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2018 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 $ 12,135 $ 2,692 $ 3,757 $ 527 $ 122 $ 866 Non-qualified pension plan 629 124 148 30 1 41 Amounts recognized in the balance sheets at December 31, 2018 and 2017 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, 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 ) December 31, 2017: Prepaid pension costs $ — $ — $ 23 $ — $ — $ — Other regulatory assets, deferred 3,273 890 1,105 158 — 217 Other deferred charges and assets — — — — — 85 Other current liabilities (53 ) (12 ) (15 ) (3 ) — (3 ) Employee benefit obligations (763 ) (150 ) (138 ) (36 ) (1 ) (198 ) Other regulatory liabilities, deferred (118 ) — — — — — AOCI 107 — — — 33 (42 ) (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. Presented below are the amounts included in regulatory assets at December 31, 2018 and 2017 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, 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 (liabilities) $ 3,458 $ 955 $ 1,230 $ 167 $ 160 Balance at December 31, 2017 Regulatory assets: Prior service cost $ 14 $ 8 $ 14 $ 3 $ (20 ) Net (gain) loss 3,140 882 1,091 155 197 Regulatory amortization (*) — — — — 40 Total regulatory assets $ 3,154 $ 890 $ 1,105 $ 158 $ 217 (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. 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, 2018 and 2017 are presented in the following table: Southern (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): Balance at December 31, 2016 $ 3,120 $ 870 $ 1,129 $ 154 $ 267 Net (gain) loss 227 64 36 12 (31 ) Change in prior service costs (26 ) — — — — Reclassification adjustments: Amortization of prior service costs (11 ) (2 ) (3 ) (1 ) — Amortization of net gain (loss) (155 ) (42 ) (57 ) (7 ) (18 ) Amortization of regulatory assets (*) — — — — (1 ) Total reclassification adjustments (166 ) (44 ) (60 ) (8 ) (19 ) Total change 35 20 (24 ) 4 (50 ) 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 (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. Presented below are the amounts included in AOCI at December 31, 2018 and 2017 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, 2018 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 100 26 (38 ) Total AOCI $ 97 $ 26 $ (44 ) Balance at December 31, 2017 AOCI: Prior service cost $ 3 $ 1 $ — Net (gain) loss 104 32 (42 ) Total AOCI $ 107 $ 33 $ (42 ) 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, 2018 and 2017 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2016 $ 100 $ — $ (43 ) Net (gain) loss 15 — 1 Change from employee transfer — 33 — Reclassification adjustments: Amortization of prior service costs (1 ) — — Amortization of net gain (loss) (7 ) — — Total reclassification adjustments (8 ) — — Total change 7 33 1 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 ) Components of net periodic pension cost for Southern Company, the traditional electric operating companies, and Southern Power were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) 2018: Service cost $ 359 $ 78 $ 87 $ 17 $ 9 Interest cost 464 101 139 20 5 Expected return on plan assets (943 ) (207 ) (296 ) (41 ) (10 ) Recognized net (gain) loss 213 54 69 10 1 Net amortization 4 1 2 — — Net periodic pension cost $ 97 $ 27 $ 1 $ 6 $ 5 2017: Service cost $ 293 $ 63 $ 74 $ 15 Interest cost 455 98 138 20 Expected return on plan assets (897 ) (196 ) (283 ) (40 ) Recognized net (gain) loss 162 42 57 7 Net amortization 12 2 3 1 Net periodic pension cost $ 25 $ 9 $ (11 ) $ 3 2016: Service cost $ 262 $ 57 $ 70 $ 13 Interest cost 422 95 136 19 Expected return on plan assets (782 ) (184 ) (258 ) (35 ) Recognized net (gain) loss 150 40 55 7 Net amortization 14 3 5 1 Net periodic pension cost $ 66 $ 11 $ 8 $ 5 Components of net periodic pension cost for Southern Company Gas were as follows: Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Service cost $ 34 $ 23 $ 15 $ 13 Interest cost 39 42 20 21 Expected return on plan assets (75 ) (70 ) (35 ) (33 ) Recognized net (gain) loss 12 18 14 13 Net amortization of regulatory asset 15 1 — — Prior service cost (2 ) — (1 ) (1 ) Net periodic pension cost $ 23 $ 14 $ 13 $ 13 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 all plan assets over five years rather than recognize the changes immediately. As a result, 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, 2018 , estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2019 $ 623 $ 132 $ 201 $ 28 $ 3 $ 59 2020 645 136 206 28 3 61 2021 664 141 209 29 4 62 2022 687 147 215 29 4 62 2023 711 152 221 30 5 62 2024 to 2028 3,869 832 1,183 166 27 313 Other Postretirement Benefits Changes in the APBO and the fair value of the registrants' plan assets during the plan years ended December 31, 2018 and 2017 were as follows: 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 ) 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 2,297 $ 501 $ 847 $ 97 $ — $ 308 Service cost 24 6 7 1 — 2 Interest cost 79 17 29 3 — 10 Benefits paid (136 ) (29 ) (51 ) (6 ) — (19 ) Actuarial (gain) loss 65 20 28 1 — 3 Plan amendments 3 — — — — 3 Retiree drug subsidy 7 2 3 1 — — Obligations assumed from employee transfer — — — — 11 — Employee contributions — — — — — 3 Balance at end of year 2,339 517 863 97 11 310 Change in plan assets Fair value of plan assets at beginning of year 944 367 354 23 — 105 Actual return (loss) on plan assets 154 60 54 3 — 20 Employer contributions 84 6 26 4 — 17 Employee contributions — — — — — 3 Benefits paid (129 ) (27 ) (48 ) (5 ) — (20 ) Fair value of plan assets at end of year 1,053 406 386 25 — 125 Accrued liability $ (1,286 ) $ (111 ) $ (477 ) $ (72 ) $ (11 ) $ (185 ) Amounts recognized in the balance sheets at December 31, 2018 and 2017 related to the registrants' other postretirement benefit plans consist of the following: Southern (a) Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2017: Other regulatory assets, deferred (a) $ 382 $ 63 $ 202 $ 18 $ — $ 46 Other current liabilities (5 ) — — — — — Employee benefit obligations (b) (1,281 ) (111 ) (477 ) (72 ) (11 ) (185 ) Other regulatory liabilities, deferred (41 ) (7 ) — (1 ) — — AOCI 4 — — — 3 (3 ) (a) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016. (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, 2018 and 2017 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 (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2018 Regulatory assets: 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 ) Balance at December 31, 2017 Regulatory assets: Prior service cost $ 21 $ 11 $ 5 $ — $ (7 ) Net (gain) loss 320 45 197 17 47 Regulatory amortization (*) — — — — 6 Total regulatory assets $ 341 $ 56 $ 202 $ 17 $ 46 (*) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016. The changes in the balance of net regulatory assets (liabilities) related to the other postretirement benefit plans for the plan years ended December 31, 2018 and 2017 are presented in the following table: Southern (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Net regulatory assets (liabilities): Balance at December 31, 2016 $ 378 $ 76 $ 213 $ 19 $ 52 Net (gain) loss (21 ) (15 ) (2 ) (1 ) (5 ) Change in prior service costs 3 — — — — Reclassification adjustments: Amortization of prior service costs (6 ) (4 ) (1 ) — 3 Amortization of net gain (loss) (13 ) (1 ) (8 ) (1 ) (4 ) Total reclassification adjustments (19 ) (5 ) (9 ) (1 ) (1 ) Total change (37 ) (20 ) (11 ) (2 ) (6 ) 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 ) (*) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016. Presented below are the amounts included in AOCI at December 31, 2018 and 2017 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, 2018 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss (5 ) 1 (5 ) Total AOCI $ (4 ) $ 1 $ (4 ) Balance at December 31, 2017 AOCI: Prior service cost $ — $ — $ — Net (gain) loss 4 3 (3 ) Total AOCI $ 4 $ 3 $ (3 ) The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2018 and 2017 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2016 $ 7 $ — $ (3 ) Net (gain) loss (3 ) — (1 ) Change from employee transfer — 3 1 Total change (3 ) 3 — Balance at December 31, 2017 $ 4 $ 3 $ (3 ) Net (gain) loss (8 ) (2 ) (2 ) Amortization of prior service costs — — 1 Total change (8 ) (2 ) (1 ) Balance at December 31, 2018 $ (4 ) $ 1 $ (4 ) Components of the other postretirement benefit plans' net periodic cost for Southern Company, the traditional electric operating companies, and Southern Power were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) 2018: Service cost $ 24 $ 6 $ 6 $ 1 $ 1 Interest cost 75 17 28 3 — Expected return on plan assets (69 ) (26 ) (25 ) (2 ) — Net amortization 21 5 10 1 — Net periodic postretirement benefit cost $ 51 $ 2 $ 19 $ 3 $ 1 2017: Service cost $ 24 $ 6 $ 7 $ 1 Interest cost 79 17 29 3 Expected return on plan assets (66 ) (25 ) (25 ) (1 ) Net amortization 20 5 9 1 Net periodic postretirement benefit cost $ 57 $ 3 $ 20 $ 4 2016: Service cost $ 22 $ 5 $ 6 $ 1 Interest cost 76 18 30 3 Expected return on plan assets (60 ) (25 ) (22 ) (1 ) Net amortization 21 6 10 1 Net periodic postretirement benefit cost $ 59 $ 4 $ 24 $ 4 Components of the other postretirement benefit plans' net periodic cost for Southern Company Gas were as follows: Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Service cost $ 2 $ 2 $ 1 $ 1 Interest cost 10 10 5 5 Expected return on plan assets (7 ) (7 ) (3 ) (3 ) Amortization: Regulatory assets 6 — 2 — Prior service costs — (3 ) — (1 ) Net (gain)/loss — 4 — 2 Net periodic postretirement benefit cost $ 11 $ 6 $ 5 $ 4 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: 2019 $ 136 $ 28 $ 51 $ 6 $ — $ 18 2020 136 28 50 6 — 18 2021 136 29 50 6 — 19 2022 137 29 50 6 1 19 2023 137 29 49 7 1 19 2024 to 2028 669 146 243 30 3 90 Subsidy receipts: 2019 $ (7 ) $ (2 ) $ (3 ) $ — $ — $ — 2020 (7 ) (2 ) (3 ) — — — 2021 (8 ) (2 ) (3 ) — — — 2022 (8 ) (2 ) (3 ) (1 ) — — 2023 (8 ) (3 ) (4 ) (1 ) — — 2024 to 2028 (41 ) (13 ) (18 ) (2 ) — — Total: 2019 $ 129 $ 26 $ 48 $ 6 $ — $ 18 2020 129 26 47 6 — 18 2021 128 27 47 6 — 19 2022 129 27 47 5 1 19 2023 129 26 45 6 1 19 2024 to 2028 628 133 225 28 3 90 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 plans 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

Stock Compensation

Stock Compensation	12 Months Ended
	Dec. 31, 2018
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 a large segment of 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, 2018 , 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 4,716 745 822 164 95 285 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 not granted in 2018. 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 2018 2017 2016 Expected volatility 14.9% 15.6% 15.0% Expected term (in years) 3 3 3 Interest rate 2.4% 1.4% 0.8% Weighted average grant-date fair value $43.75 $49.08 $45.06 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 2018 , 2017 , and 2016 was $43.49 , $49.21 , and $48.87 , 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's total unvested PSUs outstanding at December 31, 2017 was 2.9 million . In February 2018 , 1.5 million PSUs vested for the three -year performance period ended December 31, 2017 were converted into 1.9 million shares outstanding at a share price of $44.68 . During 2018 , Southern Company granted 1.3 million PSUs and 1.9 million PSUs were vested or forfeited, resulting in 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 . Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 (in millions) Southern Company Compensation cost recognized in income $ 91 $ 74 $ 96 Tax benefit of compensation cost recognized in income 24 29 37 Alabama Power Compensation cost recognized in income $ 11 $ 9 $ 15 Tax benefit of compensation cost recognized in income 3 4 6 Georgia Power Compensation cost recognized in income $ 11 $ 10 $ 15 Tax benefit of compensation cost recognized in income 3 4 6 Mississippi Power Compensation cost recognized in income $ 3 $ 2 $ 4 Tax benefit of compensation cost recognized in income 1 1 1 Southern Power Compensation cost recognized in income $ 4 N/A N/A Tax benefit of compensation cost recognized in income 1 N/A N/A Southern Company Gas Compensation cost recognized in income $ 11 $ 8 N/A Tax benefit of compensation cost recognized in income 3 3 N/A The compensation cost related to the grant of Southern Company PSUs to the employees of the traditional electric operating companies, Southern Power, and Southern Company Gas is recognized in each respective registrant's financial statements with a corresponding credit to equity representing a capital contribution from Southern Company. At December 31, 2018 , Southern Company's total unrecognized compensation cost related to PSUs was $30 million and is expected to be recognized over a weighted-average period of approximately 16 months . The total unrecognized compensation cost related to PSUs as of December 31, 2018 was immaterial for all other registrants. Restricted Stock Units Beginning in 2017 , employees are granted RSUs in addition to PSUs. One-third of the RSUs granted to employees vest each year throughout a three -year service period. Shares of Southern Company common stock are delivered to employees at the end of each vesting period. 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 2018 and 2017 were $43.81 and $49.25 , respectively. Since one-third of the RSUs vest each year throughout a three -year service period, compensation cost for RSUs is generally recognized over the corresponding one -, two -, or three -year vesting period. Southern Company had 0.7 million RSUs outstanding at December 31, 2017 . During 2018 , Southern Company granted 0.7 million RSUs and 0.3 million RSUs were vested or forfeited, resulting in 1.1 million unvested RSUs outstanding at December 31, 2018 , including RSUs related to employee retention agreements. For the years ended December 31, 2018 and 2017 , Southern Company's total compensation cost for RSUs recognized in income was $27 million and $25 million , respectively. The related tax benefit also recognized in income was $7 million and $10 million for the years ended December 31, 2018 and 2017 , respectively. Total unrecognized compensation cost related to RSUs as of December 31, 2018 for Southern Company of $13 million will be recognized over a weighted-average period of approximately 16 months . Total RSUs outstanding and total compensation cost and related tax benefit for the RSUs recognized in income for the years ended December 31, 2018 and 2017 , as well as the total unrecognized compensation cost as of December 31, 2018 , were immaterial for all other registrants. 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 no later than November 2024. As of December 31, 2018 , the weighted average remaining contractual term for the options outstanding and exercisable was approximately 4 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 years ended December 31, 2017 and 2016 were immaterial for Southern Company, Alabama Power, Georgia Power, and Mississippi Power. Southern Company's activity in the stock option program for 2018 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2017 18.6 $ 41.68 Exercised 1.1 37.82 Outstanding and Exercisable at December 31, 2018 17.5 $ 41.92 Southern Company's cash receipts from issuances related to stock options exercised under the share-based payment arrangements for the years ended December 31, 2018 , 2017 , and 2016 were $41 million , $239 million , and $448 million , respectively. At December 31, 2018 , 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 $ 39 $ 5 $ 13 $ 1 Total intrinsic value of options exercised, and the related tax benefit, for the years ended December 31, 2018 , 2017 , and 2016 are presented below: Year Ended December 31 2018 2017 2016 (in millions) Southern Company Intrinsic value of options exercised $ 9 $ 64 $ 120 Tax benefit of options exercised 2 25 46 Alabama Power Intrinsic value of options exercised $ 2 $ 12 $ 21 Tax benefit of options exercised — 5 8 Georgia Power Intrinsic value of options exercised $ 2 $ 13 $ 18 Tax benefit of options exercised — 5 7 Mississippi Power Intrinsic value of options exercised $ 1 $ 2 $ 4 Tax benefit of options exercised — 1 2 Merger Stock Compensation At the effective time of the Merger, each share of Southern Company Gas common stock, other than certain excluded shares, was converted into the right to receive $66 in cash, without interest. Also, at the effective time of the Merger: • Southern Company Gas' outstanding RSUs, restricted stock awards, and non-employee director stock awards were deemed fully vested and were canceled and converted into the right to receive an amount in cash equal to the product of (i) the total number of shares of Southern Company Gas' common stock subject to such award and (ii) the Merger consideration of $66 per share; • Southern Company Gas' outstanding stock options, all of which were fully vested, were canceled and converted into the right to receive an amount in cash equal to the product of (i) the total number of shares of Southern Company Gas' common stock subject to such options and (ii) the excess of the Merger consideration of $66 per share over the applicable exercise price per share of such options; and • each outstanding award of a Southern Company Gas PSU was converted into an award of Southern Company RSUs. The conversion ratio was the product of (i) the greater of (a) 125% of the number of units underlying such award based on target level achievement of all relevant performance goals and (b) the number of units underlying such award based on the actual level of achievement of all relevant performance goals against target and (ii) an exchange ratio based on the Merger consideration of $66 per share as compared to the volume-weighted average price per share of Southern Company common stock. 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 satisfy 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. As a portion of the fair value of the award related to pre-combination service, the grant date fair value was allocated to pre- or post-combination service and accounted for as Merger consideration or compensation cost, respectively. Approximately $13 million of the grant date fair value was allocated to Merger consideration. Southern Company Gas recognized the remaining fair value as compensation expense on a straight-line basis over the remaining vesting period. As of December 31, 2018, all RSUs are vested and compensation cost is fully recognized. For the years ended December 31, 2018, 2017, and 2016, total compensation cost for RSUs recognized in income was $2 million , $8 million , and $13 million , respectively, with the related tax benefit of $1 million , $4 million , and $4 million , respectively, also recognized in income. 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. 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 will vest and be issued one-third each year as long as the employee remains in service with Southern Company or its subsidiaries at each vest date. In addition to the change in control benefit, Southern Company common stock could be 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 are 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 is 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 is recognized in Southern Company Gas' financial statements with a corresponding credit to equity, representing a capital contribution from Southern Company. The expected payout is 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 will be based on the actual performance. For the years ended December 31, 2018, 2017, and 2016, total compensation cost for the change in control awards recognized in income was $5 million , $12 million , and $4 million , respectively, with the related tax benefit of $2 million , $6 million , and less than $1 million , respectively, also recognized in income. As of December 31, 2018, $2 million of total unrecognized compensation cost related to change in control awards will be recognized over a weighted-average period of approximately six months . Predecessor For the predecessor period of January 1, 2016 through June 30, 2016, the employees of Southern Company Gas and subsidiaries participated in the AGL Resources Inc. Omnibus Performance Incentive Plan, as amended and restated. The AGL Resources Inc. Omnibus Performance Incentive Plan, as amended and restated, and the Long-Term Incentive Plan (1999) provided for the grant of incentive and nonqualified stock options, stock appreciation rights, shares of restricted stock, RSUs, performance cash awards, and other stock-based awards to officers and key employees. Effective July 1, 2016, all Southern Company Gas shares of stock were canceled and/or converted as a result of the Merger. No further grants will be made from the Long-Term Incentive Plan (1999) or the AGL Resources Inc. Omnibus Performance Incentive Plan, as amended and restated. For the predecessor period, Southern Company Gas recognized stock-based compensation cost for its stock-based awards over the requisite service period based on the estimated fair value at the date of grant for its stock-based awards using the modified prospective method. Performance-based stock awards and performance units contained market and performance conditions. Stock options, restricted stock awards, and performance units also contained a service condition. Southern Company Gas estimated forfeitures over the requisite service period when recognizing compensation cost. These estimates were adjusted to the extent that actual forfeitures differ, or were expected to materially differ, from such estimates. The difference between the proceeds from the exercise of Southern Company Gas' stock-based awards and the par value of the stock was recorded within additional paid-in capital. Southern Company Gas granted stock awards with a grant price that was equal to the fair market value on the date of the grant. Fair market value was defined under the terms of the applicable plans as the closing price per share of Southern Company Gas' common stock on the grant date. For the predecessor period of January 1, 2016 through June 30, 2016, total compensation cost for cash and stock-based awards recognized in income was $24 million with related tax benefits of an immaterial amount also recognized in income.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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. 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. At December 31, 2017 , 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 331 $ 239 $ — $ — $ 570 Interest rate derivatives — 1 — — 1 Foreign currency derivatives — 129 — — 129 Nuclear decommissioning trusts: (c) Domestic equity 690 82 — — 772 Foreign equity 62 224 — — 286 U.S. Treasury and government agency securities — 251 — — 251 Municipal bonds — 68 — — 68 Corporate bonds 21 315 — — 336 Mortgage and asset backed securities — 57 — — 57 Private equity — — — 29 29 Other 19 12 — — 31 Cash equivalents 1,455 — — — 1,455 Other investments 9 — 1 — 10 Total $ 2,587 $ 1,378 $ 1 $ 29 $ 3,995 Liabilities: Energy-related derivatives (a)(b) $ 480 $ 253 $ — $ — $ 733 Interest rate derivatives — 38 — — 38 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ 480 $ 314 $ 22 $ — $ 816 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (d) Domestic equity 442 81 — — 523 Foreign equity 62 59 — — 121 U.S. Treasury and government agency securities — 24 — — 24 Corporate bonds 21 160 — — 181 Mortgage and asset backed securities — 18 — — 18 Private equity — — — 29 29 Other 6 — — — 6 Cash equivalents 349 — — — 349 Total $ 880 $ 346 $ — $ 29 $ 1,255 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (d)(e) Domestic equity 248 1 — — 249 Foreign equity — 166 — — 166 U.S. Treasury and government agency securities — 227 — — 227 Municipal bonds — 68 — — 68 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 40 — — 40 Other 12 12 — — 24 Cash equivalents 690 — — — 690 Total $ 950 $ 675 $ — $ — $ 1,625 Liabilities: Energy-related derivatives $ — $ 19 $ — $ — $ 19 Interest rate derivatives — 5 — — 5 Total $ — $ 24 $ — $ — $ 24 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Interest rate derivatives — 1 — — 1 Cash equivalents 224 — — — 224 Total $ 224 $ 3 $ — $ — $ 227 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 129 — — 129 Cash equivalents 21 — — — 21 Total $ 21 $ 132 $ — $ — $ 153 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ — $ 36 $ 22 $ — $ 58 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 331 $ 223 $ — $ — $ 554 Liabilities: Energy-related derivatives (a)(b) $ 479 $ 181 $ — $ — 660 (a) Energy-related derivatives exclude $11 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 $193 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under " Nuclear Decommissioning " for additional information. (e) 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 categorized as Level 3 under Fair Value Measurements that are not traded in the open market. The fair value of these investments has been determined based on market factors including comparable multiples and the expectations regarding cash flows and business plan executions. 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 $45 million and $29 million at December 31, 2018 and 2017 , respectively. Unfunded commitments related to the private equity investments totaled $50 million and $21 million at December 31, 2018 and 2017 , respectively. Private equity funds include funds-of-funds that invest in high-quality private equity funds across several market sectors, funds that invest in real estate assets, and a fund that acquires companies to create resale value. Private equity funds do not have redemption rights. Distributions from these funds will be received as the underlying investments in the funds are liquidated. At December 31, 2018 and 2017 , 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, 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 At December 31, 2017: Long-term debt, including securities due within one year: Carrying amount $ 48,151 $ 7,625 $ 11,777 $ 2,086 $ 5,841 $ 6,048 Fair value 51,348 8,305 12,531 2,076 6,079 6,471 (a) Includes long-term debt of Gulf Power, which is classified as liabilities held for sale on Southern Company's balance sheet at December 31, 2018. See Note 15 under " Southern Company's Sale of Gulf Power " 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, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	DERIVATIVES Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' wholesale gas operations use various contracts in its commercial activities that generally meet the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note 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. The registrants adopted ASU 2017-12 as of January 1, 2018. See Note 1 under " Recently Adopted Accounting Standards – Other " 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, 2018 , 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 (*) 431 2022 2029 Alabama Power 74 2022 — Georgia Power 153 2022 — Mississippi Power 63 2022 — Southern Power 15 2020 — Southern Company Gas (*) 120 2021 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 4,159 million mmBtu and short natural gas positions of 4,039 million mmBtu at December 31, 2018 , which is also included in Southern Company's total volume. At December 31, 2018 , the net volume of Southern Power's energy-related derivative contracts for power to be sold was 2 million MWHs, all of which expire by 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 4 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, 2019 are immaterial for all registrants. Interest Rate Derivatives Southern Company and certain subsidiaries may enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. At December 31, 2018 , 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) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month LIBOR + 0.92% June 2020 $ (4 ) Southern Company (*) 1,500 2.35% 1-month LIBOR + 0.87% July 2021 (43 ) Georgia Power 200 4.25% 3-month LIBOR + 2.46% December 2019 (2 ) Southern Company Consolidated $ 2,000 $ (49 ) (*) Represents the Southern Company parent entity. 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, 2019 are $(19) million for Southern Company and 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, 2037 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, 2018 , 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 $ 25 Southern Power 564 3.78% 500 1.85% June 2026 27 Total $ 1,241 € 1,100 $ 52 The estimated pre-tax gains (losses) related to Southern Power's foreign currency derivatives that will be reclassified from AOCI to earnings for the year ending December 31, 2019 are $(23) 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, 2018 and 2017 , the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2018 2017 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 $ 8 $ 23 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 9 26 7 24 Assets held for sale, current/Liabilities held for sale, current — 6 — — Total derivatives designated as hedging instruments for regulatory purposes $ 17 $ 55 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 7 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 2 — — Interest rate derivatives: Other current assets/Other current liabilities — 19 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 30 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 75 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 79 $ 81 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 561 $ 575 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 180 325 170 215 Total derivatives not designated as hedging instruments $ 741 $ 900 $ 550 $ 652 Gross amounts recognized $ 837 $ 1,036 $ 700 $ 794 Gross amounts offset (a) $ (524 ) $ (801 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 313 $ 235 $ 295 $ 196 2018 2017 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 $ 3 $ 4 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 3 6 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 10 $ 4 $ 10 Gross amounts recognized $ 6 $ 10 $ 4 $ 10 Gross amounts offset $ (4 ) $ (4 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 2 $ 6 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 8 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 4 13 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 21 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 2 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 2 $ — $ 5 Gross amounts recognized $ 6 $ 23 $ 6 $ 24 Gross amounts offset $ (6 ) $ (6 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 17 $ — $ 18 2018 2017 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 $ 1 $ 3 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 2 6 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 9 $ 2 $ 9 Gross amounts recognized $ 3 $ 9 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ 1 $ 7 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 6 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 2 — — Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 75 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 79 $ 31 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Total derivatives not designated as hedging instruments $ — $ — $ — $ 2 Gross amounts recognized $ 79 $ 31 $ 132 $ 36 Gross amounts offset $ (3 ) $ (3 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 76 $ 28 $ 129 $ 33 2018 2017 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 $ 2 $ 8 $ 5 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — — Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 9 $ 5 $ 8 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 1 $ — $ 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 1 $ — $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 559 $ 574 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 180 325 170 215 Total derivatives not designated as hedging instruments $ 739 $ 899 $ 549 $ 649 Gross amounts recognized $ 741 $ 909 $ 554 $ 660 Gross amounts offset (a) $ (508 ) $ (785 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 233 $ 124 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $277 million and $193 million at December 31, 2018 and 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $8 million and $11 million at December 31, 2018 and 2017 , respectively. Energy-related derivatives not designated as hedging instruments were immaterial for Alabama Power, Georgia Power, Mississippi Power, and Southern Power at December 31, 2018 and 2017 . At December 31, 2018 and 2017 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at 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 ) Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2017 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (34 ) $ (4 ) $ (7 ) $ (5 ) $ (4 ) Other regulatory assets, deferred (18 ) (3 ) (6 ) (2 ) — Other regulatory liabilities, current 7 1 — — 7 Other regulatory liabilities, deferred 1 — — — — Total energy-related derivative gains (losses) $ (44 ) $ (6 ) $ (13 ) $ (7 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $6 million at December 31, 2017 . For the years ended December 31, 2018 , 2017 , and 2016 , 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 2018 2017 2016 (in millions) Southern Company Energy-related derivatives $ 17 $ (47 ) $ 18 Interest rate derivatives (1 ) (2 ) (180 ) Foreign currency derivatives (78 ) 140 (58 ) Total $ (62 ) $ 91 $ (220 ) Southern Power Energy-related derivatives $ 10 $ (38 ) $ 14 Foreign currency derivatives (78 ) 140 (58 ) Total $ (68 ) $ 102 $ (44 ) Successor Predecessor Gain (Loss) Recognized in OCI on Derivative Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Southern Company Gas Energy-related derivatives $ 7 $ (9 ) $ 2 $ — Interest rate derivatives — — (5 ) (64 ) Total $ 7 $ (9 ) $ (3 ) $ (64 ) 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 years ended December 31, 2017 and 2016, there was no material ineffectiveness recorded in earnings for any registrant. Upon the adoption of ASU 2017-12, beginning in 2018, ineffectiveness was no longer separately measured and recorded in earnings. See Note 1 for additional information. The pre-tax effects of cash flow and fair value hedge accounting on income for the years ended December 31, 2018 , 2017 , and 2016 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2018 2017 2016 (in millions) Southern Company Total cost of natural gas $ 1,539 $ 1,601 $ 613 Gain (loss) on energy-related cash flow hedges (a) 2 (2 ) (1 ) Total depreciation and amortization 3,131 3,010 2,502 Gain (loss) on energy-related cash flow hedges (a) 7 (16 ) 2 Total interest expense, net of amounts capitalized (1,842 ) (1,694 ) (1,317 ) Gain (loss) on interest rate cash flow hedges (a) (21 ) (21 ) (18 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (23 ) (13 ) Gain (loss) on interest rate fair value hedges (b) (12 ) (22 ) (21 ) Total other income (expense), net 114 163 50 Gain (loss) on foreign currency cash flow hedges (a)(c) (60 ) 160 (82 ) Alabama Power Total interest expense, net of amounts capitalized $ (323 ) $ (305 ) $ (302 ) Gain (loss) on interest rate cash flow hedges (a) (6 ) (6 ) (6 ) Georgia Power Total interest expense, net of amounts capitalized $ (397 ) $ (419 ) $ (388 ) Gain (loss) on interest rate cash flow hedges (a) (4 ) (4 ) (4 ) Gain (loss) on interest rate fair value hedges (b) 2 (3 ) (1 ) Mississippi Power Total interest expense, net of amounts capitalized $ (76 ) $ (42 ) $ (74 ) Gain (loss) on interest rate cash flow hedges (a) (2 ) (2 ) 3 Southern Power Total depreciation and amortization $ 493 $ 503 $ 352 Gain (loss) on energy-related cash flow hedges (a) 7 (17 ) 2 Total interest expense, net of amounts capitalized (183 ) (191 ) (117 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (23 ) (13 ) Total other income (expense), net 23 1 6 Gain (loss) on foreign currency cash flow hedges (a)(c) (60 ) 159 (82 ) (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. Successor Predecessor Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 January 1, 2016 (in millions) (in millions) Southern Company Gas Total cost of natural gas $ 1,539 $ 1,601 $ 613 $ 755 Gain (loss) on energy-related cash flow hedges (*) 2 (2 ) (1 ) (1 ) (*) Amounts reflect gains or losses on cash flow hedges that were reclassified from AOCI into earnings. The pre-tax effects of cash flow hedge accounting on income for interest rate derivatives were immaterial for all other registrants for all years presented. At December 31, 2018 and 2017 , the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items At December 31, 2018 At December 31, 2017 At December 31, 2018 At December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (498 ) $ (746 ) $ 2 $ 3 Long-term debt (2,052 ) (2,553 ) 41 35 Georgia Power Securities due within one year $ (498 ) $ (746 ) $ 2 $ 3 Long-term debt — (498 ) — 1 The pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income for the years ended December 31, 2018 , 2017 , and 2016 for the applicable registrants were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 2016 (in millions) Southern Company Energy-related derivatives Natural gas revenues (*) $ (122 ) $ (80 ) $ 33 Cost of natural gas (6 ) (2 ) 3 Wholesale electric revenues 2 (4 ) 2 Total derivatives in non-designated hedging relationships $ (126 ) $ (86 ) $ 38 (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $5 million , $23 million , and $6 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively, as they are accounted for based on intrinsic value rather than fair value. Gain (Loss) Successor Predecessor Derivatives in Non-Designated Hedging Relationships Statements of Income Location For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 July 1, 2016 January 1, 2016 through (in millions) (in millions) Southern Company Gas Energy-related derivatives Natural gas revenues (*) $ (122 ) $ (80 ) $ 33 $ (1 ) Cost of natural gas (6 ) (2 ) 3 (62 ) Total derivatives in non-designated hedging relationships $ (128 ) $ (82 ) $ 36 $ (63 ) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $5 million and $23 million for the successor years ended December 31, 2018 and 2017 , respectively, $6 million for the successor period of July 1, 2016 through December 31, 2016 , and $3 million for the predecessor period of January 1, 2016 through June 30, 2016 , as they are accounted for based on intrinsic value rather than fair value. The pre-tax effects of energy-related derivatives and interest rate 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, 2018 , the registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the registrants with interest rate derivatives at December 31, 2018 , the fair value of interest rate derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, was immaterial. At December 31, 2018 , the fair value of energy-related derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, were immaterial for all registrants. The maximum potential collateral requirements arising from the credit-risk-related contingent features for the traditional electric operating companies and Southern Power include certain agreements that could require collateral in the event that one or more Southern Company power pool participants has a credit rating change to below investment grade. 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, 2018 , cash collateral posted in these accounts was immaterial. Southern Company Gas maintains accounts with brokers or the clearing houses of certain exchanges to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Southern Company Gas may be required to deposit cash into these accounts. At December 31, 2018 , cash collateral held on deposit in broker margin accounts was $277 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, 2018
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS Southern Company Merger with Southern Company Gas On July 1, 2016, Southern Company completed the Merger for a total purchase price of approximately $8.0 billion and Southern Company Gas became a wholly-owned, direct subsidiary of Southern Company. At the effective time of the Merger, each share of Southern Company Gas common stock, other than certain excluded shares, was converted into the right to receive $66 in cash, without interest. Also at the effective time of the Merger, all of the outstanding Southern Company Gas RSUs, restricted stock awards, non-employee director stock awards, stock options, and PSUs were either redeemed or converted into Southern Company RSUs. See Note 12 for additional information. The application of the acquisition method of accounting was pushed down to Southern Company Gas. The excess of the purchase price over the fair values of Southern Company Gas' assets and liabilities was recorded as goodwill, which represents a different basis of accounting from Southern Company Gas' historical basis prior to the Merger. The following table presents the final purchase price allocation: Southern Company Gas Successor Southern Company Gas Predecessor Southern Company Gas Purchase Price New Basis Old Basis Change in Basis (in millions) (in millions) Current assets $ 1,557 $ 1,474 $ 83 Property, plant, and equipment 10,108 10,148 (40 ) Goodwill 5,967 1,813 4,154 Other intangible assets 400 101 299 Regulatory assets 1,118 679 439 Other assets 229 273 (44 ) Current liabilities (2,201 ) (2,205 ) 4 Other liabilities (4,742 ) (4,600 ) (142 ) Long-term debt (4,261 ) (3,709 ) (552 ) Contingently redeemable noncontrolling interest (174 ) (41 ) (133 ) Total purchase price $ 8,001 $ 3,933 $ 4,068 Southern Company Gas' Results of Operations and Pro Forma Financial Information The results of operations for Southern Company Gas have been included in Southern Company's consolidated financial statements from the date of acquisition and consisted of operating revenues of $1.7 billion and net income of $114 million in 2016. The following summarized unaudited pro forma consolidated statement of earnings information assumes that the acquisition of Southern Company Gas was completed on January 1, 2015. The summarized unaudited pro forma consolidated statement of earnings information includes adjustments for (i) intercompany sales, (ii) amortization of intangible assets, (iii) adjustments to interest expense to reflect current interest rates on Southern Company Gas debt and additional interest expense associated with borrowings by Southern Company to fund the Merger, and (iv) the elimination of nonrecurring expenses associated with the Merger. 2016 Operating revenues (in millions) $ 21,791 Net income attributable to Southern Company (in millions) $ 2,591 Basic EPS $ 2.70 Diluted EPS $ 2.68 These unaudited pro forma results are for comparative purposes only and may not be indicative of the results that would have occurred had this acquisition been completed on January 1, 2015 or the results that would be attained in the future. Southern Company Acquisition of PowerSecure In May 2016, Southern Company acquired all of the outstanding stock of PowerSecure for $18.75 per common share in cash, resulting in an aggregate purchase price of $429 million . As a result, PowerSecure became a wholly-owned subsidiary of Southern Company. The acquisition of PowerSecure was accounted for using the acquisition method of accounting with the assets acquired and liabilities assumed recognized at fair value as of the acquisition date. The following table presents the final purchase price allocation: PowerSecure Purchase Price (in millions) Current assets $ 172 Property, plant, and equipment 46 Intangible assets 106 Goodwill 284 Other assets 4 Current liabilities (121 ) Long-term debt, including current portion (48 ) Deferred credits and other liabilities (14 ) Total purchase price $ 429 The results of operations for PowerSecure have been included in Southern Company's consolidated financial statements from the date of acquisition and are immaterial to the consolidated financial results of Southern Company. Pro forma results of operations have not been presented for the acquisition because the effects of the acquisition were immaterial to Southern Company's consolidated financial results for all periods presented. Southern Company's Sale of Gulf Power 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), subject to customary working capital adjustments. The assets and liabilities of Gulf Power are classified as assets held for sale and liabilities held for sale on Southern Company's balance sheet as of December 31, 2018. See " Assets Held for Sale " herein for additional information. Southern Power During 2018 and 2017 , Southern Power or one of its wholly-owned subsidiaries acquired or completed 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 the Year Ended December 31, 2018 During 2018 , Southern Power acquired and completed the project below and acquired the Wild Horse Mountain and Reading wind facilities discussed under " Construction Projects Completed and/or in Progress " below. Project Facility Resource Seller, Acquisition Date Approximate Nameplate Capacity ( MW ) Location Ownership Percentage Actual 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. Acquisitions During the Year Ended December 31, 2017 The following table presents Southern Power's acquisition activity for the year ended December 31, 2017. Project Facility Resource Seller, Acquisition Date Approximate Nameplate Capacity ( MW ) Location Ownership Percentage Actual COD PPA Contract Period Bethel Wind Invenergy Wind Global LLC, 276 Castro County, TX 100 % January 2017 12 years Cactus Flats (*) Wind RES America Developments, Inc., 148 Concho County, TX 100 % July 2018 12 years and 15 years (*) On July 31, 2017, Southern Power purchased 100% of the Cactus Flats facility. In August 2018, Southern Power closed on a tax equity partnership and owns 100% of the class B membership interests. Southern Power's aggregate purchase price for acquisitions during the year ended December 31, 2017 was $539 million . The fair values of the assets acquired and liabilities assumed were finalized in 2017 and recorded as follows: 2017 (in millions) Restricted cash $ 16 CWIP 534 Other assets 5 Accounts payable (16 ) Total purchase price $ 539 In 2017 , total revenues of $15 million and net income of $17 million , primarily as a result of PTCs, were recognized in the consolidated statements of income by Southern Power related to the 2017 acquisitions. The Bethel facility did not have operating revenues or activities prior to completion of construction and being placed in service, and the Cactus Flats facility was still under construction. Therefore, supplemental pro forma information as though the acquisitions occurred as of the beginning of 2017 is not meaningful and has been omitted. Construction Projects Completed and/or in Progress During 2018 , in accordance with its growth strategy, Southern Power started, continued, or completed construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $575 million and $640 million for the Plant Mankato expansion, Wild Horse Mountain, and Reading facilities. At December 31, 2018, construction costs included in CWIP related to these projects totaled $289 million , except for the Plant Mankato expansion which is classified as assets held for sale in the financial statements. The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Counterparties PPA Contract Period Construction Projects Completed During the Year Ended December 31, 2018 Cactus Flats (a) Wind 148 Concho County, TX July 2018 General Motors, LLC 12 years Projects Under Construction at December 31, 2018 Mankato expansion (b) Natural Gas 385 Mankato, MN Second quarter 2019 Northern States Power Company 20 years Wild Horse Mountain (c) Wind 100 Pushmataha County, OK Fourth quarter 2019 Arkansas Electric Cooperative 20 years Reading (d) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 Royal Caribbean Cruises LTD 12 years (a) In July 2017, Southern Power purchased 100% of the Cactus Flats facility. In August 2018, Southern Power closed on a tax equity partnership and now owns 100% of the class B membership interests. (b) In November 2018, Southern Power entered into an agreement to sell all of its equity interests in Plant Mankato, including this expansion currently under construction. See "Sales of Natural Gas Plants" below. (c) In May 2018, Southern Power purchased 100% of the Wild Horse Mountain facility. 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 August 2018, Southern Power purchased 100% of the membership interests of the Reading facility from the joint development arrangement with Renewable Energy Systems Americas, Inc. described below. 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. Development Projects During 2017, Southern Power purchased wind turbine equipment to be used for various development and construction projects. Any wind projects using this equipment and reaching commercial operation by the end of 2021 are expected to qualify for 80% PTCs. During 2016, Southern Power entered into a joint development agreement with Renewable Energy Systems Americas, Inc. (RES) to develop and construct wind projects. Concurrent with the agreement, Southern Power purchased wind turbine equipment from Siemens Wind Power, Inc. and Vestas-American Wind Technology, Inc. to be used for construction of these projects. Several wind projects using this equipment, as well as other purchased equipment, have successfully originated, directly or indirectly, from the partnership with RES and are expected to reach commercial operation before the end of 2020, thus qualifying for 100% PTCs. Southern Power continues to evaluate and refine the deployment of the wind turbine equipment to potential joint development and construction projects as well as the amount of MW capacity to be constructed. During the third quarter 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. Subsequent to December 31, 2018 and as part of management's continuous review of disposition options, approximately $53 million of this equipment is being marketed for sale and will be classified as held for sale. The ultimate outcome of these matters cannot be determined at this time. Sales of Renewable Facility Interests On May 22, 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 retains control of the limited partnership through its wholly-owned general partner, the sale was recorded as an equity transaction and Southern Power will continue to consolidate SP Solar in its financial statements. 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. On December 11, 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 . Since Southern Power retains control of SP Wind, it will continue to consolidate SP Wind in its financial statements. The tax equity investors together will generally receive 40% of the cash distributions from available cash and will receive a 99% allocation of tax attributes, including future PTCs. Sales of Natural Gas Plants On December 4, 2018, Southern Power completed the sale of all of its equity interests in the Florida Plants to NextEra Energy for $203 million . 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 November 5, 2018, Southern Power entered into an agreement with Northern States Power to sell all of its equity interests in Plant Mankato (including the 385 -MW expansion currently under construction) for an aggregate purchase price of approximately $650 million . The completion of the disposition is subject to the expansion unit reaching commercial operation as well as various other customary conditions to closing, including working capital and timing adjustments. The ultimate purchase price will decrease $66,667 per day for each day after June 1, 2019 that the expansion has not achieved commercial operation, not to exceed $15 million . This transaction is subject to FERC and state commission approvals and is expected to close in mid-2019. The assets and liabilities of Plant Mankato are classified as assets held for sale and liabilities held for sale on Southern Company's and Southern Power's balance sheet as of December 31, 2018. See " Assets Held for Sale " herein for additional information. The ultimate outcome of this matter cannot be determined at this time. Southern Company Gas See " Southern Company Merger with Southern Company Gas " herein for information regarding the Merger. Investment in SNG In 2016, Southern Company Gas, through a wholly-owned, indirect subsidiary, acquired a 50% equity interest in SNG from Kinder Morgan, Inc. for $1.4 billion . SNG owns a 7,000 -mile pipeline system connecting natural gas supply basins in Texas, Louisiana, Mississippi, and Alabama to markets in Louisiana, Mississippi, Alabama, Florida, Georgia, South Carolina, and Tennessee. The purchase price exceeded the underlying ownership interest in the net assets of SNG by approximately $700 million . This basis difference was attributable to goodwill and deferred tax assets. While the deferred tax assets will be amortized through deferred tax expense, the goodwill will not be amortized and is not required to be tested for impairment on an annual basis. In March 2017, Southern Company Gas made an additional $50 million contribution to maintain its 50% equity interest in SNG. See Note 7 under "Southern Company Gas" for additional information on this investment. Southern Company Gas' investment in SNG decreased by $104 million at December 31, 2017 related to 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. Sale of Pivotal Home Solutions On June 4, 2018, Southern Company Gas completed the stock sale of Pivotal Home Solutions to American Water Enterprises LLC for a total cash purchase price of $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. Sale of Elizabethtown Gas and Elkton Gas On July 1, 2018, a Southern Company Gas subsidiary, Pivotal Utility Holdings, completed the sales of the assets of two of its natural gas distribution utilities, Elizabethtown Gas and Elkton Gas, to South Jersey Industries, Inc. for a total cash purchase price of $1.7 billion , 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 On July 29, 2018, Southern Company Gas and its wholly-owned direct subsidiary, NUI Corporation, completed the stock sale of Pivotal Utility Holdings, which primarily consisted of Florida City Gas, to NextEra Energy for a total cash purchase price of $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. Assets Held for Sale As discussed previously, Southern Company and Southern Power each have assets and liabilities held for sale on their balance sheets at December 31, 2018 . Assets and liabilities held for sale have been classified separately on each company's balance sheet at the lower of carrying value or fair value less costs to sell at the time the criteria for held-for-sale classification were met. For assets and liabilities held for sale recorded at fair value on a nonrecurring basis, the fair value of assets held for sale is based primarily on unobservable inputs (Level 3), which includes the agreed upon sales prices in executed sales agreements. Upon classification as held for sale in May 2018 for the Florida Plants and November 2018 for Plant Mankato, Southern Power ceased recognizing depreciation on the property, plant, and equipment to be sold. The Florida Plants sale was completed on December 4, 2018. Since the depreciation of the assets sold in the Gulf Power transaction continued to be reflected in customer rates through the closing date and was reflected in the carryover basis of the assets when sold, Southern Company continued to record depreciation on those assets through the date the transaction closed. Likewise, since the depreciation of the assets sold in the Elizabethtown Gas, Elkton Gas, and Florida City Gas transactions continued to be reflected in customer rates and was reflected in the carryover basis of the assets when sold, Southern Company Gas continued to record depreciation on those assets through the respective date that each transaction closed. The following table provides Southern Company's and Southern Power's major classes of assets and liabilities classified as held for sale at December 31, 2018 : Southern Company Southern Power (in millions) Assets Held for Sale: Current assets $ 393 $ 8 Total property, plant, and equipment 4,623 576 Other non-current assets 727 — Total Assets Held for Sale $ 5,743 $ 584 Liabilities Held for Sale: Current liabilities $ 425 $ 15 Long-term debt 1,286 — Accumulated deferred income taxes 618 — Other non-current liabilities 932 — Total Liabilities Held for Sale $ 3,261 $ 15 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 the Florida Plants represent individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax income for these components for the years ended December 31, 2018 , 2017 , and 2016 are presented below: 2018 2017 2016 (in millions) Earnings (loss) before income taxes: Gulf Power $ 140 $ 229 $ 231 Southern Power's Florida Plants (*) $ 49 $ 37 $ 37 (*) Earnings before income taxes for the Florida Plants in 2018 represents the period from January 1, 2018 to December 4, 2018 (the divestiture date).

Segment and Related Information

Segment and Related Information (Notes)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
SEGMENT AND RELATED INFORMATION	SEGMENT AND RELATED INFORMATION Southern Company The primary businesses of the Southern Company system are electricity sales by the traditional electric operating companies and Southern Power and the distribution of natural gas by Southern Company Gas. The traditional electric operating companies – Alabama Power, Georgia Power, Gulf Power (through December 31, 2018), and Mississippi Power – are vertically integrated utilities providing electric service in four Southeastern states. On January 1, 2019, Southern Company completed its sale of Gulf Power 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 its natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. In July 2018, Southern Company Gas completed sales of three of its natural gas distribution utilities. See Note 15 for additional information regarding disposition activities. 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 $435 million , $392 million , and $419 million in 2018 , 2017 , and 2016 , respectively. Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies and Southern Power were $32 million and $119 million , respectively, in 2018 , $23 million and $119 million , respectively, in 2017 , and $11 million and $17 million , respectively, in 2016 . The "All Other" column includes the Southern Company parent entity, which does not allocate operating expenses to business segments. Also, this category includes segments below the quantitative threshold for separate disclosure. These segments include providing energy technologies and services to electric utilities and large industrial, commercial, institutional, and municipal customers, as well as investments in telecommunications and leveraged lease projects. All other inter-segment revenues are not material. Financial data for business segments and products and services for the years ended December 31, 2018 , 2017 , and 2016 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) 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)(c)(d) 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)(e)(f) (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 2016 Operating revenues $ 16,803 $ 1,577 $ (439 ) $ 17,941 $ 1,652 $ 463 $ (160 ) $ 19,896 Depreciation and amortization 1,881 352 — 2,233 238 31 — 2,502 Interest income 6 7 — 13 2 20 (15 ) 20 Earnings from equity method investments 2 — — 2 60 (3 ) — 59 Interest expense 814 117 — 931 81 317 (12 ) 1,317 Income taxes (benefit) 1,286 (195 ) — 1,091 76 (216 ) — 951 Segment net income (loss) (a)(b) 2,233 338 — 2,571 114 (230 ) (7 ) 2,448 Goodwill — 2 — 2 5,967 282 — 6,251 Total assets 72,141 15,169 (316 ) 86,994 21,853 2,474 (1,624 ) 109,697 Gross property additions 4,852 2,114 — 6,966 618 41 (1 ) 7,624 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $1.1 billion ( $722 million after tax) in 2018 , $3.4 billion ( $2.4 billion after tax) in 2017 , and $428 million ( $264 million after tax) in 2016 . 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 pre-tax impairment charges of $156 million ( $117 million after tax) in 2018. See Note 15 under " Southern Power – Development Projects " and " – Sales of Natural Gas Plants " for additional information. (d) 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. (e) Segment net income (loss) for the traditional electric operating companies includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) in 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. (f) 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) 2018 $ 15,222 $ 2,516 $ 833 $ 18,571 2017 15,330 2,426 784 18,540 2016 15,234 1,926 781 17,941 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2018 $ 3,155 $ 568 $ 186 $ 3,909 2017 3,024 860 36 3,920 2016 1,266 354 32 1,652 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 new Chief Operating Decision Maker reviews operating results and has reclassified prior years' 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 5 and 7 for additional information. Wholesale gas services provides natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. Additionally, wholesale gas services engages in natural gas storage and gas pipeline arbitrage and related activities. Gas marketing services provides natural gas marketing to end-use customers primarily in Georgia and Illinois through SouthStar. On June 4, 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 the storage and fuels operations, which was formerly included in gas midstream operations, and the other subsidiaries that fall below the quantitative threshold for separate disclosure. After the Merger, Southern Company Gas changed the segment performance measure to net income, which is utilized by its parent company. In order to properly assess net income by segment, Southern Company Gas executed various intercompany note agreements to revise interest charges to its segments. Since such agreements did not exist in the predecessor period, Southern Company Gas is unable to provide the comparable net income for that period. Financial data for business segments for the successor years ended December 31, 2018 and 2017 , the successor period of July 1, 2016 through December 31, 2016, and the predecessor period of January 1, 2016 through June 30, 2016 were as follows: Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other Eliminations Consolidated (in millions) Successor – Year ended December 31, 2018 Operating revenues $ 3,186 $ 32 $ 144 $ 568 $ 3,930 $ 55 $ (76 ) $ 3,909 Depreciation and 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 1,429 32 — 6 1,467 54 — 1,521 Successor – Total assets 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) 21,448 Successor – Year ended December 31, 2017 Operating revenues $ 3,207 $ 17 $ 6 $ 860 $ 4,090 $ 64 $ (234 ) $ 3,920 Depreciation and 391 2 2 62 457 44 — 501 Operating income (loss) 645 10 (51 ) 113 717 (57 ) — 660 Earnings from equity method — 103 — — 103 3 — 106 Interest expense (153 ) (26 ) (7 ) (5 ) (191 ) (9 ) — (200 ) Income taxes (e) 178 109 — 24 311 56 — 367 Segment net income (loss) (e) 353 (22 ) (57 ) 84 358 (115 ) — 243 Gross property additions 1,330 117 1 9 1,457 51 — 1,508 Successor – Total assets 19,358 1,699 1,096 2,147 24,300 12,726 (14,039 ) 22,987 Successor – July 1, 2016 through December 31, 2016 Operating revenues $ 1,342 $ 3 $ 24 $ 354 $ 1,723 $ 31 $ (102 ) $ 1,652 Depreciation and 185 — 1 35 221 17 — 238 Operating income (loss) 225 1 (2 ) 27 251 (52 ) — 199 Earnings from equity method — 58 — — 58 2 — 60 Interest expense (105 ) (10 ) (3 ) (1 ) (119 ) 38 — (81 ) Income taxes (benefit) 51 21 (3 ) 7 76 — — 76 Segment net income (loss) 77 29 — 19 125 (11 ) — 114 Gross property additions 561 51 1 5 618 14 — 632 Successor – Total assets 19,453 1,659 1,127 2,084 24,323 11,697 (14,167 ) 21,853 Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other Eliminations Consolidated (in millions) Predecessor – January 1, 2016 through June 30, 2016 Operating revenues $ 1,575 $ 3 $ (32 ) $ 435 $ 1,981 $ 26 $ (102 ) $ 1,905 Depreciation and 178 — 1 11 190 16 — 206 Operating income (loss) 353 3 (69 ) 109 396 (73 ) — 323 EBIT 353 3 (68 ) 109 397 (69 ) — 328 Gross property additions 484 40 1 4 529 19 — 548 (a) Operating revenues for the three gas distribution operations dispositions were $244 million , $399 million , and $168 million for the successor years ended December 31, 2018 and 2017 and the successor period of July 1, 2016 through December 31, 2016, respectively, and $215 million for the predecessor period ended June 30, 2016. 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) for the year ended December 31, 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 for the year ended December 31, 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) Successor – Year Ended $ 6,955 $ 451 $ 7,406 $ 7,262 $ 144 Successor – Year Ended 6,152 481 6,633 6,627 6 Successor – July 1, 2016 through 5,807 333 6,140 6,116 24 Predecessor – January 1, 2016 through 2,500 143 2,643 2,675 (32 ) (d) Operating revenues for the gas marketing services disposition were $55 million , $129 million , and $56 million for the successor years ended December 31, 2018 and 2017 and the successor period of July 1, 2016 through December 31, 2016, respectively, and $64 million for the predecessor period ended June 30, 2016 See Note 15 under " Southern Company Gas " for additional information. (e) 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, 2018
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 2018 and 2017 . Each registrant's business is influenced by seasonal weather conditions. 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 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 pre-tax and $(76) million after tax, $353 million pre-tax and $40 million after tax, and $(27) million pre-tax and $(15) million after tax, respectively. See Note 15 under " Southern Company Gas " for additional information. Quarter Ended Southern Company (a)(b)(c) Alabama Power Georgia Power Mississippi Power (a)(b) Southern Power (b) Southern Company Gas (b) (in millions) March 2017 Operating Revenues $ 5,771 $ 1,382 $ 1,832 $ 272 $ 450 $ 1,560 Operating Income (Loss) 1,252 361 483 (64 ) 65 389 Net Income (Loss) 665 174 260 (20 ) 66 239 Net Income (Loss) Attributable to Registrant 658 174 260 (20 ) 70 239 June 2017 Operating Revenues $ 5,430 $ 1,484 $ 2,048 $ 303 $ 529 $ 716 Operating Income (Loss) (1,649 ) 440 621 (2,956 ) 112 95 Net Income (Loss) (1,348 ) 230 347 (2,054 ) 104 49 Net Income (Loss) Attributable to Registrant (1,381 ) 230 347 (2,054 ) 82 49 September 2017 Operating Revenues $ 6,201 $ 1,740 $ 2,546 $ 341 $ 618 $ 565 Operating Income (Loss) 1,991 601 1,017 49 159 67 Net Income (Loss) 1,109 325 580 40 154 15 Net Income (Loss) Attributable to Registrant 1,069 325 580 40 124 15 December 2017 Operating Revenues $ 5,629 $ 1,433 $ 1,884 $ 271 $ 478 $ 1,079 Operating Income (Loss) 739 255 452 (180 ) 32 109 Net Income (Loss) 500 119 227 (556 ) 793 (60 ) Net Income (Loss) Attributable to Registrant 496 119 227 (556 ) 795 (60 ) (a) As a result of revisions to the cost estimate for the Kemper IGCC and the project's June 2017 suspension, Mississippi Power recorded total pre-tax charges to income related to the Kemper IGCC of $108 million ( $67 million after tax) in the first quarter 2017, $3.0 billion ( $2.1 billion after tax) in the second quarter 2017, $34 million ( $21 million after tax) in the third quarter 2017, and $208 million ( $185 million after tax) in the fourth quarter 2017. See Note 2 under " Mississippi Power – Kemper County Energy Facility " for additional information. (b) As a result of the Tax Reform Legislation, the Southern Company system recorded a total income tax benefit of $264 million in the fourth quarter 2017, comprised primarily of income tax expense of $372 million recorded at Mississippi Power, income tax benefit of $743 million recorded at Southern Power, and income tax expense of $93 million recorded at Southern Company Gas. See Note 10 for additional information. (c) Gulf Power recorded a pre-tax charge of $33 million ( $20 million after tax) for the write-down of its ownership in Plant Scherer Unit 3 in the first quarter 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. Southern Company The table below provides quarterly per share financial information for Southern Company common stock for 2018 and 2017 . Per Common Share Basic Earnings Diluted Earnings Quarter Ended Dividends March 2018 $ 0.93 $ 0.92 $ 0.5800 June 2018 (0.15 ) (0.15 ) 0.6000 September 2018 1.14 1.13 0.6000 December 2018 0.27 0.27 0.6000 March 2017 $ 0.66 $ 0.66 $ 0.5600 June 2017 (1.38 ) (1.37 ) 0.5800 September 2017 1.07 1.06 0.5800 December 2017 0.49 0.49 0.5800

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 , AND 2016 (Stated in Millions of Dollars) Additions Description Balance at Beginning of Period Charged to Income Charged to Other Accounts Acquisitions Deductions Reclassified to Held for Sale (c) Balance at End of Period Provision for uncollectible accounts (a) 2018 $ 44 $ 69 $ (1 ) $ — $ 61 $ 1 $ 50 2017 43 56 — — 55 — 44 2016 13 40 (1 ) 41 50 — 43 Tax valuation allowance (net state) (b) 2018 $ 148 $ (38 ) $ — $ — $ 10 $ — $ 100 2017 22 126 — — — — 148 2016 2 — — 20 — — 22 (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's Sale of Gulf Power " 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, 2018 , 2017 , AND 2016 (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 2018 $ 9 $ 13 $ — $ 12 $ 10 2017 10 10 — 11 9 2016 10 11 — 11 10 (*) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off. GEORGIA POWER COMPANY SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2018 , 2017 , AND 2016 (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) 2018 $ 3 $ 11 $ — $ 12 $ 2 2017 3 11 — 11 3 2016 2 15 — 14 3 Tax valuation allowance (net state) (b) 2018 $ — $ 39 $ — $ 6 $ 33 2017 — — — — — 2016 — — — — — (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, as a result of lower 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, 2018 , 2017 , AND 2016 (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) 2018 $ 1 $ 1 $ — $ 1 $ 1 2017 — 2 — 1 1 2016 — 1 — 1 — Tax valuation allowance (net state) (b) 2018 $ 124 $ (92 ) $ — $ — $ 32 2017 — 124 — — 124 2016 — — — — — (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. 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, 2018 , 2017 , AND 2016 (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) 2018 $ 10 $ 12 $ — $ — $ 22 2017 — 10 — — 10 2016 — — — — — SOUTHERN COMPANY GAS AND SUBSIDIARY COMPANIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS FOR THE SUCCESSOR PERIODS OF JULY 1, 2016 THROUGH DECEMBER 31, 2016 AND THE YEARS ENDED DECEMBER 31, 2018 AND 2017 AND THE PREDECESSOR PERIOD OF JANUARY 1, 2016 THROUGH JUNE 30, 2016 (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 Successor – December 31, 2018 Provision for uncollectible accounts (*) $ 28 $ 33 $ (1 ) $ 30 $ 30 Income tax valuation allowance (net state) 11 1 — — 12 Successor – December 31, 2017 Provision for uncollectible accounts (*) $ 27 $ 28 $ — $ 27 $ 28 Income tax valuation allowance (net state) 19 — — 8 11 Successor – December 31, 2016 Provision for uncollectible accounts (*) $ 38 $ 9 $ (1 ) $ 19 $ 27 Income tax valuation allowance (net state) 19 — — — 19 Predecessor – June 30, 2016 Provision for uncollectible accounts (*) $ 29 $ 16 $ 2 $ 9 $ 38 Income tax valuation allowance (net state) 19 — — — 19 (*) Deductions represent write-offs of accounts considered to be uncollectible, less recoveries of amounts previously written off.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
General	General Southern Company is the parent company of the traditional electric operating companies, Southern Power, Southern Company Gas (as of July 1, 2016), SCS, Southern Linc, Southern Holdings, Southern Nuclear, PowerSecure (as of May 9, 2016), and other direct and indirect subsidiaries. The traditional electric operating companies – Alabama Power, Georgia Power, Gulf Power (through December 31, 2018), and Mississippi Power – are vertically integrated utilities providing electric service in four Southeastern states. On January 1, 2019, Southern Company completed the sale of Gulf Power 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. On May 22, 2018, Southern Power sold a noncontrolling 33% equity interest in SP Solar, a limited partnership indirectly owning substantially all of Southern Power's solar facilities, and, on December 11, 2018, Southern Power sold a noncontrolling tax equity interest in SP Wind, a holding company owning a portfolio of eight operating wind facilities. On November 5, 2018, Southern Power entered into an agreement to sell all of its equity interests in Plant Mankato (including the 385 -MW expansion currently under construction). On December 4, 2018, Southern Power sold all of its equity interests in Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) to NextEra Energy. Southern Company Gas distributes natural gas through natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. In July 2018, Southern Company Gas completed sales of three of its natural gas distribution utilities (Elizabethtown Gas (New Jersey), Florida City Gas, and Elkton Gas (Maryland)). The remaining natural gas distribution utilities include Nicor Gas (Illinois), Atlanta Gas Light (Georgia), Virginia Natural Gas, and Chattanooga Gas (Tennessee). In June 2018, Southern Company Gas also completed the sale of Pivotal Home Solutions, which provided home equipment protection products and 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 investments in leveraged leases and for other electric services. 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 is a provider of energy solutions, including distributed energy infrastructure, energy efficiency products and services, and utility infrastructure services, to customers. See Note 15 for additional information regarding disposition activities. 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 control and for VIEs where a registrant has an equity investment but is not the primary beneficiary. Southern Power has consolidated renewable generation projects that are partially funded by tax equity investors. The related contractual provisions represent profit-sharing arrangements because the allocations of cash distributions and tax benefits are not based on fixed ownership percentages. Therefore, the noncontrolling interest is accounted for under a balance sheet approach utilizing the 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 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.
Consolidation	Pursuant to the Merger, Southern Company pushed down the application of the acquisition method of accounting to the financial statements of Southern Company Gas such that the assets and liabilities are recorded at their respective fair values, and goodwill was established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout Southern Company Gas' financial statements and the combined notes to the financial statements, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor." Certain predecessor period data presented in Southern Company Gas' financial statements has been modified or reclassified to conform to the presentation used by Southern Company. Changes to Southern Company Gas' statements of income include classifying operating revenues as natural gas revenues and other revenues, as well as classifying cost of goods sold as cost of natural gas and cost of other sales and presenting interest expense and AFUDC on a gross basis. Changes to Southern Company Gas' statements of cash flows include revised financial statement line item descriptions to align with the new balance sheet descriptions and expanded line items within each category of cash flow activity.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards Revenue In 2014, the FASB issued ASC 606, Revenue from Contracts with Customers (ASC 606), replacing the existing accounting standard and industry-specific guidance for revenue recognition with a five-step model for recognizing and measuring revenue from contracts with customers. The underlying principle of the standard is to recognize revenue to depict the transfer of goods or services to customers at the amount expected to be collected. ASC 606 became effective on January 1, 2018 and the registrants adopted it using the modified retrospective method applied to open contracts and only to the version of contracts in effect as of January 1, 2018. In accordance with the modified retrospective method, the registrants' previously issued financial statements have not been restated to comply with ASC 606 and the registrants did not have a cumulative-effect adjustment to retained earnings. The adoption of ASC 606 had no significant impact on the timing of revenue recognition compared to previously reported results; however, it requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows arising from contracts with customers, which are included herein and in Note 4 . ASC 606 provided additional clarity on financial statement presentation that resulted in reclassifications into other revenues and other operations and maintenance from other income/(expense), net at Alabama Power and Georgia Power primarily related to certain unregulated sales of products and services. In addition, contract assets related to certain fixed retail revenues at Georgia Power and Southern Company's unregulated distributed generation business have been reclassified from unbilled revenue in accordance with the guidance in ASC 606. These reclassifications did not affect the timing or amount of revenues recognized or cash flows. ASC 606 also provided additional guidance on revenue recognized over time, resulting in a change in the timing of revenue recognized from guaranteed and fixed billing arrangements at Southern Company Gas. The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Year Ended December 31, 2018 Statements of Income As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Natural gas revenues $ 3,854 $ 3,852 $ 2 Other revenues 1,239 1,234 5 Other operations and maintenance 5,889 5,830 59 Operating Income 4,191 4,243 (52 ) Other income (expense), net 114 60 54 Earnings Before Income Taxes 2,749 2,747 2 Income taxes 449 448 1 Consolidated Net Income 2,300 2,299 1 Consolidated Net Income Attributable to Southern Company 2,226 2,225 1 Alabama Power Other revenues $ 267 $ 230 $ 37 Other operations and maintenance 1,669 1,625 44 Taxes other than income taxes 389 388 1 Operating Income 1,477 1,485 (8 ) Other income (expense), net 20 12 8 Georgia Power Other revenues $ 481 $ 387 $ 94 Other operations and maintenance 1,860 1,772 88 Operating Income 1,289 1,283 6 Other income (expense), net 115 121 (6 ) Southern Company Gas Natural gas revenues $ 3,874 $ 3,872 $ 2 Operating Income 915 913 2 Earnings Before Income Taxes 836 834 2 Income taxes 464 463 1 Net Income 372 371 1 For the Year Ended December 31, 2018 Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 2,300 $ 2,299 $ 1 Changes in certain current assets and liabilities: Receivables (426 ) (472 ) 46 Other current assets (127 ) (81 ) (46 ) Accrued taxes 267 268 (1 ) Other current liabilities 63 61 2 Georgia Power Changes in certain current assets and liabilities: Receivables $ 8 $ 1 $ 7 Other current assets (43 ) (36 ) (7 ) Southern Company Gas Net income $ 372 $ 371 $ 1 Changes in certain current assets and liabilities: Accrued taxes 10 11 (1 ) Other current liabilities (22 ) (24 ) 2 At December 31, 2018 Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 654 $ 728 $ (74 ) Other accounts and notes receivable 813 814 (1 ) Other current assets 162 87 75 Accrued taxes 656 655 1 Other current liabilities 852 854 (2 ) Total Stockholders' Equity 29,039 29,038 1 Georgia Power Unbilled revenues $ 208 $ 243 $ (35 ) Other accounts and notes receivable 80 81 (1 ) Other current assets 70 34 36 Southern Company Gas Accrued income taxes $ 66 $ 65 $ 1 Other current liabilities 130 132 (2 ) Common Stockholder's Equity 8,570 8,569 1 Other In 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18). ASU 2016-18 eliminates the need to reflect transfers between cash and restricted cash in operating, investing, and financing activities in the statements of cash flows. In addition, the net change in cash and cash equivalents during the period includes amounts generally described as restricted cash or restricted cash equivalents. The registrants adopted ASU 2016-18 retrospectively effective January 1, 2018. Southern Company, Southern Power, and Southern Company Gas have restated prior periods in the statements of cash flows by immaterial amounts. The change in restricted cash in the statements of cash flows was previously disclosed in operating activities for Southern Company and Southern Company Gas and in investing activities for Southern Company and Southern Power. See " Restricted Cash " herein for additional information. In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 removes the requirement to compare the implied fair value of goodwill with the carrying amount as part of Step 2 of the goodwill impairment test. Under the new standard, the goodwill impairment loss will be measured as the excess of a reporting unit's carrying amount over its fair value, not exceeding the total amount of goodwill allocated to that reporting unit, which may increase the frequency of goodwill impairment charges if a future goodwill impairment test does not pass the Step 1 evaluation. ASU 2017-04 is effective prospectively for periods beginning on or after December 15, 2019, with early adoption permitted. The registrants adopted ASU 2017-04 effective January 1, 2018 with no impact on their respective financial statements. In March 2017, the FASB issued ASU No. 2017-07, Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (ASU 2017-07). ASU 2017-07 requires that an employer report the service cost component in the same line item or items as other compensation costs and requires the other components of net periodic pension and postretirement benefit costs to be separately presented in the statements of income outside of income from operations. Additionally, only the service cost component is eligible for capitalization, when applicable. The registrants adopted ASU 2017-07 effective January 1, 2018 with no material impact on their respective financial statements. ASU 2017-07 has been applied retrospectively, with the service cost component of net periodic benefit costs included in operations and maintenance expenses and all other components of net periodic benefit costs included in other income (expense), net in the statements of income for all periods presented for Southern Company, the traditional electric operating companies, and Southern Company Gas. The impacted registrants used the practical expedient provided by ASU 2017-07, which permits an employer to use the amounts disclosed in its retirement benefits note for prior comparative periods as the estimation basis for applying the retrospective presentation requirements to those periods. The amounts of the other components of net periodic benefit costs reclassified for the prior periods are presented in Note 11 . The presentation changes resulted in a decrease in operating income and an increase in other income for the years ended December 31, 2017 and 2016 for each of the impacted registrants. Since Southern Power did not participate in the qualified pension and postretirement benefit plans until December 2017, no retrospective presentation of Southern Power's net periodic benefit costs is required. The requirement to limit capitalization to the service cost component of net periodic benefit costs has been applied on a prospective basis from the date of adoption for all registrants. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12). ASU 2017-12 makes more financial and non-financial hedging strategies eligible for hedge accounting, amends the related presentation and disclosure requirements, and simplifies hedge effectiveness assessment requirements. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The registrants adopted ASU 2017-12 effective January 1, 2018 with no material impact on their respective financial statements. See Note 14 for disclosures required by ASU 2017-12. On February 14, 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (ASU 2018-02) to address the application of ASC 740, Income Taxes (ASC 740) to certain provisions of the Tax Reform Legislation. ASU 2018-02 specifically addresses the ASC 740 requirement that the effect of a change in tax laws or rates on deferred tax assets and liabilities be included in income from continuing operations, even when the tax effects were initially recognized directly in OCI at the previous rate, which strands the income tax rate differential in accumulated OCI. The amendments in ASU 2018-02 allow a reclassification from accumulated OCI to retained earnings for stranded tax effects resulting from the Tax Reform Legislation. The registrants adopted ASU 2018-02 effective January 1, 2018 with no material impact on their respective financial statements. On August 28, 2018, the FASB issued ASU No. 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General (Topic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans (ASU 2018-14). ASU 2018-14 amends ASC 715 to add, remove, and clarify disclosure requirements related to defined benefit pension and other postretirement plans. The registrants adopted ASU 2018-14 effective December 31, 2018 with no material impact on their respective financial statements. See Note 11 for disclosures required by ASU 2018-14.
Affiliate Transactions	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 power pool transactions. These costs are primarily included in other operations and maintenance expenses or capitalized to property, plant, and equipment.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities The traditional electric operating companies and 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 had no impact on the timing or amount of revenue recognized under previous guidance. See " Recently Adopted Accounting Standards – Revenue " herein and 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. The timing of revenue recognition was not affected by the adoption of ASC 606. 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, and, prior to its sale, Elkton Gas; and • Revenue true-up adjustment – included within the provisions of the Georgia Rate Adjustment Mechanism (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, 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 17.3% of Mississippi Power 's total operating revenues in 2018 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 and Southern Company Gas are amortized over the average lives of the related property, with such amortization normally applied as a credit to reduce depreciation in the statements of income. 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 2018 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. Southern Company Gas is taxed on its gas revenues by various governmental authorities, but is allowed to recover these taxes from its customers. Revenue taxes imposed on the natural gas distribution utilities are recorded at the amount charged to customers, which may include a small administrative fee, as operating revenues, and the related taxes imposed on Southern Company Gas are recorded as operating expenses on the statements of income.
Allowance for Funds Used During Construction and Interest Capitalized	Allowance for Funds Used During Construction and Interest Capitalized The traditional electric operating companies and certain of the natural gas distribution utilities (Atlanta Gas Light, Chattanooga Gas, and Nicor Gas) 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 the construction of new facilities at Southern Power and new facilities not included in the traditional electric operating companies' and Southern Company Gas' regulated rates is capitalized in accordance with standard interest capitalization requirements.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The registrants evaluate long-lived assets and finite-lived intangible assets for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. The determination of whether an impairment has occurred is based on either a specific regulatory disallowance, a sales transaction price that is less than the asset group's carrying value, or an estimate of undiscounted future cash flows attributable to the asset group, as compared with the carrying value of the assets. If an impairment has occurred, the amount of the impairment recognized is determined by either the amount of regulatory disallowance or by estimating the fair value of the assets and recording a loss if the carrying value is greater than the fair value. For assets identified as held for sale, the carrying value is compared to the estimated fair value less the cost to sell in order to determine if an impairment loss is required. Until the assets are disposed of, their estimated fair value is re-evaluated when circumstances or events change.
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. See Note 15 under " Southern Company Merger with Southern Company Gas " and " Southern Company Acquisition of PowerSecure " for additional information. Goodwill is not amortized, but is subject to an annual impairment test during the fourth quarter of each year, or more frequently if impairment indicators arise.
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. Historically, contingent consideration primarily relates to fixed amounts due to the seller once an acquired construction project is placed in service. For contingent consideration with variable payments, management fair values the arrangement with any changes recorded in the statements of income.
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 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 The registrants adopted ASU 2016-18 as of January 1, 2018. See " Recently Adopted Accounting Standards – Other " herein for additional information. At December 31, 2018 , Georgia Power had restricted cash related to the redemption of pollution control revenue bonds, which were redeemed subsequent to December 31, 2018 . See Note 8 under " Long-term Debt – Pollution Control Revenue Bonds " for additional information. At December 31, 2017 , Southern Power had restricted cash primarily related to certain acquisitions and construction projects. At December 31, 2018 and 2017 , Southern Company Gas had restricted cash held as collateral for worker's compensation, life insurance, and long-term disability insurance.
Storm Damage Reserves and Environmental Remediation Recovery	Storm Damage Reserves Each traditional electric operating company maintains a reserve to cover or is allowed to defer and recover the cost of damages from major storms to its transmission and distribution lines and, for Mississippi Power, the cost of uninsured damages to its generation facilities and other property.
Leveraged Leases	Leveraged Leases 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. 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 to the Southern Holdings subsidiary beginning in June 2018. As a result of operational improvements in 2018, the 2018 lease payments were paid in full. However, operational issues 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 operational challenges may also impact the expected residual value of the assets at the end of the lease term in 2047. 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 would result in a reduction in net income of approximately $86 million after tax based on the lease receivable balance at December 31, 2018 . Southern Company has evaluated the recoverability of the lease receivable and the expected residual value of the generation assets at the end of the lease under various scenarios and has concluded that its investment in the leveraged lease is not impaired at December 31, 2018 . 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.
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, 2018 , the Nicor Gas LIFO inventory balance was $165 million . Based on the average cost of gas purchased in December 2018 , the estimated replacement cost of Nicor Gas' inventory at December 31, 2018 was $409 million . During 2018 , Nicor Gas did not liquidate any LIFO-based inventory. Southern Company Gas' gas marketing services, wholesale gas services, and all other segments record inventory at LOCOM, with cost determined on a WACOG basis. For these segments, Southern Company Gas evaluates the weighted average cost of its natural gas inventories against market prices to determine whether any declines in market prices below the WACOG are other than temporary.
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, 2018 and 2017 , the required collateral in the event of a credit rating downgrade was $30 million and $8 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 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, 2018 , the top 20 counterparties represented 48% , or $298 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 15 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 and 2016, ineffectiveness arising from cash flow hedges was recognized in net income. Upon the adoption of ASU 2017-12 in 2018, ineffectiveness is no longer separately measured and recorded in earnings. See " Recently Adopted Accounting Standards " herein for additional information. 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, 2018 . 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. 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. 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. The registrants adopted ASU 2017-12 as of January 1, 2018. See Note 1 under " Recently Adopted Accounting Standards – Other " 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.
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 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 – Other Long-Term Debt – Alabama Power " 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, 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 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, 2016 $ 4,514 $ 1,533 $ 2,532 $ 179 $ 64 Liabilities incurred 16 — 4 — 6 Liabilities settled (177 ) (26 ) (120 ) (23 ) — Accretion 179 77 89 5 4 Cash flow revisions 292 125 133 13 4 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 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. As the level of work becomes more defined in the next 12 months, it is likely that these cost estimates will change and the change could be material. 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. 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. 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's Sale of Gulf Power " and " Assets Held for Sale " for additional information. In 2017 , Alabama Power's and Georgia Power's cash flow revisions were primarily related to changes in closure strategy for ash ponds and landfills. Georgia Power's cash flow revisions in 2017 also related to changes in closure strategy for gypsum cells. Mississippi Power's cash flow revisions in 2017 primarily related to a revision in the closure date of its lignite mine. The liabilities settled in 2017 for Alabama Power, Georgia Power, and Mississippi Power were primarily related to ash pond closure activity. The cost estimates for AROs related to the CCR Rule are based on information at December 31, 2018 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 requirements for closure. The traditional electric operating companies expect to continue to periodically update their ARO cost estimates, which could increase further, as additional information becomes available. 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, 2018 and 2017 , approximately $27 million and $76 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 $28 million and $77 million at December 31, 2018 and 2017 , 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, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2017: Equity securities $ 1,059 $ 644 $ 415 Debt securities 725 223 502 Other securities 47 35 12 Total investment securities in the Funds $ 1,831 $ 902 $ 929 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 reinvested interest and dividends and excluding the Funds' expenses, for 2018 , 2017 , and 2016 are shown in the table below. The fair value increases (decreases) included unrealized gains (losses) on securities held in the Funds at each of December 31, 2018 , 2017 , and 2016 , which are also shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2018 $ (67 ) $ (38 ) $ (29 ) 2017 233 125 108 2016 114 76 38 Unrealized gains (losses) At December 31, 2018 $ (183 ) $ (96 ) $ (87 ) At December 31, 2017 181 98 83 At December 31, 2016 48 34 14 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 $17 million and $18 million at December 31, 2018 and 2017 , 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, 2018 and 2017 , the accumulated provisions for the external decommissioning trust funds were as follows: 2018 2017 (in millions) Alabama Power Plant Farley $ 846 $ 902 Georgia Power Plant Hatch $ 547 $ 583 Plant Vogtle Units 1 and 2 326 346 Total $ 873 $ 929 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, 2018 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 2012. Significant assumptions used to determine these costs for ratemaking were an estimated inflation rate of 4.5% and 2.4% for Alabama Power and Georgia Power, respectively, and an estimated trust earnings rate of 7.0% and 4.4% 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 categorized as Level 3 under Fair Value Measurements that are not traded in the open market. The fair value of these investments has been determined based on market factors including comparable multiples and the expectations regarding cash flows and business plan executions.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of specific impacts of applying ASC 606 to revenues from contracts with customers	The specific impacts of applying ASC 606 to revenues from contracts with customers on the financial statements of Southern Company, Alabama Power, Georgia Power, and Southern Company Gas compared to previously recognized guidance is shown below. For the Year Ended December 31, 2018 Statements of Income As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Natural gas revenues $ 3,854 $ 3,852 $ 2 Other revenues 1,239 1,234 5 Other operations and maintenance 5,889 5,830 59 Operating Income 4,191 4,243 (52 ) Other income (expense), net 114 60 54 Earnings Before Income Taxes 2,749 2,747 2 Income taxes 449 448 1 Consolidated Net Income 2,300 2,299 1 Consolidated Net Income Attributable to Southern Company 2,226 2,225 1 Alabama Power Other revenues $ 267 $ 230 $ 37 Other operations and maintenance 1,669 1,625 44 Taxes other than income taxes 389 388 1 Operating Income 1,477 1,485 (8 ) Other income (expense), net 20 12 8 Georgia Power Other revenues $ 481 $ 387 $ 94 Other operations and maintenance 1,860 1,772 88 Operating Income 1,289 1,283 6 Other income (expense), net 115 121 (6 ) Southern Company Gas Natural gas revenues $ 3,874 $ 3,872 $ 2 Operating Income 915 913 2 Earnings Before Income Taxes 836 834 2 Income taxes 464 463 1 Net Income 372 371 1 For the Year Ended December 31, 2018 Statements of Cash Flows As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Consolidated net income $ 2,300 $ 2,299 $ 1 Changes in certain current assets and liabilities: Receivables (426 ) (472 ) 46 Other current assets (127 ) (81 ) (46 ) Accrued taxes 267 268 (1 ) Other current liabilities 63 61 2 Georgia Power Changes in certain current assets and liabilities: Receivables $ 8 $ 1 $ 7 Other current assets (43 ) (36 ) (7 ) Southern Company Gas Net income $ 372 $ 371 $ 1 Changes in certain current assets and liabilities: Accrued taxes 10 11 (1 ) Other current liabilities (22 ) (24 ) 2 At December 31, 2018 Balance Sheets As Reported Balances Without Adoption of ASC 606 Effect of Change (in millions) Southern Company Unbilled revenues $ 654 $ 728 $ (74 ) Other accounts and notes receivable 813 814 (1 ) Other current assets 162 87 75 Accrued taxes 656 655 1 Other current liabilities 852 854 (2 ) Total Stockholders' Equity 29,039 29,038 1 Georgia Power Unbilled revenues $ 208 $ 243 $ (35 ) Other accounts and notes receivable 80 81 (1 ) Other current assets 70 34 36 Southern Company Gas Accrued income taxes $ 66 $ 65 $ 1 Other current liabilities 130 132 (2 ) Common Stockholder's Equity 8,570 8,569 1
Schedule of costs for affiliate transactions	Transportation costs under these agreements in 2018 , 2017 , and 2016 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2018 $ 8 $ 101 $ 25 $ 32 2017 9 102 25 32 2016 (*) 2 35 7 15 (*) Represents costs incurred for the period subsequent to Southern Company Gas' investment in SNG. On November 16, 2018, SNG completed its purchase of Georgia Power's natural gas lateral pipeline serving Plant McDonough Units 4 through 6 at net book value, as approved by the Georgia PSC on January 16, 2018. SNG expects to pay $142 million to Georgia Power in the first quarter 2020. During the interim period, Georgia Power will receive a discounted shipping rate to reflect the delayed consideration. Southern Company Gas' portion of the expected capital expenditures for the purchase of this pipeline and additional construction is $122 million . 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 2018 , 2017 , and 2016 : Georgia Southern Power (in millions) 2018 $ 21 $ 119 2017 22 119 2016 (*) 10 17 (*) Represents costs incurred for the period subsequent to Southern Company's acquisition of Southern Company Gas. Mississippi Power's and Southern Power's total power purchased from affiliates through the power pool is included in purchased power on their respective statements of income and was as follows: Mississippi Power Southern Power (in millions) 2018 $ 15 $ 41 2017 16 27 2016 29 21 Costs for these services from SCS in 2018 , 2017 , and 2016 were as follows: Alabama Georgia Mississippi Southern Power (a) Southern Company Gas (b) (in millions) 2018 $ 508 $ 653 $ 104 $ 98 $ 194 2017 479 625 140 218 63 2016 460 606 231 193 17 (a) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. (b) Southern Company Gas' 2016 costs represent services provided subsequent to the Merger. The approximate rates for 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 (percent) Alabama Power 3.0 % 2.9 % 3.0 % Georgia Power 2.6 % 2.7 % 2.8 % Mississippi Power (*) 4.1 % 3.7 % 4.2 % Southern Company Gas 2.9 % 2.9 % 2.8 % (*) Mississippi Power's decrease in 2017 is primarily the result of recording a loss on its lignite mine in June 2017.
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: 2018 2017 2016 Georgia Power 9.8 % 11.3 % 16.5 % Duke Energy Corporation 6.8 % 6.7 % 7.8 % Southern California Edison 6.2 % N/A N/A Morgan Stanley Capital Group N/A 4.5 % N/A San Diego Gas & Electric Company N/A N/A 5.7 %
Schedule of total AFUDC and interest capitalized	Total AFUDC and interest capitalized for the registrants in 2018 , 2017 , and 2016 was as follows: Southern Company Alabama Georgia (a) Mississippi (b) Southern Power (in millions) 2018 $ 210 $ 84 $ 94 $ — $ 17 2017 249 54 63 72 11 2016 327 39 68 124 44 (a) 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. (b) Mississippi Power's decrease in 2017 resulted from the Kemper IGCC project suspension in June 2017. Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Southern Company Gas $ 14 $ 19 $ 6 $ 4
Schedule of average AFUDC composite rates	The average AFUDC composite rates for 2018 , 2017 , and 2016 for the traditional electric operating companies and Southern Company Gas were as follows: Alabama Georgia Mississippi 2018 8.3 % 7.3 % 3.3 % 2017 8.3 % 5.6 % 6.7 % 2016 8.2 % 6.9 % 6.5 % Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 Southern Company Gas: Atlanta Gas Light (a) 7.9 % 8.1 % 4.1 % 4.1 % Chattanooga Gas (a) 7.4 % 7.4 % 3.7 % 3.7 % Nicor Gas (b) 2.1 % 1.2 % 1.5 % 1.5 % (a) Fixed rates authorized by the Georgia PSC and Tennessee Public Utilities Commission for Atlanta Gas Light and Chattanooga Gas, respectively. (b) Variable rate determined by the FERC method of AFUDC accounting.
Schedule of goodwill balances	The following table presents 2018 changes in goodwill balances for Southern Company and Southern Company Gas: Southern Company Southern Company Gas Gas Distribution Operations Gas Marketing Services (in millions) Balance at December 31, 2017 $ 6,268 $ 4,702 $ 1,265 Impairment (a) (42 ) — (42 ) Dispositions (b) (910 ) (668 ) (242 ) Balance at December 31, 2018 $ 5,315 (c) $ 4,034 $ 981 (a) On April 11, 2018, Southern Company Gas entered into a stock purchase agreement for the sale of Pivotal Home Solutions. In contemplation of this transaction and based on the purchase price, a goodwill impairment charge of $42 million was recorded in the first quarter 2018. See Note 15 under " Southern Company Gas " for additional information. (b) Gas distribution operations reflects goodwill allocated to Elizabethtown Gas, Elkton Gas, and Florida City Gas, which were sold during the third quarter 2018. Gas marketing services reflects goodwill associated with Pivotal Home Solutions, which was sold on June 4, 2018. See Note 15 under " Southern Company Gas " for additional information. (c) Total does not add due to rounding.
Schedule of intangible assets subject to amortization	At December 31, 2018 and 2017 , other intangible assets were as follows: At December 31, 2018 At December 31, 2017 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) $ 223 $ (94 ) $ 129 $ 288 $ (83 ) $ 205 Trade names (a) 70 (21 ) 49 159 (17 ) 142 Storage and transportation contracts 64 (54 ) 10 64 (34 ) 30 PPA fair value adjustments (b) 405 (61 ) 344 456 (47 ) 409 Other 11 (5 ) 6 17 (5 ) 12 Total other intangible assets subject to amortization $ 773 $ (235 ) $ 538 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 848 $ (235 ) $ 613 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments (b) $ 405 $ (61 ) $ 344 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services (a) Customer relationships $ 156 $ (84 ) $ 72 $ 221 $ (77 ) $ 144 Trade names 26 (7 ) 19 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (54 ) 10 64 (34 ) 30 Total other intangible assets subject to amortization $ 246 $ (145 ) $ 101 $ 400 $ (120 ) $ 280 (a) Balances as of December 31, 2018 reflect the sale of Pivotal Home Solutions. See Note 15 under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. (b) Balances as of December 31, 2018 exclude Plant Mankato-related intangible assets that were reclassified as assets held for sale. See Note 15 under "Southern Power – Sales of Natural Gas Plants " for additional information.
Schedule of intangible assets not subject to amortization	At December 31, 2018 and 2017 , other intangible assets were as follows: At December 31, 2018 At December 31, 2017 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) $ 223 $ (94 ) $ 129 $ 288 $ (83 ) $ 205 Trade names (a) 70 (21 ) 49 159 (17 ) 142 Storage and transportation contracts 64 (54 ) 10 64 (34 ) 30 PPA fair value adjustments (b) 405 (61 ) 344 456 (47 ) 409 Other 11 (5 ) 6 17 (5 ) 12 Total other intangible assets subject to amortization $ 773 $ (235 ) $ 538 $ 984 $ (186 ) $ 798 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 848 $ (235 ) $ 613 $ 1,059 $ (186 ) $ 873 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments (b) $ 405 $ (61 ) $ 344 $ 456 $ (47 ) $ 409 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services (a) Customer relationships $ 156 $ (84 ) $ 72 $ 221 $ (77 ) $ 144 Trade names 26 (7 ) 19 115 (9 ) 106 Wholesale gas services Storage and transportation contracts 64 (54 ) 10 64 (34 ) 30 Total other intangible assets subject to amortization $ 246 $ (145 ) $ 101 $ 400 $ (120 ) $ 280 (a) Balances as of December 31, 2018 reflect the sale of Pivotal Home Solutions. See Note 15 under " Southern Company Gas – Sale of Pivotal Home Solutions " for additional information. (b) Balances as of December 31, 2018 exclude Plant Mankato-related intangible assets that were reclassified as assets held for sale. See Note 15 under "Southern Power – Sales of Natural Gas Plants " for additional information.
Schedule of amortization associated with other intangible assets	Amortization associated with other intangible assets in 2018 , 2017 , and 2016 was as follows: 2018 2017 2016 (in millions) Southern Company $ 89 $ 124 $ 50 Southern Power $ 25 $ 25 $ 10 Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Southern Company Gas: Wholesale gas services (a) $ 20 $ 32 $ 2 $ — Gas marketing services (b) 32 54 32 8 (a) Recorded as a reduction to operating revenues. (b) Included in depreciation and amortization.
Schedule of amortization of other intangible assets	At December 31, 2018 , the estimated amortization associated with other intangible assets for the next five years is as follows: 2019 2020 2021 2022 2023 (in millions) Southern Company (*) $ 61 $ 50 $ 43 $ 39 $ 38 Southern Power (*) 20 20 20 20 20 Southern Company Gas 29 19 13 10 9 (*) Excludes amounts related to held for sale assets. See Note 15 under "Southern Power – Sales of Natural Gas 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, 2018 and/or 2017 : Southern Company Georgia Power Southern Company Gas (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 Southern Southern Southern (in millions) At December 31, 2017 Cash and cash equivalents $ 2,130 $ 129 $ 73 Restricted cash: Other accounts and notes receivable 5 — 5 Deferred charges and other assets 12 11 — Total cash, cash equivalents, and restricted cash $ 2,147 $ 140 $ 78
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, 2018 and/or 2017 : Southern Company Georgia Power Southern Company Gas (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 Southern Southern Southern (in millions) At December 31, 2017 Cash and cash equivalents $ 2,130 $ 129 $ 73 Restricted cash: Other accounts and notes receivable 5 — 5 Deferred charges and other assets 12 11 — Total cash, cash equivalents, and restricted cash $ 2,147 $ 140 $ 78
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 2018 , 2017 , and 2016 : Southern Company (*) Alabama Georgia Mississippi (in millions) 2018 $ 74 $ 16 $ 30 $ 1 2017 41 4 30 3 2016 40 3 30 4 (*) Includes accruals at Gulf Power of $26.9 million in 2018 and $3.5 million in each of 2017 and 2016 . See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power.
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: 2018 2017 (in millions) Net rentals receivable $ 1,563 $ 1,498 Unearned income (765 ) (723 ) Investment in leveraged leases 798 775 Deferred taxes from leveraged leases (255 ) (252 ) Net investment in leveraged leases $ 543 $ 523
Summary of the components of income from leveraged leases	A summary of the components of income from the leveraged leases follows: 2018 2017 2016 (in millions) Pretax leveraged lease income $ 25 $ 25 $ 25 Net impact of Tax Reform Legislation — 48 — Income tax expense (6 ) (9 ) (9 ) Net leveraged lease income $ 19 $ 64 $ 16
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, 2017 $ (119 ) $ (70 ) $ (189 ) Adjustment to beginning balance (*) (26 ) (14 ) (40 ) Current period change 24 2 26 Balance at December 31, 2018 $ (121 ) $ (82 ) $ (203 ) Southern Power Balance at December 31, 2017 $ 25 $ (27 ) $ (2 ) Adjustment to beginning balance (*) 4 — 4 Current period change 7 7 14 Balance at December 31, 2018 $ 36 $ (20 ) $ 16 Southern Company Gas Balance at December 31, 2017 $ (6 ) $ 26 $ 20 Adjustment to beginning balance (*) (1 ) 5 4 Current period change 4 (2 ) 2 Balance at December 31, 2018 $ (3 ) $ 29 $ 26 (*) Reflects the reclassification related to stranded tax effects resulting from the Tax Reform Legislation as allowed by ASU 2018-02. See " Recently Adopted Accounting Standards – Other " herein for additional information.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Schedule of Regulatory Assets	Regulatory assets and (liabilities) reflected in the consolidated balance sheets of Southern Company at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 3,658 $ 3,931 (a,p) Asset retirement obligations-asset 2,933 1,133 (b,p) Deferred income tax charges 799 814 (b,o) Property damage reserves-asset 416 333 (c) Under recovered regulatory clause revenues 407 317 (d) Environmental remediation-asset 366 511 (e,p) Loss on reacquired debt 346 223 (f) Remaining net book value of retired assets 211 306 (g) Vacation pay 182 183 (h,p) Long-term debt fair value adjustment 121 138 (i) Deferred PPA charges — 119 (j,p) Other regulatory assets 581 625 (k) Deferred income tax credits (6,455 ) (7,261 ) (b,o) Other cost of removal obligations (2,297 ) (2,684 ) (b) Customer refunds (293 ) (188 ) (n) Property damage reserves-liability (76 ) (135 ) (l) Over recovered regulatory clause revenues (47 ) (155 ) (d) Other regulatory liabilities (132 ) (104 ) (m) Total regulatory assets (liabilities), net $ 720 $ (1,894 ) 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) Asset retirement 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 $28 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Georgia Power – Storm Damage Recovery " herein for additional information. (d) Recorded and recovered or amortized over periods generally not exceeding 10 years . (e) Recovered through environmental cost recovery mechanisms when the remediation is performed or the work is performed. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue, which may range up to 50 years . (g) Amortized over periods not exceeding eight years . (h) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (i) Recovered over the remaining life of the original debt issuances, which range up to 20 years . For additional information see Note 15 under " Southern Company Merger with Southern Company Gas ." (j) Related to Gulf Power and reclassified as assets held for sale at December 31, 2018. See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power. (k) Comprised of numerous immaterial components including nuclear outage, fuel-hedging losses, cancelled construction projects, building and generating plant leases, property tax, and other miscellaneous assets. These costs are recorded and recovered or amortized over periods generally not exceeding 50 years . (l) Amortized as storm restoration and potential reliability-related expenses are incurred. (m) Comprised of numerous components including retiree benefit plans, fuel-hedging gains, AROs, and other liabilities that are recorded and recovered or amortized over periods not exceeding 20 years . (n) At December 31, 2018, represents amounts accrued and outstanding for refund, including approximately $109 million as a result of Alabama Power's 2018 retail return exceeding the allowed range, approximately $55 million pursuant to the Georgia Power Tax Reform Settlement Agreement, and approximately $100 million , subject to review and approval by the Georgia PSC, as a result of Georgia Power's 2018 retail ROE exceeding the allowed retail ROE range. See "Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (o) 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 be determined in future rate proceedings. See "Georgia Power," "Mississippi Power," and "Southern Company Gas" herein and Note 10 for additional information. (p) 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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 947 $ 946 (a,p) Deferred income tax charges 241 240 (b,c,d,) Under recovered regulatory clause revenues 176 53 (e) Asset retirement obligations 147 (33 ) (b) Regulatory clauses 142 142 (f) Vacation pay 71 70 (g,p) Loss on reacquired debt 56 62 (h) Nuclear outage 49 56 (i) Remaining net book value of retired assets 43 54 (j) Other regulatory assets 57 58 (k,l) Deferred income tax credits (2,027 ) (2,082 ) (b,d) Other cost of removal obligations (497 ) (609 ) (b) Rate RSE refund (109 ) — (m) Natural disaster reserve (20 ) (38 ) (n) Other regulatory liabilities (45 ) (7 ) (l,o) Total regulatory assets (liabilities), net $ (769 ) $ (1,088 ) 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 15 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 50 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 $10 million for 2018 and $13 million for 2017 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 50 years . See Note 10 for additional information. (e) Recorded and recovered or amortized over periods not exceeding 10 years . See "Rate CNP PPA," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study. See " Rate RSE " herein for additional information. (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 the remaining life of the original issue, which may range up to 50 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 up to 8 years . (k) Comprised of components including generation site selection/evaluation costs, PPA capacity (to be recovered over the next 12 months ), and other miscellaneous assets. Capitalized upon initialization of related construction projects, if applicable. (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) Refund accrued as a result of the 2018 retail return exceeding the allowed range. See " Rate RSE " herein for additional information. (n) Amortized as storm restoration and potential reliability-related expenses are incurred. (o) Comprised of several components, primarily $33 million deferred as a result of the Alabama PSC accounting order regarding the Tax Reform Legislation. See "Tax Reform Accounting Order" herein for additional information. (p) Not earning a return as offset in rate base by a corresponding asset or liability. Rate RSE Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 1,295 $ 1,313 (a, l) Asset retirement obligations 2,644 945 (b, l) Deferred income tax charges 522 521 (b, c, l) Storm damage reserves 416 333 (d) Remaining net book value of retired assets 127 146 (e) Loss on reacquired debt 277 127 (f, l) Vacation pay 91 91 (g, l) Other cost of removal obligations 68 40 (b) Environmental remediation 55 49 (h) Other regulatory assets 135 106 (i) Deferred income tax credits (3,080 ) (3,248 ) (b, c) Customer refunds (165 ) (188 ) (j) Other regulatory liabilities (7 ) (3 ) (k, l) Total regulatory assets (liabilities), net $ 2,378 $ 232 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 14 years . See Note 11 for additional information. (b) Through 2019, Georgia Power is recovering approximately $60 million annually for AROs, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. See Note 6 for additional information on AROs. Other cost of removal obligations and deferred income tax assets are recovered and deferred income tax liabilities are amortized over the related property lives, which may range up to 65 years . Included in the deferred income tax assets is $17 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2022. (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 $610 million of deferred income tax liabilities, neither of which are subject to normalization. The recovery and amortization of these amounts is expected to be determined in the Georgia Power 2019 Base Rate Case. See " Rate Plans " herein and Note 10 for additional information. (d) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Storm Damage Recovery " herein and Note 1 under "Storm Damage Reserves" for additional information. (e) The net book value of Plant Branch Units 1 through 4 at December 31, 2018 was $87 million , which is being amortized over the units' remaining useful lives through 2024. The net book value of Plant Mitchell Unit 3 at December 31, 2018 was $9 million , which will continue to be amortized through December 31, 2019 as provided in the 2013 ARP. Amortization of the remaining approximately $4 million net book value of Plant Mitchell Unit 3 at December 31, 2019 and a total of approximately $31 million related to obsolete inventories of certain retired units is expected to be determined in the Georgia Power 2019 Base Rate Case. See " 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, which currently does not exceed 34 years . (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Through 2019, Georgia Power is recovering approximately $2 million annually for environmental remediation, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See Note 3 under Environmental Remediation for additional information. (i) Comprised of several components including future generation costs, deferred nuclear outage costs, cancelled construction projects, building lease, and fuel-hedging losses. The timing of recovery of approximately $50 million for a future generation site is expected to be determined in the Georgia Power 2019 Base Rate Case. Nuclear outage costs are recorded and recovered or amortized over the outage cycles of each nuclear unit, which do not exceed 24 months . Approximately $30 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. The building lease is recorded and recovered or amortized through 2020. Fuel-hedging losses are recovered through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Integrated Resource Plan " herein for additional information on future generation costs. (j) At December 31, 2018, approximately $55 million was accrued and outstanding for refund pursuant to the Georgia Power Tax Reform Settlement Agreement and approximately $100 million was accrued for refund, subject to review and approval by the Georgia PSC, as a result of the 2018 retail ROE exceeding the allowed retail ROE range. See " Rate Plans " herein for additional information. (k) Comprised of Demand-Side Management (DSM) tariff over recovery and fuel-hedging gains. The amortization of DSM tariff over recovery of $3 million at December 31, 2018 is expected to be determined in the Georgia Power 2019 Base Rate Case. Fuel-hedging gains are refunded through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Rate Plans " herein for additional information on customer refunds and DSM tariffs. (l) 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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans – regulatory assets $ 171 $ 174 (a) Asset retirement obligations 143 95 (b) Kemper County energy facility assets, net 69 88 (c) Remaining net book value of retired assets 41 44 (d) Property tax 44 43 (e) Deferred charges related to income taxes 34 36 (b) Plant Daniel Units 3 and 4 36 36 (f) ECO carryforward 26 26 (g) Other regulatory assets 28 28 (h) Deferred credits related to income taxes (377 ) (377 ) (i) Other cost of removal obligations (185 ) (178 ) (b) Property damage (56 ) (57 ) (j) Other regulatory liabilities (9 ) — (k) Total regulatory assets (liabilities), net $ (35 ) $ (42 ) 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 15 years . See Note 11 for additional information. (b) 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 . 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. (c) Includes $91 million of regulatory assets and $22 million of regulatory liabilities. The retail portion includes $75 million of regulatory assets and $22 million of regulatory liabilities that are being recovered in rates over an eight -year period through 2025 and a six -year period through 2023, respectively. Recovery of the wholesale portion of the regulatory assets in the amount of $16 million is expected to be determined in a settlement agreement with wholesale customers in 2019. For additional information, see " Kemper County Energy Facility – Rate Recovery – Kemper Settlement Agreement" herein. (d) Retail portion includes approximately $26 million being recovered over a five -year period through 2021 and 2022 for Plant Watson and Plant Greene County, respectively. Recovery of the wholesale portion of approximately $15 million is expected to be determined in a settlement agreement with wholesale customers in 2019. (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 the purchase option and the revenue requirement assuming operating lease accounting treatment for the extended term, 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 Plan" herein. (h) Comprised of $9 million related to vacation pay, $8 million related to loss on reacquired debt, and other miscellaneous assets. These costs are recorded and recovered or amortized over periods which may range up to 50 years. This amount also includes fuel-hedging assets which are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three years . Upon final settlement, actual costs incurred are recovered through the ECM. (i) Includes excess deferred income taxes primarily associated with Tax Reform Legislation of $377 million , of which $266 million is related to protected deferred income taxes to be recovered over the related property lives utilizing the average rate assumption method in accordance with IRS normalization principles and $111 million related to unprotected (not subject to normalization). The unprotected portion associated with the Kemper County energy facility is $46 million , of which $33 million is being amortized over eight years through 2025 for retail and the amortization of $15 million is expected to be determined in a settlement agreement with wholesale customers in 2019. Mississippi Power also has $9 million of excess deferred income tax benefits associated with the System Restoration Rider being amortized over an eight -year period through 2025. Amortization of the remaining portions of the unprotected deferred income taxes associated with the Tax Reform Legislation are expected to be determined in Mississippi Power's next base rate proceeding, which is scheduled to be filed in the fourth quarter 2019 (Mississippi Power 2019 Base Rate Case). See " Kemper County Energy Facility " and "FERC Matters – Mississippi Power – Municipal and Rural Associations Tariff" herein and Note 10 for additional information. (j) For additional information, see " The following table illustrates Southern Company Gas' authorized ratemaking amounts that are not recognized on its balance sheets. These amounts are primarily composed of an allowed equity rate of return on assets associated with certain regulatory infrastructure programs. These amounts will be recognized as revenues in Southern Company Gas' financial statements in the periods they are billable to customers, the majority of which will be recovered by 2025. December 31, 2018 December 31, 2017 (in millions) Atlanta Gas Light $ 95 $ 104 Virginia Natural Gas 11 11 Nicor Gas 4 2 Total $ 110 $ 117 Regulatory assets and (liabilities) reflected in the balance sheets of Southern Company Gas at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Environmental remediation $ 311 $ 410 (a,b) Retiree benefit plans 161 270 (a,c) Long-term debt fair value adjustment 121 138 (d) Under recovered regulatory clause revenues 90 98 (e) Other regulatory assets 59 79 (f) Other cost of removal obligations (1,585 ) (1,646 ) (g) Deferred income tax credits (940 ) (1,063 ) (g,i) Over recovered regulatory clause revenues (43 ) (144 ) (e) Other regulatory liabilities (46 ) (21 ) (h) Total regulatory assets (liabilities), net $ (1,872 ) $ (1,879 ) 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 is performed or the work is performed. (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, which range up to 20 years . (e) Recorded and recovered or amortized over periods generally not exceeding seven years . In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities are authorized to utilize other cost recovery mechanisms, such as regulatory riders, which vary by utility but allow recovery of certain costs, such as those related to infrastructure replacement programs, as well as environmental remediation and energy efficiency plans. (f) Comprised of several components including unamortized loss on reacquired debt, weather normalization, franchise gas, deferred depreciation, and financial instrument-hedging assets, which are recovered or amortized over periods generally not exceeding 10 years , except for financial hedging-instruments. Financial instrument-hedging assets are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed two years . Upon final settlement, actual costs incurred are recovered, and actual income earned is refunded through the energy cost recovery clause. (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 several components including amounts to be refunded to customers as a result of the Tax Reform Legislation, energy efficiency programs, and unamortized bond issuance costs and financial instrument-hedging liabilities which are recovered or amortized over periods generally not exceeding 20 years , except for financial hedging-instruments. Financial instrument-hedging liabilities are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed two years . Upon final settlement, actual 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) Includes excess deferred income tax liabilities not subject to normalization as a result of the Tax Reform Legislation, the recovery and amortization of which is expected to be determined by the applicable state regulatory agencies in future rate proceedings. See " Rate Proceedings " herein and Note 10 for additional details.
Schedule of Regulatory Liabilities	Regulatory assets and (liabilities) reflected in the consolidated balance sheets of Southern Company at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 3,658 $ 3,931 (a,p) Asset retirement obligations-asset 2,933 1,133 (b,p) Deferred income tax charges 799 814 (b,o) Property damage reserves-asset 416 333 (c) Under recovered regulatory clause revenues 407 317 (d) Environmental remediation-asset 366 511 (e,p) Loss on reacquired debt 346 223 (f) Remaining net book value of retired assets 211 306 (g) Vacation pay 182 183 (h,p) Long-term debt fair value adjustment 121 138 (i) Deferred PPA charges — 119 (j,p) Other regulatory assets 581 625 (k) Deferred income tax credits (6,455 ) (7,261 ) (b,o) Other cost of removal obligations (2,297 ) (2,684 ) (b) Customer refunds (293 ) (188 ) (n) Property damage reserves-liability (76 ) (135 ) (l) Over recovered regulatory clause revenues (47 ) (155 ) (d) Other regulatory liabilities (132 ) (104 ) (m) Total regulatory assets (liabilities), net $ 720 $ (1,894 ) 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) Asset retirement 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 $28 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2027. (c) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Georgia Power – Storm Damage Recovery " herein for additional information. (d) Recorded and recovered or amortized over periods generally not exceeding 10 years . (e) Recovered through environmental cost recovery mechanisms when the remediation is performed or the work is performed. (f) Recovered over either the remaining life of the original issue or, if refinanced, over the remaining life of the new issue, which may range up to 50 years . (g) Amortized over periods not exceeding eight years . (h) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (i) Recovered over the remaining life of the original debt issuances, which range up to 20 years . For additional information see Note 15 under " Southern Company Merger with Southern Company Gas ." (j) Related to Gulf Power and reclassified as assets held for sale at December 31, 2018. See Note 15 under " Southern Company's Sale of Gulf Power " for information regarding the sale of Gulf Power. (k) Comprised of numerous immaterial components including nuclear outage, fuel-hedging losses, cancelled construction projects, building and generating plant leases, property tax, and other miscellaneous assets. These costs are recorded and recovered or amortized over periods generally not exceeding 50 years . (l) Amortized as storm restoration and potential reliability-related expenses are incurred. (m) Comprised of numerous components including retiree benefit plans, fuel-hedging gains, AROs, and other liabilities that are recorded and recovered or amortized over periods not exceeding 20 years . (n) At December 31, 2018, represents amounts accrued and outstanding for refund, including approximately $109 million as a result of Alabama Power's 2018 retail return exceeding the allowed range, approximately $55 million pursuant to the Georgia Power Tax Reform Settlement Agreement, and approximately $100 million , subject to review and approval by the Georgia PSC, as a result of Georgia Power's 2018 retail ROE exceeding the allowed retail ROE range. See "Alabama Power – Rate RSE " and " Georgia Power – Rate Plans " herein for additional information. (o) 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 be determined in future rate proceedings. See "Georgia Power," "Mississippi Power," and "Southern Company Gas" herein and Note 10 for additional information. (p) 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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 947 $ 946 (a,p) Deferred income tax charges 241 240 (b,c,d,) Under recovered regulatory clause revenues 176 53 (e) Asset retirement obligations 147 (33 ) (b) Regulatory clauses 142 142 (f) Vacation pay 71 70 (g,p) Loss on reacquired debt 56 62 (h) Nuclear outage 49 56 (i) Remaining net book value of retired assets 43 54 (j) Other regulatory assets 57 58 (k,l) Deferred income tax credits (2,027 ) (2,082 ) (b,d) Other cost of removal obligations (497 ) (609 ) (b) Rate RSE refund (109 ) — (m) Natural disaster reserve (20 ) (38 ) (n) Other regulatory liabilities (45 ) (7 ) (l,o) Total regulatory assets (liabilities), net $ (769 ) $ (1,088 ) 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 15 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 50 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 $10 million for 2018 and $13 million for 2017 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 50 years . See Note 10 for additional information. (e) Recorded and recovered or amortized over periods not exceeding 10 years . See "Rate CNP PPA," " Rate CNP Compliance ," and" Rate ECR " herein for additional information. (f) Will be amortized concurrently with the effective date of Alabama Power's next depreciation study. See " Rate RSE " herein for additional information. (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 the remaining life of the original issue, which may range up to 50 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 up to 8 years . (k) Comprised of components including generation site selection/evaluation costs, PPA capacity (to be recovered over the next 12 months ), and other miscellaneous assets. Capitalized upon initialization of related construction projects, if applicable. (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) Refund accrued as a result of the 2018 retail return exceeding the allowed range. See " Rate RSE " herein for additional information. (n) Amortized as storm restoration and potential reliability-related expenses are incurred. (o) Comprised of several components, primarily $33 million deferred as a result of the Alabama PSC accounting order regarding the Tax Reform Legislation. See "Tax Reform Accounting Order" herein for additional information. (p) Not earning a return as offset in rate base by a corresponding asset or liability. Rate RSE Regulatory assets and (liabilities) reflected in the balance sheets of Georgia Power at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans $ 1,295 $ 1,313 (a, l) Asset retirement obligations 2,644 945 (b, l) Deferred income tax charges 522 521 (b, c, l) Storm damage reserves 416 333 (d) Remaining net book value of retired assets 127 146 (e) Loss on reacquired debt 277 127 (f, l) Vacation pay 91 91 (g, l) Other cost of removal obligations 68 40 (b) Environmental remediation 55 49 (h) Other regulatory assets 135 106 (i) Deferred income tax credits (3,080 ) (3,248 ) (b, c) Customer refunds (165 ) (188 ) (j) Other regulatory liabilities (7 ) (3 ) (k, l) Total regulatory assets (liabilities), net $ 2,378 $ 232 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 14 years . See Note 11 for additional information. (b) Through 2019, Georgia Power is recovering approximately $60 million annually for AROs, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. Asset retirement and removal liabilities will be settled and trued up following completion of the related activities. See Note 6 for additional information on AROs. Other cost of removal obligations and deferred income tax assets are recovered and deferred income tax liabilities are amortized over the related property lives, which may range up to 65 years . Included in the deferred income tax assets is $17 million for the retiree Medicare drug subsidy, which is being recovered and amortized through 2022. (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 $610 million of deferred income tax liabilities, neither of which are subject to normalization. The recovery and amortization of these amounts is expected to be determined in the Georgia Power 2019 Base Rate Case. See " Rate Plans " herein and Note 10 for additional information. (d) Through 2019, Georgia Power is recovering approximately $30 million annually for storm damage, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See " Storm Damage Recovery " herein and Note 1 under "Storm Damage Reserves" for additional information. (e) The net book value of Plant Branch Units 1 through 4 at December 31, 2018 was $87 million , which is being amortized over the units' remaining useful lives through 2024. The net book value of Plant Mitchell Unit 3 at December 31, 2018 was $9 million , which will continue to be amortized through December 31, 2019 as provided in the 2013 ARP. Amortization of the remaining approximately $4 million net book value of Plant Mitchell Unit 3 at December 31, 2019 and a total of approximately $31 million related to obsolete inventories of certain retired units is expected to be determined in the Georgia Power 2019 Base Rate Case. See " 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, which currently does not exceed 34 years . (g) Recorded as earned by employees and recovered as paid, generally within one year . This includes both vacation and banked holiday pay. (h) Through 2019, Georgia Power is recovering approximately $2 million annually for environmental remediation, which is expected to be adjusted in the Georgia Power 2019 Base Rate Case. See Note 3 under Environmental Remediation for additional information. (i) Comprised of several components including future generation costs, deferred nuclear outage costs, cancelled construction projects, building lease, and fuel-hedging losses. The timing of recovery of approximately $50 million for a future generation site is expected to be determined in the Georgia Power 2019 Base Rate Case. Nuclear outage costs are recorded and recovered or amortized over the outage cycles of each nuclear unit, which do not exceed 24 months . Approximately $30 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. The building lease is recorded and recovered or amortized through 2020. Fuel-hedging losses are recovered through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Integrated Resource Plan " herein for additional information on future generation costs. (j) At December 31, 2018, approximately $55 million was accrued and outstanding for refund pursuant to the Georgia Power Tax Reform Settlement Agreement and approximately $100 million was accrued for refund, subject to review and approval by the Georgia PSC, as a result of the 2018 retail ROE exceeding the allowed retail ROE range. See " Rate Plans " herein for additional information. (k) Comprised of Demand-Side Management (DSM) tariff over recovery and fuel-hedging gains. The amortization of DSM tariff over recovery of $3 million at December 31, 2018 is expected to be determined in the Georgia Power 2019 Base Rate Case. Fuel-hedging gains are refunded through Georgia Power's fuel cost recovery mechanism upon final settlement. See " Rate Plans " herein for additional information on customer refunds and DSM tariffs. (l) 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, 2018 and 2017 relate to: 2018 2017 Note (in millions) Retiree benefit plans – regulatory assets $ 171 $ 174 (a) Asset retirement obligations 143 95 (b) Kemper County energy facility assets, net 69 88 (c) Remaining net book value of retired assets 41 44 (d) Property tax 44 43 (e) Deferred charges related to income taxes 34 36 (b) Plant Daniel Units 3 and 4 36 36 (f) ECO carryforward 26 26 (g) Other regulatory assets 28 28 (h) Deferred credits related to income taxes (377 ) (377 ) (i) Other cost of removal obligations (185 ) (178 ) (b) Property damage (56 ) (57 ) (j) Other regulatory liabilities (9 ) — (k) Total regulatory assets (liabilities), net $ (35 ) $ (42 ) 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 15 years . See Note 11 for additional information. (b) 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 . 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. (c) Includes $91 million of regulatory assets and $22 million of regulatory liabilities. The retail portion includes $75 million of regulatory assets and $22 million of regulatory liabilities that are being recovered in rates over an eight -year period through 2025 and a six -year period through 2023, respectively. Recovery of the wholesale portion of the regulatory assets in the amount of $16 million is expected to be determined in a settlement agreement with wholesale customers in 2019. For additional information, see " Kemper County Energy Facility – Rate Recovery – Kemper Settlement Agreement" herein. (d) Retail portion includes approximately $26 million being recovered over a five -year period through 2021 and 2022 for Plant Watson and Plant Greene County, respectively. Recovery of the wholesale portion of approximately $15 million is expected to be determined in a settlement agreement with wholesale customers in 2019. (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 the purchase option and the revenue requirement assuming operating lease accounting treatment for the extended term, 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 Plan" herein. (h) Comprised of $9 million related to vacation pay, $8 million related to loss on reacquired debt, and other miscellaneous assets. These costs are recorded and recovered or amortized over periods which may range up to 50 years. This amount also includes fuel-hedging assets which are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed three years . Upon final settlement, actual costs incurred are recovered through the ECM. (i) Includes excess deferred income taxes primarily associated with Tax Reform Legislation of $377 million , of which $266 million is related to protected deferred income taxes to be recovered over the related property lives utilizing the average rate assumption method in accordance with IRS normalization principles and $111 million related to unprotected (not subject to normalization). The unprotected portion associated with the Kemper County energy facility is $46 million , of which $33 million is being amortized over eight years through 2025 for retail and the amortization of $15 million is expected to be determined in a settlement agreement with wholesale customers in 2019. Mississippi Power also has $9 million of excess deferred income tax benefits associated with the System Restoration Rider being amortized over an eight -year period through 2025. Amortization of the remaining portions of the unprotected deferred income taxes associated with the Tax Reform Legislation are expected to be determined in Mississippi Power's next base rate proceeding, which is scheduled to be filed in the fourth quarter 2019 (Mississippi Power 2019 Base Rate Case). See " Kemper County Energy Facility " and "FERC Matters – Mississippi Power – Municipal and Rural Associations Tariff" herein and Note 10 for additional information. (j) For additional information, see " Regulatory assets and (liabilities) reflected in the balance sheets of Southern Company Gas at December 31, 2018 and 2017 relate to: 2018 2017 Note (in millions) Environmental remediation $ 311 $ 410 (a,b) Retiree benefit plans 161 270 (a,c) Long-term debt fair value adjustment 121 138 (d) Under recovered regulatory clause revenues 90 98 (e) Other regulatory assets 59 79 (f) Other cost of removal obligations (1,585 ) (1,646 ) (g) Deferred income tax credits (940 ) (1,063 ) (g,i) Over recovered regulatory clause revenues (43 ) (144 ) (e) Other regulatory liabilities (46 ) (21 ) (h) Total regulatory assets (liabilities), net $ (1,872 ) $ (1,879 ) 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 is performed or the work is performed. (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, which range up to 20 years . (e) Recorded and recovered or amortized over periods generally not exceeding seven years . In addition to natural gas cost recovery mechanisms, the natural gas distribution utilities are authorized to utilize other cost recovery mechanisms, such as regulatory riders, which vary by utility but allow recovery of certain costs, such as those related to infrastructure replacement programs, as well as environmental remediation and energy efficiency plans. (f) Comprised of several components including unamortized loss on reacquired debt, weather normalization, franchise gas, deferred depreciation, and financial instrument-hedging assets, which are recovered or amortized over periods generally not exceeding 10 years , except for financial hedging-instruments. Financial instrument-hedging assets are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed two years . Upon final settlement, actual costs incurred are recovered, and actual income earned is refunded through the energy cost recovery clause. (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 several components including amounts to be refunded to customers as a result of the Tax Reform Legislation, energy efficiency programs, and unamortized bond issuance costs and financial instrument-hedging liabilities which are recovered or amortized over periods generally not exceeding 20 years , except for financial hedging-instruments. Financial instrument-hedging liabilities are recorded over the life of the underlying hedged purchase contracts, which generally do not exceed two years . Upon final settlement, actual 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) Includes excess deferred income tax liabilities not subject to normalization as a result of the Tax Reform Legislation, the recovery and amortization of which is expected to be determined by the applicable state regulatory agencies in future rate proceedings. 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) $ 8.0 Construction contingency estimate 0.4 Total project capital cost forecast (a)(b) 8.4 Net investment as of December 31, 2018 (b) (4.6 ) Remaining estimate to complete (a) $ 3.8 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $315 million . (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related Customer Refunds.

Contingencies (Tables)

Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	At December 31, 2018 and 2017 , 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, 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 December 31, 2017: Environmental remediation liability: Other current liabilities $ 73 $ 22 $ 46 Accrued environmental remediation (*) 389 — 342 Under recovered environmental remediation costs: Other regulatory assets, current $ 38 $ 2 $ 31 Other regulatory assets, deferred 473 47 379

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following tables disaggregate revenue sources for the year ended December 31, 2018 : 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 6,608 Commercial 5,266 Industrial 3,224 Other 124 Natural gas distribution revenues 3,175 Alternative revenue programs (b) (20 ) Total retail electric and gas distribution revenues $ 18,377 Wholesale energy revenues (c)(d) 1,896 Wholesale capacity revenues (d) 620 Other natural gas revenues (e) 699 Other revenues (f) 1,903 Total operating revenues $ 23,495 (a) Retail electric revenues include $75 million of leases and a net increase of $60 million from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 2 for additional information on cost recovery mechanisms. (b) See Note 1 under " Revenues " for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (c) Wholesale energy revenues include $299 million of revenues accounted for as derivatives, primarily related to short-term physical energy sales in the wholesale electricity market. See Note 1 under " Revenues – Southern Power " and Note 14 for additional information on energy-related derivative contracts. (d) Wholesale energy and wholesale capacity revenues include $384 million and $121 million , respectively, of PPA contracts accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $7.0 billion of which $3.9 billion relates to contracts that are accounted for as derivatives. See Note 16 under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other revenues include $322 million of revenues not accounted for under ASC 606. 2018 Alabama Power Georgia Power Mississippi Power (in millions) Operating revenues Retail revenues (a)(b) Residential $ 2,335 $ 3,301 $ 273 Commercial 1,578 3,023 286 Industrial 1,428 1,344 321 Other 26 84 9 Total retail electric revenues $ 5,367 $ 7,752 $ 889 Wholesale energy revenues (c) 297 133 348 Wholesale capacity revenues 101 54 6 Other revenues (b)(d) 267 481 22 Total operating revenues $ 6,032 $ 8,420 $ 1,265 (a) Retail revenues at Alabama Power, Georgia Power, and Mississippi Power include a net increase or (net reduction) of $152 million , $(19) million , and $(13) million , respectively, related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. See Note 2 for additional information on cost recovery mechanisms. (b) Retail revenues and other revenues at Georgia Power include $74 million and $135 million , respectively, of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, and Mississippi Power include $20 million , $29 million , and $4 million , respectively, accounted for as derivatives primarily related to short-term physical energy sales in the wholesale electricity market. See Note 14 for additional information on energy-related derivative contracts. (d) Other revenues at Alabama Power and Georgia Power include $57 million and $109 million , respectively, of revenues not accounted for under ASC 606. 2018 (in millions) Southern Power PPA capacity revenues (a) $ 580 PPA energy revenues (a) 1,140 Non-PPA revenues (b) 472 Other revenues 13 Total operating revenues $ 2,205 (a) PPA capacity revenues and PPA energy revenues include $186 million and $413 million , respectively, related to PPAs accounted for as leases. See Note 1 under " Revenues – Southern Power " for additional information on capacity revenues accounted for as leases. (b) Non-PPA revenues include $242 million of revenues from short-term sales related to physical energy sales in the wholesale electricity market accounted for as derivatives. See Note 1 under " Revenues – Southern Power " and Note 14 for additional information on energy-related derivative contracts. 2018 (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 1,525 Commercial 436 Transportation 944 Industrial 40 Other 230 Alternative revenue programs (a) (20 ) Total natural gas distribution revenues $ 3,155 Gas pipeline investments 32 Wholesale gas services (b) 101 Gas marketing services (c) 568 Other revenues 53 Total operating revenues $ 3,909 (a) See Note 1 under " Revenues – Southern Company Gas " for additional information on alternative revenue programs at the natural gas distribution utilities. Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $7.0 billion of which $3.9 billion relates to contracts that are accounted for as derivatives. See Note 16 under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues and Note 14 for additional information on energy-related derivative contracts. (c) Gas marketing services includes $3 million of revenues not accounted for under ASC 606.
Contract with Customer, Asset and Liability	The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers at December 31, 2018 : Receivables Contract Assets Contract Liabilities (in millions) Southern Company $ 2,630 $ 102 $ 32 Alabama Power 520 — 12 Georgia Power 721 58 7 Mississippi Power 100 — — Southern Power 118 — 11 Southern Company Gas 952 — 2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	Revenues from contracts with customers related to these performance obligations remaining at December 31, 2018 are expected to be recognized as follows: 2019 2020 2021 2022 2023 2024 and (in millions) Southern Company (*) $ 487 $ 341 $ 315 $ 315 $ 306 $ 2,103 Alabama Power 23 22 26 23 22 140 Georgia Power 41 38 40 30 31 82 Mississippi Power 3 3 1 — — — Southern Power 323 295 270 281 275 2,028 (*) Excludes amounts related to held for sale assets. See Note 15 under " Southern Company's Sale of Gulf Power " for additional information.

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, plant and equipment	The registrants' property, plant, and equipment in service consisted of the following at December 31, 2018 and 2017 : 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 At December 31, 2017: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric utilities: Generation $ 51,279 $ 14,213 $ 17,038 $ 2,801 $ 13,737 $ — Transmission 11,562 4,119 5,947 737 — — Distribution 19,239 7,034 9,978 946 — — General/other 4,402 1,960 1,898 289 18 — Electric utilities' plant in service 86,482 27,326 34,861 4,773 13,755 — Southern Company Gas: Natural gas distribution utilities transportation and distribution 13,079 — — — — 13,079 Storage facilities 1,599 — — — — 1,599 Other 1,155 — — — — 1,155 Southern Company Gas plant in service 15,833 — — — — 15,833 Other plant in service 1,227 — — — — — Total plant in service $ 103,542 $ 27,326 $ 34,861 $ 4,773 $ 13,755 $ 15,833 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
Assets acquired under a capital lease	Assets acquired under a capital lease are included in property, plant, and equipment and are further detailed in the table below for the applicable registrants: Southern Company Georgia Power (in millions) At December 31, 2018: Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 43 — Gas pipeline 7 — Less: Accumulated amortization (75 ) (84 ) Balance, net of amortization $ 191 $ 121 At December 31, 2017: Office buildings $ 216 $ 61 PPAs (*) — 144 Computer-related equipment 51 — Gas pipeline 6 — Less: Accumulated amortization (72 ) (68 ) Balance, net of amortization $ 201 $ 137 (*) Represents Georgia Power's affiliate PPAs with Southern Power. See Note 1 under " Affiliate Transactions " and Note 9 under " Fuel and Power Purchase Agreements – Affiliate " for additional information.
Composite straight-line rates	Transportation costs under these agreements in 2018 , 2017 , and 2016 were as follows: Alabama Georgia Southern Power Southern Company Gas (in millions) 2018 $ 8 $ 101 $ 25 $ 32 2017 9 102 25 32 2016 (*) 2 35 7 15 (*) Represents costs incurred for the period subsequent to Southern Company Gas' investment in SNG. On November 16, 2018, SNG completed its purchase of Georgia Power's natural gas lateral pipeline serving Plant McDonough Units 4 through 6 at net book value, as approved by the Georgia PSC on January 16, 2018. SNG expects to pay $142 million to Georgia Power in the first quarter 2020. During the interim period, Georgia Power will receive a discounted shipping rate to reflect the delayed consideration. Southern Company Gas' portion of the expected capital expenditures for the purchase of this pipeline and additional construction is $122 million . 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 2018 , 2017 , and 2016 : Georgia Southern Power (in millions) 2018 $ 21 $ 119 2017 22 119 2016 (*) 10 17 (*) Represents costs incurred for the period subsequent to Southern Company's acquisition of Southern Company Gas. Mississippi Power's and Southern Power's total power purchased from affiliates through the power pool is included in purchased power on their respective statements of income and was as follows: Mississippi Power Southern Power (in millions) 2018 $ 15 $ 41 2017 16 27 2016 29 21 Costs for these services from SCS in 2018 , 2017 , and 2016 were as follows: Alabama Georgia Mississippi Southern Power (a) Southern Company Gas (b) (in millions) 2018 $ 508 $ 653 $ 104 $ 98 $ 194 2017 479 625 140 218 63 2016 460 606 231 193 17 (a) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS. (b) Southern Company Gas' 2016 costs represent services provided subsequent to the Merger. The approximate rates for 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 (percent) Alabama Power 3.0 % 2.9 % 3.0 % Georgia Power 2.6 % 2.7 % 2.8 % Mississippi Power (*) 4.1 % 3.7 % 4.2 % Southern Company Gas 2.9 % 2.9 % 2.8 % (*) Mississippi Power's decrease in 2017 is primarily the result of recording a loss on its lignite mine in June 2017.
Ownership and investment in jointly-owned facilities	At December 31, 2018 , 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) $ 274 $ 71 $ 1 Plant Miller (coal) Units 1 and 2 91.8 (b) 2,056 619 138 Georgia Power Plant Hatch (nuclear) 50.1 % (c) $ 1,569 $ 615 $ 54 Plant Vogtle (nuclear) Units 1 and 2 45.7 (c) 3,804 2,150 84 Plant Scherer (coal) Units 1 and 2 8.4 (c) 266 96 14 Plant Scherer (coal) Unit 3 75.0 (c) 1,238 493 66 Plant Wansley (coal) 53.5 (c) 1,179 362 160 Rocky Mountain (pumped storage) 25.4 (d) 184 135 — Mississippi Power Greene County (natural gas) Units 1 and 2 40.0 % (a) $ 180 $ 93 $ 1 Plant Daniel (coal) Units 1 and 2 50.0 (e) 723 201 7 Southern Company Gas Dalton Pipeline (natural gas pipeline) 50.0 % (f) $ 270 $ 6 $ — (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. (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 also entered into an agreement to lease its 50% undivided ownership in the Dalton Pipeline that became effective when it was placed in service in August 2017. Under the lease, Southern Company Gas will receive approximately $26 million annually for an initial term of 25 years . 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, 2018
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, 2016 $ 4,514 $ 1,533 $ 2,532 $ 179 $ 64 Liabilities incurred 16 — 4 — 6 Liabilities settled (177 ) (26 ) (120 ) (23 ) — Accretion 179 77 89 5 4 Cash flow revisions 292 125 133 13 4 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
Investment securities in the Funds	Investment securities in the Funds for December 31, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Power (in millions) 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 At December 31, 2017: Equity securities $ 1,059 $ 644 $ 415 Debt securities 725 223 502 Other securities 47 35 12 Total investment securities in the Funds $ 1,831 $ 902 $ 929
Fair value increases (decreases) of the Funds	The fair value increases (decreases) of the Funds, including reinvested interest and dividends and excluding the Funds' expenses, for 2018 , 2017 , and 2016 are shown in the table below. The fair value increases (decreases) included unrealized gains (losses) on securities held in the Funds at each of December 31, 2018 , 2017 , and 2016 , which are also shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2018 $ (67 ) $ (38 ) $ (29 ) 2017 233 125 108 2016 114 76 38 Unrealized gains (losses) At December 31, 2018 $ (183 ) $ (96 ) $ (87 ) At December 31, 2017 181 98 83 At December 31, 2016 48 34 14 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. At December 31, 2017 , 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 331 $ 239 $ — $ — $ 570 Interest rate derivatives — 1 — — 1 Foreign currency derivatives — 129 — — 129 Nuclear decommissioning trusts: (c) Domestic equity 690 82 — — 772 Foreign equity 62 224 — — 286 U.S. Treasury and government agency securities — 251 — — 251 Municipal bonds — 68 — — 68 Corporate bonds 21 315 — — 336 Mortgage and asset backed securities — 57 — — 57 Private equity — — — 29 29 Other 19 12 — — 31 Cash equivalents 1,455 — — — 1,455 Other investments 9 — 1 — 10 Total $ 2,587 $ 1,378 $ 1 $ 29 $ 3,995 Liabilities: Energy-related derivatives (a)(b) $ 480 $ 253 $ — $ — $ 733 Interest rate derivatives — 38 — — 38 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ 480 $ 314 $ 22 $ — $ 816 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (d) Domestic equity 442 81 — — 523 Foreign equity 62 59 — — 121 U.S. Treasury and government agency securities — 24 — — 24 Corporate bonds 21 160 — — 181 Mortgage and asset backed securities — 18 — — 18 Private equity — — — 29 29 Other 6 — — — 6 Cash equivalents 349 — — — 349 Total $ 880 $ 346 $ — $ 29 $ 1,255 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (d)(e) Domestic equity 248 1 — — 249 Foreign equity — 166 — — 166 U.S. Treasury and government agency securities — 227 — — 227 Municipal bonds — 68 — — 68 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 40 — — 40 Other 12 12 — — 24 Cash equivalents 690 — — — 690 Total $ 950 $ 675 $ — $ — $ 1,625 Liabilities: Energy-related derivatives $ — $ 19 $ — $ — $ 19 Interest rate derivatives — 5 — — 5 Total $ — $ 24 $ — $ — $ 24 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Interest rate derivatives — 1 — — 1 Cash equivalents 224 — — — 224 Total $ 224 $ 3 $ — $ — $ 227 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 129 — — 129 Cash equivalents 21 — — — 21 Total $ 21 $ 132 $ — $ — $ 153 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ — $ 36 $ 22 $ — $ 58 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 331 $ 223 $ — $ — $ 554 Liabilities: Energy-related derivatives (a)(b) $ 479 $ 181 $ — $ — 660 (a) Energy-related derivatives exclude $11 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 $193 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under " Nuclear Decommissioning " for additional information. (e) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under " Nuclear Decommissioning " for additional information.
Accumulated provisions for the external decommissioning trust funds	At December 31, 2018 and 2017 , the accumulated provisions for the external decommissioning trust funds were as follows: 2018 2017 (in millions) Alabama Power Plant Farley $ 846 $ 902 Georgia Power Plant Hatch $ 547 $ 583 Plant Vogtle Units 1 and 2 326 346 Total $ 873 $ 929
Estimated costs of decommissioning	The estimated costs of decommissioning at December 31, 2018 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, 2018
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 years ended December 31, 2017 and 2016 : 2017 2016 (in millions) Beginning balance $ 164 $ 43 Net income attributable to redeemable noncontrolling interests 2 4 Distributions to redeemable noncontrolling interests (2 ) (1 ) Capital contributions from redeemable noncontrolling interests 2 118 Redemption of redeemable noncontrolling interests (59 ) — Reclassification to non-redeemable noncontrolling interests (114 ) — Change in fair value of redeemable noncontrolling interests 7 — Ending balance $ — $ 164
Condensed income statement	The following table presents the attribution of net income to Southern Power and the noncontrolling interests for the years ended December 31, 2017 and 2016 : 2017 2016 (in millions) Net income $ 1,117 $ 374 Less: Net income attributable to noncontrolling interests 44 32 Less: Net income attributable to redeemable noncontrolling interests 2 4 Net income attributable to Southern Power $ 1,071 $ 338
Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments at December 31, 2018 and 2017 and related income from those investments for the successor years ended December 31, 2018 and 2017 , the successor period of July 1, 2016 through December 31, 2016 , and the predecessor period of January 1, 2016 through June 30, 2016 were as follows: Investment Balance December 31, 2018 December 31, 2017 (in millions) SNG $ 1,261 $ 1,262 PennEast Pipeline 71 57 Atlantic Coast Pipeline 83 41 Other 123 117 Total $ 1,538 $ 1,477 Selected financial information of SNG at December 31, 2018 and 2017 and for the years ended December 31, 2018 and 2017 and for the period September 1, 2016 through December 31, 2016 is as follows: At December 31, Balance Sheet Information 2018 2017 (in millions) Current assets $ 104 $ 82 Property, plant, and equipment 2,606 2,439 Deferred charges and other assets 121 121 Total Assets $ 2,831 $ 2,642 Current liabilities $ 103 $ 110 Long-term debt 1,103 1,102 Other deferred charges and other liabilities 212 76 Total Liabilities $ 1,418 $ 1,288 Total Stockholders' Equity $ 1,413 $ 1,354 Total Liabilities and Stockholders' Equity $ 2,831 $ 2,642 Income Statement Information Year ended December 31, 2018 Year ended December 31, 2017 September 1, 2016 (in millions) Revenues $ 604 $ 544 $ 230 Operating income 310 242 137 Net income 261 175 115
Schedule of Other Nonoperating Income, by Component	Successor Predecessor Earnings from Equity Method Investments Year ended December 31, 2018 Year ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) SNG $ 131 $ 88 $ 56 $ — PennEast Pipeline 5 6 — — Atlantic Coast Pipeline 7 6 1 — Other 5 6 3 2 Total $ 148 $ 106 $ 60 $ 2

Financing (Tables)

Financing (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Summary of Debt	A summary of long-term securities due within one year at each of December 31, 2018 and 2017 is as follows: December 31, 2018 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Senior notes $ 2,950 $ 200 $ 500 $ — $ 600 $ 300 Revenue bonds (a) 173 — 108 40 — — First mortgage bonds 50 — — — — 50 Capitalized leases 24 1 13 — — — Other (b) 1 — (4 ) — (1 ) 7 Total $ 3,198 $ 201 $ 617 $ 40 $ 599 $ 357 (a) For Southern Company and Mississippi Power, includes $40 million in pollution control revenue bonds classified as short term since they are variable rate demand obligations supported by short-term credit facilities; however, the final maturity dates range from 2020 to 2028. (b) Represents unamortized debt related amounts, acquisition accounting fair value adjustments, and/or fair value hedges. See Note 14 for additional information regarding fair value hedges. December 31, 2017 Southern Company Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Senior notes $ 2,354 $ 750 $ — $ 350 $ 155 Long-term bank term loans 1,420 100 900 420 — Revenue bonds (a) 90 — 90 — — Capitalized leases 31 11 — — — Other (b) (3 ) (4 ) (1 ) — 2 Total $ 3,892 $ 857 $ 989 $ 770 $ 157 (a) For Southern Company and Mississippi Power, includes $50 million in revenue bonds classified as short term at December 31, 2017 that were remarketed in an index rate mode subsequent to December 31, 2017. Also for Southern Company and Mississippi Power, includes $40 million in pollution control revenue bonds classified as short term since they are variable rate demand obligations supported by short-term credit facilities; however, the final maturity dates range from 2020 to 2028. (b) Represents unamortized debt related amounts, acquisition accounting fair value adjustments, and fair value hedges. See Note 14 for additional information regarding fair value hedges. Total junior subordinated notes outstanding for Southern Company and Georgia Power at December 31, 2018 and 2017 were as follows: Southern (*) Georgia Power (in millions) December 31, 2018 $ 3,570 $ 270 December 31, 2017 3,570 270 (*) Includes $3.3 billion of junior subordinated notes at the Southern Company parent entity at both December 31, 2018 and 2017 . Total tax-exempt pollution control revenue bond obligations (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Mississippi Power (in millions) December 31, 2018 $ 2,585 $ 1,060 $ 1,460 $ 40 December 31, 2017 3,297 1,060 1,821 83 Total long-term bank term loans (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) December 31, 2018 $ 145 $ 45 $ — $ — $ — December 31, 2017 1,465 45 100 900 420 Total senior notes (including amounts due within one year) outstanding at December 31, 2018 and 2017 were as follows: Southern (a) Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (b) (in millions) December 31, 2018 $ 32,725 $ 6,875 $ 5,600 $ 1,200 $ 5,050 $ 4,000 December 31, 2017 35,148 6,375 7,100 755 5,459 4,157 (a) Includes $10.0 billion and $10.2 billion of senior notes at the Southern Company parent entity at December 31, 2018 and 2017 , respectively. (b) Represents senior notes issued by Southern Company Gas Capital, which are fully and unconditionally guaranteed by Southern Company Gas. See " Structural Considerations " herein for additional information. Outstanding secured debt at December 31, 2018 and 2017 for the applicable registrants was as follows: Georgia (a) Mississippi Power (b) Southern Company Gas (c) (in millions) December 31, 2018 $ 2,767 $ 270 $ 1,325 December 31, 2017 2,779 270 1,025 (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. These borrowings totaled $2.6 billion at both December 31, 2018 and 2017 . See " Long-term Debt – DOE Loan Guarantee Borrowings " herein for additional information. Also includes capital lease obligations of $142 million and $154 million at December 31, 2018 and 2017 , respectively. See " Long-term Debt – Capital Leases – Georgia Power " herein for additional information. (b) The revenue bonds assumed in conjunction with Mississippi Power's purchase of Plant Daniel Units 3 and 4 are secured by Plant Daniel Units 3 and 4 and certain related personal property. See " Long-term Debt – Other Long-Term Debt " herein for additional information. (c) Nicor Gas' first mortgage bonds are secured by substantially all of Nicor Gas' properties. See " Long-term Debt – Other Long-Term Debt – Southern Company Gas " herein for additional information.
Schedule of Maturities of Long-Term Debt for the Next Five Years	Maturities of long-term debt for the next five years are as follows: Southern Company (a) Alabama Power Georgia Power (a) Mississippi Power Southern Power (b) Southern Company Gas (in millions) 2019 $ 3,156 $ 200 $ 621 $ — $ 600 $ 350 2020 4,041 250 1,006 307 825 — 2021 3,186 310 375 270 300 330 2022 1,974 750 505 — 677 46 2023 2,388 300 153 — 290 400 (a) Amounts include principal amortization related to the FFB borrowings beginning in 2020; however, the final maturity date is February 20, 2044. See " Long-term Debt – 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 Committed Credit Arrangements	At December 31, 2018 , committed credit arrangements with banks were as follows: Expires Executable Term Loans Expires Within One Year Company 2019 2020 2022 Total Unused (d) One Year Two Years Term Out No Term Out (in millions) Southern Company (a) $ — $ — $ 2,000 $ 2,000 $ 1,999 $ — $ — $ — $ — Alabama Power 33 500 800 1,333 1,333 — — — 33 Georgia Power — — 1,750 1,750 1,736 — — — — Mississippi Power 100 — — 100 100 — — — 100 Southern Power (b) — — 750 750 727 — — — — Southern Company Gas (c) — — 1,900 1,900 1,895 — — — — Other 30 — — 30 30 — — — 30 Southern Company Consolidated (e) $ 163 $ 500 $ 7,200 $ 7,863 $ 7,820 $ — $ — $ — $ 163 (a) Represents the Southern Company parent entity. (b) Southern Power's subsidiaries are not parties to its bank credit arrangement. (c) Southern Company Gas provides a parent guarantee of the obligations of its subsidiary Southern Company Gas Capital, which is the borrower of $1.4 billion ( $1.395 billion unused) of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 million (all unused) 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. (d) Amounts used are for letters of credit. (e) Excludes $280 million of committed credit arrangements of Gulf Power, which was sold on January 1, 2019. See Note 15 under " Southern Company's Sale of Gulf Power " for additional information.
Details of Short-Term Borrowings	Details of short-term borrowings were as follows: Notes Payable at December 31, 2018 Notes Payable at December 31, 2017 Amount Outstanding Weighted Average Interest Rate Amount Outstanding Weighted Average Interest Rate (in millions) (in millions) Southern Company Commercial paper $ 1,064 3.0 % $ 1,832 1.8 % Short-term bank debt 1,851 3.1 % 607 2.3 % Total $ 2,915 3.1 % $ 2,439 1.9 % Alabama Power Short-term bank debt $ — — % $ 3 3.7 % Georgia Power Commercial paper $ 294 3.1 % $ — — % Short-term bank debt — — % 150 2.2 % Total $ 294 3.1 % $ 150 2.2 % Mississippi Power Short-term bank debt $ — — % $ 4 3.8 % Southern Power Commercial paper $ — — % $ 105 2.0 % Short-term bank debt 100 3.1 % — — % Total $ 100 3.1 % $ 105 2.0 % Southern Company Gas Commercial paper: Southern Company Gas Capital $ 403 3.1 % $ 1,243 1.7 % Nicor Gas 247 3.0 % 275 1.8 % Total $ 650 3.0 % $ 1,518 1.8 %
Shares Used to Compute Diluted EPS	Shares used to compute diluted EPS were as follows: Average Common Stock Shares 2018 2017 2016 (in millions) As reported shares 1,020 1,000 951 Effect of options and performance share award units 5 8 7 Diluted shares 1,025 1,008 958
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, 2015 and 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: $ 291 (a) See " Alabama Power " herein for additional information. (b) See " Mississippi Power " herein for additional information. 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

Commitments (Tables)

Commitments (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Estimated long-term obligations	Fuel expense in 2018 , 2017 , and 2016 for the Southern Company system is shown below, the majority of which was purchased under long-term commitments. Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) 2018 $ 4,637 $ 1,301 $ 1,698 $ 405 $ 699 2017 4,400 1,225 1,671 395 621 2016 4,361 1,297 1,807 343 456 Total capacity expense under these non-affiliate PPAs accounted for as operating leases in 2018 , 2017 , and 2016 was as follows: Southern Company Alabama Power Georgia Power (in millions) 2018 $ 231 $ 44 $ 113 2017 235 41 118 2016 232 42 113 Estimated total obligations under non-affiliate PPAs accounted for as operating leases at December 31, 2018 were as follows: Southern Company Alabama Power Georgia Power (in millions) 2019 $ 161 $ 41 $ 120 2020 164 42 122 2021 168 44 124 2022 171 46 125 2023 127 — 127 2024 and thereafter 642 — 642 Total $ 1,433 $ 173 $ 1,260 Georgia Power's estimated total obligations under affiliate PPAs accounted for as leases at December 31, 2018 were as follows: Georgia Power Affiliate Capital Lease PPAs Affiliate Operating Lease PPAs (in millions) 2019 $ 23 $ 64 2020 23 65 2021 24 66 2022 24 68 2023 25 69 2024 and thereafter 158 349 Total $ 277 $ 681 Less: amounts representing executory costs (a) 42 Net minimum lease payments 235 Less: amounts representing interest (b) 105 Present value of net minimum lease payments $ 130 (a) Executory costs such as taxes, maintenance, and insurance (including the estimated profit thereon) a re estimated and included in total minimum lease payments. (b) Calculated using an adjusted incremental borrowing rate to reduce the present value of the net minimum lease payments to fair value.
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, 2018 were as follows: Pipeline Charges, Storage Capacity, and Gas Supply (in millions) 2019 $ 781 2020 584 2021 520 2022 489 2023 412 2024 and thereafter 1,871 Total $ 4,657
Schedule of rent expense	Total rent expense for 2018 , 2017 , and 2016 was as follows: Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power (*) (in millions) 2018 $ 192 $ 23 $ 34 $ 4 $ 31 2017 176 25 31 3 29 2016 169 18 28 3 22 (*) 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. Southern Company Gas (in millions) 2018 $ 15 2017 15 Successor – July 1, 2016 through December 31, 2016 8 Predecessor – January 1, 2016 through June 30, 2016 6
Estimated minimum lease payments under operating leases	At December 31, 2018 , estimated minimum lease payments under operating leases were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) 2019 $ 156 $ 12 $ 23 $ 3 $ 23 $ 18 2020 134 10 18 2 24 16 2021 110 7 9 1 24 15 2022 98 6 6 1 24 13 2023 79 3 5 1 26 10 2024 and thereafter 1,040 1 13 2 874 34 Total $ 1,617 $ 39 $ 74 $ 10 $ 995 $ 106

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Details of income tax provisions	Details of income tax provisions are as follows: 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ 167 $ 91 $ 393 $ (567 ) $ 85 Deferred 231 123 (249 ) 575 (154 ) 398 214 144 8 (69 ) State — Current 188 26 81 (10 ) (9 ) Deferred (137 ) 51 (11 ) (100 ) (86 ) 51 77 70 (110 ) (95 ) Total $ 449 $ 291 $ 214 $ (102 ) $ (164 ) 2017 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ (62 ) $ 136 $ 256 $ 194 $ (566 ) Deferred (6 ) 336 504 (753 ) (312 ) (68 ) 472 760 (559 ) (878 ) State — Current 37 23 116 — (110 ) Deferred 173 73 (46 ) 27 49 210 96 70 27 (61 ) Total $ 142 $ 568 $ 830 $ (532 ) $ (939 ) 2016 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) Federal — Current $ 1,184 $ 103 $ 391 $ (31 ) $ 928 Deferred (342 ) 339 319 (60 ) (1,098 ) 842 442 710 (91 ) (170 ) State — Current (108 ) 20 6 (6 ) (60 ) Deferred 217 69 64 (7 ) 35 109 89 70 (13 ) (25 ) Total $ 951 $ 531 $ 780 $ (104 ) $ (195 ) Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Federal — Current $ 334 $ 103 $ — $ 67 Deferred 33 170 65 8 367 273 65 75 State — Current 131 27 (16 ) 12 Deferred (34 ) 67 27 — 97 94 11 12 Total $ 464 $ 367 $ 76 $ 87
Summary of amortization of tax credits	ITCs amortized in 2018 , 2017 , and 2016 were immaterial for Alabama Power, Georgia Power, Mississippi Power, and Southern Company Gas and were as follows for Southern Company and Southern Power: Southern Company Southern Power (in millions) 2018 $ 87 $ 58 2017 79 57 2016 59 37
Schedule of effective income tax reconciliation	A reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Federal statutory rate 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 ) 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 ) — 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 ) Tax impact from sale of subsidiaries 8.6 — — — — Tax Reform Legislation (1.4 ) — (4.9 ) (26.3 ) 96.1 Noncontrolling interests (0.4 ) — — — (14.9 ) Other (0.8 ) (0.1 ) 0.1 (1.4 ) 2.0 Effective income tax (benefit) rate 16.3 % 23.6 % 21.3 % (75.4 )% (198.8 )% 2017 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Federal statutory rate 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 ) 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 ) — — 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 ) Tax Reform Legislation (25.6 ) 0.3 (0.4 ) 11.9 (416.1 ) Noncontrolling interests (1.4 ) — — — (8.6 ) Other (1.1 ) 0.1 0.2 — (10.7 ) Effective income tax (benefit) rate 13.3 % 39.6 % 36.7 % (17.1 )% (525.7 )% (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2017. 2016 Southern Company Alabama Power Georgia Power Mississippi Power (*) Southern Power Federal statutory rate 35.0 % 35.0 % 35.0 % (35.0 )% 35.0 % State income tax, net of federal deduction 2.0 4.2 2.1 (5.7 ) (9.1 ) Employee stock plans' dividend deduction (1.2 ) — — — — Non-deductible book depreciation 0.9 1.0 0.8 0.7 — Flowback of excess deferred income taxes (0.1 ) — (0.1 ) (0.3 ) — AFUDC-Equity (2.0 ) (0.7 ) (0.8 ) (28.5 ) — ITC basis difference (5.0 ) — — — (96.3 ) Federal PTCs (1.2 ) — — — (23.3 ) Amortization of ITC (0.9 ) (0.2 ) (0.2 ) (0.1 ) (13.4 ) Noncontrolling interests (0.3 ) — — — (6.2 ) Other 0.1 (0.5 ) (0.1 ) 0.4 4.7 Effective income tax (benefit) rate 27.3 % 38.8 % 36.7 % (68.5 )% (108.6 )% (*) Represents effective income tax benefit rate for Mississippi Power due to a loss before income taxes in 2016. Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 Federal statutory rate 21.0% 35.0% 35.0% 35.0% State income tax, net of federal deduction 9.2 10.0 3.6 3.5 Flowback of excess deferred income taxes (3.0) (0.2) — — Amortization of ITC (0.1) (0.2) (0.4) — Tax impact on sale of subsidiaries 28.5 — — — Tax Reform Legislation (0.4) 15.0 — — Other 0.3 0.6 1.8 (0.9) Effective income tax rate 55.5% 60.2% 40.0% 37.6%
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, 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 AROs 1,232 276 925 31 — — AROs 1,210 607 575 — — — Other 593 177 141 68 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 taxes – assets $ (276 ) $ — $ — $ (150 ) $ (1,186 ) $ — Accumulated deferred income taxes – liabilities $ 6,558 $ 2,962 $ 3,062 $ 378 $ 105 $ 1,016 December 31, 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Deferred tax liabilities — Accelerated depreciation $ 9,059 $ 2,135 $ 2,889 $ 303 $ 1,922 $ 1,150 Property basis differences 1,853 725 606 207 2 204 Federal effect of net state deferred tax assets — — — 9 — — Leveraged lease basis differences 251 — — — — — Employee benefit obligations 527 162 287 28 7 4 Premium on reacquired debt 54 16 34 — — — Regulatory assets – Storm damage reserves 89 — 89 — — — Employee benefit obligations 1,044 260 349 46 — 75 AROs 821 249 501 33 — — AROs 370 220 130 — — — Other 689 147 140 73 30 208 Total deferred income tax liabilities 14,757 3,914 5,025 699 1,961 1,641 Deferred tax assets — Federal effect of net state deferred tax liabilities 330 143 85 — 42 54 Employee benefit obligations 1,339 286 448 62 8 185 Other property basis differences 343 — 59 — 184 — ITC and PTC carryforward 2,414 9 403 — 2,002 — Federal NOL carryforward 518 — — 40 333 92 Alternative minimum tax carryforward 69 — — 32 21 — Other partnership basis difference 23 — — — 23 — Other comprehensive losses 84 10 4 — 1 — AROs 1,191 469 631 33 — — Estimated loss on plants under construction 722 — — 722 — — Other deferred state tax attributes 330 — 6 133 77 — Regulatory liability associated with the Tax Reform Legislation (not subject to normalization) 304 126 123 27 — 9 Other 538 111 91 54 9 223 Total deferred income tax assets 8,205 1,154 1,850 1,103 2,700 563 Valuation allowance (184 ) — — (157 ) (13 ) (11 ) Net deferred income tax assets 8,021 1,154 1,850 946 2,687 552 Net deferred income taxes (assets)/liabilities $ 6,736 $ 2,760 $ 3,175 $ (247 ) $ (726 ) $ 1,089 Recognized in the balance sheets: Accumulated deferred income $ (106 ) $ — $ — $ (247 ) $ (925 ) $ — Accumulated deferred income taxes – liabilities $ 6,842 $ 2,760 $ 3,175 $ — $ 199 $ 1,089
Summary of tax credit carryforwards	Federal ITC/PTC carryforwards at December 31, 2018 were as follows: Southern Company Alabama Power Georgia Power Southern Power (in millions) Federal ITC/PTC carryforwards $ 2,410 $ 11 $ 108 $ 2,128 Year in which federal ITC/PTC carryforwards begin expiring 2032 2033 2032 2034 Year by which federal ITC/PTC carryforwards are expected to be utilized 2022 2021 2021 2022
Summary of operating loss carryforward	At December 31, 2018 , 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 $ 5,062 $ 200 2031 Southern Power Oklahoma 846 40 2035 Florida 264 11 2033 South Carolina 62 2 2034 Other states 42 3 2029 Southern Power Total $ 1,214 $ 56 Other (*) Georgia 358 16 2019 New York 223 11 2036 New York City 208 15 2036 Other states 278 14 Various Southern Company Total $ 7,343 $ 312 (*) Represents other Southern Company subsidiaries. Alabama Power, Georgia Power, and Southern Company Gas did not have state NOL carryforwards at December 31, 2018 .
Changes in unrecognized tax benefits	Unrecognized tax benefits changes in 2018 , 2017 , and 2016 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, 2015 $ 433 $ 421 $ 8 Tax positions changes – Increase from current periods 45 26 17 Increase from prior periods 21 18 — Decrease from prior periods (15 ) — (8 ) 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, Mississippi Power, and Southern Power, if recognized, was as follows for 2017 and 2016: Southern Company Mississippi Power Southern Power (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 $ — $ — 2016 Tax positions impacting the effective tax rate $ 20 $ 1 $ 17 Tax positions not impacting the effective tax rate 464 464 — Balance of unrecognized tax benefits $ 484 $ 465 $ 17

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Schedule of Defined Benefit Plan	The portion of the Southern Company system's pension and other postretirement benefit plans attributable to Gulf Power that is reflected in Southern Company's consolidated balance sheet as held for sale at December 31, 2018 consists of: 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. 2018 Assumptions used to determine net Southern Company Alabama Power Georgia Mississippi Power Southern Power Pension plans Discount rate – benefit obligations 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % Discount rate – interest costs 3.45 3.45 3.42 3.46 3.69 Discount rate – service costs 3.98 4.00 3.99 3.99 4.01 Expected long-term return on plan assets 7.95 7.95 7.95 7.95 7.95 Annual salary increase 4.34 4.46 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % Discount rate – interest costs 3.29 3.31 3.29 3.29 3.47 Discount rate – service costs 3.91 3.93 3.91 3.91 3.93 Expected long-term return on plan assets 6.83 6.83 6.80 6.99 — Annual salary increase 4.34 4.46 4.46 4.46 4.46 2017 Assumptions used to determine net Southern Company Alabama Georgia Mississippi Power Pension plans Discount rate – benefit obligations 4.40 % 4.44 % 4.40 % 4.44 % Discount rate – interest costs 3.77 3.76 3.72 3.81 Discount rate – service costs 4.81 4.85 4.83 4.83 Expected long-term return on plan assets 7.92 7.95 7.95 7.95 Annual salary increase 4.37 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 4.23 % 4.27 % 4.23 % 4.22 % Discount rate – interest costs 3.54 3.58 3.55 3.55 Discount rate – service costs 4.64 4.70 4.63 4.65 Expected long-term return on plan assets 6.84 6.83 6.79 6.88 Annual salary increase 4.37 4.46 4.46 4.46 2016 Assumptions used to determine net periodic costs: Southern Company Alabama Georgia Mississippi Power Pension plans Discount rate – benefit obligations 4.58 % 4.67 % 4.65 % 4.69 % Discount rate – interest costs 3.88 3.90 3.86 3.97 Discount rate – service costs 4.98 5.07 5.03 5.04 Expected long-term return on plan assets 8.16 8.20 8.20 8.20 Annual salary increase 4.37 4.46 4.46 4.46 Other postretirement benefit plans Discount rate – benefit obligations 4.38 % 4.51 % 4.49 % 4.47 % Discount rate – interest costs 3.66 3.69 3.67 3.66 Discount rate – service costs 4.85 4.96 4.88 4.88 Expected long-term return on plan assets 6.66 6.83 6.27 7.07 Annual salary increase 4.37 4.46 4.46 4.46 Southern Company Gas Successor Predecessor Assumptions used to determine net periodic costs: Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 Pension plans Discount rate – benefit obligations 3.74 % 4.39 % 3.85 % 4.60 % Discount rate – interest costs 3.41 3.76 3.21 4.00 Discount rate – service costs 3.84 4.64 4.07 4.80 Expected long-term return on plan assets 7.95 7.60 7.75 7.80 Annual salary increase 3.07 3.50 3.50 3.70 Pension band increase (*) N/A N/A 2.00 2.00 Other postretirement benefit plans Discount rate - benefit obligations 3.62 % 4.15 % 3.61 % 4.40 % Discount rate – interest costs 3.21 3.40 2.84 3.60 Discount rate – service costs 3.82 4.55 3.96 4.70 Expected long-term return on plan assets 5.89 6.03 5.93 6.60 Annual salary increase 3.07 3.50 3.50 3.70 (*) Only applicable to Nicor Gas union employees. The pension bands for the former Nicor Gas plan reflect the negotiated rates in accordance with the union agreements. 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 2017 Assumptions used to determine benefit obligations: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Pension plans Discount rate 3.80 % 3.81 % 3.79 % 3.80 % 3.94 % 3.74 % Annual salary increase 4.32 4.46 4.46 4.46 4.46 2.88 Other postretirement benefit plans Discount rate 3.68 % 3.71 % 3.68 % 3.68 % 3.81 % 3.62 % Annual salary increase 4.32 4.46 4.46 4.46 4.46 2.56
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, 2018 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Pre-65 6.50 % 4.50 % 2028 Post-65 medical 5.00 4.50 2028 Post-65 prescription 8.00 4.50 2028
Schedule of Accumulated and Projected Benefit Obligations	The projected benefit obligations for the qualified and non-qualified pension plans at December 31, 2018 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 $ 12,135 $ 2,692 $ 3,757 $ 527 $ 122 $ 866 Non-qualified pension plan 629 124 148 30 1 41 The total accumulated benefit obligation for the pension plans at December 31, 2018 and 2017 was as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) December 31, 2018 $ 11,683 $ 2,550 $ 3,613 $ 513 $ 101 $ 842 December 31, 2017 12,577 2,696 3,847 541 111 1,139
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, 2018 and 2017 were as follows: 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 ) 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 12,385 $ 2,663 $ 3,800 $ 534 $ — $ 1,133 Service cost 293 63 74 15 — 23 Interest cost 455 98 138 20 — 42 Benefits paid (596 ) (120 ) (187 ) (22 ) — (91 ) Plan amendments (26 ) — — — — (26 ) Actuarial (gain) loss 1,297 294 363 55 — 103 Obligations assumed from employee transfer — — — — 139 — Balance at end of year 13,808 2,998 4,188 602 139 1,184 Change in plan assets Fair value of plan assets at beginning of year 11,583 2,517 3,621 499 — 983 Actual return (loss) on plan assets 1,953 427 610 84 — 175 Employer contributions 52 12 14 2 — 1 Benefits paid (596 ) (120 ) (187 ) (22 ) — (91 ) Assets assumed from employee transfer — — — — 138 — Fair value of plan assets at end of year 12,992 2,836 4,058 563 138 1,068 Accrued liability $ (816 ) $ (162 ) $ (130 ) $ (39 ) $ (1 ) $ (116 )
Amounts Recognized in Balance Sheets	Presented below are the amounts included in regulatory assets at December 31, 2018 and 2017 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, 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 (liabilities) $ 3,458 $ 955 $ 1,230 $ 167 $ 160 Balance at December 31, 2017 Regulatory assets: Prior service cost $ 14 $ 8 $ 14 $ 3 $ (20 ) Net (gain) loss 3,140 882 1,091 155 197 Regulatory amortization (*) — — — — 40 Total regulatory assets $ 3,154 $ 890 $ 1,105 $ 158 $ 217 (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. Amounts recognized in the balance sheets at December 31, 2018 and 2017 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, 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 ) December 31, 2017: Prepaid pension costs $ — $ — $ 23 $ — $ — $ — Other regulatory assets, deferred 3,273 890 1,105 158 — 217 Other deferred charges and assets — — — — — 85 Other current liabilities (53 ) (12 ) (15 ) (3 ) — (3 ) Employee benefit obligations (763 ) (150 ) (138 ) (36 ) (1 ) (198 ) Other regulatory liabilities, deferred (118 ) — — — — — AOCI 107 — — — 33 (42 ) (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. Amounts recognized in the balance sheets at December 31, 2018 and 2017 related to the registrants' other postretirement benefit plans consist of the following: Southern (a) Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) 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 ) December 31, 2017: Other regulatory assets, deferred (a) $ 382 $ 63 $ 202 $ 18 $ — $ 46 Other current liabilities (5 ) — — — — — Employee benefit obligations (b) (1,281 ) (111 ) (477 ) (72 ) (11 ) (185 ) Other regulatory liabilities, deferred (41 ) (7 ) — (1 ) — — AOCI 4 — — — 3 (3 ) (a) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016. (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, 2018 and 2017 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 (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Balance at December 31, 2018 Regulatory assets: 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 ) Balance at December 31, 2017 Regulatory assets: Prior service cost $ 21 $ 11 $ 5 $ — $ (7 ) Net (gain) loss 320 45 197 17 47 Regulatory amortization (*) — — — — 6 Total regulatory assets $ 341 $ 56 $ 202 $ 17 $ 46 (*) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016.
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, 2018 and 2017 are presented in the following table: Southern (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Regulatory assets (liabilities): Balance at December 31, 2016 $ 3,120 $ 870 $ 1,129 $ 154 $ 267 Net (gain) loss 227 64 36 12 (31 ) Change in prior service costs (26 ) — — — — Reclassification adjustments: Amortization of prior service costs (11 ) (2 ) (3 ) (1 ) — Amortization of net gain (loss) (155 ) (42 ) (57 ) (7 ) (18 ) Amortization of regulatory assets (*) — — — — (1 ) Total reclassification adjustments (166 ) (44 ) (60 ) (8 ) (19 ) Total change 35 20 (24 ) 4 (50 ) 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 (*) Amounts for Southern Company exclude regulatory assets of $268 million associated with unamortized amounts in Southern Company Gas' pension plans prior to its acquisition by Southern Company on July 1, 2016. The changes in the balance of net regulatory assets (liabilities) related to the other postretirement benefit plans for the plan years ended December 31, 2018 and 2017 are presented in the following table: Southern (*) Alabama Power Georgia Mississippi Power Southern Company Gas (in millions) Net regulatory assets (liabilities): Balance at December 31, 2016 $ 378 $ 76 $ 213 $ 19 $ 52 Net (gain) loss (21 ) (15 ) (2 ) (1 ) (5 ) Change in prior service costs 3 — — — — Reclassification adjustments: Amortization of prior service costs (6 ) (4 ) (1 ) — 3 Amortization of net gain (loss) (13 ) (1 ) (8 ) (1 ) (4 ) Total reclassification adjustments (19 ) (5 ) (9 ) (1 ) (1 ) Total change (37 ) (20 ) (11 ) (2 ) (6 ) 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 ) (*) Amounts for Southern Company exclude regulatory assets of $57 million associated with unamortized amounts in Southern Company Gas' other postretirement benefit plans prior to its acquisition by Southern Company on July 1, 2016.
Amounts Included in AOCI Related to Defined Benefit Pension Plans	Presented below are the amounts included in AOCI at December 31, 2018 and 2017 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, 2018 AOCI: Prior service cost $ (3 ) $ — $ (6 ) Net (gain) loss 100 26 (38 ) Total AOCI $ 97 $ 26 $ (44 ) Balance at December 31, 2017 AOCI: Prior service cost $ 3 $ 1 $ — Net (gain) loss 104 32 (42 ) Total AOCI $ 107 $ 33 $ (42 ) Presented below are the amounts included in AOCI at December 31, 2018 and 2017 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, 2018 AOCI: Prior service cost $ 1 $ — $ 1 Net (gain) loss (5 ) 1 (5 ) Total AOCI $ (4 ) $ 1 $ (4 ) Balance at December 31, 2017 AOCI: Prior service cost $ — $ — $ — Net (gain) loss 4 3 (3 ) Total AOCI $ 4 $ 3 $ (3 )
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, 2018 and 2017 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2016 $ 100 $ — $ (43 ) Net (gain) loss 15 — 1 Change from employee transfer — 33 — Reclassification adjustments: Amortization of prior service costs (1 ) — — Amortization of net gain (loss) (7 ) — — Total reclassification adjustments (8 ) — — Total change 7 33 1 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 ) The components of OCI related to the other postretirement benefit plans for the plan years ended December 31, 2018 and 2017 are presented in the following table: Southern Company Southern Power Southern Company Gas (in millions) AOCI: Balance at December 31, 2016 $ 7 $ — $ (3 ) Net (gain) loss (3 ) — (1 ) Change from employee transfer — 3 1 Total change (3 ) 3 — Balance at December 31, 2017 $ 4 $ 3 $ (3 ) Net (gain) loss (8 ) (2 ) (2 ) Amortization of prior service costs — — 1 Total change (8 ) (2 ) (1 ) Balance at December 31, 2018 $ (4 ) $ 1 $ (4 )
Components of Net Periodic Benefit Cost	Components of net periodic pension cost for Southern Company, the traditional electric operating companies, and Southern Power were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) 2018: Service cost $ 359 $ 78 $ 87 $ 17 $ 9 Interest cost 464 101 139 20 5 Expected return on plan assets (943 ) (207 ) (296 ) (41 ) (10 ) Recognized net (gain) loss 213 54 69 10 1 Net amortization 4 1 2 — — Net periodic pension cost $ 97 $ 27 $ 1 $ 6 $ 5 2017: Service cost $ 293 $ 63 $ 74 $ 15 Interest cost 455 98 138 20 Expected return on plan assets (897 ) (196 ) (283 ) (40 ) Recognized net (gain) loss 162 42 57 7 Net amortization 12 2 3 1 Net periodic pension cost $ 25 $ 9 $ (11 ) $ 3 2016: Service cost $ 262 $ 57 $ 70 $ 13 Interest cost 422 95 136 19 Expected return on plan assets (782 ) (184 ) (258 ) (35 ) Recognized net (gain) loss 150 40 55 7 Net amortization 14 3 5 1 Net periodic pension cost $ 66 $ 11 $ 8 $ 5 Components of net periodic pension cost for Southern Company Gas were as follows: Southern Company Gas Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Service cost $ 34 $ 23 $ 15 $ 13 Interest cost 39 42 20 21 Expected return on plan assets (75 ) (70 ) (35 ) (33 ) Recognized net (gain) loss 12 18 14 13 Net amortization of regulatory asset 15 1 — — Prior service cost (2 ) — (1 ) (1 ) Net periodic pension cost $ 23 $ 14 $ 13 $ 13 Components of the other postretirement benefit plans' net periodic cost for Southern Company, the traditional electric operating companies, and Southern Power were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power (in millions) 2018: Service cost $ 24 $ 6 $ 6 $ 1 $ 1 Interest cost 75 17 28 3 — Expected return on plan assets (69 ) (26 ) (25 ) (2 ) — Net amortization 21 5 10 1 — Net periodic postretirement benefit cost $ 51 $ 2 $ 19 $ 3 $ 1 2017: Service cost $ 24 $ 6 $ 7 $ 1 Interest cost 79 17 29 3 Expected return on plan assets (66 ) (25 ) (25 ) (1 ) Net amortization 20 5 9 1 Net periodic postretirement benefit cost $ 57 $ 3 $ 20 $ 4 2016: Service cost $ 22 $ 5 $ 6 $ 1 Interest cost 76 18 30 3 Expected return on plan assets (60 ) (25 ) (22 ) (1 ) Net amortization 21 6 10 1 Net periodic postretirement benefit cost $ 59 $ 4 $ 24 $ 4 Components of the other postretirement benefit plans' net periodic cost for Southern Company Gas were as follows: Successor Predecessor Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Service cost $ 2 $ 2 $ 1 $ 1 Interest cost 10 10 5 5 Expected return on plan assets (7 ) (7 ) (3 ) (3 ) Amortization: Regulatory assets 6 — 2 — Prior service costs — (3 ) — (1 ) Net (gain)/loss — 4 — 2 Net periodic postretirement benefit cost $ 11 $ 6 $ 5 $ 4
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, 2018 and 2017 were as follows: 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 ) 2017 Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 2,297 $ 501 $ 847 $ 97 $ — $ 308 Service cost 24 6 7 1 — 2 Interest cost 79 17 29 3 — 10 Benefits paid (136 ) (29 ) (51 ) (6 ) — (19 ) Actuarial (gain) loss 65 20 28 1 — 3 Plan amendments 3 — — — — 3 Retiree drug subsidy 7 2 3 1 — — Obligations assumed from employee transfer — — — — 11 — Employee contributions — — — — — 3 Balance at end of year 2,339 517 863 97 11 310 Change in plan assets Fair value of plan assets at beginning of year 944 367 354 23 — 105 Actual return (loss) on plan assets 154 60 54 3 — 20 Employer contributions 84 6 26 4 — 17 Employee contributions — — — — — 3 Benefits paid (129 ) (27 ) (48 ) (5 ) — (20 ) Fair value of plan assets at end of year 1,053 406 386 25 — 125 Accrued liability $ (1,286 ) $ (111 ) $ (477 ) $ (72 ) $ (11 ) $ (185 )
Estimated Pension Benefit Payments	At December 31, 2018 , estimated benefit payments were as follows: Southern Company Alabama Power Georgia Mississippi Power Southern Power Southern Company Gas (in millions) Benefit Payments: 2019 $ 623 $ 132 $ 201 $ 28 $ 3 $ 59 2020 645 136 206 28 3 61 2021 664 141 209 29 4 62 2022 687 147 215 29 4 62 2023 711 152 221 30 5 62 2024 to 2028 3,869 832 1,183 166 27 313 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: 2019 $ 136 $ 28 $ 51 $ 6 $ — $ 18 2020 136 28 50 6 — 18 2021 136 29 50 6 — 19 2022 137 29 50 6 1 19 2023 137 29 49 7 1 19 2024 to 2028 669 146 243 30 3 90 Subsidy receipts: 2019 $ (7 ) $ (2 ) $ (3 ) $ — $ — $ — 2020 (7 ) (2 ) (3 ) — — — 2021 (8 ) (2 ) (3 ) — — — 2022 (8 ) (2 ) (3 ) (1 ) — — 2023 (8 ) (3 ) (4 ) (1 ) — — 2024 to 2028 (41 ) (13 ) (18 ) (2 ) — — Total: 2019 $ 129 $ 26 $ 48 $ 6 $ — $ 18 2020 129 26 47 6 — 18 2021 128 27 47 6 — 19 2022 129 27 47 5 1 19 2023 129 26 45 6 1 19 2024 to 2028 628 133 225 28 3 90
Fair Values of Plan Assets	The composition of Southern Company Gas' other postretirement benefit plan assets at December 31, 2017, along with the targets, is presented below: Target 2017 Other postretirement benefit plan assets: Equity 72 % 76 % Fixed Income 24 20 Cash 1 2 Other 3 2 Total 100 % 100 % 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, 2018: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Assets: Domestic equity (*) $ 2,102 $ 1,030 $ — $ 3,132 26 % 28 % International equity (*) 1,344 1,325 — 2,669 25 25 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: Domestic equity (*) $ 466 $ 228 $ — $ 694 26 % 28 % International equity (*) 298 293 — 591 25 25 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: Domestic equity (*) $ 663 $ 325 $ — $ 988 26 % 28 % International equity (*) 424 418 — 842 25 25 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: Domestic equity (*) $ 91 $ 45 $ — $ 136 26 % 28 % International equity (*) 59 59 — 118 25 25 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: Domestic equity (*) $ 22 $ 11 $ — $ 33 26 % 28 % International equity (*) 14 14 — 28 25 25 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: Domestic equity (*) $ 145 $ 71 $ — $ 216 26 % 28 % International equity (*) 92 91 — 183 25 25 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 % (*) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. 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, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company (a) Assets: Domestic equity (b) $ 2,559 $ 1,482 $ — $ 4,041 26 % 31 % International equity (b) 1,555 1,569 — 3,124 25 25 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 926 — 926 Mortgage- and asset-backed securities — 8 — 8 Corporate bonds — 1,241 — 1,241 Pooled funds — 650 — 650 Cash equivalents and other 301 36 48 385 Real estate investments 472 — 1,204 1,676 14 13 Special situations — — 180 180 3 1 Private equity — — 670 670 9 6 Total $ 4,887 $ 5,912 $ 2,102 $ 12,901 100 % 100 % Alabama Power Assets: Domestic equity (b) $ 572 $ 276 $ — $ 848 26 % 31 % International equity (b) 370 333 — 703 25 25 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 200 — 200 Mortgage- and asset-backed securities — 2 — 2 Corporate bonds — 286 — 286 Pooled funds — 155 — 155 Cash equivalents and other 51 3 — 54 Real estate investments 111 — 283 394 14 13 Special situations — — 43 43 3 1 Private equity — — 159 159 9 6 Total $ 1,104 $ 1,255 $ 485 $ 2,844 100 % 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, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Domestic equity (b) $ 819 $ 394 $ — $ 1,213 26 % 31 % International equity (b) 529 477 — 1,006 25 25 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 286 — 286 Mortgage- and asset-backed securities — 3 — 3 Corporate bonds — 409 — 409 Pooled funds — 221 — 221 Cash equivalents and other 74 4 — 78 Real estate investments 160 — 404 564 14 13 Special situations — — 61 61 3 1 Private equity — — 228 228 9 6 Total $ 1,582 $ 1,794 $ 693 $ 4,069 100 % 100 % Mississippi Power Assets: Domestic equity (b) $ 113 $ 55 $ — $ 168 26 % 31 % International equity (b) 73 66 — 139 25 25 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 40 — 40 Corporate bonds — 56 — 56 Pooled funds — 31 — 31 Cash equivalents and other 10 1 — 11 Real estate investments 22 — 56 78 14 13 Special situations — — 9 9 3 1 Private equity — — 32 32 9 6 Total $ 218 $ 249 $ 97 $ 564 100 % 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, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Southern Power Assets: Domestic equity (b) $ 28 $ 13 $ — $ 41 26 % 31 % International equity (b) 18 16 — 34 25 25 Fixed income: 23 24 U.S. Treasury, government, and agency bonds — 10 — 10 Corporate bonds — 14 — 14 Pooled funds — 8 — 8 Cash equivalents and other 2 — — 2 Real estate investments 5 — 14 19 14 13 Special situations — — 2 2 3 1 Private equity — — 8 8 9 6 Total $ 53 $ 61 $ 24 $ 138 100 % 100 % (a) Target and actual allocations reflect the asset allocations for only the Southern Company system pension plan prior to its merger with the Southern Company Gas pension plan on January 1, 2018. (b) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. The fair values of Southern Company Gas' pension plan assets for the period ended December 31, 2017 are presented below. The fair value measurements exclude cash, receivables related to investment income, pending investment sales, and payables related to pending investment purchases. Special situations (absolute return and hedge funds) investment assets are presented in the tables below based on the nature of the investment. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient At December 31, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company Gas Assets: Domestic equity (*) $ 155 $ 323 $ — $ 478 International equity (*) — 166 — 166 Fixed income: U.S. Treasury, government, and agency bonds — 85 — 85 Corporate bonds — 39 — 39 Cash equivalents and other 84 25 48 157 Real estate investments 3 — 16 19 Private equity — — 1 1 Total $ 242 $ 638 $ 65 $ 945 (*) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. The composition of Southern Company Gas' pension plan assets at December 31, 2017 , along with the targets, is presented below: Target 2017 Pension plan assets: Equity 53 % 65 % Fixed Income 15 19 Cash 2 6 Other 30 10 Balance at end of period 100 % 100 % The fair values of the applicable registrants' other postretirement benefit plan assets at December 31, 2018 and 2017 are presented below. The registrants did not have any investments classified as Level 3 at December 31, 2018 or 2017 . 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, 2018: (Level 1) (Level 2) (NAV) (in millions) Southern Company Assets: Domestic equity (*) $ 100 $ 76 $ — $ 176 39 % 40 % International equity (*) 45 75 — 120 23 22 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: Domestic equity (*) $ 35 $ 10 $ — $ 45 43 % 45 % International equity (*) 12 12 — 24 21 21 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 Total Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) (in millions) Georgia Power Assets: Domestic equity (*) $ 41 $ 9 $ — $ 50 36 % 35 % International equity (*) 17 32 — 49 24 24 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: Domestic equity (*) $ 3 $ 2 $ — $ 5 21 % 22 % International equity (*) 2 2 — 4 20 20 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 Total Target Allocation Actual Allocation At December 31, 2018: (Level 1) (Level 2) (NAV) (in millions) Southern Company Gas Assets: Domestic equity (*) $ 2 $ 47 $ — $ 49 51 % 51 % International equity (*) 1 17 — 18 20 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 % (*) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. 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, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Southern Company (a) Assets: Domestic equity (b) $ 135 $ 104 $ — $ 239 37 % 40 % International equity (b) 47 98 — 145 23 23 Fixed income: 30 29 U.S. Treasury, government, and agency bonds — 32 — 32 Corporate bonds — 37 — 37 Pooled funds — 79 — 79 Cash equivalents and other 12 — 1 13 Trust-owned life insurance — 426 — 426 Real estate investments 16 — 36 52 5 5 Special situations — — 5 5 1 1 Private equity — — 20 20 4 2 Total $ 210 $ 776 $ 62 $ 1,048 100 % 100 % Alabama Power Assets: Domestic equity (b) $ 52 $ 12 $ — $ 64 42 % 44 % International equity (b) 16 14 — 30 22 22 Fixed income: 28 28 U.S. Treasury, government, and agency bonds — 11 — 11 Corporate bonds — 12 — 12 Pooled funds — 7 — 7 Cash equivalents and other 2 — — 2 Trust-owned life insurance — 253 — 253 Real estate investments 5 — 12 17 4 4 Special situations — — 2 2 1 — Private equity — — 7 7 3 2 Total $ 75 $ 309 $ 21 $ 405 100 % 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, 2017: (Level 1) (Level 2) (NAV) Total (in millions) Georgia Power Assets: Domestic equity (b) $ 53 $ 11 $ — $ 64 36 % 38 % International equity (b) 14 46 — 60 24 24 Fixed income: 33 31 U.S. Treasury, government, and agency bonds — 6 — 6 Corporate bonds — 11 — 11 Pooled funds — 41 — 41 Cash equivalents and other 4 — — 4 Trust-owned life insurance — 173 — 173 Real estate investments 6 — 11 17 4 4 Special situations — — 2 2 1 1 Private equity — — 6 6 2 2 Total $ 77 $ 288 $ 19 $ 384 100 % 100 % Mississippi Power Assets: Domestic equity (b) $ 4 $ 2 $ — $ 6 21 % 25 % International equity (b) 3 2 — 5 21 20 Fixed income: 37 38 U.S. Treasury, government, and agency bonds — 5 — 5 Corporate bonds — 2 — 2 Pooled funds — 1 — 1 Cash equivalents and other 1 — — 1 Real estate investments 1 — 2 3 12 11 Special situations — — — — 2 1 Private equity — — 1 1 7 5 Total $ 9 $ 12 $ 3 $ 24 100 % 100 % (a) Target and actual allocations reflect the asset allocations for only the Southern Company other postretirement benefit plans prior to the merger of the plans with the Southern Company Gas other postretirement benefit plans on January 1, 2018. (b) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. The fair values of Southern Company Gas' other postretirement benefit plan assets for the period ended December 31, 2017 are presented below. These fair value measurements exclude cash, receivables related to investment income, pending investment sales, and payables related to pending investment purchases. Special situations (absolute return and hedge funds) investment assets are presented in the tables below based on the nature of the investment. Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets Significant Net Asset Value as a Practical Expedient Total At December 31, 2017: (Level 1) (Level 2) (NAV) (in millions) Southern Company Gas Assets: Domestic equity (*) $ 3 $ 69 $ — $ 72 International equity (*) — 22 — 22 Fixed income: Pooled funds — 24 — 24 Cash equivalents and other 2 — 1 3 Total $ 5 $ 115 $ 1 $ 121 (*) Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds.
Total Matching Contributions	Total matching contributions made to the plans for 2018 , 2017 , and 2016 were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power (in millions) 2018 $ 119 $ 24 $ 26 $ 5 $ 3 2017 118 23 26 5 N/A 2016 105 23 27 5 N/A Southern Company Gas (in millions) Successor – 2018 $ 18 Successor – 2017 19 Successor – July 1, 2016 through December 31, 2016 8 Predecessor – January 1, 2016 through June 30, 2016 12

Stock Compensation (Tables)

Stock Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Employees Participating in Stock-Based Compensation Programs	At December 31, 2018 , 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 4,716 745 822 164 95 285
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 2018 2017 2016 Expected volatility 14.9% 15.6% 15.0% Expected term (in years) 3 3 3 Interest rate 2.4% 1.4% 0.8% Weighted average grant-date fair value $43.75 $49.08 $45.06
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, 2018 , 2017 , and 2016 are presented below: Year Ended December 31 2018 2017 2016 (in millions) Southern Company Intrinsic value of options exercised $ 9 $ 64 $ 120 Tax benefit of options exercised 2 25 46 Alabama Power Intrinsic value of options exercised $ 2 $ 12 $ 21 Tax benefit of options exercised — 5 8 Georgia Power Intrinsic value of options exercised $ 2 $ 13 $ 18 Tax benefit of options exercised — 5 7 Mississippi Power Intrinsic value of options exercised $ 1 $ 2 $ 4 Tax benefit of options exercised — 1 2 Total PSU compensation cost, and the related tax benefit recognized in income, for the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 (in millions) Southern Company Compensation cost recognized in income $ 91 $ 74 $ 96 Tax benefit of compensation cost recognized in income 24 29 37 Alabama Power Compensation cost recognized in income $ 11 $ 9 $ 15 Tax benefit of compensation cost recognized in income 3 4 6 Georgia Power Compensation cost recognized in income $ 11 $ 10 $ 15 Tax benefit of compensation cost recognized in income 3 4 6 Mississippi Power Compensation cost recognized in income $ 3 $ 2 $ 4 Tax benefit of compensation cost recognized in income 1 1 1 Southern Power Compensation cost recognized in income $ 4 N/A N/A Tax benefit of compensation cost recognized in income 1 N/A N/A Southern Company Gas Compensation cost recognized in income $ 11 $ 8 N/A Tax benefit of compensation cost recognized in income 3 3 N/A
Share-based Compensation, Stock Options, Activity	Southern Company's activity in the stock option program for 2018 is summarized below: Shares Subject to Option Weighted Average Exercise Price (in millions) Outstanding at December 31, 2017 18.6 $ 41.68 Exercised 1.1 37.82 Outstanding and Exercisable at December 31, 2018 17.5 $ 41.92
Schedule of Aggregate and Total Intrinsic Value Of Options Exercised	At December 31, 2018 , 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 $ 39 $ 5 $ 13 $ 1

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value on a recurring basis	The fair value increases (decreases) of the Funds, including reinvested interest and dividends and excluding the Funds' expenses, for 2018 , 2017 , and 2016 are shown in the table below. The fair value increases (decreases) included unrealized gains (losses) on securities held in the Funds at each of December 31, 2018 , 2017 , and 2016 , which are also shown in the table below. Southern Company Alabama Power Georgia Power (in millions) Fair value increases (decreases) 2018 $ (67 ) $ (38 ) $ (29 ) 2017 233 125 108 2016 114 76 38 Unrealized gains (losses) At December 31, 2018 $ (183 ) $ (96 ) $ (87 ) At December 31, 2017 181 98 83 At December 31, 2016 48 34 14 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. At December 31, 2017 , 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 331 $ 239 $ — $ — $ 570 Interest rate derivatives — 1 — — 1 Foreign currency derivatives — 129 — — 129 Nuclear decommissioning trusts: (c) Domestic equity 690 82 — — 772 Foreign equity 62 224 — — 286 U.S. Treasury and government agency securities — 251 — — 251 Municipal bonds — 68 — — 68 Corporate bonds 21 315 — — 336 Mortgage and asset backed securities — 57 — — 57 Private equity — — — 29 29 Other 19 12 — — 31 Cash equivalents 1,455 — — — 1,455 Other investments 9 — 1 — 10 Total $ 2,587 $ 1,378 $ 1 $ 29 $ 3,995 Liabilities: Energy-related derivatives (a)(b) $ 480 $ 253 $ — $ — $ 733 Interest rate derivatives — 38 — — 38 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ 480 $ 314 $ 22 $ — $ 816 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 4 $ — $ — $ 4 Nuclear decommissioning trusts: (d) Domestic equity 442 81 — — 523 Foreign equity 62 59 — — 121 U.S. Treasury and government agency securities — 24 — — 24 Corporate bonds 21 160 — — 181 Mortgage and asset backed securities — 18 — — 18 Private equity — — — 29 29 Other 6 — — — 6 Cash equivalents 349 — — — 349 Total $ 880 $ 346 $ — $ 29 $ 1,255 Liabilities: Energy-related derivatives $ — $ 10 $ — $ — $ 10 Georgia Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (d)(e) Domestic equity 248 1 — — 249 Foreign equity — 166 — — 166 U.S. Treasury and government agency securities — 227 — — 227 Municipal bonds — 68 — — 68 Corporate bonds — 155 — — 155 Mortgage and asset backed securities — 40 — — 40 Other 12 12 — — 24 Cash equivalents 690 — — — 690 Total $ 950 $ 675 $ — $ — $ 1,625 Liabilities: Energy-related derivatives $ — $ 19 $ — $ — $ 19 Interest rate derivatives — 5 — — 5 Total $ — $ 24 $ — $ — $ 24 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, 2017: (Level 1) (Level 2) (Level 3) (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 2 $ — $ — $ 2 Interest rate derivatives — 1 — — 1 Cash equivalents 224 — — — 224 Total $ 224 $ 3 $ — $ — $ 227 Liabilities: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Southern Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 129 — — 129 Cash equivalents 21 — — — 21 Total $ 21 $ 132 $ — $ — $ 153 Liabilities: Energy-related derivatives $ — $ 13 $ — $ — $ 13 Foreign currency derivatives — 23 — — 23 Contingent consideration — — 22 — 22 Total $ — $ 36 $ 22 $ — $ 58 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 331 $ 223 $ — $ — $ 554 Liabilities: Energy-related derivatives (a)(b) $ 479 $ 181 $ — $ — 660 (a) Energy-related derivatives exclude $11 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 $193 million . (c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table. (d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under " Nuclear Decommissioning " for additional information. (e) 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, 2018 and 2017 , 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, 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 At December 31, 2017: Long-term debt, including securities due within one year: Carrying amount $ 48,151 $ 7,625 $ 11,777 $ 2,086 $ 5,841 $ 6,048 Fair value 51,348 8,305 12,531 2,076 6,079 6,471 (a) Includes long-term debt of Gulf Power, which is classified as liabilities held for sale on Southern Company's balance sheet at December 31, 2018. See Note 15 under " Southern Company's Sale of Gulf Power " 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.

Derivatives (Tables)

Derivatives (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of energy-related derivatives	At December 31, 2018 , 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 (*) 431 2022 2029 Alabama Power 74 2022 — Georgia Power 153 2022 — Mississippi Power 63 2022 — Southern Power 15 2020 — Southern Company Gas (*) 120 2021 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 4,159 million mmBtu and short natural gas positions of 4,039 million mmBtu at December 31, 2018 , which is also included in Southern Company's total volume.
Notional amount of interest rate derivatives	At December 31, 2018 , 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) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month LIBOR + 0.92% June 2020 $ (4 ) Southern Company (*) 1,500 2.35% 1-month LIBOR + 0.87% July 2021 (43 ) Georgia Power 200 4.25% 3-month LIBOR + 2.46% December 2019 (2 ) Southern Company Consolidated $ 2,000 $ (49 ) (*) Represents the Southern Company parent entity.
Schedule of foreign exchange contracts	At December 31, 2018 , 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 $ 25 Southern Power 564 3.78% 500 1.85% June 2026 27 Total $ 1,241 € 1,100 $ 52
Fair value of energy-related derivatives and interest rate derivatives	At December 31, 2018 and 2017 , the fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: 2018 2017 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 $ 8 $ 23 $ 10 $ 43 Other deferred charges and assets/Other deferred credits and liabilities 9 26 7 24 Assets held for sale, current/Liabilities held for sale, current — 6 — — Total derivatives designated as hedging instruments for regulatory purposes $ 17 $ 55 $ 17 $ 67 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 7 $ 3 $ 14 Other deferred charges and assets/Other deferred credits and liabilities 1 2 — — Interest rate derivatives: Other current assets/Other current liabilities — 19 1 4 Other deferred charges and assets/Other deferred credits and liabilities — 30 — 34 Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 75 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 79 $ 81 $ 133 $ 75 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 561 $ 575 $ 380 $ 437 Other deferred charges and assets/Other deferred credits and liabilities 180 325 170 215 Total derivatives not designated as hedging instruments $ 741 $ 900 $ 550 $ 652 Gross amounts recognized $ 837 $ 1,036 $ 700 $ 794 Gross amounts offset (a) $ (524 ) $ (801 ) $ (405 ) $ (598 ) Net amounts recognized in the Balance Sheets (b) $ 313 $ 235 $ 295 $ 196 2018 2017 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 $ 3 $ 4 $ 2 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 3 6 2 4 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 10 $ 4 $ 10 Gross amounts recognized $ 6 $ 10 $ 4 $ 10 Gross amounts offset $ (4 ) $ (4 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 2 $ 6 $ — $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 8 $ 2 $ 9 Other deferred charges and assets/Other deferred credits and liabilities 4 13 4 10 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 21 $ 6 $ 19 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 2 $ — $ 4 Other deferred charges and assets/Other deferred credits and liabilities — — — 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 2 $ — $ 5 Gross amounts recognized $ 6 $ 23 $ 6 $ 24 Gross amounts offset $ (6 ) $ (6 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ — $ 17 $ — $ 18 2018 2017 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 $ 1 $ 3 $ 1 $ 6 Other deferred charges and assets/Other deferred credits and liabilities 2 6 1 3 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 9 $ 2 $ 9 Gross amounts recognized $ 3 $ 9 $ 3 $ 9 Gross amounts offset $ (2 ) $ (2 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ 1 $ 7 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 6 $ 3 $ 11 Other deferred charges and assets/Other deferred credits and liabilities 1 2 — — Foreign currency derivatives: Other current assets/Other current liabilities — 23 — 23 Other deferred charges and assets/Other deferred credits and liabilities 75 — 129 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 79 $ 31 $ 132 $ 34 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ — $ — $ — $ 2 Total derivatives not designated as hedging instruments $ — $ — $ — $ 2 Gross amounts recognized $ 79 $ 31 $ 132 $ 36 Gross amounts offset $ (3 ) $ (3 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 76 $ 28 $ 129 $ 33 2018 2017 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 $ 2 $ 8 $ 5 $ 8 Other deferred charges and assets/Other deferred credits and liabilities — 1 — — Total derivatives designated as hedging instruments for regulatory purposes $ 2 $ 9 $ 5 $ 8 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 1 $ — $ 3 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 1 $ — $ 3 Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 559 $ 574 $ 379 $ 434 Other deferred charges and assets/Other deferred credits and liabilities 180 325 170 215 Total derivatives not designated as hedging instruments $ 739 $ 899 $ 549 $ 649 Gross amounts recognized $ 741 $ 909 $ 554 $ 660 Gross amounts offset (a) $ (508 ) $ (785 ) $ (390 ) $ (583 ) Net amounts recognized in the Balance Sheets (b) $ 233 $ 124 $ 164 $ 77 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $277 million and $193 million at December 31, 2018 and 2017 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $8 million and $11 million at December 31, 2018 and 2017 , respectively.
Pre-tax effects on the balance sheets	At December 31, 2018 and 2017 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at 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 ) Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2017 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (34 ) $ (4 ) $ (7 ) $ (5 ) $ (4 ) Other regulatory assets, deferred (18 ) (3 ) (6 ) (2 ) — Other regulatory liabilities, current 7 1 — — 7 Other regulatory liabilities, deferred 1 — — — — Total energy-related derivative gains (losses) $ (44 ) $ (6 ) $ (13 ) $ (7 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $6 million at December 31, 2017 .
Pre-tax effects of interest rate derivatives, designated as cash flow hedging instruments	For the years ended December 31, 2018 , 2017 , and 2016 , 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 2018 2017 2016 (in millions) Southern Company Energy-related derivatives $ 17 $ (47 ) $ 18 Interest rate derivatives (1 ) (2 ) (180 ) Foreign currency derivatives (78 ) 140 (58 ) Total $ (62 ) $ 91 $ (220 ) Southern Power Energy-related derivatives $ 10 $ (38 ) $ 14 Foreign currency derivatives (78 ) 140 (58 ) Total $ (68 ) $ 102 $ (44 ) Successor Predecessor Gain (Loss) Recognized in OCI on Derivative Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 through December 31, 2016 January 1, 2016 through June 30, 2016 (in millions) (in millions) Southern Company Gas Energy-related derivatives $ 7 $ (9 ) $ 2 $ — Interest rate derivatives — — (5 ) (64 ) Total $ 7 $ (9 ) $ (3 ) $ (64 )
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, 2018 , 2017 , and 2016 were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships 2018 2017 2016 (in millions) Southern Company Total cost of natural gas $ 1,539 $ 1,601 $ 613 Gain (loss) on energy-related cash flow hedges (a) 2 (2 ) (1 ) Total depreciation and amortization 3,131 3,010 2,502 Gain (loss) on energy-related cash flow hedges (a) 7 (16 ) 2 Total interest expense, net of amounts capitalized (1,842 ) (1,694 ) (1,317 ) Gain (loss) on interest rate cash flow hedges (a) (21 ) (21 ) (18 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (23 ) (13 ) Gain (loss) on interest rate fair value hedges (b) (12 ) (22 ) (21 ) Total other income (expense), net 114 163 50 Gain (loss) on foreign currency cash flow hedges (a)(c) (60 ) 160 (82 ) Alabama Power Total interest expense, net of amounts capitalized $ (323 ) $ (305 ) $ (302 ) Gain (loss) on interest rate cash flow hedges (a) (6 ) (6 ) (6 ) Georgia Power Total interest expense, net of amounts capitalized $ (397 ) $ (419 ) $ (388 ) Gain (loss) on interest rate cash flow hedges (a) (4 ) (4 ) (4 ) Gain (loss) on interest rate fair value hedges (b) 2 (3 ) (1 ) Mississippi Power Total interest expense, net of amounts capitalized $ (76 ) $ (42 ) $ (74 ) Gain (loss) on interest rate cash flow hedges (a) (2 ) (2 ) 3 Southern Power Total depreciation and amortization $ 493 $ 503 $ 352 Gain (loss) on energy-related cash flow hedges (a) 7 (17 ) 2 Total interest expense, net of amounts capitalized (183 ) (191 ) (117 ) Gain (loss) on foreign currency cash flow hedges (a) (24 ) (23 ) (13 ) Total other income (expense), net 23 1 6 Gain (loss) on foreign currency cash flow hedges (a)(c) (60 ) 159 (82 ) (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. Successor Predecessor Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships Year Ended December 31, 2018 Year Ended December 31, 2017 July 1, 2016 January 1, 2016 (in millions) (in millions) Southern Company Gas Total cost of natural gas $ 1,539 $ 1,601 $ 613 $ 755 Gain (loss) on energy-related cash flow hedges (*) 2 (2 ) (1 ) (1 ) (*) Amounts reflect gains or losses on cash flow hedges that were reclassified from AOCI into earnings.
Schedule of fair value hedging instruments, statements of financial performance and financial position, location	At December 31, 2018 and 2017 , the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items At December 31, 2018 At December 31, 2017 At December 31, 2018 At December 31, 2017 (in millions) (in millions) Southern Company Securities due within one year $ (498 ) $ (746 ) $ 2 $ 3 Long-term debt (2,052 ) (2,553 ) 41 35 Georgia Power Securities due within one year $ (498 ) $ (746 ) $ 2 $ 3 Long-term debt — (498 ) — 1
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, 2018 , 2017 , and 2016 for the applicable registrants were as follows: Gain (Loss) Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2018 2017 2016 (in millions) Southern Company Energy-related derivatives Natural gas revenues (*) $ (122 ) $ (80 ) $ 33 Cost of natural gas (6 ) (2 ) 3 Wholesale electric revenues 2 (4 ) 2 Total derivatives in non-designated hedging relationships $ (126 ) $ (86 ) $ 38 (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $5 million , $23 million , and $6 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively, as they are accounted for based on intrinsic value rather than fair value. Gain (Loss) Successor Predecessor Derivatives in Non-Designated Hedging Relationships Statements of Income Location For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 July 1, 2016 January 1, 2016 through (in millions) (in millions) Southern Company Gas Energy-related derivatives Natural gas revenues (*) $ (122 ) $ (80 ) $ 33 $ (1 ) Cost of natural gas (6 ) (2 ) 3 (62 ) Total derivatives in non-designated hedging relationships $ (128 ) $ (82 ) $ 36 $ (63 ) (*) Excludes the impact of weather derivatives recorded in natural gas revenues of $5 million and $23 million for the successor years ended December 31, 2018 and 2017 , respectively, $6 million for the successor period of July 1, 2016 through December 31, 2016 , and $3 million for the predecessor period of January 1, 2016 through June 30, 2016 , 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, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table presents the final purchase price allocation: PowerSecure Purchase Price (in millions) Current assets $ 172 Property, plant, and equipment 46 Intangible assets 106 Goodwill 284 Other assets 4 Current liabilities (121 ) Long-term debt, including current portion (48 ) Deferred credits and other liabilities (14 ) Total purchase price $ 429 The following table presents the final purchase price allocation: Southern Company Gas Successor Southern Company Gas Predecessor Southern Company Gas Purchase Price New Basis Old Basis Change in Basis (in millions) (in millions) Current assets $ 1,557 $ 1,474 $ 83 Property, plant, and equipment 10,108 10,148 (40 ) Goodwill 5,967 1,813 4,154 Other intangible assets 400 101 299 Regulatory assets 1,118 679 439 Other assets 229 273 (44 ) Current liabilities (2,201 ) (2,205 ) 4 Other liabilities (4,742 ) (4,600 ) (142 ) Long-term debt (4,261 ) (3,709 ) (552 ) Contingently redeemable noncontrolling interest (174 ) (41 ) (133 ) Total purchase price $ 8,001 $ 3,933 $ 4,068 During 2018 , Southern Power acquired and completed the project below and acquired the Wild Horse Mountain and Reading wind facilities discussed under " Construction Projects Completed and/or in Progress " below. Project Facility Resource Seller, Acquisition Date Approximate Nameplate Capacity ( MW ) Location Ownership Percentage Actual 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 fair values of the assets acquired and liabilities assumed were finalized in 2017 and recorded as follows: 2017 (in millions) Restricted cash $ 16 CWIP 534 Other assets 5 Accounts payable (16 ) Total purchase price $ 539 The following table presents Southern Power's acquisition activity for the year ended December 31, 2017. Project Facility Resource Seller, Acquisition Date Approximate Nameplate Capacity ( MW ) Location Ownership Percentage Actual COD PPA Contract Period Bethel Wind Invenergy Wind Global LLC, 276 Castro County, TX 100 % January 2017 12 years Cactus Flats (*) Wind RES America Developments, Inc., 148 Concho County, TX 100 % July 2018 12 years and 15 years (*) On July 31, 2017, Southern Power purchased 100% of the Cactus Flats facility. In August 2018, Southern Power closed on a tax equity partnership and owns 100% of the class B membership interests.
Pro Forma Information	The following summarized unaudited pro forma consolidated statement of earnings information assumes that the acquisition of Southern Company Gas was completed on January 1, 2015. The summarized unaudited pro forma consolidated statement of earnings information includes adjustments for (i) intercompany sales, (ii) amortization of intangible assets, (iii) adjustments to interest expense to reflect current interest rates on Southern Company Gas debt and additional interest expense associated with borrowings by Southern Company to fund the Merger, and (iv) the elimination of nonrecurring expenses associated with the Merger. 2016 Operating revenues (in millions) $ 21,791 Net income attributable to Southern Company (in millions) $ 2,591 Basic EPS $ 2.70 Diluted EPS $ 2.68
Schedule of Construction Projects	During 2018 , in accordance with its growth strategy, Southern Power started, continued, or completed construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $575 million and $640 million for the Plant Mankato expansion, Wild Horse Mountain, and Reading facilities. At December 31, 2018, construction costs included in CWIP related to these projects totaled $289 million , except for the Plant Mankato expansion which is classified as assets held for sale in the financial statements. The ultimate outcome of these matters cannot be determined at this time. Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Actual/Expected COD PPA Counterparties PPA Contract Period Construction Projects Completed During the Year Ended December 31, 2018 Cactus Flats (a) Wind 148 Concho County, TX July 2018 General Motors, LLC 12 years Projects Under Construction at December 31, 2018 Mankato expansion (b) Natural Gas 385 Mankato, MN Second quarter 2019 Northern States Power Company 20 years Wild Horse Mountain (c) Wind 100 Pushmataha County, OK Fourth quarter 2019 Arkansas Electric Cooperative 20 years Reading (d) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 Royal Caribbean Cruises LTD 12 years (a) In July 2017, Southern Power purchased 100% of the Cactus Flats facility. In August 2018, Southern Power closed on a tax equity partnership and now owns 100% of the class B membership interests. (b) In November 2018, Southern Power entered into an agreement to sell all of its equity interests in Plant Mankato, including this expansion currently under construction. See "Sales of Natural Gas Plants" below. (c) In May 2018, Southern Power purchased 100% of the Wild Horse Mountain facility. 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 August 2018, Southern Power purchased 100% of the membership interests of the Reading facility from the joint development arrangement with Renewable Energy Systems Americas, Inc. described below. 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.
Disposal Groups, Including Discontinued Operations	Gulf Power and the Florida Plants represent individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax income for these components for the years ended December 31, 2018 , 2017 , and 2016 are presented below: 2018 2017 2016 (in millions) Earnings (loss) before income taxes: Gulf Power $ 140 $ 229 $ 231 Southern Power's Florida Plants (*) $ 49 $ 37 $ 37 (*) Earnings before income taxes for the Florida Plants in 2018 represents the period from January 1, 2018 to December 4, 2018 (the divestiture date). The following table provides Southern Company's and Southern Power's major classes of assets and liabilities classified as held for sale at December 31, 2018 : Southern Company Southern Power (in millions) Assets Held for Sale: Current assets $ 393 $ 8 Total property, plant, and equipment 4,623 576 Other non-current assets 727 — Total Assets Held for Sale $ 5,743 $ 584 Liabilities Held for Sale: Current liabilities $ 425 $ 15 Long-term debt 1,286 — Accumulated deferred income taxes 618 — Other non-current liabilities 932 — Total Liabilities Held for Sale $ 3,261 $ 15

Segment and Related Informati_2

Segment and Related Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Financial data for business segments	Financial data for business segments and products and services for the years ended December 31, 2018 , 2017 , and 2016 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) 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)(c)(d) 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)(e)(f) (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 2016 Operating revenues $ 16,803 $ 1,577 $ (439 ) $ 17,941 $ 1,652 $ 463 $ (160 ) $ 19,896 Depreciation and amortization 1,881 352 — 2,233 238 31 — 2,502 Interest income 6 7 — 13 2 20 (15 ) 20 Earnings from equity method investments 2 — — 2 60 (3 ) — 59 Interest expense 814 117 — 931 81 317 (12 ) 1,317 Income taxes (benefit) 1,286 (195 ) — 1,091 76 (216 ) — 951 Segment net income (loss) (a)(b) 2,233 338 — 2,571 114 (230 ) (7 ) 2,448 Goodwill — 2 — 2 5,967 282 — 6,251 Total assets 72,141 15,169 (316 ) 86,994 21,853 2,474 (1,624 ) 109,697 Gross property additions 4,852 2,114 — 6,966 618 41 (1 ) 7,624 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $1.1 billion ( $722 million after tax) in 2018 , $3.4 billion ( $2.4 billion after tax) in 2017 , and $428 million ( $264 million after tax) in 2016 . 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 pre-tax impairment charges of $156 million ( $117 million after tax) in 2018. See Note 15 under " Southern Power – Development Projects " and " – Sales of Natural Gas Plants " for additional information. (d) 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. (e) Segment net income (loss) for the traditional electric operating companies includes a pre-tax charge for the write-down of Gulf Power's ownership of Plant Scherer Unit 3 of $33 million ( $20 million after tax) in 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. (f) 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 successor years ended December 31, 2018 and 2017 , the successor period of July 1, 2016 through December 31, 2016, and the predecessor period of January 1, 2016 through June 30, 2016 were as follows: Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other Eliminations Consolidated (in millions) Successor – Year ended December 31, 2018 Operating revenues $ 3,186 $ 32 $ 144 $ 568 $ 3,930 $ 55 $ (76 ) $ 3,909 Depreciation and 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 1,429 32 — 6 1,467 54 — 1,521 Successor – Total assets 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) 21,448 Successor – Year ended December 31, 2017 Operating revenues $ 3,207 $ 17 $ 6 $ 860 $ 4,090 $ 64 $ (234 ) $ 3,920 Depreciation and 391 2 2 62 457 44 — 501 Operating income (loss) 645 10 (51 ) 113 717 (57 ) — 660 Earnings from equity method — 103 — — 103 3 — 106 Interest expense (153 ) (26 ) (7 ) (5 ) (191 ) (9 ) — (200 ) Income taxes (e) 178 109 — 24 311 56 — 367 Segment net income (loss) (e) 353 (22 ) (57 ) 84 358 (115 ) — 243 Gross property additions 1,330 117 1 9 1,457 51 — 1,508 Successor – Total assets 19,358 1,699 1,096 2,147 24,300 12,726 (14,039 ) 22,987 Successor – July 1, 2016 through December 31, 2016 Operating revenues $ 1,342 $ 3 $ 24 $ 354 $ 1,723 $ 31 $ (102 ) $ 1,652 Depreciation and 185 — 1 35 221 17 — 238 Operating income (loss) 225 1 (2 ) 27 251 (52 ) — 199 Earnings from equity method — 58 — — 58 2 — 60 Interest expense (105 ) (10 ) (3 ) (1 ) (119 ) 38 — (81 ) Income taxes (benefit) 51 21 (3 ) 7 76 — — 76 Segment net income (loss) 77 29 — 19 125 (11 ) — 114 Gross property additions 561 51 1 5 618 14 — 632 Successor – Total assets 19,453 1,659 1,127 2,084 24,323 11,697 (14,167 ) 21,853 Gas Distribution Operations (a)(b) Gas Pipeline Investments Wholesale Gas Services (c) Gas Marketing Services (b)(d) Total All Other Eliminations Consolidated (in millions) Predecessor – January 1, 2016 through June 30, 2016 Operating revenues $ 1,575 $ 3 $ (32 ) $ 435 $ 1,981 $ 26 $ (102 ) $ 1,905 Depreciation and 178 — 1 11 190 16 — 206 Operating income (loss) 353 3 (69 ) 109 396 (73 ) — 323 EBIT 353 3 (68 ) 109 397 (69 ) — 328 Gross property additions 484 40 1 4 529 19 — 548 (a) Operating revenues for the three gas distribution operations dispositions were $244 million , $399 million , and $168 million for the successor years ended December 31, 2018 and 2017 and the successor period of July 1, 2016 through December 31, 2016, respectively, and $215 million for the predecessor period ended June 30, 2016. 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) for the year ended December 31, 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 for the year ended December 31, 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) Successor – Year Ended $ 6,955 $ 451 $ 7,406 $ 7,262 $ 144 Successor – Year Ended 6,152 481 6,633 6,627 6 Successor – July 1, 2016 through 5,807 333 6,140 6,116 24 Predecessor – January 1, 2016 through 2,500 143 2,643 2,675 (32 ) (d) Operating revenues for the gas marketing services disposition were $55 million , $129 million , and $56 million for the successor years ended December 31, 2018 and 2017 and the successor period of July 1, 2016 through December 31, 2016, respectively, and $64 million for the predecessor period ended June 30, 2016 See Note 15 under " Southern Company Gas " for additional information. (e) 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) 2018 $ 15,222 $ 2,516 $ 833 $ 18,571 2017 15,330 2,426 784 18,540 2016 15,234 1,926 781 17,941 Southern Company Gas' Revenues Year Gas Gas All Other Total (in millions) 2018 $ 3,155 $ 568 $ 186 $ 3,909 2017 3,024 860 36 3,920 2016 1,266 354 32 1,652

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summarized quarterly financial data	The tables below provide summarized quarterly financial information for each registrant for 2018 and 2017 . Each registrant's business is influenced by seasonal weather conditions. 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 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 pre-tax and $(76) million after tax, $353 million pre-tax and $40 million after tax, and $(27) million pre-tax and $(15) million after tax, respectively. See Note 15 under " Southern Company Gas " for additional information. Quarter Ended Southern Company (a)(b)(c) Alabama Power Georgia Power Mississippi Power (a)(b) Southern Power (b) Southern Company Gas (b) (in millions) March 2017 Operating Revenues $ 5,771 $ 1,382 $ 1,832 $ 272 $ 450 $ 1,560 Operating Income (Loss) 1,252 361 483 (64 ) 65 389 Net Income (Loss) 665 174 260 (20 ) 66 239 Net Income (Loss) Attributable to Registrant 658 174 260 (20 ) 70 239 June 2017 Operating Revenues $ 5,430 $ 1,484 $ 2,048 $ 303 $ 529 $ 716 Operating Income (Loss) (1,649 ) 440 621 (2,956 ) 112 95 Net Income (Loss) (1,348 ) 230 347 (2,054 ) 104 49 Net Income (Loss) Attributable to Registrant (1,381 ) 230 347 (2,054 ) 82 49 September 2017 Operating Revenues $ 6,201 $ 1,740 $ 2,546 $ 341 $ 618 $ 565 Operating Income (Loss) 1,991 601 1,017 49 159 67 Net Income (Loss) 1,109 325 580 40 154 15 Net Income (Loss) Attributable to Registrant 1,069 325 580 40 124 15 December 2017 Operating Revenues $ 5,629 $ 1,433 $ 1,884 $ 271 $ 478 $ 1,079 Operating Income (Loss) 739 255 452 (180 ) 32 109 Net Income (Loss) 500 119 227 (556 ) 793 (60 ) Net Income (Loss) Attributable to Registrant 496 119 227 (556 ) 795 (60 ) (a) As a result of revisions to the cost estimate for the Kemper IGCC and the project's June 2017 suspension, Mississippi Power recorded total pre-tax charges to income related to the Kemper IGCC of $108 million ( $67 million after tax) in the first quarter 2017, $3.0 billion ( $2.1 billion after tax) in the second quarter 2017, $34 million ( $21 million after tax) in the third quarter 2017, and $208 million ( $185 million after tax) in the fourth quarter 2017. See Note 2 under " Mississippi Power – Kemper County Energy Facility " for additional information. (b) As a result of the Tax Reform Legislation, the Southern Company system recorded a total income tax benefit of $264 million in the fourth quarter 2017, comprised primarily of income tax expense of $372 million recorded at Mississippi Power, income tax benefit of $743 million recorded at Southern Power, and income tax expense of $93 million recorded at Southern Company Gas. See Note 10 for additional information. (c) Gulf Power recorded a pre-tax charge of $33 million ( $20 million after tax) for the write-down of its ownership in Plant Scherer Unit 3 in the first quarter 2017. See Note 2 under " Southern Company – Gulf Power " for additional information. Southern Company The table below provides quarterly per share financial information for Southern Company common stock for 2018 and 2017 . Per Common Share Basic Earnings Diluted Earnings Quarter Ended Dividends March 2018 $ 0.93 $ 0.92 $ 0.5800 June 2018 (0.15 ) (0.15 ) 0.6000 September 2018 1.14 1.13 0.6000 December 2018 0.27 0.27 0.6000 March 2017 $ 0.66 $ 0.66 $ 0.5600 June 2017 (1.38 ) (1.37 ) 0.5800 September 2017 1.07 1.06 0.5800 December 2017 0.49 0.49 0.5800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - General (Narrative) (Details)	Dec. 12, 2018operating_facility	May 22, 2018	Jul. 31, 2018utility	Dec. 31, 2018state	Nov. 05, 2018MW
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of natural gas distribution utilities sold | utility			3
Traditional Operating Companies
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity provides utilities | state				4
Southern Power
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating wind facilities | operating_facility	8
Southern Power | Disposal Group, Held-for-sale, Not Discontinued Operations | Mankato
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expansion currently under construction (mw) | MW					385
Southern Power | SP Solar Holdings I, LP
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sale of equity interest in limited partnership (percent)		33.00%
Southern Company Gas
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity provides utilities | state				4
Number of natural gas distribution utilities sold | utility			3
SP Solar Holdings I, LP | Southern Power | SP Solar Holdings I, LP
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sale of equity interest in limited partnership (percent)		33.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Specific Impacts of Applying ASC 606 to Revenues from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Statements of Income
Revenues										$ 23,495	$ 23,031	$ 19,896
Other operations and maintenance										5,889	5,739	5,382
Taxes other than income taxes										1,315	1,250	1,113
Operating Income	$ 578	$ 2,174	$ 63	$ 1,376	$ 739	$ 1,991	$ (1,649)	$ 1,252		4,191	2,333	4,486
Other income (expense), net										114	163	50
Earnings Before Income Taxes										2,749	1,068	3,480
Income taxes										449	142	951
Net Income										2,300	926	2,529
Net Income (Loss)	269	1,222	(127)	936	500	1,109	(1,348)	665		2,226	842	2,448
Changes in certain current assets and liabilities —
Receivables										(426)	(202)	(544)
Other current assets										(127)	(143)	(206)
Accrued taxes										267	(142)	1,456
Other current liabilities										63	(45)	250
Balance Sheets
Unbilled revenues	654				810					654	810
Other accounts and notes receivable	813				698					813	698
Other current assets	162				62					162	62
Accrued taxes	656				636					656	636
Other current liabilities	852				874					852	874
Total Stockholders' Equity	29,039				25,528				$ 26,612	29,039	25,528	26,612		$ 21,982
Natural gas revenues
Statements of Income
Revenues										3,854	3,791	1,596
Other revenues
Statements of Income
Revenues										1,239	803	442
Alabama Power
Statements of Income
Revenues										6,032	6,039	5,889
Other operations and maintenance										1,669	1,709	1,557
Taxes other than income taxes										389	384	380
Operating Income	164	561	380	372	255	601	440	361		1,477	1,657	1,618
Other income (expense), net										20	43	26
Earnings Before Income Taxes										1,236	1,434	1,370
Income taxes										291	568	531
Net Income										945	866	839
Net Income (Loss)	73	373	259	225	119	325	230	174		930	848	822
Changes in certain current assets and liabilities —
Receivables										(149)	(168)	94
Other current assets										30	20	38
Accrued taxes										10	(84)	93
Other current liabilities										128	3	11
Balance Sheets
Unbilled revenues	150				162					150	162
Other accounts and notes receivable	51				55					51	55
Other current assets	18				5					18	5
Accrued taxes	44				54					44	54
Other current liabilities	161				53					161	53
Total Stockholders' Equity	7,477				6,829				6,323	7,477	6,829	6,323		5,992
Alabama Power | Other revenues
Statements of Income
Revenues										267	208	215
Georgia Power
Statements of Income
Revenues										8,420	8,310	8,383
Other operations and maintenance										1,860	1,724	2,003
Taxes other than income taxes										437	409	405
Operating Income	257	991	(472)	513	452	1,017	621	483		1,289	2,573	2,434
Other income (expense), net										115	104	81
Earnings Before Income Taxes										1,007	2,258	2,127
Income taxes										214	830	780
Net Income										793	1,428	1,347
Net Income (Loss)	173	664	(396)	352	227	580	347	260		793	1,414	1,330
Changes in certain current assets and liabilities —
Receivables										8	(256)	60
Other current assets										(43)	(28)	(38)
Accrued taxes										58	1	131
Other current liabilities										(107)	(33)	28
Balance Sheets
Unbilled revenues	208				255					208	255
Other accounts and notes receivable	80				76					80	76
Other current assets	70				14					70	14
Other current liabilities	183				198					183	198
Total Stockholders' Equity	14,323				11,931				11,356	14,323	11,931	11,356		$ 10,719
Georgia Power | Other revenues
Statements of Income
Revenues										481	383	394
Southern Company Gas
Statements of Income
Revenues									1,652	3,909	3,920
Other operations and maintenance									480	981	945
Taxes other than income taxes									71	211	184
Operating Income	104	374	49	388	109	67	95	389	199	915	660
Other income (expense), net									12	1	44
Earnings Before Income Taxes									190	836	610
Income taxes									76	464	367
Net Income									114	372	243
Net Income (Loss)	78	$ 46	$ (31)	$ 279	(60)	$ 15	$ 49	$ 239	114	372	243
Changes in certain current assets and liabilities —
Receivables									(490)	(218)	(94)
Other current assets									(31)	4	(24)
Accrued taxes									8	10	110
Other current liabilities									24	(22)	(8)
Balance Sheets
Unbilled revenues	213				285					213	285
Other accounts and notes receivable	142				91					142	91
Other current assets	50				52					50	52
Accrued taxes	66				40					66	40
Other current liabilities	130				159					130	159
Total Stockholders' Equity	8,570				$ 9,022				9,109	8,570	9,022	$ 9,109	$ 8,001
Southern Company Gas | Natural gas revenues
Statements of Income
Revenues									1,591	3,874	3,787
Southern Company Gas | Other revenues
Statements of Income
Revenues									$ 56	55	$ 129
Balances Without Adoption of ASC 606
Statements of Income
Other operations and maintenance										5,830
Operating Income										4,243
Other income (expense), net										60
Earnings Before Income Taxes										2,747
Income taxes										448
Net Income										2,299
Net Income (Loss)										2,225
Changes in certain current assets and liabilities —
Receivables										(472)
Other current assets										(81)
Accrued taxes										268
Other current liabilities										61
Balance Sheets
Unbilled revenues	728									728
Other accounts and notes receivable	814									814
Other current assets	87									87
Accrued taxes	655									655
Other current liabilities	854									854
Total Stockholders' Equity	29,038									29,038
Balances Without Adoption of ASC 606 | Natural gas revenues
Statements of Income
Revenues										3,852
Balances Without Adoption of ASC 606 | Other revenues
Statements of Income
Revenues										1,234
Balances Without Adoption of ASC 606 | Alabama Power
Statements of Income
Other operations and maintenance										1,625
Taxes other than income taxes										388
Operating Income										1,485
Other income (expense), net										12
Balances Without Adoption of ASC 606 | Alabama Power | Other revenues
Statements of Income
Revenues										230
Balances Without Adoption of ASC 606 | Georgia Power
Statements of Income
Other operations and maintenance										1,772
Operating Income										1,283
Other income (expense), net										121
Changes in certain current assets and liabilities —
Receivables										1
Other current assets										(36)
Balance Sheets
Unbilled revenues	243									243
Other accounts and notes receivable	81									81
Other current assets	34									34
Balances Without Adoption of ASC 606 | Georgia Power | Other revenues
Statements of Income
Revenues										387
Balances Without Adoption of ASC 606 | Southern Company Gas
Statements of Income
Operating Income										913
Earnings Before Income Taxes										834
Income taxes										463
Net Income										371
Net Income (Loss)										371
Changes in certain current assets and liabilities —
Accrued taxes										11
Other current liabilities										(24)
Balance Sheets
Accrued taxes	65									65
Other current liabilities	132									132
Total Stockholders' Equity	8,569									8,569
Balances Without Adoption of ASC 606 | Southern Company Gas | Natural gas revenues
Statements of Income
Revenues										3,872
Effect of Change
Statements of Income
Other operations and maintenance										59
Operating Income										(52)
Other income (expense), net										54
Earnings Before Income Taxes										2
Income taxes										1
Net Income										1
Net Income (Loss)										1
Changes in certain current assets and liabilities —
Receivables										46
Other current assets										(46)
Accrued taxes										(1)
Other current liabilities										2
Balance Sheets
Unbilled revenues	(74)									(74)
Other accounts and notes receivable	(1)									(1)
Other current assets	75									75
Accrued taxes	1									1
Other current liabilities	(2)									(2)
Total Stockholders' Equity	1									1
Effect of Change | Natural gas revenues
Statements of Income
Revenues										2
Effect of Change | Other revenues
Statements of Income
Revenues										5
Effect of Change | Alabama Power
Statements of Income
Other operations and maintenance										44
Taxes other than income taxes										1
Operating Income										(8)
Other income (expense), net										8
Effect of Change | Alabama Power | Other revenues
Statements of Income
Revenues										37
Effect of Change | Georgia Power
Statements of Income
Other operations and maintenance										88
Operating Income										6
Other income (expense), net										(6)
Changes in certain current assets and liabilities —
Receivables										7
Other current assets										(7)
Balance Sheets
Unbilled revenues	(35)									(35)
Other accounts and notes receivable	(1)									(1)
Other current assets	36									36
Effect of Change | Georgia Power | Other revenues
Statements of Income
Revenues										94
Effect of Change | Southern Company Gas
Statements of Income
Operating Income										2
Earnings Before Income Taxes										2
Income taxes										1
Net Income										1
Net Income (Loss)										1
Changes in certain current assets and liabilities —
Accrued taxes										(1)
Other current liabilities										2
Balance Sheets
Accrued taxes	1									1
Other current liabilities	(2)									(2)
Total Stockholders' Equity	$ 1									1
Effect of Change | Southern Company Gas | Natural gas revenues
Statements of Income
Revenues										$ 2

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Costs for Affiliate Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Alabama Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	$ 508	$ 479	$ 460
Alabama Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	8	9	2
Georgia Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	653	625	606
Georgia Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	101	102	35
Georgia Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	21	22	10
Mississippi Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	104	140	231
Mississippi Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	15	16	29
Southern Power | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	98	218	193
Southern Power | Alabama Power | Power Pool
Related Party Transaction [Line Items]
Costs for services	41	27	21
Southern Power | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	25	25	7
Southern Power | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	119	119	17
Southern Company Gas | Southern Company Services, Inc.
Related Party Transaction [Line Items]
Costs for services	194	63	17
Southern Company Gas | Southern Natural Gas Company, LLC
Related Party Transaction [Line Items]
Costs for services	$ 32	$ 32	$ 15

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Affiliate Transactions (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018USD ($)base	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 31, 2016location
Georgia Power
Related Party Transaction [Line Items]
Number of solar power generation facilities	2			2
Southern Nuclear Operating Company, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	$ 247,000,000	$ 248,000,000	$ 249,000,000
Southern Nuclear Operating Company, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	780,000,000	675,000,000	666,000,000
Southern Natural Gas Company, LLC | Alabama Power
Related Party Transaction [Line Items]
Costs for services	8,000,000	9,000,000	2,000,000
Southern Natural Gas Company, LLC | Georgia Power
Related Party Transaction [Line Items]
Costs for services	101,000,000	102,000,000	35,000,000
Due from affiliate	142,000,000
Southern Natural Gas Company, LLC | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	32,000,000	32,000,000	15,000,000
Due from affiliate	122,000,000
Southern Natural Gas Company, LLC | Southern Power
Related Party Transaction [Line Items]
Costs for services	25,000,000	25,000,000	7,000,000
Gulf Power | Alabama Power
Related Party Transaction [Line Items]
Amounts received related to tariff	11,000,000	11,000,000	12,000,000
Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services	8,000,000	11,000,000	8,000,000
Gulf Power | Mississippi Power
Related Party Transaction [Line Items]
Costs for services	31,000,000	31,000,000	26,000,000
PowerSecure International, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	24,000,000	11,000,000	0
PowerSecure International, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	32,000,000
Southern Power | Georgia Power
Related Party Transaction [Line Items]
Costs for services	216,000,000	235,000,000	265,000,000
Southern Company Services, Inc. | Alabama Power
Related Party Transaction [Line Items]
Costs for services	508,000,000	479,000,000	460,000,000
Southern Company Services, Inc. | Georgia Power
Related Party Transaction [Line Items]
Costs for services	653,000,000	625,000,000	606,000,000
Southern Company Services, Inc. | Southern Company Gas
Related Party Transaction [Line Items]
Costs for services	194,000,000	63,000,000	17,000,000
Southern Company Services, Inc. | Mississippi Power
Related Party Transaction [Line Items]
Costs for services	104,000,000	140,000,000	231,000,000
Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	98,000,000	218,000,000	193,000,000
Fuel Purchases | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services	0	0	0
Non-Fuel Expense | Mississippi Power | Alabama Power
Related Party Transaction [Line Items]
Costs for services	8,000,000	9,000,000	13,000,000
Purchased Power from Affiliates | Southern Power
Related Party Transaction [Line Items]
Costs for services	215,000,000	233,000,000	258,000,000
Operating Lease PPA | Southern Power
Related Party Transaction [Line Items]
Costs for services	65,000,000	81,000,000	109,000,000
Electric Transmission | Southern Company Services, Inc. | Southern Power
Related Party Transaction [Line Items]
Costs for services	$ 12,000,000	$ 13,000,000	$ 11,000,000
Plant Scherer (coal) Unit 3 | Gulf Power | Georgia Power
Related Party Transaction [Line Items]
Proportionate share of related non-fuel expenses (percent)	25.00%

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Revenues (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Southern Company Gas
Disaggregation of Revenue [Line Items]
Period for collection of revenue prior to billings	24 months

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Concentration of Revenue (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Jan. 29, 2019FacilityMW
Concentration Risk [Line Items]
Outstanding accounts receivable	$ 2,630
Mississippi Power
Concentration Risk [Line Items]
Wholesale customers representing total operating revenues (percent)	17.30%
Period of cancellation notices	10 years
Outstanding accounts receivable	$ 100
Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	118
Subsequent Event | PG&E
Concentration Risk [Line Items]
Number of solar facilities | Facility		4
Capacity of natural gas facility (mw) | MW		207
PPAs | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	1
Transmission Interconnections | Southern Power
Concentration Risk [Line Items]
Outstanding accounts receivable	36
Outstanding accounts receivable classified in other deferred charges and assets	$ 17

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Schedule of Concentration of Revenue (Details) - Southern Power - Sales Revenue, Goods, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Georgia Power
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	9.80%	11.30%	16.50%
Duke Energy Corporation
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	6.80%	6.70%	7.80%
Southern California Edison
Concentration Risk [Line Items]
Percentage of total revenues for top three customers	6.20%
Morgan Stanley Capital Group
Concentration Risk [Line Items]
Percentage of total revenues for top three customers		4.50%
San Diego Gas & Electric Company
Concentration Risk [Line Items]
Percentage of total revenues for top three customers			5.70%

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Income and Other Taxes (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Southern Power
Tax Credit Carryforward [Line Items]
Reduction in tax basis of assets (percent)			50.00%
Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected	$ 32		$ 114	$ 100
Included In Operating Expenses | Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected	$ 31		$ 111	$ 98
Predecessor | Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected		$ 57
Predecessor | Included In Operating Expenses | Southern Company Gas
Tax Credit Carryforward [Line Items]
Excise taxes collected		$ 56

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Schedule of Total AFUDC and Interest Capitalized (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized			$ 210	$ 249	$ 327
Alabama Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized			84	54	39
Georgia Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized			94	63	68
Mississippi Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized			0	72	124
Southern Power
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized			17	11	$ 44
Southern Company Gas
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized	$ 6		$ 14	$ 19
Southern Company Gas | Predecessor
Capitalized Contract Cost [Line Items]
Total AFUDC and interest capitalized		$ 4

Summary of Significant Accou_13

Summary of Significant Accounting Policies - Schedule of Average AFUDC Composite Rates (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Alabama Power
Capitalized Contract Cost [Line Items]
Composite rate	8.30%	8.30%	8.20%
Georgia Power
Capitalized Contract Cost [Line Items]
Composite rate	7.30%	5.60%			6.90%
Mississippi Power
Capitalized Contract Cost [Line Items]
Composite rate	3.30%	6.70%	6.50%
Atlanta Gas Light
Capitalized Contract Cost [Line Items]
Composite rate	7.90%	8.10%	4.10%
Atlanta Gas Light | Predecessor
Capitalized Contract Cost [Line Items]
Composite rate				4.10%
Chattanooga Gas
Capitalized Contract Cost [Line Items]
Composite rate	7.40%	7.40%	3.70%
Chattanooga Gas | Predecessor
Capitalized Contract Cost [Line Items]
Composite rate				3.70%
Nicor Gas
Capitalized Contract Cost [Line Items]
Composite rate	2.10%	1.20%	1.50%
Nicor Gas | Predecessor
Capitalized Contract Cost [Line Items]
Composite rate				1.50%

Summary of Significant Accou_14

Summary of Significant Accounting Policies - Schedule of Goodwill Balances (Details) - USD ($)	3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Beginning balance		$ 6,268,000,000		$ 6,268,000,000	$ 6,251,000,000
Impairment	$ 0			(42,000,000)
Dispositions				(910,000,000)
Ending balance	5,315,000,000		$ 6,251,000,000	5,315,000,000	6,268,000,000
Impairment charge	0			42,000,000
Southern Company Gas
Goodwill [Roll Forward]
Beginning balance		5,967,000,000		5,967,000,000
Impairment	0	(42,000,000)	0	(42,000,000)	0
Ending balance	5,015,000,000			5,015,000,000	5,967,000,000
Impairment charge	0	42,000,000	$ 0	42,000,000	0
Gas Distribution Operations | Southern Company Gas
Goodwill [Roll Forward]
Beginning balance		4,702,000,000		4,702,000,000
Impairment				0
Dispositions				(668,000,000)
Ending balance	4,034,000,000			4,034,000,000	4,702,000,000
Impairment charge				0
Gas marketing services | Southern Company Gas
Goodwill [Roll Forward]
Beginning balance		$ 1,265,000,000		1,265,000,000
Impairment				(42,000,000)
Dispositions				(242,000,000)
Ending balance	$ 981,000,000			981,000,000	$ 1,265,000,000
Impairment charge				$ 42,000,000

Summary of Significant Accou_15

Summary of Significant Accounting Policies - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 773	$ 984
Accumulated Amortization	(235)	(186)
Other Intangible Assets, Net	538	798
Intangible assets, gross	848	1,059
Intangible assets, net	613	873
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	223	288
Accumulated Amortization	(94)	(83)
Other Intangible Assets, Net	129	205
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	70	159
Accumulated Amortization	(21)	(17)
Other Intangible Assets, Net	49	142
Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(54)	(34)
Other Intangible Assets, Net	10	30
PPA fair value adjustments(b)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	405	456
Accumulated Amortization	(61)	(47)
Other Intangible Assets, Net	344	409
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11	17
Accumulated Amortization	(5)	(5)
Other Intangible Assets, Net	6	12
Southern Power
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	(61)	(47)
Southern Power | PPA fair value adjustments(b)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	405	456
Accumulated Amortization	(61)	(47)
Other Intangible Assets, Net	344	409
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	246	400
Accumulated Amortization	(145)	(120)
Other Intangible Assets, Net	101	280
Intangible assets, net	101	280
Southern Company Gas | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	156	221
Accumulated Amortization	(84)	(77)
Other Intangible Assets, Net	72	144
Southern Company Gas | Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26	115
Accumulated Amortization	(7)	(9)
Other Intangible Assets, Net	19	106
Southern Company Gas | Storage and transportation contracts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	64	64
Accumulated Amortization	(54)	(34)
Other Intangible Assets, Net	$ 10	$ 30

Summary of Significant Accou_16

Summary of Significant Accounting Policies - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets			$ 89	$ 124	$ 50
Estimated future amortization, 2019			61
Estimated future amortization, 2020			50
Estimated future amortization, 2021			43
Estimated future amortization, 2022			39
Estimated future amortization, 2023			38
Southern Power
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets			25	25	$ 10
Estimated future amortization, 2019			20
Estimated future amortization, 2020			20
Estimated future amortization, 2021			20
Estimated future amortization, 2022			20
Estimated future amortization, 2023			20
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Estimated future amortization, 2019			29
Estimated future amortization, 2020			19
Estimated future amortization, 2021			13
Estimated future amortization, 2022			10
Estimated future amortization, 2023			9
Southern Company Gas | Wholesale gas services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 2		20	32
Southern Company Gas | Wholesale gas services | Predecessor
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets		$ 0
Southern Company Gas | Gas marketing services
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets	$ 32		$ 32	$ 54
Southern Company Gas | Gas marketing services | Predecessor
Finite-Lived Intangible Assets [Line Items]
Amortization associated with other intangible assets		$ 8

Summary of Significant Accou_17

Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets and Liabilities (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment charge	$ 0			$ 42,000,000
Intangible liabilities included in other deferred credits and liabilities	465,000,000			465,000,000	$ 691,000,000
Southern Company Gas
Finite-Lived Intangible Assets [Line Items]
Impairment charge	0	$ 42,000,000	$ 0	42,000,000	0
Intangible liabilities included in other deferred credits and liabilities	105,000,000			105,000,000	$ 118,000,000
Accumulated amortization of intangible liabilities	74,000,000			74,000,000
Remaining amortization to be recorded in 2019	17,000,000			17,000,000
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

Summary of Significant Accou_18

Summary of Significant Accounting Policies - Transmission Receivables/Prepayments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Southern Power
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Period of reimbursement for transmission costs	5 years

Summary of Significant Accou_19

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,396	$ 2,130
Cash and cash equivalents classified as assets held for sale	9
Restricted cash:
Restricted cash	0
Total cash, cash equivalents, and restricted cash	1,519	2,147	$ 1,992		$ 1,420
Southern Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	181	129
Restricted cash:
Total cash, cash equivalents, and restricted cash	181	140	1,112		835
Georgia Power
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	4	852
Cash and cash equivalents classified as assets held for sale	0
Restricted cash:
Restricted cash	108
Total cash, cash equivalents, and restricted cash	112	852	3		$ 67
Southern Company Gas
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	64	73
Cash and cash equivalents classified as assets held for sale	0
Restricted cash:
Restricted cash	0
Total cash, cash equivalents, and restricted cash	70	78	$ 24	$ 19
Other accounts and notes receivable
Restricted cash:
Other accounts and notes receivable	114	5
Other accounts and notes receivable | Southern Power
Restricted cash:
Other accounts and notes receivable		0
Other accounts and notes receivable | Georgia Power
Restricted cash:
Other accounts and notes receivable	0
Other accounts and notes receivable | Southern Company Gas
Restricted cash:
Other accounts and notes receivable	$ 6	5
Deferred charges and other assets
Restricted cash:
Other accounts and notes receivable		12
Deferred charges and other assets | Southern Power
Restricted cash:
Other accounts and notes receivable		11
Deferred charges and other assets | Southern Company Gas
Restricted cash:
Other accounts and notes receivable		$ 0

Summary of Significant Accou_20

Summary of Significant Accounting Policies - Schedule of Storm Damage Reserves (Details) - Major storms - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 74	$ 41	$ 40
Alabama Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	16	4	3
Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	30	30	30
Mississippi Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	1	3	4
Gulf Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 26.9	$ 3.5	$ 3.5

Summary of Significant Accou_21

Summary of Significant Accounting Policies - Leveraged Leases (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Leveraged Lease [Line Items]
Reduction in net income after tax based on lease receivable balance	$ 86
Maximum
Leveraged Lease [Line Items]
Original term (up to)	45 years

Summary of Significant Accou_22

Summary of Significant Accounting Policies - Schedule of Net Investment in Domestic and International Leveraged Leases (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Leveraged Lease [Line Items]
Investment in leveraged leases	$ 86
Domestic and international leveraged leases
Leveraged Lease [Line Items]
Net rentals receivable	1,563	$ 1,498
Unearned income	(765)	(723)
Investment in leveraged leases	798	775
Deferred taxes from leveraged leases	(255)	(252)
Net investment in leveraged leases	$ 543	$ 523

Summary of Significant Accou_23

Summary of Significant Accounting Policies - Summary of the Components of Income from Leveraged Leases (Details) - Domestic and international leveraged leases - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leveraged Lease [Line Items]
Pretax leveraged lease income	$ 25	$ 25	$ 25
Net impact of Tax Reform Legislation	0	48	0
Income tax expense	(6)	(9)	(9)
Net leveraged lease income	$ 19	$ 64	$ 16

Summary of Significant Accou_24

Summary of Significant Accounting Policies - Natural Gas for Sale (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nicor Gas
Inventory [Line Items]
LIFO inventory balance	$ 165
Estimated replacement cost of inventory	409
Southern Company Gas
Inventory [Line Items]
LOCOM adjustments	$ 10	$ 0	$ 0

Summary of Significant Accou_25

Summary of Significant Accounting Policies - Energy Marketing Receivables and Payables (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Required collateral in the event of a credit rating downgrade	$ 30	$ 8

Summary of Significant Accou_26

Summary of Significant Accounting Policies - Provision for Uncollectible Accounts (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Uncollectible accounts, average percent of revenues (less than)	1.00%

Summary of Significant Accou_27

Summary of Significant Accounting Policies - Concentration of Credit Risk (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)counterpartycustomer
Concentration Risk [Line Items]
Receivables	$ 2,630
Southern Company Gas
Concentration Risk [Line Items]
Receivables	$ 952
Atlanta Gas Light
Concentration Risk [Line Items]
Number of customers in Georgia | customer	15
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
Concentration risk (as percent)	48.00%
Receivables	$ 298

Summary of Significant Accou_28

Summary of Significant Accounting Policies - Financial Instruments (Narrative) (Details)	Dec. 31, 2018USD ($)
Alabama Power
Derivative [Line Items]
Derivative collateral obligation to return cash	$ 0

Summary of Significant Accou_29

Summary of Significant Accounting Policies - Schedule of AOCI (Loss) Balances, Net of Tax Effects (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 21,982	$ 25,528	$ 26,612	$ 21,982
Adjustment to beginning balance						$ (40)
Current period change			26	(9)	(50)
Ending balance	$ 26,612		29,039	25,528	26,612
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(119)
Ending balance				(119)
Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustment to beginning balance						(26)
Current period change			24
Ending balance			(121)
Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(70)
Adjustment to beginning balance						(14)
Current period change			2
Ending balance			(82)	(70)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(130)	(189)	(180)	(130)
Ending balance	(180)		(203)	(189)	(180)
Southern Power
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		3,264	6,498	5,675	3,264
Adjustment to beginning balance						4
Current period change			14	(10)	31
Ending balance	5,675		7,284	6,498	5,675
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			25
Ending balance				25
Southern Power | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustment to beginning balance						4
Current period change			7
Ending balance			36
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(27)
Adjustment to beginning balance						0
Current period change			7
Ending balance			(20)	(27)
Southern Power | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		4	(2)	35	4
Ending balance	35		16	(2)	35
Southern Company Gas
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	8,001		9,022	9,109
Adjustment to beginning balance						4
Current period change	26		2	(5)
Ending balance	9,109	8,001	8,570	9,022	9,109
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(6)
Ending balance				(6)
Southern Company Gas | Qualifying Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustment to beginning balance						(1)
Current period change			4
Ending balance			(3)
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			26
Adjustment to beginning balance						$ 5
Current period change			(2)
Ending balance			29	26
Southern Company Gas | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0		20	26
Ending balance	$ 26	$ 0	$ 26	$ 20	$ 26

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of SO Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 720	$ (1,894)
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue	50 years
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (1,872)	(1,879)
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (769)	(1,088)
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue	50 years
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (35)	(42)
Regulatory amortization period	5 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 2,378	232
Customer refund liability, current	55
Customer refund	$ 40
Georgia Power | 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	$ (6,455)	(7,261)
Deferred income tax credits | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(940)	(1,063)
Deferred income tax credits | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(2,027)	(2,082)
Deferred income tax credits | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(3,080)	(3,248)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(2,297)	(2,684)
Other cost of removal obligations | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(1,585)	(1,646)
Other cost of removal obligations | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(497)	(609)
Other cost of removal obligations | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(185)	(178)
Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(293)	(188)
Customer refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(165)	(188)
Property damage reserves-liability
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(76)	(135)
Property damage reserves-liability | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(56)	(57)
Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(47)	(155)
Over recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(43)	(144)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (132)	(104)
Other regulatory liabilities | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liability amortization period	20 years
Other regulatory liabilities | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (46)	(21)
Other regulatory liabilities | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(45)	(7)
Other regulatory liabilities | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (9)	0
Regulatory amortization period	1 year
Other regulatory liabilities | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (7)	(3)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	3,658	3,931
Regulatory asset	$ 28
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Retiree benefit plans | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 161	270
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	$ 947	946
Retiree benefit plans | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Retiree benefit plans | Mississippi Power
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	$ 1,295	1,313
Retiree benefit plans | Georgia 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	$ 2,933	1,133
Asset retirement obligations-asset | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 143	95
Regulatory amortization period	48 years
Asset retirement obligations-asset | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 2,644	945
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 799	814
Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	80 years
Deferred income tax charges | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 241	240
Regulatory amortization period	50 years
Deferred income tax charges | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Deferred income tax charges | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 34	36
Deferred income tax charges | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	522	521
Property damage reserves-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	416	333
Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	407	317
Under recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 90	98
Regulatory amortization period	7 years
Under recovered regulatory clause revenues | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 142	142
Environmental remediation-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	366	511
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	346	223
Loss on reacquired debt | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	56	62
Loss on reacquired debt | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	8
Loss on reacquired debt | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	277	127
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 211	306
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Remaining net book value of retired assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Remaining net book value of retired assets | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 41	44
Remaining net book value of retired assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 127	146
Remaining net book value of retired assets | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	3 years
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 182	183
Regulatory amortization period	1 year
Vacation pay | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 71	70
Regulatory amortization period	1 year
Vacation pay | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 9
Vacation pay | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 91	91
Regulatory amortization period	1 year
Long-term debt fair value adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 121	138
Long-term debt fair value adjustment | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 121	138
Long-term debt fair value adjustment | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	20 years
Deferred PPA charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 0	119
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 581	625
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Other regulatory assets | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 59	79
Other regulatory assets | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Other regulatory assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 57	58
Regulatory amortization period	12 months
Other regulatory assets | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 28	28
Regulatory amortization period	3 years
Other regulatory assets | Mississippi Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Other regulatory assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 135	106
Regulatory amortization period	24 months
Asset Group 1 | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Kemper IGCC | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 69	88
Regulatory asset	91
Storm damage reserves | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	416	333
Major storms
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves	74	41	$ 40
Major storms | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves	16	4	3
Major storms | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves	1	3	4
Major storms | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm damage reserves	$ 30	$ 30	$ 30

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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 720	$ (1,894)
Fuel hedging asset and liabilities amortization period	3 years
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue	50 years
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ (6,455)	(7,261)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(2,297)	(2,684)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(132)	(104)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 3,658	3,931
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 799	814
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	$ 407	317
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 182	183
Regulatory amortization period	1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 346	223
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 581	625
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 211	306
Remaining net book value of retired 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	$ (769)	(1,088)
Medicare drug subsidy obligation related to subsidiary	$ 10	13
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue	50 years
Alabama Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 147	(33)
Alabama Power | Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(2,027)	(2,082)
Alabama Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(497)	(609)
Alabama Power | Rate RSE refund
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(109)	0
Alabama Power | Natural disaster reserve
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(20)	(38)
Alabama Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	(45)	(7)
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	$ 947	946
Alabama Power | Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Alabama Power | Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 241	240
Regulatory amortization period	50 years
Alabama Power | Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Alabama Power | Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 176	53
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	$ 71	70
Regulatory amortization period	1 year
Alabama Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 56	62
Alabama Power | Nuclear outage
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 49	56
Regulatory amortization period	18 months
Alabama Power | Nuclear outage | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Alabama Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 43	54
Alabama Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net	$ 57	$ 58
Regulatory amortization period	12 months
Alabama Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years

Regulatory Matters - APC Regula

Regulatory Matters - APC Regulatory Matters (Details) - Alabama Power MW in Thousands	May 01, 2018USD ($)$ / KWH_Kilowatt_hour	Jan. 31, 2019	Dec. 31, 2025	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)$ / KWH_Kilowatt_hour	Dec. 31, 2017USD ($)$ / KWH_Kilowatt_hour	Feb. 19, 2019USD ($)MW	Feb. 06, 2019USD ($)	Feb. 05, 2019USD ($)	Feb. 28, 2017USD ($)	Jan. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Rate adjustment period					2 years
Maximum percentage of rate RSE					4.00%
Maximum annual percentage of ratio rate					5.00%
Adjusting point of weighted cost of equity					5.98%
Percent of basis points					0.07%
Percent of designated customer value benchmark survey					33.33%
Rate RSE refund liability												$ 73,000,000
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					47.00%
Weighted common equity return						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%
Under recovered certified power purchase agreements					$ 25,000,000	$ 12,000,000
Over (under) recovered environmental clause					$ (42,000,000)	$ (17,000,000)
Current billing rates under rate ECR (usd per KWH) | $ / KWH_Kilowatt_hour	0.02353				0.05910	0.02015
Under recovered fuel cost					$ 109,000,000	$ 25,000,000
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					63,000,000
Amount offset under recovered balance					30,000,000
Amount remaining for benefit of customers					33,000,000
Minimum natural disaster reserve balance, triggering establishment charge						50,000,000
Natural disaster reserve authorized limit					75,000,000	75,000,000
Natural disaster reserve, expected collection annually until reserve is restored						$ 16,000,000
Natural disaster reserve					$ 20,000,000
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
Maximum rate NDR charge per month, monthly residential customer account					5
Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Contract with customer, liability, bill credits				$ 50,000,000
Public utilities, approved return on equity			55.00%
Weighted common equity return		6.15%
Retail revenue requirement for environmental compliance				205,000,000
Rate case settlement annual increase base rates				183,000,000
Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements					$ 69,000,000							$ 142,000,000
Over (under) recovered environmental clause										$ (36,000,000)
Minimum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity					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%
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity					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%
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered fuel cost					$ 18,000,000
Unrecovered Investment Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset					42,000,000
Regulatory assets, current					10,000,000
Regulatory assets, noncurrent					32,000,000
Rate RSE refund
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities					109,000,000
Rate ECR refunds | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Contract with customer, liability, bill credits				$ 34,000,000
Under/(over) recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered fuel cost					$ 91,000,000
Subsequent Event
Schedule of Regulatory Assets and Liabilities [Line Items]
Rate RSE refund liability								$ 75,000,000	$ 75,000,000
Subsequent Event | Plant Gorgas Units 8, 9, And 10
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of retired plants (mw) | MW							1
Net investment costs to be transferred upon retirement							$ 740,000,000

Regulatory Matters - Schedule_3

Regulatory Matters - Schedule of GPC Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 720	$ (1,894)
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue		50 years
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ (6,455)	(7,261)
Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(293)	(188)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(132)	(104)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 3,658	3,931
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		$ 2,933	1,133
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 799	814
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		$ 211	306
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		8 years
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 346	223
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 182	183
Regulatory amortization period		1 year
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 581	625
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		50 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 2,378	232
Costs recovered annually		2
Customer refund liability, current		55
Customer refund		$ 40
Georgia Power | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Customer refund	$ 100
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue		34 years
Georgia Power | Maximum | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
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		$ (3,080)	(3,248)
Georgia Power | Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(165)	(188)
Georgia Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		(7)	(3)
Amortization of regulatory assets()		3
Costs associated with construction to be completed		30
Georgia Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 1,295	1,313
Georgia Power | Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period		14 years
Georgia Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 2,644	945
ARO annual recovery		60
Georgia Power | Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		522	521
Deferred tax assets related to CWIP		145
Deferred tax liabilities		610
Georgia Power | Storm damage reserves
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		416	333
Georgia Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 127	146
Georgia Power | Remaining net book value of retired assets | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Amortization of regulatory assets()	$ 4
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		$ 277	127
Georgia Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 91	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		$ 68	40
Georgia Power | Environmental remediation
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		55	49
Georgia Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 135	$ 106
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		65 years
Georgia Power | Retiree Medicare Drug Subsidy
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		$ 17
Georgia Power | Obsolete Inventories of Retired Units
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net		31
Plant Branch Units 1 Through 4 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		87
Plant Mitchell Unit 3 | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net book value of planned units retirements		$ 9

Regulatory Matters - GPC Regula

Regulatory Matters - GPC Regulatory Matters (Details) $ in Millions

Jan. 31, 2019MW

Apr. 03, 2018USD ($)

Jan. 01, 2013

Feb. 29, 2020USD ($)

Jun. 30, 2019USD ($)

Oct. 31, 2018USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)capacity_based_requestMW

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2022

May 01, 2016USD ($)

Schedule of Regulatory Assets and Liabilities [Line Items]

Effective income tax rate

16.30%

13.30%

27.30%

Deferred income taxes

$ 94

$ 166

$ (127)

Total regulatory assets (liabilities), net

720

(1,894)

Other regulatory assets, current

525

604

Other regulatory assets

8,308

6,943

Remaining net book value of retired assets

Schedule of Regulatory Assets and Liabilities [Line Items]

Total regulatory assets (liabilities), net

$ 211

$ 306

Maximum | Remaining net book value of retired assets

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory amortization period

8 years

Scenario, Forecast | Customers

Schedule of Regulatory Assets and Liabilities [Line Items]

Percentage basis net merger savings

60.00%

Georgia Power And Atlanta Gas Light Company | Scenario, Forecast

Schedule of Regulatory Assets and Liabilities [Line Items]

Percentage basis net merger savings

40.00%

Georgia Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Retail rate of return on common equity

10.95%

Portion of actual earnings above approved ROE band retained by subsidiary company

33.33%

Portion of actual earnings above approved ROE band refunded to customers

66.67%

Customer refund liability, noncurrent

$ 330

Customer refund

40

Customer refund liability in absence of base rate case

$ 185

$ 4

Contract with customer, liability, bill credits

$ 130

Effective income tax rate

21.30%

36.70%

36.70%

Deferred income taxes

$ (700)

$ (260)

$ 458

$ 383

Retail regulatory equity ratio

0.55

Approved capacity of units for solar generation resources (mw) | MW

1,000

Proposed capacity of units for investment portfolio (mw) | MW

50

Proposed capacity of units for certification (in mw) | MW

25

Number of capacity-based requests | capacity_based_request

2

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

$ 115

165

Required period for options and hedges

48 months

Total regulatory assets (liabilities), net

$ 2,378

232

Other regulatory assets, current

199

205

Other regulatory assets

4,902

2,932

Georgia Power | Remaining net book value of retired assets

Schedule of Regulatory Assets and Liabilities [Line Items]

Total regulatory assets (liabilities), net

127

146

Georgia Power | Storm damage reserves

Schedule of Regulatory Assets and Liabilities [Line Items]

Total regulatory assets (liabilities), net

416

333

Georgia Power | Property damage reserves-liability

Schedule of Regulatory Assets and Liabilities [Line Items]

Other regulatory assets, current

30

Other regulatory assets

$ 386

$ 303

Georgia Power | Minimum

Schedule of Regulatory Assets and Liabilities [Line Items]

Retail rate of return on common equity

10.00%

Georgia Power | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Retail rate of return on common equity

12.00%

Retail regulatory equity ratio

0.55

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]

Customer refund

$ 100

Contract with customer, liability, bill credits

$ 105

$ 95

Georgia Power | Scenario, Forecast | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Cost recovery, new nuclear

$ 99

Cost recovery, estimate, nuclear fuel

$ 50

Georgia Power | Deferred income tax charges

Schedule of Regulatory Assets and Liabilities [Line Items]

Regulatory liabilities

$ 610

Georgia Power | State and Local Jurisdiction

Schedule of Regulatory Assets and Liabilities [Line Items]

Effective income tax rate

6.00%

Georgia Power | State and Local Jurisdiction | Scenario, Forecast

Schedule of Regulatory Assets and Liabilities [Line Items]

Effective income tax rate

5.75%

Hurricane Michael | Georgia Power | Storm damage reserves

Schedule of Regulatory Assets and Liabilities [Line Items]

Incremental restoration costs

115

Hurricanes Irma and Matthew | Georgia Power | Storm damage reserves

Schedule of Regulatory Assets and Liabilities [Line Items]

Incremental restoration costs

250

Plant Hammond Units 1 through 4 | Georgia Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Net book value of planned units retirements

520

Plant McIntosh Unit 1 | Georgia Power

Schedule of Regulatory Assets and Liabilities [Line Items]

Net book value of planned units retirements

$ 40

Subsequent Event | 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

Subsequent Event | 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

Regulatory Matters - Nuclear Co

Regulatory Matters - Nuclear Construction (Details) - Georgia Power $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2009utilityMW
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 financing costs		$ 1,900
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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments [Line Items]
Total AFUDC and interest capitalized	$ 210	$ 249	$ 327
Georgia Power
Commitments [Line Items]
Total AFUDC and interest capitalized	94	$ 63	$ 68
Maximum guarantee	30
Customer refund	40
Georgia Power | Plant Vogtle Units 3 And 4
Commitments [Line Items]
Base project capital cost forecast	8,000
Construction contingency estimate	400
Total project capital cost forecast	8,400
Net investment	(4,600)
Remaining estimate to complete	3,800
Total AFUDC and interest capitalized	315
Maximum guarantee	1,700
Customer refund	$ 188

Regulatory Matters - Nuclear _2

Regulatory Matters - Nuclear Construction Joint Owner Contracts (Details) - Georgia Power - Plant Vogtle Units 3 And 4	12 Months Ended
	Dec. 31, 2018USD ($)MW	Dec. 31, 2015USD ($)	Aug. 31, 2018
Loss Contingencies [Line Items]
Ownership interest percentage required for voting for continuing construction	90.00%		90.00%
Total project capital cost forecast	$ 8,400,000,000
Additional construction capital costs		$ 3,300,000,000
Additional qualifying construction costs	$ 2,100,000,000
Percent of remaining share of total construction costs	100.00%
Percentage of cost savings	60.70%
Nonqualifying construction costs threshold	$ 100,000
Percentage of costs disallowed for recovery	6.00%
Costs disallowed for recovery, period	6 months
Public utilities extension project schedule term	1 year
Percentage of approval required to change primary construction contractor	90.00%
Percentage of approval required for material amendments	67.00%
Continued construction voted in favor, period	30 days
Percentage of continued construction voted in favor	50.00%
Share of plants (mw) | MW	206
Purchase rights to PTCs, period	30 days
Aggregate purchase price of PTCs	$ 300,000,000
Maximum aggregate funding	$ 250,000,000
Vogtle Owners
Loss Contingencies [Line Items]
Percentage of cost savings	39.30%
Category I
Loss Contingencies [Line Items]
Additional construction capital costs	$ 800,000,000
Category II
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	55.70%
Category II | Vogtle Owners
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	44.30%
Category II | Minimum
Loss Contingencies [Line Items]
Additional construction capital costs	$ 80,000,000
Additional qualifying construction costs	800,000,000
Category II | Maximum
Loss Contingencies [Line Items]
Additional qualifying construction costs	$ 1,600,000,000
Category III
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	65.70%
Category III | Vogtle Owners
Loss Contingencies [Line Items]
Percentage of construction costs responsible to pay	34.30%
Category III | Minimum
Loss Contingencies [Line Items]
Additional construction capital costs	$ 100,000,000
Additional qualifying construction costs	1,600,000,000
Category III | Maximum
Loss Contingencies [Line Items]
Additional qualifying construction costs	$ 2,100,000,000

Regulatory Matters - Nuclear _3

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

Jan. 01, 2021

Jan. 01, 2020

Feb. 19, 2019USD ($)

Dec. 21, 2018appeal

Dec. 18, 2018USD ($)

Aug. 31, 2018USD ($)

Jan. 01, 2018

Jan. 01, 2016

Jun. 30, 2018USD ($)subcontractor

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Dec. 31, 2009USD ($)

Dec. 31, 2022USD ($)

Jan. 01, 2013

Loss Contingencies [Line Items]

Proceeds from recovery of financing costs

$ 1,900

Retail rate of return on common equity

10.95%

Potential decrease each month, percentage

0.01%

Number of appeals dismissed | appeal

2

Maximum guarantee

$ 30

Approval of construction capital costs

$ 578

Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Estimated in-service capital cost

$ 4,418

Project capital cost forecast

7,300

Increase (decrease) in tariff

$ 88

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

100

$ 25

$ 20

Increase to base capital cost forecast

$ 700

Pre-tax charge to income

1,100

After-tax charge to income

$ 800

Maximum guarantee

$ 1,700

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

$ 75

$ 615

Subsequent Event

Loss Contingencies [Line Items]

Approval of construction capital costs

$ 5,400

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

$ 51.6

Minimum

Loss Contingencies [Line Items]

Retail rate of return on common equity

10.00%

Minimum | Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Number of subcontractors (more than) | subcontractor

60

Regulatory Matters - Nuclear _4

Regulatory Matters - Nuclear Construction DOE Financing (Details) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Loss Contingencies [Line Items]
Line of credit facility, maximum borrowing capacity		$ 7,863,000,000
Georgia Power
Loss Contingencies [Line Items]
Line of credit facility, maximum borrowing capacity		1,750,000,000
Eligible project costs to be reimbursed	$ 3,460,000,000
Georgia Power | Loan Guarantee Agreement
Loss Contingencies [Line Items]
Credit facility conditional borrowing commitment				$ 1,670,000,000
Georgia Power | FFB Loan
Loss Contingencies [Line Items]
Line of credit facility, maximum borrowing capacity		$ 2,625,000,000	$ 2,600,000,000

Regulatory Matters - Schedule_5

Regulatory Matters - Schedule of MPC Regulatory Assets and Labilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 720	$ (1,894)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,297)	(2,684)
Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(76)	(135)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(132)	(104)
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	2,933	1,133
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	211	306
Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	799	814
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	581	625
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	3,658	3,931
Regulatory asset	28
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 182	183
Regulatory amortization period	1 year
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 346	223
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (35)	(42)
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	$ (377)	(377)
Regulatory amortization period	8 years
Tax Cuts and Jobs Act of 2017, deferred tax assets	$ 377
Tax Cuts and Jobs Act of 2017, protected deferred tax assets	266
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	111
System Restoration Rider, deferred tax assets	9
Mississippi Power | Deferred credits related to income taxes | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	$ 46
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	$ 33
Mississippi Power | Deferred credits related to income taxes | Wholesale | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Tax Cuts and Jobs Act of 2017, unprotected deferred tax assets	15
Mississippi Power | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(185)	(178)
Mississippi Power | Property damage
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(56)	(57)
Mississippi Power | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (9)	0
Regulatory amortization period	1 year
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	6 years
Regulatory liabilities	$ 22
Mississippi Power | Retiree benefit plans – regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	171	174
Mississippi Power | Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 143	95
Regulatory amortization period	48 years
Mississippi Power | Kemper County energy facility
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 69	88
Regulatory asset	91
Regulatory assets, noncurrent	22
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	41	44
Mississippi Power | Remaining net book value of retired assets | Retail electric revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	26
Mississippi Power | Remaining net book value of retired assets | Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	15
Mississippi Power | Property tax
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 44	43
Regulatory amortization period	12 months
Mississippi Power | Deferred charges related to income taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 34	36
Mississippi Power | Plant Daniel Units 3 and 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	36	36
Mississippi Power | ECO carryforward
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	26	26
Mississippi Power | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 28	$ 28
Regulatory amortization period	3 years
Mississippi Power | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	15 years
Mississippi Power | Kemper Retail
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 years
Regulatory asset	$ 75
Mississippi Power | Kemper Wholesale
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 16
Mississippi Power | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	5 years
Mississippi Power | Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 9
Mississippi Power | Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 8
Maximum | Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	8 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	50 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	50 years

Regulatory Matters - MPC Regula

Regulatory Matters - MPC Regulatory Matters (Details) customer in Thousands

May 08, 2018USD ($)

Feb. 14, 2018USD ($)

Feb. 07, 2018USD ($)

Feb. 06, 2018USD ($)

Jan. 16, 2018USD ($)

May 31, 2017USD ($)

Aug. 31, 2016USD ($)

Sep. 30, 2018USD ($)

Dec. 31, 2018USD ($)filing

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Jan. 10, 2019USD ($)

Aug. 07, 2018USD ($)

Aug. 03, 2018USD ($)

Jul. 31, 2017USD ($)

Jan. 31, 2017USD ($)

Jul. 31, 2016USD ($)

Dec. 31, 2013USD ($)customer

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ 720,000,000

$ (1,894,000,000)

Major storms

Schedule of Regulatory Assets and Liabilities [Line Items]

Storm damage reserves

$ 74,000,000

41,000,000

$ 40,000,000

Mississippi Power

Schedule of Regulatory Assets and Liabilities [Line Items]

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

2

Annual PEP lookback refund to customers

$ 5,000,000

Gain contingency, surcharge revenue

$ 5,000,000

$ 5,000,000

Annual PEP filing rate increase

4.00%

Annual PEP filing rate increase amount

$ 26,000,000

$ 38,000,000

Public utilities, approved return on equity

9.33%

Regulatory equity ratio

55.00%

Increase in annual base rate revenues

$ 21,600,000

$ 17,000,000

Amount approved for recovery

$ 2,000,000

Net regulatory assets

$ (35,000,000)

(42,000,000)

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%

Recognized revenues

$ 5,000,000

Required customers for energy efficiency programs | customer

25

Public utilities, approved rate increase (decrease), amount

$ 18,000,000

$ 18,000,000

$ 22,000,000

Regulatory amortization period

5 years

Public utilities requested revenue requirement increase (decrease)

$ 26,000,000

$ 26,000,000

Percentage of PSC retail rate increase (decrease)

0.80%

0.85%

(0.07%)

PSC retail increase (decrease)

$ 7,000,000

$ 8,000,000

$ (1,000,000)

$ 55,000,000

Threshold above which actual damages are charged to the reserve

$ 50,000

Period to agree on system restoration rider

120 days

Wholesale accrual per annual SSR rate

$ 300,000

SRR rate

0.00%

0.00%

0.00%

Psc approved annual property damage reserve accrual

$ 2,000,000

$ 4,000,000

$ 3,000,000

Storm restoration costs

$ 9,000,000

Mississippi Power | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Proposed property damage reserve

55,000,000

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

3,000,000

$ 4,000,000

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 | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 3,000,000

$ 39,000,000

Under recovered fuel cost

$ 8,000,000

$ 6,000,000

Mississippi Power | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Allowed equity ratio

51.00%

Public utilities approved rate increase (decrease)

2.00%

2.00%

2.00%

2.00%

Public utilities requested rate increase (decrease)

$ 17,000,000

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 | Contested Compensation Costs

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

4,000,000

Mississippi Power | Subsequent Event | Retail electric revenues

Schedule of Regulatory Assets and Liabilities [Line Items]

PSC retail increase (decrease)

$ (35,000,000)

Mississippi Power | Deferred credits related to income taxes

Schedule of Regulatory Assets and Liabilities [Line Items]

Net regulatory assets

$ (377,000,000)

$ (377,000,000)

Regulatory amortization period

8 years

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

$ 111,000,000

Mississippi Power | Deferred credits related to income taxes | Kemper IGCC

Schedule of Regulatory Assets and Liabilities [Line Items]

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

$ 46,000,000

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

$ 33,000,000

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

Regulatory Matters - Kemper Reg

Regulatory Matters - Kemper Regulatory Matters (Details) $ in Millions	Aug. 06, 2018	Feb. 07, 2018	Feb. 06, 2018USD ($)	Apr. 30, 2018USD ($)	Jun. 30, 2017USD ($)	May 31, 2017USD ($)	Aug. 31, 2016USD ($)	Dec. 31, 2018USD ($)mi	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)miMW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2023USD ($)	May 31, 2017USD ($)	Dec. 31, 2018USD ($)mi	Jan. 31, 2017USD ($)	Dec. 17, 2015USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs																$ 29	$ 16
Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
After tax charge to income																$ 722	2,400	$ 264
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Plant capacity under coal gasification combined cycle technology | MW																582
Co two pipeline infrastructure | mi								61								61							61
Maximum cap construction costs																			$ 2,880
Pre-tax charge to income								$ (9)
After tax charge to income								(95)
Period costs																$ 0	0
PSC retail increase (decrease)								7		$ 8				$ 8		7	8	$ (1)					$ 7	$ 55
Public utilities, approved rate increase (decrease), amount						$ 18	$ 18										$ 22
Public utilities, approved return on equity		9.33%
Mississippi Power | Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Maximum cap construction costs					$ 5,950														2,400
Cost cap exceptions																			$ 570
Estimated cost					7,380
Cost related to grant funding					137
Pre-tax charge to income					2,800				$ 44	208	$ 34	$ 3,000	$ 108	242		37						$ 3,070
After tax charge to income					$ 2,000			95	$ 33	185	$ 21	$ 2,100	$ 67	206								$ 1,890
Estimated cost								$ 10								10							10
Period costs, net of tax																$ 27
After tax charge to income, cost during suspension period														$ 164
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																				$ 270
Government grants received																							387
Mississippi Power | Kemper IGCC | In-Service Asset Proposal
Schedule of Regulatory Assets and Liabilities [Line Items]
PSC retail increase (decrease)																									$ 126
Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs															$ 11
Mississippi Power | Plant Watson Unit 4
Schedule of Regulatory Assets and Liabilities [Line Items]
Accelerated retirement period	2 years
Mississippi Power | Plant Watson Unit 5
Schedule of Regulatory Assets and Liabilities [Line Items]
Accelerated retirement period	7 years
Mississippi Power | Plant Greene County Units 1 And 2
Schedule of Regulatory Assets and Liabilities [Line Items]
Accelerated retirement period	4 years
Mississippi Power | Mine
Schedule of Regulatory Assets and Liabilities [Line Items]
Term of management fee contract																				40 years
Minimum | Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs																					$ 2
Maximum | Mississippi Power | Kemper IGCC | Scenario, Forecast
Schedule of Regulatory Assets and Liabilities [Line Items]
Period costs																					$ 4
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 - Schedule_6

Regulatory Matters - Schedule of GAS Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 720	$ (1,894)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(2,297)	(2,684)
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(6,455)	(7,261)
Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(47)	(155)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(132)	(104)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 3,658	3,931
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	$ 121	138
Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	407	317
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 581	625
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	50 years
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ (1,872)	(1,879)
Southern Company Gas | Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(1,585)	(1,646)
Southern Company Gas | Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(940)	(1,063)
Southern Company Gas | Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(43)	(144)
Southern Company Gas | Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	(46)	(21)
Southern Company Gas | Environmental remediation
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	311	410
Southern Company Gas | Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 161	270
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	$ 121	138
Southern Company Gas | Long-term debt fair value adjustment | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	20 years
Southern Company Gas | Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 90	98
Regulatory amortization period	7 years
Southern Company Gas | Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Net regulatory assets	$ 59	$ 79
Southern Company Gas | Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	10 years
Southern Company Gas | Financial Instrument Hedging | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	2 years
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
Southern Company Gas | Other regulatory liabilities | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period	20 years

Regulatory Matters - GAS Regula

Regulatory Matters - GAS Regulatory Matters (Details) $ in Millions

Dec. 31, 2018USD ($)

Dec. 17, 2018USD ($)

Nov. 09, 2018USD ($)

May 15, 2018

May 05, 2018USD ($)

Feb. 23, 2018USD ($)

Feb. 08, 2018USD ($)

Dec. 21, 2017USD ($)

Oct. 10, 2017USD ($)

Oct. 31, 2018USD ($)

Jul. 31, 2018USD ($)

Feb. 28, 2017USD ($)

Mar. 31, 2018USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)mi

Dec. 31, 2015USD ($)

Dec. 31, 2014USD ($)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2017USD ($)

Jan. 01, 2018USD ($)

Nicor Gas

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ (230)

$ (44)

$ 137

Public utilities, approved return on equity

10.60%

9.80%

9.80%

Regulatory equity ratio

54.00%

52.00%

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

$ 93

Nicor Gas | energySMART

Schedule of Regulatory Assets and Liabilities [Line Items]

Energy efficiency and term reduction expenditures

$ 29

$ 107

Approved infrastructure replacement program

$ 113

$ 160

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

5 years

Regulated operations, natural gas pipeline length, approved for replacement | mi

200

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

$ 13

Virginia Natural Gas | Year 2016 | SAVE | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

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

$ 30

Virginia Natural Gas | Year 2017 through 2021 | SAVE | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

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

35

35

Atlanta Gas Light

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved rate increase (decrease), amount

$ 16

$ 20

Public utilities, approved return on equity

10.75%

Annual proceeds from strategic economic development projects

$ 15

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

10.55%

10.55%

Atlanta Gas Light | Maximum

Schedule of Regulatory Assets and Liabilities [Line Items]

Public utilities, approved return on equity

10.95%

10.95%

Atlanta Gas Light | Favorable Regulatory Action

Schedule of Regulatory Assets and Liabilities [Line Items]

Litigation settlement

$ 144

Proceeds from legal settlements

$ 7

$ 20

Atlanta Gas Light | True Up Recovery

Schedule of Regulatory Assets and Liabilities [Line Items]

Gain contingency, unrecorded amount

171

171

Atlanta Gas Light | True-Up Recovery, Unrecognized Equity

Schedule of Regulatory Assets and Liabilities [Line Items]

Gain contingency, unrecorded amount

$ 95

$ 95

Regulatory Matters - Schedule_7

Regulatory Matters - Schedule of GAS Unrecognized Ratemaking Amounts (Details) - Regulatory Asset Off Balance Sheet - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 95	$ 104
Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	11	11
Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	4	2
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset	$ 110	$ 117

Regulatory Matters - FERC Matte

Regulatory Matters - FERC Matters (Details) - SCS	May 10, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved return on equity	11.25%
Public utilities, approved return on equity, maximum amount	8.65%

Regulatory Matters - MPC FERC R

Regulatory Matters - MPC FERC Regulatory Matters (Details) - Mississippi Power - USD ($) $ in Millions	Jan. 01, 2019	Feb. 06, 2018	May 01, 2016	Jan. 31, 2018	Sep. 30, 2017	May 31, 2017	Aug. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Increase in base rate under cost based electric tariff			$ 7
AFUDC cost								$ 22
Period of notice to cancel counterparty					10 years
Period of notice required for contract termination					1 year
Public utilities, approved rate increase (decrease), amount						$ 18	$ 18		$ 22
Kemper IGCC
Schedule of Regulatory Assets and Liabilities [Line Items]
Period of amortization of regulatory assets								36 months
Public utilities, approved rate increase (decrease), amount		$ 99.3
MRA Revenue
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 11
Over recovered fuel cost										$ 6
MB Revenue
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 1
Subsequent Event | MRA Revenue
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount	$ (16)

Regulatory Matters - GAS FERC R

Regulatory Matters - GAS FERC Regulatory Matters (Details) - Pipelines - Southern Company Gas $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)pipeline	Oct. 31, 2017USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of gas construction projects | pipeline	2
Percentage of construction costs responsible to pay	5.00%
Investment	$ 83
Minimum
Schedule of Regulatory Assets and Liabilities [Line Items]
Estimated project costs	7,000	$ 6,000
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Estimated project costs	$ 7,800	$ 6,500

Contingencies - SO Litigation (

Contingencies - SO Litigation (Details) - Shareholder Derivative Lawsuits - Pending Litigation - claim	May 04, 2018	Apr. 25, 2018	Aug. 31, 2017
Loss Contingencies [Line Items]
Number of claims			2
Stay period	30 days	30 days

Contingencies - APC Litigation

Contingencies - APC Litigation (Details) - Alabama Department of Environmental Management (ADEM) - Alabama Power $ in Thousands	Sep. 27, 2018USD ($)	Mar. 02, 2018generating_plant
Schedule of Regulatory Assets and Liabilities [Line Items]
Penalty for unpermitted discharges | $	$ 1,250
Number of generating plants with unpermitted discharges | generating_plant		5

Contingencies - GPC Litigation

Contingencies - GPC Litigation (Details) - Pending Litigation - Subsequent Event - Georgia Power - Municipal Franchise Fees Class Action	Feb. 13, 2019
Loss Contingencies [Line Items]
Stay period	60 days
Petition period	20 days

Contingencies - MPC Litigation

Contingencies - MPC Litigation (Details) $ in Millions	Nov. 21, 2018plaintiff	May 18, 2018USD ($)
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

Contingencies - SPC Litigation

Contingencies - SPC Litigation (Details) - Southern Power $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Loss Contingencies [Line Items]
Construction contract payment withheld	$ 26
RE Roserock, LLC
Loss Contingencies [Line Items]
Noncontrolling ownership percentage held by parent	51.00%

Contingencies - GAS Litigation

Contingencies - GAS Litigation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Minimum insurance coverage	$ 11
Nicor Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Litigation settlement, expense	$ 11

Contingencies - GPC and GAS Env

Contingencies - GPC and GAS Environmental Remediation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)statesite	Dec. 31, 2017USD ($)
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Accrued environmental remediation	$ 268	$ 389
Georgia Power
Environmental Exit Cost [Line Items]
Costs recovered annually	2
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	23	22
Accrued environmental remediation	0	0
Under recovered environmental remediation costs, other regulatory assets, current	2	2
Under recovered environmental remediation costs, other regulatory assets, deferred	53	47
Southern Company Gas
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	26	46
Accrued environmental remediation	268	342
Under recovered environmental remediation costs, other regulatory assets, current	19	31
Under recovered environmental remediation costs, other regulatory assets, deferred	$ 292	379
Southern Company Gas | Manufactured Gas Plants
Environmental Exit Cost [Line Items]
# of sites | site	40
Number of states in which subject to environmental remediation liabilities | state	4
Southern Company Gas | Location One
Environmental Exit Cost [Line Items]
Environmental remediation liabilities of former sites	$ 2
Southern Company Gas | Location One | Elizabethtown Gas
Environmental Exit Cost [Line Items]
Environmental remediation liabilities of former sites		85
Southern Company
Accrual for Environmental Loss Contingencies, Balance Sheet Classification [Abstract]
Environmental remediation liability, current	49	73
Accrued environmental remediation	268	389
Under recovered environmental remediation costs, other regulatory assets, current	21	38
Under recovered environmental remediation costs, other regulatory assets, deferred	$ 345	$ 473

Contingencies - Nuclear Fuel Di

Contingencies - Nuclear Fuel Disposal Costs and Nuclear Insurance (Details)	12 Months Ended
	Dec. 31, 2018USD ($)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	$ 14,100,000,000
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	26 weeks
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	56,000,000
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 - Other Matters (

Contingencies - Other Matters (Details)	May 14, 2018USD ($)	Dec. 31, 2018USD ($)cavern	Dec. 31, 2017USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Property, plant and equipment		$ 80,797,000,000	$ 79,872,000,000
Natural Gas Storage - Salt Dome Caverns
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of salt dome caverns | cavern		2
Property, plant and equipment		$ 109,000,000
Property, Plant and Equipment | Natural Gas Storage - Salt Dome Caverns
Schedule of Regulatory Assets and Liabilities [Line Items]
Concentration risk (as percent)		20.00%
Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Property, plant and equipment		$ 3,574,000,000	3,532,000,000
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Property, plant and equipment		11,357,000,000	$ 11,728,000,000
Impairment of long-lived assets		$ 0
Deepwater Horizon Oil Spill Litigation Case | Mississippi Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Litigation settlement awarded from other party	$ 18,000,000

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total operating revenues		$ 23,495	$ 23,031	$ 19,896
Other income		322
Retail electric revenues
Disaggregation of Revenue [Line Items]
Leases revenues		75
Increase (decrease) in revenue from cost recovery mechanisms		60
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues		6,608
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues		5,266
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues		3,224
Other
Disaggregation of Revenue [Line Items]
Total operating revenues		124
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		3,175
Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues		(20)
Total retail electric and gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		18,377
Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		1,896
Revenue from transactions accounted for as derivatives		299
Lease income from PPA contracts		384
Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		620
Lease income from PPA contracts		121
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		699
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		1,903
Southern Company Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,652	3,909	3,920
Southern Company Gas | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		3,155
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues		1,525
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues		436
Southern Company Gas | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues		944
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues		40
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Total operating revenues		230
Southern Company Gas | Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues		(20)
Southern Company Gas | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues		568
Other income		3
Southern Company Gas | Wholesale gas services
Disaggregation of Revenue [Line Items]
Total operating revenues		101
Southern Company Gas | Gas midstream operations
Disaggregation of Revenue [Line Items]
Total operating revenues		32
Southern Company Gas | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		53
Alabama Power
Disaggregation of Revenue [Line Items]
Total operating revenues		6,032	6,039	5,889
Other income		57
Alabama Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		5,367
Increase (decrease) in revenue from cost recovery mechanisms		152
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues		2,335
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues		1,578
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues		1,428
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues		26
Alabama Power | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		297
Revenue from transactions accounted for as derivatives		20
Alabama Power | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		101
Alabama Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		267
Georgia Power
Disaggregation of Revenue [Line Items]
Total operating revenues		8,420	8,310	8,383
Other income		109
Georgia Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		7,752
Leases revenues		74
Increase (decrease) in revenue from cost recovery mechanisms		(19)
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues		3,301
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues		3,023
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues		1,344
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues		84
Georgia Power | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		133
Revenue from transactions accounted for as derivatives		29
Georgia Power | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		54
Georgia Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		481
Leases revenues		135
Mississippi Power
Disaggregation of Revenue [Line Items]
Total operating revenues		1,265	1,187	1,163
Mississippi Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		889
Increase (decrease) in revenue from cost recovery mechanisms		(13)
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues		273
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues		286
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues		321
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Total operating revenues		9
Mississippi Power | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		348
Revenue from transactions accounted for as derivatives		4
Mississippi Power | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		6
Mississippi Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		22
Southern Power
Disaggregation of Revenue [Line Items]
Total operating revenues		2,205	2,075	$ 1,577
Southern Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		580
Lease income from PPA contracts		186
Southern Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		1,140
Revenue from transactions accounted for as derivatives		242
Lease income from PPA contracts		413
Southern Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		472
Southern Power | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		13
Operating Segments | Southern Company Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	1,723	3,930	4,090
Wholesale gas services | Operating Segments | Southern Company Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	24	144	6
Wholesale gas services | Third Party Gross Revenues | Operating Segments | Southern Company Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 5,807	6,955	$ 6,152
Revenue from transactions accounted for as derivatives		$ 3,900

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,630
Contract Assets	102
Contract Liabilities	32
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	39
Contract Liabilities	11
Alabama Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	520
Contract Assets	0
Contract Liabilities	12
Georgia Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	721
Contract Assets	58
Contract Liabilities	$ 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 to unregulated service agreements where payment is contingent upon project completion. Georgia Power also had contract liabilities for outstanding performance obligations primarily related to unregulated service agreements.
Mississippi Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 100
Contract Assets	0
Contract Liabilities	0
Southern Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	118
Contract Assets	0
Contract Liabilities	11
Southern Company Gas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	952
Contract Assets	0
Contract Liabilities	$ 2

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	Dec. 31, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 487
Expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 341
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	$ 315
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	$ 315
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	$ 306
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	$ 2,103
Expected timing of satisfaction
Alabama Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 23
Expected timing of satisfaction	1 year
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	$ 22
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	$ 26
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	$ 23
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	$ 140
Expected timing of satisfaction
Georgia Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 41
Expected timing of satisfaction	1 year
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	$ 38
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	$ 40
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	$ 30
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	$ 31
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	$ 82
Expected timing of satisfaction
Mississippi Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 3
Expected timing of satisfaction	1 year
Mississippi 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	$ 3
Expected timing of satisfaction	1 year
Mississippi 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	$ 1
Expected timing of satisfaction	1 year
Mississippi 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	$ 0
Expected timing of satisfaction	1 year
Mississippi 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	$ 0
Expected timing of satisfaction	1 year
Mississippi 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	$ 0
Expected timing of satisfaction
Southern Power | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 323
Expected timing of satisfaction	1 year
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	$ 295
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	$ 270
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	$ 275
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	$ 2,028
Expected timing of satisfaction

Property, Plant, and Equipmen_3

Property, Plant, and Equipment - Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Electric utilities:
Generation	$ 52,324	$ 51,279
Transmission	11,344	11,562
Distribution	18,746	19,239
General/other	4,446	4,402
Electric utilities' plant in service	86,860	86,482
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	12,409	13,079
Storage facilities	1,640	1,599
Other	1,128	1,155
Southern Company Gas plant in service	15,177	15,833
Other plant in service	1,669	1,227
Total plant in service	103,706	103,542
Alabama Power
Electric utilities:
Generation	16,533	14,213
Transmission	4,380	4,119
Distribution	7,389	7,034
General/other	2,100	1,960
Electric utilities' plant in service	30,402	27,326
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	30,402	27,326
Georgia Power
Electric utilities:
Generation	19,145	17,038
Transmission	6,156	5,947
Distribution	10,389	9,978
General/other	1,985	1,898
Electric utilities' plant in service	37,675	34,861
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	37,675	34,861
Mississippi Power
Electric utilities:
Generation	2,849	2,801
Transmission	769	737
Distribution	968	946
General/other	314	289
Electric utilities' plant in service	4,900	4,773
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	4,900	4,773
Southern Power
Electric utilities:
Generation	13,246	13,737
Transmission	0	0
Distribution	0	0
General/other	25	18
Electric utilities' plant in service	13,271	13,755
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	13,271	13,755
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	12,409	13,079
Storage facilities	1,640	1,599
Other	1,128	1,155
Southern Company Gas plant in service	15,177	15,833
Other plant in service	0	0
Total plant in service	$ 15,177	$ 15,833
Natural gas | Southern Power
Southern Company Gas:
Useful life	45 years
Biomass | Southern Power
Southern Company Gas:
Useful life	40 years
Solar | Southern Power
Southern Company Gas:
Useful life	35 years
Wind | Southern Power
Southern Company Gas:
Useful life	30 years

Property, Plant, and Equipmen_4

Property, Plant, and Equipment - Additional Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
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) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Capital Leased Assets [Line Items]
Less: Accumulated amortization	$ (75)	$ (72)
Balance, net of amortization	191	201
Office buildings
Capital Leased Assets [Line Items]
Capital leased assets, gross	216	216
PPAs
Capital Leased Assets [Line Items]
Capital leased assets, gross	0	0
Computer-related equipment
Capital Leased Assets [Line Items]
Capital leased assets, gross	43	51
Gas pipeline
Capital Leased Assets [Line Items]
Capital leased assets, gross	7	6
Georgia Power
Capital Leased Assets [Line Items]
Less: Accumulated amortization	(84)	(68)
Balance, net of amortization	121	137
Georgia Power | Office buildings
Capital Leased Assets [Line Items]
Capital leased assets, gross	61	61
Georgia Power | PPAs
Capital Leased Assets [Line Items]
Capital leased assets, gross	144	144
Georgia Power | Computer-related equipment
Capital Leased Assets [Line Items]
Capital leased assets, gross	0	0
Georgia Power | Gas pipeline
Capital Leased Assets [Line Items]
Capital leased assets, gross	$ 0	$ 0

Property, Plant, and Equipmen_6

Property, Plant, and Equipment - Composite Straight-Line Rates (Details) - Utility plant in service	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Alabama Power
Property, Plant and Equipment [Line Items]
Composite rate	3.00%	2.90%	3.00%
Georgia Power
Property, Plant and Equipment [Line Items]
Composite rate	2.60%	2.70%	2.80%
Mississippi Power
Property, Plant and Equipment [Line Items]
Composite rate	4.10%	3.70%	4.20%
Southern Company Gas
Property, Plant and Equipment [Line Items]
Composite rate	2.90%	2.90%	2.80%

Property, Plant, and Equipmen_7

Property, Plant, and Equipment - Depreciation and Amortization (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended		36 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 31,038	$ 31,457
Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 766	673
Other plant in service | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	65 years
Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 30,300	30,800
Georgia Power
Property, Plant and Equipment [Line Items]
Amortization of remaining regulatory liability			$ 14
Accumulated depreciation	12,096	11,704
Gulf Power
Property, Plant and Equipment [Line Items]
Decrease in depreciation		34
Southern Company Gas
Property, Plant and Equipment [Line Items]
Accumulated depreciation	4,400	4,596
Southern Company Gas | Other plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 129	75
Southern Company Gas | Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	5 years
Southern Company Gas | Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	15 years
Southern Company Gas | Storage facilities | Minimum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	40 years
Southern Company Gas | Storage facilities | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	60 years
Southern Company Gas | Other assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciation of original cost	65 years
Southern Company Gas | Utility plant in service
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 4,300	$ 4,500

Property, Plant, and Equipmen_8

Property, Plant, and Equipment - Ownership and Investment in Jointly-Owned Facilities (Details) $ in Millions	1 Months Ended
	Aug. 31, 2017USD ($)	Dec. 31, 2018USD ($)mi
Alabama Power
Other Ownership Interests [Line Items]
Percent Ownership		14.00%
Alabama Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership		60.00%
Plant in Service		$ 274
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		$ 2,056
Accumulated Depreciation		619
CWIP		$ 138
Georgia Power | Plant Hatch (nuclear)
Other Ownership Interests [Line Items]
Percent Ownership		50.10%
Plant in Service		$ 1,569
Accumulated Depreciation		615
CWIP		$ 54
Georgia Power | Plant Vogtle (nuclear) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership		45.70%
Plant in Service		$ 3,804
Accumulated Depreciation		2,150
CWIP		$ 84
Georgia Power | Plant Scherer (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership		8.40%
Plant in Service		$ 266
Accumulated Depreciation		96
CWIP		$ 14
Georgia Power | Plant Scherer (coal) Unit 3
Other Ownership Interests [Line Items]
Percent Ownership		75.00%
Plant in Service		$ 1,238
Accumulated Depreciation		493
CWIP		$ 66
Georgia Power | Plant Wansley (coal)
Other Ownership Interests [Line Items]
Percent Ownership		53.50%
Plant in Service		$ 1,179
Accumulated Depreciation		362
CWIP		$ 160
Georgia Power | Rocky Mountain (pumped storage)
Other Ownership Interests [Line Items]
Percent Ownership		25.40%
Plant in Service		$ 184
Accumulated Depreciation		135
CWIP		$ 0
Mississippi Power | Plant Daniel (coal) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership		50.00%
Plant in Service		$ 723
Accumulated Depreciation		201
CWIP		$ 7
Southern Company Gas | Dalton Pipeline (natural gas pipeline)
Other Ownership Interests [Line Items]
Percent Ownership		50.00%
Plant in Service		$ 270
Accumulated Depreciation		6
CWIP		$ 0
Pipeline infrastructure (miles) | mi		115
Agreement to lease undivided ownership (percent)	50.00%
Future minimum payments receivable	$ 26
Initial term of contract	25 years
Alabama Power | Mississippi Power | Greene County (natural gas) Units 1 and 2
Other Ownership Interests [Line Items]
Percent Ownership		40.00%
Plant in Service		$ 180
Accumulated Depreciation		93
CWIP		$ 1

Property, Plant, and Equipmen_9

Property, Plant, and Equipment - Joint Ownership Agreements (Narrative) (Details) - USD ($)	60 Months Ended
	Jan. 15, 2024	Dec. 31, 2018	Dec. 04, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 7,254,000,000		$ 6,904,000,000
Georgia Power
Property, Plant and Equipment [Line Items]
Construction work in progress		4,833,000,000		4,613,000,000
Southern Power
Property, Plant and Equipment [Line Items]
Construction work in progress		430,000,000		511,000,000
Mississippi Power
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 103,000,000		$ 84,000,000
Plant Vogtle Units 3 And 4 | Georgia Power
Property, Plant and Equipment [Line Items]
Percent ownership		45.70%
Construction work in progress		$ 4,500,000,000
Plant Stanton Unit A | Southern Power
Property, Plant and Equipment [Line Items]
Ownership percentage sold			65.00%
Subsequent Event | Scenario, Forecast | Plant Daniel Units 1 And 2 | Gulf Power
Property, Plant and Equipment [Line Items]
Ownership interest to be sold	50.00%
Ownership interest in one unit	100.00%
Subsequent Event | Scenario, Forecast | Plant Daniel Units 1 And 2 | Mississippi Power
Property, Plant and Equipment [Line Items]
Payments to acquire businesses	$ 1
Option to purchase, period	120 days

Property, Plant, and Equipme_10

Property, Plant, and Equipment - Assets Subject to Lien (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Oct. 02, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	$ 116,914		$ 111,005	$ 109,697
Mississippi Power
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	4,886		4,866
Mississippi Power | Chevron
Property, Plant and Equipment [Line Items]
Net book value of co-generation assets		$ 101
Southern Power
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	14,883		$ 15,206
Southern Power | Senior Lien
Property, Plant and Equipment [Line Items]
Assets, primarily related to property, plant, and equipment, subject to lien	$ 563

Asset Retirement Obligations -

Asset Retirement Obligations - Details of AROs Included in the Balance Sheets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 4,824	$ 4,514
Liabilities incurred	29	16
Liabilities settled	(244)	(177)
Accretion	217	179
Cash flow revisions	4,737	292
Reclassification to held for sale	(169)
Balance at end of year	9,394	4,824
Alabama Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	1,709	1,533
Liabilities incurred	0	0
Liabilities settled	(55)	(26)
Accretion	106	77
Cash flow revisions	1,450	125
Reclassification to held for sale	0
Balance at end of year	3,210	1,709
Georgia Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	2,638	2,532
Liabilities incurred	27	4
Liabilities settled	(116)	(120)
Accretion	94	89
Cash flow revisions	3,186	133
Reclassification to held for sale	0
Balance at end of year	5,829	2,638
Mississippi Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	174	179
Liabilities incurred	0	0
Liabilities settled	(35)	(23)
Accretion	5	5
Cash flow revisions	16	13
Reclassification to held for sale	0
Balance at end of year	160	174
Southern Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	78	64
Liabilities incurred	2	6
Liabilities settled	0	0
Accretion	4	4
Cash flow revisions	0	4
Reclassification to held for sale	0
Balance at end of year	$ 84	$ 78

Asset Retirement Obligations _2

Asset Retirement Obligations - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2014	Dec. 31, 2017
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Increase to AROs		$ 1,200
Estimated inflation rate			4.50%
Estimated trust earnings rate			7.00%
Alabama Power | Internal reserves
Jointly Owned Utility Plant Interests [Line Items]
Accumulated provisions for decommissioning	$ 17		$ 17		$ 18
Alabama Power | Plant Farley
Jointly Owned Utility Plant Interests [Line Items]
Increase to AROs		300
Mississippi Power | Plant Greene County
Jointly Owned Utility Plant Interests [Line Items]
Increase to AROs		$ 11
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Increase to AROs	3,100
Fair market value of securities on loan and pledged to creditors	27		27		76
Fair value of collateral received	28		$ 28		$ 77
Estimated inflation rate			2.40%
Estimated trust earnings rate			4.40%
Georgia Power | Plant Hatch and Plant Vogtle Units 1 And 2
Jointly Owned Utility Plant Interests [Line Items]
Increase to AROs	$ 130
Georgia Power | Plant Hatch
Jointly Owned Utility Plant Interests [Line Items]
Annual decommissioning cost for ratemaking				$ 4
Georgia Power | Plant Vogtle
Jointly Owned Utility Plant Interests [Line Items]
Annual decommissioning cost for ratemaking				$ 2

Asset Retirement Obligations _3

Asset Retirement Obligations - Investment Securities in the Funds (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 1,719	$ 1,831
Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	919	1,059
Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	726	725
Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	74	47
Alabama Power
Marketable Securities [Line Items]
Total investment securities in the Funds	846	902
Alabama Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	594	644
Alabama Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	201	223
Alabama Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	51	35
Georgia Power
Marketable Securities [Line Items]
Total investment securities in the Funds	873	929
Georgia Power | Equity securities
Marketable Securities [Line Items]
Total investment securities in the Funds	325	415
Georgia Power | Debt securities
Marketable Securities [Line Items]
Total investment securities in the Funds	525	502
Georgia Power | Other securities
Marketable Securities [Line Items]
Total investment securities in the Funds	$ 23	$ 12

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair value increases (decreases)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ (67)	$ 233	$ 114
Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	(183)	181	48
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	(38)	125	76
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	(96)	98	34
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	(29)	108	38
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	$ (87)	$ 83	$ 14

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, 2018	Dec. 31, 2017
Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 873	$ 929
Plant Farley | Alabama Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	846	902
Plant Hatch | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	547	583
Plant Vogtle Units 1 and 2 | Georgia Power
Public Utilities, General Disclosures [Line Items]
Accumulated provisions for decommissioning	$ 326	$ 346

Asset Retirement Obligations _6

Asset Retirement Obligations - Estimated Costs of Decommissioning (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Alabama Power | Plant Farley
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2,037
Decommissioning periods: Completion year	2,076
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	2,034
Decommissioning periods: Completion year	2,075
Site study costs	$ 962
Georgia Power | Plant Vogtle Units 1 and 2
Public Utilities, General Disclosures [Line Items]
Decommissioning periods: Beginning year	2,047
Decommissioning periods: Completion year	2,079
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, 2018USD ($)MW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity | MW	1,000
Ownership percentage, equity method investment	50.00%
Percent ownership	14.00%
Alabama Power | Southern Electric Generating Company
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity | MW	1,020
Share of purchased power	$ 102	$ 76	$ 55
Alabama Power | SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Dividends paid by equity method investment	$ 18	24	24
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%
Georgia Power | Southern Electric Generating Company
Jointly Owned Utility Plant Interests [Line Items]
Share of purchased power	$ 105	$ 78
Purchased Power from Affiliates | Georgia Power | Southern Electric Generating Company
Jointly Owned Utility Plant Interests [Line Items]
Share of purchased power			$ 57
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	Sep. 30, 2018operating_facility	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Oct. 31, 2017	Apr. 30, 2017USD ($)
Global Atlantic
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage				33.00%
Southern Power
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, cash distributions paid, percentage				67.00%
Number of wind facilities | operating_facility			8
Reclassification from redeemable noncontrolling interest				$ 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
Turner Renewable Energy | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest						10.00%
SP Solar Holdings I, LP | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership (percent)		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
SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Sale of equity interest in limited partnership (percent)	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%
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
Liabilities				113,000,000
Noncontrolling interests related to other partners' interest				1,200,000,000
Variable Interest Entity, Primary Beneficiary | SP Wind | Southern Power
Redeemable Noncontrolling Interest [Line Items]
Assets				2,500,000,000
Liabilities				51,000,000
Noncontrolling interests related to other partners' interest				$ 47,000,000

Consolidated Entities and Equ_5

Consolidated Entities and Equity Method Investments - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Roll Forward]
Redemption of redeemable noncontrolling interests		$ (129)
Southern Power
Noncontrolling Interest [Roll Forward]
Beginning balance	$ 164	43
Net income attributable to redeemable noncontrolling interests	2	4
Distributions to redeemable noncontrolling interests	(2)	(1)
Capital contributions from redeemable noncontrolling interests	2	118
Redemption of redeemable noncontrolling interests	(59)	(129)
Reclassification to non-redeemable noncontrolling interests	(114)
Change in fair value of redeemable noncontrolling interests	7
Ending balance	$ 0	$ 164

Consolidated Entities and Equ_6

Consolidated Entities and Equity Method Investments - Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Net income									$ 2,300	$ 926	$ 2,529
Less: Net income attributable to noncontrolling interests									(58)	(44)	(32)
Net income attributable to Southern Power	$ 278	$ 1,164	$ (154)	$ 938	$ 496	$ 1,069	$ (1,381)	$ 658
Southern Power
Noncontrolling Interest [Line Items]
Net income									246	1,117	374
Less: Net income attributable to noncontrolling interests									$ 59	44	32
Less: Net income attributable to redeemable noncontrolling interests										2	4
Net income attributable to Southern Power	$ (48)	$ 92	$ 22	$ 121	$ 795	$ 124	$ 82	$ 70		$ 1,071	$ 338

Consolidated Entities and Equ_7

Consolidated Entities and Equity Method Investments - GAS Equity Method Investments Narrative (Details) $ in Millions	6 Months Ended		10 Months Ended	12 Months Ended
	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Oct. 31, 2016USD ($)	Dec. 31, 2018USD ($)gal	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015	Dec. 31, 2014miBcf
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ 15	$ 148	$ 106	$ 59
Distributions to noncontrolling interests				153	119	$ 72
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 60			148	106
Distributions to noncontrolling interests	15			$ 0	0
Southern Company Gas | Southern Natural Gas Company, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment				50.00%
Southern Company Gas | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment								20.00%
Pipeline infrastructure | mi								118
Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	1			$ 7	$ 6
Ownership percentage, equity method investment								5.00%
Pipeline infrastructure | mi								594
Southern Company Gas | Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage, equity method investment				50.00%
Southstar | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Agreement to purchase remaining interest			$ 160
Piedmont | Southstar
Schedule of Equity Method Investments [Line Items]
Payments of ordinary dividends to noncontrolling interests	$ 15
Predecessor | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 2
Distributions to noncontrolling interests		19
Predecessor | Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		0
Predecessor | Piedmont | Southstar
Schedule of Equity Method Investments [Line Items]
Distributions to noncontrolling interests		$ 19
Minimum | Southern Company Gas | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas pipeline capacity (volume) | Bcf								1
Minimum | Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas pipeline capacity (volume) | Bcf								1.5
Southstar | Southstar | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Ownership percentage of noncontrolling interest	85.00%					85.00%
Southstar | Southstar | Piedmont
Schedule of Equity Method Investments [Line Items]
Ownership percentage of noncontrolling interest							15.00%
Georgia Natural Gas | Georgia Natural Gas | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Noncontrolling ownership percentage held by parent							100.00%
Liquefied Natural Gas (LNG) | Southern Company Gas | Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Storage facility capacity | gal				2,000,000
Liquefied Natural Gas (LNG) | Minimum | Southern Company Gas | Pivotal JAX LNG, LLC
Schedule of Equity Method Investments [Line Items]
Storage facility production capacity | gal				120,000

Consolidated Entities and Equ_8

Consolidated Entities and Equity Method Investments - Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,580	$ 1,513
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,538	1,477
SNG | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,261	1,262
Current assets	104	82
Property, plant, and equipment	2,606	2,439
Deferred charges and other assets	121	121
Total Assets	2,831	2,642
Current liabilities	103	110
Long-term debt	1,103	1,102
Other deferred charges and other liabilities	212	76
Total Liabilities	1,418	1,288
Total Stockholders' Equity	1,413	1,354
Total Liabilities and Stockholders' Equity	2,831	2,642
PennEast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	71	57
Atlantic Coast Pipeline | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	83	41
Other | Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 123	$ 117

Consolidated Entities and Equ_9

Consolidated Entities and Equity Method Investments - Income Statement Information (Details) - USD ($) $ in Millions	4 Months Ended	6 Months Ended		10 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Jun. 30, 2016	Oct. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments				$ 15	$ 148	$ 106	$ 59
Southern Company Gas
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 60			148	106
Southern Company Gas | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		56			131	88
Revenues	$ 230				604	544
Operating income	137				310	242
Net income	$ 115				261	175
Southern Company Gas | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		0			5	6
Southern Company Gas | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		1			7	6
Southern Company Gas | Other
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 3			$ 5	$ 6
Southern Company Gas | Predecessor
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ 2
Southern Company Gas | Predecessor | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			0
Southern Company Gas | Predecessor | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			0
Southern Company Gas | Predecessor | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			0
Southern Company Gas | Predecessor | Other
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ 2

Financing - Securities Due With

Financing - Securities Due Within One Year (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Line Items]
Senior notes	$ 2,950	$ 2,354
Long-term bank term loans		1,420
Revenue bonds	173	90
First mortgage bonds	50
Capitalized leases	24	31
Other	1	(3)
Total	3,198	3,892
Alabama Power
Debt Disclosure [Line Items]
Senior notes	200
Revenue bonds	0
First mortgage bonds	0
Capitalized leases	1
Other	0
Total	201
Georgia Power
Debt Disclosure [Line Items]
Senior notes	500	750
Long-term bank term loans		100
Revenue bonds	108	0
First mortgage bonds	0
Capitalized leases	13	11
Other	(4)	(4)
Total	617	857
Mississippi Power
Debt Disclosure [Line Items]
Senior notes	0	0
Long-term bank term loans		900
Revenue bonds	40	90
First mortgage bonds	0
Capitalized leases	0	0
Other	0	(1)
Total	40	989
Long-term pollution control bond, current	40	40
Revenue bonds, current	50	50
Southern Power
Debt Disclosure [Line Items]
Senior notes	600	350
Long-term bank term loans		420
Revenue bonds	0	0
First mortgage bonds	0
Capitalized leases	0	0
Other	(1)	0
Total	599	770
Southern Company Gas
Debt Disclosure [Line Items]
Senior notes	300	155
Long-term bank term loans		0
Revenue bonds	0	0
First mortgage bonds	50
Capitalized leases	0	0
Other	7	2
Total	$ 357	$ 157

Financing - Maturities of Long-

Financing - Maturities of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Line Items]
2,019	$ 3,156
2,020	4,041
2,021	3,186
2,022	1,974
2,023	2,388
Alabama Power
Debt Disclosure [Line Items]
2,019	200	$ 200
2,020	250	250
2,021	310
2,022	750	750
2,023	300	300
Georgia Power
Debt Disclosure [Line Items]
2,019	621
2,020	1,006
2,021	375
2,022	505
2,023	153
Mississippi Power
Debt Disclosure [Line Items]
2,019	0	125
2,020	307
2,021	270
2,022	0
2,023	0
Southern Power
Debt Disclosure [Line Items]
2,019	600
2,020	825
2,021	300
2,022	677
2,023	290
Southern Company Gas
Debt Disclosure [Line Items]
2,019	350
2,020	0
2,021	330	330
2,022	46	$ 46
2,023	$ 400

Financing - Long-Term Debt (Det

Financing - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Line Items]
Senior notes	$ 32,725	$ 35,148
Long-term pollution control bonds	2,585	3,297
Long-term bank term loans	145	1,465
Junior Subordinated Debt
Debt Disclosure [Line Items]
Long-term debt	3,570	3,570
Alabama Power
Debt Disclosure [Line Items]
Senior notes	6,875	6,375
Long-term pollution control bonds	1,060	1,060
Long-term bank term loans	45	45
Georgia Power
Debt Disclosure [Line Items]
Senior notes	5,600	7,100
Long-term pollution control bonds	1,460	1,821
Long-term bank term loans	0	100
Georgia Power | Junior Subordinated Debt
Debt Disclosure [Line Items]
Long-term debt	270	270
Mississippi Power
Debt Disclosure [Line Items]
Senior notes	1,200	755
Long-term pollution control bonds	40	83
Long-term bank term loans	0	900
Southern Power
Debt Disclosure [Line Items]
Senior notes	5,050	5,459
Long-term bank term loans	0	420
Southern Company Gas
Debt Disclosure [Line Items]
Senior notes	4,000	4,157
Southern Company
Debt Disclosure [Line Items]
Senior notes	10,000	10,200
Southern Company | Junior Subordinated Debt
Debt Disclosure [Line Items]
Long-term debt	$ 3,300	$ 3,300

Financing - Long-Term Debt Narr

Financing - Long-Term Debt Narrative (Details) - USD ($)

1 Months Ended

2 Months Ended

Nov. 30, 2018

May 31, 2018

Mar. 31, 2018

Feb. 19, 2019

Jan. 31, 2019

Dec. 31, 2018

Oct. 31, 2018

Aug. 31, 2018

Jul. 31, 2018

Jun. 30, 2018

Apr. 30, 2018

Jan. 31, 2018

Floating Rate Bank Term Loan Agreement | Notes Payable to Banks

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 900,000,000

Senior Notes | Series 2018A Floating Rate Senior Notes due February 14, 2020

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 750,000,000

Senior Notes | Subsequent Event

Debt Disclosure [Line Items]

Repayments of debt

$ 1,200,000,000

Senior Notes | Subsequent Event | Series 2018A Floating Rate Senior Notes due February 14, 2020

Debt Disclosure [Line Items]

Debt instrument, face amount

750,000,000

Debt instrument, repurchase amount

504,000,000

Senior Notes | Subsequent Event | Senior Notes 1.85% Due July 1, 2019

Debt Disclosure [Line Items]

Debt instrument, face amount

1,000,000,000

Debt instrument, repurchase amount

$ 522,000,000

Fixed stated interest rate of debt obligation

1.85%

Senior Notes | Subsequent Event | Series 2014B 2.15% Senior Notes Due September 1, 2019

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 350,000,000

Debt instrument, repurchase amount

$ 180,000,000

Fixed stated interest rate of debt obligation

2.15%

Alabama Power | Senior Notes | Series 2018A Floating Rate Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 500,000,000

Fixed stated interest rate of debt obligation

4.30%

Alabama Power | Senior Notes | Series 2008B 5.40% Senior Notes due June 1, 2018

Debt Disclosure [Line Items]

Fixed stated interest rate of debt obligation

5.40%

Debt instrument, repurchased face amount

$ 250,000,000

Alabama Power | Municipal bonds | The Industrial Development Board Of The City Of Mobile, Alabama Pollution Control Revenue Bonds (Alabama Power Company Plant Barry Project), Series 2008

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 120,000,000

Alabama Power | Maturity December 1, 2018 | SEGCO

Debt Disclosure [Line Items]

Guarantee of unsecured senior notes

$ 100,000,000

$ 100,000,000

Georgia Power | Senior Notes

Debt Disclosure [Line Items]

Repayments of debt

$ 902,000,000

Georgia Power | Senior Notes | Series 2007A 5.65% Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

250,000,000

Debt instrument, repurchase amount

$ 89,000,000

Fixed stated interest rate of debt obligation

5.65%

Georgia Power | Senior Notes | Series 2009A 5.95% Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 500,000,000

Debt instrument, repurchase amount

$ 326,000,000

Fixed stated interest rate of debt obligation

5.95%

Georgia Power | Senior Notes | Series 2010B 5.40% Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 600,000,000

Debt instrument, repurchase amount

$ 335,000,000

Fixed stated interest rate of debt obligation

5.40%

Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1995

Debt Disclosure [Line Items]

Debt instrument, face amount

105,000,000

Georgia Power | Municipal bonds | Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 1997

Debt Disclosure [Line Items]

Debt instrument, face amount

173,000,000

Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994

Debt Disclosure [Line Items]

Debt instrument, face amount

55,000,000

Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bnds (Georgia Power Company Plant Vogtle Project), Second Series 2008

Debt Disclosure [Line Items]

Debt instrument, face amount

65,000,000

Georgia Power | Municipal bonds | Development Authority Of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2013

Debt Disclosure [Line Items]

Debt instrument, face amount

72,000,000

Georgia Power | Municipal bonds | Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2018 Due November 1, 2052

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 108,000,000

Georgia Power | Municipal bonds | Subsequent Event

Debt Disclosure [Line Items]

Debt instrument, repurchased face amount

$ 108,000,000

Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project) First Series 1992

Debt Disclosure [Line Items]

Debt instrument, repurchased face amount

$ 13,000,000

Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Eighth Series 1994

Debt Disclosure [Line Items]

Debt instrument, repurchased face amount

20,000,000

Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 1995

Debt Disclosure [Line Items]

Debt instrument, repurchased face amount

$ 75,000,000

Georgia Power | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 3

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 100,000,000

Mississippi Power

Debt Disclosure [Line Items]

Fixed stated interest rate of debt obligation

7.13%

Mississippi Power | Senior Notes | Series 2018A Floating Rate Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

300,000,000

Mississippi Power | Senior Notes | Series 2018B 3.95% Senior Notes

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 300,000,000

Fixed stated interest rate of debt obligation

3.95%

Mississippi Power | Senior Notes | Series G 5.40% Senior Notes Due July 1, 2035

Debt Disclosure [Line Items]

Fixed stated interest rate of debt obligation

5.40%

Debt instrument, repurchased face amount

$ 30,000,000

Mississippi Power | Senior Notes | Series 2009A 5.55% Senior Notes Due March 1, 2019

Debt Disclosure [Line Items]

Fixed stated interest rate of debt obligation

5.55%

Debt instrument, repurchased face amount

$ 125,000,000

Mississippi Power | Municipal bonds | Pollution Control Revenue Bonds

Debt Disclosure [Line Items]

Debt instrument, repurchase amount

$ 43,000,000

Mississippi Power | Unsecured Term Loan | Unsecured Term Loan

Debt Disclosure [Line Items]

Repayments of debt

$ 900,000,000

Southern Power | Floating Rate Bank Term Loan Agreement | Notes Payable to Banks

Debt Disclosure [Line Items]

Debt instrument, face amount

$ 100,000,000

Debt instrument, repurchased face amount

$ 420,000,000

SEGCO | Senior Notes | Series 2013A Senior Notes

Debt Disclosure [Line Items]

Repayments of debt

$ 100,000,000

Scenario, Forecast | Senior Notes | Series 2018A Floating Rate Senior Notes due February 14, 2020

Debt Disclosure [Line Items]

Fixed stated interest rate of debt obligation

1.85%

Financing - DOE Loan Guarantee

Financing - DOE Loan Guarantee Borrowings (Details) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 7,863,000,000
Georgia Power
Debt Instrument [Line Items]
Percent of eligible project costs	70.00%
Eligible project costs to be reimbursed	$ 3,460,000,000
Basis spread on variable rate	0.375%
Line of credit facility, maximum borrowing capacity		1,750,000,000
Amortization period	5 years
Georgia Power | Loan Guarantee Agreement
Debt Instrument [Line Items]
Credit facility conditional borrowing commitment				$ 1,670,000,000
Plant Vogtle Units 3 And 4 | Georgia Power
Debt Instrument [Line Items]
Percent ownership	45.70%
FFB Loan | Georgia Power
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 2,625,000,000	$ 2,600,000,000

Financing - Other Long-Term Deb

Financing - Other Long-Term Debt Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2018	Aug. 31, 2018
Debt Instrument [Line Items]
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042		$ 206,000,000	$ 206,000,000
Trust Preferred Securities Subject to Mandatory Redemption
Debt Instrument [Line Items]
Trust preferred securities		200,000,000	200,000,000
Alabama Power
Debt Instrument [Line Items]
Long-term debt payable to affiliated trusts — variable rate (5.50% at 12/31/18) due 2042		206,000,000	206,000,000
Mississippi Power
Debt Instrument [Line Items]
Revenue bond obligations face value		$ 270,000,000	270,000,000
Fixed stated interest rate of debt obligation		7.13%
Revenue bonds, current		$ 50,000,000	50,000,000
Mississippi Power | Plant Daniel Units 3 and 4
Debt Instrument [Line Items]
Significant acquisitions and disposals, acquisition costs, assumption of debt, at fair value		346,000,000
Fair value adjustment at date of purchase		76,000,000
Nicor Gas
Debt Instrument [Line Items]
First mortgage bonds		1,300,000,000	1,000,000,000
Nicor Gas | First Mortgage Bonds
Debt Instrument [Line Items]
Debt instrument, face amount		300,000,000
Nicor Gas | First Mortgage Bonds Issued August 2018 | First Mortgage Bonds
Debt Instrument [Line Items]
Debt instrument, face amount					$ 100,000,000
Nicor Gas | First Mortgage Bonds Issued November 2018 | First Mortgage Bonds
Debt Instrument [Line Items]
Debt instrument, face amount				$ 200,000,000
Pivotal Utility Holdings | Gas Facility Revenue Bonds
Debt Instrument [Line Items]
Debt redeemed	$ 200,000,000
Atlanta Gas Light | Medium-term Notes
Debt Instrument [Line Items]
Long-term debt		$ 159,000,000	$ 159,000,000

Financing - Capital Leases Narr

Financing - Capital Leases Narrative (Details) $ in Millions	Dec. 31, 2018USD ($)leased_asset_unit	Dec. 31, 2017USD ($)leased_asset_unit
Debt Instrument [Line Items]
Capitalized lease obligations	$ 197	$ 204
SCS
Debt Instrument [Line Items]
Capitalized lease obligations	$ 178	177
SCS | Capital Lease Obligations | Minimum
Debt Instrument [Line Items]
Fixed stated interest rate of debt obligation	1.60%
SCS | Capital Lease Obligations | Maximum
Debt Instrument [Line Items]
Fixed stated interest rate of debt obligation	4.70%
Georgia Power
Debt Instrument [Line Items]
Capitalized lease obligations	$ 142	154
Georgia Power | Office buildings
Debt Instrument [Line Items]
Capitalized lease obligations	15	22
Georgia Power | PPAs
Debt Instrument [Line Items]
Capitalized lease obligations	$ 128	$ 132
Capital leased assets, number of units | leased_asset_unit	2	2
Georgia Power | Minimum | PPAs
Debt Instrument [Line Items]
Fixed stated interest rate of debt obligation	11.00%
Georgia Power | Maximum | PPAs
Debt Instrument [Line Items]
Fixed stated interest rate of debt obligation	12.00%
Georgia Power | Capital Lease Obligations
Debt Instrument [Line Items]
Fixed stated interest rate of debt obligation	7.90%

Financing - Secured Debt (Detai

Financing - Secured Debt (Details)	Dec. 31, 2018USD ($)series	Dec. 31, 2017USD ($)	Dec. 31, 2014
Debt Disclosure [Line Items]
Total	$ 7,863,000,000
Capitalized lease obligations	197,000,000	$ 204,000,000
Georgia Power
Debt Disclosure [Line Items]
Total	1,750,000,000
Capitalized lease obligations	142,000,000	154,000,000
Georgia Power | FFB Loan
Debt Disclosure [Line Items]
Total	2,625,000,000	2,600,000,000
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	2,767,000,000	2,779,000,000
Mississippi Power
Debt Disclosure [Line Items]
Total	100,000,000
Mississippi Power | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	270,000,000	270,000,000
Southern Company Gas
Debt Disclosure [Line Items]
Total	1,900,000,000
Southern Company Gas | Secured Debt
Debt Disclosure [Line Items]
Long-term debt	1,325,000,000	1,025,000,000
Gulf Power
Debt Disclosure [Line Items]
Total	280,000,000
Secured debt	$ 41,000,000	$ 41,000,000
Number of series of pollution controls revenue bonds | series	2

Financing - Bank Credit Arrange

Financing - Bank Credit Arrangements (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Expires, 2019	$ 163,000,000
Expires, 2020	500,000,000
Expires, 2022	7,200,000,000
Total	7,863,000,000
Unused	7,820,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	163,000,000
Southern Company
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	2,000,000,000
Total	2,000,000,000
Unused	1,999,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	0
Alabama Power
Line of Credit Facility [Line Items]
Expires, 2019	33,000,000
Expires, 2020	500,000,000
Expires, 2022	800,000,000
Total	1,333,000,000
Unused	1,333,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	33,000,000
Georgia Power
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,750,000,000
Total	1,750,000,000
Unused	1,736,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	0
Mississippi Power
Line of Credit Facility [Line Items]
Expires, 2019	100,000,000
Expires, 2020	0
Expires, 2022	0
Total	100,000,000
Unused	100,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	100,000,000
Southern Power
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	750,000,000
Total	750,000,000
Unused	727,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	0
Southern Power | Continuing Letter of Credit Facility
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	103,000,000	$ 19,000,000
Southern Company Gas
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	1,900,000,000
Total	1,900,000,000
Unused	1,895,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	0
Other Subsidiaries
Line of Credit Facility [Line Items]
Expires, 2019	30,000,000
Expires, 2020	0
Expires, 2022	0
Total	30,000,000
Unused	30,000,000
Executable term-loans, one year	0
Executable term-loans, two years	0
Due within one year, term out	0
Due within one year, no term out	30,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	500,000,000
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,400,000,000
Unused	1,395,000,000
Gulf Power
Line of Credit Facility [Line Items]
Total	$ 280,000,000

Financing - Bank Credit Arran_2

Financing - Bank Credit Arrangements Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 19, 2019	Dec. 31, 2017
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	$ 1,600,000,000
Remarketed pollution control bonds	403,000,000
Line of credit facility, maximum borrowing capacity	7,863,000,000
Unused credit with banks	$ 7,820,000,000
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
Line of credit facility, maximum borrowing capacity	1,333,000,000
Unused credit with banks	1,333,000,000
Georgia Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	659,000,000
Remarketed pollution control bonds	345,000,000
Line of credit facility, maximum borrowing capacity	1,750,000,000
Unused credit with banks	1,736,000,000
Georgia Power | Municipal bonds | Subsequent Event
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount		$ 108,000,000
Gulf Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	82,000,000
Remarketed pollution control bonds	58,000,000
Line of credit facility, maximum borrowing capacity	280,000,000
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	100,000,000
Unused credit with banks	100,000,000
Southern Power
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity	750,000,000
Unused credit with banks	727,000,000
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	103,000,000		$ 19,000,000
Southern Power | Power Purchase Agreement
Debt Disclosure [Line Items]
Unused credit with banks	17,000,000
Debt instrument, collateral amount	$ 103,000,000		$ 113,000,000

Financing - Notes Payable (Deta

Financing - Notes Payable (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Amount Outstanding	$ 2,915	$ 2,439
Weighted Average Interest Rate	3.10%	1.90%
Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 1,064	$ 1,832
Weighted Average Interest Rate	3.00%	1.80%
Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 1,851	$ 607
Weighted Average Interest Rate	3.10%	2.30%
Alabama Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 3
Weighted Average Interest Rate	0.00%	3.70%
Georgia Power
Short-term Debt [Line Items]
Amount Outstanding	$ 294	$ 150
Weighted Average Interest Rate	3.10%	2.20%
Georgia Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 294	$ 0
Weighted Average Interest Rate	3.10%	0.00%
Georgia Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 150
Weighted Average Interest Rate	0.00%	2.20%
Mississippi Power
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 4
Mississippi Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 4
Weighted Average Interest Rate	0.00%	3.80%
Southern Power
Short-term Debt [Line Items]
Amount Outstanding	$ 100	$ 105
Weighted Average Interest Rate	3.10%	2.00%
Southern Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 105
Weighted Average Interest Rate	0.00%	2.00%
Southern Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 100	$ 0
Weighted Average Interest Rate	3.10%	0.00%
Southern Company Gas
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 1,518
Southern Company Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 1,518
Weighted Average Interest Rate	3.00%	1.80%
Southern Company Gas Capital | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 403	$ 1,243
Weighted Average Interest Rate	3.10%	1.70%
Nicor Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 247	$ 275
Weighted Average Interest Rate	3.00%	1.80%

Financing - Notes Payable Narra

Financing - Notes Payable Narrative (Details)	1 Months Ended				3 Months Ended		12 Months Ended
	Aug. 31, 2018USD ($)	Jun. 30, 2018USD ($)agreement	May 31, 2018USD ($)agreement	Apr. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Mar. 31, 2018USD ($)	Jan. 31, 2018USD ($)
Short-term Debt [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required							70.00%
Repayments of short-term debt							$ 1,900,000,000	$ 659,000,000	$ 478,000,000
Floating rate Promissory Note Due July 2018
Short-term Debt [Line Items]
Debt instrument, face amount											$ 100,000,000
Notes Payable to Banks | Floating Rate Bank Term Loan Agreement
Short-term Debt [Line Items]
Debt instrument, face amount										$ 900,000,000
Notes Payable to Banks | Uncommitted Bank Credit Arrangement
Short-term Debt [Line Items]
Debt instrument, face amount				$ 250,000,000
Payable by demand from bank, term				30 days
Repayments of short-term debt	$ 250,000,000
Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 6
Short-term Debt [Line Items]
Debt instrument, face amount	$ 1,500,000,000
Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 4
Short-term Debt [Line Items]
Debt instrument, face amount		$ 100,000,000				$ 100,000,000
Number of loan agreements | agreement		2
Alabama Power and Southern Power
Short-term Debt [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required							65.00%
Georgia Power
Short-term Debt [Line Items]
Repayments of short-term debt							$ 150,000,000	550,000,000	0
Georgia Power | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 2
Short-term Debt [Line Items]
Debt instrument, face amount											$ 150,000,000
Georgia Power | Senior Notes
Short-term Debt [Line Items]
Repayments of debt			$ 902,000,000
Mississippi Power
Short-term Debt [Line Items]
Repayments of short-term debt							300,000,000	109,000,000	478,000,000
Mississippi Power | Senior Notes | Series 2018A Floating Rate Senior Notes
Short-term Debt [Line Items]
Debt instrument, face amount										$ 300,000,000
Mississippi Power | Promissory Notes | Promissory Notes
Short-term Debt [Line Items]
Repayments of debt					$ 100,000,000	$ 200,000,000
Southern Power
Short-term Debt [Line Items]
Repayments of short-term debt							$ 100,000,000	$ 0	$ 0
Southern Power | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement
Short-term Debt [Line Items]
Debt instrument, face amount			$ 100,000,000
Number of loan agreements | agreement			2
Southern Company Gas | Notes Payable to Banks | Uncommitted Bank Credit Arrangement
Short-term Debt [Line Items]
Debt instrument, face amount			$ 95,000,000
Payable by demand from bank, term			30 days
Southern Company Gas | Senior Notes | Series 2017A
Short-term Debt [Line Items]
Debt instrument, face amount				$ 181,000,000

Financing - Outstanding Classes

Financing - Outstanding Classes of Capital Stock Narrative (Details)	Oct. 23, 2018USD ($)shares	Oct. 31, 2017USD ($)shares	Sep. 30, 2017USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2018USD ($)shares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)shares
Debt Instrument [Line Items]
Stock issued employee and director stock plans (in shares)						11,600,000
Proceeds from issuance of shares under share-based compensation plans | $						$ 442,000,000
Cash proceeds | $						$ 1,090,000,000	$ 793,000,000	$ 3,758,000,000
Common stock fees and commissions | $				$ 1,000,000	$ 5,000,000
Number of shares reserved for issuance to stock-based compensation plan (in shares)						92,000,000
Preference stock redemption | $							$ 609,000,000
Total redeemable preferred stock - percent capitalization				0.40%		0.40%	0.50%
Southern Company Common Stock
Debt Instrument [Line Items]
Remaining shares available for awards (in shares)				10,000,000		10,000,000
Alabama Power
Debt Instrument [Line Items]
Total redeemable preferred stock - percent capitalization				1.90%		1.90%	2.00%
Alabama Power | 5.00% Class A Preferred Stock
Debt Instrument [Line Items]
Shares outstanding (in shares)			10,000,000	10,000,000		10,000,000
Temporary equity, dividend rate percentage			0.05			0.05
Preferred stock, par value (in dollars per share) | $ / shares			$ 1
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		0.065
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
Georgia Power | Senior Notes | Preferred Class A
Debt Instrument [Line Items]
Preferred stock redemption (in shares)		1,800,000
Preference stock redemption | $		$ 45,000,000
Preferred stock, dividend rate		6.125%
Georgia Power | Senior Notes | Series 2007A Preference Stock
Debt Instrument [Line Items]
Preferred stock redemption (in shares)		2,250,000
Preference stock redemption | $		$ 225,000,000
Preferred stock, dividend rate		6.50%
Mississippi Power
Debt Instrument [Line Items]
Shares outstanding (in shares)				0		0	334,210
Preferred stock, par value (in dollars per share) | $ / shares				$ 100		$ 100	$ 100
Total redeemable preferred stock - percent capitalization				0.00%		0.00%	1.30%
Mississippi Power | 4.40% Series Preferred Stock
Debt Instrument [Line Items]
Temporary equity, dividend rate percentage	0.044
Par value/stated capital per share | $	$ 886,700
Preferred stock redemption (in shares)	8,867
Mississippi Power | 4.60% Series Preferred Stock
Debt Instrument [Line Items]
Temporary equity, dividend rate percentage	0.046
Par value/stated capital per share | $	$ 864,300
Preferred stock redemption (in shares)	8,643
Mississippi Power | 4.72% Series Preferred Stock
Debt Instrument [Line Items]
Temporary equity, dividend rate percentage	0.0472
Par value/stated capital per share | $	$ 1,670,000
Preferred stock redemption (in shares)	16,700
Mississippi Power | 5.25% Series Preferred Stock
Debt Instrument [Line Items]
Temporary equity, dividend rate percentage	0.0525
Par value/stated capital per share | $	$ 30,000,000
Preferred stock redemption (in shares)	1,200,000
Total redeemable preferred stock - percent capitalization	25.00%
Common Stock
Debt Instrument [Line Items]
Stock issued (in shares)						26,209,000	17,319,000	76,140,000
At-The-Market | Common Stock
Debt Instrument [Line Items]
Stock issued (in shares)				2,500,000	12,100,000
Cash proceeds | $				$ 108,000,000	$ 540,000,000

Financing - Diluted Earnings Pe

Financing - Diluted Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
As reported shares	1,020	1,000	951
Effect of options and performance share award units	5	8	7
Diluted shares	1,025	1,008	958

Financing - Schedule of Tempora

Financing - Schedule of Temporary Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Redeemable preferred stock	$ 324	$ 324
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	324
Redeemed	(33)	(658)	$ 0
Issuance costs		(6)
Ending balance	291	324
Redeemable Preferred Stock
Temporary Equity [Line Items]
Redeemable preferred stock	324	118	118
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	324	118	118
Issued		250
Redeemed	(33)	(38)
Ending balance	$ 291	$ 324	$ 118

Financing - Preferred Stock Red

Financing - Preferred Stock Redemption (Details) - Alabama Power	1 Months Ended	12 Months Ended
	Sep. 30, 2017$ / sharesshares	Dec. 31, 2018$ / sharesshares	Oct. 02, 2022$ / shares
4.92% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.0492
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		80,000
Redemption Price Per Share (in dollars per share)		$ 103.23
4.72% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.0472
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		50,000
Redemption Price Per Share (in dollars per share)		$ 102.18
4.64% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.0464
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		60,000
Redemption Price Per Share (in dollars per share)		$ 103.14
4.60% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.046
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		100,000
Redemption Price Per Share (in dollars per share)		$ 104.20
4.52% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.0452
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		50,000
Redemption Price Per Share (in dollars per share)		$ 102.93
4.20% Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage		0.042
Par Value/Stated Capital Per Share (in dollars per share)		$ 100
Shares outstanding (in shares) | shares		135,115
Redemption Price Per Share (in dollars per share)		$ 105
5.00% Class A Preferred Stock
Debt Instrument, Redemption [Line Items]
Temporary equity, dividend rate percentage	0.05	0.05
Par Value/Stated Capital Per Share (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, 2018USD ($)
Variable Interest Entity [Line Items]
Undistributed retained earnings of subsidiaries	$ 4,900
Southern Company Gas
Variable Interest Entity [Line Items]
Retained earnings, unappropriated	$ 814
Southern Company Gas | Southern Company Gas Capital | Southern Company Gas Capital
Variable Interest Entity [Line Items]
Noncontrolling ownership percentage held by parent	100.00%

Commitments - Fuel and Power Pu

Commitments - Fuel and Power Purchase Agreements Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, contingent rent expense	$ 43	$ 44	$ 18
Georgia Power | Plant Vogtle (nuclear) Units 1 and 2
Recorded Unconditional Purchase Obligation [Line Items]
Capacity payments	8	9	$ 11
Total	59
2,019	6
2,020	5
2,021	5
2,022	4
2,023	3
2024 and thereafter	36
Mississippi Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, contingent rent expense	$ 10	$ 5
MEAG Power | Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Percent ownership	5.00%

Commitments - Fuel Expenses (De

Commitments - Fuel Expenses (Details) - Fuel - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Cost of goods and services sold	$ 4,637	$ 4,400	$ 4,361
Alabama Power
Long-term Purchase Commitment [Line Items]
Cost of goods and services sold	1,301	1,225	1,297
Georgia Power
Long-term Purchase Commitment [Line Items]
Cost of goods and services sold	1,698	1,671	1,807
Mississippi Power
Long-term Purchase Commitment [Line Items]
Cost of goods and services sold	405	395	343
Southern Power
Long-term Purchase Commitment [Line Items]
Cost of goods and services sold	$ 699	$ 621	$ 456

Commitments - Capacity Expenses

Commitments - Capacity Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Recorded Unconditional Purchase Obligation [Line Items]
Expense under purchase power agreements accounted for as operating leases	$ 231	$ 235	$ 232
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Expense under purchase power agreements accounted for as operating leases	44	41	42
Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Expense under purchase power agreements accounted for as operating leases	$ 113	$ 118	$ 113

Commitments - Estimated Long-te

Commitments - Estimated Long-term Obligations (Details) $ in Millions	Dec. 31, 2018USD ($)
Minimum Lease Payments, Operating Leases [Abstract]
2,019	$ 156
2,020	134
2,021	110
2,022	98
2,023	79
2024 and thereafter	1,040
Total	1,617
Alabama Power
Minimum Lease Payments, Operating Leases [Abstract]
2,019	12
2,020	10
2,021	7
2,022	6
2,023	3
2024 and thereafter	1
Total	39
Georgia Power
Minimum Lease Payments, Operating Leases [Abstract]
2,019	23
2,020	18
2,021	9
2,022	6
2,023	5
2024 and thereafter	13
Total	74
Mississippi Power
Minimum Lease Payments, Operating Leases [Abstract]
2,019	3
2,020	2
2,021	1
2,022	1
2,023	1
2024 and thereafter	2
Total	10
Southern Power
Minimum Lease Payments, Operating Leases [Abstract]
2,019	23
2,020	24
2,021	24
2,022	24
2,023	26
2024 and thereafter	874
Total	995
Southern Company Gas
Minimum Lease Payments, Operating Leases [Abstract]
2,019	18
2,020	16
2,021	15
2,022	13
2,023	10
2024 and thereafter	34
Total	106
Non-Affiliate Operating Lease PPA
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	161
2,020	164
2,021	168
2,022	171
2,023	127
2024 and thereafter	642
Total	1,433
Non-Affiliate Operating Lease PPA | Alabama Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	41
2,020	42
2,021	44
2,022	46
2,023	0
2024 and thereafter	0
Total	173
Non-Affiliate Operating Lease PPA | Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	120
2,020	122
2,021	124
2,022	125
2,023	127
2024 and thereafter	642
Total	1,260
Affiliate Capital Lease PPA | Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	23
2,020	23
2,021	24
2,022	24
2,023	25
2024 and thereafter	158
Total	277
Minimum Lease Payments, Capital Leases [Abstract]
Less: amounts representing executory costs	42
Net minimum lease payments	235
Less: amounts representing interest	105
Present value of net minimum lease payments	130
Affiliate Operating Lease PPA | Georgia Power
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	64
2,020	65
2,021	66
2,022	68
2,023	69
2024 and thereafter	349
Total	$ 681

Commitments - GPC Fuel and Purc

Commitments - GPC Fuel and Purchased Power, Affiliate Narrative (Details) - Georgia Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, contingent rent expense	$ 43	$ 44	$ 18
Affiliate PPA
Recorded Unconditional Purchase Obligation [Line Items]
Capacity payments	93	107	133
Affiliate Operating Lease PPA
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, contingent rent expense	$ 29	$ 29	$ 21

Commitments - Pipeline Charges,

Commitments - Pipeline Charges, Storage Capacity, and Gas Supply Narrative (Details) - Nicor Gas and Southstar MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)MMBTU
Recorded Unconditional Purchase Obligation [Line Items]
Natural gas pipeline capacity | MMBTU	47
Long-term purchase commitment amount | $	$ 150

Commitments - Contractual Oblig

Commitments - Contractual Obligations - Pipeline Charges, Storage Capacity, and Gas Supply (Details) - Pipeline Charges, Storage Capacity, and Gas Supply - Southern Company Gas $ in Millions	Dec. 31, 2018USD ($)
Long-term Purchase Commitment [Line Items]
2,019	$ 781
2,020	584
2,021	520
2,022	489
2,023	412
2024 and thereafter	1,871
Total	$ 4,657

Commitments - Rent Expense (Det

Commitments - Rent Expense (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			$ 192	$ 176	$ 169
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			23	25	18
Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			34	31	28
Mississippi Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			4	3	3
Southern Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense			31	29	$ 22
Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense	$ 8		$ 15	$ 15
Predecessor | Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases rent expense		$ 6

Commitments - Operating Leases,

Commitments - Operating Leases, Guarantees, and Assets Subject to Lien Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2013	Nov. 30, 2018	Dec. 31, 2017	Oct. 31, 2017	Dec. 31, 2014
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2023 and thereafter	$ 1,040
Operating leases, future minimum lease payments due	1,617
Short-term debt	2,915			$ 2,439
Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2023 and thereafter	1
Operating leases, future minimum lease payments due	39
Jointly owned affiliate equity	90
Jointly owned affiliate long term debt	125
Jointly owned affiliate long term debt annual interest requirement	$ 4
Ownership percentage, equity method investment	50.00%
Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2023 and thereafter	$ 13
Operating leases, future minimum lease payments due	74
Short-term debt	294			150
Maximum guarantee	$ 30
Ownership percentage, equity method investment	50.00%
Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2023 and thereafter	$ 34
Operating leases, future minimum lease payments due	106
Short-term debt	650			$ 1,518
Southern Electric Generating Company | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Unconditional guarantee to pay outstanding pollution control revenue bond principal	25
SEGCO | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Short-term debt	5
Maturity December 1, 2018 | Southern Electric Generating Company | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Guarantee of unsecured senior notes	100		$ 100
Plant McIntosh | Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Period of service for gas transportation supplier		15 years
Residual Value, Leased Property | Alabama Power
Recorded Unconditional Purchase Obligation [Line Items]
Leasing commitment, 2023 and thereafter	12
2024 | Residual Value, Leased Property | Georgia Power
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases, future minimum lease payments due	9
Atlantic Coast Pipeline | Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Maximum guarantee	$ 72
Ownership percentage, equity method investment						5.00%
Revolving Credit Facility | Atlantic Coast Pipeline | Southern Company Gas
Recorded Unconditional Purchase Obligation [Line Items]
Revolving credit facility executed					$ 3,400

Income Taxes - Current and Defe

Income Taxes - Current and Deferred Income Tax Provisions (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Federal —
Current				$ 167	$ (62)	$ 1,184
Deferred				231	(6)	(342)
Total federal taxes				398	(68)	842
State —
Current				188	37	(108)
Deferred				(137)	173	217
Total state taxes				51	210	109
Income taxes				449	142	951
Alabama Power
Federal —
Current				91	136	103
Deferred				123	336	339
Total federal taxes				214	472	442
State —
Current				26	23	20
Deferred				51	73	69
Total state taxes				77	96	89
Income taxes				291	568	531
Georgia Power
Federal —
Current				393	256	391
Deferred				(249)	504	319
Total federal taxes				144	760	710
State —
Current				81	116	6
Deferred				(11)	(46)	64
Total state taxes				70	70	70
Income taxes				214	830	780
Mississippi Power
Federal —
Current				(567)	194	(31)
Deferred				575	(753)	(60)
Total federal taxes				8	(559)	(91)
State —
Current				(10)	0	(6)
Deferred				(100)	27	(7)
Total state taxes				(110)	27	(13)
Income taxes				(102)	(532)	(104)
Southern Power
Federal —
Current				85	(566)	928
Deferred				(154)	(312)	(1,098)
Total federal taxes				(69)	(878)	(170)
State —
Current				(9)	(110)	(60)
Deferred				(86)	49	35
Total state taxes				(95)	(61)	(25)
Income taxes	$ 75			(164)	(939)	$ (195)
Southern Company Gas
Federal —
Current		$ 0		334	103
Deferred		65		33	170
Total federal taxes		65		367	273
State —
Current		(16)		131	27
Deferred		27		(34)	67
Total state taxes		11		97	94
Income taxes		$ 76		$ 464	$ 367
Predecessor | Southern Company Gas
Federal —
Current			$ 67
Deferred			8
Total federal taxes			75
State —
Current			12
Deferred			0
Total state taxes			12
Income taxes			$ 87

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 ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Income Tax Disclosure [Line Items]
Deferred income tax assets			$ 9,048,000,000	$ 9,048,000,000	$ 8,205,000,000
Income tax benefit				(449,000,000)	(142,000,000)	$ (951,000,000)
Unrecognized tax benefits			0	$ 0	18,000,000	484,000,000	$ 433,000,000
Significantly increase or decrease in the amount of the unrecognized tax benefits associated with a majority of Southern				12 months
Decrease in unrecognized tax benefits from prior periods				$ 18,000,000	196,000,000	15,000,000
ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,730,000,000	2,730,000,000	2,414,000,000
Georgia Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			3,078,000,000	3,078,000,000	1,850,000,000
Income tax benefit				(214,000,000)	(830,000,000)	(780,000,000)
State investment tax credit carryforward				341,000,000
Georgia Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			430,000,000	430,000,000	403,000,000
Southern Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,631,000,000	$ 2,631,000,000	2,700,000,000
Reduction in tax basis of assets (percent)				50.00%
Number of wind facilities | operating_facility	8
Income tax benefit			(75,000,000)	$ 164,000,000	939,000,000	195,000,000
Unrecognized tax benefits			0	0	0	17,000,000	8,000,000
Decrease in unrecognized tax benefits from prior periods				0	17,000,000	8,000,000
Southern Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				5,000,000	0	0
Southern Power | ITC and PTC carryforward
Income Tax Disclosure [Line Items]
Deferred income tax assets			2,128,000,000	2,128,000,000	2,002,000,000
Southern Power | ITC and PTC carryforward | Nacogdoches Biomass Generating Plant
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				1,000,000	18,000,000	173,000,000
Southern Power | Production Tax Credit Carryforward
Income Tax Disclosure [Line Items]
Effective income tax rate reconciliation, tax credit, production, amount				141,000,000	139,000,000	50,000,000
Mississippi Power
Income Tax Disclosure [Line Items]
Deferred income tax assets			515,000,000	515,000,000	1,103,000,000
Income tax benefit				102,000,000	532,000,000	104,000,000
Unrecognized tax benefits			0	0	0	465,000,000	$ 421,000,000
Decrease in unrecognized tax benefits from prior periods				0	177,000,000	0
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 | Georgia Power
Income Tax Disclosure [Line Items]
Valuation allowance			33,000,000	33,000,000
State and Local Jurisdiction | Georgia Power | ITCs and other credits carryforward
Income Tax Disclosure [Line Items]
Reduction in income tax expense, investment tax credits				21,000,000	37,000,000	31,000,000
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	7,000,000
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	128,000,000	$ 316,000,000	$ 1,130,000,000
Mississippi | State and Local Jurisdiction | Mississippi Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			32,000,000	32,000,000
Oklahoma | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			9,000,000	9,000,000
Florida | State and Local Jurisdiction | Southern Power
Income Tax Disclosure [Line Items]
Operating loss carryforwards, valuation allowance			$ 11,000,000	$ 11,000,000

Income Taxes - Amortization of

Income Taxes - Amortization of Deferred Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 87	$ 79	$ 59
Southern Power
Income Tax Disclosure [Line Items]
Amortization of deferred investment tax credits	$ 58	$ 57	$ 37

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Details)	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate			21.00%	35.00%	35.00%
State income tax, net of federal deduction			1.80%	12.50%	2.00%
Employee stock plans' dividend deduction			(1.00%)	(4.00%)	(1.20%)
Non-deductible book depreciation			0.80%	3.10%	0.90%
Flowback of excess deferred income taxes			(4.00%)	(0.30%)	(0.10%)
AFUDC-Equity			(1.00%)	(2.60%)	(2.00%)
ITC basis difference			(0.60%)	(1.70%)	(5.00%)
AFUDC-Equity portion of Kemper IGCC charge				15.70%
Federal PTCs			(4.70%)	(12.10%)	(1.20%)
Amortization of ITC			(2.00%)	(4.20%)	(0.90%)
Tax impact on sale of subsidiaries			8.60%
Tax Reform Legislation			(1.40%)	(25.60%)
Noncontrolling interests			(0.40%)	(1.40%)	(0.30%)
Other			(0.80%)	(1.10%)	0.10%
Effective income tax (benefit) rate			16.30%	13.30%	27.30%
Alabama Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate			21.00%	35.00%	35.00%
State income tax, net of federal deduction			5.00%	4.50%	4.20%
Employee stock plans' dividend deduction			(0.00%)	(0.00%)	(0.00%)
Non-deductible book depreciation			0.60%	0.90%	1.00%
Flowback of excess deferred income taxes			(1.80%)	0.00%	0.00%
AFUDC-Equity			(1.00%)	(1.00%)	(0.70%)
ITC basis difference			(0.00%)	(0.00%)	(0.00%)
AFUDC-Equity portion of Kemper IGCC charge				(0.00%)
Federal PTCs			(0.00%)	(0.00%)	(0.00%)
Amortization of ITC			(0.10%)	(0.20%)	(0.20%)
Tax impact on sale of subsidiaries			0.00%
Tax Reform Legislation			0.00%	0.30%
Noncontrolling interests			(0.00%)	(0.00%)	(0.00%)
Other			(0.10%)	0.10%	(0.50%)
Effective income tax (benefit) rate			23.60%	39.60%	38.80%
Georgia Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate			21.00%	35.00%	35.00%
State income tax, net of federal deduction			5.50%	2.00%	2.10%
Employee stock plans' dividend deduction			(0.00%)	(0.00%)	(0.00%)
Non-deductible book depreciation			1.20%	0.70%	0.80%
Flowback of excess deferred income taxes			0.00%	(0.10%)	(0.10%)
AFUDC-Equity			(1.40%)	(0.60%)	(0.80%)
ITC basis difference			(0.00%)	(0.00%)	(0.00%)
AFUDC-Equity portion of Kemper IGCC charge				(0.00%)
Federal PTCs			(0.00%)	(0.00%)	(0.00%)
Amortization of ITC			(0.20%)	(0.10%)	(0.20%)
Tax impact on sale of subsidiaries			0.00%
Tax Reform Legislation			(4.90%)	(0.40%)
Noncontrolling interests			(0.00%)	(0.00%)	(0.00%)
Other			0.10%	0.20%	(0.10%)
Effective income tax (benefit) rate			21.30%	36.70%	36.70%
Mississippi Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate			21.00%	35.00%	35.00%
State income tax, net of federal deduction			(65.10%)	(0.60%)	5.70%
Employee stock plans' dividend deduction			(0.00%)	(0.00%)	(0.00%)
Non-deductible book depreciation			0.70%	(0.10%)	(0.70%)
Flowback of excess deferred income taxes			(4.10%)	0.00%	0.30%
AFUDC-Equity			(0.00%)	(0.00%)	28.50%
ITC basis difference			(0.00%)	(0.00%)	(0.00%)
AFUDC-Equity portion of Kemper IGCC charge				(5.30%)
Federal PTCs			(0.00%)	(0.00%)	(0.00%)
Amortization of ITC			(0.20%)	(0.00%)	0.10%
Tax impact on sale of subsidiaries			0.00%
Tax Reform Legislation			(26.30%)	(11.90%)
Noncontrolling interests			(0.00%)	(0.00%)	(0.00%)
Other			(1.40%)	0.00%	(0.40%)
Effective income tax (benefit) rate			(75.40%)	17.10%	68.50%
Southern Power
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate			21.00%	35.00%	35.00%
State income tax, net of federal deduction			(90.80%)	(22.20%)	(9.10%)
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			(0.20%)	(10.00%)	(96.30%)
AFUDC-Equity portion of Kemper IGCC charge				(0.00%)
Federal PTCs			(156.60%)	(72.50%)	(23.30%)
Amortization of ITC			(55.40%)	(20.60%)	(13.40%)
Tax impact on sale of subsidiaries			0.00%
Tax Reform Legislation			96.10%	(416.10%)
Noncontrolling interests			(14.90%)	(8.60%)	(6.20%)
Other			2.00%	(10.70%)	4.70%
Effective income tax (benefit) rate			(198.80%)	(525.70%)	(108.60%)
Southern Company Gas
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%		21.00%	35.00%
State income tax, net of federal deduction	3.60%		9.20%	10.00%
Flowback of excess deferred income taxes	0.00%		(3.00%)	(0.20%)
Amortization of ITC	(0.40%)		(0.10%)	(0.20%)
Tax impact on sale of subsidiaries	0.00%		28.50%	0.00%
Tax Reform Legislation	0.00%		(0.40%)	15.00%
Other	1.80%		0.30%	0.60%
Effective income tax (benefit) rate	40.00%		55.50%	60.20%
Predecessor | Southern Company Gas
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate		35.00%
State income tax, net of federal deduction		3.50%
Flowback of excess deferred income taxes		0.00%
Amortization of ITC		(0.00%)
Tax impact on sale of subsidiaries		0.00%
Tax Reform Legislation		0.00%
Other		(0.90%)
Effective income tax (benefit) rate		37.60%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax liabilities —
Deferred income tax liabilities		$ 15,207	$ 14,757
Deferred tax assets —
Deferred income tax assets		9,048	8,205
Valuation allowance		(123)	(184)
Net deferred income tax assets		8,925	8,021
Net deferred income taxes liabilities		6,282	6,736
Accumulated deferred income taxes – assets		(276)	(106)
Accumulated deferred income taxes – liabilities		6,558	6,842
Federal tax benefit		(167)	62	$ (1,184)
Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		8,461	9,059
Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		1,807	1,853
Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities		253	251
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities		477	527
Deferred tax assets —
Deferred income tax assets		1,273	1,339
Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities		88	54
Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities		111	89
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities		975	1,044
AROs
Deferred tax liabilities —
Deferred income tax liabilities		1,232	821
AROs
Deferred tax liabilities —
Deferred income tax liabilities		1,210	370
Other
Deferred tax liabilities —
Deferred income tax liabilities		593	689
Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities		0	0
Deferred tax assets —
Deferred income tax assets		260	330
Other property basis differences
Deferred tax assets —
Deferred income tax assets		251	343
ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets		2,730	2,414
Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			518
Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		62	69
Other partnership basis difference
Deferred tax assets —
Deferred income tax assets		162	23
Other comprehensive losses
Deferred tax assets —
Deferred income tax assets		82	84
AROs
Deferred tax assets —
Deferred income tax assets		2,442	1,191
Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets		346	722
Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets		415	330
Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets		294	304
Other
Deferred tax assets —
Deferred income tax assets		731	538
Alabama Power
Deferred tax liabilities —
Deferred income tax liabilities		4,584	3,914
Deferred tax assets —
Deferred income tax assets		1,622	1,154
Valuation allowance		0	0
Net deferred income tax assets		1,622	1,154
Net deferred income taxes liabilities		2,962	2,760
Accumulated deferred income taxes – assets		0	0
Accumulated deferred income taxes – liabilities		2,962	2,760
Federal tax benefit		(91)	(136)	(103)
Alabama Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		2,236	2,135
Alabama Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		865	725
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		149	162
Deferred tax assets —
Deferred income tax assets		286	286
Alabama Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities		14	16
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		260	260
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		276	249
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		607	220
Alabama Power | Other
Deferred tax liabilities —
Deferred income tax liabilities		177	147
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		155	143
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	9
Alabama Power | Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			0
Alabama Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		0	0
Alabama Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets		0	0
Alabama Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets		10	10
Alabama Power | AROs
Deferred tax assets —
Deferred income tax assets		883	469
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		130	126
Alabama Power | Other
Deferred tax assets —
Deferred income tax assets		147	111
Georgia Power
Deferred tax liabilities —
Deferred income tax liabilities		6,098	5,025
Deferred tax assets —
Deferred income tax assets		3,078	1,850
Valuation allowance		(42)	0
Net deferred income tax assets		3,036	1,850
Net deferred income taxes liabilities		3,062	3,175
Accumulated deferred income taxes – assets		0	0
Accumulated deferred income taxes – liabilities		3,062	3,175
Federal tax benefit		(393)	(256)	(391)
Georgia Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		3,005	2,889
Georgia Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		633	606
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		290	287
Deferred tax assets —
Deferred income tax assets		444	448
Georgia Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities		74	34
Georgia Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities		111	89
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities		344	349
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		925	501
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		575	130
Georgia Power | Other
Deferred tax liabilities —
Deferred income tax liabilities		141	140
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		71	85
Georgia Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets		61	59
Georgia Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets		430	403
Georgia Power | Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			0
Georgia Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		0	0
Georgia Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets		0	0
Georgia Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets		3	4
Georgia Power | AROs
Deferred tax assets —
Deferred income tax assets		1,500	631
Georgia Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets		283	0
Georgia Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets		19	6
Georgia Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets		127	123
Georgia Power | Other
Deferred tax assets —
Deferred income tax assets		140	91
Mississippi Power
Deferred tax liabilities —
Deferred income tax liabilities		702	699
Deferred tax assets —
Deferred income tax assets		515	1,103
Valuation allowance		(41)	(157)
Net deferred income tax assets		474	946
Net deferred income taxes liabilities		228
Net deferred income taxes assets			(247)
Accumulated deferred income taxes – assets		(150)	(247)
Accumulated deferred income taxes – liabilities		378	0
Federal tax benefit		567	(194)	31
Mississippi Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		335	303
Mississippi Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		162	207
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		25	28
Deferred tax assets —
Deferred income tax assets		62	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		45	46
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		31	33
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities		0	0
Mississippi Power | Other
Deferred tax liabilities —
Deferred income tax liabilities		68	73
Mississippi Power | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities		36	9
Deferred tax assets —
Deferred income tax assets		0	0
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 | Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			40
Mississippi Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		32	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		31	33
Mississippi Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets		63	722
Mississippi Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets		251	133
Mississippi Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets		29	27
Mississippi Power | Other
Deferred tax assets —
Deferred income tax assets		47	54
Southern Power
Deferred tax liabilities —
Deferred income tax liabilities		1,523	1,961
Deferred tax assets —
Deferred income tax assets		2,631	2,700
Valuation allowance		(27)	(13)
Net deferred income tax assets		2,604	2,687
Net deferred income taxes assets		(1,081)	(726)
Accumulated deferred income taxes – assets		(1,186)	(925)
Accumulated deferred income taxes – liabilities		105	199
Federal tax benefit		(85)	566	$ (928)
Southern Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		1,483	1,922
Southern Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		0	2
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		6	7
Deferred tax assets —
Deferred income tax assets		7	8
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 | 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		34	30
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		22	42
Southern Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets		172	184
Southern Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets		2,128	2,002
Southern Power | Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			333
Southern Power | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		21	21
Southern Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets		162	23
Southern Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets			1
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	77
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		47	9
Southern Company Gas
Deferred tax liabilities —
Deferred income tax liabilities		1,493	1,641
Deferred tax assets —
Deferred income tax assets		489	563
Valuation allowance		(12)	(11)
Net deferred income tax assets		477	552
Net deferred income taxes liabilities		1,016	1,089
Accumulated deferred income taxes – assets		0	0
Accumulated deferred income taxes – liabilities		1,016	1,089
Federal tax benefit	$ 0	(334)	(103)
Southern Company Gas | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities		1,176	1,150
Southern Company Gas | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities		134	204
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		6	4
Deferred tax assets —
Deferred income tax assets		150	185
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	75
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		132	208
Southern Company Gas | Federal effect of net state deferred tax liabilities
Deferred tax liabilities —
Deferred income tax liabilities			0
Deferred tax assets —
Deferred income tax assets		46	54
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 | Federal NOL carryforward
Deferred tax assets —
Deferred income tax assets			92
Southern Company Gas | Alternative minimum tax carryforward
Deferred tax assets —
Deferred income tax assets		0	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		0	0
Southern Company Gas | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets		8	9
Southern Company Gas | Other
Deferred tax assets —
Deferred income tax assets		$ 285	$ 223

Income Taxes - Federal ITC_PTC

Income Taxes - Federal ITC/PTC Carryforwards (Details) - ITC and PTC carryforward $ in Millions	Dec. 31, 2018USD ($)
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 2,410
Alabama Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	11
Georgia Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	108
Southern Power
Operating Loss Carryforwards [Line Items]
Federal ITC/PTC carryforwards	$ 2,128

Income Taxes - NOL Carryforward

Income Taxes - NOL Carryforwards (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	$ 312
Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	200
Southern Power
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	56
Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	40
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	3
Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	14
Other Subsidiaries | Georgia
Operating Loss Carryforwards [Line Items]
Approximate Net State Income Tax Benefit	16
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	7,343
State and Local Jurisdiction | Mississippi Power | Mississippi
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	5,062
State and Local Jurisdiction | Southern Power
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	1,214
State and Local Jurisdiction | Southern Power | Oklahoma
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	846
State and Local Jurisdiction | Southern Power | Florida
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	264
State and Local Jurisdiction | Southern Power | South Carolina
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	62
State and Local Jurisdiction | Southern Power | Other states
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	42
State and Local Jurisdiction | Other Subsidiaries | Other states
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	278
State and Local Jurisdiction | Other Subsidiaries | Georgia
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	358
State and Local Jurisdiction | Other Subsidiaries | New York
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	223
State and Local Jurisdiction | Other Subsidiaries | New York City
Operating Loss Carryforwards [Line Items]
Approximate NOL Carryforwards	$ 208

Income Taxes - Changes in Unrec

Income Taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 18,000,000	$ 484,000,000	$ 433,000,000
Increase from current periods		10,000,000	45,000,000
Increase from prior periods		10,000,000	21,000,000
Decrease from prior periods	(18,000,000)	(196,000,000)	(15,000,000)
Reductions due to settlements		(290,000,000)
Balance at end of year	0	18,000,000	484,000,000
Mississippi Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	465,000,000	421,000,000
Increase from current periods		0	26,000,000
Increase from prior periods		2,000,000	18,000,000
Decrease from prior periods	0	(177,000,000)	0
Reductions due to settlements		(290,000,000)
Balance at end of year	0	0	465,000,000
Southern Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	17,000,000	8,000,000
Increase from current periods		0	17,000,000
Increase from prior periods		0	0
Decrease from prior periods	0	(17,000,000)	(8,000,000)
Reductions due to settlements		0
Balance at end of year	$ 0	$ 0	$ 17,000,000

Income Taxes - Impact of Unreco

Income Taxes - Impact of Unrecognized Tax Benefits on Effective Tax Rate, If Recognized (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impact on effective tax rate
Tax positions impacting the effective tax rate		$ 18,000,000	$ 20,000,000
Tax positions not impacting the effective tax rate		0	464,000,000
Balance of unrecognized tax benefits	$ 0	18,000,000	484,000,000	$ 433,000,000
Mississippi Power
Impact on effective tax rate
Tax positions impacting the effective tax rate		0	1,000,000
Tax positions not impacting the effective tax rate		0	464,000,000
Balance of unrecognized tax benefits	0	0	465,000,000	421,000,000
Southern Power
Impact on effective tax rate
Tax positions impacting the effective tax rate		0	17,000,000
Tax positions not impacting the effective tax rate		0	0
Balance of unrecognized tax benefits	$ 0	$ 0	$ 17,000,000	$ 8,000,000

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details)	1 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)employee	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
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		$ 36,000,000
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 55,000,000	52,000,000
Projected benefit obligation	13,808,000,000	12,763,000,000	13,808,000,000	$ 12,385,000,000
Plan assets	$ 12,992,000,000	11,611,000,000	12,992,000,000	11,583,000,000
Actuarial gain (loss)		$ 1,143,000,000	$ (1,297,000,000)
Change in discount rate		0.69%	(0.60%)
Pension plans | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 0
Expected future employer contributions, next fiscal year		0
Projected benefit obligation		12,135,000,000
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]
Employer contributions		0	$ 0
Projected benefit obligation	$ 139,000,000	123,000,000	139,000,000	0
Plan assets	138,000,000	123,000,000	138,000,000	0
Actuarial gain (loss)		24,000,000	0
Pension plans | Southern Power | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation		122,000,000
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		73,000,000	84,000,000
Expected future employer contributions, next fiscal year		0
Projected benefit obligation	2,339,000,000	1,865,000,000	2,339,000,000	2,297,000,000
Plan assets	1,053,000,000	928,000,000	1,053,000,000	944,000,000
Actuarial gain (loss)		432,000,000	(65,000,000)
Other postretirement benefit plans | Southern Power
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		1,000,000	0
Projected benefit obligation	11,000,000	9,000,000	11,000,000	0
Plan assets	$ 0	0	0	$ 0
Actuarial gain (loss)		$ 2,000,000	$ 0

Retirement Benefits - Defined B

Retirement Benefits - Defined Benefit Plan Related to Gulf Power (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 12,763	$ 13,808	$ 12,385
Plan assets	11,611	12,992	11,583
Accrued liability	(1,152)	(816)
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	1,865	2,339	2,297
Plan assets	928	1,053	$ 944
Accrued liability	(937)	$ (1,286)
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)	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.58%		3.80%	4.40%	4.58%
Expected long-term return on plan assets			7.95%	7.92%	8.16%
Annual salary increase, net periodic costs			4.34%	4.37%	4.37%
Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.45%	3.77%	3.88%
Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.98%	4.81%	4.98%
Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.49%	3.80%
Annual salary increase			4.34%	4.32%
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.38%		3.68%	4.23%	4.38%
Expected long-term return on plan assets			6.83%	6.84%	6.66%
Annual salary increase, net periodic costs			4.34%	4.37%	4.37%
Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.29%	3.54%	3.66%
Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.91%	4.64%	4.85%
Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.37%	3.68%
Annual salary increase			4.34%	4.32%
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.67%		3.81%	4.44%	4.67%
Expected long-term return on plan assets			7.95%	7.95%	8.20%
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			3.45%	3.76%	3.90%
Alabama Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			4.00%	4.85%	5.07%
Alabama Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.51%	3.81%
Annual salary increase			4.46%	4.46%
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.51%		3.71%	4.27%	4.51%
Expected long-term return on plan assets			6.83%	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			3.31%	3.58%	3.69%
Alabama Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.93%	4.70%	4.96%
Alabama Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.40%	3.71%
Annual salary increase			4.46%	4.46%
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.65%		3.79%	4.40%	4.65%
Expected long-term return on plan assets			7.95%	7.95%	8.20%
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			3.42%	3.72%	3.86%
Georgia Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.99%	4.83%	5.03%
Georgia Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.48%	3.79%
Annual salary increase			4.46%	4.46%
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.49%		3.68%	4.23%	4.49%
Expected long-term return on plan assets			6.80%	6.79%	6.27%
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			3.29%	3.55%	3.67%
Georgia Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.91%	4.63%	4.88%
Georgia Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.36%	3.68%
Annual salary increase			4.46%	4.46%
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.69%		3.80%	4.44%	4.69%
Expected long-term return on plan assets			7.95%	7.95%	8.20%
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			3.46%	3.81%	3.97%
Mississippi Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.99%	4.83%	5.04%
Mississippi Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.49%	3.80%
Annual salary increase			4.46%	4.46%
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations	4.47%		3.68%	4.22%	4.47%
Expected long-term return on plan assets			6.99%	6.88%	7.07%
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			3.29%	3.55%	3.66%
Mississippi Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.91%	4.65%	4.88%
Mississippi Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.35%	3.68%
Annual salary increase			4.46%	4.46%
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			3.94%
Expected long-term return on plan assets			7.95%
Annual salary increase, net periodic costs			4.46%
Southern Power | Pension plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.69%
Southern Power | Pension plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			4.01%
Southern Power | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.65%	3.94%
Annual salary increase			4.46%	4.46%
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			3.81%
Expected long-term return on plan assets			0.00%
Annual salary increase, net periodic costs			4.46%
Southern Power | Other postretirement benefit plans | Discount rate – interest costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.47%
Southern Power | Other postretirement benefit plans | Discount rate – service costs
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs			3.93%
Southern Power | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.50%	3.81%
Annual salary increase			4.46%	4.46%
Southern Company Gas | Pension plans | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.85%		3.74%	4.39%
Expected long-term return on plan assets	7.75%		7.95%	7.60%
Annual salary increase, net periodic costs	3.50%		3.07%	3.50%
Pension band increase	2.00%
Southern Company Gas | Pension plans | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		4.60%
Expected long-term return on plan assets		7.80%
Annual salary increase, net periodic costs		3.70%
Pension band increase		2.00%
Southern Company Gas | Pension plans | Discount rate – interest costs | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.21%		3.41%	3.76%
Southern Company Gas | Pension plans | Discount rate – interest costs | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		4.00%
Southern Company Gas | Pension plans | Discount rate – service costs | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	4.07%		3.84%	4.64%
Southern Company Gas | Pension plans | Discount rate – service costs | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		4.80%
Southern Company Gas | Pension plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.47%	3.74%
Annual salary increase			3.07%	2.88%
Southern Company Gas | Other postretirement benefit plans | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.61%		3.62%	4.15%
Expected long-term return on plan assets	5.93%		5.89%	6.03%
Annual salary increase, net periodic costs	3.50%		3.07%	3.50%
Southern Company Gas | Other postretirement benefit plans | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		4.40%
Expected long-term return on plan assets		6.60%
Annual salary increase, net periodic costs		3.70%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	2.84%		3.21%	3.40%
Southern Company Gas | Other postretirement benefit plans | Discount rate – interest costs | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		3.60%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs | Successor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs	3.96%		3.82%	4.55%
Southern Company Gas | Other postretirement benefit plans | Discount rate – service costs | Predecessor
Defined Benefit Plan Disclosure [Line Items]
Discount rate, net periodic benefit costs		4.70%
Southern Company Gas | Other postretirement benefit plans | Employee benefit obligations
Defined Benefit Plan Disclosure [Line Items]
Discount rate – benefit obligations			4.32%	3.62%
Annual salary increase			3.07%	2.56%

Retirement Benefits - Schedule

Retirement Benefits - Schedule of Health Care Cost Trend Rates (Details) - Other postretirement benefit plans	Dec. 31, 2018
Pre65
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate	6.50%
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	8.00%
Ultimate Cost Trend Rate	4.50%

Retirement Benefits - Accumulat

Retirement Benefits - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 11,683	$ 12,577
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	2,550	2,696
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	3,613	3,847
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	513	541
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	101	111
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Total accumulated benefit obligation for the pension plans	$ 842	$ 1,139

Retirement Benefits - Changes i

Retirement Benefits - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		$ 13,808,000,000	$ 12,385,000,000
Dispositions		(107,000,000)
Service cost		359,000,000	293,000,000	$ 262,000,000
Interest cost		464,000,000	455,000,000	422,000,000
Benefits paid		(618,000,000)	(596,000,000)
Actuarial (gain) loss		(1,143,000,000)	1,297,000,000
Plan amendments			(26,000,000)
Obligations assumed from employee transfer			0
Balance at end of year	$ 12,385,000,000	12,763,000,000	13,808,000,000	12,385,000,000
Change in plan assets
Fair value of plan assets at beginning of year		12,992,000,000	11,583,000,000
Dispositions		(107,000,000)
Actual return (loss) on plan assets		(711,000,000)	1,953,000,000
Employer contributions		55,000,000	52,000,000
Benefits paid		(618,000,000)	(596,000,000)
Assets assumed from employee transfer			0
Fair value of plan assets at end of year	11,583,000,000	11,611,000,000	12,992,000,000	11,583,000,000
Accrued liability		(1,152,000,000)	(816,000,000)
Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		2,339,000,000	2,297,000,000
Dispositions		(18,000,000)
Service cost		24,000,000	24,000,000	22,000,000
Interest cost		75,000,000	79,000,000	76,000,000
Benefits paid		(129,000,000)	(136,000,000)
Actuarial (gain) loss		(432,000,000)	65,000,000
Plan amendments			3,000,000
Retiree drug subsidy		6,000,000	7,000,000
Obligations assumed from employee transfer			0
Employee contributions			0
Balance at end of year	2,297,000,000	1,865,000,000	2,339,000,000	2,297,000,000
Change in plan assets
Fair value of plan assets at beginning of year		1,053,000,000	944,000,000
Dispositions		(18,000,000)
Actual return (loss) on plan assets		(57,000,000)	154,000,000
Employer contributions		73,000,000	84,000,000
Employee contributions			0
Benefits paid		(123,000,000)	(129,000,000)
Fair value of plan assets at end of year	944,000,000	928,000,000	1,053,000,000	944,000,000
Accrued liability		(937,000,000)	(1,286,000,000)
Alabama Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		2,998,000,000	2,663,000,000
Dispositions		0
Service cost		78,000,000	63,000,000	57,000,000
Interest cost		101,000,000	98,000,000	95,000,000
Benefits paid		(124,000,000)	(120,000,000)
Actuarial (gain) loss		(237,000,000)	294,000,000
Plan amendments			0
Obligations assumed from employee transfer			0
Balance at end of year	2,663,000,000	2,816,000,000	2,998,000,000	2,663,000,000
Change in plan assets
Fair value of plan assets at beginning of year		2,836,000,000	2,517,000,000
Dispositions		0
Actual return (loss) on plan assets		(150,000,000)	427,000,000
Employer contributions		13,000,000	12,000,000
Benefits paid		(124,000,000)	(120,000,000)
Assets assumed from employee transfer			0
Fair value of plan assets at end of year	2,517,000,000	2,575,000,000	2,836,000,000	2,517,000,000
Accrued liability		(241,000,000)	(162,000,000)
Alabama Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		517,000,000	501,000,000
Dispositions		0
Service cost		6,000,000	6,000,000	5,000,000
Interest cost		17,000,000	17,000,000	18,000,000
Benefits paid		(28,000,000)	(29,000,000)
Actuarial (gain) loss		(111,000,000)	20,000,000
Plan amendments			0
Retiree drug subsidy		2,000,000	2,000,000
Obligations assumed from employee transfer			0
Employee contributions			0
Balance at end of year	501,000,000	403,000,000	517,000,000	501,000,000
Change in plan assets
Fair value of plan assets at beginning of year		406,000,000	367,000,000
Dispositions		0
Actual return (loss) on plan assets		(25,000,000)	60,000,000
Employer contributions		5,000,000	6,000,000
Employee contributions			0
Benefits paid		(26,000,000)	(27,000,000)
Fair value of plan assets at end of year	367,000,000	360,000,000	406,000,000	367,000,000
Accrued liability		(43,000,000)	(111,000,000)
Georgia Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		4,188,000,000	3,800,000,000
Dispositions		0
Service cost		87,000,000	74,000,000	70,000,000
Interest cost		139,000,000	138,000,000	136,000,000
Benefits paid		(191,000,000)	(187,000,000)
Actuarial (gain) loss		(318,000,000)	363,000,000
Plan amendments			0
Obligations assumed from employee transfer			0
Balance at end of year	3,800,000,000	3,905,000,000	4,188,000,000	3,800,000,000
Change in plan assets
Fair value of plan assets at beginning of year		4,058,000,000	3,621,000,000
Dispositions		0
Actual return (loss) on plan assets		(218,000,000)	610,000,000
Employer contributions		14,000,000	14,000,000
Benefits paid		(191,000,000)	(187,000,000)
Assets assumed from employee transfer			0
Fair value of plan assets at end of year	3,621,000,000	3,663,000,000	4,058,000,000	3,621,000,000
Accrued liability		(242,000,000)	(130,000,000)
Georgia Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		863,000,000	847,000,000
Dispositions		0
Service cost		6,000,000	7,000,000	6,000,000
Interest cost		28,000,000	29,000,000	30,000,000
Benefits paid		(47,000,000)	(51,000,000)
Actuarial (gain) loss		(178,000,000)	28,000,000
Plan amendments			0
Retiree drug subsidy		3,000,000	3,000,000
Obligations assumed from employee transfer			0
Employee contributions			0
Balance at end of year	847,000,000	675,000,000	863,000,000	847,000,000
Change in plan assets
Fair value of plan assets at beginning of year		386,000,000	354,000,000
Dispositions		0
Actual return (loss) on plan assets		(20,000,000)	54,000,000
Employer contributions		22,000,000	26,000,000
Employee contributions			0
Benefits paid		(44,000,000)	(48,000,000)
Fair value of plan assets at end of year	354,000,000	344,000,000	386,000,000	354,000,000
Accrued liability		(331,000,000)	(477,000,000)
Mississippi Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		602,000,000	534,000,000
Dispositions		0
Service cost		17,000,000	15,000,000	13,000,000
Interest cost		20,000,000	20,000,000	19,000,000
Benefits paid		(24,000,000)	(22,000,000)
Actuarial (gain) loss		(58,000,000)	55,000,000
Plan amendments			0
Obligations assumed from employee transfer			0
Balance at end of year	534,000,000	557,000,000	602,000,000	534,000,000
Change in plan assets
Fair value of plan assets at beginning of year		563,000,000	499,000,000
Dispositions		0
Actual return (loss) on plan assets		(37,000,000)	84,000,000
Employer contributions		3,000,000	2,000,000
Benefits paid		(24,000,000)	(22,000,000)
Assets assumed from employee transfer			0
Fair value of plan assets at end of year	499,000,000	505,000,000	563,000,000	499,000,000
Accrued liability		(52,000,000)	(39,000,000)
Mississippi Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		97,000,000	97,000,000
Dispositions		0
Service cost		1,000,000	1,000,000	1,000,000
Interest cost		3,000,000	3,000,000	3,000,000
Benefits paid		(5,000,000)	(6,000,000)
Actuarial (gain) loss		(15,000,000)	1,000,000
Plan amendments			0
Retiree drug subsidy		0	1,000,000
Obligations assumed from employee transfer			0
Employee contributions			0
Balance at end of year	97,000,000	81,000,000	97,000,000	97,000,000
Change in plan assets
Fair value of plan assets at beginning of year		25,000,000	23,000,000
Dispositions		0
Actual return (loss) on plan assets		(1,000,000)	3,000,000
Employer contributions		4,000,000	4,000,000
Employee contributions			0
Benefits paid		(5,000,000)	(5,000,000)
Fair value of plan assets at end of year	23,000,000	23,000,000	25,000,000	23,000,000
Accrued liability		(58,000,000)	(72,000,000)
Southern Power | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		139,000,000	0
Dispositions		(3,000,000)
Service cost		9,000,000	0
Interest cost		5,000,000	0
Benefits paid		(3,000,000)	0
Actuarial (gain) loss		(24,000,000)	0
Plan amendments			0
Obligations assumed from employee transfer			139,000,000
Balance at end of year	0	123,000,000	139,000,000	0
Change in plan assets
Fair value of plan assets at beginning of year		138,000,000	0
Dispositions		(3,000,000)
Actual return (loss) on plan assets		(9,000,000)	0
Employer contributions		0	0
Benefits paid		(3,000,000)	0
Assets assumed from employee transfer			138,000,000
Fair value of plan assets at end of year	0	123,000,000	138,000,000	0
Accrued liability		0	(1,000,000)
Southern Power | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		11,000,000	0
Dispositions		0
Service cost		1,000,000	0
Interest cost		0	0
Benefits paid		(1,000,000)	0
Actuarial (gain) loss		(2,000,000)	0
Plan amendments			0
Retiree drug subsidy		0	0
Obligations assumed from employee transfer			11,000,000
Employee contributions			0
Balance at end of year	0	9,000,000	11,000,000	0
Change in plan assets
Fair value of plan assets at beginning of year		0	0
Dispositions		0
Actual return (loss) on plan assets		0	0
Employer contributions		1,000,000	0
Employee contributions			0
Benefits paid		(1,000,000)	0
Fair value of plan assets at end of year	0	0	0	0
Accrued liability		(9,000,000)	(11,000,000)
Southern Company Gas | Pension plans
Change in benefit obligation
Benefit obligation at beginning of year		1,184,000,000	1,133,000,000
Dispositions		(104,000,000)
Service cost	15,000,000	34,000,000	23,000,000
Interest cost	20,000,000	39,000,000	42,000,000
Benefits paid		(98,000,000)	(91,000,000)
Actuarial (gain) loss		(148,000,000)	103,000,000
Plan amendments			(26,000,000)
Obligations assumed from employee transfer			0
Balance at end of year	1,133,000,000	907,000,000	1,184,000,000	1,133,000,000
Change in plan assets
Fair value of plan assets at beginning of year		1,068,000,000	983,000,000
Dispositions		(104,000,000)
Actual return (loss) on plan assets		(70,000,000)	175,000,000
Employer contributions		2,000,000	1,000,000
Benefits paid		(98,000,000)	(91,000,000)
Assets assumed from employee transfer			0
Fair value of plan assets at end of year	983,000,000	798,000,000	1,068,000,000	983,000,000
Accrued liability		(109,000,000)	(116,000,000)
Southern Company Gas | Other postretirement benefit plans
Change in benefit obligation
Benefit obligation at beginning of year		310,000,000	308,000,000
Dispositions		(18,000,000)
Service cost	1,000,000	2,000,000	2,000,000
Interest cost	5,000,000	10,000,000	10,000,000
Benefits paid		(17,000,000)	(19,000,000)
Actuarial (gain) loss		(43,000,000)	3,000,000
Plan amendments			3,000,000
Retiree drug subsidy		0	0
Obligations assumed from employee transfer			0
Employee contributions			3,000,000
Balance at end of year	308,000,000	244,000,000	310,000,000	308,000,000
Change in plan assets
Fair value of plan assets at beginning of year		125,000,000	105,000,000
Dispositions		(18,000,000)
Actual return (loss) on plan assets		(5,000,000)	20,000,000
Employer contributions		13,000,000	17,000,000
Employee contributions			3,000,000
Benefits paid		(17,000,000)	(20,000,000)
Fair value of plan assets at end of year	$ 105,000,000	98,000,000	125,000,000	$ 105,000,000
Accrued liability		(146,000,000)	$ (185,000,000)
Qualified Pension Plans | Pension plans
Change in benefit obligation
Balance at end of year		12,135,000,000
Change in plan assets
Employer contributions		0
Qualified Pension Plans | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year		2,692,000,000
Qualified Pension Plans | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year		3,757,000,000
Qualified Pension Plans | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year		527,000,000
Qualified Pension Plans | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year		122,000,000
Qualified Pension Plans | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year		866,000,000
Non Qualified Pension Plans | Pension plans
Change in benefit obligation
Balance at end of year		629,000,000
Non Qualified Pension Plans | Alabama Power | Pension plans
Change in benefit obligation
Balance at end of year		124,000,000
Non Qualified Pension Plans | Georgia Power | Pension plans
Change in benefit obligation
Balance at end of year		148,000,000
Non Qualified Pension Plans | Mississippi Power | Pension plans
Change in benefit obligation
Balance at end of year		30,000,000
Non Qualified Pension Plans | Southern Power | Pension plans
Change in benefit obligation
Balance at end of year		1,000,000
Non Qualified Pension Plans | Southern Company Gas | Pension plans
Change in benefit obligation
Balance at end of year		$ 41,000,000

Retirement Benefits - Amounts R

Retirement Benefits - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	$ 8,308,000,000	$ 6,943,000,000
Other deferred charges and assets	1,463,000,000	1,577,000,000
Other current liabilities	(852,000,000)	(874,000,000)
Employee benefit obligations	(2,147,000,000)	(2,256,000,000)
Other regulatory liabilities, deferred	(169,000,000)	(239,000,000)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	3,566,000,000	3,273,000,000
Other deferred charges and assets	0	0
Other current liabilities	(55,000,000)	(53,000,000)
Employee benefit obligations	(1,097,000,000)	(763,000,000)
Other regulatory liabilities, deferred	(108,000,000)	(118,000,000)
AOCI	97,000,000	107,000,000
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	99,000,000	382,000,000
Other current liabilities	(6,000,000)	(5,000,000)
Employee benefit obligations	(931,000,000)	(1,281,000,000)
Other regulatory liabilities, deferred	(77,000,000)	(41,000,000)
AOCI	(4,000,000)	4,000,000
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	1,386,000,000	1,272,000,000
Other deferred charges and assets	189,000,000	189,000,000
Other current liabilities	(161,000,000)	(53,000,000)
Employee benefit obligations	(314,000,000)	(304,000,000)
Other regulatory liabilities, deferred	(69,000,000)	(84,000,000)
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	955,000,000	890,000,000
Other deferred charges and assets	0	0
Other current liabilities	(12,000,000)	(12,000,000)
Employee benefit obligations	(229,000,000)	(150,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	0	63,000,000
Other current liabilities	0	0
Employee benefit obligations	(43,000,000)	(111,000,000)
Other regulatory liabilities, deferred	(8,000,000)	(7,000,000)
AOCI	0	0
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	4,902,000,000	2,932,000,000
Other deferred charges and assets	514,000,000	548,000,000
Other current liabilities	(183,000,000)	(198,000,000)
Employee benefit obligations	(599,000,000)	(659,000,000)
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	23,000,000
Other regulatory assets, deferred	1,230,000,000	1,105,000,000
Other deferred charges and assets	0	0
Other current liabilities	(15,000,000)	(15,000,000)
Employee benefit obligations	(227,000,000)	(138,000,000)
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	60,000,000	202,000,000
Other current liabilities	0	0
Employee benefit obligations	(331,000,000)	(477,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	474,000,000	437,000,000
Other deferred charges and assets	3,000,000	33,000,000
Other current liabilities	(40,000,000)	(47,000,000)
Employee benefit obligations	(115,000,000)	(116,000,000)
Other regulatory liabilities, deferred	(81,000,000)	(79,000,000)
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	167,000,000	158,000,000
Other deferred charges and assets	0	0
Other current liabilities	(3,000,000)	(3,000,000)
Employee benefit obligations	(49,000,000)	(36,000,000)
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	6,000,000	18,000,000
Other current liabilities	0	0
Employee benefit obligations	(58,000,000)	(72,000,000)
Other regulatory liabilities, deferred	(2,000,000)	(1,000,000)
AOCI	0	0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Other deferred charges and assets	373,000,000	566,000,000
Other current liabilities	(142,000,000)	(148,000,000)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	1,000,000	0
Other regulatory assets, deferred	0	0
Other deferred charges and assets	0	0
Other current liabilities	0	0
Employee benefit obligations	(1,000,000)	(1,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	26,000,000	33,000,000
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	(9,000,000)	(11,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	1,000,000	3,000,000
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	669,000,000	901,000,000
Other deferred charges and assets	193,000,000	218,000,000
Other current liabilities	(130,000,000)	(159,000,000)
Employee benefit obligations	(357,000,000)	(415,000,000)
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	0	0
Other regulatory assets, deferred	160,000,000	217,000,000
Other deferred charges and assets	74,000,000	85,000,000
Other current liabilities	(3,000,000)	(3,000,000)
Employee benefit obligations	(179,000,000)	(198,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	(44,000,000)	(42,000,000)
Regulatory asset			$ 268,000,000
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	(4,000,000)	46,000,000
Other current liabilities	0	0
Employee benefit obligations	146,000,000	(185,000,000)
Other regulatory liabilities, deferred	0	0
AOCI	$ (4,000,000)	$ (3,000,000)
Regulatory asset			$ 57,000,000

Retirement Benefits - Component

Retirement Benefits - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($)	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	$ 26,612,000,000	$ 21,982,000,000	$ 25,528,000,000	$ 26,612,000,000	$ 21,982,000,000	$ 29,039,000,000	$ 25,528,000,000	$ 26,612,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		21,982,000,000	25,528,000,000	26,612,000,000	21,982,000,000
Total other comprehensive income (loss)			26,000,000	(9,000,000)	(50,000,000)
Ending balance	26,612,000,000		29,039,000,000	25,528,000,000	26,612,000,000
Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity			(70,000,000)	(70,000,000)		(82,000,000)	(70,000,000)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			(70,000,000)
Total other comprehensive income (loss)			2,000,000
Ending balance			(82,000,000)	(70,000,000)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						(3,000,000)	3,000,000
Net (gain) loss						100,000,000	104,000,000
AOCI						97,000,000	107,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments			(9,000,000)
Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						17,000,000	14,000,000
Net (gain) loss						3,441,000,000	3,140,000,000
Regulatory amortization						0	0
Regulatory asset						3,458,000,000	3,154,000,000
Pension plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	100,000,000		107,000,000	100,000,000	100,000,000	97,000,000	107,000,000	100,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			107,000,000	100,000,000
Reclassification adjustments				(8,000,000)
Total other comprehensive income (loss)			(10,000,000)	7,000,000
Ending balance	100,000,000		97,000,000	107,000,000	100,000,000
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	3,120,000,000		3,155,000,000	3,120,000,000	3,120,000,000	3,458,000,000	3,155,000,000	3,120,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			3,155,000,000	3,120,000,000
Reclassification adjustments			(208,000,000)	(166,000,000)
Total other comprehensive income (loss)			303,000,000	35,000,000
Ending balance	3,120,000,000		3,458,000,000	3,155,000,000	3,120,000,000
Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			(7,000,000)	(15,000,000)
Reclassification adjustments			(9,000,000)	(7,000,000)
Pension plans | Net (gain) loss | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			(498,000,000)	(227,000,000)
Reclassification adjustments			(204,000,000)	(155,000,000)
Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments				(1,000,000)
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			(1,000,000)	26,000,000
Reclassification adjustments			(4,000,000)	(11,000,000)
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 | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			8,000,000
Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			(12,000,000)
Pension plans | Change from employee transfer
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss				0
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						1,000,000	0
Net (gain) loss						(5,000,000)	4,000,000
AOCI						(4,000,000)	4,000,000
Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						14,000,000	21,000,000
Net (gain) loss						8,000,000	320,000,000
Regulatory amortization						0	0
Regulatory asset						22,000,000	341,000,000
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	7,000,000		4,000,000	7,000,000	7,000,000	(4,000,000)	4,000,000	7,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			4,000,000	7,000,000
Total other comprehensive income (loss)			(8,000,000)	(3,000,000)
Ending balance	7,000,000		(4,000,000)	4,000,000	7,000,000
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	378,000,000		341,000,000	378,000,000	378,000,000	22,000,000	341,000,000	378,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			341,000,000	378,000,000
Reclassification adjustments			(21,000,000)	(19,000,000)
Total other comprehensive income (loss)			(319,000,000)	(37,000,000)
Ending balance	378,000,000		22,000,000	341,000,000	378,000,000
Other postretirement benefit plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			(8,000,000)	(3,000,000)
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			298,000,000	21,000,000
Reclassification adjustments			(14,000,000)	(13,000,000)
Other postretirement benefit plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			0
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	(3,000,000)
Reclassification adjustments			(7,000,000)	(6,000,000)
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
Other postretirement benefit plans | Change from employee transfer
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss				0
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	6,323,000,000	5,992,000,000	6,829,000,000	6,323,000,000	5,992,000,000	7,477,000,000	6,829,000,000	6,323,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		5,992,000,000	6,829,000,000	6,323,000,000	5,992,000,000
Total other comprehensive income (loss)			4,000,000	4,000,000	2,000,000
Ending balance	6,323,000,000		7,477,000,000	6,829,000,000	6,323,000,000
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
AOCI						0	0
Alabama Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						6,000,000	8,000,000
Net (gain) loss						949,000,000	882,000,000
Regulatory amortization						0	0
Regulatory asset						955,000,000	890,000,000
Alabama Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	870,000,000		890,000,000	870,000,000	870,000,000	955,000,000	890,000,000	870,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			890,000,000	870,000,000
Reclassification adjustments			(55,000,000)	(44,000,000)
Total other comprehensive income (loss)			65,000,000	20,000,000
Ending balance	870,000,000		955,000,000	890,000,000	870,000,000
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			(120,000,000)	(64,000,000)
Reclassification adjustments			(54,000,000)	(42,000,000)
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	0
Reclassification adjustments			(1,000,000)	(2,000,000)
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 | 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
Defined Benefit Plan Disclosure [Line Items]
AOCI						0	0
Alabama Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						8,000,000	11,000,000
Net (gain) loss						(16,000,000)	45,000,000
Regulatory amortization						0	0
Regulatory asset							56,000,000
Regulatory liabilities						(8,000,000)
Alabama Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	76,000,000		56,000,000	76,000,000	76,000,000	(9,000,000)	56,000,000	76,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			56,000,000	76,000,000
Reclassification adjustments			(5,000,000)	(5,000,000)
Total other comprehensive income (loss)			(65,000,000)	(20,000,000)
Ending balance	76,000,000		(9,000,000)	56,000,000	76,000,000
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			60,000,000	15,000,000
Reclassification adjustments			(1,000,000)	(1,000,000)
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			(4,000,000)	(4,000,000)
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
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	11,356,000,000	10,719,000,000	11,931,000,000	11,356,000,000	10,719,000,000	14,323,000,000	11,931,000,000	11,356,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		10,719,000,000	11,931,000,000	11,356,000,000	10,719,000,000
Total other comprehensive income (loss)			3,000,000	3,000,000	2,000,000
Ending balance	11,356,000,000		14,323,000,000	11,931,000,000	11,356,000,000
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
AOCI						0	0
Georgia Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						12,000,000	14,000,000
Net (gain) loss						1,218,000,000	1,091,000,000
Regulatory amortization						0	0
Regulatory asset						1,230,000,000	1,105,000,000
Georgia Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	1,129,000,000		1,105,000,000	1,129,000,000	1,129,000,000	1,230,000,000	1,105,000,000	1,129,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			1,105,000,000	1,129,000,000
Reclassification adjustments			(71,000,000)	(60,000,000)
Total other comprehensive income (loss)			125,000,000	(24,000,000)
Ending balance	1,129,000,000		1,230,000,000	1,105,000,000	1,129,000,000
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			(196,000,000)	(36,000,000)
Reclassification adjustments			(69,000,000)	(57,000,000)
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	0
Reclassification adjustments			(2,000,000)	(3,000,000)
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 | 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
Defined Benefit Plan Disclosure [Line Items]
AOCI						0	0
Georgia Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						4,000,000	5,000,000
Net (gain) loss						56,000,000	197,000,000
Regulatory amortization						0	0
Regulatory asset						60,000,000	202,000,000
Georgia Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	213,000,000		202,000,000	213,000,000	213,000,000	60,000,000	202,000,000	213,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			202,000,000	213,000,000
Reclassification adjustments			(10,000,000)	(9,000,000)
Total other comprehensive income (loss)			(142,000,000)	(11,000,000)
Ending balance	213,000,000		60,000,000	202,000,000	213,000,000
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			132,000,000	2,000,000
Reclassification adjustments			(9,000,000)	(8,000,000)
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			(1,000,000)	(1,000,000)
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
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	2,943,000,000	2,359,000,000	1,358,000,000	2,943,000,000	2,359,000,000	1,609,000,000	1,358,000,000	2,943,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		2,359,000,000	1,358,000,000	2,943,000,000	2,359,000,000
Total other comprehensive income (loss)			0	0	2,000,000
Ending balance	2,943,000,000		1,609,000,000	1,358,000,000	2,943,000,000
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
AOCI						0	0
Mississippi Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						2,000,000	3,000,000
Net (gain) loss						165,000,000	155,000,000
Regulatory amortization						0	0
Regulatory asset						167,000,000	158,000,000
Mississippi Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	154,000,000		158,000,000	154,000,000	154,000,000	167,000,000	158,000,000	154,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			158,000,000	154,000,000
Reclassification adjustments			(10,000,000)	(8,000,000)
Total other comprehensive income (loss)			9,000,000	4,000,000
Ending balance	154,000,000		167,000,000	158,000,000	154,000,000
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			(19,000,000)	(12,000,000)
Reclassification adjustments			(10,000,000)	(7,000,000)
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	0
Reclassification adjustments			0	(1,000,000)
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 | 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
Defined Benefit Plan Disclosure [Line Items]
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						4,000,000	17,000,000
Regulatory amortization						0	0
Regulatory asset						4,000,000	17,000,000
Mississippi Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	19,000,000		17,000,000	19,000,000	19,000,000	4,000,000	17,000,000	19,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			17,000,000	19,000,000
Reclassification adjustments			(1,000,000)	(1,000,000)
Total other comprehensive income (loss)			(13,000,000)	(2,000,000)
Ending balance	19,000,000		4,000,000	17,000,000	19,000,000
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			12,000,000	1,000,000
Reclassification adjustments			(1,000,000)	(1,000,000)
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 | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments			0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	5,675,000,000	3,264,000,000	6,498,000,000	5,675,000,000	3,264,000,000	7,284,000,000	6,498,000,000	5,675,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		3,264,000,000	6,498,000,000	5,675,000,000	3,264,000,000
Total other comprehensive income (loss)			14,000,000	(10,000,000)	31,000,000
Ending balance	5,675,000,000		7,284,000,000	6,498,000,000	5,675,000,000
Southern Power | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity			(27,000,000)	(27,000,000)		(20,000,000)	(27,000,000)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			(27,000,000)
Total other comprehensive income (loss)			7,000,000
Ending balance			(20,000,000)	(27,000,000)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						0	1,000,000
Net (gain) loss						26,000,000	32,000,000
AOCI						26,000,000	33,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments			(2,000,000)
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	0		33,000,000	0	0	26,000,000	33,000,000	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			33,000,000	0
Reclassification adjustments				0
Total other comprehensive income (loss)			(7,000,000)	33,000,000
Ending balance	0		26,000,000	33,000,000	0
Southern Power | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			5,000,000	0
Reclassification adjustments			(2,000,000)	0
Southern Power | Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments				0
Southern Power | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			0
Southern Power | Pension plans | Change from employee transfer
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss				(33,000,000)
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						0	0
Net (gain) loss						1,000,000	3,000,000
AOCI						1,000,000	3,000,000
Southern Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	0		3,000,000	0	0	1,000,000	3,000,000	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			3,000,000	0
Total other comprehensive income (loss)			(2,000,000)	3,000,000
Ending balance	0		1,000,000	3,000,000	0
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			(2,000,000)	0
Southern Power | Other postretirement benefit plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			0
Southern Power | Other postretirement benefit plans | Change from employee transfer
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss				3,000,000
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	8,001,000,000	8,001,000,000	9,022,000,000	9,109,000,000	9,109,000,000	8,570,000,000	9,022,000,000	9,109,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	8,001,000,000		9,022,000,000	9,109,000,000
Total other comprehensive income (loss)	26,000,000		2,000,000	(5,000,000)
Ending balance	9,109,000,000	$ 8,001,000,000	8,570,000,000	9,022,000,000	9,109,000,000
Southern Company Gas | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity			26,000,000	26,000,000		29,000,000	26,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			26,000,000
Total other comprehensive income (loss)			(2,000,000)
Ending balance			29,000,000	26,000,000
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						(6,000,000)	0
Net (gain) loss						(38,000,000)	(42,000,000)
AOCI						(44,000,000)	(42,000,000)
Regulatory asset								268,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments			0
Southern Company Gas | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						(17,000,000)	(20,000,000)
Net (gain) loss						83,000,000	197,000,000
Regulatory amortization						94,000,000	40,000,000
Regulatory asset						160,000,000	217,000,000
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	(43,000,000)		(42,000,000)	(43,000,000)	(43,000,000)	(44,000,000)	(42,000,000)	(43,000,000)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			(42,000,000)	(43,000,000)
Reclassification adjustments				0
Total other comprehensive income (loss)			(2,000,000)	1,000,000
Ending balance	(43,000,000)		(44,000,000)	(42,000,000)	(43,000,000)
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	267,000,000		217,000,000	267,000,000	267,000,000	160,000,000	217,000,000	267,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			217,000,000	267,000,000
Reclassification adjustments			(25,000,000)	(19,000,000)
Total other comprehensive income (loss)			(57,000,000)	(50,000,000)
Ending balance	267,000,000		160,000,000	217,000,000	267,000,000
Southern Company Gas | Pension plans | Net (gain) loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			(6,000,000)	(1,000,000)
Reclassification adjustments			0	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			(20,000,000)	31,000,000
Reclassification adjustments			(12,000,000)	(18,000,000)
Southern Company Gas | Pension plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments				0
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			18,000,000	0
Reclassification adjustments			2,000,000	0
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			(15,000,000)	(1,000,000)
Southern Company Gas | Pension plans | Dispositions
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			8,000,000
Southern Company Gas | Pension plans | Dispositions | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			34,000,000
Southern Company Gas | Pension plans | Change from employee transfer
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						1,000,000	0
Net (gain) loss						(5,000,000)	(3,000,000)
AOCI						(4,000,000)	(3,000,000)
Regulatory asset								57,000,000
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost						2,000,000	(7,000,000)
Net (gain) loss						(43,000,000)	47,000,000
Regulatory amortization						37,000,000	6,000,000
Regulatory asset							46,000,000
Regulatory liabilities						(4,000,000)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	(3,000,000)		(3,000,000)	(3,000,000)	(3,000,000)	(4,000,000)	(3,000,000)	(3,000,000)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			(3,000,000)	(3,000,000)
Total other comprehensive income (loss)			(1,000,000)	0
Ending balance	(3,000,000)		(4,000,000)	(3,000,000)	(3,000,000)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Total Stockholders' Equity	52,000,000		46,000,000	52,000,000	52,000,000	$ (4,000,000)	$ 46,000,000	$ 52,000,000
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			46,000,000	52,000,000
Reclassification adjustments			(6,000,000)	(1,000,000)
Total other comprehensive income (loss)			(50,000,000)	(6,000,000)
Ending balance	$ 52,000,000		(4,000,000)	46,000,000	$ 52,000,000
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			(2,000,000)	(1,000,000)
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			42,000,000	5,000,000
Reclassification adjustments			0	(4,000,000)
Southern Company Gas | Other postretirement benefit plans | Change in prior service costs
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss			1,000,000
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			2,000,000	0
Reclassification adjustments			0	3,000,000
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			$ (6,000,000)
Southern Company Gas | Other postretirement benefit plans | Change from employee transfer
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive (income) loss				$ 1,000,000

Retirement Benefits - Compone_2

Retirement Benefits - Components of Net Periodic Benefit Cost and Estimated Future Benefit Payments (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension plans
Components of net periodic
Service cost			$ 359	$ 293	$ 262
Interest cost			464	455	422
Expected return on plan assets			(943)	(897)	(782)
Recognized net (gain) loss			213	162	150
Net amortization			4	12	14
Total change			97	25	66
Benefit payments:
Benefit Payments, 2019			623
Benefit Payments, 2020			645
Benefit Payments, 2021			664
Benefit Payments, 2022			687
Benefit Payments, 2023			711
Benefit Payments, 2024 to 2028			3,869
Other postretirement benefit plans
Components of net periodic
Service cost			24	24	22
Interest cost			75	79	76
Expected return on plan assets			(69)	(66)	(60)
Net amortization			21	20	21
Total change			51	57	59
Benefit payments:
Benefit Payments, 2019			136
Benefit Payments, 2020			136
Benefit Payments, 2021			136
Benefit Payments, 2022			137
Benefit Payments, 2023			137
Benefit Payments, 2024 to 2028			669
Subsidy receipts:
Subsidy Receipts, 2019			(7)
Subsidy Receipts, 2020			(7)
Subsidy Receipts, 2021			(8)
Subsidy Receipts, 2022			(8)
Subsidy Receipts, 2023			(8)
Subsidy Receipts, 2024 to 2028			(41)
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			129
Benefit Payments and Subsidy Receipts, 2020			129
Benefit Payments and Subsidy Receipts, 2021			128
Benefit Payments and Subsidy Receipts, 2022			129
Benefit Payments and Subsidy Receipts, 2023			129
Benefit Payments and Subsidy Receipts, 2024 to 2028			628
Alabama Power | Pension plans
Components of net periodic
Service cost			78	63	57
Interest cost			101	98	95
Expected return on plan assets			(207)	(196)	(184)
Recognized net (gain) loss			54	42	40
Net amortization			1	2	3
Total change			27	9	11
Benefit payments:
Benefit Payments, 2019			132
Benefit Payments, 2020			136
Benefit Payments, 2021			141
Benefit Payments, 2022			147
Benefit Payments, 2023			152
Benefit Payments, 2024 to 2028			832
Alabama Power | Other postretirement benefit plans
Components of net periodic
Service cost			6	6	5
Interest cost			17	17	18
Expected return on plan assets			(26)	(25)	(25)
Net amortization			5	5	6
Total change			2	3	4
Benefit payments:
Benefit Payments, 2019			28
Benefit Payments, 2020			28
Benefit Payments, 2021			29
Benefit Payments, 2022			29
Benefit Payments, 2023			29
Benefit Payments, 2024 to 2028			146
Subsidy receipts:
Subsidy Receipts, 2019			(2)
Subsidy Receipts, 2020			(2)
Subsidy Receipts, 2021			(2)
Subsidy Receipts, 2022			(2)
Subsidy Receipts, 2023			(3)
Subsidy Receipts, 2024 to 2028			(13)
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			26
Benefit Payments and Subsidy Receipts, 2020			26
Benefit Payments and Subsidy Receipts, 2021			27
Benefit Payments and Subsidy Receipts, 2022			27
Benefit Payments and Subsidy Receipts, 2023			26
Benefit Payments and Subsidy Receipts, 2024 to 2028			133
Georgia Power | Pension plans
Components of net periodic
Service cost			87	74	70
Interest cost			139	138	136
Expected return on plan assets			(296)	(283)	(258)
Recognized net (gain) loss			69	57	55
Net amortization			2	3	5
Total change			1	(11)	8
Benefit payments:
Benefit Payments, 2019			201
Benefit Payments, 2020			206
Benefit Payments, 2021			209
Benefit Payments, 2022			215
Benefit Payments, 2023			221
Benefit Payments, 2024 to 2028			1,183
Georgia Power | Other postretirement benefit plans
Components of net periodic
Service cost			6	7	6
Interest cost			28	29	30
Expected return on plan assets			(25)	(25)	(22)
Net amortization			10	9	10
Total change			19	20	24
Benefit payments:
Benefit Payments, 2019			51
Benefit Payments, 2020			50
Benefit Payments, 2021			50
Benefit Payments, 2022			50
Benefit Payments, 2023			49
Benefit Payments, 2024 to 2028			243
Subsidy receipts:
Subsidy Receipts, 2019			(3)
Subsidy Receipts, 2020			(3)
Subsidy Receipts, 2021			(3)
Subsidy Receipts, 2022			(3)
Subsidy Receipts, 2023			(4)
Subsidy Receipts, 2024 to 2028			(18)
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			48
Benefit Payments and Subsidy Receipts, 2020			47
Benefit Payments and Subsidy Receipts, 2021			47
Benefit Payments and Subsidy Receipts, 2022			47
Benefit Payments and Subsidy Receipts, 2023			45
Benefit Payments and Subsidy Receipts, 2024 to 2028			225
Mississippi Power | Pension plans
Components of net periodic
Service cost			17	15	13
Interest cost			20	20	19
Expected return on plan assets			(41)	(40)	(35)
Recognized net (gain) loss			10	7	7
Net amortization			0	1	1
Total change			6	3	5
Benefit payments:
Benefit Payments, 2019			28
Benefit Payments, 2020			28
Benefit Payments, 2021			29
Benefit Payments, 2022			29
Benefit Payments, 2023			30
Benefit Payments, 2024 to 2028			166
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)	(1)	(1)
Net amortization			1	1	1
Total change			3	4	$ 4
Benefit payments:
Benefit Payments, 2019			6
Benefit Payments, 2020			6
Benefit Payments, 2021			6
Benefit Payments, 2022			6
Benefit Payments, 2023			7
Benefit Payments, 2024 to 2028			30
Subsidy receipts:
Subsidy Receipts, 2019			0
Subsidy Receipts, 2020			0
Subsidy Receipts, 2021			0
Subsidy Receipts, 2022			(1)
Subsidy Receipts, 2023			(1)
Subsidy Receipts, 2024 to 2028			(2)
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			6
Benefit Payments and Subsidy Receipts, 2020			6
Benefit Payments and Subsidy Receipts, 2021			6
Benefit Payments and Subsidy Receipts, 2022			5
Benefit Payments and Subsidy Receipts, 2023			6
Benefit Payments and Subsidy Receipts, 2024 to 2028			28
Southern Power | Pension plans
Components of net periodic
Service cost			9	0
Interest cost			5	0
Expected return on plan assets			(10)
Recognized net (gain) loss			1
Net amortization			0
Total change			5
Benefit payments:
Benefit Payments, 2019			3
Benefit Payments, 2020			3
Benefit Payments, 2021			4
Benefit Payments, 2022			4
Benefit Payments, 2023			5
Benefit Payments, 2024 to 2028			27
Southern Power | Other postretirement benefit plans
Components of net periodic
Service cost			1	0
Interest cost			0	0
Expected return on plan assets			0
Net amortization			0
Total change			1
Benefit payments:
Benefit Payments, 2019			0
Benefit Payments, 2020			0
Benefit Payments, 2021			0
Benefit Payments, 2022			1
Benefit Payments, 2023			1
Benefit Payments, 2024 to 2028			3
Subsidy receipts:
Subsidy Receipts, 2019			0
Subsidy Receipts, 2020			0
Subsidy Receipts, 2021			0
Subsidy Receipts, 2022			0
Subsidy Receipts, 2023			0
Subsidy Receipts, 2024 to 2028			0
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			0
Benefit Payments and Subsidy Receipts, 2020			0
Benefit Payments and Subsidy Receipts, 2021			0
Benefit Payments and Subsidy Receipts, 2022			1
Benefit Payments and Subsidy Receipts, 2023			1
Benefit Payments and Subsidy Receipts, 2024 to 2028			3
Southern Company Gas | Pension plans
Components of net periodic
Service cost	$ 15		34	23
Interest cost	20		39	42
Expected return on plan assets	(35)		(75)	(70)
Recognized net (gain) loss	14		12	18
Amortization of regulatory assets()	0		15	1
Net amortization	(1)		(2)	0
Total change	13		23	14
Benefit payments:
Benefit Payments, 2019			59
Benefit Payments, 2020			61
Benefit Payments, 2021			62
Benefit Payments, 2022			62
Benefit Payments, 2023			62
Benefit Payments, 2024 to 2028			313
Southern Company Gas | Other postretirement benefit plans
Components of net periodic
Service cost	1		2	2
Interest cost	5		10	10
Expected return on plan assets	(3)		(7)	(7)
Amortization of regulatory assets()	2		6	0
Net amortization	0		0	(3)
Amortization of net gain (loss)	0		0	4
Total change	$ 5		11	$ 6
Benefit payments:
Benefit Payments, 2019			18
Benefit Payments, 2020			18
Benefit Payments, 2021			19
Benefit Payments, 2022			19
Benefit Payments, 2023			19
Benefit Payments, 2024 to 2028			90
Subsidy receipts:
Subsidy Receipts, 2019			0
Subsidy Receipts, 2020			0
Subsidy Receipts, 2021			0
Subsidy Receipts, 2022			0
Subsidy Receipts, 2023			0
Subsidy Receipts, 2024 to 2028			0
Benefit Payments and Subsidy Receipts, Total
Benefit Payments and Subsidy Receipts, 2019			18
Benefit Payments and Subsidy Receipts, 2020			18
Benefit Payments and Subsidy Receipts, 2021			19
Benefit Payments and Subsidy Receipts, 2022			19
Benefit Payments and Subsidy Receipts, 2023			19
Benefit Payments and Subsidy Receipts, 2024 to 2028			$ 90
Predecessor | Southern Company Gas | Pension plans
Components of net periodic
Service cost		$ 13
Interest cost		21
Expected return on plan assets		(33)
Recognized net (gain) loss		13
Amortization of regulatory assets()		0
Net amortization		(1)
Total change		13
Predecessor | Southern Company Gas | Other postretirement benefit plans
Components of net periodic
Service cost		1
Interest cost		5
Expected return on plan assets		(3)
Amortization of regulatory assets()		0
Net amortization		(1)
Amortization of net gain (loss)		2
Total change		$ 4

Retirement Benefits - Fair Valu

Retirement Benefits - Fair Values of Pension Plan and Other Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets Fair Value
Target plan asset allocations (as percent)	100.00%
Actual plan asset allocations (as percent)	100.00%
Pension plans
Assets Fair Value
Fair value, plan assets	$ 11,631	$ 12,901
Target plan asset allocations (as percent)		100.00%
Actual plan asset allocations (as percent)		100.00%
Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 3,132	$ 4,041
Target plan asset allocations (as percent)	26.00%	26.00%
Actual plan asset allocations (as percent)	28.00%	31.00%
Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 2,669	$ 3,124
Target plan asset allocations (as percent)	25.00%	25.00%
Actual plan asset allocations (as percent)	25.00%	25.00%
Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 930	$ 926
Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	7	8
Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1,195	1,241
Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	654	650
Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	272	385
Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 1,780	$ 1,676
Target plan asset allocations (as percent)	14.00%	14.00%
Actual plan asset allocations (as percent)	15.00%	13.00%
Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 171	$ 180
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 821	$ 670
Target plan asset allocations (as percent)	9.00%	9.00%
Actual plan asset allocations (as percent)	7.00%	6.00%
Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 926	$ 1,048
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 176	$ 239
Target plan asset allocations (as percent)	39.00%	37.00%
Actual plan asset allocations (as percent)	40.00%	40.00%
Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 120	$ 145
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	22.00%	23.00%
Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	29.00%	30.00%
Actual plan asset allocations (as percent)	30.00%	29.00%
Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 34	$ 32
Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	35	37
Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	81	79
Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	13	13
Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	386	426
Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 53	$ 52
Target plan asset allocations (as percent)	5.00%	5.00%
Actual plan asset allocations (as percent)	5.00%	5.00%
Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 4	$ 5
Target plan asset allocations (as percent)	1.00%	1.00%
Actual plan asset allocations (as percent)	0.00%	1.00%
Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 24	$ 20
Target plan asset allocations (as percent)	3.00%	4.00%
Actual plan asset allocations (as percent)	3.00%	2.00%
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Fair value, plan assets	$ 4,135	$ 4,887
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	2,102	2,559
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	1,344	1,555
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	270	301
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	419	472
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	171	210
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	100	135
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	45	47
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	13	12
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	13	16
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	5,143	5,912
Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	1,030	1,482
Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	1,325	1,569
Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	930	926
Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	7	8
Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1,195	1,241
Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	654	650
Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	2	36
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	687	776
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	76	104
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	75	98
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	34	32
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	35	37
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	81	79
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	386	426
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 | Pension plans
Assets Fair Value
Fair value, plan assets	2,353	2,102
Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | 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 | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	48
Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	1,361	1,204
Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	171	180
Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	821	670
Net Asset Value as a Practical Expedient | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	68	62
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | 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 | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	1
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	0	0
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	40	36
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	4	5
Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	24	20
Alabama Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 2,579	$ 2,844
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Alabama Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 694	$ 848
Target plan asset allocations (as percent)	26.00%	26.00%
Actual plan asset allocations (as percent)	28.00%	31.00%
Alabama Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 591	$ 703
Target plan asset allocations (as percent)	25.00%	25.00%
Actual plan asset allocations (as percent)	25.00%	25.00%
Alabama Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Alabama Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 206	$ 200
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	265	286
Alabama Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	145	155
Alabama Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	61	54
Alabama Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 395	$ 394
Target plan asset allocations (as percent)	14.00%	14.00%
Actual plan asset allocations (as percent)	15.00%	13.00%
Alabama Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 38	$ 43
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Alabama Power | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 182	$ 159
Target plan asset allocations (as percent)	9.00%	9.00%
Actual plan asset allocations (as percent)	7.00%	6.00%
Alabama Power | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 359	$ 405
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Alabama Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 45	$ 64
Target plan asset allocations (as percent)	43.00%	42.00%
Actual plan asset allocations (as percent)	45.00%	44.00%
Alabama Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 24	$ 30
Target plan asset allocations (as percent)	21.00%	22.00%
Actual plan asset allocations (as percent)	21.00%	22.00%
Alabama Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	28.00%	28.00%
Actual plan asset allocations (as percent)	28.00%	28.00%
Alabama Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 10	$ 11
Alabama Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	12
Alabama Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	6	7
Alabama Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	3	2
Alabama Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	233	253
Alabama Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 17	$ 17
Target plan asset allocations (as percent)	4.00%	4.00%
Actual plan asset allocations (as percent)	4.00%	4.00%
Alabama Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 2	$ 2
Target plan asset allocations (as percent)	1.00%	1.00%
Actual plan asset allocations (as percent)	0.00%	0.00%
Alabama Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 8	$ 7
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	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	$ 917	$ 1,104
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	466	572
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	298	370
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	60	51
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	93	111
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	54	75
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	35	52
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	12	16
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	3	2
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	4	5
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	1,140	1,255
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	228	276
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	293	333
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	206	200
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	265	286
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	145	155
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	1	3
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	282	309
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	10	12
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	12	14
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	11
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	11	12
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	6	7
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	233	253
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 | Pension plans
Assets Fair Value
Fair value, plan assets	522	485
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | 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 | 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 | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	302	283
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	38	43
Alabama Power | Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	182	159
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	23	21
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | 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 | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Alabama Power | Net Asset Value as a Practical Expedient | 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 | 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 | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	13	12
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	2	2
Alabama Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	8	7
Georgia Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 3,669	$ 4,069
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Georgia Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 988	$ 1,213
Target plan asset allocations (as percent)	26.00%	26.00%
Actual plan asset allocations (as percent)	28.00%	31.00%
Georgia Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 842	$ 1,006
Target plan asset allocations (as percent)	25.00%	25.00%
Actual plan asset allocations (as percent)	25.00%	25.00%
Georgia Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Georgia Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 294	$ 286
Georgia Power | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	2	3
Georgia Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	377	409
Georgia Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	206	221
Georgia Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	86	78
Georgia Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 561	$ 564
Target plan asset allocations (as percent)	14.00%	14.00%
Actual plan asset allocations (as percent)	15.00%	13.00%
Georgia Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 54	$ 61
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Georgia Power | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 259	$ 228
Target plan asset allocations (as percent)	9.00%	9.00%
Actual plan asset allocations (as percent)	7.00%	6.00%
Georgia Power | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 342	$ 384
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Georgia Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 50	$ 64
Target plan asset allocations (as percent)	36.00%	36.00%
Actual plan asset allocations (as percent)	35.00%	38.00%
Georgia Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 49	$ 60
Target plan asset allocations (as percent)	24.00%	24.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Georgia Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	33.00%	33.00%
Actual plan asset allocations (as percent)	35.00%	31.00%
Georgia Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 7	$ 6
Georgia Power | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	10	11
Georgia Power | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	44	41
Georgia Power | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	5	4
Georgia Power | Other postretirement benefit plans | Trust-owned life insurance
Assets Fair Value
Fair value, plan assets	153	173
Georgia Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 15	$ 17
Target plan asset allocations (as percent)	4.00%	4.00%
Actual plan asset allocations (as percent)	4.00%	4.00%
Georgia Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 2	$ 2
Target plan asset allocations (as percent)	1.00%	1.00%
Actual plan asset allocations (as percent)	0.00%	1.00%
Georgia Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 7	$ 6
Target plan asset allocations (as percent)	2.00%	2.00%
Actual plan asset allocations (as percent)	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	$ 1,304	$ 1,582
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	663	819
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	424	529
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	85	74
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	132	160
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	67	77
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	41	53
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	17	14
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	5	4
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	4	6
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	1,623	1,794
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	325	394
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	418	477
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	294	286
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities
Assets Fair Value
Fair value, plan assets	2	3
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	377	409
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	206	221
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	1	4
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	255	288
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	9	11
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	32	46
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	6
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	10	11
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	44	41
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	153	173
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 | Pension plans
Assets Fair Value
Fair value, plan assets	742	693
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | 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 | 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 | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	429	404
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	54	61
Georgia Power | Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	259	228
Georgia Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	20	19
Georgia Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | 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 | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Georgia Power | Net Asset Value as a Practical Expedient | 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 | 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 | 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 | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	2	2
Georgia Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	7	6
Mississippi Power | Pension plans
Assets Fair Value
Fair value, plan assets	$ 506	$ 564
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Mississippi Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 136	$ 168
Target plan asset allocations (as percent)	26.00%	26.00%
Actual plan asset allocations (as percent)	28.00%	31.00%
Mississippi Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 118	$ 139
Target plan asset allocations (as percent)	25.00%	25.00%
Actual plan asset allocations (as percent)	25.00%	25.00%
Mississippi Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Mississippi Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 40	$ 40
Mississippi Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	52	56
Mississippi Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	28	31
Mississippi Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	12	11
Mississippi Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 77	$ 78
Target plan asset allocations (as percent)	14.00%	14.00%
Actual plan asset allocations (as percent)	15.00%	13.00%
Mississippi Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 7	$ 9
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Mississippi Power | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 36	$ 32
Target plan asset allocations (as percent)	9.00%	9.00%
Actual plan asset allocations (as percent)	7.00%	6.00%
Mississippi Power | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 23	$ 24
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Mississippi Power | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 5	$ 6
Target plan asset allocations (as percent)	21.00%	21.00%
Actual plan asset allocations (as percent)	22.00%	25.00%
Mississippi Power | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 4	$ 5
Target plan asset allocations (as percent)	20.00%	21.00%
Actual plan asset allocations (as percent)	20.00%	20.00%
Mississippi Power | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	38.00%	37.00%
Actual plan asset allocations (as percent)	39.00%	38.00%
Mississippi Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 6	$ 5
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	1	1
Mississippi Power | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 3	$ 3
Target plan asset allocations (as percent)	11.00%	12.00%
Actual plan asset allocations (as percent)	12.00%	11.00%
Mississippi Power | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 0	$ 0
Target plan asset allocations (as percent)	3.00%	2.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Mississippi Power | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 1	$ 1
Target plan asset allocations (as percent)	7.00%	7.00%
Actual plan asset allocations (as percent)	6.00%	5.00%
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Fair value, plan assets	$ 180	$ 218
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	91	113
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	59	73
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	12	10
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	18	22
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	7	9
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	4
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	2	3
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	1	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	224	249
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	45	55
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	59	66
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	40	40
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	52	56
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	28	31
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	1
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	13	12
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	2	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	5
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 | Pension plans
Assets Fair Value
Fair value, plan assets	102	97
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | 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 | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	59	56
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	7	9
Mississippi Power | Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	36	32
Mississippi Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	3	3
Mississippi Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | 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 | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | 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 | 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 | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0	0
Mississippi Power | Net Asset Value as a Practical Expedient | 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	$ 124	$ 138
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Southern Power | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 33	$ 41
Target plan asset allocations (as percent)	26.00%	26.00%
Actual plan asset allocations (as percent)	28.00%	31.00%
Southern Power | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 28	$ 34
Target plan asset allocations (as percent)	25.00%	25.00%
Actual plan asset allocations (as percent)	25.00%	25.00%
Southern Power | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%	23.00%
Actual plan asset allocations (as percent)	24.00%	24.00%
Southern Power | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 10	$ 10
Southern Power | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	13	14
Southern Power | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	7	8
Southern Power | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	3	2
Southern Power | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 19	$ 19
Target plan asset allocations (as percent)	14.00%	14.00%
Actual plan asset allocations (as percent)	15.00%	13.00%
Southern Power | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 2	$ 2
Target plan asset allocations (as percent)	3.00%	3.00%
Actual plan asset allocations (as percent)	1.00%	1.00%
Southern Power | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 9	$ 8
Target plan asset allocations (as percent)	9.00%	9.00%
Actual plan asset allocations (as percent)	7.00%	6.00%
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Fair value, plan assets	$ 43	$ 53
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	22	28
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	14	18
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	3	2
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	4	5
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	55	61
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	11	13
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	14	16
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	10	10
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	13	14
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	7	8
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 | Pension plans
Assets Fair Value
Fair value, plan assets	26	24
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient | 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 | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	0
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	15	14
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	2	2
Southern Power | Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	9	8
Southern Company Gas | Pension plans
Assets Fair Value
Fair value, plan assets	$ 800	945
Target plan asset allocations (as percent)	100.00%
Actual plan asset allocations (as percent)	100.00%
Southern Company Gas | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 216	478
Target plan asset allocations (as percent)	26.00%
Actual plan asset allocations (as percent)	28.00%
Southern Company Gas | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	$ 183	166
Target plan asset allocations (as percent)	25.00%
Actual plan asset allocations (as percent)	25.00%
Southern Company Gas | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	23.00%
Actual plan asset allocations (as percent)	24.00%
Southern Company Gas | Pension plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 64	85
Southern Company Gas | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	82	39
Southern Company Gas | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	45
Southern Company Gas | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	19	157
Southern Company Gas | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 123	19
Target plan asset allocations (as percent)	14.00%
Actual plan asset allocations (as percent)	15.00%
Southern Company Gas | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 12
Target plan asset allocations (as percent)	3.00%
Actual plan asset allocations (as percent)	1.00%
Southern Company Gas | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 56	1
Target plan asset allocations (as percent)	9.00%
Actual plan asset allocations (as percent)	7.00%
Southern Company Gas | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	$ 96	$ 121
Target plan asset allocations (as percent)	100.00%	100.00%
Actual plan asset allocations (as percent)	100.00%	100.00%
Southern Company Gas | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	$ 49	$ 72
Target plan asset allocations (as percent)	51.00%
Actual plan asset allocations (as percent)	51.00%
Southern Company Gas | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	$ 18	$ 22
Target plan asset allocations (as percent)	20.00%
Actual plan asset allocations (as percent)	18.00%
Southern Company Gas | Other postretirement benefit plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	25.00%	24.00%
Actual plan asset allocations (as percent)	28.00%	20.00%
Southern Company Gas | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	$ 1
Southern Company Gas | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1
Southern Company Gas | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	24	$ 24
Southern Company Gas | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	1	$ 3
Southern Company Gas | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	$ 1
Target plan asset allocations (as percent)	2.00%
Actual plan asset allocations (as percent)	2.00%
Southern Company Gas | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	$ 0
Target plan asset allocations (as percent)	1.00%
Actual plan asset allocations (as percent)	0.00%
Southern Company Gas | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 1
Target plan asset allocations (as percent)	1.00%
Actual plan asset allocations (as percent)	1.00%
Southern Company Gas | Other postretirement benefit plans | Equity securities
Assets Fair Value
Target plan asset allocations (as percent)		72.00%
Actual plan asset allocations (as percent)		76.00%
Southern Company Gas | Other postretirement benefit plans | Cash
Assets Fair Value
Target plan asset allocations (as percent)		1.00%
Actual plan asset allocations (as percent)		2.00%
Southern Company Gas | Other postretirement benefit plans | Other Types Of Investments
Assets Fair Value
Target plan asset allocations (as percent)		3.00%
Actual plan asset allocations (as percent)		2.00%
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans
Assets Fair Value
Fair value, plan assets	$ 285	$ 242
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	145	155
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	92	0
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 | 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
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	19	84
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	29	3
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
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	4	5
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	3
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	1	0
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
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
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	1	2
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	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
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans
Assets Fair Value
Fair value, plan assets	353	638
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	71	323
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	91	166
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	64	85
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	82	39
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	45
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	25
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
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	90	115
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity
Assets Fair Value
Fair value, plan assets	47	69
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity
Assets Fair Value
Fair value, plan assets	17	22
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
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds
Assets Fair Value
Fair value, plan assets	24	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
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
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans
Assets Fair Value
Fair value, plan assets	162	65
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Domestic equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | International equity
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient | 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 | Pension plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0	0
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Pooled funds
Assets Fair Value
Fair value, plan assets	0
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	48
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Real estate investments
Assets Fair Value
Fair value, plan assets	94	16
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Special situations
Assets Fair Value
Fair value, plan assets	12
Southern Company Gas | Net Asset Value as a Practical Expedient | Pension plans | Private equity
Assets Fair Value
Fair value, plan assets	56	1
Southern Company Gas | Net Asset Value as a Practical Expedient | Other postretirement benefit plans
Assets Fair Value
Fair value, plan assets	2	1
Southern Company Gas | Net Asset Value as a Practical Expedient | 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 | 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 | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds
Assets Fair Value
Fair value, plan assets	0
Southern Company Gas | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Corporate bonds
Assets Fair Value
Fair value, plan assets	0
Southern Company Gas | Net Asset Value as a Practical Expedient | 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 | Other postretirement benefit plans | Cash equivalents and other
Assets Fair Value
Fair value, plan assets	0	$ 1
Southern Company Gas | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Real estate investments
Assets Fair Value
Fair value, plan assets	1
Southern Company Gas | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Special situations
Assets Fair Value
Fair value, plan assets	0
Southern Company Gas | Net Asset Value as a Practical Expedient | Other postretirement benefit plans | Private equity
Assets Fair Value
Fair value, plan assets	$ 1
AGL Resources Inc. Retirement Plan | Southern Company Gas | Pension plans
Assets Fair Value
Target plan asset allocations (as percent)	100.00%
Actual plan asset allocations (as percent)		100.00%
AGL Resources Inc. Retirement Plan | Southern Company Gas | Pension plans | Fixed income
Assets Fair Value
Target plan asset allocations (as percent)	15.00%
Actual plan asset allocations (as percent)		19.00%
AGL Resources Inc. Retirement Plan | Southern Company Gas | Pension plans | Equity securities
Assets Fair Value
Target plan asset allocations (as percent)	53.00%
Actual plan asset allocations (as percent)		65.00%
AGL Resources Inc. Retirement Plan | Southern Company Gas | Pension plans | Cash
Assets Fair Value
Target plan asset allocations (as percent)	2.00%
Actual plan asset allocations (as percent)		6.00%
AGL Resources Inc. Retirement Plan | Southern Company Gas | Pension plans | Other Types Of Investments
Assets Fair Value
Target plan asset allocations (as percent)	30.00%
Actual plan asset allocations (as percent)		10.00%

Retirement Benefits - 401K Plan

Retirement Benefits - 401K Plan Matching Contributions (Details) - Employee Savings Plan - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost			$ 119	$ 118	$ 105
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost			24	23	23
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost			26	26	27
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost			5	5	$ 5
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost			3
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost		$ 8	$ 18	$ 19
Predecessor | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 12

Stock Compensation - Schedule o

Stock Compensation - Schedule of Employees Participating in Stock-Based Compensation Programs (Details)	Dec. 31, 2018employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	4,716
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	745
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	822
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	164
Southern Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees	95
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. 19, 2019$ / sharesshares	Feb. 28, 2018$ / sharesshares	Dec. 31, 2018USD ($)type$ / sharesshares	Dec. 31, 2017$ / sharesshares	Dec. 31, 2016$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares converted (in shares)		1,900,000
Shares converted (in dollars per share) | $ / shares		$ 44.68
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of performance share units issued under performance share plan			3 years	3 years
Minimum percentage of transfer performance shares to common stock based on actual total shareholder return			0.00%
Maximum percentage of transfer performance shares to common stock based on actual total shareholder return			200.00%
Number of types of PSUs | type			3
Performance share units, unvested (in shares)			2,500,000	2,900,000
Equity instruments, vested (in shares)		1,500,000	1,900,000
Equity instrument, granted (in shares)			1,300,000
Unrecognized compensation cost | $			$ 30
Total unrecognized compensation cost related to award, weighted average period			16 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			$ 43.49	$ 49.21	$ 48.87
Subsequent Event
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

Stock Compensation - Performa_2

Stock Compensation - Performance Shares, Assumptions Used (Details) - Performance Shares - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	14.90%	15.60%	15.00%
Expected term (in years)	3 years	3 years	3 years
Interest rate	2.40%	1.40%	0.80%
Weighted average grant-date fair value (in dollars per share)	$ 43.75	$ 49.08	$ 45.06

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	$ 91	$ 74	$ 96
Tax benefit of compensation cost recognized in income	24	29	37
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	11	9	15
Tax benefit of compensation cost recognized in income	3	4	6
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	11	10	15
Tax benefit of compensation cost recognized in income	3	4	6
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	3	2	4
Tax benefit of compensation cost recognized in income	1	1	$ 1
Southern Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	4
Tax benefit of compensation cost recognized in income	1
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized in income	11	8
Tax benefit of compensation cost recognized in income	$ 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, 2018	Dec. 31, 2017
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period		3 years
Shares vested and issued each year employee remains in service		33.00%
Total unrecognized compensation cost related to award, weighted average period		16 months
Restricted stock units, unvested (in shares)		1.1	0.7
Equity instrument, granted (in shares)		0.7
Vested or forfeited (in shares)		0.3
Total compensation cost for award recognized in income		$ 27	$ 25
Total compensation cost for award recognized in income, tax benefit		7	$ 10
Total unrecognized compensation cost related to award		$ 13
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	$ 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term for options exercisable	0 years
Cash received from issuance related to option exercise	$ 41	$ 239	$ 448
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term for options outstanding	4 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, 2018$ / sharesshares
Shares Subject to Option
Outstanding at December 31, 2017 (in shares) | shares	18.6
Exercised (in shares) | shares	1.1
Outstanding and Exercisable at December 31, 2018 (in shares) | shares	17.5
Weighted Average Exercise Price
Outstanding at December 31, 2017 (in dollars per share) | $ / shares	$ 41.68
Exercised (in dollars per share) | $ / shares	37.82
Outstanding and Exercisable at December 31, 2018 (in dollars per share) | $ / shares	$ 41.92

Stock Compensation - Aggregate

Stock Compensation - Aggregate Intrinsic Value for Options Exercised (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	$ 39
Aggregate intrinsic value for options exercisable	39
Intrinsic value of options exercised	9	$ 64	$ 120
Tax benefit of options exercised	2	25	46
Alabama Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	5
Aggregate intrinsic value for options exercisable	5
Intrinsic value of options exercised	2	12	21
Tax benefit of options exercised	0	5	8
Georgia Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	13
Aggregate intrinsic value for options exercisable	13
Intrinsic value of options exercised	2	13	18
Tax benefit of options exercised	0	5	7
Mississippi Power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value for options outstanding	1
Aggregate intrinsic value for options exercisable	1
Intrinsic value of options exercised	1	2	4
Tax benefit of options exercised	$ 0	$ 1	$ 2

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	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Jul. 01, 2016
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period			3 years
Equity instrument, granted (in shares)			0.7
Total compensation cost for award recognized in income			$ 27	$ 25
Total compensation cost for award recognized in income, tax benefit			$ 7	$ 10
Total unrecognized compensation cost related to award, weighted average period			16 months
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		$ 43.81	$ 49.25
Merger-related expenses			$ 13
Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Merger-related expenses	$ 41		$ 0	$ 0
Southern Company Gas | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period			3 years
Southern Company Gas | Restricted Stock Units (RSUs), Pre-acquisition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost for award recognized in income	13		$ 2	8
Total compensation cost for award recognized in income, tax benefit	4		$ 1	4
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	4		$ 5	12
Tax credit carryforward	$ 1		2	$ 6
Compensation not yet recognized			$ 2
Total unrecognized compensation cost related to award, weighted average period			6 months
Southern Company Gas | Predecessor
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Merger-related expenses		$ 56
Southern Company Gas | Predecessor | Cash and Stock-based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost for award recognized in income		$ 24
Southern Company | Southern Company Gas
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Business acquisition share price (in dollars per share)					$ 66
Conversion ratio, percentage of underlying stock award units					125.00%

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Weather derivative premium	$ 8	$ 11
Collateral already posted, aggregate fair value	277	193
Recurring
Assets:
Foreign currency derivatives	75
Non-qualified deferred compensation trusts:
Cash equivalents	766	1,455
Other investments	12	10
Total	3,387	3,995
Liabilities:
Contingent consideration	21	22
Total	1,057	816
Recurring | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	708	772
Recurring | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	226	286
Recurring | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	261	251
Recurring | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	83	68
Recurring | Pooled funds – fixed income
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	14
Recurring | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	314	336
Recurring | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	68	57
Recurring | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	29
Recurring | Cash and cash equivalents
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	16
Recurring | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	38	31
Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	761	570
Liabilities:
Energy-related derivatives	964	733
Recurring | Interest rate derivatives
Assets:
Interest rate derivatives		1
Liabilities:
Interest rate derivatives	49	38
Recurring | Foreign currency derivatives
Assets:
Foreign currency derivatives	129
Liabilities:
Foreign currency derivatives	23	23
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Foreign currency derivatives	0
Non-qualified deferred compensation trusts:
Cash equivalents	765	1,455
Other investments	0	9
Total	1,962	2,587
Liabilities:
Contingent consideration	0	0
Total	648	480
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	601	690
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	53	62
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds – fixed income
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	24	21
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	16
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	34	19
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	469	331
Liabilities:
Energy-related derivatives	648	480
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives
Assets:
Interest rate derivatives		0
Liabilities:
Interest rate derivatives	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign currency derivatives
Assets:
Foreign currency derivatives	0
Liabilities:
Foreign currency derivatives	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Foreign currency derivatives	75
Non-qualified deferred compensation trusts:
Cash equivalents	1	0
Other investments	12	0
Total	1,380	1,378
Liabilities:
Contingent consideration	0	0
Total	388	314
Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	107	82
Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	173	224
Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	261	251
Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	83	68
Recurring | Significant Other Observable Inputs (Level 2) | Pooled funds – fixed income
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	14
Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	290	315
Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	68	57
Recurring | Significant Other Observable Inputs (Level 2) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Recurring | Significant Other Observable Inputs (Level 2) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	4	12
Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	292	239
Liabilities:
Energy-related derivatives	316	253
Recurring | Significant Other Observable Inputs (Level 2) | Interest rate derivatives
Assets:
Interest rate derivatives		1
Liabilities:
Interest rate derivatives	49	38
Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives
Assets:
Foreign currency derivatives	129
Liabilities:
Foreign currency derivatives	23	23
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Foreign currency derivatives	0
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Other investments	0	1
Total	0	1
Liabilities:
Contingent consideration	21	22
Total	21	22
Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Pooled funds – fixed income
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Recurring | Significant Unobservable Inputs (Level 3) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Assets:
Interest rate derivatives		0
Liabilities:
Interest rate derivatives	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Foreign currency derivatives
Assets:
Foreign currency derivatives	0
Liabilities:
Foreign currency derivatives	0	0
Recurring | Fair Value Measured at Net Asset Value Per Share
Non-qualified deferred compensation trusts:
Total	45	29
Recurring | Fair Value Measured at Net Asset Value Per Share | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	29
Alabama Power
Assets:
Energy-related derivatives	6	4
Liabilities:
Energy-related derivatives	10	10
Alabama Power | Recurring
Non-qualified deferred compensation trusts:
Cash equivalents	117	349
Other investments	12
Total	981	1,255
Alabama Power | Recurring | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	491	523
Alabama Power | Recurring | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	103	121
Alabama Power | Recurring | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	18	24
Alabama Power | Recurring | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1
Alabama Power | Recurring | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	159	181
Alabama Power | Recurring | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	23	18
Alabama Power | Recurring | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	29
Alabama Power | Recurring | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	6	6
Alabama Power | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	6	4
Liabilities:
Energy-related derivatives	10	10
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Non-qualified deferred compensation trusts:
Cash equivalents	116	349
Other investments	0
Total	595	880
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	396	442
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	53	62
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	24	21
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	6	6
Alabama Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2)
Non-qualified deferred compensation trusts:
Cash equivalents	1	0
Other investments	12
Total	341	346
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	95	81
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	50	59
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	18	24
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	135	160
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	23	18
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	6	4
Liabilities:
Energy-related derivatives	10	10
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3)
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Other investments	0
Total	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Alabama Power | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Alabama Power | Recurring | Fair Value Measured at Net Asset Value Per Share
Non-qualified deferred compensation trusts:
Total	45	29
Alabama Power | Recurring | Fair Value Measured at Net Asset Value Per Share | Private equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	29
Georgia Power
Assets:
Energy-related derivatives	6	6
Liabilities:
Energy-related derivatives	23	24
Georgia Power | Recurring
Non-qualified deferred compensation trusts:
Cash equivalents		690
Total	879	1,625
Liabilities:
Total	23	24
Georgia Power | Recurring | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	206	249
Georgia Power | Recurring | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	119	166
Georgia Power | Recurring | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	243	227
Georgia Power | Recurring | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	82	68
Georgia Power | Recurring | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	155	155
Georgia Power | Recurring | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	40
Georgia Power | Recurring | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	23	24
Georgia Power | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	6	6
Liabilities:
Energy-related derivatives	21	19
Georgia Power | Recurring | Interest rate derivatives
Liabilities:
Interest rate derivatives	2	5
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Non-qualified deferred compensation trusts:
Cash equivalents		690
Total	224	950
Liabilities:
Total	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	205	248
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	19	12
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Georgia Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives
Liabilities:
Interest rate derivatives	0	0
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2)
Non-qualified deferred compensation trusts:
Cash equivalents		0
Total	655	675
Liabilities:
Total	23	24
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	1	1
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	119	166
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	243	227
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	82	68
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	155	155
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	45	40
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	4	12
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	6	6
Liabilities:
Energy-related derivatives	21	19
Georgia Power | Recurring | Significant Other Observable Inputs (Level 2) | Interest rate derivatives
Liabilities:
Interest rate derivatives	2	5
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3)
Non-qualified deferred compensation trusts:
Cash equivalents		0
Total	0	0
Liabilities:
Total	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Other
Nuclear decommissioning trusts:
Nuclear decommissioning trusts	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Georgia Power | Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Liabilities:
Interest rate derivatives	0	0
Mississippi Power
Assets:
Energy-related derivatives	3	3
Liabilities:
Energy-related derivatives	9	9
Mississippi Power | Recurring
Non-qualified deferred compensation trusts:
Cash equivalents	255	224
Total	258	227
Mississippi Power | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	3	2
Liabilities:
Energy-related derivatives	9	9
Mississippi Power | Recurring | Interest rate derivatives
Assets:
Interest rate derivatives		1
Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Non-qualified deferred compensation trusts:
Cash equivalents	255	224
Total	255	224
Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Mississippi Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives
Assets:
Interest rate derivatives		0
Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2)
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Total	3	3
Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	3	2
Liabilities:
Energy-related derivatives	9	9
Mississippi Power | Recurring | Significant Other Observable Inputs (Level 2) | Interest rate derivatives
Assets:
Interest rate derivatives		1
Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3)
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Total	0	0
Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Mississippi Power | Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Assets:
Interest rate derivatives		0
Southern Power
Assets:
Energy-related derivatives	79	132
Liabilities:
Energy-related derivatives	31	36
Southern Power | Recurring
Non-qualified deferred compensation trusts:
Cash equivalents	46	21
Total	125	153
Liabilities:
Contingent consideration	21	22
Total	52	58
Southern Power | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	4	3
Liabilities:
Energy-related derivatives	8	13
Southern Power | Recurring | Foreign currency derivatives
Assets:
Foreign currency derivatives	75	129
Liabilities:
Foreign currency derivatives	23	23
Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Non-qualified deferred compensation trusts:
Cash equivalents	46	21
Total	46	21
Liabilities:
Contingent consideration	0	0
Total	0	0
Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Southern Power | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign currency derivatives
Assets:
Foreign currency derivatives	0	0
Liabilities:
Foreign currency derivatives	0	0
Southern Power | Recurring | Significant Other Observable Inputs (Level 2)
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Total	79	132
Liabilities:
Contingent consideration	0	0
Total	31	36
Southern Power | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	4	3
Liabilities:
Energy-related derivatives	8	13
Southern Power | Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives
Assets:
Foreign currency derivatives	75	129
Liabilities:
Foreign currency derivatives	23	23
Southern Power | Recurring | Significant Unobservable Inputs (Level 3)
Non-qualified deferred compensation trusts:
Cash equivalents	0	0
Total	0	0
Liabilities:
Contingent consideration	21	22
Total	21	22
Southern Power | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0	0
Liabilities:
Energy-related derivatives	0	0
Southern Power | Recurring | Significant Unobservable Inputs (Level 3) | Foreign currency derivatives
Assets:
Foreign currency derivatives	0	0
Liabilities:
Foreign currency derivatives	0	0
Southern Company Gas
Assets:
Energy-related derivatives	741	554
Liabilities:
Energy-related derivatives	909	660
Weather derivative premium	8	11
Collateral already posted, aggregate fair value	277	193
Southern Company Gas | Energy-related derivatives
Liabilities:
Collateral already posted, aggregate fair value		6
Southern Company Gas | Recurring
Non-qualified deferred compensation trusts:
Cash equivalents	40
Total	814
Southern Company Gas | Recurring | Domestic equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	11
Southern Company Gas | Recurring | Foreign equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	4
Southern Company Gas | Recurring | Pooled funds – fixed income
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	14
Southern Company Gas | Recurring | Cash and cash equivalents
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	4
Southern Company Gas | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives	741
Liabilities:
Energy-related derivatives	909
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Non-qualified deferred compensation trusts:
Cash equivalents	40
Total	513
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds – fixed income
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	4
Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives	469
Liabilities:
Energy-related derivatives	648
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2)
Non-qualified deferred compensation trusts:
Cash equivalents	0
Total	301
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	11
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	4
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Pooled funds – fixed income
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	14
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives	272
Liabilities:
Energy-related derivatives	261
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3)
Non-qualified deferred compensation trusts:
Cash equivalents	0
Total	0
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Pooled funds – fixed income
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Non-qualified deferred compensation trusts:
Non-qualified deferred compensation trusts	0
Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives	0
Liabilities:
Energy-related derivatives	$ 0
Predecessor | Southern Company Gas | Recurring | Energy-related derivatives
Assets:
Energy-related derivatives		554
Liabilities:
Energy-related derivatives		660
Predecessor | Southern Company Gas | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives
Assets:
Energy-related derivatives		331
Liabilities:
Energy-related derivatives		479
Predecessor | Southern Company Gas | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives
Assets:
Energy-related derivatives		223
Liabilities:
Energy-related derivatives		181
Predecessor | Southern Company Gas | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Assets:
Energy-related derivatives		0
Liabilities:
Energy-related derivatives		$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - Private equity - Alabama Power - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Alternative investment	$ 45	$ 29
Unfunded commitments	$ 50	$ 21

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments, Carrying Amount Not Equal to Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	$ 45,023	$ 48,151
Fair Value	44,824	51,348
Alabama Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	8,120	7,625
Fair Value	8,370	8,305
Georgia Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	9,838	11,777
Fair Value	9,800	12,531
Mississippi Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	1,579	2,086
Fair Value	1,546	2,076
Southern Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	5,017	5,841
Fair Value	4,980	6,079
Southern Company Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Amount	5,940	6,048
Fair Value	$ 5,965	$ 6,471

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)MMBTUMWh	Dec. 31, 2017USD ($)
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 | $	$ (19)
Collateral already posted, aggregate fair value | $	$ 277	$ 193
Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	431
Longest hedge date	2,022
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	2
Southern Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	15
Longest hedge date	2,020
Alabama Power
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	4
Alabama Power | Energy-related, Natural Gas
Derivative [Line Items]
Net Purchased mmBtu	74
Longest hedge date	2,022
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	153
Longest hedge date	2,022
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	63
Longest hedge date	2,022
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ (23)

Derivatives - Energy-Related De

Derivatives - Energy-Related Derivative Contracts (Details) - Energy-related, Natural Gas MMBTU in Millions	12 Months Ended
	Dec. 31, 2018MMBTU
Derivative [Line Items]
Net Purchased mmBtu	431
Longest Hedge Date	2,022
Longest Non-Hedge Date	2,029
Alabama Power
Derivative [Line Items]
Net Purchased mmBtu	74
Longest Hedge Date	2,022
Georgia Power
Derivative [Line Items]
Net Purchased mmBtu	153
Longest Hedge Date	2,022
Mississippi Power
Derivative [Line Items]
Net Purchased mmBtu	63
Longest Hedge Date	2,022
Southern Power
Derivative [Line Items]
Net Purchased mmBtu	15
Longest Hedge Date	2,020
Southern Company Gas
Derivative [Line Items]
Net Purchased mmBtu	120
Longest Hedge Date	2,021
Longest Non-Hedge Date	2,029
Long | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	4,159
Short | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	4,039

Derivatives - Interest Rate Der

Derivatives - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Derivative [Line Items]
Notional Amount	$ 2,000
Fair value gain (loss) at December 31, 2018	(49)
Southern Company | Maturity Date June 2020 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 300
Interest Rate Received	2.75%
Weighted Average Interest Rate Paid	0.92%
Fair value gain (loss) at December 31, 2018	$ (4)
Southern Company | Maturity Date June 2021 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Weighted Average Interest Rate Paid	0.87%
Fair value gain (loss) at December 31, 2018	$ (43)
Georgia Power | Maturity Date December 2019 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 200
Interest Rate Received	4.25%
Weighted Average Interest Rate Paid	2.46%
Fair value gain (loss) at December 31, 2018	$ (2)

Derivatives - Foreign Currency

Derivatives - Foreign Currency Derivatives (Details) - 12 months ended Dec. 31, 2018 - 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) at December 31, 2018	52
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) at December 31, 2018	$ 25
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) at December 31, 2018	$ 27

Derivatives - Financial Stateme

Derivatives - Financial Statement Presentation (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value	$ 277	$ 193
Weather derivative premium	8	11
Parent Company
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	837	700
Derivative asset, gross amount offset	(524)	(405)
Derivative asset, net amounts recognized in the balance sheets	313	295
Derivative liability, gross amounts recognized	1,036	794
Derivative liability, gross amounts offset	(801)	(598)
Derivative liability, gross amounts recognized in balance sheets	235	196
Parent Company | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	741	550
Derivative liability, gross amounts recognized	900	652
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	561	380
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	575	437
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	180	170
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	325	215
Alabama Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	6	4
Derivative asset, gross amount offset	(4)	(4)
Derivative asset, net amounts recognized in the balance sheets	2	0
Derivative liability, gross amounts recognized	10	10
Derivative liability, gross amounts offset	(4)	(4)
Derivative liability, gross amounts recognized in balance sheets	6	6
Georgia Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	6	6
Derivative asset, gross amount offset	(6)	(6)
Derivative asset, net amounts recognized in the balance sheets	0	0
Derivative liability, gross amounts recognized	23	24
Derivative liability, gross amounts offset	(6)	(6)
Derivative liability, gross amounts recognized in balance sheets	17	18
Mississippi Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	3	3
Derivative asset, gross amount offset	(2)	(2)
Derivative asset, net amounts recognized in the balance sheets	1	1
Derivative liability, gross amounts recognized	9	9
Derivative liability, gross amounts offset	(2)	(2)
Derivative liability, gross amounts recognized in balance sheets	7	7
Southern Power
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	79	132
Derivative asset, gross amount offset	(3)	(3)
Derivative asset, net amounts recognized in the balance sheets	76	129
Derivative liability, gross amounts recognized	31	36
Derivative liability, gross amounts offset	(3)	(3)
Derivative liability, gross amounts recognized in balance sheets	28	33
Southern Power | Not 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	0	2
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	0	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	0	2
Southern Company Gas
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	741	554
Derivative asset, gross amount offset	(508)	(390)
Derivative asset, net amounts recognized in the balance sheets	233	164
Derivative liability, gross amounts recognized	909	660
Derivative liability, gross amounts offset	(785)	(583)
Derivative liability, gross amounts recognized in balance sheets	124	77
Collateral already posted, aggregate fair value	277	193
Weather derivative premium	8	11
Southern Company Gas | Not Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	739	549
Derivative liability, gross amounts recognized	899	649
Southern Company Gas | Energy-related derivatives
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value		6
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	180	170
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	325	215
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	559	379
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	574	434
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	17	17
Derivative liability, gross amounts recognized	55	67
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	8	10
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	23	43
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	9	7
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	26	24
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	6	0
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	6	4
Derivative liability, gross amounts recognized	10	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	3	2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	4	6
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	3	2
Hedging Instruments for Regulatory Purposes | Alabama Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	6	4
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	6	6
Derivative liability, gross amounts recognized	21	19
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	2	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	8	9
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	4	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	13	10
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	3	2
Derivative liability, gross amounts recognized	9	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	1	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	3	6
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	2	1
Hedging Instruments for Regulatory Purposes | Mississippi Power | Energy-related derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	6	3
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	2	5
Derivative liability, gross amounts recognized	9	8
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	0
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	2	5
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	8	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	79	133
Derivative liability, gross amounts recognized	81	75
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	3	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	7	14
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	1	0
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	2	0
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	0	1
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	19	4
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	30	34
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	23	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	75	129
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	2	5
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	2	4
Cash Flow and Fair Value Hedging | Georgia Power | 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 | Georgia Power | Interest rate derivatives | Other deferred credits and liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	0	1
Cash Flow and Fair Value Hedging | Southern Power | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	79	132
Derivative liability, gross amounts recognized	31	34
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	3	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	6	11
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	1	0
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	2	0
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current assets | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross amounts recognized	0	0
Cash Flow and Fair Value Hedging | Southern Power | Foreign currency derivatives | Other current liabilities | Designated as Hedging Instrument
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross amounts recognized	23	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	75	129
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	0	0
Derivative liability, gross amounts recognized	1	3
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	$ 1	$ 3

Derivatives - Pre-Tax Effects o

Derivatives - Pre-Tax Effects of Unrealized Derivative Gains (Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 277	$ 193
Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(40)	(44)
Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(19)	(34)
Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(16)	(18)
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)	1	7
Energy-related derivatives | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		1
Alabama Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(6)	(6)
Alabama Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(3)	(4)
Alabama Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(3)	(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)	0	1
Alabama Power | Energy-related derivatives | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Georgia Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(15)	(13)
Georgia Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(6)	(7)
Georgia Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(9)	(6)
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
Georgia Power | Energy-related derivatives | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Mississippi Power | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(6)	(7)
Mississippi Power | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(2)	(5)
Mississippi Power | Energy-related derivatives | Other regulatory assets, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(4)	(2)
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
Mississippi Power | Energy-related derivatives | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		0
Southern Company Gas
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	277	193
Southern Company Gas | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(7)	3
Collateral already posted, aggregate fair value		6
Southern Company Gas | Energy-related derivatives | Other regulatory assets, current
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)	(8)	(4)
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)	$ 1	7
Southern Company Gas | Energy-related derivatives | Other regulatory liabilities, deferred
Derivatives, Fair Value [Line Items]
Total energy-related derivative gains (losses)		$ 0

Derivatives - Pre-Tax Effects_2

Derivatives - Pre-Tax Effects of Derivatives Designated as Cash Flow Hedging (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			$ (62)	$ 91	$ (220)
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			17	(47)	18
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			(1)	(2)	(180)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			(78)	140	(58)
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			(68)	102	(44)
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			10	(38)	14
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative			(78)	140	$ (58)
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		$ (3)	7	(9)
Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		2	7	(9)
Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		$ (5)	$ 0	$ 0
Predecessor | Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (64)
Predecessor | Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	0
Predecessor | Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (64)

Derivatives - Pre-Tax Effects_3

Derivatives - Pre-Tax Effects of Derivatives Designated as Cash Flow and Fair Value Hedging (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2018	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				$ (62)	$ 91	$ (220)
Depreciation and amortization				3,131	3,010	2,502
Interest expense, net of amounts capitalized				(1,842)	(1,694)	(1,317)
Other income (expense), net				114	163	50
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				17	(47)	18
Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		$ (1)		2	(2)	(1)
Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				7	(16)	2
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(1)	(2)	(180)
Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(21)	(21)	(18)
Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(12)	(22)	(21)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(78)	140	(58)
Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(24)	(23)	(13)
Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(60)	160	(82)
Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenue				1,539	1,601	613
Alabama Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization				764	736	703
Interest expense, net of amounts capitalized				(323)	(305)	(302)
Other income (expense), net				20	43	26
Alabama Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(6)	(6)	(6)
Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization				923	895	855
Interest expense, net of amounts capitalized				(397)	(419)	(388)
Other income (expense), net				115	104	81
Georgia Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(4)	(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	(3)	(1)
Mississippi Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization				169	161	132
Interest expense, net of amounts capitalized				(76)	(42)	(74)
Other income (expense), net				17	1	(2)
Mississippi Power | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(2)	(2)	3
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(68)	102	(44)
Depreciation and amortization				493	503	352
Interest expense, net of amounts capitalized				(183)	(191)	(117)
Other income (expense), net				23	1	6
Southern Power | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				10	(38)	14
Southern Power | Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				7	(17)	2
Southern Power | Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(78)	140	(58)
Southern Power | Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(24)	(23)	(13)
Southern Power | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative				(60)	159	$ (82)
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		(3)		7	(9)
Interest expense, net of amounts capitalized		(81)		(228)	(200)
Other income (expense), net		12		1	44
Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		2		7	(9)
Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative		(5)		0	0
Southern Company Gas | Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenue		$ 613		$ 1,539	$ 1,601
Predecessor | Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (1)
Predecessor | Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(64)
Interest expense, net of amounts capitalized			$ (96)
Other income (expense), net			3
Predecessor | Southern Company Gas | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	0
Predecessor | Southern Company Gas | Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(64)
Predecessor | Southern Company Gas | Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenue	$ 755		$ 755

Derivatives - Cumulative Basis

Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Securities due within one year
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	$ (498)	$ (746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	2	3
Securities due within one year | Georgia Power
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(498)	(746)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	2	3
Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(2,052)	(2,553)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	41	35
Long-term debt | 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	$ 1

Derivatives - Pre-Tax Effects_4

Derivatives - Pre-Tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Energy-related derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net			$ (126)	$ (86)	$ 38
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			(122)	(80)	33
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			(6)	(2)	3
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	(4)	$ 2
Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	$ 6		5	23
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net	3		19	24
Southern Company Gas | Energy-related derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	36		(128)	(82)
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	33		(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	$ 3		$ (6)	$ (2)
Predecessor | Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net		$ (162)
Predecessor | Southern Company Gas | Energy-related derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net		(63)
Predecessor | 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		(1)
Predecessor | 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		(62)
Predecessor | Southern Company Gas | Weather Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, gain (loss) on derivative, net		$ 3

Acquisitions and Dispositions -

Acquisitions and Dispositions - SO Acquisitions and Dispositions Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2019	Jul. 01, 2016	May 31, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total operating revenues													$ 23,495	$ 23,031	$ 19,896
Net income (loss) after dividends on preferred and preference stock				$ 269	$ 1,222	$ (127)	$ 936	$ 500	$ 1,109	$ (1,348)	$ 665		2,226	842	$ 2,448
PowerSecure International, Inc.
Business Acquisition [Line Items]
Business acquisition share price (in dollars per share)			$ 18.75
Business combination, consideration transferred, equity interests issued and issuable			$ 429
Southern Company Gas
Business Acquisition [Line Items]
Payments to acquire businesses		$ 8,000
Southern Company Gas
Business Acquisition [Line Items]
Total operating revenues												$ 1,652	3,909	3,920
Net income (loss) after dividends on preferred and preference stock				$ 78	$ 46	$ (31)	$ 279	$ (60)	$ 15	$ 49	$ 239	$ 114	$ 372	$ 243
Southern Company Gas | Southern Company
Business Acquisition [Line Items]
Business acquisition share price (in dollars per share)		$ 66
Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Business Acquisition [Line Items]
Cash proceeds from sale of business	$ 5,800
Indebtedness assumed	$ 1,300

Acquisitions and Dispositions_2

Acquisitions and Dispositions - Acquisitions and Dispositions Table (Details) $ in Millions	Jan. 26, 2018MW	Jul. 31, 2017MW	Jan. 06, 2017MW	Jul. 31, 2018MW	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Aug. 31, 2018	Dec. 31, 2017USD ($)	Jul. 01, 2016USD ($)	May 31, 2016USD ($)
Purchase Price Allocation
Goodwill					$ 6,251	$ 5,315		$ 6,268
Southern Company Gas
Purchase Price Allocation
Current assets									$ 1,557
Property, plant, and equipment									10,108
Goodwill									5,967
Intangible assets									400
Regulatory assets									1,118
Other assets									229
Current liabilities									(2,201)
Other liabilities									(4,742)
Long-term debt									(4,261)
Noncontrolling interest									(174)
Total purchase price									8,001
PowerSecure International, Inc.
Purchase Price Allocation
Current assets										$ 172
Property, plant, and equipment										46
Goodwill										284
Intangible assets										106
Other assets										4
Current liabilities										(121)
Other liabilities										(14)
Long-term debt, including current portion										(48)
Total purchase price										$ 429
Southern Power
Purchase Price Allocation
Other assets								5
Restricted cash								16
CWIP								534
Accounts payable								(16)
Total purchase price								$ 539
Southern Power | Gaskell West 1
Acquisition Information, by Acquisition [Abstract]
Approximate Nameplate Capacity (MW) | MW	20
PPA Contract Period	20 years
Southern Power | Bethel
Acquisition Information, by Acquisition [Abstract]
Approximate Nameplate Capacity (MW) | MW			276
PPA Contract Period			12 years
Southern Power | Cactus Flats
Acquisition Information, by Acquisition [Abstract]
Approximate Nameplate Capacity (MW) | MW		148		148
Minimum | Southern Power | Cactus Flats
Acquisition Information, by Acquisition [Abstract]
PPA Contract Period		12 years		12 years
Maximum | Southern Power | Cactus Flats
Acquisition Information, by Acquisition [Abstract]
PPA Contract Period		15 years		15 years
Gaskell West 1 | Class B Membership Interest | Southern Power | Gaskell West 1
Acquisition Information, by Acquisition [Abstract]
Ownership Percentage	100.00%
Cactus Flats | Southern Power | Cactus Flats
Acquisition Information, by Acquisition [Abstract]
Ownership Percentage		100.00%
Cactus Flats | Class B Membership Interest | Southern Power | Cactus Flats
Acquisition Information, by Acquisition [Abstract]
Ownership Percentage							100.00%
Bethel | Southern Power | Bethel
Acquisition Information, by Acquisition [Abstract]
Ownership Percentage			100.00%
Predecessor | Southern Company Gas
Purchase Price Allocation
Current assets									1,474
Property, plant, and equipment									10,148
Goodwill									1,813
Intangible assets									101
Regulatory assets									679
Other assets									273
Current liabilities									(2,205)
Other liabilities									(4,600)
Long-term debt									(3,709)
Noncontrolling interest									(41)
Total purchase price									$ 3,933
Change in Basis
Current assets					83
Property, plant, and equipment					(40)
Goodwill					4,154
Other intangible assets					299
Regulatory assets					439
Other assets					(44)
Current liabilities					4
Other liabilities					(142)
Long-term debt					(552)
Contingently redeemable noncontrolling interest					(133)
Total purchase price/equity					$ 4,068

Acquisitions and Dispositions_3

Acquisitions and Dispositions - SPC Acquisitions and Dispositions Narrative (Details)

Dec. 11, 2018USD ($)wind_farm

Dec. 04, 2018USD ($)

Nov. 05, 2018USD ($)MW

May 22, 2018USD ($)

Jun. 30, 2019USD ($)

Sep. 30, 2018operating_facility

May 31, 2018USD ($)

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Mar. 31, 2019USD ($)

Jul. 31, 2018MW

Jan. 26, 2018MW

Jul. 31, 2017MW

Business Acquisition [Line Items]

Aggregate purchase price

$ 539,000,000

Construction work in progress

7,254,000,000

$ 6,904,000,000

Impairment charges

210,000,000

0

$ 0

Assets held for sale

393,000,000

12,000,000

Sale of noncontrolling interests

1,273,000,000

Southern Power

Business Acquisition [Line Items]

Revenue of acquiree

15,000,000

Net income of acquiree

17,000,000

Construction work in progress

430,000,000

511,000,000

Impairment charges

156,000,000

$ 0

$ 0

Sale of noncontrolling interests

[1]

$ 1,273,000,000

Number of wind facilities | operating_facility

8

Distribution made to limited partner, cash distributions paid, percentage

67.00%

Southern Power | Gaskell West 1

Business Acquisition [Line Items]

Approximate Nameplate Capacity (MW) | MW

20

Southern Power | Cactus Flats

Business Acquisition [Line Items]

Approximate Nameplate Capacity (MW) | MW

148

148

Southern Power | Minimum | Series of Business Acquisitions

Business Acquisition [Line Items]

Aggregate construction costs

$ 575,000,000

Southern Power | Maximum | Series of Business Acquisitions

Business Acquisition [Line Items]

Aggregate construction costs

640,000,000

Series of Construction Projects | Southern Power

Business Acquisition [Line Items]

Construction work in progress

289,000,000

Wind Generating Facility | Southern Power

Business Acquisition [Line Items]

Impairment charges

$ 36,000,000

Scenario, Forecast | Wind Generating Facility | Southern Power

Business Acquisition [Line Items]

Project qualification for production tax credits, percentage

80.00%

100.00%

Assets held for sale

$ 53,000,000

SP Solar Holdings I, LP | Southern Power

Business Acquisition [Line Items]

Sale of equity interest in limited partnership (percent)

33.00%

SP Solar Holdings I, LP | SP Solar Holdings I, LP | Southern Power

Business Acquisition [Line Items]

Sale of equity interest in limited partnership (percent)

33.00%

Proceeds from sale of equity method investments

$ 1,200,000,000

Sale of noncontrolling interests

511,000,000

SP Wind

Business Acquisition [Line Items]

Number of wind facilities | wind_farm

8

SP Wind | Southern Power

Business Acquisition [Line Items]

Sale of equity interest in limited partnership (percent)

100.00%

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%

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

$ 1,200,000,000

Common stockholders' equity | Southern Power

Business Acquisition [Line Items]

Sale of noncontrolling interests

$ (410,000,000)

$ (417,000,000)

[1]

Disposal Group, Held-for-sale, Not Discontinued Operations | Florida Plants | Southern Power

Business Acquisition [Line Items]

Cash proceeds from sale of business

$ 203,000,000

Asset impairment charge

$ 119,000,000

After tax impairment charges

$ 89,000,000

Disposal Group, Held-for-sale, Not Discontinued Operations | Mankato | Southern Power

Business Acquisition [Line Items]

Cash proceeds from sale of business

$ 650,000,000

Approximate Nameplate Capacity (MW) | MW

385

Disposal Group, Held-for-sale, Not Discontinued Operations | Mankato | Scenario, Forecast | Southern Power

Business Acquisition [Line Items]

Decrease per day after June 1, 2019

$ 66,667

Maximum price decrease

$ 15,000,000

[1]

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

Acquisitions and Dispositions_4

Acquisitions and Dispositions - Pro Forma Consolidated Information (Details) - Southern Company Gas $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)$ / shares
Business Acquisition [Line Items]
Operating revenues (in millions) | $	$ 21,791
Net income attributable to Southern Company (in millions) | $	$ 2,591
Basic EPS (in dollars per share) | $ / shares	$ 2.70
Diluted EPS (in dollars per share) | $ / shares	$ 2.68

Acquisitions and Dispositions_5

Acquisitions and Dispositions - Construction Projects (Details) - Southern Power - MW	Jul. 31, 2017	Jul. 31, 2018	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Aug. 31, 2018	May 31, 2018
Cactus Flats
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	148	148
Minimum | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	12 years	12 years
Maximum | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	15 years	15 years
Cactus Flats | Cactus Flats
Business Acquisition [Line Items]
Ownership Percentage	100.00%
Cactus Flats | Class B Membership Interest | Cactus Flats
Business Acquisition [Line Items]
Ownership Percentage						100.00%
Wild Horse Mountain | Wild Horse Mountain
Business Acquisition [Line Items]
Ownership Percentage							100.00%
Wild Horse Mountain | Class B Membership Interest | Wild Horse Mountain
Business Acquisition [Line Items]
Ownership Percentage							100.00%
Reading | Reading
Business Acquisition [Line Items]
Ownership Percentage						100.00%
Reading | Class B Membership Interest | Reading
Business Acquisition [Line Items]
Ownership Percentage						100.00%
Scenario, Forecast | Mankato Expansion
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					385
PPA Contract Period					20 years
Scenario, Forecast | Wild Horse Mountain
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				100
PPA Contract Period				20 years
Scenario, Forecast | Reading
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			200
PPA Contract Period			12 years

Acquisitions and Dispositions_6

Acquisitions and Dispositions - GAS Acquisitions and Dispositions Narrative (Details)	Jul. 29, 2018USD ($)	Jul. 01, 2018USD ($)utility	Jun. 04, 2018USD ($)	Mar. 31, 2017USD ($)	Jul. 31, 2018utility	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2016USD ($)mi	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)mi
Business Acquisition [Line Items]
Payments to acquire equity method investments											$ 114,000,000	$ 152,000,000	$ 1,444,000,000
Goodwill impairment						$ 0					42,000,000
Number of natural gas distribution utilities sold | utility					3
Southern Company Gas
Business Acquisition [Line Items]
Payments to acquire equity method investments										$ 1,444,000,000	110,000,000	145,000,000
Goodwill impairment						$ 0			$ 42,000,000	$ 0	$ 42,000,000	0
Number of natural gas distribution utilities sold | utility					3
Southern Company Gas | Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Pipeline infrastructure | mi										7,000			7,000
Southern Company Gas | Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Ownership percentage, equity method investment						50.00%					50.00%
Payments to acquire equity method investments				$ 50,000,000
Tax Cuts And Jobs Act Of 2017, incomplete accounting, provisional income tax expense (benefit)												$ 104,000,000
Southern Company Gas | Southern Natural Gas Company, LLC | Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Ownership percentage, equity method investment										50.00%			50.00%
Equity method investment, aggregate cost										$ 1,400,000,000			$ 1,400,000,000
Equity method investment, difference between carrying amount and underlying equity										$ 700,000,000			$ 700,000,000
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)
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)
Tax on sale of business			$ 34,000,000
Goodwill impairment									$ 42,000,000		$ 42,000,000
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
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
Subsidiaries
Business Acquisition [Line Items]
Proceeds from sale of oil and gas property and equipment		$ 1,700,000,000

Acquisitions and Dispositions_7

Acquisitions and Dispositions - Held For Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations $ in Millions	Dec. 31, 2018USD ($)
Assets Held for Sale:
Current assets	$ 393
Total property, plant, and equipment	4,623
Other non-current assets	727
Total Assets Held for Sale	5,743
Liabilities Held for Sale:
Current liabilities	425
Long-term debt	1,286
Accumulated deferred income taxes	618
Other non-current liabilities	932
Total Liabilities Held for Sale	3,261
Southern Power
Assets Held for Sale:
Current assets	8
Total property, plant, and equipment	576
Other non-current assets	0
Total Assets Held for Sale	584
Liabilities Held for Sale:
Current liabilities	15
Long-term debt	0
Accumulated deferred income taxes	0
Other non-current liabilities	0
Total Liabilities Held for Sale	$ 15

Acquisitions and Dispositions_8

Acquisitions and Dispositions - Pre-tax Profit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gulf Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 140	$ 229	$ 231
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	$ 37

Segment and Related Informati_3

Segment and Related Information - Narrative (Details) $ in Millions	1 Months Ended	6 Months Ended	12 Months Ended
	Jul. 31, 2018utility	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)statepipelinesegment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities sold | utility	3
Total operating revenues			$ 23,495	$ 23,031	$ 19,896
Traditional Operating Companies
Segment Reporting Information [Line Items]
Number of states in which entity operates (states) | state			4
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues			$ 2,205	2,075	1,577
Southern Company Gas
Segment Reporting Information [Line Items]
Number of states in which entity operates (states) | state			4
Number of natural gas distribution utilities sold | utility	3
Total operating revenues		$ 1,652	$ 3,909	3,920
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%
Traditional Electric Operating Companies | Southern Company Gas
Segment Reporting Information [Line Items]
Natural gas revenues			$ 32	23	11
Southern Power | Southern Company Gas
Segment Reporting Information [Line Items]
Natural gas revenues			119	119	17
Wholesale revenues, affiliates | Southern Power
Segment Reporting Information [Line Items]
Total operating revenues			$ 435	$ 392	$ 419
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 and Products and Services (Details)	3 Months Ended								6 Months Ended		10 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)utility	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Oct. 31, 2016USD ($)	Dec. 31, 2018USD ($)utility	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Total operating revenues												$ 23,495,000,000	$ 23,031,000,000	$ 19,896,000,000
Depreciation and amortization												3,131,000,000	3,010,000,000	2,502,000,000
Interest income												38,000,000	26,000,000	20,000,000
Earnings from equity method investments											$ 15,000,000	148,000,000	106,000,000	59,000,000
Interest expense												1,842,000,000	1,694,000,000	1,317,000,000
Income taxes												449,000,000	142,000,000	951,000,000
Segment net income (loss)	$ 269,000,000	$ 1,222,000,000	$ (127,000,000)	$ 936,000,000	$ 500,000,000	$ 1,109,000,000	$ (1,348,000,000)	$ 665,000,000				2,226,000,000	842,000,000	2,448,000,000
Goodwill	5,315,000,000				6,268,000,000				$ 6,251,000,000			5,315,000,000	6,268,000,000	6,251,000,000
Total Assets	116,914,000,000				111,005,000,000				109,697,000,000			116,914,000,000	111,005,000,000	109,697,000,000
Gross property additions												8,205,000,000	5,984,000,000	7,624,000,000
Depreciation and amortization												3,549,000,000	3,457,000,000	2,923,000,000
Operating Income	578,000,000	2,174,000,000	63,000,000	1,376,000,000	739,000,000	1,991,000,000	(1,649,000,000)	1,252,000,000				4,191,000,000	2,333,000,000	4,486,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on plants under construction												1,097,000,000	3,362,000,000	428,000,000
Impairment charges												210,000,000	0	0
Gain (loss) on asset sales												301,000,000	42,000,000	2,000,000
Goodwill impairment	0											42,000,000
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)					264,000,000
Kemper IGCC
Segment and Related Information (Textual) [Abstract]
After tax charge to income												722,000,000	2,400,000,000	264,000,000
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												18,571,000,000	18,540,000,000	17,941,000,000
Depreciation and amortization												2,565,000,000	2,457,000,000	2,233,000,000
Interest income												31,000,000	21,000,000	13,000,000
Earnings from equity method investments												(1,000,000)	1,000,000	2,000,000
Interest expense												1,035,000,000	1,011,000,000	931,000,000
Income taxes												207,000,000	82,000,000	1,091,000,000
Segment net income (loss)												2,304,000,000	878,000,000	2,571,000,000
Goodwill	2,000,000				2,000,000				2,000,000			2,000,000	2,000,000	2,000,000
Total Assets	93,959,000,000				87,085,000,000				86,994,000,000			93,959,000,000	87,085,000,000	86,994,000,000
Gross property additions												6,392,000,000	4,104,000,000	6,966,000,000
Traditional Operating Companies
Segment and Related Information (Textual) [Abstract]
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)													367,000,000
Traditional Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												16,843,000,000	16,884,000,000	16,803,000,000
Depreciation and amortization												2,072,000,000	1,954,000,000	1,881,000,000
Interest income												23,000,000	14,000,000	6,000,000
Earnings from equity method investments												(1,000,000)	1,000,000	2,000,000
Interest expense												852,000,000	820,000,000	814,000,000
Income taxes												371,000,000	1,021,000,000	1,286,000,000
Segment net income (loss)												2,117,000,000	(193,000,000)	2,233,000,000
Goodwill	0				0				0			0	0	0
Total Assets	79,382,000,000				72,204,000,000				72,141,000,000			79,382,000,000	72,204,000,000	72,141,000,000
Gross property additions												6,077,000,000	3,836,000,000	4,852,000,000
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												2,205,000,000	2,075,000,000	1,577,000,000
Depreciation and amortization												493,000,000	503,000,000	352,000,000
Interest income												8,000,000	7,000,000	7,000,000
Earnings from equity method investments												0	0	0
Interest expense												183,000,000	191,000,000	117,000,000
Income taxes												(164,000,000)	(939,000,000)	(195,000,000)
Segment net income (loss)												187,000,000	1,071,000,000	338,000,000
Goodwill	2,000,000				2,000,000				2,000,000			2,000,000	2,000,000	2,000,000
Total Assets	14,883,000,000				15,206,000,000				15,169,000,000			14,883,000,000	15,206,000,000	15,169,000,000
Gross property additions												315,000,000	268,000,000	2,114,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues												3,909,000,000	3,920,000,000	1,652,000,000
Depreciation and amortization												500,000,000	501,000,000	238,000,000
Interest income												4,000,000	3,000,000	2,000,000
Earnings from equity method investments												148,000,000	106,000,000	60,000,000
Interest expense												228,000,000	200,000,000	81,000,000
Income taxes												464,000,000	367,000,000	76,000,000
Segment net income (loss)												372,000,000	243,000,000	114,000,000
Goodwill	5,015,000,000				5,967,000,000				5,967,000,000			5,015,000,000	5,967,000,000	5,967,000,000
Total Assets	21,448,000,000				22,987,000,000				21,853,000,000			21,448,000,000	22,987,000,000	21,853,000,000
Gross property additions												1,399,000,000	1,525,000,000	618,000,000
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												1,213,000,000	741,000,000	463,000,000
Depreciation and amortization												66,000,000	52,000,000	31,000,000
Interest income												8,000,000	11,000,000	20,000,000
Earnings from equity method investments												2,000,000	(1,000,000)	(3,000,000)
Interest expense												580,000,000	490,000,000	317,000,000
Income taxes												(222,000,000)	(307,000,000)	(216,000,000)
Segment net income (loss)												(453,000,000)	(279,000,000)	(230,000,000)
Goodwill	298,000,000				299,000,000				282,000,000			298,000,000	299,000,000	282,000,000
Total Assets	3,285,000,000				2,552,000,000				2,474,000,000			3,285,000,000	2,552,000,000	2,474,000,000
Gross property additions												414,000,000	355,000,000	41,000,000
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues												(198,000,000)	(170,000,000)	(160,000,000)
Depreciation and amortization												0	0	0
Interest income												(5,000,000)	(9,000,000)	(15,000,000)
Earnings from equity method investments												(1,000,000)	0	0
Interest expense												(1,000,000)	(7,000,000)	(12,000,000)
Income taxes												0	0	0
Segment net income (loss)												3,000,000	0	(7,000,000)
Goodwill	0				0				0			0	0	0
Total Assets	(1,778,000,000)				(1,619,000,000)				(1,624,000,000)			(1,778,000,000)	(1,619,000,000)	(1,624,000,000)
Gross property additions												0	0	(1,000,000)
Intersegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues												(477,000,000)	(419,000,000)	(439,000,000)
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
Total Assets	(306,000,000)				(325,000,000)				(316,000,000)			(306,000,000)	(325,000,000)	(316,000,000)
Gross property additions												0	0	0
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues												2,205,000,000	2,075,000,000	1,577,000,000
Depreciation and amortization												493,000,000	503,000,000	352,000,000
Interest expense												183,000,000	191,000,000	117,000,000
Income taxes	75,000,000											(164,000,000)	(939,000,000)	(195,000,000)
Segment net income (loss)	(60,000,000)	146,000,000	45,000,000	115,000,000	793,000,000	154,000,000	104,000,000	66,000,000				187,000,000	1,071,000,000	338,000,000
Total Assets	14,883,000,000				15,206,000,000							14,883,000,000	15,206,000,000
Depreciation and amortization												524,000,000	536,000,000	370,000,000
Operating Income	30,000,000	136,000,000	16,000,000	60,000,000	32,000,000	159,000,000	112,000,000	65,000,000				242,000,000	368,000,000	290,000,000
Segment and Related Information (Textual) [Abstract]
Impairment charges												156,000,000	0	0
After tax impairment charges												117,000,000
Gain (loss) on asset sales												(2,000,000)	0	0
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)					(743,000,000)
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									1,652,000,000			3,909,000,000	3,920,000,000
Earnings from equity method investments									60,000,000			148,000,000	106,000,000
Interest expense									81,000,000			228,000,000	200,000,000
Income taxes									76,000,000			464,000,000	367,000,000
Segment net income (loss)	78,000,000	46,000,000	(31,000,000)	279,000,000	(60,000,000)	15,000,000	49,000,000	239,000,000	114,000,000			372,000,000	243,000,000
Goodwill	5,015,000,000				5,967,000,000							5,015,000,000	5,967,000,000
Total Assets	21,448,000,000				22,987,000,000				21,853,000,000			21,448,000,000	22,987,000,000	21,853,000,000
Gross property additions									632,000,000			1,521,000,000	1,508,000,000
Depreciation and amortization									238,000,000			500,000,000	501,000,000
Operating Income	104,000,000	$ 374,000,000	$ 49,000,000	388,000,000	109,000,000	$ 67,000,000	$ 95,000,000	$ 389,000,000	199,000,000			915,000,000	660,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on asset sales									0			291,000,000	0
Goodwill impairment	0			42,000,000					0			42,000,000	0
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)					93,000,000
Southern Company Gas | Gas Distribution Operations
Segment Reporting Information [Line Items]
Goodwill	4,034,000,000				4,702,000,000							4,034,000,000	4,702,000,000
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
Goodwill impairment												0
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Goodwill	981,000,000				1,265,000,000							981,000,000	1,265,000,000
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)
Goodwill impairment												42,000,000
Southern Company Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues									(102,000,000)			(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	(11,582,000,000)				(14,039,000,000)				(14,167,000,000)			(11,582,000,000)	(14,039,000,000)	(14,167,000,000)
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									1,723,000,000			3,930,000,000	4,090,000,000
Earnings from equity method investments									58,000,000			145,000,000	103,000,000
Interest expense									119,000,000			227,000,000	191,000,000
Income taxes									76,000,000			495,000,000	311,000,000
Segment net income (loss)									125,000,000			435,000,000	358,000,000
Total Assets	21,918,000,000				24,300,000,000				24,323,000,000			21,918,000,000	24,300,000,000	24,323,000,000
Gross property additions									618,000,000			1,467,000,000	1,457,000,000
Depreciation and amortization									221,000,000			453,000,000	457,000,000
Operating Income									251,000,000			1,013,000,000	717,000,000
Southern Company Gas | Operating Segments | All other
Segment Reporting Information [Line Items]
Total operating revenues									31,000,000			55,000,000	64,000,000
Earnings from equity method investments									2,000,000			3,000,000	3,000,000
Interest expense									(38,000,000)			1,000,000	9,000,000
Income taxes									0			(31,000,000)	56,000,000
Segment net income (loss)									(11,000,000)			(63,000,000)	(115,000,000)
Total Assets	11,112,000,000				12,726,000,000				11,697,000,000			11,112,000,000	12,726,000,000	11,697,000,000
Gross property additions									14,000,000			54,000,000	51,000,000
Depreciation and amortization									17,000,000			47,000,000	44,000,000
Operating Income									(52,000,000)			(98,000,000)	(57,000,000)
Southern Company Gas | Operating Segments | Gas Distribution Operations
Segment Reporting Information [Line Items]
Total operating revenues									1,342,000,000			3,186,000,000	3,207,000,000
Earnings from equity method investments									0			0	0
Interest expense									105,000,000			178,000,000	153,000,000
Income taxes									51,000,000			409,000,000	178,000,000
Segment net income (loss)									77,000,000			334,000,000	353,000,000
Total Assets	17,266,000,000				19,358,000,000				19,453,000,000			17,266,000,000	19,358,000,000	19,453,000,000
Gross property additions									561,000,000			1,429,000,000	1,330,000,000
Depreciation and amortization									185,000,000			409,000,000	391,000,000
Operating Income									225,000,000			904,000,000	645,000,000
Segment and Related Information (Textual) [Abstract]
Revenue on disposition									168,000,000			244,000,000	399,000,000
Southern Company Gas | Operating Segments | Gas Pipeline Investments
Segment Reporting Information [Line Items]
Total operating revenues									3,000,000			32,000,000	17,000,000
Earnings from equity method investments									58,000,000			145,000,000	103,000,000
Interest expense									10,000,000			34,000,000	26,000,000
Income taxes									21,000,000			28,000,000	109,000,000
Segment net income (loss)									29,000,000			103,000,000	(22,000,000)
Total Assets	1,763,000,000				1,699,000,000				1,659,000,000			1,763,000,000	1,699,000,000	1,659,000,000
Gross property additions									51,000,000			32,000,000	117,000,000
Depreciation and amortization									0			5,000,000	2,000,000
Operating Income									1,000,000			20,000,000	10,000,000
Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									24,000,000			144,000,000	6,000,000
Earnings from equity method investments									0			0	0
Interest expense									3,000,000			9,000,000	7,000,000
Income taxes									(3,000,000)			4,000,000	0
Segment net income (loss)									0			38,000,000	(57,000,000)
Total Assets	1,302,000,000				1,096,000,000				1,127,000,000			1,302,000,000	1,096,000,000	1,127,000,000
Gross property additions									1,000,000			0	1,000,000
Less Gross Gas Costs									6,116,000,000			7,262,000,000	6,627,000,000
Depreciation and amortization									1,000,000			2,000,000	2,000,000
Operating Income									(2,000,000)			70,000,000	(51,000,000)
Southern Company Gas | Operating Segments | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues									354,000,000			568,000,000	860,000,000
Earnings from equity method investments									0			0	0
Interest expense									1,000,000			6,000,000	5,000,000
Income taxes									7,000,000			54,000,000	24,000,000
Segment net income (loss)									19,000,000			(40,000,000)	84,000,000
Total Assets	$ 1,587,000,000				$ 2,147,000,000				2,084,000,000			1,587,000,000	2,147,000,000	$ 2,084,000,000
Gross property additions									5,000,000			6,000,000	9,000,000
Depreciation and amortization									35,000,000			37,000,000	62,000,000
Operating Income									27,000,000			19,000,000	113,000,000
Segment and Related Information (Textual) [Abstract]
Revenue on disposition									56,000,000			55,000,000	129,000,000
Predecessor | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues										$ 1,905,000,000
Earnings from equity method investments										2,000,000
Interest expense										96,000,000
Income taxes										87,000,000
Segment net income (loss)										131,000,000
Gross property additions										548,000,000
Depreciation and amortization										206,000,000
Operating Income										323,000,000
EBIT										328,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on asset sales										0
Goodwill impairment										0
Predecessor | Southern Company Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues										(102,000,000)
Gross property additions										0
Depreciation and amortization										0
Operating Income										0
EBIT										0
Predecessor | Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues										1,981,000,000
Gross property additions										529,000,000
Depreciation and amortization										190,000,000
Operating Income										396,000,000
EBIT										397,000,000
Predecessor | Southern Company Gas | Operating Segments | All other
Segment Reporting Information [Line Items]
Total operating revenues										26,000,000
Gross property additions										19,000,000
Depreciation and amortization										16,000,000
Operating Income										(73,000,000)
EBIT										(69,000,000)
Predecessor | Southern Company Gas | Operating Segments | Gas Distribution Operations
Segment Reporting Information [Line Items]
Total operating revenues										1,575,000,000
Gross property additions										484,000,000
Depreciation and amortization										178,000,000
Operating Income										353,000,000
EBIT										353,000,000
Segment and Related Information (Textual) [Abstract]
Revenue on disposition										215,000,000
Predecessor | Southern Company Gas | Operating Segments | Gas Pipeline Investments
Segment Reporting Information [Line Items]
Total operating revenues										3,000,000
Gross property additions										40,000,000
Depreciation and amortization										0
Operating Income										3,000,000
EBIT										3,000,000
Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues										(32,000,000)
Gross property additions										1,000,000
Less Gross Gas Costs										2,675,000,000
Depreciation and amortization										1,000,000
Operating Income										(69,000,000)
EBIT										(68,000,000)
Predecessor | Southern Company Gas | Operating Segments | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues										435,000,000
Gross property additions										4,000,000
Depreciation and amortization										11,000,000
Operating Income										109,000,000
EBIT										109,000,000
Segment and Related Information (Textual) [Abstract]
Revenue on disposition										64,000,000
Third Party Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									5,807,000,000			6,955,000,000	6,152,000,000
Third Party Gross Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues										2,500,000,000
Intercompany Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									333,000,000			451,000,000	481,000,000
Intercompany Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues										143,000,000
Total Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									$ 6,140,000,000			$ 7,406,000,000	$ 6,633,000,000
Total Gross Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues										$ 2,643,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Number of natural gas distribution utilities disposed | utility	3											3
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Gain (loss) on asset sales												$ 291,000,000
Net gain (loss) on dispositions, net of tax												(51,000,000)
Goodwill impairment				$ 42,000,000								$ 42,000,000

Segment and Related Informati_5

Segment and Related Information - Electric Utilities' Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Total operating revenues	$ 23,495	$ 23,031	$ 19,896
Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	15,222	15,330	15,234
Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	664	681	698
Electric Utilities
Revenue from External Customer [Line Items]
Total operating revenues	18,571	18,540	17,941
Electric Utilities | Retail electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	15,222	15,330	15,234
Electric Utilities | Wholesale
Revenue from External Customer [Line Items]
Total operating revenues	2,516	2,426	1,926
Electric Utilities | Other electric revenues
Revenue from External Customer [Line Items]
Total operating revenues	833	784	781
Electric Utilities | Electric Utilities
Revenue from External Customer [Line Items]
Total operating revenues	$ 18,571	$ 18,540	$ 17,941

Segment and Related Informati_6

Segment and Related Information - Gas Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total operating revenues	$ 23,495	$ 23,031	$ 19,896
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues	3,909	3,920	1,652
Southern Company Gas | Gas Distribution Operations
Segment Reporting Information [Line Items]
Total operating revenues	3,155	3,024	1,266
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues	568	860	354
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Total operating revenues	$ 186	$ 36	$ 32

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($)	Jun. 04, 2018	Jun. 30, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2017
Summarized quarterly financial information
Operating revenues			$ 5,337,000,000	$ 6,159,000,000	$ 5,627,000,000	$ 6,372,000,000	$ 5,629,000,000	$ 6,201,000,000	$ 5,430,000,000	$ 5,771,000,000
Operating Income			578,000,000	2,174,000,000	63,000,000	1,376,000,000	739,000,000	1,991,000,000	(1,649,000,000)	1,252,000,000			$ 4,191,000,000	$ 2,333,000,000	$ 4,486,000,000
Net Income (Loss)			269,000,000	1,222,000,000	(127,000,000)	936,000,000	500,000,000	1,109,000,000	(1,348,000,000)	665,000,000			2,226,000,000	842,000,000	2,448,000,000
Consolidated Net Income Attributable to Southern Company			278,000,000	$ 1,164,000,000	$ (154,000,000)	$ 938,000,000	496,000,000	$ 1,069,000,000	$ (1,381,000,000)	$ 658,000,000
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)							$ 264,000,000
Impairment charges													210,000,000	0	0
Income taxes													449,000,000	142,000,000	951,000,000
Goodwill impairment			$ 0										42,000,000
Gain (loss) on dispositions													$ (291,000,000)	$ (40,000,000)	$ 1,000,000
Basic (in dollars per share)			$ 0.27	$ 1.14	$ (0.15)	$ 0.93	$ 0.49	$ 1.07	$ (1.38)	$ 0.66			$ 2.18	$ 0.84	$ 2.57
Diluted (in dollars per share)			0.27	1.13	(0.15)	0.92	0.49	1.06	(1.37)	0.66			2.17	0.84	2.55
Cash dividends (in dollars per share)			$ 0.60	$ 0.60	$ 0.60	$ 0.58	$ 0.58	$ 0.58	$ 0.58	$ 0.56			$ 2.3800	$ 2.3000	$ 2.2225
Alabama Power
Summarized quarterly financial information
Operating revenues			$ 1,316,000,000	$ 1,740,000,000	$ 1,503,000,000	$ 1,473,000,000	$ 1,433,000,000	$ 1,740,000,000	$ 1,484,000,000	$ 1,382,000,000
Operating Income			164,000,000	561,000,000	380,000,000	372,000,000	255,000,000	601,000,000	440,000,000	361,000,000			$ 1,477,000,000	$ 1,657,000,000	$ 1,618,000,000
Net Income (Loss)			73,000,000	373,000,000	259,000,000	225,000,000	119,000,000	325,000,000	230,000,000	174,000,000			930,000,000	848,000,000	822,000,000
Consolidated Net Income Attributable to Southern Company			73,000,000	373,000,000	259,000,000	225,000,000	119,000,000	325,000,000	230,000,000	174,000,000
Income taxes													291,000,000	568,000,000	531,000,000
Georgia Power
Summarized quarterly financial information
Operating revenues			1,818,000,000	2,593,000,000	2,048,000,000	1,961,000,000	1,884,000,000	2,546,000,000	2,048,000,000	1,832,000,000
Operating Income			257,000,000	991,000,000	(472,000,000)	513,000,000	452,000,000	1,017,000,000	621,000,000	483,000,000			1,289,000,000	2,573,000,000	2,434,000,000
Net Income (Loss)			173,000,000	664,000,000	(396,000,000)	352,000,000	227,000,000	580,000,000	347,000,000	260,000,000			793,000,000	1,414,000,000	1,330,000,000
Consolidated Net Income Attributable to Southern Company			173,000,000	664,000,000	(396,000,000)	352,000,000	227,000,000	580,000,000	347,000,000	260,000,000
Income taxes													214,000,000	830,000,000	780,000,000
Mississippi Power
Summarized quarterly financial information
Operating revenues			308,000,000	358,000,000	297,000,000	302,000,000	271,000,000	341,000,000	303,000,000	272,000,000
Operating Income			52,000,000	80,000,000	54,000,000	7,000,000	(180,000,000)	49,000,000	(2,956,000,000)	(64,000,000)			193,000,000	(3,151,000,000)	(200,000,000)
Net Income (Loss)			149,000,000	47,000,000	46,000,000	(7,000,000)	(556,000,000)	40,000,000	(2,054,000,000)	(20,000,000)			235,000,000	(2,590,000,000)	(50,000,000)
Consolidated Net Income Attributable to Southern Company			149,000,000	47,000,000	46,000,000	(7,000,000)	(556,000,000)	40,000,000	(2,054,000,000)	(20,000,000)
Pre-tax charge (credit) to income			(9,000,000)
After tax charge (credit) to income			(95,000,000)
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)							372,000,000
Income taxes													(102,000,000)	(532,000,000)	(104,000,000)
Southern Power
Summarized quarterly financial information
Operating revenues			506,000,000	635,000,000	555,000,000	509,000,000	478,000,000	618,000,000	529,000,000	450,000,000
Operating Income			30,000,000	136,000,000	16,000,000	60,000,000	32,000,000	159,000,000	112,000,000	65,000,000			242,000,000	368,000,000	290,000,000
Net Income (Loss)			(60,000,000)	146,000,000	45,000,000	115,000,000	793,000,000	154,000,000	104,000,000	66,000,000			187,000,000	1,071,000,000	338,000,000
Consolidated Net Income Attributable to Southern Company			(48,000,000)	92,000,000	22,000,000	121,000,000	795,000,000	124,000,000	82,000,000	70,000,000				1,071,000,000	338,000,000
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)							(743,000,000)
Impairment charges													156,000,000	0	0
After tax impairment charges													117,000,000
Income taxes			75,000,000										(164,000,000)	(939,000,000)	(195,000,000)
Southern Company Gas
Summarized quarterly financial information
Operating revenues			1,048,000,000	492,000,000	730,000,000	1,639,000,000	1,079,000,000	565,000,000	716,000,000	1,560,000,000
Operating Income			104,000,000	374,000,000	49,000,000	388,000,000	109,000,000	67,000,000	95,000,000	389,000,000		$ 199,000,000	915,000,000	660,000,000
Net Income (Loss)			78,000,000	46,000,000	(31,000,000)	279,000,000	(60,000,000)	15,000,000	49,000,000	239,000,000		114,000,000	372,000,000	243,000,000
Consolidated Net Income Attributable to Southern Company			78,000,000	46,000,000	(31,000,000)	279,000,000	(60,000,000)	15,000,000	49,000,000	239,000,000
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)							93,000,000
Income taxes												76,000,000	464,000,000	367,000,000
Goodwill impairment			0			42,000,000						0	42,000,000	0
Gain (loss) on dispositions												$ 0	(291,000,000)	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
Summarized quarterly financial information
After tax charge (credit) to income													722,000,000	$ 2,400,000,000	$ 264,000,000
Kemper IGCC | Mississippi Power
Summarized quarterly financial information
Pre-tax charge (credit) to income		$ 2,800,000,000				44,000,000	208,000,000	34,000,000	3,000,000,000	108,000,000	$ 242,000,000		37,000,000			$ 3,070,000,000
After tax charge (credit) to income		$ 2,000,000,000	95,000,000			33,000,000	$ 185,000,000	$ 21,000,000	$ 2,100,000,000	67,000,000	$ 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
Plant Scherer Unit 3
Summarized quarterly financial information
Pre-tax charge (credit) to income										33,000,000
After tax charge (credit) to income										$ 20,000,000
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 | Pivotal Home Solutions | Southern Company Gas
Summarized quarterly financial information
Goodwill impairment						$ 42,000,000							$ 42,000,000
Gain (loss) on dispositions, after tax	$ (67,000,000)

Valuation and Qualifying Acco_2

Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 13	$ 44	$ 43	$ 13
Charged to Income			69	56	40
Charged to Other Accounts			(1)	0	(1)
Acquisitions			0	0	41
Deductions			61	55	50
Reclassified to Held for Sale			1	0	0
Balance at End of Period	$ 43		50	44	43
Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2	148	22	2
Charged to Income			(38)	126	0
Charged to Other Accounts			0	0	0
Acquisitions			0	0	20
Deductions			10	0	0
Reclassified to Held for Sale			0	0	0
Balance at End of Period	22		100	148	22
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	10
Charged to Income			13	10	11
Charged to Other Accounts			0	0	0
Deductions			12	11	11
Balance at End of Period	10		10	9	10
Georgia Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2	3	3	2
Charged to Income			11	11	15
Charged to Other Accounts			0	0	0
Deductions			12	11	14
Balance at End of Period	3		2	3	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		0	0	0	0
Charged to Income			39	0	0
Charged to Other Accounts			0	0	0
Deductions			6	0	0
Balance at End of Period	0		33	0	0
Mississippi Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	1	0	0
Charged to Income			1	2	1
Charged to Other Accounts			0	0	0
Deductions			1	1	1
Balance at End of Period	0		1	1	0
Mississippi Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	124	0	0
Charged to Income			(92)	124	0
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period	0		32	124	0
Southern Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	10	0	0
Charged to Income			12	10	0
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period	0		22	10	0
Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	38		28	27
Charged to Income	9		33	28
Charged to Other Accounts	(1)		(1)	0
Deductions	19		30	27
Balance at End of Period	27	38	30	28	27
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	19		11	19
Charged to Income	0		1	0
Charged to Other Accounts	0		0	0
Deductions	0		0	8
Balance at End of Period	19	19	$ 12	$ 11	19
Predecessor | Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	38	29			29
Charged to Income		16
Charged to Other Accounts		2
Deductions		9
Balance at End of Period		38
Predecessor | 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	$ 19	19			$ 19
Charged to Income		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		$ 19

Uncategorized Items - so-201812

Label	Element	Value
Southern Company Gas [Member]
Interest Paid, Excluding Capitalized Interest, Operating Activities	us-gaap_InterestPaidNet	$ 135,000,000
Proceeds from Divestiture of Businesses, Net of Cash Divested	us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested	0
Payments of Ordinary Dividends, Common Stock	us-gaap_PaymentsOfDividendsCommonStock	126,000,000
Payment for Pension and Other Postretirement Benefits	us-gaap_PensionAndOtherPostretirementBenefitContributions	125,000,000
Income Taxes Paid, Net	us-gaap_IncomeTaxesPaidNet	23,000,000
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	(8,000,000)
Payments for Removal Costs	us-gaap_PaymentsForRemovalCosts	40,000,000
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	2,399,000,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	5,000,000
Deferred Income Tax Expense (Benefit)	us-gaap_DeferredIncomeTaxExpenseBenefit	92,000,000
Proceeds from Issuance of First Mortgage Bond	us-gaap_ProceedsFromIssuanceOfFirstMortgageBond	0
Repayments of Senior Debt	us-gaap_RepaymentsOfSeniorDebt	420,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(2,067,000,000)
Repayments Of Gas Facility Revenue Bonds	so_RepaymentsOfGasFacilityRevenueBonds	0
Increase (Decrease) in Accounts Payable	us-gaap_IncreaseDecreaseInAccountsPayable	194,000,000
Proceeds from Contributions from Parent	us-gaap_ProceedsFromContributionsFromParent	1,085,000,000
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	614,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	(4,000,000)
Payments to Acquire Additional Interest in Subsidiaries	us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries	160,000,000
Change in Construction Payables	so_ChangeInConstructionPayables	22,000,000
Hedge Settlements	so_HedgeSettlements	35,000,000
Proceeds from Issuance of Senior Long-term Debt	us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt	900,000,000
Repayments of Medium-term Notes	us-gaap_RepaymentsOfMediumTermNotes	0
Proceeds from Equity Method Investment, Distribution, Return of Capital	us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital	5,000,000
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	1,143,000,000
Increase (Decrease) in Prepaid Taxes	us-gaap_IncreaseDecreaseInPrepaidTaxes	23,000,000
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	(327,000,000)
Increase (Decrease) in Accrued Salaries	us-gaap_IncreaseDecreaseInAccruedSalaries	(13,000,000)
Capital Expenditures Incurred but Not yet Paid	us-gaap_CapitalExpendituresIncurredButNotYetPaid	63,000,000
Increase (Decrease) in Energy Related Inventory, Natural Gas in Storage	so_IncreaseDecreaseinEnergyRelatedInventoryNaturalGasinStorage	226,000,000
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	51,000,000
Repayments of First Mortgage Bond	us-gaap_RepaymentsOfFirstMortgageBond	0
Southern Company Gas [Member] | Predecessor [Member]
Interest Paid, Excluding Capitalized Interest, Operating Activities	us-gaap_InterestPaidNet	119,000,000
Proceeds from Divestiture of Businesses, Net of Cash Divested	us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested	0
Payments of Ordinary Dividends, Common Stock	us-gaap_PaymentsOfDividendsCommonStock	128,000,000
Payment for Pension and Other Postretirement Benefits	us-gaap_PensionAndOtherPostretirementBenefitContributions	0
Income Taxes Paid, Net	us-gaap_IncomeTaxesPaidNet	(100,000,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	19,000,000
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	10,000,000
Payments for Removal Costs	us-gaap_PaymentsForRemovalCosts	32,000,000
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	(558,000,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	(3,000,000)
Deferred Income Tax Expense (Benefit)	us-gaap_DeferredIncomeTaxExpenseBenefit	8,000,000
Proceeds from Issuance of First Mortgage Bond	us-gaap_ProceedsFromIssuanceOfFirstMortgageBond	250,000,000
Repayments of Senior Debt	us-gaap_RepaymentsOfSeniorDebt	0
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(556,000,000)
Repayments Of Gas Facility Revenue Bonds	so_RepaymentsOfGasFacilityRevenueBonds	0
Increase (Decrease) in Accounts Payable	us-gaap_IncreaseDecreaseInAccountsPayable	43,000,000
Proceeds from Contributions from Parent	us-gaap_ProceedsFromContributionsFromParent	0
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	509,000,000
Increase (Decrease) in Other Operating Liabilities	us-gaap_IncreaseDecreaseInOtherOperatingLiabilities	(30,000,000)
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	(3,000,000)
Payments to Acquire Additional Interest in Subsidiaries	us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries	0
Change in Construction Payables	so_ChangeInConstructionPayables	(7,000,000)
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	(179,000,000)
Hedge Settlements	so_HedgeSettlements	26,000,000
Payments to Acquire Equity Method Investments	us-gaap_PaymentsToAcquireEquityMethodInvestments	14,000,000
Proceeds from Issuance of Senior Long-term Debt	us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt	350,000,000
Repayments of Medium-term Notes	us-gaap_RepaymentsOfMediumTermNotes	0
Increase (Decrease) in Other Operating Assets	us-gaap_IncreaseDecreaseInOtherOperatingAssets	(37,000,000)
Proceeds from Equity Method Investment, Distribution, Return of Capital	us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital	3,000,000
Increase Decrease in Accrued Taxes	so_IncreaseDecreaseInAccruedTaxes	41,000,000
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	(896,000,000)
Increase (Decrease) in Prepaid Taxes	us-gaap_IncreaseDecreaseInPrepaidTaxes	(151,000,000)
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	1,111,000,000
Increase (Decrease) in Accrued Salaries	us-gaap_IncreaseDecreaseInAccruedSalaries	(21,000,000)
Capital Expenditures Incurred but Not yet Paid	us-gaap_CapitalExpendituresIncurredButNotYetPaid	41,000,000
Increase (Decrease) in Energy Related Inventory, Natural Gas in Storage	so_IncreaseDecreaseinEnergyRelatedInventoryNaturalGasinStorage	(273,000,000)
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	57,000,000
Repayments of First Mortgage Bond	us-gaap_RepaymentsOfFirstMortgageBond	$ 125,000,000